祁连山及其邻区大地构造基本特征──兼论早古生代海相火山岩的成因环境

作者对中、南祁连的大地构造属性提出了新的见解，认为它们和柴达木地块具有同一前震旦纪基底，三者共同构成了柴达木板块。北祁连山的主体是介于中朝板块和柴达木板块间的早古生代缝合带。中朝板块的南缘有一个活动陆缘，由走廊弧后盆地和走廊南山北缘岛弧构成。从中寒武世以来，祁连山及其邻区构造演化经历了古大陆克拉通裂解，大洋克拉通演化阶段和新大陆克拉通演化阶段。现今的祁连山是这些构造演化共同作用的结果。早古生代海相火山岩的生成环境在南祁连为单一的裂谷环境。而在北祁连及走廊带，则不同时期具有不同的生成环境：（１）中寒武世为初始大洋裂谷环境，（２）早中奥陶世为具沟弧盆体系的政熟大洋，（３）晚奥陶世为残留洋盆，（４）志留纪为前陆盆地环境。     

Decoding earth's plate tectonic history using sparse geochemical data

Accurately mapping plate boundary types and locations through time is essential for understanding the evolution of the plate-mantle system and the exchange of material between the solid Earth and surface environments.However,the complexity of the Earth system and the cryptic nature of the geological record make it difficult to discriminate tectonic environments through deep time.Here we present a new method for identifying tectonic paleo-environments on Earth through a data mining approach using global geochemical data.We first fingerprint a variety of present-day tectonic environments utilising up to 136 geochemical data attributes in any available combination.A total of 38301 geochemical analyses from basalts aged from 5-0 Ma together with a well-established plate reconstruction model are used to construct a suite of discriminatory models for the first order tectonic environments of subduction and mid-ocean ridge as distinct from intraplate hotspot oceanic environments,identifying 41,35,and 39 key discriminatory geochemical attributes,respectively.After training and validation,our model is applied to a global geochemical database of 1547 basalt samples of unknown tectonic origin aged between 1000-410 Ma,a relatively ill-constrained period of Earth’s evolution following the breakup of the Rodinia supercontinent,producing 56 unique global tectonic environment predictions throughout the Neoproterozoic and Early Paleozoic.Predictions are used to discriminate between three alternative published Rodinia configuration models,identifying the model demonstrating the closest spatio-temporal consistency with the basalt record,and emphasizing the importance of integrating geochemical data into plate reconstructions.Our approach offers an extensible framework for constructing full-plate,deeptime reconstructions capable of assimilating a broad range of geochemical and geological observations,enabling next generation Earth system models.     

Diffuse magnetic anomalies in marginal basins: Their possible tectonic and petrologic significance

Marginal basins, areas of oceanic lithosphere peripheral to large ocean basins, may be formed by several processes, but the young active marginal basins have the geophysical and geochemical characteristics of young normal oceanic lithosphere. We recognize two distinct tectonic settings in which new oceanic lithosphere may be formed in areas which would be termed marginal basins:

1. (1) Upwelling of fractional melts of mantle material from the region above subducted lithospheric slabs leads to the generation of new oceanic lithosphere behind island arcs. The general case for this tectonic setting involves random location of magma leaks and does not produce correlatable magnetic anomalies. In special cases, an orthogonal ridge—transform system may duplicate the magnetic patterns found on ocean-basin crust.

2. (2) The second tectonic setting develops on very long “leaky” transform faults separating spreading ridges. In areas where the transform has dislocated a block of continental crust, or an island arc, the map view of the resulting marginal basin may resemble the setting of a basin behind an active island arc. However, the “leaky” transform setting is unrelated to active plate convergence or to Benioff zones.

At “normal” ridge-crests, and possibly in some marginal basins, basalt is erupted on long linear magma leaks and rapid cooling forms thick lithosphere with correlatable linear magnetic anomalies. Some marginal basins have high thermal flux, spread slowly and may have thick sediment cover. Slow cooling, numerous point-source magma leaks and extensive hydrothermal alteration diminish magnetic intensities and cause diffuse magnetic patterns. The correlation problems caused by diffuse magnetic anomalies make interpretations of spreading rates and directions in young marginal basins a difficult, if not futile, task.It is likely that fragments of marginal-basin lithosphere form some of the ophiolite complexes; their recognition is critical to paleo-tectonic interpretations. The geochemical characteristics of marginal-basin basalts do not appear to be useful criteria for distinguishing them from ocean-ridge basalts. However, the abundance of short ridges and seamounts in many young marginal basins suggests that an abundance of seamount material, as well as differentiated volcanic and plutonic rocks, in ophiolites may be an indication of derivation from marginal-basin lithosphere.     

A plate tectonic scenario for the Iapetus and Rheic oceans

The tectonics, dynamics, and biogeographic landscape of the early Paleozoic were dominated by the opening and expansion of one large ocean—the Rheic—and the diminution to terminal closure of another—Iapetus. An understanding of the evolution of these oceans is thus central to an understanding of the early Paleozoic, but their chronicle also presents a rich temporal profile of the Wilson cycle, illustrating continental-scale rifting, microcontinent formation, ocean basin development, arc accretion, and continent–continent collision. Nevertheless, contemporary paleogeographic models of the Iapetus and Rheic oceans remain mostly schematic or spatiotemporally disjointed, which limits their utility and hinders their testing. Moreover, many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios. With the specific aim to resolve some of the uncertainties in the evolution of this early Paleozoic domain, and a broader aim to instigate the application of quantitative kinematic models to the early Paleozoic, I present a new plate tectonic model for the Iapetus and Rheic oceans. The model has realistic tectonic plates, which include oceanic lithosphere, that are defined by explicit and rigorously managed plate boundaries, the nature and kinematics of which are derived from geological evidence and plate tectonic principles. Accompanying the presentation and discussion of the plate model, an extensive review of the underlying geological and paleogeographic data is also presented.     

Tectonic evolution of Northeastern Siberia and adjacent regions

Previous models for the tectonic evolution of northeastern Siberia have proposed the existence of a Kolyma plate composed of the Kolyma and Omolon massifs of presumed Precambrian age. Lithologic similarities between the Siberian platform and the Cherskiy Mountains and the presence of oceanic and island arc type deposits in the Kolyma-Indigirka interfluve suggest that no such plate exists. The eastern margin of the Siberian plate is suggested to lie along a line between the Ulakhan Sis Range, the Alazeya uplift and the Arga Tas Range; the Cherskiy Mountains and the Verkhoyansk fold belt are parts of the Siberian plate. The Paleozoic deposits of the Omolon massif are unlike those found in the Cherskiys or Siberia. Paleomagnetic data from the Omolon massif are discordant from data from Siberia. It is suggested that the Omolon massif represents a microplate which accreted onto Siberia in the Jurassic. Ophiolites in central Chukotka are of the same emplacement age as in the western Brooks Range and may have been emplaced at the initiation of the rotation of Arctic Alaska. Geometric and limited stratigraphic data suggest that the East Siberian Sea may be floored by oceanic crust left by an incomplete closure between Arctic Alaska, Siberia and Omolon. The tectonic position of the Prikolymsk massif remains ambiguous.     

从全球对比探讨华北克拉通早期地质演化与板块构造过程

板块构造理论为 2 0世纪取得的重大科学成就。如何在新世纪发展板块构造、推动大陆动力学研究成为新的挑战。世界古大陆前寒武纪地质研究在花岗岩绿岩带、高级变质区 ,新太古代造山作用 ,早期大洋地质记录与古板块构造 ,以及超级大陆等方面取得新进展。在此全球构造背景下 ,华北早期地质演化的相关重大问题包括 :新太古代典型造山带地质演化、碰撞过程及其盆山耦合作用。围绕新太古代蛇绿岩的研究 ,特别是豆荚状铬铁矿及地幔岩 ,将提供早期大洋岩石圈性质、扩张运移过程的重要线索 ,并提出早期板块边界划分标志及其洋陆作用过程。华北中部造山带及蛇绿岩混杂带的洲际对比 ,对认识华北与最古老超级大陆聚合过程具有重要意义     

东北亚晚古生代—中生代岩浆时空演化:多重板块构造体制范围及叠合的鉴别证据

东北亚大地构造发展经历了古亚洲洋、蒙古—鄂霍茨克洋和古太平洋的俯冲-碰撞作用。如何鉴别和厘定这三种构造体制的时空影响范围和叠合过程一直是一个难题。本文通过巨型岩浆岩带的建库编图,揭示了该地区晚古生代—中生代岩浆岩的时空迁移规律;据此,探讨和厘定了这三大板块构造体制的时空分布范围和构造叠合过程。二叠纪到三叠纪早期间,古亚洲洋体制经历了俯冲到碰撞,主要作用于阿拉善—华北北缘—大兴安岭一带;期间,鄂霍茨克洋主要为陆缘环境,影响范围限于中北部蒙古—外贝加尔一带,并在侏罗纪逐渐向蒙古—鄂霍茨克主缝合带迁移,到白垩纪,其造山带伸展垮塌阶段,影响范围增大,远程效应波及阿拉善—华北北缘—大兴安岭一带,叠加于古亚洲洋体制产物之上。古太平洋构造体制主要发育于三叠纪—侏罗纪时期,其平板俯冲影响范围抵达大兴安岭—太行山,在白垩纪,俯冲板片后撤,影响范围迁移至东亚大陆最东缘。这些作用叠加于古亚洲洋体制产物之上;并与蒙古—鄂霍茨克洋体制同时叠合于大兴安岭一带。     

东天山大南湖岛弧带石炭纪岩石地层与构造演化

详细的地质解剖工作表明,东天山地区大南湖岛弧带石炭纪出露4套岩石地层组合,即早石炭世小热泉子组火山岩、晚石炭世底坎儿组碎屑岩和碳酸盐岩、晚石炭世企鹅山组火山岩、晚石炭世脐山组碎屑岩夹碳酸盐岩。根据其岩石组合、岩石地球化学、生物化石、同位素资料以及彼此的产出关系,认为这4套岩石地层组合的沉积环境分别为岛弧、残余海盆、岛弧和弧后盆地。结合区域资料重塑了大南湖岛弧带晚古生代的构造格架及演化模式。早、晚石炭世的4套岩石地层组合并置体现了东天山的复杂增生过程。     

构造动力体制与成矿环境及成矿作用——以三江复合造山带为例

现代矿产地质勘查工作正在由过去的单一找矿向系统找矿转变,系统找矿依赖于对成矿环境的厘定以及对不同环境中成矿系统/成矿作用的确认和与之相应的矿床组合时空和成因联系的构筑。构造动力体制是研究成矿环境的基础,其演化决定了成矿环境的区域配置和时空变换。每一种构造动力体制下的成矿环境都可归结为挤压和拉张两种性质。在大洋构造动力体制下,成矿环境与成矿作用主要发生在板块边缘,包括离散和汇聚两种边缘。洋中脊、岛弧和陆缘弧以及在弧构造中发育的不同性质和规模的盆地是成矿的重要场所,板块自身特点、俯冲过程、深度和状态的变化是决定板块边缘成矿环境配置和成矿作用的重要因素;在大陆构造动力体制下,主要地质环境包括(大陆内部)深大断裂构造活动、地幔柱或热点、岩石圈加厚到大规模减薄、陆内造山、陆内裂谷等,不同环境形成了独具特色的成矿作用和矿床类型;在转换构造动力体制下,碰撞-伸展造山和造洋裂谷是两个相对应的构造过程,由其形成的成矿环境独具特色,成矿作用丰富多彩。以西南江三复合造山带为例,具体讨论了不同成矿环境下成矿作用特点,形成的矿床类型及相关矿床组合,可视为复合造山成矿论的雏形。     

The Mesoarchean emergence of modern-style subduction

Well-preserved volcanic sequences span the Paleoarchean to Neoarchean evolution of the Pilbara Craton, in northwestern Australia. This region provides the best physical evidence bearing on the stage of Earth's history when modern-style tectonic processes began. Paleoarchean assemblages in the eastern nucleus of the craton (the 3.51–3.24 Ga Pilbara Supergroup) show few features that can reasonably be interpreted as evidence for modern-style subduction processes. Incompatible trace element-enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust, but this evidence, on its own, can equally well be interpreted in terms of either a subduction-enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the Pilbara Supergroup. Viewed in context within the thick autochthonous and consistently upward-younging Pilbara Supergroup, these felsic units are most likely related to the same plume-dominated processes that formed the basalts that dominate the supergroup. It is very unlikely that modern-style plate tectonic processes played any role in the Paleoarchean evolution of the Pilbara Craton, although some form of non-uniformitarian (e.g. flat) subduction process may have operated.In stark contrast, the Mesoarchean units of the West Pilbara Terrane and the late-tectonic basins that cover that boundary between the West and East Pilbara Terranes, show clear evidence for modern-style convergent margin processes. Igneous rocks in this belt, which flanks the old eastern cratonic nuclei, have enriched geochemical signatures that cannot be accounted for by crustal contamination. This region is also characterised by a linear magmatic and structural fabric, by the presence of lithologically and geochronologically exotic belts, and by the presence of a broad belt of isotopically more juvenile crust. The collective strength of these arguments provides compelling evidence that a modern-style oceanic arc fringed the East Pilbara Terrane at 3.12 Ga and accreted to that terrane by 2.97 Ga. These assemblages mark the minimum age for the birth of modern-style plate subduction process.     

东天山北部古生代重大构造事件及其对中亚造山带演化的启示：基于1∶5万板房沟幅和小柳沟幅地质调查新证据

本文基于新疆哈密地区1∶5万板房沟幅和小柳沟幅区域地质调查新成果,对东天山北部古生代的重大构造事件以及演化历史进行了系统的梳理。基于下志留统与奥陶系之间角度不整合、下石炭统与泥盆系之间平行不整合以及上石炭统二道沟组与下伏岩系之间的角度不整合的确定,揭示奥陶纪与志留纪之交、泥盆纪与石炭纪之交以及晚石炭世期间存在几次重大构造事件。结合古生代不同时期沉积大地构造背景转换、岩浆活动构造环境转换以及构造变形格式转换的地质新纪录,提出奥陶纪与志留纪之交的造山事件为北部阿尔曼太洋闭合导致准噶尔—吐哈地块与阿尔泰地块碰撞的响应;泥盆纪与早石炭世之间的造陆构造事件可能是北部卡拉麦里洋盆初始汇拢碰撞的响应,其平行不整合以及下伏的志留纪—泥盆纪较稳定环境的沉积序列预示着介于卡拉麦里洋盆与南部北天山洋盆之间的准噶尔—吐哈地块为古亚洲洋盆体系中相对刚性的稳定陆块区,研究区作为准噶尔—吐哈地块的北部被动陆缘受卡拉麦里洋盆汇聚的影响较小;晚石炭世的造山事件则表现为响应卡拉麦里洋盆闭合后周缘前陆盆地的演化,是早石炭世沿卡拉麦里缝合带发生陆块碰撞以来挤压构造作用峰期的产物,其奠定了东天山北部北西-南东向构造基本格局。本文还重新界定莫钦乌拉断裂为北天山构造带(准噶尔—吐哈地块)与东准噶尔构造带的构造-地层分区界线,推断其为卡拉麦里缝合带向南东的延伸,并讨论了早石炭世受控不同构造体制的沉积和岩浆纪录的空间差异性,认为早石炭世北部莫钦乌拉山区域为与北侧卡拉麦里洋盆闭合后周缘挤压前陆盆地的发育过程,而南部博格达—哈尔里克山则总体呈现为响应南侧北天山洋盆闭合后的碰撞后伸展裂谷发育过程。     

东、西昆仑山晚新生代以来构造隆升作用对比

东、西昆仑晚新生代以来隆升过程和程度存在明显差异。东昆仑山现代地貌格局主要是在第四纪以来经过早中更新世之交的昆黄运动和中更新世晚期的共和运动形成的,山系的崛起在时空演化上呈现出由北向南的迁移趋势,而西昆仑山在第三纪已有明显的地貌反差,第四纪地貌反差加剧。东昆仑地区在昆黄运动后尽管形成了近东西向的东流水系,但向南的强烈溯源侵蚀并奠定现代河流水系格局主要发生于中更新世晚期,与共和运动大体同时,而西昆仑地区向南的强烈溯源侵蚀主要发生于早更新世晚期,与东昆仑的昆—黄运动大体同时。在剥蚀程度上,东昆仑最上部3km的去顶至少延续了45Ma,而西昆仑公格尔—塔什库尔干地貌单元只延续了2~5Ma。控制东、西昆仑晚新生代构造隆升的动力背景可能取决于强烈加厚及强烈隆升的青藏高原岩石圈边缘的重力伸展垮塌与来自南部的挤压应力之间的动态平衡。考察青藏高原隆升过程与机制,不仅要注意隆升作用的共性,更要强调不同部位隆升过程及动力学的差异性。     

Lithospheric architecture and tectonic evolution of the Hudson Bay region

Hudson Bay conceals several fundamental tectonic elements of the North American continent, including most of the ca. 1.9–1.8 Ga Trans-Hudson orogen (THO) and the Paleozoic Hudson Bay basin. Formed due to a collision between two cratons, the THO is similar in scale and tectonic style to the modern Himalayan–Karakorum orogen. During collision, the lobate shape of the indentor (Superior craton) formed an orogenic template that, along with the smaller Sask craton, exerted a persistent influence on the tectonic evolution of the region resulting in anomalous preservation of juvenile Proterozoic crust. Extensive products of 2.72–2.68 Ga and 1.9–1.8 Ga episodes of subduction are preserved, but the spatial scale of corresponding domains increases by roughly an order-of-magnitude (to 1000 km, comparable to modern subduction environments) from the Archean to the Proterozoic. Based on analysis of gravity and magnetic data and published field evidence, we propose a new tectonic model in which Proterozoic crust in the southeastern third of Hudson Bay formed within an oceanic or marginal-basin setting proximal to the Superior craton, whereas the northwestern third is underlain by Archean crust. An intervening central belt truncates the southeastern domains and is interpreted to be a continental magmatic arc.Thick, cold and refractory lithosphere that underlies the Bay is well imaged by surface-wave studies and comprises a large component of the cratonic mantle keel beneath North America. The existence of an unusually thick mantle root indicates that subduction and plate collision during the Trans-Hudson orogeny were ‘root-preserving’ (if not ‘root-forming’) processes. Although the Hudson Bay basin is the largest by surface area of four major intracratonic basins in North America, it is also the shallowest. Available evidence suggests that basin subsidence may have been triggered by eclogitization of lower-crustal material. Compared to other basins of similar age in North America, the relatively stiff lithospheric root may have inhibited subsidence of the Hudson Bay basin.     

Volcanic arcs as archives of plate tectonic change

Processing of the oceanic lithosphere in subduction zones gives rise to arc magmatism, and strong compositional links exist between trench input and arc output. Here we address the question whether these compositional links are sufficiently strong to allow for ‘tracing’ the composition of the sedimentary and igneous oceanic crust through the chemistry of arcs. The tracing approach hinges critically on whether key characteristics of the subducted slab are transmitted to arcs. Results from forward and inverse modeling, verified by observations from modern arc settings, demonstrate that elements Sr, Pb, Nd and Hf that are associated with radiogenic isotopes may preserve chemical characteristics of the subducted slab in arc magmas. The data indicate that the much thicker igneous subducted crust dominates the recycled flux to arcs. The flux from the highly enriched, but thin sediment layer is buffered, and may be even concealed, by the concomitant contributions from igneous crust, and/or subarc mantle, despite the much better visibility of sediment components in trace element and isotope space. Arc Pb and Pb isotopes are the most promising tracers that may capture the isotopic diversity of subducted MORB-type and OIB-type crust with sufficient temporal and spatial resolution. While arc Sr is also strongly controlled by the flux from the subducted crust, arc data may allow for distinguishing among radiogenic Sr recycled from altered oceanic crust or from subducted sediment in moderately radiogenic arcs (⁸⁷Sr/⁸⁶Sr < ~ 0.7045). Co-mingling of Nd and Hf from igneous subducted crust with mantle contributions mostly hinders the isotopic identification of subducted crust through arc chemistry. However, Nd and Hf may provide complementary information about the efficiency of recycling, and recycling via subduction erosion.The tracing approach appears feasible in Cenozoic arcs where much of the original subduction context is preserved. First results from the Izu Bonin and Central American arcs show that plate tectonic events like oceanic plate formation and destruction, subduction of hotspot tracks and the closure of oceanic gateways are recorded in the chemistry of arcs. A comparative evaluation of Cenozoic global arcs may hence significantly complement the information from the modern oceanic basins, help to obtain a more complete image of the oceanic crustal composition and implicate the geochemical processes by which it formed. Possibly, the tracing approach may also be useful in ancient, inactive arcs to obtain information on the composition of oceanic crust subducted in the geological past.     

The Bastar craton,central India: A window to Archean – Paleoproterozoic crustal evolution

The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3 Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny.     

Slab behaviour and its surface expression: new insights from gravity modelling in the SE-Carpathians

We use lithosphere-scale gravity models to calculate gravity anomalies resulting from oceanic subduction, continental collision, slab steepening, delamination, and break-off. Local isostasy was assumed for determining vertical movements caused by mass changes related to these tectonic processes. Our results show that subduction is accompanied by basin subsidence on the upper plate caused by the heavy lithospheric root of the subducting slab. The basin evolution goes parallel with the slab evolution and shows considerable modifications when the processes at depth change (slab steepening, delamination, break-off). Characteristic gravity anomaly curves were acquired for the different tectonic scenarios. These curves together with other data (e.g. basin evolution on the upper and the lower plate) were used for the reconstruction of the tectonic evolution of the SE-Carpathians which includes Tertiary subduction and collision followed by slab steepening and delamination.     

揭开南岭地壳形成演化之谜

南岭的形成演化目前尚不清楚,作为板内造山的一个典型,研究南岭地区的地壳构造对大陆动力学有重要意义。本文对南岭地区重力异常进行了多尺度密度反演,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各等效层场源的平均深度,然后利用广义线性反演方法进行各层密度反演,取得区域地壳多个深度上的密度扰动图像。用小波变换多尺度分析和三维密度结构反演确定了南岭中上地壳存在独立的构造单元,它具有低密度性质,反映区域规模的大花岗岩基。南岭中上地壳的构造单元位于北纬24°～26°,东经100°～116°,深达22 km左右。深度22 km以下南岭地壳低密度带与武夷低密度带连通为武夷—云开构造带。南岭最终形成与100 Ma以前特提斯洋俯冲和亚欧板块与加里曼丹地体的陆岛碰撞直接有关。同期发生的区域规模的燕山晚期南岭花岗岩基对应特提斯洋向华南俯冲的第二岩浆带。基于地球物理资料提出的这个陆岛俯冲碰撞假说能否成立,还需要更多岩石学的直接证据证实。     

Subsurface imaging,TAIGER experiments and tectonic models of Taiwan

The seismicity, deformation rates and associated erosion in the Taiwan region clearly demonstrate that plate tectonic and orogenic activities are at a high level. Major geologic units can be neatly placed in the plate tectonic context, albeit critical mapping in specific areas is still needed, but the key processes involved in the building of the island remain under discussion. Of the two plates in the vicinity of Taiwan, the Philippine Sea Plate (PSP) is oceanic in its origin while the Eurasian Plate (EUP) is comprised partly of the Asian continental lithosphere and partly of the transitional lithosphere of the South China Sea basin. It is unanimously agreed that the collision of PSP and EU is the cause of the Taiwan orogeny, but several models of the underlying geological processes have been proposed, each with its own evolutionary history and implied subsurface tectonics.TAIGER (TAiwan Integrated GEodynamics Research) crustal- and mantle-imaging experiments recently made possible a new round of testing and elucidation. The new seismic tomography resolved structures under and offshore of Taiwan to a depth of about 200 km. In the upper mantle, the steeply east-dipping high velocity anomalies from southern to central Taiwan are clear, but only the extreme southern part is associated with seismicity; toward the north the seismicity disappears. The crustal root under the Central Range is strongly asymmetrical; using 7.5 km/s as a guide, the steep west-dipping face on the east stands in sharp contrast to a gradual east-dipping face on the west. A smaller root exists under the Coastal Range or slightly to the east of it. Between these two roots lies a well delineated high velocity rise spanning the length from Hualien to Taitung. The 3-D variations in crustal and mantle structures parallel to the trend of the island are closely correlated with the plate tectonic framework of Taiwan. The crust is thickest in the central Taiwan collision zone, and although it thins toward the south, the crust is over 30 km thick over the subduction in the south; in northern Taiwan, the northward subducting PSP collides with Taiwan and the crust thins under northern Taiwan where the subducting indenter reaches 50 km in depth. The low Vp/Vs ratio of around 1.6 at a mid-crustal depth of 25 km in the Central Range indicates that current temperatures could exceed 700 °C. The remarkable thickening of the crust under the Central Range, its rapid uplift without significant seismicity, its deep exhumation and its thermal state contribute to make it the core of orogenic activities on Taiwan Island.The expanded network during the TAIGER deployment captured broadband seismic data yielding enhanced S-splitting results with mainly SKS/SKKS data. The polarization directions of the fast S-waves follow very closely the structural trends of the island, supporting the concept of a vertically coherent Taiwan orogeny in the outer few hundred kilometers of the Earth.     

Recycling of oceanic crust and the origin of intraplate volcanism

Source models for intraplate volcanism (IPV) include vertical introduction of material from deep in the mantle (plume model), contamination of the shallow mantle (perisphere and continental mantle delamination models) and derivation by selective partial melting of oceanic crust recycled into the depleted mantle (SUMA/streaky mantle models). The plume hypothesis became the ruling model after a flawed interpretation of helium isotope data in the mid 1980s that led to plumes being imposed on models for crustal recycling into the depleted mantle. This incorporation of otherwise competing concepts, is the cause of unnecessary complexity in modern geodynamic models. The plume model cannot explain all manifestations of IPV and a comprehensive explanation can only be found by invoking the alternative options, combined with their tapping by plate tectonic processes.     

Cretaceous accretionary–collision complexes in central Indonesia

The geology of Cretaceous accretionary–collision complexes in central Indonesia is reviewed in this paper. The author and his colleagues have investigated the Cretaceous accretionary–collision complexes by means of radiolarian biostratigraphy and metamorphic petrology, as well as by geological mapping. The results of their work has revealed aspects of the tectonic development of the Sundaland margin in Cretaceous time. The Cretaceous accretionary–collision complexes are composed of various tectonic units formed by accretionary or collision processes, forearc sedimentation, arc volcanism and back arc spreading. The tectonic units consist of chert, limestone, basalt, siliceous shale, sandstone, shale, volcanic breccia, conglomerate, high P/T and ultra high P metamorphic rocks and ultramafic rocks (dismembered ophiolite). All these components were accreted along the Cretaceous convergent margin of the Sundaland Craton. In the Cretaceous, the southeastern margin of Sundaland was surrounded by a marginal sea. An immature volcanic arc was developed peripherally to this marginal sea. An oceanic plate was being subducted beneath the volcanic arc from the south. The oceanic plate carried microcontinents which were detached fragments of Gondwanaland. Oceanic plate subduction caused arc volcanism and formed an accretionary wedge. The accretionary wedge included fragments of oceanic crust such as chert, siliceous shale, limestone and pillow basalt. A Jurassic shallow marine allochthonous formation was emplaced by the collision of continental blocks. This collision also exhumed very high and ultra-high pressure metamorphic rocks from the deeper part of the pre-existing accretionary wedge. Cretaceous tectonic units were rearranged by thrusting and lateral faulting in the Cenozoic era when successive collision of continental blocks and rotation of continental blocks occurred in the Indonesian region.