喜马拉雅造山带东段上三叠统复理石沉积地质研究
发布时间：2018-07-24 18:11
【摘要】：西藏南部大面积分布上三叠统复理石(即山南地体郎杰学群),它位于喜马拉雅造山带东段,构造-地层上多归属特提斯喜马拉雅北亚带,被认为系印度大陆北部被动大陆边缘(半)深海沉积；或者与修康群一起被划为雅鲁藏布江缝合带内的构造增生楔。这两种不同构造归属不仅有碍于其自身物源和沉积盆地分析,而且对晚三叠世特提斯古地理(如基末利大陆、新特提斯、冈瓦纳大陆北缘)、古构造格局及其演化的重建有重要影响。近年来,郎杰学群受到了越来越多的关注,尽管业已取得了较多研究成果,但是一些重要的科学问题尚未得到很好的解决或达成共识。这些问题主要涉及沉积体系、物源、盆地性质、古地理位置、构造演化等方面。本文对17条地质路线及32条地层剖面进行了观测记录,对70余个观察点的岩性厚度、90余组近千数据的古水流进行了测量和统计,对30余件砂岩样品的碎屑组分、近60件重矿物组合及其指数等进行了统计、计算分析；重点对20件砂岩的近1600枚碎屑锆石、6件辉绿岩的80余枚锆石进行了U-Pb同位素定年,并测试分析了170余枚碎屑锆石的Hf同位素和140余枚碎屑铬尖晶石的地球化学。在上述大量野外资料和室内测试数据基础上,作者综合研究了微相、岩相、沉积物分散样式、沉积体系和物源,并试图对沉积盆地性质、古地理和构造演化进行了探讨,初步获得以下结果和认识：沉积物分散样式方面,重矿物指数ZTR值、S/M(砂／泥)比值和古水流流向结果均指示沉积物主体由北向南供给。其中,古水流流向平均205°,复原后平均185°,并显示有多组向西南、东南方向的物源供给。三种参数组合呈现弧形-放射状沉积物分散样式,暗示郎杰学群的碎屑组分可能是通过分支水道在中扇和外扇区域扇状分散开堆积沉积,同时也可能反映了海底扇水道系统的分布形式。岩相和沉积体系方面,共识别出水道(A)、舌状体(B)、天然堤-水道间(C)和盆地平原(D)4种相,以及相应的9个亚相单元(A1-3,B1-3和C1-3)。它们构筑了海底扇6个相组合,分别是水道-水道间、漫滩-天然堤、决口扇、外扇舌状体、扇缘和盆地平原。通过岩相和沉积物分散样式分析,在原始地层分布恢复基础上,提出郎杰学群由一个以海底扇为主的深海沉积体系组成。该沉积体系规模可达400-500 km×600-700 km大小或更大,是目前报道的前新生代最大海底扇之一；它由4个横向分布、至少6次垂向叠加的海底扇体联合组成,发育中扇和外扇亚沉积体系,缺失内扇记录；垂向叠加格局显示为从进积到退积样式,指示海底扇的发育可能受海平面上升或区域构造沉降加剧控制；砂岩和板岩比例关系显示海底扇属于富泥-砂型,指示沉积物从源区经历了中-远距离(可达400-600 km)的搬运。物源分析结果显示,郎杰学群的母源区存在各种不同的岩性。重矿物组合表现出沉积岩、花岗岩、变质岩等多种原岩类型,其中辉石和铬尖晶石说明存在基性和超基性的物源。重矿物指数RuZi显示研究区东西两侧存在不同,可能是源区岩石类型变化所致,暗示至少存在两个以上不同的源区。砂岩碎屑组分比例Dickinson三角图解投点大多落入再旋回造山带,次为岩浆弧和混合区,说明物源区可能有多种构造背景。铬尖晶石地球化学成分指示源区母岩存在玄武岩、橄榄岩和玻安岩,它们可能由洋中脊和／或洋岛／海山提供。上述结果证明郎杰学群由多个母源区提供碎屑物质。多物源还进一步得到碎屑锆石U-Pb同位素年龄不同分布主值区间的证实。分析结果显示,这套上三叠统复理石砂岩中的锆石有两组年龄,分别是600-460 Ma(峰值大约520 Ma)和260-200 Ma(峰值大约240 Ma)。更为重要的是,前者与泛非造山带有关,同时表明为山南盆地提供碎屑的源区可能是拉萨地体、西澳大利亚、羌塘地体和冈瓦纳大陆其它地块,或是其中某一个或某二个以上。后者强烈支持山南地体与特提斯喜马拉雅无亲缘性的观点。特殊的碎屑锆石年龄分布区间260-200 Ma(峰值大约240Ma)、400-290 Ma的碎屑锆石较正的εHf (t)值、铬尖晶石的存在和～130 Ma的大量辉绿岩岩脉侵入体,说明山南地体与拉萨地体存在较大物源差异,至少证明拉萨地体不是山南地体的唯一物源区。基于多物源供给特性、物源区多构造背景特征,在与错美-班伯里大型火成岩省有关的早白垩世中期(大约140-128 Ma)的辉绿岩脉古地理限制下,本次工作提出,郎杰学群很可能沉积于冈瓦纳北侧的一个残留洋盆,它位于印度东部与澳大利亚西部之间。从物源区方向和岩性特征判断,北侧拉萨地体及其南北侧的岩浆弧与弧后区、新特提斯洋南侧的古海山和洋中脊可能是主要的物源区,西澳大利亚和印度东部可能会提供少量物源或者提供了其中部分泛非期相关的物源。在这种盆地模式和古地理格局下,本文推测了山南地体古地理和构造演化过程：三叠纪末期,山南盆地随着拉萨地体(弧后扩张和洋脊增生)北向漂移(构造格局发生变化)而快速终结不再接受其物源供给,随后被构造上驮在大印度东北部；侏罗纪-早白垩世早期,山南地体可能成为了大印度东北边缘部分盆地基底保持在这个位置；早白垩世中期(132 Ma以后)开始,随着印度洋打开,山南地体与印度大陆一起向北漂移,直到印度与亚洲的碰撞、隆升；始新世-至今,它与特提斯喜马拉雅一起变形变质,接受侵蚀和剥蚀。这种古地理和古构造演化暗示,山南地体可能不是雅鲁藏布江缝合带内侏罗纪-白垩纪的增生楔。
[Abstract]:The large area of the three stack complex in southern Tibet, which is located in the eastern section of the Himalaya orogenic belt, is located in the eastern section of the Himalaya orogenic belt. It is considered as the northern subzone of the Tethys of Himalaya, which is considered to be a passive continental margin (half) deep sea deposit in the northern part of the mainland of India, or in the Yarlung Zangbo Suture belt together with the Kacang group. The two types of tectonic settings not only impede the analysis of their own source and sedimentary basins, but also have important effects on the paleogeography of the late three Triassic Tethys, such as the base Continental, the new Tethys, the northern margin of the Gondwana continent, and the reconstruction of the paleotectonic pattern and its evolution. Although many research achievements have been achieved, some important scientific problems have not been well solved or reached consensus. These problems are mainly related to sedimentary system, source, basin nature, paleogeographic position and tectonic evolution. This paper has recorded 17 geological routes and 32 stratigraphic sections, and more than 70 observation points. The lithology thickness and more than 90 groups of paleo currents of nearly 1000 data were measured and counted. The debris components of more than 30 sandstone samples, nearly 60 pieces of heavy mineral assemblages and their index were calculated and analyzed. The emphasis was on the nearly 1600 detrital zircon of 20 sandstone and more than 80 zircons of 6 diabase rocks, and the test scores were tested. The geochemistry of more than 170 detrital zircon Hf isotopes and more than 140 clastic chromite spinel are analyzed. On the basis of a large amount of field data and indoor test data, the authors have studied the microfacies, lithofacies, sediment dispersion patterns, depositional systems and provenances, and tried to explore the nature, paleogeography and tectonic evolution of the sedimentary basins. The following results and understanding are obtained: the sediment dispersion style, the ZTR value of heavy mineral index, the ratio of S/M (sand / mud) and the result of paleo flow direction all indicate that the sediment main body is supplied from north to south, of which the average flow direction is 205 degrees, the average 185 degree after recovery, and the supply of many groups to the south-west and southeastern sources. Three parameter combinations The scattered patterns of arc - Radial sediments suggest that the debris components of the Lang Jiro group may be dispersed and deposited in the middle fan and outer fan area by the branch channel, and may also reflect the distribution of the seabed fan channel system. In the aspects of lithofacies and depositional systems, the A, the tongue (B), the natural dike and the waterway are identified. 4 phases (C) and basin plain (D), and the corresponding 9 subfacies units (A1-3, B1-3 and C1-3). They construct 6 facies combinations of the seabed fan, which are waterways and waterways, floodplain - natural levee, crevasse fan, outer fan tongue, fan margin and basin plain. Based on the distribution pattern of lithofacies and sediments, it is based on the restoration of the distribution of the original strata. The Jie Xue group is composed of a deep-sea sedimentary system dominated by seabed fan. The size of the sedimentary system can reach 400-500 km x 600-700 km size or larger. It is one of the largest subsea fans in the pre Cenozoic. It is composed of 4 horizontal distribution, at least 6 vertical superimposed subsea fans, and the middle and outer fan subfacies. The vertical superposition pattern shows that the development of the submarine fan may be controlled by the rise of sea level or the regional tectonic subsidence, and the relation between the sandstone and the slate shows that the seabed fan belongs to the rich mud sand type, indicating the sediment transport from the source area to the medium distance (up to 400-600 km). The results show that there are various types of lithology in the parent source area of the Lang Jie group. The combination of heavy minerals shows sedimentary rocks, granites and metamorphic rocks, among which pyroxene and chrome spinel indicate the existence of basic and ultrabasic source. The heavy mineral index RuZi shows that the East and west sides of the study area are different and may be the change of the source rock types. The result indicates that there are at least two different source regions. The Dickinson triangle diagram of sandstone debris components falls mostly into the re gyratory orogenic belt, which is the magma arc and the mixed area, indicating that there may be a variety of tectonic settings in the source area. The geochemical composition of chromium spinel indicates that the parent rock of the source region is basalt, peridotite and Bosite. It may be provided by the mid ocean ridge and / or ocean island / seamount. The results show that the Lang Jie group is provided with detrital materials from multiple parent sources. The source of U-Pb isotopes of detrital zircons is further confirmed by the main range of the main value range of different distribution of zircon. The results show that the zircon in this set of upper three series of complex stone sandstone has two groups of ages, respectively, 60 0-460 Ma (peak about 520 Ma) and 260-200 Ma (peak about 240 Ma). More importantly, the former is related to the Pan African orogenic belt, and indicates that the source area for Shannan basins may be Lhasa, Western Australia, Qiangtang, and other blocks of the Gondwana continent, or one or more of one or more of them. The latter is strongly supported. The special detrital zircon age distribution is 260-200 Ma (peak 240Ma), the 400-290 Ma detrital zircon is more than positive epsilon Hf (T), the presence of chromium spinel and a large number of diabase vein intrusions to 130 Ma, indicating that there is a great difference between the Sannan and the Lhasa terrain. At least, it is proved that Lhasa is not the only source area in the south of Shannan. Based on the supply characteristics of multi source source and the multi tectonic setting of the source area, under the restriction of the palaeogeography of the Middle Early Cretaceous (about 140-128 Ma) in the Middle Early Cretaceous (about 140-128) in the large igneous province of the wrong United States, this work suggests that the Lang Jie group is likely to be deposited in Gondwana. A residual oceanic basin on the north side, located between eastern India and Western Australia. Judging from the direction and lithologic characteristics of the source area, the magma arc and the back arc of the north side of Lhasa and its north and south sides, the ancient seamounts and mid ocean ridges on the southern side of the new Tethys ocean may be the main source areas, and a small amount may be provided in Western Australia and Eastern India. In this basin model and palaeogeographic pattern, this paper deduces the process of paleogeography and tectonic evolution in this basin: at the end of the Triassic, the Sannan basin was no longer quickly terminated with the northern drift of the Lhasa ground (after the expansion of the arc and the ridge of the ocean ridge). In the early period of the Jurassic Early Cretaceous, the southern part of the northeastern part of the great India may be maintained at this position, and in the early Cretaceous period of the early Cretaceous (132 Ma after the early Cretaceous), with the opening of the India ocean, the Sannan was drifting northward along with the mainland of India. The paleogeography and Paleogeographic Evolution suggested that the Sannan earth may not be a Jurassic Cretaceous accretionary wedge in the Yarlung Zangbo Suture Zone, which is deformed and metamorphosed together with Tethys Himalaya.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P534.51
，
本文编号：2142226
[Abstract]:The large area of the three stack complex in southern Tibet, which is located in the eastern section of the Himalaya orogenic belt, is located in the eastern section of the Himalaya orogenic belt. It is considered as the northern subzone of the Tethys of Himalaya, which is considered to be a passive continental margin (half) deep sea deposit in the northern part of the mainland of India, or in the Yarlung Zangbo Suture belt together with the Kacang group. The two types of tectonic settings not only impede the analysis of their own source and sedimentary basins, but also have important effects on the paleogeography of the late three Triassic Tethys, such as the base Continental, the new Tethys, the northern margin of the Gondwana continent, and the reconstruction of the paleotectonic pattern and its evolution. Although many research achievements have been achieved, some important scientific problems have not been well solved or reached consensus. These problems are mainly related to sedimentary system, source, basin nature, paleogeographic position and tectonic evolution. This paper has recorded 17 geological routes and 32 stratigraphic sections, and more than 70 observation points. The lithology thickness and more than 90 groups of paleo currents of nearly 1000 data were measured and counted. The debris components of more than 30 sandstone samples, nearly 60 pieces of heavy mineral assemblages and their index were calculated and analyzed. The emphasis was on the nearly 1600 detrital zircon of 20 sandstone and more than 80 zircons of 6 diabase rocks, and the test scores were tested. The geochemistry of more than 170 detrital zircon Hf isotopes and more than 140 clastic chromite spinel are analyzed. On the basis of a large amount of field data and indoor test data, the authors have studied the microfacies, lithofacies, sediment dispersion patterns, depositional systems and provenances, and tried to explore the nature, paleogeography and tectonic evolution of the sedimentary basins. The following results and understanding are obtained: the sediment dispersion style, the ZTR value of heavy mineral index, the ratio of S/M (sand / mud) and the result of paleo flow direction all indicate that the sediment main body is supplied from north to south, of which the average flow direction is 205 degrees, the average 185 degree after recovery, and the supply of many groups to the south-west and southeastern sources. Three parameter combinations The scattered patterns of arc - Radial sediments suggest that the debris components of the Lang Jiro group may be dispersed and deposited in the middle fan and outer fan area by the branch channel, and may also reflect the distribution of the seabed fan channel system. In the aspects of lithofacies and depositional systems, the A, the tongue (B), the natural dike and the waterway are identified. 4 phases (C) and basin plain (D), and the corresponding 9 subfacies units (A1-3, B1-3 and C1-3). They construct 6 facies combinations of the seabed fan, which are waterways and waterways, floodplain - natural levee, crevasse fan, outer fan tongue, fan margin and basin plain. Based on the distribution pattern of lithofacies and sediments, it is based on the restoration of the distribution of the original strata. The Jie Xue group is composed of a deep-sea sedimentary system dominated by seabed fan. The size of the sedimentary system can reach 400-500 km x 600-700 km size or larger. It is one of the largest subsea fans in the pre Cenozoic. It is composed of 4 horizontal distribution, at least 6 vertical superimposed subsea fans, and the middle and outer fan subfacies. The vertical superposition pattern shows that the development of the submarine fan may be controlled by the rise of sea level or the regional tectonic subsidence, and the relation between the sandstone and the slate shows that the seabed fan belongs to the rich mud sand type, indicating the sediment transport from the source area to the medium distance (up to 400-600 km). The results show that there are various types of lithology in the parent source area of the Lang Jie group. The combination of heavy minerals shows sedimentary rocks, granites and metamorphic rocks, among which pyroxene and chrome spinel indicate the existence of basic and ultrabasic source. The heavy mineral index RuZi shows that the East and west sides of the study area are different and may be the change of the source rock types. The result indicates that there are at least two different source regions. The Dickinson triangle diagram of sandstone debris components falls mostly into the re gyratory orogenic belt, which is the magma arc and the mixed area, indicating that there may be a variety of tectonic settings in the source area. The geochemical composition of chromium spinel indicates that the parent rock of the source region is basalt, peridotite and Bosite. It may be provided by the mid ocean ridge and / or ocean island / seamount. The results show that the Lang Jie group is provided with detrital materials from multiple parent sources. The source of U-Pb isotopes of detrital zircons is further confirmed by the main range of the main value range of different distribution of zircon. The results show that the zircon in this set of upper three series of complex stone sandstone has two groups of ages, respectively, 60 0-460 Ma (peak about 520 Ma) and 260-200 Ma (peak about 240 Ma). More importantly, the former is related to the Pan African orogenic belt, and indicates that the source area for Shannan basins may be Lhasa, Western Australia, Qiangtang, and other blocks of the Gondwana continent, or one or more of one or more of them. The latter is strongly supported. The special detrital zircon age distribution is 260-200 Ma (peak 240Ma), the 400-290 Ma detrital zircon is more than positive epsilon Hf (T), the presence of chromium spinel and a large number of diabase vein intrusions to 130 Ma, indicating that there is a great difference between the Sannan and the Lhasa terrain. At least, it is proved that Lhasa is not the only source area in the south of Shannan. Based on the supply characteristics of multi source source and the multi tectonic setting of the source area, under the restriction of the palaeogeography of the Middle Early Cretaceous (about 140-128 Ma) in the Middle Early Cretaceous (about 140-128) in the large igneous province of the wrong United States, this work suggests that the Lang Jie group is likely to be deposited in Gondwana. A residual oceanic basin on the north side, located between eastern India and Western Australia. Judging from the direction and lithologic characteristics of the source area, the magma arc and the back arc of the north side of Lhasa and its north and south sides, the ancient seamounts and mid ocean ridges on the southern side of the new Tethys ocean may be the main source areas, and a small amount may be provided in Western Australia and Eastern India. In this basin model and palaeogeographic pattern, this paper deduces the process of paleogeography and tectonic evolution in this basin: at the end of the Triassic, the Sannan basin was no longer quickly terminated with the northern drift of the Lhasa ground (after the expansion of the arc and the ridge of the ocean ridge). In the early period of the Jurassic Early Cretaceous, the southern part of the northeastern part of the great India may be maintained at this position, and in the early Cretaceous period of the early Cretaceous (132 Ma after the early Cretaceous), with the opening of the India ocean, the Sannan was drifting northward along with the mainland of India. The paleogeography and Paleogeographic Evolution suggested that the Sannan earth may not be a Jurassic Cretaceous accretionary wedge in the Yarlung Zangbo Suture Zone, which is deformed and metamorphosed together with Tethys Himalaya.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P534.51
，
本文编号：2142226
本文链接：https://www.wllwen.com/kejilunwen/diqiudizhi/2142226.html
