Detrital apatite fission track constraints on Cenozoic tectonic evolution of the northeastern Qinghai-Tibet Plateau,China: Evidence from Cenozoic strata in Lulehe section,Northern Qaidam Basin

The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due to compressional deformation during the Indo-Asian collision. In this paper, we used detrital apatite fission-track thermochronology, including 4 sandstones and 2 conglomerates samples from the Lulehe section, to reveal the Cenozoic evolution of the northern Qaidam Basin. Fission-track dating indicated the source region of the Lulehe section has experienced important cooling and uplifting in the Late Cretaceous (at ~85.1 Ma and ~65 Ma) and the Eocene (~52 Ma), respectively. The AFT age distribution on the section suggested that the provenance of Lulehe section sediments were mainly derived from the south Qilian Shan (Qilian Mountains) and Altun Shan (Altun Mountains), and two significantly provenance changes may occur at 43.4-46.1 Ma and ~37.8 Ma, respectively. The results may have strong constrains on the Cenozoic deformation and tectonic evolution of the northern Qaidam Basin and Qinghai-Tibet Plateau.     

Formation and syn-rifting process of the Wan’an Basin, South China Sea

Based on seismic and drilling data, we calculated tectonic subsidence amounts and rates of the Wan’an Basin by backstripping. The genetic mechanism and syn-rifting process of the basin were analyzed in combination with the regional geological setting. The results reveal that the basin syn-rifted in the Eocene and early Miocene under the control of the dextral strike-slip Wan’an Fault Zone. The transtensional/extentional stresses along this fault zone may be attributed to seafloor spreading of the South China Sea (SCS) in multiple episodes. Extensive basal faults and some small initial rifts in the early Paleogene can be related to southeastward extrusion and clockwise rotation of the Indochina Block. During the Oligocene, the nearly N-S directed spreading of the SCS derived the transtensional stresses in a roughly NW-SE orientation. The basin subsided rapidly in the middle and north to form two major subsidence centers. In the early Miocene, the SCS spread again in a nearly NW-SE direction, resulting in rapid subsidence in the southern basin continuous extending until the period ～16.3 Ma.     

现今绝对板块运动

根据热点假设,热点对于中间层是固定的.相对热点的板块运动叫做绝对板块运动.绝对板块运动模型可以通过反演火山链传播的速率和走向数据以确定相对板块运动在角速度空间的原点来得到.利用一组近来(0～7.8 Ma)全球分布的热点的迁移速率和走向数据,结合板块运动模型NNR-NUVEL1A,已研制出一个叫做APM2的现今绝对板块运动模型.按照该模型,太平洋板块围绕60.063°S、102.210°E处的极以(0.833 0°±0.013 3°)/Ma的速率运动,非洲板块围绕46.849°N、44.372°W的极以(0.101 5°±0.013 4°)/Ma的速率运动,南极板块的运动则以46.871°N、146.942°E为极,速率为(0.084 6°±0.017 7°)/Ma,欧亚板块的运动更慢,极为27.291°N、171.925°W,速率为(0.065 5°±0.020 6°)/Ma.这一模型表明,岩石圈相对深部地幔有一个以49.423°S、90.625°E为极,速率为(0.198 3°±0.013 5°)/Ma的净旋转.表明太平洋热点同印度-大西洋热点不一致,显示太平洋热点的运动也不一致.为了分析和比较,还给出了仅用全球分布的热点的走向数据和仅用印度-大西洋热点的走向数据得到的板块绝对运动的角速度.     

青藏高原及周缘深部结构的重力异常解释与尼泊尔Ms8.1地震

利用离散小波变换获得青藏高原布格重力异常不同尺度的总水平梯度(HGM)和横向、纵向、对角分量平方和的平方根(HVDM)图像。结果表明:1)4、5阶小波细节之和的HGM高值区域存在于尼泊尔喜马拉雅地区、喜马拉雅东构造结和阿尔金断裂带中段,即青藏高原周缘较为活跃的构造带;2)尼泊尔喜马拉雅地区和阿尔金断裂带西段存在5阶小波逼近高值HGM,较高值HGM带呈现环青藏高原形态,反映了青藏高原与周缘构造块体地壳深度变化和岩石圈地幔顶部物质性质的差异性变化特征;3)HVDM高值带分布于喜马拉雅地区、喜马拉雅东构造结地区、阿尔金断裂带和龙门山断裂带,体现了青藏高原周缘构造带形态特征;4)2015尼泊尔Ms8.1地震发生在地壳深部的HGM高-低-高分布形态的低值区和HVDM高值带的边界,是印度板块和欧亚板块持续汇聚及周缘大型走滑断裂带的调节作用、累积能量释放的结果。     

辽东湾坳陷东部新生代构造发育与成因机制

以三维地震资料为基础,刻画了辽东湾坳陷东部地区新生代断裂体系平面和剖面发育特征,对以断裂特征为主的构造样式进行了分析,并结合区域动力背景探讨了构造的发育演化与成因机制。结果表明:辽东湾凹陷东部古新世-渐新世的构造主要由NNE向的拉张正断层组成;渐新世时期以走滑构造样式为主,主干断裂附近出现走滑效应产生的增压区和释压区,同时发育似花状构造和多级“Y”字型构造样式,次级断裂多表现为NEE向的雁列状构造样式;新近纪时期断裂体系仍以雁列状断裂为主,发育共轭状剪切破裂以及“背形负花状”构造样式。构造特征体现了研究区新生代走滑构造系统与伸展构造系统的叠加改造过程,可以将辽东湾坳陷东部地区的构造演化阶段划分为古新世-始新世的弱走滑强拉张时期、渐新世的弱拉张强走滑时期以及新近纪的弱挤压弱走滑时期。      

柴达木盆地北缘麻粒岩的发现及地质特征

在柴达木盆地北缘东段,首次从古元古代达肯大坂岩群中发现太古宙麻粒岩,并取得3450Ma Sm-Nd等时线同位素年龄。该麻粒岩以包体产出于元古代变质侵入体中,原岩为拉斑玄武质岩石,其形成于大洋岛弧构造环境,经高温高压麻粒岩相变质作用形成。     

PRESENT-DAY CRUSTAL MOVEMENT OF NORTH-EASTERN QINGHAI-TIBET PLATEAU

1　IntroductionEnclosedbyBayankalablockatsouth ,Alashanblockatnorth ,Tarimblockatwest,OrdosatnortheastandSouthChinablocksateast,thenorth easternQinghai Tibetanplateau ,geologicallynamedasQilianblockanditsadjacentarea ,isanidealre gionforstudyingcontinentaldynamics,suchascrustalthickening ,extrusionandblockinteraction(Fig .1 ) .ThetectonicmovementsofnortheasternQinghai Tibetanplateau ,thestrongnappe (thrust ing)movementofnorthernQilianmountainandtheextensiveleft lateralslipalongQilian Hai…     

Characteristics of helium isotopes in natural gas and its tectonic implication in Bohai Bay Basin

1 INTRODUCTION Helium is a trace element in natural gas and the lightest element of all rare gases. It is formed during natural nuclear processes and it is chemi- cally stable. Because of its strong diffusibility and permeability, it is used as a very sen…     

Late Cenozoic Tectonic Deformation in the Dongsha Islands and Adjacent Sea Area

Dongsha Island and the adjacent sea area locate at the northern continental margin of the South China Sea (SCS), and is connected to the east by the Manila Trench. Analyses of seismic stratigraphy and gravity, magnetic and drilling wells data led to the discovery of three post-fault sequences (Ⅴ, Ⅵ, Ⅶ). Extensive tectonic uplift, magma activity and erosion occurred in Dongsha Island and the adjacent area, where most of the faults in the northeastern SCS were still active during Pliocene and Quaternary. Two groups of faults trending NEE and NW were developed during Late Cenozoic. We conclude that three important tectonic movements, especially Dongsha movement(4.4 - 5.2 Ma) and Liuhua movement (1.4 - 1.89 Ma), controlled the structural framework in the Dongsha rise; whose deformation in the east is stronger than that in the west and whose stress field variation suggests that the tectonic uplift in the study area contributed to magmato-tectonic events correlated to the main collision phases between the East China and Taiwan 5 - 3 and 3 - 0 Ma ago.     

扬马延微陆块构造特征及火山型被动陆缘远端带构造演化模式

随着全球油气勘探的不断深入,北大西洋极地逐渐成为油气勘探研究的前沿领域,而扬马延矿区勘探程度极低。基于中海油冰岛矿区新采集的地震及重磁资料,结合其他有关扬马延微陆块最新的研究资料,开展了扬马延微陆块的地层和构造特征分析,以及与共轭盆地的对比,建立了扬马延火山型被动陆缘远端带的构造演化模式。研究表明:位于北大西洋格陵兰与挪威之间海域的扬马延微陆块,与北大西洋两侧陆架盆地古生代-中生代地层具有共轭特征;构造呈NE-SE向展布,发育拆离断裂体系,与挪威西部陆架盆地中生界拆离断裂体系具有相似性;构造内部受岩浆侵入及喷出等强烈影响,发育向海倾斜反射层(SDR)及岩浆溢流相沉积。在上述研究基础上,探讨了扬马延微陆块与格陵兰古陆和波罗的海古陆拉断分离的构造演化过程,认为扬马延在古生代-中生代与格陵兰古陆和波罗的海古陆为一体,在经历了古生代-中生代陆内碰撞、弱伸展到陆内裂谷和陆内热沉降后,受北大西洋拉开影响,经历了古近纪和新近纪火山型被动陆缘远端带的形成演化过程,在55 Ma第一次洋中脊扩张期,与波罗的海古陆挪威陆缘盆地分离,在25 Ma第二次洋脊跃迁时期,新生洋脊扩张导致扬马延微陆块与格陵兰古陆分离,在沉积与构造上开始与北大西洋火山型被动陆缘盆地产生分异,最终扬马延微陆块成为孤立在洋壳上的一个"弃子"。本次关于扬马延微陆块的研究揭示了火山型被动陆缘远端带在岩浆活动、拆离断裂作用下,减薄-破裂的残余陆壳及内部新生洋壳的构造面貌及板块构造背景下的演化过程。      

阿尔金断裂带中段现今构造形变模式的InSAR研究

利用2007～2010年间14景ALOS PALSAR数据及SBAS InSAR技术,获取阿尔金断裂带中段91°E附近现今地壳形变速率场,并反演该地区断层的滑动速率和闭锁深度。结果表明,阿尔金断裂中段地区的形变速率自北向南呈3个线性梯度变化区,分别为阿尔金山东段8～12 mm/a、索尔库里盆地6～7 mm/a、阿尔金断裂带以南约0 mm/a。3个速率梯度变化区主要集中在喀腊达坂断裂和阿尔金主断裂上;拟合的断层就位于金雁山南缘、喀腊达坂断裂南邻,走滑速率从西（7.1 mm/a）向东（14.0 mm/a）逐渐增大,闭锁深度自西(4.5 km)向东(10.6 km)逐渐趋深。结合前人研究推测,金雁山（阿尔金山链东部）与索尔库里拉分盆地组成的复合破裂构造模式,是转换断层运动时应力和应变调整的主要驱动机制。     

塔里木盆地顺北地区中新生界断裂构造特征及演化

塔里木盆地顺北地区古生界油气资源非常丰富,此外在中新生界也发现了良好的油气显示,揭示出该区中新生界也具有较好的油气勘探潜力。因此,为了揭示对顺北地区中新生界油气成藏具有关键控制因素的断裂构造特征及其发育机制,通过对顺北地区最新三维地震资料的精细构造解释,系统分析了该区中新生界断裂构造的类型、几何学特征及其成因演化。研究表明：顺北地区中新生界断裂以张性正断层为主,发育少量逆断层和走滑断层,该区断裂发育数量众多但单条断裂规模较小、平面上呈杂乱展布且具有明显的分区分层的差异活动特征。与区域动力背景和盆地演化阶段相统一,顺北地区中新生界断裂演化经历了印支、燕山和喜山期3个阶段多期次伸展-挤压构造旋回,而且该区所处的构造位置、下伏中二叠统火成岩地层特征及下三叠统柯吐尔组砂泥岩塑性层等对中新生界断裂的形成演化具有重要控制作用。通过对顺北地区连通T₉⁰～T₅⁰界面通源断裂的精细刻画,揭示出在5号断裂带中部和7号断裂带中南部存在两大通源断裂发育区,上述两地区部分断裂由T₉⁰     

东海盆地西湖凹陷西北缘中始新世构造变革厘定及成因探讨

通过西湖凹陷西北缘断裂体系、构造格局、火成岩演变等构造条件综合分析，首次明确了区内中始新世存在构造变革。研究结果表明，构造变革在平湖组底界形成了显著的不整合，主要表现为削平、削超，愈向西邻近长江坳陷不整合愈发显著；构造变革前后西湖凹陷格局发生了显著变化，在杭州斜坡带主要表现为大断裂走向由早期差异到后期逐步趋同，最终导致早期分隔、多沉积中心在后期连片统一。认为中始新世这期构造变革作用的发生与周缘板块俯冲调整有关，构造变革期在时间上与西部印度板块俯冲引发高原隆升和东部太平洋板块俯冲转向、后撤作用相同步，是在西部挤压作用逐步增强背景下，盆地由整体拉张背景到西压、东张的差异化发育转变作用的主要响应。在西湖凹陷内这种构造变革作用具有广泛性，在平湖组与下伏宝石组地层的烃源岩特征上形成差异，对油气资源差异富集的贡献需要做更深入的研究。      

海南岛北部晚中-新生代剥露过程的低温年代学约束

【目的】研究海南岛大地构造在中-新生代的隆升剥露过程与热演化史,为华南地块的构造演化提供有力证据。【方法】利用磷灰石裂变径迹(AFT)、磷灰石及锆石(U-Th)/He等构造热年代学研究方法,重建海南岛北部岩体的构造-热演化历史,分析侵入岩体在不同构造热演化阶段的冷却剥蚀速率,并进一步探讨岩体隆升过程的动力学过程。【结果】AFT年龄介于(33.3±2.5)~(45.0±3.5)Ma之间,磷灰石平均长度为(12.68±0.28)~(13.04±0.9)μm;磷灰石(U-Th)/He(AHe)单颗粒年龄(36.3±2.2)~(60.2±3.7)Ma,锆石(U-Th)/He(ZHe)单颗粒年龄为(79.5±4.9)~(98.4±6.1)Ma及(37.1±2.3)~(59.6±3.7)Ma。联合反演热史揭示,研究区岩体自晚白垩世(约100 Ma)以来的冷却过程有明显的差异性,可分为4个阶段:1)约100~45 Ma相对缓慢冷却阶段;2)约45~35 Ma快速冷却剥蚀阶段;3)约30~35 Ma至10 Ma缓慢冷却过程;4)约10 Ma以来再次快速冷却剥露。【结论】海南岛北部花岗岩体阶段性抬升冷却与(古)太平洋板块的俯冲后撤、西南部印度-欧亚大陆碰撞和中新世晚期菲律宾海板块向西俯冲挤压有关。海南岛北部在Ⅰ、Ⅱ期(始新世晚期)剥蚀阶段基本造成总剥蚀量的2/3。     

青藏高原西部及邻区构造应力场反演和断层滑动趋势分析

基于Global CMT提供的1976-01-01~2015-12-31期间1 255个M_W≥3.5地震的震源机制解,利用FMSI方法对青藏高原西部及邻区（新疆西部地区）应力场进行反演,得到区域应力场特征,并分析西昆仑断裂带及阿尔金断裂带的断层滑动趋势。结果表明,青藏高原西部及邻区的最大主压应力轴σ1整体呈NNE-SSW向,自西向东顺时针旋转;最小主压应力轴σ3整体呈NWW-SEE向。最大主压应力轴σ1倾角大小约为5°~9°,说明该地区的构造应力场以水平运动为主。西昆仑断裂带及阿尔金断裂带具有较强的滑动趋势（T_s≥0.5）,说明西昆仑断裂带及阿尔金断裂带未来失稳滑动的可能性较大。     

Episodic orogeny deduced from coeval sedimentary sequences in the foreland basin and its implication for uplift process of Longmen Mountain, China

Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be the cause for the Wenchuan Earthquake and the apparent paradox of high relief,little shortening,the relative dearth of historical seismicity in the region.     

Structural feature and tectonic evolution of Awati——Bachu area in Tarim Basin

The research area is situated in the western part of Tarim basin, which includes Awati depression and Bachu uplifted block. It underwent three times processes of compression in a large scale and a near term extension since Cambrian. The first compression occurred during Middle Cambrian to Devonian, which formed fault band folds in NW axial direction. They were ＂under-water uplift＂ and distributed all over the research area. The second compression occurred in Late Permian and formed fault band folds and a few fault propagation folds in NS axial direction. They are developed near Tumuxiuke fault belt and the northern research area. The western anticline is bigger than the eastern one in extent and size. The third compression occurred during Palaeogene to Quaternary and formed tumuxiuke fault belt and fault propagation folds in NW direction. They are distributed over the south part of the research area. Tumuxiuke fault belt is a big scale dextral reversed strike-slip fault belt; it transformed or destroyed the fold structure of the research area. A short-term extension occurred during Early Permian. Tarim Basin is in the rift forming stage of craton, and there exist widespread basic vol- canic rocks, basic intrusive bodies and dikes.     

Tectonic Characteristics and Evolution of Bohai Bay Basin, China

Synthetical analyzing the deep geophysical data within Bohai bay basin the authors detect the deep crustal structure presenting high geothermal flux, thinned crust and arched Moho discontinuity, and the basin basement belongs to rigid continental crust. The development of the basin was controlled by two - dimensional faults in NNE and NWW directions. The tectonic units of the basin can be subdivided into three structural divisions: the east, middle and west division. The basin is considered as a continental rift. The tectonic background and regional right - lateral stress field during the late Cretaceous and Paleogene were a compound result of the Kula Plate W - directional subducting under Eurasia Continental Plate in 80 ～ 74Ma and the Philippine sea Plate W -directional subducting under the Eurasia Continental Plate since 60Ma, the long-rang effect of the India Continental Plate wedging into the Eurasia Continental Plate and of the Siberia Plate SE - directional relatively moving.     

ON TECTONIC PROBLEMS OF THE OKINAWA TROUGH

The Okinawa Trough is a very active tectonic zone at the margin of the Northwest Pacific and is typical of back-arc rifting at the young stage of tectonic evolution. Many scientists from Japan,China, Germany, France, the U. S.A. and Russia have done a lot of geologic and geophysical investigations there. It is well known that the Okinawa Trough is an active back-arc rift with extremely high heat flow, very strong hydrothermal circulation, strong volcanic and magmatic activity, frequent earthquakes,rapid subsidence and rifting, well-developed fault and central graben. But up to now, there are still some important tectonic problems about the Okinawa Trough that require clarification on some aspects such as the type of its crust, its forming time, its tectonic evolution, the distribution of its central grabens, the relationship between its high heat flow and tectonic activity. Based on the data obtained from seismic sur-vey, geomagnetic and gravity measurements, submarine sampling and heat flow measurements in the last 15 years, the author discusses the following tectonic problems about the Okinawa Trough: (1) If the Okinawa Trough develops oceanic crust or not. (2) Is the South Okinawa Trough tectonically more active than the North Okinawa Trough with shallower water and few investigation data on it. (3) The formation time of the Okinawa Trough and its tectonic evolution. The Okinawa Trough has a very thin continental crust. Up to now, there is no evidence of oceanic crust in the Okinawa Trough. The North, Middle and South Okinawa Trough are all very strongly active areas. From 6 Ma B.P. , the Okinawa Trough began to form. Since 2 Ma, the Okinawa Trough has been very active.     

Petrogenesis and tectonic setting of granite porphyry in Keyouzhongqi area,Inner Mongolia

The authors studied the geochemistry,zircon U-Pb ages,Hf isotope of the granite porphyry and its petrogenesis and tectonic setting in the studied area． The zircon U-Pb dating indicates the formation of the gran- ite porphyry is in Early Cretaceous (125． 1 ±1． 5 Ma)． The granite porphyry has high-SiO2and alkali-rich fea- tures,which belongs to high-K calc-alkaline series rocks (A/CNK = 0． 95%--1． 25%)． The analyses of trace elements show the characteristics of a swallow-shaped ＲEE distribution pattern with enrichment in LＲEEs and most of LILEs and HFSEs,depletion in Ba,Sr,Nb,P and Ti,and especially strong depletion in Eu,which indicates the granite porphyry belongs to the aluminous A-type granite． Their εHf(t)range from 5． 94 to 8． 80 with Hf two-stage model ages (TDM2) of 620 Ma to 803 Ma． Combining with the regional tectonic background, we conclude that the source of the rocks is the new crust materials accreted from depleted mantle in Neoprotero- zoic and is the product of partial melting of middle and lower crustal rocks,which may be suffered from the dual impact of the subduction of the Palaeo-Pacific Ocean and the closure of the Mongol-Okhotsk Ocean．