S B Nielsen

K Gallagher

D L Egholm

O R Clausen

M Summerfield

. We reject them and maintain all our suggestions regarding western Scandinavia

A c c e p t e d M a n u s c r i p t paper and spend the first part of our response with a number of clarifying remarks, prompted by our reading of the comment: "In summary, we suggest it is worth considering the possibility that western Scandinavian topography has evolved from higher to lower elevation from the Caledonide Orogen until the present-day, without intervening peneplanation and Cenozoic tectonic uplift. Initially, gravitational collapse and backsliding was the dominant contributor to destroying topography (and in bringing eclogite into exhumation distance of the surface). Rifting in Permo-Carboniferous time produced further offshore subsidence and was the last major rift phase seriously affecting the onshore through rift flank formation in places along the coast, onshore rifting and lowering of erosional base level. Later onshore rifting activity apparently was much reduced as compared to the Permo-Carboniferous phase; at least it has not succeeded in destroying the topography entirely. During this, onshore erosion and commensurate flexural isostatic uplift of the crustal column contributed to topography reduction and landscape A c c e p t e d M a n u s c r i p t 2 evolution. Erosion rates were high during the early periods of tectonic activity, but decreased with the declining onshore tectonic activity during late Palaeozoic-early Mesozoic, and probably were very low during the warm climates of the Late Cretaceous-early Palaeogene when a relatively large fraction of the topography could have been covered by vegetation.

Although wet based alpine glaciers, cirques and periglacial processes may have been active in the inner highlands all along, the efficiency of these processes depend much on climate and they suddenly gained importance by occupying a larger area of the inner highlands with the greenhouse-icehouse climatic deterioration on the Eocene-Oligocene boundary. Most importantly, these processes are known to limit mountain height and possess the capability of producing flattish surfaces, suggesting an alternative to the traditional tectonic interpretation of these landscape elements in western Scandinavia. Given this, it is possible that similar issues of ambiguity during interpretation have led to the incorrect identification of Neogene tectonic activity elsewhere."

Contrary to what the commentators perceived, the ICE hypothesis hence operates with two primary controls on erosion: 1) climate (and climate change) and 2) onshore tectonic activity, i.e. relief production. As the onshore tectonic activity declined strongly from the Caledonide collapse and back-sliding phases through the late Palaeozoic rifting into the early Mesozoic [START_REF] Dunlap | Early Palaeozoic orogenic collapse, tectonic stability, and late Palaeozoic continental rifting revealed through thermochronology of K-feldspars, southern Norway[END_REF][START_REF] Andersen | Permian and Mesozoic extensional faulting within the Caledonides of Central south Norway[END_REF][START_REF] Mosar | Scandinavia's North Atlantic passive margin[END_REF], so did the erosion directly forced by tectonism. That there exists a causal relationship between tectonism and erosion is a well established observational fact of geomorphology related to the control on erosion by relief and the continued refreshment of relief by tectonism (e.g. [START_REF] Summerfield | Natural controls of fluvial denudation rates in major world drainage basins[END_REF]. In the absence of significant tectonism, the western Scandinavian landscape developed into a quasi steady state of slow fluvial erosion. This does not imply the absence of rock column uplift, quite on the contrary. Topography in this state evolves only slowly and owes its longevity to the fact that a reduction of average elevation by 1 km requires 5-6 km of erosion (as a consequence of isostasy), which with a fluvial erosion rate of, say, 30 m/Myr would last 200 Myr. If the average topography were twice as high, or if the average erosion rate were only half, the topography survival time would be twice as long. The ICE hypothesis therefore implies large magnitudes of rock column uplift in response to isostatic reboundmuch more than the Neogene tectonic surface uplift hypothesis seems to require. However, We further emphasize that the alpine glaciers and periglacial processes of the ICE hypothesis not are confined to the Eocene and the Oligocene, as implied by the commentators.

Depending on the glacier equilibrium line altitude (ELA) dictated by past climate, such processes were active all along in the inner highlands as they are at present e.g. in the Himalayas, the Andes or the Cascade Ranges of the western United States, but we believe that they gained much importance in western Scandinavia by a significant drop in ELA on the Eocene-Oligocene transition when the global climate changed from a greenhouse world to an icehouse world. The ELA of course always has varied in concert with the changing climate, and in western Scandinavia must also have been influenced by changes in precipitation patterns brought about by the North Atlantic opening and onset at some point of the thermohaline circulation [START_REF] Via | Evolution of Atlantic thermohaline circulation: Early Oligocene onset of deep-water production in the North Atlantic[END_REF].

Rather than being unable to find a suitable tectonic uplift mechanism, which seems to be the impression of the commentators, it was a number of arguments that led us to dismiss an arcane Cenozoic tectonic uplift mechanism and suggest other avenues of explanation for the present landforms of western Scandinavian. These arguments are detailed in our paper, but we reiterate them here because it seems that the commentators consider them to carry little weight as compared to qualitative landform arguments. To us, however, our arguments are indispensable, and it is exactly the gravity of these arguments combined with the demonstrable existence of processes that very likely are fully capable of explaining the western Scandinavian landforms that led us to proposing the ICE hypothesis.

We found that much of the evidence used to argue for tectonic uplift of unknown origin involves observations that can readily be explained in terms of prolonged exhumation from ancestral topography, coupled with flexural isostatic response, and deep (~1 km in places) erosion by Quaternary glaciers of the coast-proximal sedimentary section. These observations include 1) overburial and tilting of coast proximal sediments, 2) geophysical data, notably the correlation between topography, Bouguer gravity and crustal thickness in western Scandinavia, which provide a straight forward demonstration of close to local, and mainly A c c e p t e d M a n u s c r i p t 4 shallow (crust-upper mantle) isostatic support of the present day topography, and 3) the geographical distribution of apatite fission track ages and lengths. The latter in the past has been used as an argument for tectonic uplift, but in fact the available fission track data set cannot distinguish between the different evolutional models because fission tracks are sensitive to the thermal history. The detection of active surface uplift requires information from outside the fission track system. The pattern of fission track ages and track lengths in southern Norway are, as demonstrated in our paper, satisfactorily explained by passive flexural isostatic exhumation of ancestral topography, in places in the presence of fault activity [START_REF] Redfield | Mesozoic and Cenozoic tectonics of the Møre Trøndelag Fault Complex, central Norway: constraints from new apatite fission track data[END_REF]Leighton, 2008).

None of these key arguments, which must be taken seriously in any plausible explanation of the evolution of the topography, were adequately addressed in the comment.

The other relevant observations that need to be considered are the existence of flattish landforms at high elevation in western Scandinavia and the history of sediment production as seen in the offshore record, which generally cannot be explained by variation in fluvial processes. This is where we invoke a response to climate change in the glacier ELA and associated erosion. This idea grew from another fundamental observation: Lithological changes on the Eocene-Oligocene boundary in the eastern North Sea area appear to be driven by climate change, and further into the Oligocene the climatic control on sequence boundaries prevail [START_REF] Sliwinska | Glacio-eustatic control on the morphology of an Oligocene surface in the Eastern North Sea[END_REF]. We consider this to be a key observation that was not discussed in the comment. A change in precipitation intensity driving changes to the fluvial system is a poor candidate to explaining the climate-lithology correlation. The mountains are already there in the ICE hypothesis and so obvious choices of causal agents are alpine glacial activity and periglacial processes. These erosional agents are known to be orders of magnitudes more efficient than are fluvial processes in stable bedrock terrains [START_REF] Hallet | Rates of erosion and sediment evacuation by glaciers: a review of field data and their implications[END_REF]von Blankenburg, 2006). Observations and ideas concerning how such processes control the overall morphology of mountain ranges and limit their height and even produce flattish surfaces flourish in the main stream parts of the geomorphological community (Nielsen et al., 2009).

A c c e p t e d M a n u s c r i p t 5 It is perhaps relevant here to point out that the ICE hypothesis, with its use of established processes to explain a wide range of observations, satisfies the principle of Ockham's razor, which states that the explanation of any phenomena should make as few assumptions as possible. This principle is also expressed in the "law of parsimony", which advises us to pick the theory of maximum parsimony, being the theory which postulates the fewest (i.e., most parsimonious) number of assumptions. Being able by the ICE hypothesis to eliminate the assumption of Neogene tectonic uplift in our opinion strongly maximises parsimony in the understanding of western Scandinavian landforms.

In spite of this, the ICE hypothesis is just that -a hypothesis. We do not claim to explain all observations at all scales, but we believe the ICE hypothesis provides a more integrated and wide-ranging interpretation than many previous propositions, which have tended to focus on a single aspect of the problem.

Further discussion of the comments

We were not able to follow the exact subdivision of the comment of Lidmar-Bergström and Bonow, but respond in the sections given below to what we consider the main issues that have been raised by Lidmar-Bergström and Bonow.

The landscape

We are criticised that we do not focus on valley incision but rather on flattish landscape elements at a high elevation as (quoting Lidmar-Bergström and Bonow) " Nielsen et al. (2009)

state (p. 74) that the origin of the high topography in western Scandinavia is the cause of some controversy. They say that 'it has long been thought that ancestral topography had been destroyed by rifting and eroded close to sea level towards the end of the Mesozoic era whereafter the widely advocated Cenozoic (mainly Neogene) tectonic uplift hypothesis should have produced the present high topography by a series of tectonically driven Cenozoic uplift events on the ~1-2 km scale and wavelengths in the 400-500 km range'. They refer to several authors lumped together without noting their rather different approaches and views and claim

A c c e p t e d M a n u s c r i p t 6 as a summary that one of the observational bases of this hypothesis is 'the presence of accordant summits (summit envelopes) and low relief landscape elements at high-elevation interpreted as remnants of extensive erosion surfaces originally graded to sea level'. This description is not correct. The observational basis is another."

We actually do discuss individual authors independently in order to demonstrate an apparently methodical adherence to the Davisian landscape evolution model. Furthermore, it is precisely the Davisian tectonic interpretation of high elevation flattish landforms that is the central and controversial element of the Neogene tectonic uplift hypothesis. Had the conventional and more than a century old interpretation of the high-level flat surfaces not existed, or, conversely, had there existed unequivocal evidence such as high elevation post-Caledonian marine sediments in western Scandinavia, there would have been no discussion.

Valley incision on the other hand occurs anywhere positive topography exists and therefore is not at all surprising and surrounded by the controversies that flat landscapes previously graded to sea level and later episodically uplifted are. The suggestion that we do not believe in valley incision in high topography we find surprising, so we are happy to acknowledge we do believe.

Furthermore, according to [START_REF] Lidmar-Bergström | Landforms and uplift history of southern Norway[END_REF], "The envelope surface is a surface constructed from summit heights (p. 213)". We probably have to admit that a surface constructed from summit heights and "accordant summits", "summit envelopes", or "envelope surface" carries congruent meanings to us. That this concept should not be of central importance -and therefore our focus wrong -to the understanding of the landscape of southern Norway is contradicted by17 occurrences of the phrase "envelope surface" and the 13 occurrences of the phrase(s) "summit surface(s)" in [START_REF] Lidmar-Bergström | Landforms and uplift history of southern Norway[END_REF] as well as by the figures (Fig. 2 and Fig. 3) that like the comment's Fig. 2 show qualitative reconstructions of these surfaces, which, together with apparent steps in the present-day landscape are entirely central to the episodic, Davisian tectonic uplift interpretation of [START_REF] Lidmar-Bergström | Landforms and uplift history of southern Norway[END_REF].

In general, we find the tectonic significance that is assigned by Lidmar-Bergström and Bonow to observations of common glacial landforms in Norway and tilted plateaus in west Greenland Mesozoic sediments at high elevation in east Greenland. Furthermore, we note that also the observation of marine Paleocene sediments at an elevation of ~ 1300 on the Nuussuaq peninsula in the Disko area, west Greenland, comfortlably lends itself to explanation by the flexural isostatic uplift mechanism, combined with a measure of rifting induced differential vertical motions such as footwall uplift. So, even along the Greenland coasts where geology has been kind to us and provided unequivocal evidence for uplift in the form of high-elevation patches of relatively young marine sediments there seems to be a simple explanation. Therefore, we do not disagree on the existence of uplift along the margins of Greenland, only we believe that rather simple and well established mechanisms -erosion induced flexural isostasy and differential vertical movements by faulting -are responsible. Of course, flexural uplift also contributed to elevating the peaks of western Scandinavia, as mentioned in our paper (e.g. [START_REF] Small | Pleistocene relief production in Laramide Mountain Ranges, western[END_REF], but not to the extent seen in some places along the Greenland margin because the western Scandinavian fjord systems are less prominent than those of the Greenland margins.

Erosion by cirques and wet-based glaciers

We are criticised that we understand little about how ice and peri-glacial processes modify fluvial landscapes as (quoting Lidmar-Bergström and Bonow) "Glaciers thus do not form landscapes of low relief at a distinct level" and "The main result of studies of glacial impact on different landscapes is that flat landscapes remain flat, hilly relief gets more accentuated, and mountainous relief increases (see also Kleman et al. 2007 and refs. therein). Nielsen et al. (2009) suggest the opposite." In order to clarify matters we distinguish between two very different situations: 1) the cold Quaternary periods characterised by extensive ice shields and 2) all other periods (including the warm Quaternary inter glacials) when alpine glaciers and peri-glacial activity at the latitude range of western Scandinavia were restricted to areas around and above a snowline at some elevation, just like the present day. The latter case 2) has prevailed during the vast majority of the Mesozoic and Cenozoic Earth history, and this is the realm of the glacial buzzsaw in western Scandinavia. The idea that this mechanism efficiently limits mountain height and concentrates area near the snowline across tectonic uplift rates and lithologies at this point in time is subscribed to by many authoritative geomorphologists (e.g. [START_REF] Brozovic | Climatic limits on landscape development in the northwestern Himalaya[END_REF]Whipple et al., 1999;[START_REF] Montgomery | Climate, tectonics, and the morphology of the Andes[END_REF][START_REF] Mitchell | Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State, USA[END_REF]Foster et al., 2008). The activity of the glacial buzzsaw mechanism reveals itself [START_REF] Brocklehurst | Hypsometry of glaciated landscapes[END_REF]) by a local maximum in the hypsometric curve in the vicinity of the snowline. Yielding the percentage of surface area in a given elevation interval between, say, elevations h 1 and h 2 by integration from h 1 and h 2 , there can be little doubt that the elevation interval of a hypsometric maxima also must be associated with an elevation interval of relatively lower relief. These are elementary facts based on the definition of the hypsometric curve and observations across many mountain ranges. In fact the glacial buzzsaw mechanism has recently seen a global extension (Pedersen et al., 2009) based on the highresolution DEM of the Shuttle Radar Topography Mission. That the glacial buzzsaw may not everywhere leave a flat surface behind but perhaps a high-frequency, rugged terrain we tried to accommodate by the following statement in our paper and a discussion of periglacial processes: "While the glacial buzzsaw is the rough tool that efficiently takes the top of mountain ranges, it may not be able to finish the job and produce flattish surfaces. For this we may turn to the finer 'sanding' tools of periglacial processes". We may add here that the steepening of the topography resulting from the backward excavation into higher topography of cirques working in the vicinity of the equilibrium line altitude (ELA) will also, in due time, cause relief reduction because of the finite stability of high slopes. Therefore, our suggestion is that the flattish landscapes at high elevation in western Scandinavia are a consequence of long-term glacial buzzsaw and peri-glacial activity, not a consequence of Quaternary ice shield effects such as the carving of fjords.

A c c e p t e d M a n u s c r i p t 9 Incidentally, the 1000 m surface shown in Lidmar-Bergström and Bonow's Fig. 2, and which by them is interpreted as a consequence of late tectonic uplift, in our global buzzsaw compilation of the latitude and altitude distribution of hypsometric maxima (Pedersen et al., 2009) corresponds closely to the lower limit of buzzsaw activity at the latitude of central southern Norway. Our alternative, non-tectonic interpretation would therefore be that buzzsaw and peri-glacial activity, commensurate with flexural isostatic uplift because of erosional unloading, has the level ~ 1000 m as base level in southern Norway. The occurrence of higher topography implies that the buzzsaw has not yet completed its job. However, it is in this higher topography that present and past cirques and small ice assemblies should be located, which we believe they are. It is an aspect of the buzzsaw mechanism that over time it undermines its own existence by lowering the landscape. We would expect the buzzsaw partial base level to be lower further to the north because of lower average temperatures and to depend also on the intensity of precipitation (e.g. the distance from the cost like in [START_REF] Mitchell | Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State, USA[END_REF]). Some of the findings of [START_REF] Riis | Quantification of Cenozoic vertical movements of Scandinavia by correlation of morphological surfaces with offshore data[END_REF] in fact point in this direction and, furthermore, the high-elevation autochthonous block fields that he considers to have an origin as a Mesozoic peneplain to us merely could be regoliths of periglacial origin (e.g. [START_REF] Anderson | Modeling the tor-dotted crests, bedrock edges, and parabolic profiles of high alpine surfaces of the Wind River Range[END_REF]. However, this is the subject of ongoing investigations.

The role of the Quaternary ice-shields is entirely different. At this time, mainly cold based ice, which partially or fully preserved the pre-Quaternary high elevation landscape (and in other cold places such as Sweden, also the low-elevation landscape), steered by topography drained through fluvial valley systems and in the process excavated the deeply incised fjords of western Scandinavia, Greenland, western Canada and other places [START_REF] Kessler | Fjord insertion into continental margins driven by topographic steering of ice[END_REF]. In discussing this paper, [START_REF] Kleman | Where glaciers cut deep[END_REF] states in the caption of Fig. 1 "Deep glacially eroded fjords co-exist side-by-side with uplands that are almost untouched by glacial erosion despite having been overridden by ice." This is consistent with our ideas that the glacial buzzsaw landscape developed through the by far dominating periods without extensive ice-shields. Therefore, we did not dwell much on the Quaternary period as this is not (apart from the interglacials) the primary buzzsaw era in Scandinavia. Rather we invoked the well established erosional power of large glaciers on the sedimentary margin and the consequent rebound to explain the observed sediment over burial and coast proximal tilting, respectively. Furthermore, we reiterate -following the Norwegian epigram "Vend i tide, det er ingen skam A c c e p t e d M a n u s c r i p t 10 å snu! " -that "Indeed, in an earlier study (e.g. [START_REF] Nielsen | Paleocene initiation of Cenozoic uplift in Norway[END_REF], we also missed the role of the ice: first by causing sediment production mimicking tectonic uplift since the latest Eocene, and secondly, during the Plio-Pleistocene glaciations by producing effects which also could be mistaken for active tectonic uplift, including sedimentary structures resulting from the extreme lowering of erosional base level by glaciers on the continental shelf and increases in local elevation as a result of the isostatic response to highly selective glacial erosion inland."

Basins and swells, hinge lines, and cover rocks through time

In a section with the title above Lidmar-Bergström and Bonow mix a range of different subjects together, which we believe also mix with the discussion in previous sections entitled "The hilly relief on the flanks" and "Re-exposed relief". We therefore attempt to treat them together in our response.

Initially we learn that (quoting Lidmar-Bergström and Bonow) " Nielsen et al. (2009) propose that the Caledonian/Precambrian basement of southern Norway has risen continuously and slowly and has been delimited by a stable hinge line along the present coast. Studies of the shelf off western Norway (Faleide et al., 2008) show that deep basins alternate with shallow covers of different extent, mirroring a history of vertical movements within different segments.

The Mesozoic and Cenozoic strata are tilted along the coast and cut off and thus must have continued further, whether they are eroded by glaciers or by normal denudation. These conditions are strong arguments for their former onlap on the mainland (e.g. Jensen and Schmidt, 1992;[START_REF] Riis | Quantification of Cenozoic vertical movements of Scandinavia by correlation of morphological surfaces with offshore data[END_REF]."

We note that the actual description, not to mention discussion of the mechanisms that we propose keep the coast line relatively stable, vertically and laterally, in the absence of tectonism -and which agrees with quantitative models -are left out of Lidmar-Bergström and Bonow's discussion. Furthermore, the above arguments are in no way strong arguments for a former onlap of sediments far onto the mainland. First, rifting does indeed produce laterally varying subsidence as a function of the actual realisations of the major faults. This is not in A c c e p t e d M a n u s c r i p t 11 any way surprising and we fail to see its relationship to the postulated tectonic uplift in the hinterland. Second, the many published geological cross sections perpendicular to the coast indeed all show an angular unconformity at the base of the Quaternary, and the higher the vertical exaggeration (some time by a factor more than 60) the more conspicuous it isapparently in many cases to the extent that it is mistaken for solid proof of active onshore and coast proximal uplift. In our paper we clearly demonstrate in two cases, by physically-based quantitative modelling, how such sedimentary geometries (with tilting, over-burial and everything) can be reproduced by glacial erosion of a sedimentary margin -a solution of maximum parsimony that satisfies most observations (perhaps not the high-altitude surfaces, though) using only processes known to have been active. This argument seems to be totally ignored by Lidmar-Bergström and Bonow who instead choose to echo inherited interpretations and entirely unsubstantiated ideas regarding a former sediment cover. Good scientific practice involves awareness of the always present danger of inheriting interpretations which are based more on tradition than on substance. Interdisciplinary groups are, although not immune, less susceptible to such temptations.

To provide an example, the results of [START_REF] Fossen | The Bjorøy Formation: a newly discovered occurrence of Jurassic sediments in the Bergen Arc System[END_REF], who describe near-surface Jurassic sediments of perhaps Oxfordian age in a location along the west coast of southern Norway, could be interpreted in terms of shallow burial. However, an interpretation in terms of no post-depositional burial is at least equally valid. Vitrinite reflectance values in the range 0.28-0.29 %R o in the unconsolidated sands and with an average of 0.32 %Ro on the background of considerable scatter, and possibly due to pre-depositional oxidation, in the sandstone are not compelling evidence for, and do not suggest with any reasonable confidence, burial of up to 1 km depth. Given the uncertainty of vitrinite reflectance values, densely sampled and extensive vitrinite reflectance depth profiles are required to conclude anything about the depth of erosion. The reason that this possibility is mentioned by [START_REF] Fossen | The Bjorøy Formation: a newly discovered occurrence of Jurassic sediments in the Bergen Arc System[END_REF] might reflect the prevailing hypothesis, which they reference through [START_REF] Doré | The impact of late Cenozoic uplift and erosion on hydrocarbon exploration: offshore Norway and some other uplifted basins[END_REF] and [START_REF] Riis | Quantification of Cenozoic vertical movements of Scandinavia by correlation of morphological surfaces with offshore data[END_REF].

However, these two papers themselves take the tectonic uplift hypothesis for granted by quoting earlier papers that take it for granted and then interpret data in terms of the prevailing idea (and displaying vertically strongly enhanced geological cross sections). The solution of maximum parsimony, which [START_REF] Fossen | The Bjorøy Formation: a newly discovered occurrence of Jurassic sediments in the Bergen Arc System[END_REF] almost display in their final Fig. 19 with A c c e p t e d M a n u s c r i p t 12 Bjorøy being the hinge -apart from the Late Cretaceous onshore topography being lower than the present -remains as described in our paper.

We find that the remnants of Mesozoic sedimentary rocks onlapping the Fennoscandian Shield in southern Sweden are not necessarily relevant to our discussion of western Scandinavian topography, and that stratigraphically unconstrained extrapolation from southern Sweden to western Scandinavia is at best suspect. We quote Lidmar-Bergström and Bonow: "In areas with no preserved cover rocks it is of course easier to speculate that they never were there, but the stratigraphical record and relief interpreted as re-exposed suggests that cover rocks of different age rest or have rested directly on basement in many areas of Fennoscandia (e.g. Lidmar-Bergström, 1996;Lidmar-Bergström et al., 1999) indicating periods of subsidence. This is not discussed by Nielsen et al. (2009)." It appears that the presence of this sediment is taken as a sign of a previously much more extensive Mesozoic sediment cover of southern Sweden, implying vertical movements and, furthermore, as a prerequisite for the existence of a landscape with hilly relief in southern Norway. First, we question that vertical movements involving sedimentary covers are required to understand the hilly relief landscapes in southern Norway and in Sweden. We refer to the phrase "relief interpreted as re-exposed' of the above and propose that Lidmar-Bergström and Bonow instead attempt a maximum parsimony interpretation of these landscapes in terms of very slow fluvial exhumation, and with more recent stripping of the weathering mantle. Second, we strongly question the validity of extrapolating observed remains of sediments at a low elevation in southern Sweden to an extensive cover elsewhere. Mesozoic marine sediment remains at low elevation and some marine Eocene sediment with traces of diatoms [START_REF] Fenner | The occurrence of pre-Quaternary diatoms in Scandinavia reconsidered[END_REF] occur in southern Sweden and in vicinity of the Baltic Sea. How were they emplaced?

Because of vertical movements of the Fennoscandian Shield by unknown tectonic agents, or by some other, non-tectonic agent such as a higher eustatic sea level in the past? We prefer the latter because the present sediments are within reach of the higher sea level that existed during their time of deposition, under due consideration of the flexural isostasy from loading by the higher sea and the material that has been removed by erosion since then. We consider this to be an adequate explanation for the presence of the sediments. Hence, extrapolation of Mesozoic cover rocks over the higher elevation Fennoscandic Shield or to southern Norway remains pure speculation. Therefore, a plausible mechanism exists that can place the [START_REF] Lazauskiene | 3-D flexural modelling of the Silurian Baltic Basin[END_REF]. At the present day, when a large fraction of the load responsible for the formation of the basin, including the foreland basin fill itself, has been removed, the remnant marine late Palaeozoic sediments occur at an elevated position in the Fennoscandian Shield, which by a first glance is not compatible with their marine origin. However, the tectonic mechanism responsible for this is not very clandestine being simply the interesting but in reality quite trivial consequence of flexural isostatic loading and later partial unloading of the Fennoscandian Shield by the Caledonide range and the foredeep sediments themselves.

Regarding the formation of the topography of southern Norway, we suggest that it was the result of crustal shortening and thickening during the Caledonian Orogen (which incidentally would have created problems in preserving a sub-Cambrian peneplain). However, we will not rule out the possibility that this topography is in fact a stubborn survivor from Sveconorwegian time. One reason is that Palaeozoic and Mesozoic fault systems seem to have been avoiding central southern Norway [START_REF] Mosar | Scandinavia's North Atlantic passive margin[END_REF], which therefore stands out as an unusually resistant rock (at least compared to the surroundings) that might have had high topography for ~1 Gy (which incidentally also would rule out the existence of a sub-Cambrian peneplain). That not all areas affected by the Sveconorwegian Orogeny have high topography at the present day does not worry us unduly. There can be many reasons for this, for example, crustal extension which is an excellent agent for destroying topography, as witnessed by the topography of the middle Carboniferous Hercynian orogeny, which, although younger than the Caledonides, has been destroyed in central Europe by late Palaeozoic and Mesozoic rifting (Ziegler, 1990). We note here that the approaching Caledonide orogen easily could have 'climbed' topography higher than at present day in Southern Norway by acting as a surface load producing flexural isostatic subsidence. We therefore maintain that there are very good reasons to believe that the Scottish Caledonides, like western Scandinavia, have remained positive features since Caledonide time essentially having been exhumed from ancestral topography without intervening peneplanation and tectonic uplift. Also for Scotland this is in fact the maximum parsimony solution.

Finally, we should like to emphasize that our proposed model of rifting and erosional exhumation of the present day topography of western Scandinavia from ancient topography without peneplanation and ensuing tectonic uplift does not mean that we dismiss tectonic explanations of high-level low relief landscapes elsewhere, as perhaps perceived by the commentators. Why should we do this in places where there are good reasons? Unfortunately, such good reasons do not exist for western Scandinavia during the Cenozoic.

Conclusions

We have no doubt that taking tectonic uplift of unknown origin for granted can lead to numerous interesting tectonic interpretations of western Scandinavian landforms and elsewhere following the approach of Lidmar-Bergström and Bonow. However, these remain cooling, although with a rather blurred resolution (e.g. [START_REF] Ketcham | Forward and inverse modelling of low-temperature thermochronology data[END_REF]. They do, however, not contain information regarding the cause of cooling. This is frequently erosion and it seems that it is then easy to suffer the mental short circuiting that cooling means erosion means uplift means tectonic uplift. More generally, the use of geomorphology to resolve vertical tectonic movements of rock surfaces is problematic as there is a fundamental issue of nonuniqueness.

Regarding the landscapes of western Scandinavia, we actually initially were inclined to pursue the traditional path, but eventually learned that the prevailing ideas regarding the morpho-tectonic evolution of the Fennoscandian Shield and the methodologies involved were severely wanting. In the approach of Lidmar-Bergström and Bonow it is not possible both to unravel landform evolution and tectonic movements. The interpretations are unphysical as the fundamental concept of isostasy is not in any way actively integrated. Given that significant amounts of surface mass move around as landscapes evolve, the consequence of omitting this particular elementary mechanism is severe. Furthermore, the glacial buzzsaw mechanism, which has a very strong explanatory potential regarding high elevation landform evolution, and which affects any mountain range that, at any time, crosses the local snow line, is not integrated in their interpretations.

It is apparent that Lidmar-Bergström and Bonow from an insular landform perspective are of the opinion that the ICE hypothesis is on thin ice. Although we are credited for a multidisciplinary approach, it is apparent that when it comes to geomorphological issues we should rather have adopted existing ideas. Unfortunately, this has not been possible for us. In considering a physically based maximum parsimony solution involving a range of established processes including rifting, climate, isostasy, the glacial buzzsaw and periglacial processes, we found that it was unnecessary to invoke a tectonic uplift mechanism of unknown origin for western Scandinavia. Given this, we suggest that the tectonic interpretation of high altitude landforms in western Scandinavia for more than a century has been the obstacle for the understanding of western Scandinavian landscape evolution.

  uplift of the ICE hypothesis is distributed in time in close concert with the removal of mass.

  A c c e p t e d M a n u s c r i p t 7 bizarre when the fundamental mechanism of isostasy as a function of erosion and redeposition of mass is not at all considered by them. The absence of any active consideration of the fundamental effects of flexural isostasy renders tectonic interpretations of the observations of Lidmar-Bergström and Bonow at best suspect. After all, isostasy is the one mechanism which almost everyone acknowledges is inescapably always present. For example, Medvedev et al. (2008) demonstrated how erosion and flexural isostasy can explain the occurrence of marine

  marine sediments where they are found at present, so the maximum parsimony solution rules in favour of dismissing any "Deus ex machina" tectonism. At the very least the plea for tectonism should be tempered with what can be achieved by simple eustatic and isostatic means. Contrary to the case of Mesozoic and Eocene sediments there are good tectonic reasons why there are remnants of post-Silurian sediments in relatively high elevations. They were deposited in the foreland basin that developed as a consequence of Caledonide loading of the Fennoscandian Shield

  of the Scottish Caledonides, which is doubted by Lidmar-Bergström and Bonow on the grounds of the paper by[START_REF] Macdonald | Modelling and comparing the Caledonian and Permo-Triassic erosion surfaces across Highland Scotland: implications for landscape inheritance[END_REF], which they believe we say the opposite of, which we do not, we have obtained the following personal comment(David Macdonald, 20 February 2009): "I believe that the Caledonian surface controls the present-day surface of the east Highlands and the eastern part of the Northern Highlands. I think that this block has been mostly above sea-level since the Devonian. Most denudation would have involved removal of Old Red Sandstone and Carboniferous sediments, plus some of the higher peaks of basement." However, we could also have quoted[START_REF] Thomas | Geological structure and landscape of the Cairngorm Mountains[END_REF] from which we have extracted the following concluding statement: "Uplift and erosion during the waning of Caledonian orogenic events resulted in the Cairngorm Granite being exposed at the surface in the Devonian, probably sometime around 390 million years ago. The Cairngorms have remained a positive landscape feature since this time, probably remaining exposed even through late Palaeozoic and Mesozoic marine incursions that covered much of the rest of the country."

  and the presence of fission track data does not change this. Fission tracks are sensitive to the thermal history and in some cases contain such information, e.g.


Stefano Catalano

Giorgio De Guidi

Gianni Lanzafame

Carmelo Monaco

Luigi Tortorici
email: tortoric@unict.it

Late Quaternary deformation on the island on Pantelleria: new constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Keywords: extensional tectonics, Quaternary, volcanism, Pantelleria island, southern Italy

Structural observations carried out on the volcanic island of Pantelleria show that the tectonic setting is dominated by NNE-trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a  N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE-SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE-WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW-SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on

Introduction

The island of Pantelleria, as for Linosa, represents the top of a large active composite Quaternary volcano belonging to the magmatic district of the Sicily Channel. Offshore geophysical and geological information [START_REF] Calanchi | The Strait of Sicily continental rift system: physiography and petrochemistry of the submarine volcanic centres[END_REF]CNR, 1991;[START_REF] Grasso | Structural and stratigraphic framework of the Tunisia shelf surrounding the islands of Lampione and Lampedusa (Pelagian Sea)[END_REF][START_REF] Rotolo | Petrology and Geochemistry of Submarine Volcanism in the Sicily Channel Rift[END_REF]Civile et al., 2008) show that the magmatic district of the Sicily Channel, which is part of the Pelagian Block [START_REF] Burollet | The Geology of the Pelagian block: the margins and basins off Southern Tunisia and Tripolitania[END_REF], includes several submerged volcanic edifices. Their distribution, that has been usually considered to have a NW-SE alignment, actually depict, as a whole, a roughly N-S oriented belt crosscutting the entire channel from the surroundings of the island of Lampedusa, to the South, to the Graham Bank, to the North (Figure 1). N-S trend of the submarine volcanic centres is also recognizable at a local scale as shown by morphotectonic analyses carried out on detailed bathymetric maps of the Graham Bank area (Civile et al., 2008).

The volcanism is mainly characterized by basic and poorly evolved products and only subordinately by evolved rocks exposed on the island of Pantelleria and dragged on a seamount located at about 30 km to the E [START_REF] Rotolo | Petrology and Geochemistry of Submarine Volcanism in the Sicily Channel Rift[END_REF]. Magmatism displays alkaline, peralkaline and tholeiitic affinities and it has been related to the occurrence of extensional tectonics that, during Late Neogene-Quaternary times, caused the development of three major distinct tectonic depressions (Pantelleria, Linosa and Malta troughs). These features, from a morphological point of view, are defined by deep furrows with depths of about -1300 m, -1500 m and -1700 m in the Pantelleria, Linosa and Malta troughs, respectively [START_REF] Morelli | Bathymetry, gravity (and magnetism) in the Strait of Sicily and the Ionian Sea[END_REF]. Available seismic reflection lines (Finetti, 1984;[START_REF] Torelli | Sezione geologica crostale dall'avampaese pelagiano al bacino di retroarco tirrenico (Mediterraneo centrale)[END_REF][START_REF] Finetti | Crustal Tectono-Stratigraphic Setting of the Pelagian Foreland from new CROP Seismic data[END_REF] show that these depressions, partially filled by Pliocene-Pleistocene turbidites reaching thicknesses of about 1000 m, 2000 m and 1500 m in the Pantelleria, Linosa and Malta basins, respectively [START_REF] Colantoni | Note di geologia marina sul Canale di Sicilia[END_REF] [START_REF] Maldonado | Lithofacies as a function of depth in the Strait of Sicily[END_REF]Winnock, 1981;[START_REF] Calanchi | The Strait of Sicily continental rift system: physiography and petrochemistry of the submarine volcanic centres[END_REF], are bounded by NW-SE trending sub-vertical conjugate normal faults (Figure 1). The crustal stretching was associated with thinning of the African continental crust [START_REF] Colombi | Preliminary report on the seismic refraction profile Gargano-Salerno-Palermo-Pantelleria[END_REF][START_REF] Boccaletti | The Calabrian Arc and the Ionian Sea in the dynamic evolution of the Central Mediterranean[END_REF][START_REF] Scarascia | A seismic and gravimetric model of crustal structures across the Sicily Channel Rift zone[END_REF] that reaches thicknesses of 17-18 km beneath the Pantelleria and Linosa troughs [START_REF] Finetti | Crustal Tectono-Stratigraphic Setting of the Pelagian Foreland from new CROP Seismic data[END_REF]Civile et al., 2008). These areas are also characterized by a relatively high heat-flow as high as 130 mW/m 2 (Della [START_REF] Vedova | Heat flow in the tectonic provinces crossed by the southern segment of the European Geotraverse[END_REF] and by positive Bouguer anomalies ranging between +40 and +80 mGal [START_REF] Morelli | Bathymetry, gravity (and magnetism) in the Strait of Sicily and the Ionian Sea[END_REF]. In order to explain the overall tectonic setting of the Sicily Channel in the framework of the geodynamic evolution of the central Mediterranean different models have been proposed. The structures of the Sicily Channel have been interpreted as an intraplate rift related to the NE directed displacement of the northern part of the Pelagian Block including Sicily, away from the Africa continent [START_REF] Illies | Graben formation -the Maltese Islands -a case history[END_REF]Winnock, 1981;[START_REF] Beccaluva | Neogene to Recent volcanism of the southern Tyrrhenian-Sicilian area: implication for a geodynamic evolution of the Calabrian Arc[END_REF]Finetti, 1984;Corti et al., 2005). The tectonic depressions of the Sicily Channel have also been interpreted as large and discrete pull-apart basins involving deep crustal levels that developed in front of the Africa-Europe collisional belt within a large dextral wrench zone [START_REF] Cello | Transtensive tectonics in the Strait of Sicily: structural and volcanological evidence from the Island of Pantelleria[END_REF][START_REF] Jongsma | Geologic structure and neotectonics of the North African continental margin south of Sicily[END_REF][START_REF] Reuther | Pantelleria rift-crustal extension in a convergent intraplate settino[END_REF][START_REF] Ben-Avraham | Active transcurrent fault system along the north African passive margin[END_REF][START_REF] Boccaletti | Transtensional tectonics in the Sicily Channel[END_REF][START_REF] Cello | Structure and deformation processes in the Strait of Sicily "rift zone[END_REF]Reuther, 1990;[START_REF] Finetti | Crustal Tectono-Stratigraphic Setting of the Pelagian Foreland from new CROP Seismic data[END_REF]. A further interpretation is proposed by [START_REF] Argnani | The strait of Sicily rift zone: foreland deformation related to the evolution of a back-arc basin[END_REF] who suggests that the rifting is due to mantle convections developing during the rollback of the African lithosphere beneath the Tyrrhenian basin. In this paper we present new geological data from the Pantelleria Island based on structural analyses carried out on the different sets of structures affecting the volcanic products of the island and on morpho-structural investigation of the major volcano-tectonic features accompanied by a detailed levelling of the main Holocene raised palaeoshorelines. The collected data provide new constraints for defining the Late Quaternary kinematics of the major tectonic lineaments characterizing the Pantelleria Island in terms of the regional setting of this portion of the Pelagian Block and for evaluating the modes and the rates of the Holocene vertical deformation in order to test possible relations between tectonic deformation and volcanism.

A c c e p t e d M a n u s c r i p t

Structural features of the Pantelleria Island

The island of Pantelleria consists entirely of volcanic rocks erupted from about 300 to 3 ka BP [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF]. The volcanic products, grouped in distinct eruptive cycles [START_REF] Civetta | The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka[END_REF], are dominantly represented by acidic rocks, mainly peralkaline rhyolites (pantellerites) with subordinate trachytes and minor transitional basalts that crop out only in the north-western portion of the island [START_REF] Civetta | Geology, geochronology and chemical evolution of the Island of Pantelleria[END_REF][START_REF] Civetta | The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka[END_REF][START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF]. The volcanic activity of Pantelleria was mainly explosive and produced large volumes of ignimbrites and pyroclastics associated with the development of large volcano-tectonic collapses that, forming as a whole a caldera complex (sensu [START_REF] Cole | Calderas and caldera structures: a review[END_REF], occur at present in the south-eastern portion of the island [START_REF] Civetta | Geology, geochronology and chemical evolution of the Island of Pantelleria[END_REF][START_REF] Civetta | The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka[END_REF]. The most impressive ignibritic episode caused the emplacement, at about 45 ka BP, of the "Green Tuff" that drapes all the pre-existing volcanic features on the whole island and represents a well-defined stratigraphic key-horizon useful for defining the youngest volcanic activity of the island. An analysis of the most recent volcanics shows that the acidic products erupted in the south-eastern areas during the last 45 ka derive from the differentiation of primary basic magmas stored at a shallow-depth (3-4 km) chamber [START_REF] Civetta | The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka[END_REF]. Its presence is also suggested by the thermal anomalies that characterize the island [START_REF] Squarci | Preliminary results of geothermal prospecting on the Island of Pantelleria (Italy)[END_REF]. The most recent eruption of Pantelleria was submarine and occurred in 1891 about 5 km NW of the western coast of the island [START_REF] Riccò | Terremoti, sollevamenti ed eruzione sottomarina a Pantelleria nella seconda metà dell'ottobre 1891[END_REF][START_REF] Washington | The submarine eruption of 1831 and 1891 near Pantelleria[END_REF]. The structural setting of the island (Figure 2) is defined by different volcano-tectonic features and by tectonic structures mainly comprising fault segments and minor fracture systems that usually affect the entire volcanic succession.

Volcano-tectonic structures

The major volcano-tectonic features exposed on the island are represented by caldera rims, emission centres and dyke swarms. The most impressive feature is constituted by a caldera complex formed by two large nested calderas that developed on the south-eastern portion of the island (Figure 2). The oldest caldera, named La Vecchia Caldera by [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF] or Serra A c c e p t e d M a n u s c r i p t Ghirlanda Caldera by [START_REF] Cello | Transtensive tectonics in the Strait of Sicily: structural and volcanological evidence from the Island of Pantelleria[END_REF], is defined by a of 2 km-long remnant rim that, completely mantled by the  45 ka-old Green Tuff, bounds to the west, with a maximum height of 100 m, the arc-shaped Serra Ghirlanda ridge. Volcanic horizons exposed on small sections along the southern coastal cliff of the island on relics of palaeo-escarpments attributed to La Vecchia caldera rims, constrains the age of this volcano-tectonic collapse to between 175 ka and 106 ka [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF]. The more recent Zichidi Caldera [START_REF] Cello | Transtensive tectonics in the Strait of Sicily: structural and volcanological evidence from the Island of Pantelleria[END_REF], that corresponds to the Monastero Caldera of [START_REF] Cornette | Recent volcanic history of Pantelleria : a new interpretation[END_REF] and to the Cinque Denti Caldera of [START_REF] Mahood | Nested calderas and trap-door uplift at Pantelleria, Strait of Sicily[END_REF], exhibits well developed rims that, extending more or less continuously, define a sub-circular subsided area located on the central portion of the island inside the older Serra Ghirlanda Caldera (Figure 2). The Zichidi Caldera rim is well preserved along the eastern side of Piano di Ghirlanda, along the Costa Zichidi and to the north of Bagno dell'Acqua from the Khartibucale ridge and Cala Cinque Denti. From Cala Cinque Denti to Piano di Ghirlanda the rim is buried beneath post-caldera volcanic products even if it is recognizable on the surface by the occurrence of small topographic ridges (e.g. on the Khaggiar pantelleritic lava flow) and/or by abrupt slope breaks (e.g. Cuddia Gadir-Cuddia Kamma-Tracino alignment) as the result of the infilling of the subsided floor related to dam effect of the caldera wall. To the northwest, the Zichidi Caldera is abruptly truncated by NE trending normal fault segments that run along the Monastero and the Zinedi escarpments (see below). The walls of the Zichidi Caldera reach maximum heights of 70-90 m at Piano di Ghirlanda and along the Khartibucale ridge and are carved on the oldest rocks of the island. The wall scarp is also partially mantled by thin layers of the  45 ka-old Green Tuff that thicken outside the caldera rim (e.g. the airport area) and form a conspicuous intra-caldera filling as shown by a well drilled at Bagno dell'Acqua that penetrated this volcanic unit for at least 35 m [START_REF] Villari | Studio petrologico di alcuni campioni dei pozzi Bagno dell'Acqua e Gadir[END_REF]. According to [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF], the Zichidi Caldera formed at  45 ka during the eruption of the Green Tuff.

The eruptive centres of Pantelleria are represented by a large range of features. Cinder cones associated with basaltic eruptions are common in the north-western portion of the island A c c e p t e d M a n u s c r i p t while pumice and lava cones and lava shields [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF], related to silicic magma eruptions, occur in the rest of the island. Eruptive centres that apparently spread all over the island actually depict NNE trending belts on the south-eastern part of the island and NW trending alignments, mainly located on the north-western sector. In place, they also develop along NNE-SSW trending eruptive fissures as on the north-western edge of Montagna Grande slope or on the south-easternmost part of the island along the Cuddioli di Dietro Isola ridge (Figure 2). Less impressive NW-SE trending fissures marked by aligned eruptive centres are also present in Contrada Caffefi. Assuming that each eruptive centre is fed by a sub-vertical dyke that develops perpendicular to the minor principal stress, to minimize the local magmatic field-effects related to the structure of the major volcano a statistical analysis of their surface density distribution has been performed to better define the regional tectonic regime (Figure 3). Considering that 100 eruptive centres have been mapped on the island, a grid with steps of 500 m along x-y coordinates was constructed using four overlapping series of circles with a surface equal to 1% of the total area of the island ( 84 km 2 ). For each step, the density of the eruptive centres was calculated as the rate between the percent of the total number of the vent points occurring in the sample area and the percent of the sample area relative to the total surface of the island. Contour lines of distinct density values have been drawn showing the clustering areas of the eruptive centres. Contour lines depict a prominent NNE-SSW trending area that extends from coast to coast along the central portion of the island including most of vents of the island (Figure 3). It is characterized by a well-defined belt that extends to the Montagna Grande area and a lobe defined by a sub-maximum of density elongated from the northern border of Montagna Grande to Punta Gadir. A further NNE-SSW trending belt occurs to the southwest at Cuddioli Dietro Isola. In the area located between these two major belts, distinct scattered areas depicting, as a whole, a NNE trend are also recognizable. In the northwestern part of the island contour lines indeed define a major sigmoidal shaped NW-SE trending belt accompanied by two lower density areas (Figure 3). The different areas defined by the contouring could be interpreted as the surface effect of sub-crustal magma-injection, thus implying A c c e p t e d M a n u s c r i p t that the distinct belts of the island may represent the preferential zones where crustal cracking occurs. Considering that most of the described belts trend NNE-SSW, a WNW-ESE directed extension ( N120°E) could be considered as the dominant mode of deformation of the island of Pantelleria. Following this line of evidence, the NW-SE trending belts occurring on the northwestern part of the island could be consequently interpreted as the result of coalescent NNE-SSW trending cracks developing along a deep-seated NW-SE strike-slip zone with a left-stepping enechelon array (Figure 3).

The volcanic rocks of the island are also intruded by dykes of a few cm to 10-15 m thickness, that are well exposed along the sea cliff of the island from the southeastern coast to Scauri village [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF]. Dykes, mainly pantelleritic in composition, form local swarms and show a sub-vertical attitude trending roughly NNE-SSW thus indicating a N 100°E oriented extension (Figure 4a).

Fault structures

The major faults exposed on Pantelleria Island are represented by NE and NW trending segments that affect all the products cropping out on the island (Figure 2). The NE-trending faults exhibit well developed steep and linear cumulative escarpments. The most important structure is the Zinedi fault (ZF), a roughly east-facing, 6 km-long segment crossing the whole island in its northwestern sector. The ZF (Figure 2) extends from Punta Pozzolana to the NE, to Grotta Calda to the SW and separates the north-western part of the island, characterized by the occurrence of alkalibasalts effusion, from the south-eastern portion where only peralkaline products, ranging from pantellerites to trachytes, have been erupted. The ZF escarpment shows different heights along strike reaching a maximum value of 120 m on its north-eastern segment. Along the western border of Bagno dell'Acqua, the fault scarp truncates 130-190 ka-old lavas that are partially mantled by the 45-ka-old Green Tuff, which is, in turn displaced by about 20 m. In its central portion, the fault trace is buried by the  17-ka-old pyroclastics while on the south-western edge it is characterized by a smoothed scarp onlapped by 14-ka-old pantelleritic lava flows.

A c c e p t e d M a n u s c r i p t

To the East the Monastero fault (MF) is a 2-km-long normal fault segment that affects the Zichidi caldera at Costa Monastero where it forms a 30-m-high escarpment that offsets the 47-kaold lavas capped by the Green Tuff (Figure 2). The most impressive fault scarp of this system is represented by the Montagna Grande fault (MGF), a 3-km-long fault segment that bounds to the East the Montagna Grande massif with a 300-m-high escarpment (Figure 2). The MGF separates the 44-ka-old trachytes of Montagna Grande from the Monte Gibele trachytic lavas that flow along the fault scarp. Considering that the youngest lava flows of Monte Gibele have been dated at 28 ka, the entire fault scarp developed during 16 ka with a vertical uplift-rate of about 1.9 cm/a. This very high value suggests a volcano-tectonic origin associated with the emplacement of the trachytic body of Montagna Grande. Structural data collected on the cataclastic belts of these major structures show fault planes oriented between N170°E and N210°E, with slickenlines ranging from 65° to 90° thus documenting normal dip-slip kinematics (Figure 4b).

The NW trending fault system is represented by the Scauri Fault (SF), a roughly 5-km-long structure that mainly runs along the shore defining the south-western sea cliff of the island where the oldest products of the island (ages from  320 to 80 ka) crop out, draped locally by the Green Tuff (Figure 2). In places, the fault zone is well exposed along the sea cliff showing clear negative flower geometries that suggest horizontal components of motion. Minor fault planes related to the major structure trend along N110°-145°E directions and show sub-horizontal slickenlines ranging from 10° to 30°, indicating right lateral motion (Figure 4b). Inversion of striated fault planes collected on NE and NW-striking major structures indicates that both systems are kinematically compatible with a E-W extension direction (Figure 4b).

Minor fractures

The volcanic products of the island of Pantelleria are pervasively affected by two main regional minor fracture sets characterized by a consistency of orientation. A statistic analysis of the total minor fracture measurements collected at selected sites shows that the dominant set affecting the products of the island is oriented along a roughly NNE-SSW direction with a mean direction of A c c e p t e d M a n u s c r i p t N 15°E (Figure 4c). This set is constituted by sub-vertical systematic extensional joints characterized by spacing ranging from a few decimetres to 1 m; they are frequently represented by open fractures filled by secondary material and locally marked by fumarolic activity [START_REF] Cello | Transtensive tectonics in the Strait of Sicily: structural and volcanological evidence from the Island of Pantelleria[END_REF]. In place, at both large and small scales, this set appears to be constituted by pairs of conjugate hybrid joints that define the dihedral angles containing the shortening and the extension directions. A statistical analysis of measurements carried out on 18 clearly exposed pairs of conjugate joints suggests an extension direction oriented N 105°E (Figure 4d). The minor fractures of the second set trend in a NW-SE direction with an average orientation of N 140° E and are characterized by metric spacing and lengths of several metres. Considering that right-lateral strikeslip fault segments extend in a NW-SE direction on the island, this minor fracture set has been interpreted as synthetic shear fractures associated with a dextral shear zone, being also kinematically compatible with a dominant roughly E-W directed extension.

Vertical deformation

The island of Pantelleria is affected by an intense vertical deformation, which caused a severe uplift of the wave-cut platforms and marine caves and notches carved at the base of the coastal cliffs of the island. Episodes of vigorous uplift have been reported also in historical times by [START_REF] Riccò | Terremoti, sollevamenti ed eruzione sottomarina a Pantelleria nella seconda metà dell'ottobre 1891[END_REF] who described an uplift of about 1 m of the north-eastern coast of the island before a shallow sub-marine eruption occurred in October 1891 about 5 km northwest of the island. In order to evaluate the extent of the uplift affecting Pantelleria we mapped in detail the distribution of marine platforms and palaeoshorelines occurring on the island (De Guidi and [START_REF] De Guidi | Late Holocene vertical deformation along the coast of Pantelleria Island (Sicily Channel, Italy)[END_REF].

These features have been recognized all over the coast of Pantelleria where they reach heights up to about 1.5 m along the southern coast (e.g. Scauri) and up to 4.5 m on the northern coastline thus indicating that the entire island in recent times, mostly during the Holocene, suffered a severe uplift.

In particular, along the northern coast, from the village of Pantelleria to Punta Cortigliolo, three well-developed palaeoshorelines characterized by biogenic encrustations of calcareous algae, A c c e p t e d M a n u s c r i p t vermetids and corals have been recognized at different elevations (Figure 5). 14 C age determinations carried out on several samples of biogenic material constrained the age of these distinct palaeoshorelines [START_REF] De Guidi | Late Holocene vertical deformation along the coast of Pantelleria Island (Sicily Channel, Italy)[END_REF]. The lowest one (line a in Figure 5) shows an age of 197  97 years BP (2 samples) whereas the intermediate one (line b in Figure 5) is characterized by ages ranging from 911  37 years BP to 506  21 years BP (8 samples) representing the period during which the palaeoshoreline developed. The uppermost palaeoshoreline (line c in Figure 5) is carved on the 5.5-ka-old Khaggiar pantelleritic lava flow [START_REF] Mahood | Geology of the peralkaline volcano at Pantelleria, Strait of Sicily[END_REF]) and shows an age of 963  87 years BP (2 samples) constraining the time interval during which this shoreline developed between about 5000 and about 1000 years BP. As a whole, these uplifted strandlines are also deformed into a large antiform with an axial trace almost perpendicular to the coastline and a hinge zone located around the central portion of the island that is characterized by the occurrence of the NNE trending eruptive belts (inset a in Figure 5). Along the antiform limbs, the palaeoshorelines dip with a convergent array and form steep ramps reaching at the antiformal crest the maximum elevation of 4.5, 3.1 and 1.3 m, respectively (Figure 5). Assuming that in the island uplift processes occurred as discrete episodes as documented by [START_REF] Riccò | Terremoti, sollevamenti ed eruzione sottomarina a Pantelleria nella seconda metà dell'ottobre 1891[END_REF] and strongly supported by overlapping ages for lines a and b, and that the growth of the biogenic encrustations on the palaeoshorelines developed continuously, three main episodes of uplift, characterized by values of 1.4, 1.8 and 1.3 m, can be thus estimated at about 900, 500 and 120 years BP. The high values of these repeated uplift episodes suggest that the vertical deformation acting in this portion of the island could be associated with magmatic processes active along the NNE trending eruptive belts occurring within the caldera complex of the central portion of the island. Along these zones, cracking processes could have been accompanied at shallow crustal levels by magma intrusion causing large scale inflation phenomena. These data apparently contrast with geodetic measurements (Bonaccorso and Mattia, 2000;[START_REF] Behncke | Ground deformation and gravity changes on the Island of Pantelleria in the geodynamic framework of the Sicily Channel[END_REF] showing that the caldera complex of the island is at present affected by subsidence (about 11 cm from 1980 to 1996 AD).

Considering that an analogous behavior characterized by uplift and subsidence has been detected

A c c e p t e d M a n u s c r i p t for the Campi Flegrei Caldera [START_REF] Bellucci | Ground deformation at Campi Flegrei, Italy: implications for hazard assessment[END_REF], we propose a similar mechanism for the Pantelleria caldera complex. In this view the subsidence should represent the typical background state of the area interrupted by discrete and faster uplift events related to magma intrusions. The result of the superimposed uniform subsidence and episodic uplift processes is thus represented, in the last 900 years, by a positive large vertical deformation resulting in the observed doming of the southeastern portion of the island.

Summary and discussion

Geological and structural analyses carried out on the island of Pantelleria point out that the main tectonic structures are represented by NNE trending dip-slip normal faults and by NW striking right-lateral strike-slip faults with normal component of motion. The major fault segments represent deep-seated structures [START_REF] Behncke | Ground deformation and gravity changes on the Island of Pantelleria in the geodynamic framework of the Sicily Channel[END_REF] that separate the southeastern portion of the island characterized by a shallow-depth magma reservoir [START_REF] Civetta | The eruptive history of Pantelleria (Sicily Channel) in the last 50 ka[END_REF] from the northwestern sector where basaltic eruptions occurred. Minor structures are represented by two main regional fracture sets (NNE-SSW extensional and hybrid joints and NW-SE synthetic shear fractures) that pervasively affect the entire pile of volcanic products. The distribution of eruptive fissures, dykes and eruptive centres shows, as a whole, alignment along NNE-SSW belts thus suggesting that crustal cracking with associated magma intrusions has occurred with a similar trend. As a whole, the structural observations carried out on the island of Pantelleria emphasize that both the tectonic structures (faults and joints) and the volcano-tectonic features (eruptive fissures, eruptive centre distribution, dyke swarms, fumaroles) are all kinematically compatible and appear to have a common tectonic origin controlled by a  N 105 ± 15°E directed extension. At a large-scale, this mode of deformation is compatible with the development of the roughly N-S oriented volcanic belt that extends from Linosa to the Graham Bank, thus implying that the entire region of the Sicily channel is affected by a regional ESE-WNW oriented extension. This regional extension is also suggested by geodetic data collected at permanent observation sites located on the African and A c c e p t e d M a n u s c r i p t Sicilian shoulders of the channel (D' Agostino and Selvaggi, 2004). The African motion is well represented by data collected at the Lampedusa station (LAMP) which show a NW oriented convergence towards Europe (Figure 6). The motion of the Sicilian shoulder with respect to Europe is represented by data collected at the permanent sites of MILO, located on the westernmost sides of Sicily, and NOTO located on the Hyblean plateau, on the southeastern edge of the island. On the western side of the channel a roughly E-W extension direction is obtained, combining the different directions and rates between the velocity vectors of LAMP and MILO, the latter being clockwise rotated and characterized by a lower magnitude (Figure 6a). On the eastern portion of the channel, the combined velocity vector of LAMP and NOTO indicates indeed a NE-SW extension direction.

Considering that between the two sites a major N10°E oriented left-lateral fault zone (Scicli line) accommodate about 1 mm/a [START_REF] Catalano | The migration of plate boundaries in SE Sicily: Influence on the large-scale kinematic model of the African promontory in southern Italy[END_REF] the NE-SW extension in this portion of the Sicily Channel has to be re-oriented into an E-W direction (Figure 6a). This deformation pattern is also consistent with seismological data from strong earthquakes that have occurred in the Tunisia-Libya seismic zone [START_REF] Westaway | The Tripoli, Lybia, earthquake of September 4, 1974: implicationsfor the active tectonics of the central Mediterranean[END_REF]1991). Seismological information, based mainly on focal mechanisms of the strongest earthquakes (Sirte earthquake of April 19, 1935 andTripoli earthquake of September 4, 1974) indicate in fact that the NW-SE trending regional faults affecting the Pelagian Block are characterized by a right lateral component of motion related to an oblique extension (oriented along  N 100°E direction) between Tunisia and Sicily [START_REF] Westaway | The Tripoli, Lybia, earthquake of September 4, 1974: implicationsfor the active tectonics of the central Mediterranean[END_REF]1991). Geodetic and seismological data together show, therefore, that the entire Sicily Channel experiences a regional Late Quaternary ESE-striking extension that is consistent with that which controls the Siculo Calabrian Rift Zone (SCRZ in Figure 6) along the Ionian coast of Sicily and the Tyrrhenian side of the Calabrian arc [START_REF] Monaco | Late Quaternary slip rates on the Acireale-Piedimonte normal faults and tectonic origin of Mt. Etna (Sicily)[END_REF][START_REF] Monaco | Active faulting in the Calabrian arc and eastern Sicily[END_REF]. We suggest that, at a larger scale, this extension direction may be considered as a second-order deformation process induced by first order Africa-Europe kinematics defined by a NNW convergence. The Late Quaternary extension reactivates the older crustal and/or lithospheric structures responsible for the crustal stretching the Pelagian Block developed mainly during Late [START_REF] Torelli | Sezione geologica crostale dall'avampaese pelagiano al bacino di retroarco tirrenico (Mediterraneo centrale)[END_REF][START_REF] Finetti | Crustal Tectono-Stratigraphic Setting of the Pelagian Foreland from new CROP Seismic data[END_REF]Civile et al., 2008) highlight, in fact, that the boundary master faults appear to be undoubtedly sealed by Late (?) Quaternary sediments well imaged along lines CS89-01 (see Fig. 5 in [START_REF] Torelli | Sezione geologica crostale dall'avampaese pelagiano al bacino di retroarco tirrenico (Mediterraneo centrale)[END_REF] and CROP MS25 (see Fig. 7 in Civile et al., 2008). that preferentially develop at the tip of the major strike-slip fault zones (Figure 6b). The Late Quaternary volcanism of the Pelagian Block is thus confined along the NNE-striking younger extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust therefore linking the already up-welled mantle with the surface.

The prominent magmatism of the island of Pantelleria, as well as the NNE-SSW trending volcanic belt of the Sicily Channel together with the occurrence of Mt. Etna volcano [START_REF] Monaco | Late Quaternary slip rates on the Acireale-Piedimonte normal faults and tectonic origin of Mt. Etna (Sicily)[END_REF], appears to be a consequence of crustal cracking related to the large-scale Late Quaternary extensional processes that govern the whole of southern Italy. This implies that magmatism is the result of a new, Late Quaternary tectonic extensional regime superimposed on the long-lived Late

  Quaternary rifting. Seismic reflection profiles across the Pantelleria trough

  This implies that the major NW-SE trending tectonic troughs of the Sicily Channel, with the associated mantle doming, fully developed during the Early Pliocene-Early Pleistocene as a consequence of a NE-SW oriented extension. We tentatively propose that during this stage the NE-SW oriented extension responsible for the rift process occurring in the Sicily Channel may represent the effect of the NW-SE directed impingement of the Africa continental crust (Pelagian Block) against the Maghrebian collisional belt. This caused the consequent lateral extrusion of the northeastern portion of the Pelagian Block towards weak segments of the continental margin represented by residual basin-areas (e.g. Caltanissetta Basin). Subsequently, since the Late Quaternary, the northeastward extrusion was locked and the NE-directed rift process ceased. The Sicily Channel is thus affected by a new extensional regime mainly related to the development of an incipient divergent margin. The Late Quaternary extension thus partially reactivates the NW-SE to E-W trending fault segments bounding the Pantelleria, Malta and Linosa troughs as right-lateral strike slip faults and produces new NNE trending pure extensional features (normal faulting and cracking)

Figure 1 .

 1 Figure 1. Schematic structural map of the Sicily Channel. PT: Pantelleria trough; MT: Malta trough;

Figure 2 .

 2 Figure 2. Structural map of the island of Pantelleria (modified from Civile et al., 2008). Digital elevation model has been generated on a geographic grid of 40 x 40 points per km 2 with

Figure 3 .

 3 Figure 3. Cartoon showing the surface density distribution of the eruptive centres occurring on the

Figure 4 .

 4 Figure 4. Lower hemisphere equal area stereographic projections of the main structures affecting

Figure 5 .

 5 Figure 5. Vertical projected profiles of the elevations of the three Holocene palaeoshorelines (a to c)

Figure 6 .

 6 Figure 6. Structural sketch map showing the Late Quaternary deformation pattern of the Sicily

  Figure 1

Figure 6

 6 Figure 6

A c c e p t e d M a n u s c r i p t Neogene-Early Quaternary rifting that originated the NW-SE trending troughs of the Sicily Channel. Magmatic processes are also responsible for the impressive vertical deformation that produced a large dome having maximum elevations located along the axis of the south-eastern portion of the island. During Late Holocene times, doming was the result of at least three distinct uplift events that inverted the uniform subsidence state likely associated with magma intrusions along NNE-SSW crustal cracks within the shallow-depth reservoir(s) of the south-eastern part of the island. The vertical deformations of Pantelleria also indicate a magmatic behavior similar to that described for the Campi Flegrei Caldera [START_REF] Bellucci | Ground deformation at Campi Flegrei, Italy: implications for hazard assessment[END_REF] thus implying that the island in the last 5 ka has been dominated by intrusion processes rather than eruptive activity.