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51.
陕西南部北大巴山地区早志留世滔河口组碱基性火山岩,分布层位稳定,岩性标志特征。根据火山岩岩石类型和地层学以及古生物组合特征对其岩石地层单位重新进行了厘定,研究了火山岩的成因,探讨了火山岩形成的机制和构造环境。 相似文献
52.
中国兴蒙—新疆北部及邻区早石炭世地层十分发育,动植物化石丰富。根据生物群综合分析,将该研究区归入哈萨克斯坦—西伯利亚域和特提斯域,并进一步划分为3个省,8个亚省。西伯利业省以管孔贝大量发育为特征,缺少大长身贝类,珊瑚不甚发育,植物少见,为安加拉植物群;哈萨克斯坦—蒙古—兴安省以管孔贝类和大长身贝类共同发育为突出特征,珊瑚较发育,但分区特征不明显,并有大量异珊瑚类,植物为安加拉植物群;塔里木北缘—西秦岭省以南方型生物群大量发育为主要特征,大长身贝类最为发育,缺少管孔贝类,珊瑚数量十分丰富,并有假乌拉珊瑚大量发育,植物以华夏植物群为主。早石炭世古生物地理分区与板块关系密切,晚泥盆世末,西伯利亚板块南移,与哈萨克斯坦板块汇聚,到早石炭世早、中期,两大板块基本上处于相近似的古生物地理环境,与此同时,塔里木板块逐渐北移,与哈萨克斯坦板块海水相通,致使哈萨克斯坦板块广大海域出现南、北动物群混生现象。早石炭世末,三大板块海域相连,除各地沉积和构造古地理环境尚有差异外,中石炭世开始,腕足类,类及珊瑚等动物群均显示出明显的一致性。 相似文献
53.
In the Dharwar tectonic province, the Peninsular Gneiss was considered to mark an event separating the deposition of the older
supracrustal Sargur Group and the younger supracrustal Dharwar Supergroup. Compelling evidence for the evolution of the Peninsular
Gneiss, a polyphase migmatite, spanning over almost a billion years from 3500 Ma to 2500 Ma negates a stratigraphic status
for this complex, so that the decisive argument for separating the older and younger supracrustal groups loses its basis.
Correlatable sequence of superposed folding in all the supracrustal rocks, the Peninsular Gneiss and the banded granulites,
indicate that the gneiss ‘basement’ deformed in a ductile manner along with the cover rocks. An angular unconformity between
the Sargur Group and the Dharwar Super-group, suggested from some areas in recent years, has been shown to be untenable on
the basis of detailed studies, A number of small enclaves distributed throughout the gneissic terrane, with an earlier deformational,
metamorphic and migmatitic history, provide the only clue to the oldest component which has now been extensively reworked. 相似文献
54.
55.
强余震持续时间的早期估计 总被引:2,自引:0,他引:2
本研究旨在解决地震序列中强余震持续时间的早期估计问题。文中首先给出了强余震的震级定义,指出:主震型与强震群型序列的强作震持续时间存在差异。使用模式识别方法对主震型序列中强余震持续时间大于1天,小于1天及无强余震等3种情况进行划分之后,给出了两类序列的强余震持续时间与序列和第一震震级的粗略相关关系。 相似文献
56.
本文通过年代学资料和其它地质依据建立了冀西北及邻区麻粒岩地体早前寒武纪主要地质事件的年代格架。早期的基性火山喷发事件发生在2868—2932Ma期间,形成本区的早期地壳。在2761Ma左右发生了大规模的TTG岩浆侵位事件,在2650Ma时发生了基性岩浆侵位,使地壳加厚。在2561—2503Ma期间,花岗闪长质岩浆在本区广泛侵入,使地壳进一步加厚。2477—2461Ma期间,紫苏花岗岩以岩株形式侵入,同时发生区域麻粒岩相变质,早期地壳受到改造。大约在2300Ma时发生第二阶段的麻粒岩相变质。此后,在2144—2087Ma期间红色花岗岩侵位,形成花岗岩带。 相似文献
57.
Rob Westaway Malcolm Pringle Sema Yurtmen Tuncer Demir David Bridgland George Rowbotham Darrel Maddy 《Tectonophysics》2004,391(1-4):121
Along the upper reaches of the Gediz River in western Turkey, in the eastern part of the Aegean extensional province, the land surface has uplifted by 400 m since the Middle Pliocene. This uplift is revealed by progressive gorge incision, and its rate can be established because river terraces are capped by basalt flows that have been K–Ar and Ar–Ar dated. At present, the local uplift rate is 0.2 mm a−1. Uplift at this rate began around the start of the Middle Pleistocene, following a span of time when the uplift was much slower. This was itself preceded by an earlier uplift phase, apparently in the late Late Pliocene and early Early Pleistocene, when the uplift rate was comparable to the present. The resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change. We suggest that this present phase of surface uplift, amounting so far to 150 m, is being caused by the nonsteady-state thermal and isostatic response of the crust to erosion, following an increase in erosion rates in the late Early Pleistocene, most likely as a result of the first large northern-hemisphere glaciation during oxygen isotope stage 22 at 870 ka. We suggest that the earlier uplift phase, responsible for the initial 250 m of uplift, resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3.1 Ma. This uplift thus has no direct relationship to the crustal extension occurring in western Turkey, the rate and sense of which are thought not to have changed significantly on this time scale. Our results thus suggest that the present, often deeply incised, landscape of western Turkey has largely developed from the Middle Pleistocene onwards, for reasons not directly related to the active normal faulting that is also occurring. The local isostatic consequences of this active faulting are instead superimposed onto this “background” of regional surface uplift. Modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of Turkey is of the order of 1019 Pa s, similar to a recent estimate for beneath central Greece. The lower uplift rates observed in western Turkey, compared with central Greece, result from the longer typical distances of fluvial sediment transport, which cause weaker coupling by lower-crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source. 相似文献
58.
59.
This study investigates the controls on three-dimensional stratigraphic geometries and facies of shallow-water carbonate depositional sequences. A 15 km2 area of well-exposed Mid to Late Miocene carbonates on the margin of the Níjar Basin of SE Spain was mapped in detail. An attached carbonate platform and atoll developed from a steeply sloping basin margin over a basal topographic unconformity and an offshore dacite dome (Late Miocene). The older strata comprise prograding bioclastic (mollusc and coralline algae) dominated sediments and later Messinian Porites reefs form prograding and downstepping geometries (falling stage systems tract). Seven depositional sequences, their systems tracts and facies have been mapped and dated (using Sr isotopes) to define their morphology, stratigraphic geometries, and palaeo-environments. A relative sea-level curve and isochore maps were constructed for the three Messinian depositional sequences that precede the late Messinian evaporative drawdown of the Mediterranean. The main 3D controls on these depositional sequences are interpreted as being: (i) local, tectonically driven relative sea-level changes; (ii) the morphology of the underlying sequence boundary; (iii) the type of carbonate producers [bioclastic coralline algal and mollusc-dominated sequences accumulated in lows and on slopes of < 14° whereas the Porites reef-dominated sequence accumulated on steep slopes (up to 25°) and shallow-water highs]. Further controls were: (iv) the inherited palaeo-valleys and point-sourced clastics; (v) the amount of clastic sediments; and (vi) erosion during the following sequence boundary development. The stratigraphy is compared with that of adjacent Miocene basins in the western Mediterranean to differentiate local (tectonics, clastic supply, erosion history, carbonate-producing communities) versus regional (climatic, tectonic, palaeogeographic, sea-level) controls. 相似文献
60.
R.M. Hernndez T.E. Jordan A. Dalenz Farjat L. Echavarría B.D. Idleman J.H. Reynolds 《Journal of South American Earth Sciences》2005,19(4):495-512
Marine transgression onto the South American continent took place at least twice in the Miocene along distinct paleogeographic corridors. The first event occurred between 15 and 13 Ma and the second between 10 and 5? Ma. Each event has particular dominant variables (tectonism, eustacy, sediment accumulation rate) that permitted the preservation of the record and development of the sea on the continent. The 15–13 Ma transgression was tectonically and eustatically controlled, flooding older sedimentary accommodation zones on the South American plate during a global high sea level, whereas the 105? Ma event was predominantly tectonically controlled, generated by tectonic loading created in the Cordillera Oriental fold-and-thrust belt. A new 7.72±0.31 Ma 40Ar/39Ar date from the Río Parapetí in Bolivia suggests that the 15–13 Ma transgression registered in Argentina produced no continental connection to the Caribbean transgression, registered in Bolivia, because of temporal constraints. 相似文献