五台山区太古宙/元古宙界线划分及其地球演化意义

太古宙/元古宙界线代表地球演化历史上的重大事件,如何准确标定和划分这一界线对认识早期演化历史具有重要意义。区域构造及同位素地质年代学研究表明,华北克拉通新太古代构造演化明显滞后于欧美澳等克拉通,成为有利于建立太古宙/元古宙界线的关键地区。山西五台山区保留了较完整的新太古代-古元古代地层记录。先前研究主要依据该区地层、区域构造、叠层石记录进行界线划分,并对界线争议较多。本文在五台山区长期野外研究的基础上,通过对磨拉石沉积、同构造花岗岩、裂解环境相关玄武岩的综合探讨,建议这一界线划分在东冶亚群与豆村亚群之间。初步的同位素年龄制约表明,这一界线的时代介于2549±22Ma到2450±10Ma之间,与早期大陆克拉通伸展裂解、隆升剥蚀相关,并涉及岩石圈、水圈、大气圈性质的重大变化。     

陕西周户地区“秦岭群”的解体

根据区内传统秦岭群包含不同原岩建造、不同变质岩石组合以及变形变质、副矿物和微量元素特征的差异，将其解作为丹凤岩群、深成侵入体、浅成一超浅成侵入体、片麻岩套等5个部分，首次区分出两类不同性质的混合岩，确认了秦岭群在该区的存在。     

西昆仑北缘新元古代片麻状花岗岩锆石SHRIMP年龄及其意义

在西昆仑北缘早前寒武纪变质地层中,笔者等识别出大量不同时代的片麻状花岗岩,其中包括新元古代片麻状花岗岩。获得最新的新元古代片麻状花岗岩的单颗粒锆石SHRIMP年龄为815±57Ma,片麻状花岗岩的岩石学特征反映它们形成于裂解构造背景,结合对区域上新元古代地层及中元古代末期构造事件的研究,笔者认为新元古代片麻状花岗岩反映了古塔里木板块作为Rodinia超大陆一员发生裂解的时间,这对研究古塔里木板块在Rodinia超大陆中的位置及中国Rodinia超大陆裂解的研究提供了重要的地质依据。     

Rift fault geometry and evolution in the Cretaceous Potiguar Basin (NE Brazil) based on fault growth models

We investigated the Cretaceous Potiguar Basin in the Equatorial margin of Brazil to understand how the geometry of major faults evolved to form the basin internal architecture. Previous studies pointed out that the rift is an asymmetrical half-graben elongated along the NE-SW direction. We used 2D seismic, well logs and 3D gravity modeling to analyze faults that constitute the rift boundary and determine their maximum displacement (D_max) and length (L) ratio in the Potiguar Rift. We constrained the 3D gravity modeling with well data and the interpretation of seismic sections. The difference of the fault displacement and depth of the basement obtained in the gravity model is in the order of 10% compared to seismic and well data. The fault-growth curves allowed us to divide the faulted rift border into four main fault systems, which provide roughly similar D_max/L ratios. Fault-growth curves suggest that a regional uniform tectonic mechanism influenced growth of these faults. These fault systems are composed of minor faults that we define as segments. The variation of the displacements along the fault segments indicates that the fault systems were formed independently during rift initiation and were linked by hard and soft linkages. The latter formed relay ramps. In the interconnection zones the D_max/L ratios are highest due to interference of fault segment motions. We divided the evolution of the Potiguar Rift into five stages based on these ratios and correlated them with the major tectonic stages of the breakup between South America and Africa in the Early Cretaceous.     

Mesozoic exhumation history of the Grenvillian Oaxacan Complex,southern Mexico

We present the first fission‐track results from the Grenvillian Oaxacan Complex, southern Mexico. Time–temperature modelling of the data indicates that two significant Mesozoic cooling episodes are recorded in the Oaxacan Complex and these are interpreted as resulting from exhumation. The older cooling event took place from the Late Triassic to Middle Jurassic and is possible linked to the break‐up of Pangea (including the initial opening of the Gulf of Mexico during the Jurassic). The younger exhumation period in the Early Cretaceous is contemporaneous with the final stages of rifting of the Gulf of Mexico. Key stratigraphic records also provide independent evidence for these exhumation episodes. In our view, both Mesozoic rapid exhumation events were controlled by the activity of the Caltepec Fault Zone and the Oaxaca Fault. Our data suggest that both these large fault systems have remained active since, at least, the Late Triassic.     

大火成岩省及其在古大陆重建及裂解研究中的应用

大火成岩省是地质历史上与地球深部过程（如地幔柱）密切相关的极端地质事件,以相对较短时期内形成规模宏大的板内幔源基性岩浆活动为主要特征,对研究全球性大气—海洋环境的巨变与生物灭绝、大规模成矿及超大陆的重建和裂解均有重要意义。从潘吉亚超大陆的裂解过程可以看出,尽管不是所有的大火成岩省都与大陆裂解有关,但几乎每一次重要的裂解事件都伴有大火成岩省的出现,因此大火成岩省对于研究前潘吉亚超大陆,特别是对于缺少古生物等重建标志,古地磁数据偏少的前寒武纪超大陆重建及裂解研究有重要价值。近20多年来随着年代学技术的进步及研究工作的不断深入,大火成岩省在古大陆重建及裂解方面取得了一些重要进展,并发挥了越来越重要的作用。前寒武纪大火成岩省由于经历了多次裂解事件改造及后期抬升剥蚀或覆盖的影响,现今保留的是一些分散在不同大陆上的大火成岩省残片或碎片。用大火成岩省开展古大陆重建及裂解的目标就是通过不同陆块大火成岩省或大规模基性岩浆活动的年代学、岩石学及地球化学对比,结合其他证据,恢复大火成岩省形成时的时空分布特征,据此来确定这些陆块在超大陆中的相对或绝对位置。与其他前寒武纪大陆重建标志相似,大火成岩省也有一些局限性及不确定性,因此应用大火成岩省开展古大陆重建及裂解研究中要与前岩浆期沉积地层中的特殊事件层（如冰碛岩、火山灰、黑色页岩、不整合面、古生物等）对比、岩墙几何学产状、基性岩浆事件序列对比、古地磁、大型构造（如造山带）对比及深部地球物理等多学科方法相结合。     

Edge tectonics (trench rollback, terrane export) of Gondwanaland-Pangea synchronized by supercontinental heat

From 650–500 Ma assembly, 320 Ma merger in Pangea, to 185 Ma breakup, Gondwanaland developed by the accretion of lithosphere along the convergent edge on the south and by the export of terranes from the divergent edges on the west and northeast. The interior underwent epeirogenic movement except in areas affected during the merger by farfield shortening. Synchronous or near-synchronous events on the edges and interior are linked hypothetically by convection currents in the asthenosphere driven by supercontinent-induced heat. On the convergent edge, currents countered the sinking slab to roll back the trench and generate a backarc basin. On the divergent edge, currents initiated an ocean that prised off continental rims in the form of terranes. In the interior, currents extended the lithosphere in basins and rifts.     

盆地演化认识中的几个问题

本文论述了盆地演化认识中的几个主要问题。一是陆缘裂解过程，华南边缘传统上认为是被动裂谷边缘的一个例子，其东部沉积物记录了压实的历史，它明显不同于被动裂谷作用模式，而是显示早第三纪大规模上隆和侵蚀的特征；而且，该地区覆盖在下地壳楔形体上面，具有比周围地壳明显要高的地震速度和密度，指示岩浆底侵作用。这些证据说明，与被动裂谷作用模式相比，华南边缘与主动裂谷作用模式较为一致，它是由早第三纪华南边缘东部底下地幔柱形成的主动裂谷。另一个问题是关于页岩的浅部破裂作用机理。大多数研究者认为，微裂隙的形成需要高孔隙压力，它限于深埋、低渗透率的岩石。然而，最近从北海观察表明，在第三纪页岩中，整个盆地范围内的破裂型式从未达到大于几百米的埋藏深度。这说明泥质源岩经历了水压破裂和浅部脱水，在破裂前可能达到深埋后生作用所需要的深度，实质上渗透率的改变是由于源岩的浅部破裂作用可能根本上改变了烃类的初次运移时间和效率。     

Lithospheric structure of the Southwest South China Sea: implications for rifting and extension

ABSTRACT

The South China Sea (SCS) is an excellent site for studying the process of conjugate margin rifting, and the origin and evolution of oceanic basins. Compared with the well-defined northern margin of the SCS, the western and southern segments of the SCS margin have not been researched in significant detail. To investigate the regional structure of the southwestern SCS, a gravity model is constructed, along with the lithospheric thermal structure along a wide-angle seismic profile. The profile extends across the conjugate margins of the Southwest Sub-Basin (SWSB) of the SCS and is based on the latest multiple geophysical measurements (including heat flow and thermo-physical parameters). The results show that the average thicknesses of the crust and thermal lithosphere along the profile are about 15 km and 57 km, respectively. The overall amount of extension of continental crust and lithosphere is more than 200 km. Thermal structure of the lithosphere shows that the continental margins are in a warm thermal state. The southwest SCS is characterized by ultra-wide, thinned continental crust and lithosphere, high Moho heat flow, early syn-rift faulted basins, undeformed late syn-rifting, and high seismic velocities in the lower crust. These various pieces of evidence suggest that the break-up of the mantle lithosphere occurred before that of the continental crust favouring a depth-dependent extension of the southwestern SCS margin.