East Asia plate tectonics since 15 Ma: constraints from the Taiwan region

15 Ma ago, a major plate reorganization occurred in East Asia. Seafloor spreading ceased in the South China Sea, Japan Sea, Taiwan Sea, Sulu Sea, and Shikoku and Parece Vela basins. Simultaneously, shear motions also ceased along the Taiwan–Sinzi zone, the Gagua ridge and the Luzon–Ryukyu transform plate boundary. The complex system of thirteen plates suddenly evolved in a simple three-plate system (EU, PH and PA). Beneath the Manila accretionary prism and in the Huatung basin, we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations. These two patterns are rotated by 15°. They were formed by seafloor spreading before 15 Ma and belonged to the same ocean named the Taiwan Sea. Half-spreading rate in the Taiwan Sea was 2 cm/year from chron 23 to 20 (51 to 43 Ma) and 1 cm/year from chron 20 (43 Ma) to 5b (15 Ma). Five-plate kinematic reconstructions spanning from 15 Ma to Present show implications concerning the geodynamic evolution of East Asia. Amongst them, the 1000-km-long linear Gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the PH Sea plate; the formation of Taiwan was driven by two simple lithospheric motions: (i) the subduction of the PH Sea plate beneath Eurasia with a relative westward motion of the western end (A) of the Ryukyu subduction zone; (ii) the subduction of Eurasia beneath the Philippine Sea plate with a relative southwestward motion of the northern end (B) of the Manila subduction zone. The Luzon arc only formed south of B. The collision of the Luzon arc with Eurasia occurred between A and B. East of A, the Luzon arc probably accreted against the Ryukyu forearc.     

四川木里海相侏罗纪地层的发现及地质意义

在川滇金沙江－哀牢山结合带以东,从未发现过海相侏罗纪地层。笔者最近在其以东数百公里的四川省木里县瓦厂地区的甘孜－理塘结合带以东发现广泛分布的含层孔Claodocoropsis mirabilis,珊瑚Thecosmilia cf。Weberi Regny,Pratethmos of.discus,水螅Spongiomorpha cf.robusta等生物群的海相侏罗纪地层。此套地层下部为陆源碎屑岩,上部为富产层孔虫、珊瑚、水螅的正常广海台地相碳酸盐岩,底部以底砾岩与下伏晚三叠世曲嗄寺组平行不整合接触。其岩性、生物组合均可与西藏昌都地块侏罗纪地层对比。本区侏罗纪沉积盆 地是在晚三叠世古特提斯洋闭合的基础上,随新特提斯洋开合而发展演化的,消亡于古近纪初期。     

Geodynamic evolution of Jbel Cheid (Northern Tunisian Atlas) from geophysical and geological data

Understanding the formation and the development of salt structures is very important especially because they are of significant economical interest. Detailed understanding of this process will help reservoir prediction and hydrocarbon recovery. In this work, we use a combination of geological observations along with the interpretation of geophysical data (seismic and Bouguer anomaly data) to better constrain the geology of the Jbel Cheid structure. The shape of Triassic body of Jbel Cheid (Northern Tunisian Atlas) structure and its geodynamic evolution have been determined by gravity analyses and 2.5D modeling, correlated with others geophysical data (seismic) and geological observations. Semi-automatic structural analysis was performed before modeling, to identify lateral gravity discontinuities. The complete Bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the Triassic evaporitic outcrop (Jbel Cheid) and prominent NE–SW-trending features associated with the boundary of the Triassic rocks and surrounded layers. The seismic profile shows a thickness variation of post-salt layers. Taking into account the 2.5D gravity model, seismic profile and surface data, geodynamic evolution of Jbel Cheid can be subdivided on three stages (reactive, active, and passive) which well correlated to the model proposed by Vendeville (2002).     

Palaeomagnetic,geochronological and geological constraints on the tectonic evolution of the Mejillones Peninsula,northern Chile

Palaeomagnetic and geochronological data from an Early Palaeozoic high grade metamorphic complex (Jorgina Formation) and Jurassic layered basic intrusion (Moreno Complex) are reported from the Mejillones Peninsula of northern Chile (23–23°30'S). ⁴⁰Ar–³⁹Ar dates from the Lower Palaeozoic Jorgina Formation and the Moreno Complex are between 170 and 158 Ma, coincident with a phase of emplacement of the north Chilean coastal batholith. This suggests that intrusion and magnetization of the Moreno Complex and the metamorphism and remagnetization of the Jorgina Formation were related to batholith emplacement. Extracted stable components of magnetization from all units (17 sites) define site-mean directions with a scattered distribution. The scatter in site-mean directions is interpreted as being due to minor, localized, non-uniform, block-fault related (normal or strike-slip, or both) rotation after 158 Ma. The palaeomagnetic and geochronological data indicate that no significant large-scale latitudinal translation of crustal blocks has taken place in this part of northern Chile since the Late Jurassic. In addition, they indicate that the uniform clockwise rotation after the mid-Cretaceous which affected the adjacent Cordillera de la Costa either did not extend into the Mejillones Peninsula or took the form of localized block-fault rotations. The restriction of palaeomagnetically defined styles of rotation to discrete areas within the north Chilean forearc indicates that forearc wide block-fault rotation models are not applicable to the Pacific margin of northern Chile.     

Seismological, geological and geophysical constraints for the Gualdo Tadino fault, Umbria–Marche Apennines (central Italy)

The April 3, 1998 Mw = 5.1 Gualdo Tadino earthquake (central Italy) was the last significant event in the 6-month-long Umbria–Marche seismic crisis. This event and its aftershocks occurred in an area where active faulting produces no striking geological and geomorphological effects. In this study, we investigated the ruptured fault using detailed seismological data and a re-processed and re-interpreted seismic reflection profile. Aftershock location and focal mechanisms were used to constrain the geometry and kinematics of the ruptured fault and a comparison was made with the subsurface image provided by the seismic profile. We found that the 1998 Gualdo Tadino earthquake occurred on a WSW-dipping, normal fault, with a length of about 8 km and a relatively gentle dip (30°–40°), confined between 3.5 and 7 km in depth. Kinematics of the mainshock and aftershocks revealed a NE-trending extension, in agreement with the regional stress field active in the Northern Apennines belt. The Mw = 5.1 earthquake originated above the top of the basement and ruptured within the sedimentary cover, which consists of an evaporites–carbonates multilayer. We hypothesised that the active fault does not reach the surface (blind normal fault).     

Structure and evolution of the Cauvery Shear Zone system, Southern Granulite Terrain, India: Evidence from deep seismic and other geophysical studies

The Southern Granulite Terrain with exposed Archean lower crustal rocks is studied using various geophysical tools. The crustal structure derived from seismic reflection and refraction/wide-angle reflection studies is used to understand the tectonic evolution of the region. Deep seismic reflection section along the Kolattur–Palani segment shows an oppositely dipping reflection fabric near the Moyar–Bhavani shear zone, which is interpreted as a signature of collision between the Dharwar craton and another crustal block in the south. The thickened crust due to collision was delaminated during the orogenic collapse and modified the central part, covering the Cauvery Shear Zone system, located between the Moyar–Bhavani and Karur–Oddanchatram shear zones. The delaminated lower crust is altered by magmatic underplating as evidenced by the high velocity layer just above the Moho. The velocity model of the region indicates crustal thickening at the boundary of the Dharwar craton and Moyar–Bhavani shear zone and thinning further south. Back-scattered seismic wave field with negative moveout and the Moho-offset indicate the spatial location and strike-slip nature of the shear zones. Present study suggests that the late Archean collision and suturing of the Dharwar craton with the southern crustal block at the Moyar–Bhavani shear zone may be responsible for the evolution of late Archean granulites. Late Neoproterozoic rifting is observed along the paleo-fault zones. The seismic studies constrained by gravity, magnetic and magnetotelluric data suggest that the Moyar–Bhavani and Karur–Oddanchatram shear zones of the Cauvery Shear Zone system mark terrane boundaries/suture zones.     

Geodynamic evolution of the European Variscan fold belt: palaeomagnetic and geological constraints

The Variscan fold belt of Europe resulted from the collision of Africa, Baltica, Laurentia and the intervening microplates in early Paleozoic times. Over the past few years, many geological, palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt. Whereas it is now fairly well established that Avalonia drifted from the northern margin of Gondwana in Early Ordovician times and collided with Baltica in the late Ordovician/early Silurian, the nature of the Gondwana derived Armorican microplate is more enigmatic. Geological and new palaeomagnetic data suggest Armorica comprises an assemblage of terranes or microblocks. Palaeobiogeographic data indicate that these terranes had similar drift histories, and the Rheic Ocean separating Avalonia from the Armorican Terrane Assemblage closed in late Silurian/early Devonian times. An early to mid Devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow Rhenohercynian basin which closed progressively between the late Devonian and early Carboniferous. In this contribution, we review the constraints provided by palaeomagnetic data, compare these with geological and palaeobiogeographic evidence, and present a sequence of palaeogeographic reconstructions for these circum-Atlantic plates and microplates from Ordovician through to Devonian times.     

Magmato-sedimentary Carboniferous to Jurassic evolution of the western Tauern window,Eastern Alps (constraints from U-Pb zircon dating and geochemistry)

New geochronological U-Pb (LA-ICP-MS) zircon data and geochemical analyses from the Variscan orthogneisses and metavolcanic rocks in the western Tauern window are presented and used to reconstruct the pre-Alpine evolution of this area. The late- and post-Variscan stage in the Tauern window was characterised by distinct magmatic pulses accompanied by the formation of volcano-sedimentary basins. The magmatic activity started in the Visean (335.4 ± 1.5 Ma) with the intrusion of a K-rich, durbachitic biotite-granite (protolith of the Ahorn gneiss). Following a period of exhumation and erosion, Westfalian–Stefanian volcanics were deposited (Grierkar meta-rhyodacite: 309.8 ± 1.5 Ma; Venntal meta-rhyolite: 304.0 ± 3.0 Ma). A renewed magmatic pulse occurred in the Early Permian, producing large volumes of tonalites and granodiorites (Tux meta-granodiorite: 292.1 ± 1.9 Ma). The youngest magmatism is characterised by pyroclastic and tuffitic deposits (Pfitsch meta-rhyolite: 280.5 ± 2.6 Ma; Schönach valley meta-andesite: 279.0 ± 4.8 Ma). This volcanism was probably related to crustal extensional faulting within an intra-continental graben and horst setting, asthenospheric upwelling and heat flow increase due to the onset of the Permian rifting. The Permo-Triassic peneplanation and subsidence is documented by shallow marine and evaporitic deposits. Probably in the Middle Jurassic times, the area was flooded and in the Late Jurassic the whole area was covered by limestones, representing post-rift sediments on the southern European continental margin.     

扬子板块北缘新元古代构造属性的岩浆事件制约

黄陵地区新元古代侵入杂岩可为研究扬子板块北缘新元古代构造演化过程及其深部动力学机制提供关键信息。依据岩石组合及分布特征,可将黄陵杂岩划分为黄陵庙岩套、三斗坪岩套、大老岭岩套和晓峰岩套四个单元。本文以黄陵杂岩的围岩崆岭杂岩中花岗片麻岩、黄陵庙黑云母花岗岩和三斗坪闪长岩为研究对象,在系统的野外地质和岩石学研究基础上,开展了LA-ICP-MS锆石U-Pb年代学分析。结果表明,崆岭杂岩花岗片麻岩原岩年龄为1978±13 Ma,且记录了2.5 Ga的构造-热事件。黄陵庙黑云母花岗岩和三斗坪闪长岩分别形成于815±9 Ma和813±6 Ma,与黄陵庙岩套和三斗坪岩套的侵位时限基本一致。综合分析本次研究结果与前人资料,认为黄陵杂岩主要形成于863～794 Ma,为新元古代早期岩浆活动的产物。通过综述区域地质和地球化学研究资料,认为黄陵杂岩形成于新元古代早期活动大陆边缘的构造环境,提出扬子板块北缘在新元古代早期经历了长期的俯冲-增生造山过程。     

Tectonomagmatic evolution of a Jurassic Cordilleran flare-up along the Korean Peninsula: Geochronological and geochemical constraints from granitoid rocks

This study used new and published U-Pb geochronological, chemical, and Sr-Nd-Hf-O isotopic data (n > 2500) from Jurassic granite-granodiorite-diorite-monzonite-gabbro plutons in the southern part of the Korean Peninsula to assess the spatiotemporal evolution of a flare-up magmatism, its tectonic connection, and specific contributions of mantle and crustal reservoirs to the magmas generated. After a ~15 m.y. magmatic gap in the Late Triassic, calc-alkaline granitoids intruded into the outboard Yeongnam Massif, then magmatic activity migrated systematically toward the inboard Gyeonggi Massif. The early phase of the Jurassic magmatism is represented by relatively sodic plutons showing distinctly primitive isotopic signatures. The crustal signature of the plutons became increasingly prominent with decreasing age. Voluminous inboard plutons in the Gyeonggi Massif and the intervening Okcheon Belt are dominated by Middle Jurassic peraluminous granites that show isotopic compositions conspicuously shifted toward old crustal values. The Nd-Hf isotopic compositions of the inboard plutons are distinctly less radiogenic than those of Jurassic plutons in Southwest Japan and southeastern China, which corroborates the North China affinity of the Yeongnam and Gyeonggi massifs. The geochronological and geochemical data compiled in this study suggest a tectonomagmatic model consisting sequentially of (1) an extension-dominated arc system in the margin of the Yeongnam Massif (ca. 200–190 Ma); (2) low-angle subduction and the development of an advancing arc system (ca. 190–180 Ma); (3) continued low-angle subduction, extensive underthrusting of fertile crustal materials to the arc root, and consequent magmatic flare-up (ca. 180–170 Ma); and (4) flat subduction and the development of the Honam Shear Zone (ca. 170–160 Ma). The subsequent magmatic lull and previous dating results for synkinematic rocks and minerals indicate that the compressional arc system was maintained until the Early Cretaceous.     

藏南贡嘎晚侏罗世—早白垩世海相地层地球化学特征与古海洋环境演化

西藏南部有出露良好的海相侏罗纪—白垩纪地层。本研究针对采自藏南贡嘎东拉剖面的样品进行了常量、微量和稀土元素分析,探讨晚侏罗世—早白垩世海洋沉积环境的演化。Fe_2O_3+MgO与TiO_2、Al_2O_3/SiO_2关系判别图显示,从晚侏罗世维美组到早白垩世桑秀组,研究区经历了从大陆岛弧到大洋岛弧的构造演化。Mn、Fe、V、Co、Ni、REE等指标元素,和U/Th、V/Cr、Sr/Ba、Lan/Ybn、V/(V+Ni)等比值结合显示:沉积条件也从维美组浅海富氧、低盐、高沉积速率的环境演化为早白垩世桑秀组深海、水体分层、盐度升高、沉积速率降低,具有明显深海沉积特征的环境。地化数据分析结果总体上与岩性成因分析相一致,即维美组砂岩所指示的浅海相沉积,桑秀组从下部的粉砂岩到上部钙质泥岩,经历了水体由浅到深的变化过程。     

Constraints on the geodynamic evolution of the AfricaeIberia plate margin across the Gibraltar Strait from seismic tomography

Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomographic images show strong seismic waves velocity contrasts in the upper mantle. The...     

西藏海相三叠系-侏罗系界线及晚三叠世生物绝灭事件研究

1998—2004年间在西藏聂拉木、林周、墨竹工卡和洛扎等地进行的三叠系/侏罗系界线地层研究表明,西藏隆子县和洛扎县尚未发现具有连续菊石层序的三叠系/侏罗系界线地层剖面。拉萨以北地区广泛分布的火山岩时代确定为晚三叠世—早侏罗世早期,这有助于解释晚三叠世末期生物绝灭与晚三叠世岩浆侵入和大规模的火山活动有关,但T/J界线尚待精确限定。聂拉木县格米格剖面是特提斯地区唯一未曾“压缩”的三叠系/侏罗系界线地层剖面,具有瑞替阶MARSHI菊石带、赫塘阶Tibeticum、Callyphyllum和Pleuro-notum菊石带。格米格剖面三叠系/侏罗系界线碳稳定同位素曲线记录了晚三叠世瑞替阶末期(Marshi菊石带)突然的负偏移,它很有可能和晚三叠世末期的由超级温室效应所产生的生物绝灭事件相对应。     

Cenozoic tectonic and geodynamic evolution of the Kyrgyz Tien Shan Mountains: A review of geological,thermochronological and geophysical data

The complex crustal structure of the Tien Shan has a strong impact on the distribution of strain induced by the India–Eurasia collision, with intracontinental deformation in Eurasia’s interior as a distant effect. The northward propagation of the India–Eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins. The Tien Shan basement is formed by the rigid, heterogeneous Precambrian blocks (microcontinents) of Tarim, Issyk-Kul (or Central Tien Shan) and Aktyuz-Boordin, surrounded by a ‘soft’ matrix of Paleozoic accretion–collision belts. The Kyrgyz Tien Shan Mountains are situated between the active structures of the Tarim Plate and the Pamir indenter (south), and the stable Kazakhstan Shield (north). Underplating by the Tarim Plate and thrusting by the Pamirs are responsible for the building of the Cenozoic Tien Shan, the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area. Large earthquakes (M > 6) delineate the northern and southern margins of the Issyk-Kul microcontinent, indicating that crustal heterogeneity influenced the location of active structures in the northern Kyrgyz Tien Shan.     

南北构造带北部石炭纪东西沉积边界分合演变及其地质意义

南北构造带是中国大陆地质构造及深部过程和地表系统的重要分界线,也是地震活动的多发地带,对其在前中生代是否存在、不同时期各区带的构造属性和联系研究薄弱。文中以南北构造带北部为研究对象,重点讨论其中南段,探讨研究区石炭纪地质构造特征及其与具分区意义的南北构造带形成演化的联系。研究表明,在石炭纪,今南北构造带北部所在地区处于伸展裂陷环境,断裂活动强烈,总体控制着河西走廊—北祁连沉积域的东界和隆拗格局及沉积厚度等变化。南北构造带北部及其西沉积区的断裂活动和沉积演化,经历了前黑山期初始裂陷、臭牛沟期进一步(向北)扩张、土坡期沉积-沉降鼎盛及太原期衰减4个阶段。其中于晚石炭世土坡晚期(本溪期)和太原期,东(华北)、西沉积域的沉积范围均向南北构造带北部扩展,先后经历了北部连通到全部相通的演变过程。石炭纪各期诸断裂与中、新生代断裂在位置和方向上具有明显的相关性,反映二者成生和演化联系密切。南北构造带北部及邻区,在石炭纪主要时期分隔华北和河西走廊—北祁连两大沉积域,东、西沉积域的沉积边界在该区带的分合演变和建造特征及断裂的主控因素,显示该区带在石炭纪已属具明显分区作用的重要地质构造单元,为此后南北构造带北部的进一步发展演化和重要的构造地位奠定了基础。     

藏北羌塘盆地晚侏罗世海相油页岩生物标志物特征、沉积环境分析及意义

胜利河油页岩位于青藏高原腹地的羌塘盆地,具单层厚度薄、区域延伸长的特点,为羌塘盆地新发现的又一处海相油页岩.采用GC-MS(IRMS)分析方法对该油页岩进行了研究,结果表明,胜利河油页岩(11层以及13层)含有丰富的正烷烃、类异戊二烯烃、萜类化合物和甾类化合物.正构烷烃呈前高后低的单峰型分布,nC15、nC16为主峰碳,轻烃组分占有绝对优势,OEP值0.96～0.97,接近平衡值1.00,Pr/Ph为0.57～0.75,显示弱的植烷优势;萜烷丰度顺序为五环三萜烷》三环萜烷》四环萜烷;规则甾烷呈不对称的"V"字型分布,表现为C27》C29》C28的分布特征.这些特征与剖面中其他岩性的生物标志物特征存在一定的差异,9层泥晶灰岩C21-/C21 值为0.86,轻烃优势并不明显;14层泥灰岩C21-/C21 值为0.41,具有明显的重碳优势;9层泥晶灰岩以及12层泥灰岩规则甾烷呈C29》C27》C28的特征也与油页岩层存在显著的差异.这些差异不仅反映了油页岩层与其他岩性间生物母源输入的差异,也反映了他们之间沉积环境的不同.胜利河地区油页岩的形成是综合因素控制的结果,古地理变化、海平面升降、生物群差异以及气候的变化均对该区油页岩的形成有一定的影响.     

非震综合物探方法在辽西牛营子地区油气地质调查中的应用

为系统研究辽西牛营子地区的地层及断裂展布、深部构造特征等关键基础地质问题, 开展油气远景区评价, 在建立该区物性结构模型的基础上, 综合处理解译重磁电等地球物理资料, 确定了本区断裂特征、构造格架、中生代地层展布及有利生储盖组合的综合物探异常特征。结果显示: 研究区内共有断裂26条, 走向主要有NNE—NE向、NW向, 前者以逆冲为主, 后者以平移为主, 兼具逆冲, NNE向断裂控制了本区的构造格架; 区内划分出5个二级构造单元, 呈"三凹二凸、凹凸相间"的格局, 其中, 牛营子凹陷夹持于逆冲断裂间, 中生界底面最大深度达2400 m, 侏罗系发育全, 厚度大; 宋杖子凹陷呈断坡, 中生界底面最大深度达1200 m; 三家子凹陷为东倾单斜, 中生界底面最大深度达1400 m。依据石油地质条件及解释成果, 牛营子凹陷北票组-海房沟组烃源岩发育, 确定为油气勘探有利区。研究成果为辽西牛营子地区油气勘探及工作部署提供了重要的地球物理学依据。     

Relationship between geological,geophysical and geochemical data obtained from blind lead-zinc mineralization at Keban,Turkey

The Keban Pb-Zn deposit is an old and important mine in Turkey, and intensive geological, geophysical exploration and diamond drilling have been carried out in the area in an attempt to find new ore reserves. Graphitic schist in the hanging wall of the ore zone, which has sealed the deposit, has produced many false geophysical anomalies. Thus, it is apparently difficult to distinguish the geophysical anomalies related to ore deposits from those caused by the graphitic schist and other geological features of the area. Geochemical data obtained from soil samples over the deposite show significant leakage anomalies indicating the mineralization at depth. The geochemical data are also helpful in the interpretation of geophysical data.     

The deep structure of the central Alps inferred from both geophysical and geological data

Gravity surveys of the past century established that mountains have roots, seismic refraction lines shot in the second half of this century confirmed the downbulge of the Moho under the Alps, and recent reflection traverses provided new details on the behaviour of crustal layers in the deep part of the Alps. However, geophysical data are ambiguous geologically. For models of the root in terms of rock distribution to be tectonophysically acceptable, they must be the retrodeformable result of kinematic sequence that fits the geological surface data. For a cross-section through the Swiss Alps based on refraction data and somewhat modified by the recent reflection traverses, a kinematic model compatible with large-scale geological data may be obtained by the superposition of three Neogene phases with alternating vergence. Although Alpine collision is largely dextrally compressive in the central Alps, the N-S component may be discussed in a cross-section. Particularly puzzling geophysical features include a high-velocity body in the middle crust and the disappearance of the layered foreland crust in the root. In order to account for these phenomena, it is proposed that the crustal root is interpreted as the result of complex reshuffling of middle and lower crustal masses as well as large-scale phase transformations. The mid-crustal highvelocity body is interpreted as a delaminated section of the lower crust of the Adria plate that was wedged into the middle crust of the Alps in the middle Miocene. The disappearance of the foreland lower crust is attributed to eclogitization attendant on the subduction of continental crust. Material balance estimates suggest that during Alpine collision large volumes of continental crust have disappeared through subduction.