Mesozoic and Cenozoic reconstructions of the South Atlantic

The movement of Antarctica with respect to South America has a number of implications for paleocirculation as well as for the reconstructions of Gondwanaland. Recent papers on the Southwest Indian Ridge have published new or revised poles of opening for Africa and Antarctica which can be combined with the poles of opening between South America and Africa to give resultant motions between South America and Antarctica.The first indication of a complete closure between South America and the Antarctic Peninsula is at anomaly 28 time (64 Ma) as the two continents are now configured. Between anomaly 28 time (64 Ma) and anomaly M0 time (119 Ma) the amount of closure does not change greatly, and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between East and West Antarctica. By 135 Ma some rotation or translation of the Antarctic Peninsula with respect to East Antarctica must be postulated in addition to any presumed extension between East and West Antarctica in order to avoid an overlap of South America with the Antarctic Peninsula.Having determined what we feel to be a viable reconstruction of Western Gondwanaland and holding South America fixed, we rotated Africa and Antarctica, with respect to South America, for eight different times during the past. Africa moved away from South America in a more or less consistent manner throughout the time period, closure to present, while Antarctica moved away from Africa in a consistent manner only between 160 Ma and 64 Ma. At 64 Ma its motion changed abruptly: it slowed its north-south motion with respect to Africa and began slow east-west extension with respect to South America. This change supports the hypothesis that a major reorganization of the triple junction between Africa, Antarctica and South America occurred between 60 and 65 Ma. The triple junction changed from ridge-ridge-ridge to ridge-fault-fault at the time of the major westward jump of the Mid-Atlantic Ridge just south of the Falkland-Agulhas Fracture Zone.The Mesozoic opening of the Somali Basin moved Madagascar from its presumed original position with Africa in Gondwanaland. The closure of Sri Lanka with India produces a unique fit for India and Sri Lanka with respect to Africa, Madagascar and Antarctica. This fit juxtaposes geological localities in Southeast India against similar localities in Enderhy Land. East Antarctica. The late Jurassic opening in the Somali Basin is tied to opening of the same age in the Mozambique Basin. Since this late Jurassic movement represents the initial break-up of Gondwanaland, it is assumed that similar movement must have occurred in what is now the western Weddell Sea and may also explain the opening evidenced by the Rocas Verdes region of southern South America.     

中新生代南北天山差异性抬升历史的磷灰石裂变径迹证据

堆积于天山山前坳陷内部的巨厚新生代地层不仅记录所在沉积区的热历史信息,还记录了物源区的信息。本文选择天山南北两侧山前坳陷中3条地质剖面进行了大量的磷灰石裂变径迹测试和部分样品的热历史模拟分析,来揭示上新世以来天山在南北方向上隆升过程的差异性。采样剖面的选取较前人更加靠近前陆盆地方向,样品所在地层年代更新。结果显示,东秋里塔格背斜剖面中的样品记录了中天山、南天山和背斜区分别在55~65Ma、20~25Ma和5Ma经历了构造隆升。玛纳斯背斜剖面中的样品记录了北天山的三次构造隆升事件分别发生于55~65Ma、20~25Ma和5Ma,其中距今5Ma为玛纳斯背斜带起始隆升的时代。结合前人在相同区域的研究成果,分析得出天山的不同部分经历了不同的构造演化历史,自150Ma以来经历了三期差异性隆升。中生代时期(150~125Ma)表现为山体整体抬升,中生代晚期-新生代早期(100~50Ma)北天山明显早于南天山开始构造隆升,新生代以来(~50Ma)的构造运动以向前陆盆地方向扩展为特征,而隆升起始时间南北差异变小。虽然在南北方向上天山山体隆起时间上存在明显的差异,但是中新生代以来山体物源区的剥蚀速率大体相同。因此,隆升起始时间与隆升量之间并不存在必然的定量关系。天山的不同块体具有不同的构造演化历史的事实提示在研究大范围构造隆升作用时,应将构造作用作为一个过程来对待。变形在传递的过程中,在时间和空间上存在一定的滞后现象。     

南海北部古构造格局对中、新生界发育的影响

南海北部中生界是南海海域进一步油气勘探的新领域和新层系。对于中生界的形成演化背景与分布特征一直广受关注,南海北部的地质地球物理调查研究成果揭示, 该区与华南东部陆区分块明确,其边界是珠外-台湾海峡断裂带和丽水-海丰-琼东南断裂带。由此划分的南海北缘-台湾地块与南华活动区有亲缘关系,即可视为南华活动区的组成部分,其形成演化过程与华南加里东构造旋回密切相关。南海北部陆缘区与华南东部陆区在加里东造山期所遗留的古缝合带和地壳分块性仍不同程度影响区内中、新生界的发育特征,南海东北部出现大套海相海陆交互相上三叠统-下侏罗统、上侏罗统-下白垩统和上白垩统-始新统见证了这一现象。     

Glacial history of southernmost South America

In southernmost South America, an incomplete radiometrically dated glacial chronology has been obtained by KAr dating for the interval 3.5-1 MY ago, and a more detailed chronology by C-14 dating for the last 25,000 years, with some older minimal ages. The first major glaciation was about 3.5 MY ago during the middle Pliocene. Little is yet known about glacial fluctuations during the interval 3.5-2.1 MY ago. Between 2.1 and 1 MY ago many glaciations occurred, probably including the greatest of late Cenozoic time which took place after 1.2 MY and, according to inconclusive evidence, before 1 MY ago. The Patagonian Gravel in its type area is mid-Pliocene to early Pleistocene glacial outwash that accumulated from the first to the greatest glaciations. During the late Pleistocene several glaciations occurred, but only the most recent has been radiometrically dated. During the last glaciation the glaciers were most extensive before 56,000 BP. Successively smaller advances that culminated about 19,500 BP and, probably, about 13,000 BP were separated by an interstade when glaciers shrank by more than half. The glaciers receded rapidly after 13,000 BP and were within their present borders by 11,000 BP; they remained so during the European Younger Dryas Stade 11,000-10,000 BP. Neoglacial regional readvances culminated 4600-4200 BP, probably 2700-2000 BP, and during the last three centuries; most glaciers reached their Neoglacial maxima during the first episode. Between readvances, the glaciers shrank within their present borders.     

东天山地区中—新生代隆升-剥露过程:来自磷灰石裂变径迹的证据

前人已经对西天山及邻区以及阿尔金断裂带进行了大量中—新生代隆升-剥露的研究工作,但对东天山地区的研究工作很少。天山造山带中—新生代期间的隆升-剥露过程是否具有均一性,目前仍没有确切的认识。为了获得东天山地区中生代以来的隆升-剥露信息,对吐哈盆地东南缘雅满苏地区磷灰石裂变径迹进行了研究。研究表明,在不同构造位置采集的花岗岩、砂岩、火山岩样品年龄集中分布在81~53Ma,样品年龄记录了东天山地区晚白垩世—古新世发生的冷却事件。磷灰石裂变径迹平均长度为13.60~14.36μm,接近于磷灰石初始径迹长度约14.5μm,表明径迹形成后没有发生过明显的退火作用。根据地温梯度计算得到东天山晚白垩世以来的平均隆升速率约为4.31×10-2 mm/a。进一步的热史模拟表明,晚白垩世—古新世(80~50Ma)期间东天山地区经历了一次隆升-剥露事件;始新世以后(50 Ma),东天山地区地壳处于稳定状态,东天山隆起带现在的构造面貌基本继承了中生代的特征。     

Mesozoic and Cenozoic thermal history of the Western Reguibat Shield (West African Craton)

Using low‐temperature thermochronology on apatite and zircon crystals, we show that the western Reguibat Shield, located in the northern part of the West African Craton, experienced significant cooling and heating events between Jurassic and present times. The obtained apatite fission track ages range between 49 and 102 Ma with mean track lengths varying between 11.6 and 13.3 μm and Dpar values between 1.69 and 3.08 μm. Zircon fission track analysis yielded two ages of 159 and 118 Ma. Apatite (U–Th)/He uncorrected single‐grain ages range between 76 and 95 Ma. Thermal inverse modelling indicates that the Reguibat Shield was exhumed during the Early Cretaceous, Late Cretaceous, Palaeocene–Eocene and Quaternary. These exhumation events were coeval with regional tectonic and geodynamic events, and were probably driven by a combined effect of plate tectonics and mantle dynamics.     

中新生代以来中国大陆的稳定地块

中国大陆主要由塔里木、华北和扬子三个比较大的古老克拉通组成。中、新生代以来,由于受到环太平洋和喜马拉雅两大构造域的影响,这三个克拉通发生了巨大变化。从地壳和岩石圈结构来看,其中相当一部分已不具备了稳定地块的特点。从这些地块目前所处的大地构造位置、地壳及岩石圈的改造方面（主要包括：其上主要盆地和演化史、盆地结构、地壳和岩石圈（软流圈）结构、以及地球物理场、可能的动力学机制等）的对比可以看出,中国各稳     

华南中新生代构造-岩浆活动驱动机制与铀成矿研究进展

华南地区大规模金属成矿作用主要发生在中生代,区内的铀成矿作用明显不同于其它金属的成矿作用,如成矿时代上从中生代延续到新生代、矿岩时差大、铀矿聚集分布、铀源及矿化剂具慢源性等。基于众多铀成矿理论,从构造一岩浆活动的驱动力与铀成矿的关系出发,系统总结华南中新生代构造一岩浆活动与铀成矿的关系,认为当前华南铀成矿的动力学观点有四个,即构造体制转换铀成矿观、热点（地慢柱）铀成矿观、幔汁活动铀成矿观、原地重熔铀成矿观。     

Mesozoic and early Cenozoic tectonic convergence-to-rifting transition prior to opening of the South China Sea

We have investigated Mesozoic geological problems around the South China Sea (SCS) based on gravimetric, magnetic, seismic, and lithofacies data. Three-dimensional analytical signal amplitudes (ASA) of magnetic anomalies clearly define the inland tectonic boundaries and the residual Mesozoic basins offshore. The ASA suggest that the degree of magmatism and/or the average magnetic susceptibility of igneous rocks increase southeastwards and that late-stage A-type igneous rocks present along the coast of southeast China possess the highest effective susceptibility. The geophysical data define Mesozoic sedimentary and tectonic structures and reveal four major unconformities [Pz/T–J, T–J/J, J/K, and Mesozoic/Cenozoic (Pz, Palaeozic; T, Triassic; J, Jurassic; K, Cretaceous)], corresponding to regional tectonic events revealed by nine palaeogeographic time slices based on prior geological surveys and our new fieldwork. Showing both sedimentary and volcanic facies and regional faults, our palaeogeographic maps confirm an early Mesozoic northwestward-migrating orogeny that gradually obliterated the Tethyan regime, and a middle-to-late Mesozoic southeastward migration and younging in synchronized extension, faulting, and magmatism. Three major phases of marine deposition developed but were subsequently terminated by tectonic compression, uplift, erosion, faulting, rifting, and/or magmatism. The tectonic transition from the Tethyan to Pacific regimes was completed by the end of the Middle Triassic (ca. 220 Ma), reflecting widespread Mesozoic orogeny. The transition from an active to a passive continental margin occurred at the end of the Early Cretaceous (ca. 100 Ma); this was accompanied by significant changes in sedimentary environments, due likely to an eastward retreat of the palaeo-Pacific subduction zone and/or to the collision of the West Philippine block with Eurasia. The overall Mesozoic evolution of southeast China comprised almost an entire cycle of orogenic build-up, peneplanation, and later extension, all under the influence of the subducting palaeo-Pacific plate. Continental margin extension and rifting continued into the early Cenozoic, eventually triggering the Oligocene opening of the SCS.     

鄂尔多斯盆地中新生代构造应力场

鄂尔多斯盆地是位于华北克拉通西部的保罗－白垩纪沉积盆地。本文利用中、小型构造的解析成果重建了该盆地中、新生代的区域构造应力场，其中，印支、燕山和喜马拉雅运动最大主压力轴的产状分别为１７９°～３５９°∠２°～３°，１３０°～３１０°∠２°～４°，３０°～２１０°∠１°～２°。这一成果为解释它的形成与演化机制提供了一个重要窗口。     

Successor Characteristics of the Mesozoic and Cenozoic Songliao Basins

The Songliao basin is a complex successor basin that was initiated in the Mesozoic and experienced multiple periods of reactivation. Based on seismic and drilling data, as well as regional geologic research, we suggest that the Songliao basin contains several different successor basins resting on top of Carboniferous-Permian folded strata forming the basement to the Songliao basin. These basins include the Triassic-Mid Jurassic Paleo-foreland basin, the Late Jurassic-Early Cretaceous downfaulted basin, and an early Cretaceous depressed basin （since the Denglouku Group）. This paper presents a systematic study of the basin-mountain interactions, and reveals that there are different types of prototype basin at different geologic times. These prototype basins sequentially superimposed and formed the large Songliao basin. Discovery of the Triassic-early Middle Jurassic paleo-foreland basin fills a Triassic-early Middle Jurassic gap in the geologic history of the Songliao basin. The paleo- foreland basin, downfaulted basin, and depressed thermal subsidence basin all together represent the whole Mesozoic-Cenozoic geologic history and deformation of the Songliao basin. Discovery of the Triassic-early Middle Jurassic paleo-foreland basin plays an important role both for deep natural gas exploration and the study of basin-mountain coupling in north China and eastern China in general. This example gives dramatic evidence that we should give much more attention to the polyphase tectonic evolution of related basins for the next phase of exploration and study.     

Structure and tectonic history of the foreland basins of southernmost South America

The common elements and differences of the neighboring Austral (Magallanes), Malvinas and South Malvinas (South Falkland) sedimentary basins are described and analyzed. The tectonic history of these basins involves Triassic to Jurassic crustal stretching, an ensuing Early Cretaceous thermal subsidence in the retroarc, followed by a Late Cretaceous–Paleogene compressional phase, and a Neogene to present-day deactivation of the fold–thrust belt dominated by wrench deformation. A concomitant Late Cretaceous onset of the foreland phase in the three basins and an integrated history during the Late Cretaceous–Cenozoic are proposed. The main lower Paleocene–lower Eocene initial foredeep depocenters were bounding the basement domain and are now deformed into the thin-skinned fold–thrust belts. A few extensional depocenters developed in the Austral and Malvinas basins during late Paleocene–early Eocene times due to a temporary extensional regime resulting from an acceleration in the separation rate between South America and Antarctica preceding the initial opening of the Drake Passage. These extensional depocenters were superimposed to the previous distal foredeep depocenter, postdating the initiation of the foredeep phase and the onset of compressional deformation. Another pervasive set of normal faults of Paleocene to Recent age that can be recognized throughout the basins are interpreted to be a consequence of flexural bending of the lithosphere, in agreement with a previous study from South Malvinas basin. Contractional deformation was replaced by transpressive kinematics during the Oligocene due to a major tectonic plate reorganization. Presently, while the South Malvinas basin is dominated by the transpressive uplift of its active margin with minor sediment supply, the westward basins undergo localized development of pull-apart depocenters and transpressional uplift of previous structures. The effective elastic thickness of the lithosphere for different sections of each basin is calculated using a dynamic finite element numerical model that simulates the lithospheric response to advancing tectonic load with active sedimentation.     

鄂尔多斯盆地中、新生代后期改造

鄂尔多斯盆地周缘和内部在中、新生代都受到后期改造作用,周缘存在挤压逆冲推覆和拉张断陷等不同性质的构造改造作用。在盆地内部,后期改造过程中发育在盖层中的断裂具有很强的规律性,受到了基底断裂的控制。盆地中部东西向断裂带对盆地的构造特征具有分区性,南北构造特征有别,北部地区北东、北西、近东西向断裂均有发育,正断裂、逆断裂和由断裂控制的挠曲构造等有规律发育,在不同方向基底断裂交汇部位的盖层内断裂最发育。南部则主要发育北东方向断层。     

中新生代库车-南天山盆山系统隆升历史的裂变径迹证据

通过对库车河剖面中新生界砂岩中碎屑磷灰石裂变径迹分析测试,得出磷灰石样品可分为3组,分别反映库车盆地边缘或其物源区天山的剥露冷却。对测试数据分析和热史模拟表明,南天山及库车盆地在中新生代经历了3次主要隆升事件,且山盆隆升时间上具有差异性的特点。从142Ma南天山开始隆升,使天山地区从准平原化状态开始盆山分异;96~75Ma为晚白垩世开始的盆地与天山共同经历的区域性隆升;54~30Ma为天山与盆地边缘差异隆升阶段,是盆山边界处盆地基底向天山方向的阶梯式抬升所导致的。     

塔里木盆地中—新生界构造单元划分

塔里木盆地作为典型的多旋回叠合盆地,中生代以来经历了印支、燕山和喜山等多期构造运动,造成中—新生界构造格局与古生界构造格局差异较大.应用航磁、重力、钻井、测井以及地震等资料,获得了盆地中-新生界地层分布、区域构造变形特点和含油气性特征,兼顾基底形态和后期改造作用影响,对塔里木盆地中-新生界构造单元划分为“三坳一隆一斜坡”,即北部坳陷区、西南坳陷区、东南坳陷区、中央隆起区和东北斜坡区5个一级构造单元和11个二级构造单元.显然,该构造单元的划分对盆地中—新生界次生油气蘸和隐蔽油气藏勘探具有重要意义.     

华南东部陆缘新生代隆升历史及其动力学机制

华南陆缘在新生代期间经历了千米量级的上覆盖层剥蚀和山脉隆升;同时,其东侧的东海陆架盆地经历多次构造应力场的反转并发育多期反转构造。东海陆架盆地内的构造反转与华南陆缘隆升的发生时间和触发机制是否一致有待研究。为此,本文对浙江地区的岩石样品进行磷灰石裂变径迹测试和热演化史反演分析其隆升历史,并通过地震剖面分析东海陆架盆地的反转时间及其反转所导致的地层剥蚀量;最后,将二者进行对比分析并研究其动力学机制。结果发现,华南东部陆缘地区至少存在晚始新世（34.5~33.5Ma）、中中新世（16~11.5Ma）、上新世以来（5~0Ma）三期明显的快速隆升事件,三期隆升导致的地层剥蚀量分别为227m、593m和865m;东海陆架盆地经历了古新世末-始新世初（~56Ma）、始新世末-渐新世初（~32Ma）和晚中新世（~10Ma）三期构造反转,三期反转导致的局部地层最大剥蚀量分别可达1200m、1300m和2000m。在时间上,东海陆架盆地的始新世末-渐新世初（~32Ma）和晚中新世（~10Ma）的构造反转分别滞后于浙江的晚始新世（34.5~33.5Ma）和中中新世（16~11.5Ma）的隆升时间,说明这两期挤压-剥蚀事件分别具有自西向东的迁移性,即印度-欧亚板块碰撞的远程效应可能是导致该迁移特征的原因;在强度上,东海陆架盆地的反转剥蚀量大于浙江境内的地层隆升量、挤压强度东强西弱,中新世晚期菲律宾海板块向西俯冲导致冲绳海槽弧后伸展产生向西的挤压力、这种挤压应力向陆内传递且强度变弱可能是导致该特征的原因。

     

合肥盆地中、新生代沉积相初步研究

合肥盆地是与大别山造山带有密切关系的山前前陆盆地，盆地中、新生界沉积物主要来自南面大别山区以及盆地东部、北部剥蚀区。通过野外实际踏勘、室内岩石薄片显微分析，认为合肥盆地中、新生界发育的沉积相主要有冲积扇相、河流相和湖泊相，其中以河流相最为发育。该盆地中、新生界油气源条件比较丰富，储盖条件良好，生储盖组合形式多样，存在多种油气圈闭类型，是一个油气勘探潜力较大的陆相沉积盆地。     

The first Mesozoic turtle from South Korea

The partial carapace of a “macrobaenid” turtle from the Geoncheonri Formation (Lower Cretaceous) in Gyeongsan City near Daegu Metropolian City, South Korea, is referred to Kirgizemys Nessov and Khozsatzky, 1973. The specimen most closely resembles K. exaratus Nessov and Khozsatzky, 1973 from the Albian of Kyrgyzstan. It is the first turtle fossil described from the Mesozoic sediments on the Korean peninsula.