TECTONIC SIGNIFICANCE OF STRATIGRAPHIC AND STRU ~ CT URAL CONTRASTS BETWEEN THE PURCELL ANTICLINORIUM ANC THE KOOTENAY ARC , EAST OF DUNCAN LAKE
The main goal of this study is to elucidate the wture and tectonic significance of the profound stratigraphic and struttural changes that occur between the crest of the Purcell anticlinorium and the Kootenay Arc. Reconnaissance (12.50 000) mapping by Reesor (1973) outlined conspicuous contrasts between the thick hasal Paleozoic (Hamill-Badshot) succession that overlies the Windermere Supergroup in the western Purcell Range and the thin, condensed early Paleozoic succession with overlapping Upper Devonian strata that occurs in the eastern Purcell Range. Reesor also described the abrupt contrast between the tight upright fold structures in this area and the refolded, west-verging, recumbent isoclinal folds that occur immediately to the west in the Kootcney Arc. He also showed that several small granitic plutons in the area probably were emplaced while the folding was still underway. The rocks exposed in this area (Figure 1-l-l ) record both the Late Proterozoic early Paleozoic birth and development of the Cordilleran miogeoclinal passive margin of North America (Bond and Kominz, 1984; Bond of a/., 1983, and the late Mesozoic -early Cenozoic deformation, regional metamorphism and granitic plutonism resulting from “collisions” between North America and a series of allochthonous terranes that have been accreted to it (Monger et al., 1982). Detailed geological mapping (I:50 000 and greater) was completed during July and August of 199 I and 1992 within an area of about 900 square kilometres in the western Purcell Mountains, between Duncan Lake and the headwaters of Tohy and Jumbo creeks (Figure I-I-2). This work will link the detailed mapping along the Kootcnay Arc by Fyles (I 964) to the detailed mapping by Root (I 987) and Pope (1990) in the central and eastern Purcell anticlinorium. The main objectives of this study are: (I) to establish the nature and tectonic significance of the stratigraphic rclationships within the thick sequence of Windermere, Hamill and Badshot strata in the study area; (2) to investigate the stratigraphic and tectonic relationships between these strata and the condensed onlapping early Paleozoic succession that occurs on “the Windermere high” to the east. below the Mount Forster thrust fault in the central and eastern Purcell Mountains (Root, 19X5: Reesor, 1973); (3) to establish the nature, evolution and regional tectonic significance of the change in structural style between the study area and the adjacent areas in the Kootenay Arc and in the central Purcell Mountains; and (4) to invest&ate the relation ship hetaeeo the initial structural configuration of the rifts d margin and the major structures that develc#ped during Me iozoic tenam: accretion and deformation of the margin.
The southeastern Canadian Cordillera: Thrust faulting, tectonic wedging, and delamination of the lithosphere
Abstract Displacement of tectonic wedges, bounded above and below by zones of thrust faulting with opposing vergence, has produced tectonic delamination at various stratigraphic levels and times in the Rocky Mountain fold and thrust belt of Canada. The ‘triangle zone’, along the eastern edge of the belt, comprises an easterly tapering wedge of imbricate thrust-slices and delaminated Upper Cretaceous molasse deposits. The Porcupine Creek anticlinorium is a fan fold resulting from the insertion of a wedge of Proterozoic rocks along a zone of delamination at the base of the Lower Paleozoic shale succession. In the Selkirk fan structure, which involves the metamorphic infrastructure of the Cordillera, delamination has occurred as the result of the insertion of an apparently allochthonous mass (a ‘suspect terrane’) between the detached parautochthonous supracrustal rocks and the autochthonous basement complex. The diagnostic feature of tectonic wedging and delamination is a reversal in vergence between the bottom and the top of the wedge. Conspicuous tectonic overprinting (‘polyphase folding’) characteristically occurs above the wedge, and is commonly described as ‘backfolding’ and ascribed to polyphase orogeny. Tectonic wedging and delamination are widepread in compressional fold belts of various ages. Examples occur in the Cordilleran tectonic collage of accreted terranes and in early Proterozoic (Wopmay Orogen), Paleozoic (Caledonide-Appalachian) and Cenozoic (Alps) mountain belts. Moreover, tectonic wedging and delamination occur over the whole spectrum of scales from the microscopic to the lithospheric. They are an inherent feature of ‘flake tectonics’ and of the development of large overthrusts such as crystalline basement sheets and obducted ophiolites, all of which comprise a strong upper layer that has been delaminated from the rest of one lithospheric plate, and has overlapped another lithospheric plate that has been wedged beneath it. Geometric and kinematic relationships discernible in well-documented natural prototypes of tectonic wedging and delamination on a small scale provide a basis for elucidating relationships that are more difficult to establish directly on a large scale.
Study on essential drug use status and its influencing factors among cerebral infarction inpatients in county level hospitals of Anhui Province, China
Background and purpose Drug costs is one of the main components of hospitalization expenditure for cerebral infarction inpatients. In China, the National Essential Medicine System (NEMS) was created to relieve the heavy drug-cost burden for patients. The objective of this study was to investigate essential drug-use status and its influencing factors among cerebral infarction inpatients in county-level hospitals of Anhui province, China. Methods Three county-level hospitals were selected through a multi-stage cluster random sampling method. The hospitalization cost data of cerebral infarction inpatients in the three hospitals were extracted from the Anhui provincial information platform of the New Rural Cooperative Insurance System (NCMS), and whether the proportion of essential drug cost in the total drug cost reached the median value of 33.05% which was set as the evaluation index for essential drug-use status. Questionnaires for hospitals and physicians were designed and given to them to assess influencing factors. Results We retrieved the cost data of 2,189 inpatients from the NCMS platform and investigated 51 corresponding physicians in total. The drug costs accounted for 52.6% of the total hospitalization cost, and essential drug costs alone accounted for 37.0% of the total drug costs. The essential drug-cost proportion was high among physicians with a higher recognition degree on NEMS, older age, lower final academic degree, longer work experience and lower professional title. Married physicians and those with tight organizational affiliation also prescribed more essential drugs. Conclusions Increasing the proportion of essential drugs was an effective way to reduce the disease burden for cerebral infarction patients. Perfecting the NEMS, increasing government investment, reinforcing education and propaganda, and formulating relevant incentive and restrictive mechanisms were all effective ways to promote and increase the number of essential drug prescriptions written by physicians.