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1.
Late Miocene to Early Pliocene blueschist from Taiwan and its exhumation via forearc extraction 
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下载免费PDF全文 Sascha Sandmann Thorsten J. Nagel Nikolaus Froitzheim Kamil Ustaszewski Carsten Münker 《地学学报》2015,27(4):285-291
Blueschist facies rocks in the Yuli Belt of Taiwan's Central Range record ongoing subduction of the Eurasian plate. We present a prograde Lu–Hf garnet–whole‐rock age of 5.1 ± 1.7 Ma from a retrogressed blueschist in the Yuli Belt. This age is considerably younger than the previously assumed age of 14–8 Ma for high‐pressure metamorphism in the Yuli Belt and represents the youngest Lu–Hf garnet age ever recorded for blueschist facies metamorphism. The age sheds new light on the palaeogeographic origin and exhumation scenario of the Yuli Belt. We propose that the Yuli Belt originated from the ocean–continent boundary of the Chinese passive margin. It was subducted eastward during collision with the Luzon island arc and rapidly exhumed when the forearc lithosphere was removed from above the continental slab by discrete subduction (extraction). This process reduces the pressure above the continental slab and may prompt the ascent of subducted crust into the opening gap. Thus, it can control the exhumation of high‐pressure rocks. 相似文献
2.
DONG Shuwen Chinese Academy of Geological Sciences Baiwanzhuang Ro Beijing WU Hongling LIU Xiaochun XUE Huaimin Institute of Geomechanics Chinese Academy of Geological Sciences Beijing Fei Zhenbi 《《地质学报》英文版》2002,76(1):69-80
Up to now it is known that almost all ultrahigh-pressure (UHP) metamorphism of non-impact origin occurred in continent-continent collisional orogenic belt, as has been evidenced by many outcrops in the eastern hemisphere. UHP metamorphic rocks are represented by coesite- and diamond-bearing eclogites and eclogite facies metamorphic rocks formed at 650-800℃ and 2.6-3.5 GPa, and most of the protoliths of UHP rocks are volcanic-sedimentary sequences of continental crust. From these it may be deduced that deep subduction of continental crust may have occurred. However, UHP rocks are exposed on the surface or occur near the surface now, which implies that they have been exhumed from great depths. The mechanism of deep subduction of continental crust and subsequent exhumation has been a hot topic of the research on continental dynamics, but there are divergent views. The focus of the dispute is how deep continental crust is subducted so that UHP rocks can be formed and what mechanism causes it to be subducte 相似文献
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台湾造山带是中新世晚期以来相邻菲律宾海板块往北西方向移动,导致北吕宋岛弧系统及弧前增生楔与欧亚大陆边缘斜碰撞形成的。目前该造山带仍在活动,虽然规模很小,但形成了多数大型碰撞造山带中的所有构造单元,是研究年轻造山系统的理想野外实验室,为理解西太平洋弧-陆碰撞过程和边缘海演化提供了一个独特的窗口。本文总结了二十一世纪以来对台湾造山带的诸多研究进展,讨论了其构造单元划分及演化过程。我们将台湾造山带重新划分为6个构造单元,由西至东分依次为:(1)西部前陆盆地;(2)中央山脉褶皱逆冲带;(3)太鲁阁带;(4)玉里-利吉蛇绿混杂岩带;(5)纵谷磨拉石盆地;(6)海岸山脉岛弧系统。其中,西部前陆盆地为6.5Ma以来伴随台湾造山带的隆升剥蚀形成沉积盆地。中央山脉褶皱逆冲带为新生代(57~5.3Ma)欧亚大陆东缘伸展盆地沉积物由于弧-陆碰撞受褶皱、逆冲及变质作用改造形成的。太鲁阁带是造山带中的古老陆块,主要记录中生代古太平洋俯冲在欧亚大陆活动边缘形成的岩浆、沉积和变质岩作用。玉里-利吉蛇绿混杂岩带和海岸山脉岛弧系统分别为中新世中期(~18Ma)以来南中国海板块向菲律宾海板块之下俯冲形成的岛弧和弧前增生楔,其中玉里混杂岩中有典型低温高压变质作用记录,变质年龄为11~9Ma;岛弧火山作用的主要时限为9.2~4.2Ma。纵谷磨拉石盆地记录1.1Ma以来的山间盆地沉积。台湾造山带的构造演化可划分为4个阶段:(a)古太平洋板块俯冲与欧亚大陆边缘增生阶段(200~60Ma);(b)欧亚大陆东缘伸展和南中国海扩张阶段(60~18Ma);(c)南中国海俯冲阶段(18~4Ma);(d)弧-陆碰撞阶段(<6Ma)。台湾弧-陆碰撞造山带是一个特殊案例,其弧-陆碰撞并不伴随着弧-陆之间的洋盆消亡,而是由于北吕宋岛弧及弧前增生楔伴随菲律宾海板块运动向西北方走滑,仰冲到欧亚大陆边缘,形成现今的台湾造山带。 相似文献
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中国大陆构造及动力学若干问题的认识 总被引：17，自引：2，他引：15
中国(东亚)大陆受特提斯、古亚洲和太平洋构造体系的制约,具有复杂的地体构架和特殊的岩石圈结构。本文从地学前沿——大陆动力学的视野出发,围绕中国大陆构造及动力学四个方面的研究,总结已有的进展并提出新的思考:①中国大陆板块下的构造和整个地幔运动的构架:地震层析资料揭示西太平洋板片向西俯冲到东亚大陆之下,其倾角逐渐减小,最后近水平地插进400～600km深度的地幔过渡带中,成为箕状几何形态的超深俯冲板片。印度岩石圈板片超深俯冲至青藏高原之下～800km的深度,在喜马拉雅西构造结部位发生双向不对称深俯冲,印度岩石圈板片向东俯冲至东构造结东侧之下300～500km的深度。②中国大陆变质基底的再活化:中国大陆的大部分陆块未受显生宙以来构造、变质和岩浆事件的改造与激活,在冈瓦纳大陆北缘的印度陆块和阿拉伯陆块北缘还发育有形成于泛非期(530～470Ma)的造山带,其影响范围至高喜马拉雅、拉萨地体和三江地区。新生代的变质活化普遍出现在喜马拉雅、南迦巴瓦、拉萨地体和三江-缅甸地区,最新的变质年龄仅2～1Ma(南迦巴瓦)。③中国主要高压-超高压变质带的大地构造背景及深俯冲-折返机制:中国及邻区含榴辉岩的高压-超高压(HP/UHP)变质带有洋壳(深)俯冲和陆壳(深)俯冲之分。青藏高原中,大部分洋壳俯冲形成的高压/超高压变质带与原-古特提斯洋盆中诸多微陆块之间的小洋盆的汇聚碰撞有关,陆壳深俯冲作用有两种机制,它们分别是大陆块之间剪式碰撞和撕裂式岩石圈舌形板片的深俯冲。④中国大陆造山带的深部物质可经3类机制挤出,即深部地壳物质"牙膏式"挤出、侧向挤出和"挤压转换式"挤出。 相似文献
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大别山超高压变质岩折返机制与华北-华南陆块碰撞过程 总被引：18，自引：0，他引：18
古地磁研究表明华北和华南陆块的碰撞始于三叠纪初 ,止于晚侏罗世 ;同位素年代学研究及大别山北部中—上侏罗统砾岩层中榴辉岩砾石的发现表明大别山超高压变质岩形成于三叠纪初 ,并在中—晚侏罗世出露于地表。因此 ,超高压变质岩是在陆陆碰撞过程中完成它的折返出露过程。揭示超高压变质岩的折返历史与机制有助于我们认识大陆的碰撞过程。大别山超高压变质岩及其围岩θ t冷却曲线显示超高压变质岩从 80 0℃到 3 0 0℃经历了三个阶段 :( 2 2 6± 3 )～ ( 2 1 9± 7)Ma期间从80 0℃到 5 0 0℃的第一次快速冷却 ,1 80～ 1 70Ma期间从 4 5 0℃到 3 0 0℃的第二次快速冷却 )和介于两者之间的等温过程。这一具有两次快速冷却的θ t曲线已被近年来的若干年代学数据所证实。超高压变质岩的两次快速冷却事件反映了两次快速抬升过程。在东秦岭及苏鲁地体东端发育的同碰撞花岗岩U Pb年龄值为 2 2 5～ 2 0 5Ma,与超高压变质岩第一次快速冷却时代吻合。这种时代耦合关系表明俯冲板片断离可能是超高压变质岩第一次快速抬升和冷却的重要机制。大别山Pb同位素填图揭示出南大别带超高压变质岩具有高反射成因Pb特征 ,因而源于俯冲的上地壳 ;而北大别带超高压变质岩具有低放射成因Pb特征 ,源于俯冲长英质下地壳。这表明在俯 相似文献
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低温超高压变质岩具有极低的地热梯度,其变质演化对于认识板块间相互作用的动力学过程以及弧地壳的生长机制具有重要意义。西南天山造山带发育了世界上少有的经历过深俯冲作用且具有洋壳属性的典型低温超高压变质地质体。近几年来对该造山带中的超高压变质岩开展了大量深入细致的岩石学研究工作,取得了一系列新进展。变基性岩和变沉积岩系岩石中柯石英的普遍发现,直接证明西南天山变质蛇绿混杂岩曾经俯冲到上地幔深度,且具有极低的地热梯度,与热力学模拟结果一致。柯石英的稀少以及大量不同类型柯石英假像的存在,说明在折返过程中发生了强烈的退变质叠加,只有刚性较大且没有经历碎裂-愈合作用的矿物(如石榴石)才有可能保存柯石英。综合岩相学证据和相平衡计算结果,确定西南天山造山带北部的高压地质体(即哈布腾苏-科布尔特单元)整体经历过超高压变质作用,南部的高压地质体峰期压力未达到柯石英稳定域。超高压和高压变质地体的空间分布特点指示了古天山洋由南向北的俯冲极性。这些基础岩石学研究工作的开展对于揭示冷俯冲带的深部物理化学过程以及建立中亚南天山造山带演化的精细模型具有重要意义。 相似文献
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南阿尔金造山带是目前报道的具有最深俯冲记录的大陆超高压变质带,其内出露有高压-超高温麻粒岩,它们对深入理解大陆地壳岩石超深俯冲与折返过程具有重要意义.介绍了对南阿尔金巴什瓦克地区长英质麻粒岩和基性麻粒岩的岩相学、矿物化学、相平衡模拟及锆石U-Pb年代学研究成果.其中基性麻粒岩主要记录了深俯冲大陆地壳折返过程的变质演化:包括高压榴辉岩相、高压-超高温麻粒岩相、低压-超高温麻粒岩相及随后的近等压降温演化阶段;长英质麻粒岩除了记录与基性麻粒岩相似的折返过程外,还记录了从角闪岩相到超高压榴辉岩相的进变质演化过程.结合已有研究资料,确定超高压榴辉岩阶段峰期条件> 7~9 GPa和>1 000℃,可达到斯石英稳定域.锆石年代学显示两种岩石类型的原岩和变质年龄均分别在900 Ma和500 Ma左右.变质作用与年代学研究表明,南阿尔金大陆地壳岩石在早古生代发生超深俯冲至200~300 km后,折返至加厚地壳底部发生高压-超高温变质作用,随后被快速抬升至地壳浅部发生低压-超高温变质作用并经历迅速冷却. 相似文献
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自20世纪80年代在大陆地壳岩石中发现柯石英和金刚石等超高压变质矿物以来,大陆深俯冲和超高压变质作用就成为了固体地球科学研究的前沿和热点领域之一。经过三十余年的研究,已经在大陆地壳的俯冲深度、深俯冲岩石变质P-T-t轨迹、俯冲地壳岩石的折返机制、深俯冲岩石的原岩性质、大陆碰撞过程中的熔/流体活动与元素活动性、俯冲隧道内部不同类型壳幔相互作用、碰撞后岩浆岩的成因、大陆碰撞造山带成矿作用等方面取得了许多重要成果。本文重点对大陆俯冲带超高压岩石部分熔融和不同类型壳幔相互作用近十年来的研究进展进行回顾和总结,并对存在的相关科学问题和未来的研究方向进行了展望。深俯冲大陆地壳的部分熔融主要出现在两个阶段:折返的初期阶段和碰撞后阶段,前者产生了碱性熔体,后者产生了钙碱性熔体。大陆俯冲带壳幔相互作用有两种类型,涉及地幔楔与两种俯冲带流体的交代反应:一是来自深俯冲陆壳的变质脱水/熔融,二是来自先前俯冲古洋壳的变质脱水/熔融。 相似文献
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地壳放射性生热效应对大陆俯冲过程影响的数值模拟研究 总被引：1，自引：0，他引：1
岩体中的放射性生热是地幔对流和地壳变质作用的关键热源之一,但地壳放射性生热率是如何影响大陆俯冲-碰撞的动力学过程,尤其是大陆碰撞区域的热结构演化,尚未获得共识。本文使用热-力学数值模拟方法对上、下地壳放射性生热率进行系统的模拟实验,以研究其对大陆俯冲动力学演化过程的影响。模型实验表明,由于大陆上地壳富集U、Th和K等主要放射性生热元素,且放射性生热率的变化区间较大(1.0~3.0μW/m~3),导致其对大陆俯冲碰撞动力学演化过程的影响较为显著,主要包括进入俯冲通道内的上地壳体积大小、碰撞区域内地壳熔融范围、俯冲下地壳物质折返的规模和两大陆的耦合程度等四个方面。而大陆下地壳则以中-基性岩为主,相对亏损U、Th、K等主要放射性生热元素,且放射性生热率的变化区域较小(0.2~0.8μW/m~3),致使其对大陆俯冲演化过程的影响相对有限,主要通过控制俯冲下地壳以及大陆板片的粘滞度和流变强度的大小,进而制约大陆俯冲过程下地壳物质折返的规模以及板片倾角的大小。 相似文献
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三维P波速度解析研究结果表明，苏鲁-大别超高压变质带岩石圈地壳速度结构均具有上地壳明显高速且上凸、中地壳增厚、下地壳埋藏较深且莫霍面下凹等基本特征。与大别地区相比较，苏鲁超高压变质带存在着上地壳波速更高，且地表高速区面积与上地壳高速体体积大于大别；而莫霍面下凹程度不如大别地区，地壳山根已逐步趋向消失等独特的区域特征。显示了苏鲁地区曾发生过更激烈的俯冲与折返构造运动，与大别地区相比，有更多高速、高密度的超高压变质岩折返到上地壳与地表；然而在造山运动过程中比大别更早进入了造山运动后期等特征。对比研究结果表明，苏鲁-大别地段的造山、演化过程中，在构造运动基本相似的背景下，存在着区域性特征。苏鲁地区的造山运动以及超高压变质作用，有起始略晚、发生时期较短但相对激烈、结束早、比大别更早进入了造山运动的后期等特征。笔者分析了苏鲁区域性特征形成的主要构造原因是，郯庐断裂带的大规模左旋走滑运动以及通过中国华北区域的大范围NXV—SE向扩张应力场的影响。其中，中生代以来大华北地区的大区域扩张应力场的影响可能是该区俯冲到地幔内的超高压变质岩能够大量折返回地表或上地壳的重要构造原因。 相似文献
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The Indian subcontinent has been colliding against Asia along the Himalayas. Hindu Kush and Burma in this collision zone have intermediate-depth seismicities beneath them, with most of the continental crust subducted into a few hundred km depth. The subduction, not collision, in these regions is an enigma long time. We show that the continental lithosphere subducted beneath Hindu Kush and Burma traveled over the Reunion and Kerguelen hotspots from 100 Ma to 126 Ma and is likely to have been metasomatized by upwelling plumes beneath those hotspots. The devolatilization of the metasomatized lithosphere impinging on the collision boundary would have provided a high pore fluid pressure ratio at the thrust zones and made the subduction of the continental lithosphere in these regions possible. The subducted lithosphere could give intermediate-depth seismicities by devolatilization embrittlement. Such subduction of hotspot-affected lithosphere without accompanying any oceanic plate would be one candidate for producing ultrahigh-pressure metamorphic rocks by deep subduction of the continental crust. 相似文献
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本文在讨论中国东部现有构造演化模式基础上，着重从华北与华南地块之间板块尺度的动力学过程剖析秦岭－大别中生代造山带构造演化，以及大别－苏鲁超高压变质地体的形成和折返过程。晚二叠世－中三叠世华南地块向华北地块持续挤压，陆壳大规模俯冲导致超高压变质作用的产生，而华北地块在晚三叠世至早侏罗世发生快速逆时针旋转，使得这一地区上地幔深度的超高压变质地体快速折返至下地壳。由于超高压变质地体侵位后，地壳结构、构造的差异，在南北地块的进一步挤压下，造成中国东部晚侏罗世－早白垩世郯庐断裂带的巨大左行剪切。 相似文献
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本文根据现实主义原则和现代地质学理论,分析综合了东亚构造地质、古地磁、古生物地理、地质年代学等方面的一些最新研究成果,提出东亚古亚洲洋构造系和古特堤斯构造系向环太平洋主动陆缘的转变最终出现在中侏罗世,著名的燕山运动正是这一重要构造转折的产物。 相似文献
14.
当前,增生型造山带和碰撞型造山带的研究均取得了丰富的成果和创新性认识。二者过渡期间常常发生陆壳俯冲。然而,该俯冲具有什么样的构造变形特点,并如何影响造山带演化过程,长期未受到足够的关注。基于此,文中选择曾发生了陆壳俯冲的两个新生代时期的造山带（中国台湾造山带和雅鲁藏布江造山带）和一个中生代时期的造山带（羌塘造山带）开展研究,以期阐明陆壳俯冲的独特构造变形特征以及和造山过程的交互作用。研究发现,陆壳俯冲常常在造山带形成双层结构,上部为一套由史密斯地层组成的逆冲叠瓦扇构造体系,下部为一套具“岩块–基质”结构特征的俯冲杂岩。双层结构的上下部分物质组成相似,均以斜坡相–海底扇相沉积为主,也有陆棚相沉积。因此,由于构造变形时间相近,双层结构应是由同一套被动陆缘物质俯冲形成的深浅不同的构造体系。研究认为,在陆壳俯冲过程中,早期的斜坡–海底扇俯冲是形成双层结构的主要因素。后续的陆棚俯冲则对碰撞作用的发生起到了主导作用,从而使应变逐渐向克拉通内部扩展,形成前陆褶皱–冲断带。随着碰撞作用的持续,双层结构常常遭到构造破坏,深部的俯冲杂岩因此得以剥露至浅表。因此,文章的研究强调了陆壳俯冲和深俯冲物质的折返在造山带演化中的重要意义。 相似文献
15.
Five domains (microplates) have been recognized by seismic anisotropy in the mantle lithosphere of the Bohemian Massif. The mantle domains correspond to major crustal units and each of the domains bears a consistent fossil olivine fabric formed before their Variscan assembly. The present-day mantle fabric indicates that this process consisted of at least three oceanic subductions, each followed by an underthrusting of the continental lithosphere. The seismic anisotropy does not detect remnants of the oceanic subductions, but it can trace boundaries of the preserved continental domains subsequently underthrust along the paths of previous oceanic subductions. The most robust continent–continent collision was followed by westward underthrusting of the Brunovistulian mantle lithosphere, still detectable by seismic anisotropy more than 100 km beneath the Moldanubian mantle lithosphere. Major occurrences of the high-pressure/ultra high-pressure (HP–UHP) rocks follow the ENE and NNE oriented sutures and boundaries of the mantle–lithosphere domains mapped from three-dimensional modeling of body-wave anisotropy. The HP–UHP rocks are products of oceanic subductions and the following underthrusting of the continental crust and mantle lithosphere exhumed along the mantle boundaries. The close relation of the mantle sutures and occurrences of the HP–UHP rocks near the paleosubductions testifies for models interpreting the granulite–garnet peridotite association by oceanic/continental subduction/underthrusting followed by the exhumation of deep-seated rocks. Our findings support the bivergent subduction model of tectonic development of the central part of the Bohemian Massif. The inferences from seismic anisotropy image the Bohemian Massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric. The collisional mantle boundaries, blurred by tectonometamorphic processes in easily deformed overlying crust, served as major exhumation channels of the HP–UHP rocks. 相似文献
16.
Basic concepts of structural restoration are applied to crustal cross-sections through mountain belts to explore large-scale tectonic models and deep structure. However, restored sections should account for variations in pre-orogenic crustal thicknesses. Crustal balancing approaches are reviewed and applied to two Alpine sections, coinciding with deep seismic experiments: NRP-20 East (Central Alps) and ECORS-CROP (Western Alps). Existing studies assume large (>300 km) orogenic contraction and only moderately thinned pre-orogenic crust. The resulting restored sections contain more crust than is imaged beneath the present-day Alps, the missing crust generally assumed to be subducted. Two kinematic modifications reduce the requirement for subduction: thinning and buoyancy-driven return flow of ultra-high-pressure metamorphic rocks during orogenesis; and pre-orogenic hyperextension. Using large stretching factors for the pre-orogenic crust negates crustal subduction on both Alpine transects. If the lower crust was approximately rigid, restorations of the Central Alps require strongly depth-heterogeneous stretching of upper and lower crust during Mesozoic rifting. Relaxing this requirement allows uniform lithospheric stretching, a corollary consistent with published subsidence estimates. Restorations make implicit statements on the form of pre-orogenic basins and the structure of continental margins incorporated into mountain belts that can in turn provide tests of tectonic models. 相似文献
17.
R. J. Jenchuraeva 《Mineralium Deposita》1997,32(5):434-440
Ore deposits in the fold belts of the northern Tien Shan have been formed in two stages and occur in two types of tectonic
settings. The first type is represented by Early Ordovician island arcs hosting the Karakol ore district. These east–west
trending island arcs are interpreted to have evolved above the south dipping subduction of oceanic crust of the Central Asian
paleo-ocean. The second type of tectonic setting hosting the Octorkoy Ore District, has evolved on a Devonian-Carboniferous
active continental margin of the Central Asian paleo-ocean above north dipping subduction of the oceanic crust. The second
type is superposed on the first tectonic setting. The Oktorkoy ore district is characterized by thrusting and similar circular
structures as in the first stage and its polygenic mineralization is associated with multiphase granitoid complexes. Zonality
of porphyry copper deposits of the Kyrghyz Range is associated with the following hydrothermal alteration sequence: potassium
alteration - phyllization (beresitization) - prophyllitization (epidote-chlorite-albite) - tourmalinization - argillization
- prophyllitization (epidote-actinolite-albite).
Received: 3 June 1996 / Accepted: 10 January 1997 相似文献
18.
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. 相似文献
19.
The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two‐dimensional thermo‐mechanical numerical modelling based on the geology of the Anatolia–Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far‐field plate kinematics appear to be essential for the obduction of ~80‐Ma‐old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10–20 Ma before obduction, at the onset of Africa–Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite‐free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far‐field plate kinematics resulting from renewed Neotethys oceanic subduction beneath Eurasia. 相似文献
20.
Jingsui Yang Zhiqin Xu Larissa F. Dobrzhinetskaya Harry W. Green II Xianzhi Pei Rendeng Shi Cailai Wu Joseph L. Wooden Jianxin Zhang Yusheng Wan Haibing Li 《地学学报》2003,15(6):370-379
The Central Orogenic Belt (COB) of China is a major continental collision zone that contains extensive outcrops of deeply subducted and exhumed rocks at both the eastern and the western end of the belt. Here we report discovery of microdiamonds from both eclogites and felsic gneisses in the North Qinling zone in the central portion of the COB. This discovery demonstrates that the country rocks of continental affinity shared in the ultra‐high‐pressure metamorphic (UHPM) event and provides a bridge connecting the two previously recognized UHPM terranes, thereby establishing the existence of a UHPM belt extending more than 4000 km. Geochronological dating yields Early Palaeozoic ages in the west and Early Mesozoic ages in the east, recording two separate continental collisions overprinted within the COB. Occurrence of UHP metamorphism during recurrent continental collision here and in the Alps suggests that deep subduction of continental material during such collisions is probably common rather than exceptional, with significant implications for processes of plate tectonic reorganization and mantle mixing over time. 相似文献