青藏高原岩石圈结构、隆升机制及对大陆变形影响

根据近年古生物区系、岩相古地理、地质构造以及古地磁等的研究,特别是晚古生代—白垩纪古生物区系、分异指数特征以及古地磁数据等,作者认为,从晚古生代—白垩纪印度板块和青藏高原(欧亚板块)之间不存在至今还流传引用的浩瀚深邃宽达6000～7000km、向东敞开的特提斯大洋(R.S.Di-etz,J.C.Holden,1970及其他地质学家),其时印度板块与欧亚大陆之间呈现小洋盆、海湾、裂陷槽与微古陆相间构造格局;也未发生过印度大陆和青藏高原南部地体跨越这一特提斯大洋自南向北作长距离漂移。早年魏根纳(Wegener,A,1924)提出的印度大陆未远离欧亚大陆的论点,基本是正确的。     

新生代阿尔金断层中、东段右行走滑特征

从柴达木、准噶尔、塔里木3个地块近4个古地磁样品中得出的古纬度数据表明,新生代阿尔金断层中、东段的右行走滑特征明显。白垩纪以来,新疆板块相对柴达木地块向北移动了0.6°-5.4°。据此将断裂两侧各地块复原到白垩纪末的位置,天山-北山地体与祁连山地体相联,柴达木地体成为塔里木地体的东延部分。     

青藏高原拉萨地块早白垩纪火山岩古地磁结果及其构造意义

对青藏高原拉萨地块早白垩纪火山岩15个采点的古地磁测定,揭示了一组高温特征剩磁分量.实验结果表明采样剖面获得的早白垩统卧荣沟组的古地磁结果全部为正极性,显示与早白垩纪正极性超静带的极性特征相似.对岩石的显微镜观察表明岩石未受后期热液化学交代作用和风化作用,这表明所获得的高温分量很可能代表岩石形成时的原生剩磁.其特征剩磁方向为:偏角D=18.4°,倾角I=26.5°,α95=8.6°;相应的极位置为:经度ψp=220.3°E,纬度λp=66.4°N,dp=9.3°,dm=6.9°,古纬度plat=14.0°.通过对比拉萨地块以北诸地块早白垩纪古地磁结果,认为拉萨地块在早白垩纪已与芜塘地块碰撞拼合在一起,而自早白垩纪以来相对欧亚大陆发生了1500±600km的构造缩短.结合拉萨地块已有的晚白垩纪和古新纪古地磁数据,认为欧亚大陆的最南缘(拉萨地块)在印度/欧亚大陆发生碰撞前自早白垩纪一始新纪一直处于北纬12.8°～14°N低纬度位置,并未发生明显的纬向运动.     

新疆北部古地磁研究

通过和布克赛尔、克拉玛依、玛纳斯—乌鲁木齐地区泥盆纪到白垩纪古地磁研究,主要取得以下结果:(1)首次建立了准噶尔西北缘及南缘石炭纪—白垩纪古地磁极移曲线,由石炭纪到二叠纪的古地磁极位置基本在同一区间,说明该时期这些地区为一个统一的构造单元,而其古地磁极明显与塔里木、哈萨克斯坦、西伯利亚地块存在着差异。(2)该地区侏罗纪及白垩纪古地磁结果与塔里木地块结果一致,侏罗纪乌鲁木齐与和布克赛尔磁偏角相差30°左右,说明和布克赛尔地区相对乌鲁木齐地区逆时针旋转了30°左右,晚古生代以后曾发生过南向移动,而侏罗、白垩纪以来均向北发生了相当规模的北向运动,并发生了相对旋转,目前东、西准噶尔的构造格局可能就是由于局部相对旋转造成的。(3)中国大陆在早二叠世还不是一个联合的整体,而是以相互分离的独立块体分布于45°N—15°S的古特提斯洋中。(4)该地区二叠纪的磁偏角为165°—168°,而塔里木为218°,哈萨克斯坦为229°,说明存在35°—55°的逆时针旋转,这个旋转可能是由于西部推覆构造造成的。如果将西准噶尔超基性岩带顺时针旋转35°—55°后,东准噶尔超基性岩带、西准噶尔超基性岩带和斋桑泊—鲁布佐夫斯克超基性岩带应在同一构造带上。(5)该地区晚古生代古纬度变化不明显,位于30°—45     

佳木斯地体晚侏罗世—白垩纪古地磁研究及其构造意义

对佳木斯地体盖层鸡西群和桦山群１９８个标本的古地磁研究，确定了该地体晚侏罗世和白垩纪的古磁极位置和古地理纬度。白垩纪以后，佳木斯地体相对于松辽地体有又有大幅度的位移。     

弗兰西斯科组石灰岩地体的起源与运移

弗兰西斯科组中央带混杂堆积的深海灰岩增生块体和其同期的弗兰西斯科地体的古地磁成果的详细分析,说明了将该组灰岩就位到北美科迪勒拉之内的那些大洋板块的相互作用.该组已研究过的所有地层剖面都是在白垩纪正向极性超期期间的沉积,所以沉积作用时的地磁极性已经知晓.各增生块体的方位已由有孔虫生物地层学和沉积岩石学所决定.因为增生块体就位于弗兰西斯科组混杂堆积内的时候,相互之间多半发生旋转;所以每一块体的古地磁倾角需单独计算.由于地磁极性和地层极性二者都已知道,那么,唯一与古水平线有关的磁倾角就限定了地层沉积时的古纬度.古地磁的年龄.可由调试巨型砾岩来确定.     

海南岛白垩纪古地磁结果及其构造地质意义

对海南岛地区白垩系鹿母湾组和报万组碎屑岩219个独立定向岩芯样品(29个采点)的岩石磁学和古地磁学研究表明,白垩纪的碎屑岩以赤铁矿为主要载磁矿物。逐步热退磁分析表明,绝大多数样品可分离出特征剩磁分量。综合前人的结果,获早白垩世特征剩磁方向D=6.5°,I=42.7°,κ=73.4,α95=8.2°;晚白垩世特征剩磁方向D=6.7°,I=44.7°,κ=125.5,α95=5.4°。其早白垩世古纬度24.8°(+6.2°/-5.8°),晚白垩世古纬度26.3°(+4.6°/-4.0°);均位于现在地理位置以北约5°～6°。与华南板块东南缘白垩纪的古地磁数据对比表明,晚白垩世海南地块仍是华南板块的一部分。海南岛白沙断裂东西两侧早白垩世古地磁数据的差异,表明存在一个北东向的构造走滑带,白沙断裂可能是华南沿海北东向构造带的南延部分。海南岛白垩纪古地磁结果也表明,相对印支地块,海南岛在早白垩世时发生了25°左右局部顺时针旋转。推测此局部旋转很可能与晚侏罗世—晚白垩世早期,印度洋开始第一次海底扩张,印度板块向北运动有关。     

塔里木西南早第三纪古地磁和地壳缩短

属于帕米尔弧山前带的乌帕尔剖面和属于南天山山前带的巴对布拉克剖面，现今的纬度差为０．５６°，但是下第三系古地磁测定结果表明其古纬度差很大．乌帕尔剖面齐姆根组上部的古纬度为８°Ｎ，而巴什布拉克剖面巴什布拉克组第５段的古纬度为３６．１°Ｎ。若考虑到当时板块的相对运移速度，估计始新世早期巴什布拉克地区的古纬度大致为３１°Ｎ，与当时乌帕尔所处位置的纬差达２３°。又根据Ｋｌｏｏｔｗｉｊｋ测得的帕米尔西北缘利什坦层的古纬度值，在始新世末期．包括乌帕尔在内的帕米尔前缘与以巴什布拉区为代表的南天山山前带之间还有至少１０°的纬度差。古地磁资料表明，始新世早期，塔里木海宽达２０００ｋｍ，此时印度板块西北端已与欧亚板块局部碰撞，至始新世末，印度板块向北推进２０°，帕米尔弧前缘与南天山山前的距离缩短到约１０００ｋｍ，原塔里木海的两侧上升为山前平原。     

印度支那地块第三纪构造滑移与青藏高原岩石圈构造演化

印度支那地块于早第三纪至中新世发生大规模地向东南方向走滑,同时伴随着15°顺时针旋转。青藏高原及邻区晚自垩世以来的古地磁古构造及地质年代学研究新成果,说明青藏高原岩石圈的构造演化过程,即古新世初印度板块与欧亚大陆的南缘拉萨地块碰撞,至49 Ma左右印度与拉萨地块发生全面拼合,随着印度板块进一步向北挤压,从碰撞期至16 Ma,印度支那地块沿红河大型走滑断裂发生侧向滑移;印度与“欧亚大陆”之间的构造缩短通过岩右圈板块沿着大型走滑断裂系的挤出以及板块间的消减得到调整。青藏高原大规模的岩石圈构造缩短很可能始于中新世27 Ma左右沿着早期陆块间的接合带发生。一些事实还说明青藏高原的总体隆起很可能是通过10 Ma前后和3 Ma以后多期非均匀隆升形成的。     

帕米尔-西昆仑地区新生代古地磁结果及其构造意义

通过对帕米尔-西昆仑地区新生代地层51个采点古地磁样品系统的古地磁测试,获得了研究区新生代较可靠的古地磁数据。尽管上述研究剖面因为单斜地层无法对所获得的古地磁结果进行褶皱检验,但从实验结果可以看出,其地理坐标下平均的高温特征剩磁方向远离现代地磁场方向,且和田朗如乡古近纪、策勒恰恰古近纪、叶城柯克亚乡新近纪剖面所获得的古地磁结果具有正、反2种极性,由此,我们认为以上剖面的高温特征剩磁很可能代表了岩石形成时的原生剩磁方向。结合研究区已有的古地磁数据,认为在新生代印度板块向北挤压作用下,塔里木地块西缘地区(帕米尔高原东北缘)早白垩世-晚白垩世始相对欧亚大陆在古地磁误差范围内并没有发生明显的构造旋转作用(1°~1.6°),而始新世以来相对欧亚大陆则发生了明显的逆时针旋转(22°~38°),该地区的逆时针旋转作用可能与塔拉斯-费尔干纳断裂新生代以来的右旋走滑作用有关,而在帕米尔高原以东则主要以沿大型走滑断裂的走滑作用为主,并没有发生明显的旋转作用。     

晚白垩世后青藏高原和塔里木地块的整体北移

本文根据塔里木地块及其以南的昆仑、羌塘和拉萨地块晚中生代特别是晚白垩世古地磁数据,提出青藏高原自晚白垩世后北向移动两千余公里,主要并不是通过它本身的大规模地壳缩短来完成,而是与塔里木地块一起作大规模整体北移的结果。一种可能的解释是,在欧亚大陆北部稳定区和塔里木地块之间广大的中亚构造带,自晚白垩世后发生了大规模的地壳缩短。     

Gondwanaland origin, dispersion, and accretion of East and Southeast Asian continental terranes

East and Southeast Asia is a complex assembly of allochthonous continental terranes, island arcs, accretionary complexes and small ocean basins. The boundaries between continental terranes are marked by major fault zones or by sutures recognized by the presence of ophiolites, mélanges and accretionary complexes. Stratigraphical, sedimentological, paleobiogeographical and paleomagnetic data suggest that all of the East and Southeast Asian continental terranes were derived directly or indirectly from the Iran-Himalaya-Australia margin of Gondwanaland. The evolution of the terranes is one of rifting from Gondwanaland, northwards drift and amalgamation/accretion to form present day East Asia. Three continental silvers were rifted from the northeast margin of Gondwanaland in the Silurian-Early Devonian (North China, South China, Indochina/East Malaya, Qamdo-Simao and Tarim terranes), Early-Middle Permian (Sibumasu, Lhasa and Qiangtang terranes) and Late Jurassic (West Burma terrane, Woyla terranes). The northwards drift of these terranes was effected by the opening and closing of three successive Tethys oceans, the Paleo-Tethys, Meso-Tethys and Ceno-Tethys. Terrane assembly took place between the Late Paleozoic and Cenozoic, but the precise timings of amalgamation and accretion are still contentious. Amalgamation of South China and Indochina/East Malaya occurred during the Early Carboniferous along the Song Ma Suture to form “Cathaysialand”. Cathaysialand, together with North China, formed a large continental region within the Paleotethys during the Late Carboniferous and Permian. Paleomagnetic data indicate that this continental region was in equatorial to low northern paleolatitudes which is consistent with the tropical Cathaysian flora developed on these terranes. The Tarim terrane (together with the Kunlun, Qaidam and Ala Shan terranes) accreted to Kazakhstan/Siberia in the Permian. This was followed by the suturing of Sibumasu and Qiangtang to Cathaysialand in the Late Permian-Early Triassic, largely closing the Paleo-Tethys. North and South China were amalgamated in the Late Triassic-Early Jurassic and finally welded to Laurasia around the same time. The Lhasa terrane accreted to the Sibumasu-Qiangtang terrane in the Late Jurassic and the Kurosegawa terrane of Japan, interpreted to be derived from Australian Gondwanaland, accreted to Japanese Eurasia, also in the Late Jurassic. The West Burma and Woyla terranes drifted northwards during the Late Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was destroyed by subduction beneath Eurasia and were accreted to proto-Southeast Asia in the Early to Late Cretaceous. The Southwest Borneo and Semitau terranes amalgamated to each other and accreted to Indochina/East Malaya in the Late Cretaceous and the Hainanese terranes probably accreted to South China sometime in the Cretaceous.     

Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context

East and Southeast Asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments (terranes) together with volcanic arcs, and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the Eurasian, Indo-Australian and Pacific Plates. The former wide separation of Asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation, different palaeoclimates, and biogeographic isolation. The boundaries between Asian terranes are marked by major geological discontinuities (suture zones) that represent former ocean basins that once separated them. In some cases, the ocean basins have been completely destroyed, and terrane boundaries are marked by major fault zones. In other cases, remnants of the ocean basins and of subduction/accretion complexes remain and provide valuable information on the tectonic history of the terranes, the oceans that once separated them, and timings of amalgamation and accretion. The various allochthonous crustal fragments of East Asia have been brought into close juxtaposition by geological convergent plate tectonic processes. The Gondwana-derived East Asia crustal fragments successively rifted and separated from the margin of eastern Gondwana as three elongate continental slivers in the Devonian, Early Permian and Late Triassic–Late Jurassic. As these three continental slivers separated from Gondwana, three successive ocean basins, the Palaeo-Tethys,. Meso-Tethys and Ceno-Tethys, opened between these and Gondwana. Asian terranes progressively sutured to one another during the Palaeozoic to Cenozoic. South China and Indochina probably amalgamated in the Early Carboniferous but alternative scenarios with collision in the Permo–Triassic have been suggested. The Tarim terrane accreted to Eurasia in the Early Permian. The Sibumasu and Qiangtang terranes collided and sutured with Simao/Indochina/East Malaya in the Early–Middle Triassic and the West Sumatra terrane was transported westwards to a position outboard of Sibumasu during this collisional process. The Permo–Triassic also saw the progressive collision between South and North China (with possible extension of this collision being recognised in the Korean Peninsula) culminating in the Late Triassic. North China did not finally weld to Asia until the Late Jurassic. The Lhasa and West Burma terranes accreted to Eurasia in the Late Jurassic–Early Cretaceous and proto East and Southeast Asia had formed. Palaeogeographic reconstructions illustrating the evolution and assembly of Asian crustal fragments during the Phanerozoic are presented.     

Reinterpretation of the Ordovician rotations in NW Argentina and Northern Chile: a consequence of the Precordillera collision?

Early Paleozoic paleomagnetic data from NW Argentina and Northern Chile have shown large systematic rotations within two domains: one composed of the Western Puna that yields very large (up to 80°) counter-clockwise rotations, and the other formed by the Famatina Ranges and the Eastern Puna that shows (~40°) clockwise rotations around vertical axes. In several locations, lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the Paleozoic. Previous tectonic models have explained these rotations as indicative of rigid-body rotations of large para-autochthonous crustal blocks or terranes. A different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of Precordillera in the Late Ordovician. This collision should have generated dextral shear zones in the back arc region of the convergent SW Gondwana margin, where systematic domino-like clockwise rotations of small crustal blocks accommodate crustal shortening. The Western Puna block, bordering the Precordillera terrane to the north, might have rotated counterclockwise as an independent microplate due to tectonic escape processes, in a fashion similar to the present-day relationship between the Anatolia block and the Arabian microplate.     

Mesozoic transtensional basin history of the Eastern Cordillera, Colombian Andes: Inferences from tectonic models

Backstripping analysis and forward modeling of 162 stratigraphic columns and wells of the Eastern Cordillera (EC), Llanos, and Magdalena Valley shows the Mesozoic Colombian Basin is marked by five lithosphere stretching pulses. Three stretching events are suggested during the Triassic–Jurassic, but additional biostratigraphical data are needed to identify them precisely. The spatial distribution of lithosphere stretching values suggests that small, narrow (<150 km), asymmetric graben basins were located on opposite sides of the paleo-Magdalena–La Salina fault system, which probably was active as a master transtensional or strike-slip fault system. Paleomagnetic data suggesting a significant (at least 10°) northward translation of terranes west of the Bucaramanga fault during the Early Jurassic, and the similarity between the early Mesozoic stratigraphy and tectonic setting of the Payandé terrane with the Late Permian transtensional rift of the Eastern Cordillera of Peru and Bolivia indicate that the areas were adjacent in early Mesozoic times. New geochronological, petrological, stratigraphic, and structural research is necessary to test this hypothesis, including additional paleomagnetic investigations to determine the paleolatitudinal position of the Central Cordillera and adjacent tectonic terranes during the Triassic–Jurassic. Two stretching events are suggested for the Cretaceous: Berriasian–Hauterivian (144–127 Ma) and Aptian–Albian (121–102 Ma). During the Early Cretaceous, marine facies accumulated on an extensional basin system. Shallow-marine sedimentation ended at the end of the Cretaceous due to the accretion of oceanic terranes of the Western Cordillera. In Berriasian–Hauterivian subsidence curves, isopach maps and paleomagnetic data imply a (>180 km) wide, asymmetrical, transtensional half-rift basin existed, divided by the Santander Floresta horst or high. The location of small mafic intrusions coincides with areas of thin crust (crustal stretching factors >1.4) and maximum stretching of the subcrustal lithosphere. During the Aptian–early Albian, the basin extended toward the south in the Upper Magdalena Valley. Differences between crustal and subcrustal stretching values suggest some lowermost crustal decoupling between the crust and subcrustal lithosphere or that increased thermal thinning affected the mantle lithosphere. Late Cretaceous subsidence was mainly driven by lithospheric cooling, water loading, and horizontal compressional stresses generated by collision of oceanic terranes in western Colombia. Triassic transtensional basins were narrow and increased in width during the Triassic and Jurassic. Cretaceous transtensional basins were wider than Triassic–Jurassic basins. During the Mesozoic, the strike-slip component gradually decreased at the expense of the increase of the extensional component, as suggested by paleomagnetic data and lithosphere stretching values. During the Berriasian–Hauterivian, the eastern side of the extensional basin may have developed by reactivation of an older Paleozoic rift system associated with the Guaicáramo fault system. The western side probably developed through reactivation of an earlier normal fault system developed during Triassic–Jurassic transtension. Alternatively, the eastern and western margins of the graben may have developed along older strike-slip faults, which were the boundaries of the accretion of terranes west of the Guaicáramo fault during the Late Triassic and Jurassic. The increasing width of the graben system likely was the result of progressive tensional reactivation of preexisting upper crustal weakness zones. Lateral changes in Mesozoic sediment thickness suggest the reverse or thrust faults that now define the eastern and western borders of the EC were originally normal faults with a strike-slip component that inverted during the Cenozoic Andean orogeny. Thus, the Guaicáramo, La Salina, Bitúima, Magdalena, and Boyacá originally were transtensional faults. Their oblique orientation relative to the Mesozoic magmatic arc of the Central Cordillera may be the result of oblique slip extension during the Cretaceous or inherited from the pre-Mesozoic structural grains. However, not all Mesozoic transtensional faults were inverted.     

Closure of a hyperextended system in an orogenic lithospheric pop‐up,Western Pyrenees: The role of mantle buttressing and rift structural inheritance

The Early Cretaceous hyperextended Mauléon rift is localized in the north‐western Pyrenean orogen. We infer the Tertiary evolution of the Mauléon basin through the restoration of a 153‐km‐long crustal‐scale balanced cross‐section of the Pyrenean belt, which documents at least 67 km (31%) of orogenic shortening in the Western Pyrenees. Initial shortening, accommodated through inversion of inherited crustal structures, led to formation of a pop‐up structure, in which the opposite edges underwent similar shortening with different tectonic reactivation styles, localized versus. distributed. Underthrusting of the Iberian margin accommodated further convergence, forming the Axial Zone antiformal stack of crustal nappes within a lithospheric pop‐up. Thin‐skinned and thick‐skinned structures propagated outward from the heart of this pop‐up, a block of strong mantle acting as a buttress inhibiting complete inversion of the Mauléon rift basin.     

PALEOMAGNETIC ESTIMATE OF THE MESOZOIC—CENOZOIC LATITUDINAL DISPLACEMENT OF TERRENES IN THE QINGHAI—TIBET PLATEAU AND ITS SIGNIFICANCE

PALEOMAGNETIC ESTIMATE OF THE MESOZOIC—CENOZOIC LATITUDINAL DISPLACEMENT OF TERRENES IN THE QINGHAI—TIBET PLATEAU AND ITS SIGNIFICANCE1　QianFang ,PreliminarystudyonthehorizontalmovementofNgariarea ,Tibet,sincePliocene[A].AbstractfromInterna tionalSymposiumonHimalayaGeologySciences[C].1984,2 49～ 2 5 0 . 2　JiangChunfa .OpeningandclosingstructuresofKunlun[M ].Beijing :GeologicalPublishingHouse ,1992 ,15 4～ 2 17. 3　XuZhiqin ,…     

How does the elevation changing response to crustal thickening process in the central Tibetan Plateau since 120 Ma?

When and how the Tibetan Plateau formed and maintained its thick crust and high elevation on Earth is continuing debated. Specifically, the coupling relationship between crustal thickening and corresponding paleoelevation changing has not been well studied. The dominant factors in crustal thickness changing are crustal shortening, magmatic input and surface erosion rates. Crustal thickness change and corresponding paleoelevation variation with time were further linked by an isostatic equation in this study. Since 120 Ma crustal shortening, magmatic input and surface erosion rates data from the central Tibetan Plateau are took as input parameters. By using a one-dimensional isostasy model, the authors captured the first-order relationship between crustal thickening and historical elevation responses over the central Tibetan Plateau, including the Qiangtang and Lhasa terranes. Based on the modeling results, the authors primarily concluded that the Qiangtang terrane crust gradually thickened to ca. 63 km at ca. 40 Ma, mainly due to tectonic shortening and minor magmatic input combined with a slow erosion rate. However, the Lhasa terrane crust thickened by a combination of tectonic shortening, extensive magmatic input and probably Indian plate underthrusting, which thickened the Lhasa crust over 75 km since 25 Ma. Moreover, a long-standing elevation >4000 m was strongly coupled with a thickened crust since about 35 Ma in the central Tibetan Plateau.©2021 China Geology Editorial Office.     

Eocene paleomagnetism of the Caucasus (southwest Georgia): oroclinal bending in the Arabian syntaxis

The Caucasus is very important for our understanding of tectonic evolution of the Alpine belt, but only a few reliable paleomagnetic results were reported from this region so far. We studied a collection of more than 300 samples of middle Eocene volcanics and volcano-sedimentary rocks from 10 localities in the Adjaro–Trialet tectonic zone (ATZ) in the western part of the Caucasus. Stepwise thermal demagnetization isolates a characteristic remanent magnetization (ChRM) in 19 sites out of 31 studied. ChRM reversed directions prevail, and a few vectors of normal polarity are antipodal to the reversed ones after tilt correction. The fold test is positive too, and we consider the ChRM primary. Analysis of Tertiary declinations and strikes of Alpine folds in the Adjaro–Trialet zone and the Pontides in Northern Turkey shows a large data scatter; Late Cretaceous data from the same region, however, reveal good correlation between paleomagnetic and structural data. Combining Late Cretaceous and Tertiary data indicates oroclinal bending of the Alpine structures which are locally complicated with different deformation. The overall mean Tertiary inclination is slightly shallower than the reference Eurasian inclination recalculated from one apparent polar wander path (APWP), but agrees with other. This finding is in accord with geological evidence on moderate post-Eocene shortening across the Caucasus. We did not find any indication of long-lived paleomagnetic anomalies, such as to Cenozoic anomalously shallow inclinations further to the east in Central Asia.     

塔里木盆地北部隆起负反转构造及其地质意义

塔里木盆地北部隆起负反转构造带长达２００ｋｍ以上,宽１０～３０ｋｍ,位于南天山山前库车前陆拗陷的前缘隆起部位。主要负反转构造类型包括大型负反转断裂、反转掀斜断块和“垒堑叠加型”反转构造。塔北隆起大型负反转断裂经历了早期冲断和后期反转过程（如轮台和牙哈断裂带）,往往有基底层序卷入。平衡剖面分析结果揭示,反转构造的主反转期为白垩纪—第三纪,塔北隆起北部圈闭形成期和油气成藏期与主反转期相对应。塔北隆起负反转构造带形成机制受先存基底构造形迹或软弱带及前陆拗陷前缘隆起部位局部引张应力场控制。塔北隆起负反转构造的存在不仅决定了油气藏的形成与分布特征,而且对于揭示中国西北地区构造变形类型和变形方式具有重要的地质意义。