华北陆块中奥陶世绝对位置探讨

"幔柱生成带理论"认为现今的热点以及显生宙经过古板块重建后的板块上的大岩浆岩省和金伯利岩岩体的位置大致位于大剪切波低速省在地表投影的边缘.在板块上具有可识别且年代确定的大岩浆岩省或金伯利岩岩体时,可依据"幔柱生成带理论"对板块的绝对位置进行恢复.本文在前人对华北陆块中奥陶世金伯利岩岩体研究的基础上,对华北陆块中奥陶世的古地磁数据进行分析和筛选,并结合前期奥陶纪的全球古板块再造及全球构造格局研究,辅以岩相生物古地理分析,将华北陆块中奥陶世的绝对位置确定为:纬度在约16.6°~19.1°S,经度在约10°W.在地理位置上位于西伯利亚和冈瓦纳大陆之间,靠近西伯利亚板块.且在寒武纪-奥陶纪,华北陆块在经向上具有逐渐远离冈瓦纳大陆并向西伯利亚板块靠拢的趋势.     

塔里木早二叠世大火成岩省

塔里木早二叠世大火成岩省是继峨眉山大火成岩省之后在中国境内确认的又一个大火成岩省,是当前研究的热点和前沿问题.论文系统总结了塔里木大火成岩省近20年研究取得的成果,指出了下一步重点研究领域.塔里木大火成岩省火山岩的残余分布面积大于25万平方公里,最大残余厚度达780 m,大规模玄武岩的喷出发生在290～288 Ma期间,属于快速喷发的大火成岩省岩浆事件.塔里木大火成岩省中最为发育的玄武岩和辉绿岩岩墙的微量元素特征与OIB的特征相似,且以高钛型为主体;但在同位素特征上明显的可以分为两类,柯坪地区玄武岩具有负的εNd值,重稀土值相对较高,来自富集型地幔;塔北玄武岩和辉绿岩具有正的εNd值和相对低的重稀土值,来自亏损型地幔.早二叠世大规模地壳抬升、苦橄岩与大规模岩墙群发育和瓦基里塔格大型钒钛磁铁矿矿床都支持塔里木大火成岩省与地幔柱活动有关.塔里木大火成岩省与中亚地区广泛发育的二叠纪基性和超基性岩浆作用存在着时空联系,它们是代表了一次具有重要地球动力学意义的构造岩浆事件.论文指出了塔里木大火成岩省的深部地质过程、成矿作用、与地幔柱关系、与盆地环境变化和生命演化的关系及其大火成岩省的地球动力学意义等方面研究将是下一阶段的重点研究领域.     

塔里木早二叠世大火成岩省的成因模式

近20年来,塔里木早二叠世大火成岩省在各类火成岩的空间分布、时间序列、地球化学特征、地幔源区和岩浆演化等方面有了深入的认识,为揭示大火成岩省的成因模式和演化过程奠定了坚实的基础.本文将主要基于塔里木大火成岩省存在的两阶段岩浆产物,结合前期研究基础和前人研究成果,系统论证塔里木早二叠世大火成岩省成因的两阶段熔融模式.模式认为塔里木大火成岩省的形成与地幔柱活动有关,其地幔柱作用形式兼具"巴哈纳型"和"德干型"两种特点,即早期高热的地幔柱引起了岩石圈地幔的低程度部分熔融,后期地幔柱上升绝热减压引起地幔柱自身部分熔融.在早期熔融事件中,地幔柱主要表现为上部岩石圈熔融所需的热供给,后期熔融过程中地幔柱成为熔融发生的主要场所和物质供给源.第一阶段喷发的两类玄武岩具有高~(87)Sr/~(86)Sr、低~(143)Nd/~(144)Nd的同位素特征,富集大离子亲石元素和高场强元素,为富集的大陆岩石圈地幔部分熔融的产物,具有"巴哈纳型"特征;而第二阶段产出的基性-超基性侵入岩具有相对两类玄武岩较低的~(87)Sr/~(86)Sr,较高的~(143)Nd/~(144)Nd比值,为地幔热柱熔融的产物,具有"德干型"特征.其中第一阶段,可细分为Group1和Group2两类玄武岩,Group2玄武岩相对Group1玄武岩具有较低的~(87)Sr/~(86)Sr,较高的~(143)Nd/~(144)Nd比值.Group2玄武岩显示连接Group1玄武岩和第二阶段岩浆作用的过渡类型特征,表明塔里木早二叠世大火成岩省是地幔柱与岩石圈地幔持续相互作用的结果.关于塔里木大火成岩省成因模式的研究有助于增进对塔里木大火成岩省岩浆作用、深部地质过程和地球动力学过程的全面认识,有利于丰富大火成岩省的成因理论和地幔柱活动理论.     

欧亚大陆地震面波层析成像(摘要)

本文介绍了利用宽频带瑞雷波和勒夫波频散对欧亚大陆的地壳和上地幔进行层析成像系统研究的结果。多数周期的分辨率为 5°～ 7 5°。解释结果表明 ,塔里木盆地、四川盆地以及西藏高原的地壳显示低速异常 ;以乌拉尔山脉为界的东欧地台和西伯利亚地盾之下有延伸到上地幔的大陆根 ,它们以高速异常为特征 ,在几个较小的地盾或岩石圈地块之下也是高速异常的上地幔 ,如波罗的海地盾、塔里木地块、哈萨克地台、印度地盾、华南地块等。亚洲大陆东部边缘的上地幔具有突出的低速异常特征 ,西藏北部的上地幔是低速异常区。欧亚大陆地震面波层析成像(摘要)@Michael H.Ritzwoller @Anatoli L.Levshin     

新疆塔里木地台晚古生代古地磁极移曲线及其地质构造含义

用热退磁辅以交变退磁方法对采自塔里木盆地阿克苏地区四石厂剖面47个采样点518块标本进行了逐步磁清洗和测试。由本征剩磁方向统计得到塔里木地台晚古生代的古地磁极位置(晚泥盆世φ=10.5°S、λ=151.2°E;晚石炭世φ=52.2°N、λ=179.5°E;早二叠世φ=56.5°N,λ=190.1°E)。古地磁结果表明:塔里木地台在晚古生代是北方大陆的块体之一。从晚石炭世至早二叠世塔里木地台已和北方的哈萨克斯坦板块、西伯利亚地台、俄罗斯地台等连成一片,并且从中生代以来它们之间的相对位置没有发生过大规模的变动     

华北克拉通东北部及邻区地壳和地幔转换带厚度研究

本文利用宽频流动台阵记录的远震波形资料和接收函数波动方程叠后偏移方法,获得了华北克拉通东北部边界及其邻近地区的地壳和地幔转换带的间断面结构图像.结果显示研究区域的地壳厚度存在显著的横向变化:以南北重力梯度带为界,西北部的兴蒙造山带地壳较厚(~40 km),东南部的燕山带、松辽盆地和辽东台隆地壳明显较薄(30~35 km).这有可能反映,研究区南北重力梯度带两侧地壳在中-新生代区域构造伸展过程中经历了不同程度的改造和减薄.地幔转换带成像结果显示,研究区410 km和660 km间断面结构存在横向差异.经度121°E-122°E之间,上地幔底部出现双重间断面,深度分别为660 km和690 km.经度122.5°E以东(北黄海地区),410 km间断面有5~20 km幅度的下沉,660 km间断面有5~15 km幅度的抬升;该地区地幔转换带厚度相对全球平均偏薄10~20 km,指示着该地区较热的上地幔底部温度环境.我们认为太平洋俯冲板块可能停滞在研究区119°E-122°E经度范围的地幔转换带中,但未延伸至118°E以西;而俯冲板块在124°E以东可能局部穿透了上地幔底部而进入下地幔,同时引起小尺度的地幔对流,导致北黄海地区下地幔物质的上涌.     

中国南北带地壳和上地幔的三维速度图象

本文采用作者提出的地震层析成象法得到了中国南北带地壳和上地幔的三维速度图象。通过误差和分辨分析,以及同爆炸地震测深剖面的比较,证明了成象结果的可靠性。 成象结果表明:1.南北带的地壳和上地幔存在显著的横向不均匀性,深达450km这种不均匀性还依然存在;2.地壳上部的速度图象与地表的已知地质特征明显相关:四川盆地显著低速,康滇地轴显著高速;3.中地壳在很大范围内存在低速层,其最低速度值达5.60km/s;4.在25°N-38°N和100.0°E-103.2°E的长条带内,上地幔顶部出现低速异常,异常速度值约为7.49km/s。 成象结果还清晰地勾划了各块体间的焊接边界。120km深度的速度图象表明,扬子准地台自秦岭以南以龙门-大巴和盐源-丽江台缘褶带为其西部边界;西南以哀劳山褶皱带为界;东南则以右江褶皱带内的南盘江为界。 统计表明,地震活动与南北带的速度结构相关:从20km以上的速度图象发现,大地震大都发生在高速和低速间的过渡条带上。     

东亚及西太平洋边缘海高分辨率面波层析成像

根据欧亚大陆及西太平洋地区58个数字地震台站约12000个长周期波形记录,挑选出4100条面波大圆传播路径,采用面波频散及波形拟合反演方法,对东亚及西太平洋边缘海地区(60°E-160°E,20°S-60°N)的地壳上地幔进行了高分辨率三维S波速度成像. 结果表明,从上地壳到70km深,在东亚东部及西太平洋边缘海地区为高速分布,西部以青藏高原为中心呈极低速分布. 自地中海经土耳其、伊朗、喜马拉雅山到缅甸、印尼群岛的特提斯汇聚碰撞带,显示为低速异常链. 从85km至250km深,在东亚东部及西太平洋边缘海,自北向南显示出一条巨型低速异常带,西部地区为高速异常分布.以东经110°E为界,东西两部分岩石圈、软流圈的结构与深部动力过程有着巨大的差异. 此界线以西主要是印度板块与欧亚板块碰撞引起的岩石圈汇聚增厚区,东部则主要是由于软流圈上涌(地幔热物质上升)引起的岩石圈拉张减薄区.     

磁异常揭示的峨眉山大火成岩省的深部结构

峨眉山大火成岩省位于中国西南部,在晚二叠纪约260 Ma喷发出巨量的大陆溢流型玄武岩.对于大火成岩省的岩浆喷发,在地下必定有一个相应的大规模岩浆聚集和运移系统.地球物理方法是探测岩石圈内部的有效方式.峨眉山大火成岩省为镁铁质岩浆喷发,由于镁铁质-超镁铁质岩石一般具有强磁性,因此,在喷发结束之后,地下岩浆系统如果被镁铁质岩浆填充,冷却固化成为岩石圈的一部分,很有可能会引起磁异常.本文使用区域磁异常数据来对峨眉山大火成岩省的深部构造进行研究.该区域的磁异常由一系列离散的异常组成,通过3D磁化率反演可以得到磁性体的空间分布.由于磁异常中具有明显的剩磁,直接使用经典的反演方法会有较大误差,我们首先将磁异常转换为弱敏感于磁化方向的磁异常模量,再使用模量数据进行3D反演,得到地下空间内磁异常源的分布.经过分析认为这些离散分布的磁异常源反映了岩石圈内部的镁铁质-超镁铁质侵入体.侵入体的位置可能反映了底侵和内侵的镁铁质岩浆固化形成的侵入体,代表镁铁质岩浆房位置或者岩浆运移的主要通道.     

全球下地幔波速异常结构综述

下地幔体积占地球总体积50%以上,对地球的演化具有重要的影响.早期研究认为下地幔的组分比较均一,但1970年代以来,地震层析成像揭示了地球的深部速度结构,发现下地幔存在很多复杂的波速异常区.进入21世纪以后,台阵数据的积累和计算机技术的进步使我们能够进一步约束这些下地幔波速异常区的空间范围和波速结构,由于这些异常结构通常与俯冲板片和地幔柱等有紧密的联系,了解这些波速异常体的精细结构对于古板块的重建和地幔动力学有重要的意义.本文重点总结了近30年以来利用地震数据研究下地幔异常体的方法和结果,详细地描述了不同类型的波速异常区在全球范围内的分布情况及其特征,并逐一分析了不同类型波速异常构造体的成因.下地幔LLSVP主要有两个,分别是非洲LLSVP和太平洋LLSVP,它们在横向上可扩展至数千千米,垂直方向上从核幔边界的高度超过1 000 km.现在观测结果发现LLSVP边界处的速度突变较大,主流的观点认为含有成分异常的热化学作用形成了LLSVP. ULVZ位于下地幔底部,其横向扩展大部分小于1 000 km,但部分ULVZ的范围可以超过1 000 km,高度仅为十几到几十千米,相应的S波速度异...     

Plume Generation Zones at the margins of Large Low Shear Velocity Provinces on the core–mantle boundary

Large Igneous Province (LIP) eruption sites of the past 300 My lie vertically above 1% slow shear wave velocity (V_s) contours bounding the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) at the core–mantle boundary (CMB), or in the cases of the Siberian and Columbia River LIPs, bounding one or other of two smaller, Low Shear Velocity Provinces (LSVPs). Steep gradients in V_s at the CMB coincide with those 1% slow contours. The sites of 24 active hotspot volcanoes project down to the same narrowly defined borders of the LLSVPs at the CMB. Plumes that have generated LIPs and major hotspot volcanoes have risen only from the immediate neighbourhoods of the 1% slow V_s contours at the CMB which thus define Plume Generation Zones (PGZs). PGZs projected vertically upward approximately match the + 10 m elevation contour of the geoid showing that the LLSVPs are a dominant control on the positively elevated geoid. Minima in the frequency distribution of shear wave velocities in the lowermost mantle near V_s = ? 1% indicate that regions with more negative velocities, forming ～ 2% of total mantle mass, are likely to be of material compositionally different from the rest of the mantle. Because all LIP eruption sites with ages younger than 300 Ma lie above the borders of LLSVPs or LSVPs at the CMB, PGZ footprints are inferred to have remained in the same places for the past 300 My. Because no plumes have risen from the interior of the LLSVPs and because no lithospheric slabs have penetrated those bodies the volumes of the LLSVPs are inferred to have also remained unchanged for the past 300 My. Because the LLSVPs are the dominant control on the positively elevated areas of the geoid those too must have remained as they now are since 300 Ma. The LLSVPs are not rising buoyant objects but stable features of the deep mantle. LIPs have been erupted throughout the past 2.5 Gy indicating that PGZs comparable to those of the past 0.3 Gy and LLSVPs (of which PGZs mark the margins at the CMB) have also existed for at least that long. LLSVPs could thus form the isolated reservoir invoked by some to explain the distinctive isotopic compositions of terrestrial rocks. PGZs lie at places where the boundaries of: (i) The outer core, (ii) one of the LLSVPs or LSVPs, and (iii) the seismically faster part of the deep mantle meet. Horizontal temperature gradients across the steeply inclined margins to the LLSVPs, the interiors of which are hotter than the surrounding mantle, at the CMB are key controls for the generation of plumes. Near the CMB the association of the high temperature of the outer core with an inclined thermal boundary layer at the margins of LLSVPs facilitates the generation of mantle plumes in the PGZs.     

Early Permian Tarim Large Igneous Province in northwest China

Tarim Large Igneous Province (TLIP) is the second Late Paleozoic LIPs in China after the recognition of Emeishan LIP, and is a hot research topic in geosciences. On the basis of the analysis of research history about TLIP, this paper summarizes the research result during last twenty years and suggests the key research area in the future. The residual distribution range of TLIP is up to 250000 km², and the largest residual thickness is 780 m. The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma. The lithological units of the TLIP include basalt, diabase, layered intrusive rock, breccia pipe mica-olivine pyroxenite, olivine pyroxenite, gabbro, ultramafic dyke, quartz syenite, quartz syenite porphyry and bimodal dyke. The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE, and mainly belong to high TiO₂ series. There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin. The basalt from Keping with negative ? _Nd and high REE value derives from enriched mantle, and the diabase and basalt from the northern Tarim Basin with positive ? _Nd and low REE value are related to depleted mantle. The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V-Ti-Magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume. The TLIP has a temporal-spatial relationship with Permian basic to ultra-basic igneous rock, which is distributed widely in Central Asia, and they represent a tectono-magmatic event with very important geodynamic setting. This paper also suggests that the deep geological process, the relation with mantle plume, mineralization, the relation with environmental change and biological evolution, and the geodynamics of the TLIP will be the key research topics in the future.     

Core–mantle boundary topography as a possible constraint on lower mantle chemistry and dynamics

The origin of large low shear-wave velocity provinces (LLSVPs) in the lowermost mantle beneath the central Pacific and Africa is not well constrained. We explore numerical convection calculations for two proposed hypotheses for these anomalies, namely, thermal upwellings (e.g., plume clusters) and large intrinsically dense piles of mantle material (e.g., thermochemical piles), each of which uniquely affects the topography on Earth's core–mantle boundary (CMB). The thermochemical pile models predict a relatively flat but elevated CMB beneath piles (presumed LLSVPs), with strong upwarping along LLSVP margins. The plume cluster models predict CMB upwarping beneath upwellings that are less geographically organized. Both models display CMB depressions beneath subduction related downwelling. While each of the two models produces a unique, characteristic style of CMB topography, we find that seismic models will require shorter length scales than are currently being employed in order to distinguish between the end-member dynamic models presented here.     

Peperites in the Permian Tarim large igneous province in Northwest China and their constraints on the local eruption environments

Peperites are special kinds of volcaniclastic materials generated by mingling of magma and unconsolidated sediments.They directly demonstrate the contemporaneity of volcanism and sedimentation,and hence they can be used to constrain the local paleoenvironments during volcanic eruptions.We identified peperites in the lower sequence of the northwest outcrops(Inggan-Kalpin area)of Permian Tarim large igneous province(TLIP),Northwest China.In Inggan,blocky peperites were observed at the base of lava flows generated in the second eruption phase.This kind of peperites is generated by quenching of magma in a brittle fragmentation mechanism.While in Kalpin,both the second and the fourth eruption phases preserved peperites in the base of lava flows.Not only blocky but also fluidal peperites can be observed in Kalpin.The fluidal peperites were generated in vapor films,which insulated the magmas from cold sediments and avoided direct thermal shock,and therefore kept the fluidal forms of magma.All of these peperites are hosted by submarine carbonates.In lava sequences generated in the same eruption phases but located in Kaipaizileike,~15 km east to Inggan,terrestrial flood basalts developed while peperites are absent,implying a paleoenvironmental transition between Kaipaizileike and Inggan-Kalpin area.Gathering information from observed peperites,TLIP lava flows,and the Lower Permian sedimentary strata,we precisely constrained the spatial distribution and temporal evolution of sedimentary facies of the early stage of TLIP.As a result,two marine transgressions were identified.The first transgression occurred contemporaneous with the second eruption phase.The transition from submarine to subaerial is located between Kaipaizileike and Inggan.The second transgression occurred contemporaneous with the forth eruption phase,and the transition from submarine to subaerial occurred between Inggan and Kalpin.     

塔里木盆地石炭-二叠纪异常热演化及其对深部构造-岩浆活动的指示

本文分析了塔里木盆地大量实测镜质体反射率(Ro)数据,显示盆地西北部石炭系与二叠系之间Ro值演化不连续,记录了石炭-二叠纪间发生的构造-热事件,是地层抬升剥蚀和高温热事件共同作用的结果.热史模拟得出盆地在石炭纪末地温梯度开始升高,至~300 Ma达到峰值,分布在4.8~5.6℃/100m之间,早二叠世迅速降低,随后进入缓慢稳定降低阶段.区域上高温热效应空间分布与塔里木大火成岩省的分布范围存在较好的相关性,但早于大规模玄武岩喷发的时间(290—288Ma),且后者热效应范围有限.因此推断这种高温异常是大规模的深部岩浆活动,即深部岩浆房相对长时间热烘烤的结果.该研究结果为塔里木盆地热演化机制及相关热效应提供了新的线索.     

Permo-Triassic magnetostratigraphy in China: northern Tarim

The upper boundary of the Permo-Carboniferous Reversed Polarity Superchron has been identified in a palaeomagnetic study of the Permo-Triassic of the northern part of the Tarim Basin, China. This boundary serves as an important marker horizon for correlation with other Permo-Triassic sequences both in China and world-wide. A Permo-Triassic palaeomagnetic pole for the Tarim Block is estimated to be at 71.8°N, 187.6°E.Comparison with similar age poles from the adjacent blocks of China and Asia suggests that the Tarim was widely separated from the Sino-Korean Block in Permo-Triassic times but was not yet sutured to Kazakhstan.     

Petrogenetic model of the Permian Tarim Large Igneous Province

Over the last two decades great strides have been made in characterizing the spatial distribution, time sequence,geochemical characteristics, mantle sources, and magma evolution processes for various igneous rocks in the Early Permian Tarim Large Igneous Province(TLIP). This work has laid a solid foundation for revealing the evolutionary processes and genetic models of large igneous provinces(LIPs). This study systematically demonstrates the two-stage melting model for the TLIP based on our previous research work and predecessor achievements, and highlights the two types of magmatic rocks within the TLIP.The two-stage melting model suggests that the formation of the TLIP is mantle plume related. The early hot mantle plume caused the low-degree partial melting of the lithosphere mantle, while in the later stage, the plume partially melted due to adiabatic uplift and decompression. Therefore, this model carries signatures of both the "Parana" and "Deccan" models in terms of mantle plume activity. During the early stage, the mantle plume provided the heat required for partial melting of sub-continental lithosphere mantle(SCLM), similar to the "Parana Model", while later the plume acted as the main avenue for melting, as in the "Deccan Model". Basalts that erupted in the first stage have higher 87Sr/86 Sr, lower 143Nd/144 Nd ratios, and are enriched in large ion lithophile elements and high field strength elements, indicating a possible origin from the enriched continental lithosphere mantle,similar to the Parana type geochemical features. The basic-ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86 Sr,higher 143Nd/144 Nd ratios relative to the basalts, consistent with the involvement of a more depleted asthenospheric material,such as a mantle plume, similar to the Deccan type geochemical features. The first stage basalts can be further subdivided into two categories, i.e., Group 1 and Group 2 basalts. Group 2 basalts have lower 87Sr/86 Sr and higher 143Nd/144 Nd ratios than Group 1 basalts, and lie between compositions of the Group 1 basalts and second stage magmatism. Group 2 basalts may be the intermediate component of the TLIP, and the whole TLIP is the result of plume and lithosphere interaction. Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes. Furthermore, this work enriches the theories describing the origin of large igneous province and mantle plume activity.     

Origin of ULVZs near the African LLSVP: Implications from their distribution and characteristics

Ultra-low velocity zones (ULVZs) provide important information on the composition and dynamics of the core-mantle boundary (CMB). However, their global distribution and characteristics are not well constrained, especially near African large low-shear velocity provinces (LLSVPs). Here, we used ScS precursor (SdS) and postcursor (ScscS) phases recorded by various seismic networks in Africa and South America to investigate the ULVZ characteristics underlying the South Atlantic Ocean. We found no evidence of ULVZs near the SE boundary of South America, but an ULVZ was found within the SW boundary of the African LLSVP, with thicknesses ranging from 11–18 km and reductions in S-wave velocities of 18%–34%. Our results, combined with the global distribution of ULVZs, suggest that thermal activity may be essential to ULVZ formation. Moreover, subducted slab and mantle flow may also play a key role, depending on the location of the ULVZs.     

华南二叠系卡匹敦阶高分辨率浮点年代标尺

基于详细的生物地层学研究,以磁化率为古气候替代指标,对广西来宾铁桥剖面卡匹敦阶地层开展时间序列分析,建立高分辨率浮点年代标尺(FPTS).结果表明,磁化率记录了铁桥剖面中二叠世晚期沉积序列中的米兰科维奇旋回,卡匹敦阶上部磁化率突然增加与峨眉山玄武岩喷发和卡匹敦晚期全球性海退有关,这些事件导致同期沉积物中碎屑物质增加.铁桥剖面瓜德鲁普—乐平统界线附近磁化率和蓬莱滩剖面(乐平统底界GSSP)表现出一致的变化趋势,具可对比性.利用多窗谱法(MTM)和傅里叶变换(FT)从磁化率序列中识别出五个米兰科维奇周期:长偏心率周期(E2,405ka)、短偏心率周期(E1,100ka)、长地轴斜率周期(O2,44.1ka)、长岁差周期(P2,20.95ka)和短岁差周期(P1,17.7ka).对比基于E2周期建立的磁性地层磁化率(MSS)带和标准参考带(SRZ),建立整个沉积序列的高分辨率(200ka)FPTS,提出卡匹敦阶的时限为3.85 Ma(存在+0~0.28 Ma误差),整段沉积序列的平均沉积速率为2.91cm·ka-1.同时计算出卡匹敦阶内部七个牙形石带的时限,从最短26.6ka到最长2.3 Ma.另外,估算出峨眉山大火成岩省喷发启动时间为262.67 Ma,位于瓜德鲁普—乐平统界线之下1.42 Ma.     

Tectonics of Precambrian basement of the Tarim craton

The Altyn Tagh Mountain is the main area where the Precambrian basements of Tarim craton are exposed. There are two ophiolitic belts in Altyn Tagh: one belt is exposed in the northern margin of Altyn Tagh whose formation age is about (829±60) Ma, the other is situated along the southern margin of Altyn Tagh and has a formation age of about (1449±270) Ma. This paper proposes a simple tectonic model for the Precambrian basement of Tarim craton established from ophiolites in Altyn Tagh area. The south Tarim block had amalgamated with Qaidam block during about 1400-1500 Ma along the present Altyn fault, while the south Tarim-Qaidam united block was still separated from the north Tarim block by an ocean. The united block of south Tarim and Qaidam collided with north Tarim block along the zone of high positive anomaly of central Tarim, Hongliugou and Lapeiquan in about 800 Ma. So since the Sinian (beginning at 800 Ma) there has been an integrated basement for Tarim craton.