Evidence for large-scale Laramide tectonic inversion and a mid-Tertiary caldera ring fracture zone at the Lightening Dock geothermal system, New Mexico
Stratigraphy in a recent intermediate depth (2100 ft) geothermal test hole is interpreted along side previous deep (7001 to 7404 ft depth) exploration holes to study large-scale structural controls for the Lightning Dock geothermal system and refine the stratigraphic and structural characterization of the shallow reservoir. Laramide compression and large-scale tectonic inversion of a northwest-trending Late Jurassic-Early Cretaceous extensional structure at the Lightning Dock geothermal site represents deformation that may exceed Neogene extensional processes in magnitude and duration and provide potential for a significant volume of shattered rock. Also, volcanic stratigraphy supports the hypothesis of Elston et al. (1983) for a midTertiary caldera ring fracture zone in the vicinity the geothermal area. Northeastand north-trending Neogene normal faults that cross cut older structures provide additional preparation of fractured ground. A north-trending Pleistocene normal fault may reopen older fractures that are favorably oriented and allow concentration and upward flow of deep-seated geothermal fluids. Because the Lightning Dock geothermal system is “blind” and has no surface manifestations, a better understanding of structures buried beneath Neogene alluvial basin fill may have application in geothermal exploration to find similar “blind” geothermal systems elsewhere in southern New Mexico and southeastern Arizona. FIGURE 1. Shaded relief topographic location map of the Lightning Dock geothermal area.
Residual Aeromagnetic Map of Arizona
Residual magnetic intensity values are given in gammas. The original total field data were corrected for diurnal variation as observed at the Tucson Magnetic Observatory during the flight period.
Mesozoic rifting and basin inversion along the northern African Tethyan margin: an overview
Abstract The northern African Tethyan margin registered three major rifting episodes from the latest Palaeozoic-earliest Mesozoic to the earliest Cenozoic. Break-up of Gondwana was initiated in the late Carboniferous. Along the northern African-Arabian plate margin rifting propagated westward from the northeastern Arabian margin to Morocco during the Permian and Triassic, and was accompanied by Mid-Late Triassic-earliest Liassic extensive alkaline flow basalts. Rifting continued during the Liassic, e.g. in the Moghrebian Atlas troughs. A second stage of rifting occurred in the Late Jurassic and continued into, or was rejuvenated during, the Early Cretaceous. Along the east Mediterranean margin, some large E-W trending rifts formed, often with associated volcanism, e.g. southern Sirt and Abu Gharadig. Most researchers believe the oceanization of the eastern Mediterranean basin occurred at this time. Flexural subsidence affected the Moghrebian Atlas, including the Riffian-Tellian domain, where a thick flysch series was deposited. Two short-lived, but widespread and tectonically important, compressional or wrench-dominated events occurred during the Santonian and the latest Maastrichtian. From Morocco to Oman, most sedimentary basins were folded and inverted at these times. The Santonian event resulted from onset of the collision between the African-Arabian and Eurasian plates. New stress-fields favoured NE-SW extension along the African plate margin, generating or rejuvenating some rifts, e.g. in the Euphrates trough and in the Libya-Tunisia region (northwestern Sirt, Pelagian Sea). Rifting and magmatism continued in these regions into the Paleocene. During the Mesozoic, therefore, the northern margin of the African-Arabian plate registered both rifting resulting in the oceanization of the Tethys and rifting resulting from the initiation of the closure of the Tethys. The intraplate domain exhibited echoes of the tectonic events affecting the margin.