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首页> 外文期刊>Journal of Asian earth sciences >Upper Silurian And Devonian Pelagic Deep-water Radiolarian Chert From The Khangai-khentei Belt Of Central Mongolia: Evidence For Middle Paleozoic Subduction-accretion Activity In The Central Asian Orogenic Belt
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Upper Silurian And Devonian Pelagic Deep-water Radiolarian Chert From The Khangai-khentei Belt Of Central Mongolia: Evidence For Middle Paleozoic Subduction-accretion Activity In The Central Asian Orogenic Belt

机译：蒙古中部康艾-昆泰带上志留统和泥盆纪远洋深水Radio虫Cher：中亚造山带中古生代俯冲增生活动的证据

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摘要

Recent mapping projects undertaken in Central Mongolia have revealed the widespread occurrence of radiolarian chert within a Paleozoic accretionary complex. We present the results of the first detailed tec-tonostratigraphic and radiolarian biostratigraphic investigations of the Gorkhi Formation in the Khangai-Khentei belt of the Central Asian Orogenic Belt. The Gorkhi Formation consists of sandstone shale, alternating sandstone and shale of turbidite affinity and chert with small amounts of siliceous shale, basalt, limestone, and clast-bearing mudstone. Radiolarian chert that is completely devoid of terrigenous clastic material is commonly associated with underlying basalt (sedimentary contact) and with conformably overlying siliceous shale and turbidite deposits. The tectonic stacking of basalt-chert and chert-turbidite successions is the most remarkable structural feature of the formation. The recovery of moderately well-preserved radiolarians and conodonts from red chert led to the recognition of four radiolarian assemblages that have a combined age range from the latest Silurian (Pridolian) to the Late Devonian (Frasnian). No age control exists for the siliceous shale, shale, and sandstone, although they are considered to be latest Devonian or slightly younger on the basis of stratigraphic relationships with underlying chert. The Gorkhi Formation has previously been interpreted as a thick sedimentary basin deposit overlying an unexposed Archean-Neoproterozoic basement; however, the stratigraphy within individual tectonic slices clearly corresponds to that of an ocean plate stratigraphy of an accretionary complex generated by the trenchward movement of an oceanic plate. From the lowermost to uppermost units, the stratigraphy comprises ocean floor basalt, pelagic deep-water radiolarian chert, hemipelagic siliceous shale, and terrigenous turbidite deposits. The biostratigraphic data obtained in the present study provide corroborating evidence for the existence of an extensive deep-water ocean that enabled the continuous sedimentation of pelagic chert over a period of nearly 50 million years. These data, together with structural data characterized by tectonic repetition of the stratigraphy, indicate that these rocks formed as an accretionary wedge along an active continental margin, possibly that of the Angara Craton. The mid-oceanic chert was probably deposited in the Northern Hemisphere portion of the Paleo-Pacific Ocean that faced the Angara Craton and the North China-Tarim blocks. Thus, we propose that subduction-accretion processes along the Paleo-Pacific rim played an important role in the accretionary growth of the active continental margin of the Angara Craton, directly influencing the evolution of the Central Asian Orogenic Belt.
机译：最近在蒙古中部进行的测绘项目表明，在古生代增生复合物中广泛存在放射l石石。我们介绍了中亚造山带Khangai-Khentei带中Gorkhi组的首次详细构造-地层学和放射虫生物地层学调查的结果。 Gorkhi地层由砂岩页岩，交替的砂岩和浊浊的页岩和硅质的页岩以及少量的硅质页岩，玄武岩，石灰石和含克拉斯特泥岩组成。完全不含陆源碎屑物质的放射l石通常与下伏玄武岩（沉积物接触）以及上覆硅质页岩和浊积岩沉积物有关。玄武岩-黑钙石和黑钙石-浊积岩演替的构造叠加是该地层最显着的结构特征。从红石中恢复了保存良好的放射虫和牙形石，导致人们认识到四种放射虫组合，它们的组合年龄范围从最新的志留纪（普里道纪）到晚泥盆纪（Frasnian）。尽管硅质页岩，页岩和砂岩根据与下伏硅质岩的地层关系被认为是最新的泥盆纪或更年轻，但没有年龄控制。 Gorkhi组以前被解释为覆盖在未暴露的太古宙—新元古界基底上的厚沉积盆地沉积。但是，单个构造切片内的地层学显然对应于由大洋板块向海运动所产生的增生复合物的大洋板块地层。从最低层到最高层，地层包括海床玄武岩，深海放射状l石石，半硅质硅质页岩和陆源浊质沉积物。在本研究中获得的生物地层学数据为存在广泛的深水海洋提供了确凿的证据，深海海洋使中上白垩质t石在近五千万年的时间内得以连续沉积。这些数据以及以地层构造重复为特征的结构数据表明，这些岩石沿着活动大陆边缘（可能是安加拉克拉通）形成了增生楔。大洋中部的t石可能沉积在古太平洋的北半球部分，面对安加拉克拉通和华北-塔里木块。因此，我们认为沿古太平洋边缘的俯冲增生过程在安加拉克拉通活跃大陆边缘的增生增长中起重要作用，直接影响中亚造山带的演化。

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