榆木山地区玉门砾岩磁性地层及其对青藏高原东北部变形隆升意义

青藏高原新生代变形隆升过程是青藏高原新生代构造演化研究的热点问题,地处于高原东北部祁连山东北缘的榆木山是研究高原变形隆升时空过程的关键研究区之一.榆木山地区发育了一套粗砾相磨拉石——玉门砾岩,磁性地层研究表明其底部地质年代约为3.58 Ma.经古水流、磁化率、野外考察等推断玉门砾岩可能主要为构造隆升的产物,同时在榆木山地区还发育3个与玉门砾岩有关的不整合面,其跨越年龄分别约为:5.23～3.58Ma、2.88～2.58 Ma和＜1.77～0.8 Ma.综合分析认为该地区变形隆升不晚于3.58 Ma,之后至少经历两期构造变形隆升,该结果比北东向分步生长变形隆升模式推测的变形隆升时间明显早约1Ma,应该是对高原东北部青藏-昆黄运动的响应结果.     

Formation of the Yalong Downstream Terraces in the SE Tibetan Plateau and Its Implication for the Uplift of the Plateau

The Yalong River is an important river that runs across the abruptly changing terrain of the SE Tibetan Plateau. The terraces and Quaternary sediments in its valleys preserve the information of tectonic uplift,climate changes,and landform evolution since the Middle Pleistocene. Based on geomorphological,sedimentological,and chronological investigations,6–8 terraces are identified in the lower reaches of Yalong catchment and its tributary—the Anning River. The electron spin resonance(ESR) or optically stimulated luminescence(OSL) data on the alluvial sediments in the upper portion of terraces indicate that they formed in 1.10,0.90,0.72,0.06–0.04,0.03–0.02,and 0.01 Ma. Tectonic uplift and the climatic cycle controlled the formation of the Yalong River terraces. The former dominated the dissection depths and incision rates,whereas the latter controlled the transformation between accumulation,which developed during the glacial period,and incision,which developed during the glacial-interglacial transition. The Yalong downstream incised rapidly from 1.10 to 0.72 Ma and rapidly from 0.06 Ma until the present; the terraces developed during these two periods. The incision rates in space during the two periods indicate the uplifting extent of the Jinpingshan area,which decreases toward the east and the south. The results reveal two rapidly uplifting stages in the SE Tibetan Plateau,including an accelerated uplifting since 0.06 Ma. Since the Middle Pleistocene,the tectonic uplift of the SE and NE parts of the Tibetan Plateau is synchronous,according to the same development stages of the river terraces of the Yalong downstream and the Yellow River in the Lanzhou area of the NE Tibetan Plateau. The difference in the horizontal displacement between the Xianshuihe Fault and the Anninghe Fault bend resulted in the rapid uplift of the Jinpingshan area. The incision rate for the spatial distribution of the Yalong downstream is the geomorphological response of crustal shortening and uplift differences in the SE margin block of the Tibetan Plateau. The southeastward diffusion process of the Tibetan Plateau was recorded.     

西藏高原西、中、东的分段性及其意义

经过近几十年的研究,人们已经普遍认为青藏高原是由几条近东西向的块体先后拼贴而成,大型的东西向构造是高原内部最明显的构造特征。然而根据最近所获得的有关西藏高原以及附近地区的重力场、地震层析成像、地震活动性、水平位移速度场以及地质等资料,发现整个西藏高原内部存在着明显的两条重要的南北向或近南北向构造和一些小型的南北向构造,它们将西藏高原划分为西、中、东三个有各自构造特点的部分;西侧的南北向构造沿84°～85°E延伸,东侧的近南北向构造位于92°～94°E之间。这两个构造带在上述的多种地球物理资料中均有良好的显示,是重要的重力异常变异带、重要的热结构边界带、重要的地震活动带,也是明显的地貌陡变带,等等。高原西部地形崎岖,剥蚀最深,布格重力异常最高,目前向北北西方向运动;中部地区地表平坦,发育众多的南北向地堑裂谷,东西向伸展活动最明显,海拔最高,集中分布了7座超过8000m的高峰,目前向北东东方向运动;而东部地区地形也比较崎岖,发育许多目前仍在强烈活动的走滑断层,在这些断层之间,地块相对转动,目前向北东甚至南东方向运动。造成西藏高原东西分段的原因现在还不清楚,笔者等倾向认为造成这种现象可能是由于与欧亚板块发生碰撞的印度板块在横向上也是西、中、东分段的,印度     

Evidence for Tibetan Plateau Uplift in Qaidam Basin before Eocene-Oligocene Boundary and Its Climatic Implications

Geometry analysis of the Hongsanhan (红三旱) Section in the northwestern Qaidam basin illustrates the typical growth strata in the Xiaganchaigou (下干柴沟) Formation. The age and sedimentation rates of the Xiaganchaigou and the Shangganchaigou (上干柴沟) formations were determined by the high-resolution magnetostratigraphy. This result shows that the growth strata began to form at ca. 38.0 Ma and increased sedimentation rates occurred at ca. 37.0 Ma. The uplift of the Tibetan plateau before the Eocene-Oligocene boundary is confirmed, which enables us to better understand the relationship between climatic changes and the tectonic uplift. This uplift event could have resuited in the regional drying by blocking the moisture and contributed to the Eocene-Oligocene boundary global cooling event due to the declining atmospheric CO2 concentrations by increased weathering of the mountains.     

Normal Faulting Type Earthquake Activities in the Tibetan Plateau and Its Tectonic Implication

Abstract: This paper analyzes various earthquake fault types, mechanism solutions, stress field as well as other geophysical data to study the crust movement in the Tibetan plateau and its tectonic implications. The results show that a lot of normal faulting type earthquakes concentrate in the central Tibetan plateau. Many of them are nearly perfect normal fault events. The strikes of the fault planes of the normal faulting earthquakes are almost in the N-S direction based on the analyses of the equal area projection diagrams of fault plane solutions. It implies that the dislocation slip vectors of the normal faulting type events have quite great components in the E-W direction. The extension is probably an eastward extensional motion, mainly a tectonic active regime in the altitudes of the plateau. The tensional stress in the E-W or WNW-ESE direction predominates the earthquake occurrence in the normal event region of the central plateau. A number of thrust fault and strike-slip fault type earthquakes with strong compressive stress nearly in the NNE-SSW direction occurred on the edges of the plateau. The eastward extensional motion in the Tibetan plateau is attributable to the eastward movement of materials in the upper mantle based on seismo-tomographic results. The eastward extensional motion in the Tibetan plateau may be related to the eastward extrusion of hotter mantle materials beneath the east boundary of the plateau. The northward motion of the Tibetan plateau shortened in the N-S direction probably encounters strong obstructions at the western and northern margins. Extensional motions from the relaxation of the topography and/or gravitational collapse in the altitudes of the plateau occur hardly in the N-S direction. The obstruction for the plateau to move eastward is rather weak.     

Vortex Motion of the Crust Deformation in the Tibetan Plateau and Its Foreland

VORTEX MOTION OF THE CRUST DEFORMATION IN THE TIBETAN PLATEAU AND ITS FORELANDFromtheresultsofthecooperativeprojectbetweenChengduInstituteofGeologyandMineralResources andMassachusettsInstituteofTechnology     

中国新近纪哺乳动物群的演化与青藏高原隆升的关系

新近纪哺乳动物的起源、辐射、扩散、绝灭等方面反映了气候环境的重大变化,晚新生代青藏高原的形成对东亚地区哺乳动物的演化具有直接而深远的影响。高原的隆升使自然环境发生改变,环境的变化又导致动物组成和分布的分异,以及动物对环境适应性的调整。中国新近纪哺乳动物化石研究的结果不仅表明哺乳动物群的组成和特征具有明显的区域性差异,而且中国还是一些代表性门类的起源扩散中心,也是哺乳动物洲际迁徙的关键通道。青藏高原新近纪晚期的哺乳动物群具有非常重要的意义,因为在随之而来的第四纪冰期中这些寒冷适应性动物获得了优势地位,由此成为现代动物地理区系和多样性的基础。通过以点带面的综合研究,将能够全面地认识新近纪动物地理区系对重大气候事件的响应,更准确地判断青藏高原隆升对陆地生态系统的影响。     

青藏高原莫霍面形态的重力模拟及其对探讨高原隆升机制的意义

青藏高原是印度板块板欧亚板块碰撞形成的巨大变形带，岩石圈地幔的变形特征对高原的隆或意义重大。本文分析了远震ＰＫＰ走时残差沿高原中部剖面的变化，发现莫霍面的断错在整个高原是普遍存在的；利用人工地震资料作为约束，用重力资料对莫霍面的形态进行了反演模拟，认为岩石圈地幔的断错和叠覆可能是青藏高原隆升的重要机制；最后讨论了板块中部热和密度不均匀性以及地幔流动对青藏高原岩石圈变形的影响。     

Typical Geochemical Elements in Loess Deposit in the Northeastern Tibetan Plateau and Its Paleoclimatic Implication

Widespread and thick loess deposit in the northeastern Tibetan Plateau records paleoclimatic changes over the Quaternary period. In this study, we investigate a loess section located in a high terrace of the Huangshui River in the Xining Basin, and collect samples at 20-cm intervals by digging a well of 16-m depth （including paleosol S1 and SO and several loess interlayers over the last glacial-interglacial cycle and the Holocene）. Concentration of some active elements （Sr and Ca） and inert elements （Rb, Zr, Ti） in these loess samples are measured. The results show that ratios of those elements （oxide）, such as Rb/Sr, Ti/Sr, and Zr/CaO ratios, would indicate sensitively paleoclimatic changes, especially the history of precipitation over the last glacial-interglacial and the Holocene. Moreover, the curves of Rb/Sr, Ti/Sr, and Zr/CaO ratios had almost the same variable trends from the bottom to the top and also closely correlated with values of magnetic susceptibility and the global marine δ^18O record. But compared with the curves of magnetic susceptibility, the changes of ratios of these elements （oxide） are clearer and easy to understand. Therefore, the ratios of these typical chemical elements in the loess deposit may be used as an excellent index to investigate the history of paleoclimate, particularly precipitation changes in the northeastern Tibetan Plateau.     

青藏高原草地土壤有机碳库及其全球意义

定量分析了青藏高原各类草地0～0.65m深度范围内有机碳储量,结果表明:青藏高原总面积为1.6027×10hm²的草地有机碳量达到335.1973×10⁸tC,其中以高原草甸土和高原草原土有机碳积累量为主,两者之和达到232.36×10⁸tC,占全国土壤有机碳量的23.44%,是全球土壤碳库的2.4%.在有机碳储量分析的基础上,按土壤碳释放的两种主要途径:土壤呼吸作用和土地利用方式变化与草地退化,对草地土壤碳排放进行了估算,揭示出青藏高原草地土壤通过呼吸每年排放的CO₂达到11.7×10⁸tC·a^-1,约占中国土壤呼吸总量的2.3%,明显高于全国乃至全球平均值;近30a来,青藏高原草地土壤由于土地利用变化和草地退化所释放的CO₂估计约有30.23×10⁸tC.保护青藏高原草地对于全球变化意义重大.定量分析了青藏高原各类草地0～0.65m深度范围内有机碳储量,结果表明:青藏高原总面积为1.6027×10hm²的草地有机碳量达到335.1973×10⁸tC,其中以高原草甸土和高原草原土有机碳积累量为主,两者之和达到232.36×10⁸tC,占全国土壤有机碳量的23.44%,是全球土壤碳库的2.4%.在有机碳储量分析的基础上,按土壤碳释放的两种主要途径:土壤呼吸作用和土地利用方式变化与草地退化,对草地土壤碳排放进行了估算,揭示出青藏高原草地土壤通过呼吸每年排放的CO₂达到11.7×10⁸tC·a^-1,约占中国土壤呼吸总量的2.3%,明显高于全国乃至全球平均值;近30a来,青藏高原草地土壤由于土地利用变化和草地退化所释放的CO₂估计约有30.23×10⁸tC.保护青藏高原草地对于全球变化意义重大.     

Apatite Fission Track Evidence of Uplift Cooling in the Qiangtang Basin and Constraints on the Tibetan Plateau Uplift

The Qiangtang basin is located in the central Tibetan Plateau. This basin has an important structural position,and further study of its tectonic and thermal histories has great significance for understanding the evolution of the Tibetan Plateau and the hydrocarbon potential of marine carbonates in the basin. This study focuses on low temperature thermochronology and in particular conducted apatite fission track analysis. Under constraints provided by the geological background,the thermal history in different tectonic units is characterized by the degree of annealing of samples,and the timing of major(uplift-erosion related) cooling episodes is inferred. The cooling history in the Qiangtang basin can be divided into two distinct episodes. The first stage is mainly from the late Early Cretaceous to the Late Cretaceous(69.8 Ma to 108.7 Ma),while the second is mainly from the MiddleLate Eocene to the late Miocene(10.3 Ma to 44.4 Ma). The first cooling episode records the uplift of strata in the central Qiangtang basin caused by continued convergent extrusion after the BangongNujiang ocean closed. The second episode can be further divided into three periods,which are respectively 10.3 Ma,22.6–26.1 Ma and 30.8–44.4 Ma. The late Oligocene-early Miocene(22.6–26.1 Ma) is the main cooling period. The distribution and times of the earlier uplift-related cooling show that the effect of extrusion after the collision between Eurasian plate and India plate obviously influenced the Qiangtang basin at 44.4 Ma. The Qiangtang basin underwent compression and started to be uplifted from the middle-late Eocene to the early Oligocene(45.0–30.8 Ma). Subsequently,a large-scale and intensive uplift process occurred during the late Oligocene to early Miocene(26.1–22.6 Ma) and the basin continued to undergo compression and uplift up to the late Miocene(10.3 Ma). Thus,uplift-erosion in the Qiangtang basin was intensive from 44.5 Ma to about 10 Ma. The timing of cooling in the second episode shows that the uplift of the Qiangtang basin was caused by the strong compression after the collision of the Indian plate and Eurasian plate. On the whole,the new apatite fission-track data from the Qiangtang basin show that the Tibetan Plateau started to extrude and uplift during 45–30.8 Ma. The main period of uplift and formation of the Tibetan Plateau took place about 22.6–26.1 Ma,and uplift and extrusion continued until the late Miocene(10.3 Ma).     

祁连山东段剥蚀面与青藏高原隆升

祁连山北麓广泛分布着一级剥蚀面, 它是山地阶段性隆升的产物. 通过对剥蚀面之上砾石层中细砂物质的ESR测年以及黄土地层的古地磁测定, 认为祁连山东段的剥蚀面最终解体于1.4 Ma BP. 这与邻近区域陇西盆地的剥蚀面解体时代(1.8 Ma BP)有所差异, 这或许是第四纪期间青藏高原阶段性隆升在区域间存在着差异特征的重要表现.     

Uplift of Northwest Margin of Tibetan Plateau: Indicated by Zircon LA ICP-MS U-Pb Dating of Conglomerate from Mazartagh, Tarim Basin

Radiometric age dating of detrital zircons is highly advantageous for analysis of the depositional environment and to identify source areas. Aiming at the uplift and denudation of the surrounding ranges, LA ICP-MS U-Pb analysis has been performed on zircon grains from a conglomerate collected at the Lower Pilocene of Mazartagh, which is in the center of the Tarim basin, Xinjinng (新疆), China. A wide range of ages mainly failing into three groups was yielded: 200-500, 800-1 100, and 1 800-2 000 Ma. Zircon features principally indicate magmatic origin. According to the comparison between the analyzed zircons with those from surrounding orogenic belts, the younger grains are mainly related to the west while the older ones are to the regions more eastward. The variations might imply the W-E propagation tectonic activation and uplift of the surrounding orogenic belts. The west segment uplifted and was denuded firstly, driven by the approximate W-E height difference, upon the denudation, transportation and deposition, acting as the source of young zircons analyzed. With the eastward spreading of tectonic movement, the segment more to the east rose, the meridional relief in creased rapidly and began to control the flow direction, then more zircons joined in the Pliocene in Mazartagh. It is difficult to definitely explain the source of grains with similar values to that from the Altyn Mountain region, more detailed data and chronological ages with higher precision will be helpful for making more credible conclusion.     

晚新生代岷江下蚀速率及其对青藏高原东缘山脉隆升机制和形成时限的定量约束

青藏高原东缘具有青藏高原地貌、龙门山高山地貌和山前冲积平原三个一级地貌单元 ,本文以岷江作为切入点 ,研究了该地区河流下蚀速率与山脉的隆升作用之间的相互关系。在建立岷江阶地序列的基础上 ,利用阶地高程和热释光年代学测年资料分别定量计算了岷江在川西高原、龙门山和成都盆地的下蚀速率 ,结果表明岷江各河段的下蚀速率明显不同 ,分别为 1.0 7～ 1.6 1mm / a、1.81m m/ a和 0 .5 9mm / a;在龙门山地区岷江的下蚀速率最高 ,约为川西高原地区的 1.5倍 ,约为成都平原地区的 3倍 ;而同一河段不同时期岷江的下蚀速率基本是连续的 ,具有很好的线性关系 ,可作为该河段整个河谷的下蚀速率。基于龙门山的表面隆升速率 (0 .3～ 0 .4 mm / a) ,在约束局部侵蚀基准面和气候变化对阶地形成的控制作用的基础上 ,本文建立了青藏高原东缘岷江下蚀速率与龙门山表面隆升速率之间的线性关系 ,结果表明河流下蚀速率约为山脉表面隆升速率的 5倍。根据龙门山表面在隆升速率和下切速率等方面均大于川西高原 ,并结合龙门山活动构造以走滑作用为主 ,笔者认为青藏高原东缘的边缘山脉以剥蚀隆升为主 ,兼有构造隆升作用。最后 ,根据岷江最大切割深度所需的时间 (3.4 8Ma)和成都盆地最古老的岷江冲积扇大邑砾岩的时间 (3.6 Ma     

青藏高原东北缘六盘山地区新生代构造旋转及其意义

青藏高原东北缘构造变形的研究是认识高原隆起过程、机制和印度-欧亚板块碰撞远程效应的重要途径。新生代时期,海原-六盘山断裂、香山-天景山断裂、烟筒山-窑山断裂和青铜峡-固原断裂控制的青藏高原最东北缘六盘山地区山前盆地群,接受了巨厚的新生代沉积,较完整地记录了高原东北部的变形隆升历史。通过六盘山地区丁家二沟剖面的精细古地磁研究发现,白垩纪结束后至中新世六盘山地区发生了约23°的长期顺时针构造旋转,并主要发生在三个时期:可能于晚始新世至早渐新世六盘山地区发生了约9°的顺时针旋转、早渐新世晚期顺时针快速旋转约9°、早中新世初顺时针快速旋转约5°,同时它们也被地层变形侵蚀和沉积演化所记录,说明印度-欧亚板块碰撞变形的前峰最迟在约始新世末-渐新世初就已经达到六盘山地区。这比目前普遍认同的六盘山地区变形隆升是青藏高原隆起中最晚形成(第四纪以来)的观点早了至少3千多万年,它为深入认识高原隆升过程和环境效应提供了新的证据。     

Implications of Late Pleistocene Glaciation of the Tibetan Plateau for Present-Day Uplift Rates and Gravity Anomalies

Minimal and maximal models of Late Pleistocene Glaciation on the Tibetan Plateau are considered. The large ice sheet models indicate that disintegration of the ice sheet could have contributed up to 7 mm/yr of present vertical uplift and 2 mm/yr of horizontal extension. The former value can account for more than 50% of the observed uplift in central Tibet. The peak free-air gravity anomaly arising from the deglaciation would be around −5.4 mGal. In contrast, the smaller ice sheet models do not contribute significantly to the signals of present uplift and gravity anomalies. Modern geodetic measurements therefore have the potential to constrain the Late Pleistocene glaciation of the Tibetan Plateau. Assuming a large ice sheet over the Tibetan Plateau, the disintegration can contribute up to 6 m of eustatic sea-level rise.