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1.
Tectonics and Topography of the Tibetan Plateau in Early Miocene 总被引：1，自引：0，他引：1
Early Miocene stratigraphy, major structural systems, magmatic emplacement, volcanic eruption, vegetation change and paleo-elevation were analyzed for the Tibetan Plateau after regional geological mapping at a scale of 1:250,000 and related researches, revealing much more information for tectonic evolution and topographic change of the high plateau caused by Indian-Asian continental collision. Lacustrine deposits of dolostone, dolomite limestone, limestone, marl, sandstone and conglomerate of weak deformation formed extensively in the central Tibetan Plateau, indicating that vast lake complexes as large as 100,000–120,000 km2 existed in the central plateau during Early Miocene. Sporopollen assemblages contained in the lacustrine strata indicate the disappearance of most tropical-subtropical broad-leaved trees since Early Miocene and the flourishing of dark needleleaved trees during Early Miocene. Such vegetation changes adjusted for latitude and global climate variations demonstrate that the central Tibetan Plateau rose to ca. 4,000–4,500 m and the northeastern plateau uplifted to ca. 3,500–4,000 m before the Early Miocene. Intensive thrust and crustal thickening occurred in the areas surrounding central Tibetan Plateau in Early Miocene, formed Gangdise Thrust System(GTS) in the southern Lhasa block, Zedong-Renbu Thrust(ZRT) in the northern Himalaya block, Main Central Thrust(MCT) and Main Boundary Thrust(MBT) in the southern Himalaya block, and regional thrust systems in the Qaidam, Qilian, West Kunlun and Songpan-Ganzi blocks. Foreland basins formed in Early Miocene along major thrust systems, e.g. the Siwalik basin along MCT, Yalung-Zangbu Basin along GTS and ZRT, southwestern Tarim depression along West Kunlun Thrust, and large foreland basins along major thrust systems in the northeastern margin of the plateau. Intensive volcanic eruptions formed in the Qiangtang, Hoh-Xil and Kunlun blocks, porphyry granites and volcanic eruptions formed in the Nainqentanglha and Gangdise Mts., and leucogranites and granites formed in the Himalaya and Longmenshan Mts. in Early Miocene. The K2O weight percentages of Early Miocene magmatic rocks in the Gangdise and Himlayan Mts. are found to increase with distance from the MBT, indicating the genetic relationship between regional magmatism and subduction of Indian continental plate in Early Miocene. 相似文献
2.
Ralf Halama Khachatur Meliksetian Ivan P. Savov Patrick J. Sugden Krzysztof Sokół 《Geology Today》2020,36(3):101-108
Located in the heart of the Lesser Caucasus mountains, where the Arabian and Eurasian tectonic plates collide, Armenia occupies an exceptional geological position shaped through millions of years of subduction and collision. It is a unique place on the Earth recording extensive intrusive and volcanic activity related to the long-standing continental convergence. The volcanoes of Armenia provide a rare opportunity to study the sources and processes involved in this unusual type of magmatism. More than 500 Quaternary volcanoes have been mapped in Armenia, most of them formed from single eruptive episodes. Among several large composite volcanoes, the mighty Aragats stands out as the largest volcano in Armenia and the region altogether. Volcanic deposits testify to the range of eruptive styles—from the ignimbrites formed in eruptions as explosive and voluminous as any seen globally in the modern era to the enormous fissure-fed lava flows that form the Southern Caucasus flood basalt province, the smallest and youngest Large Igneous Province in the world. Several pre-historical and historical eruptions have been documented, highlighting the potential for future volcanic activity in the region. In recent years, research has focused on the volcanic hazards associated with the Armenian Nuclear Power Plant, located in the foothills of Aragats volcano. This article highlights some of the extraordinary volcanic and intrusive features observed in Armenia and summarizes aspects of recent volcanological and petrological research. 相似文献
3.
鉴于大陆岩浆弧上盘广泛分布有碳酸盐岩,岩体上升侵位过程使其碳通量明显的高于洋内岛弧,从而有可能影响着地质历史长时间尺度(百万年)的气候变化。陆弧碳的排放可分为两部分,一部分是与喷出岩相关的火山作用,另一部分是与侵入岩相关的脱碳过程。侵入岩的体量一般是喷出岩体量的10倍以上,由此与侵入岩有关的脱碳作用释放的碳通量不可忽视,可能类似与喷出岩有关的火山作用释放的碳通量甚至更大。火山作用能够将气体直接排入大气中,因此在以往的工作中研究较为充分。但与侵入岩相关的脱碳过程如:矽卡岩化,发生在地下,关于地下脱碳过程如何将碳释放到大气中还缺少详细的工作。本文,通过对比研究火山地区和非火山地区与侵入岩相关的深部脱碳过程,发现深部碳可以通过区域断层系统、地下水系统和热泉、火山通道、隐爆角砾岩筒、高频率的岩浆热液事件等途径瞬时地释放进入大气。通过初步估算,发现单个矽卡岩矿化事件所产生的二氧化碳通量(0.02~0.2Mt/yr)能够与目前地球绝大部分的普通单个火山的碳通量(<0.5Mt/yr)类比。因此岩浆深部脱碳过程对大气的影响至少与火山相当,其对气候的影响不可忽视。 相似文献
4.
青藏高原新生代地壳变形对同碰撞岩浆侵位的制约 总被引：1，自引：0，他引：1
同碰撞岩浆作用是青藏高原新生代构造-岩浆活动的一种重要形式，各种类型岩浆岩广泛分布于高原内不同的构造单元中，其中有的来自地幔，不过规模都不大，它们是如何穿过异常厚的地壳侵位到近地表或喷出地表，这还是个未解之谜。根据构造分析，这些岩浆岩均侵位于新生代向斜构造中，例如侵入于高原东南边缘的楚雄复向斜、兰坪．思茅复向斜和老君山向斜的碱性岩，侵入于高原南缘的北喜马拉雅拉轨岗日向斜的片麻状花岗岩以及喷出于高原北部巴颜喀拉和雁石坪复向斜的安山-玄武岩。文中通过一个力学模式，说明这些岩浆岩的侵位受控于地壳应力场特征，即：向斜构造的下部承受的是张应力，地壳发生减薄和张裂，下地壳或上地幔熔融物质以此为通道发生向上的侵位。不过，因向斜顶部地壳承受的是挤压应力，地壳发生挤压缩短，所以只有少量岩浆能侵位到近地表并发生变形。与此相反，背斜构造的下部地壳产生的是挤压应力，阻止了下伏地壳内岩浆的侵入。因此，岩浆的侵位一般不会沿背斜发生。这一力学机制解释了为什么青藏高原规模很小的同碰撞岩浆能穿过异常厚的地壳沿一系列向斜构造侵位到近地表或喷出地表的原因。 相似文献
5.
The southwestern Pacific region consists of segmented and translated continental fragments of the Gondwanan margin. Tectonic reconstructions of this region are challenged by the fact that many fragmented continental blocks are submerged and/or concealed under younger sedimentary cover. The Queensland Plateau (offshore northeastern Australia) is one such submerged continental block. We present detrital zircon geochronological and morphological data, complemented by petrographic observations, from samples obtained from the only two drill cores that penetrated the Paleozoic metasedimentary strata of the Queensland Plateau (Ocean Drilling Program leg 133, sites 824 and 825). Results provide maximum age constraints of 319.4 ± 3.5 and 298.9 ± 2.5 Ma for the time of deposition, which in conjunction with evidence for deformation, indicate that the metasedimentary successions are most likely upper Carboniferous to lower Permian. A comparison of our results with a larger dataset of detrital zircon ages from the Tasmanides suggests that the Paleozoic successions of the Queensland Plateau formed in a backarc basin that was part of the northern continuation of the New England Orogen and/or the East Australian Rift System. However, unlike most of the New England Orogen, a distinctive component of the detrital zircon age spectra of the Mossman Orogen is also recognised, suggesting the existence of a late Paleozoic drainage system that crossed the northern Tasmanides en route from the North Australian Craton. A distinctive shift from abraded zircon grains to grains with well-preserved morphology at ca 305 Ma reflects a direct drainage of first-cycle sediments, most likely from an outboard arc and/or backarc magmatism. 相似文献
6.
Paul C. Buchanan Christian Koeberl Wolf Uwe Reimold 《Contributions to Mineralogy and Petrology》1999,137(1-2):133-146
The Precambrian Dullstroom Formation of South Africa, which is predominantly composed of basaltic andesites interbedded with
subordinate sedimentary and felsic volcanic strata, represents the first phase of an extended period of magmatism that was
responsible for the Bushveld Magmatic Province, including the extrusive Rooiberg Group and the intrusive Bushveld Complex.
New geochemical and isotopic data for the Dullstroom Formation are presented in an effort to elucidate the petrogenetic processes
operative during the initiation of this magmatic episode. The volcanic units of the central portion of the Dullstroom Formation
have been subdivided into at least three interbedded compositional groups: low Ti mafic to intermediate units, high-Ti mafic
to intermediate units, and high Mg felsic units. High Ti and low Ti volcanic units are similar in some compositional characteristics
to basalts of the nearby northern and southern provinces, respectively, of the Mesozoic Karoo continental flood basalts. Isotopic
and compositional data for low Ti Dullstroom strata are consistent with bulk assimilation into a melt similar in composition
to a southern Karoo basalt of 20% upper continental crust accompanied by 20% fractional crystallization of pyroxene and plagioclase.
Isotopic and compositional data for high Ti Dullstroom strata are consistent with magma mixing of 30% northern Karoo K-rich
basalt and 70% southern Karoo basalt followed by 20% assimilation of upper continental crust and 20% fractional crystallization
of pyroxene and plagioclase. Compositions of high Mg felsic volcanic strata are consistent with 25% assimilation of a mixture
of silica-rich sedimentary rock and upper continental crust into a melt similar in composition to low Ti volcanic units with
25% fractional crystallization of pyroxene and plagioclase. However, it has been suggested that compositions of these high
Mg felsic strata may also be consistent with interaction of a crustal melt. Assimilation, fractional crystallization, and
magma mixing that apparently affected these Dullstroom Formation volcanic strata may have occurred in a series of shallow
magma chambers. These data are consistent with the suggestion that Dullstroom Formation volcanic rocks are the result of a
mantle plume. Mantle plume origin also is suggested by the large volume of intrusive and extrusive strata associated with
this magmatic episode. These data do not support the hypothesis that the Bushveld Complex and the Rooiberg Group formed by
impacts of a cluster of comets or asteroids.
Received: 14 October 1998 / Accepted: 17 May 1999 相似文献
7.
Prof. Guillermo Chong Díaz 《International Journal of Earth Sciences》1977,66(1):374-404
This work describes a geological scheme of the pre- And ean Domeyko Range of Northern Chile. This pre- And ean area consists of a basement formed by Paleozoic granitic, volcanic, and marine sedimentary rocks, and by Triassic acidic volcanics with continental intercalations. The Andean Basin developed in the Lias over the basement, with initial stages that include volcanic and continental sequences. A continuous marine environment existed in the Hettangian-Tithonian span, with volcanic events in the Bajocian, Callovian, Kimmeridgian, and Tithonian. Evaporitic facies developed in the Oxfordian-Kirnmeridgian. A marine-continental basin is recognized in the Neocomian, the Upper Cretaceous being represented by volcanic and continental deposits, a development similar to the Tertiary one; over these sequences volcanic, detrital, and saline deposits were laid down in the Plio-Pleistocene. Compressional tectonic cycles developed in the Upper Paleozoic, Upper Lias?, Upper Jurassic, Upper Cretaceous, and Tertiary, and tensional phases occured in the Triassic, Cretaceous, and Tertiary. The compressional stages were characterized by intrusive cycles while the tensional phases witnessed volcanic sedimentary events. 相似文献
8.
洋-陆过渡带是理解大陆岩石圈破裂和海底初始扩张的关键位置,但是在南海北部地区仍然存在关于相关地质过程的诸多疑问.通过近年开展的国际大洋发现计划航次以及深部地质地球物理探测,取得以下4个方面的认识.（1）南海北部的洋-陆边界一般与自由空间重力异常的正-负值过渡位置对应,而更加准确地限定需要结合反射、折射地震资料.稳定大洋岩石圈生成与大陆岩石圈最终破裂之间的洋-陆过渡边界的位置比以往认为的还应往深海盆方向移动.（2）洋-陆过渡带代表了远端带构造作用减弱和岩浆作用逐渐增强的区域.陆坡地壳发育扩张后岩浆底侵、洋-陆过渡带发育同破裂期岩浆喷出结构和侵入反射体.（3）在中生代的古俯冲带弧前区域,新生代的断裂沿着早期的构造开始活动,岩石圈多处发生强烈的共轭韧性剪切作用.随着大陆岩石圈的进一步拉伸减薄,部分靠陆一侧的裂谷中心停止张裂,成为夭折裂谷,以台西南盆地南部凹陷、白云凹陷、西沙海槽为代表,而南海陆缘异常伸展和最终破裂的地方集中在南侧裂谷中心.夭折裂谷下亦发现地幔蛇纹石化,进一步反映了较弱的同破裂岩浆活动.（4）南海初始洋壳的增生沿着大陆边缘走向具有显著的变化,南海东北部洋-陆过渡带下伏地幔明显抬升和部分蛇纹石化,地震纵、横波速度以及折射波衰减特征都支持此观点,反映南海东北部是一个贫岩浆型大陆边缘.未来,南海北部洋-陆过渡带有望成为南海“莫霍钻”的理想备选钻探区. 相似文献
9.
HETEROGENEITY OF THE LITHOSPHERE IN TIBETAN PLATEAU ON THE CONSTRAINTS OF MAGMATISM 相似文献
10.
A. A. Peyve 《Geotectonics》2010,44(1):60-75
The magmatic and tectonic activity of eastern South America and the western South Atlantic shows that extension of the continental
crust is the determinant factor of magmatism. Heating of the upper mantle is a necessary condition of its manifestation. Ascending
plume material is a source of additional heat. In the Early Mesozoic, Eastern Brazil was situated above a large, ascending
and probably ramifying plume, which has supplied heat and material since the Triassic, creating favorable conditions for continental
magmatism. Magmatic activity continued, gradually waning, until the Neogene as evidence for long-term retention of heat energy
beneath the continental lithosphere after the plume ascent. It has been shown that heated mantle material can be displaced
from the continent to the ocean for a significant distance beneath the lithosphere with the formation of linear tectonomagmatic
rises of the oceanic crust. The structural elements inherited certain directions on the continent and in the ocean, beginning
from the Neoproterozoic. These directions were reactivated and continued to control the younger structural grain and magmatic
activity. In Southeastern Brazil, these were the structural units striking in the southeastern (about 120° SE) and northeastern
directions parallel to the continent-ocean boundary. In Northeastern Brazil, the W-E- and N—S-trending structural units are
predominant. All these directions are manifested in oceanic structural units (Rio Grande, Vitória-Trindadi, Fernando de Noronha,
Pernambuco rises, etc.). 相似文献
11.
G. L. Leitchenkov Yu. B. Guseva V. V. Gandyukhin S. V. Ivanov L. V. Safonova 《Geotectonics》2014,48(1):5-23
The Southern Indian Ocean comprises large sedimentary basins of the Riiser-Larsen Sea (western sector); the Cosmonauts, Cooperation (Commonwealth), Davis seas (central sector); and the Mawson-d’Urville seas (eastern sector). The main tectonic provinces of the Southern Indian Ocean (Antarctica) have been outlined as a result of comprehensive interpretation of the geophysical data. Special attention is paid to determining the boundary between the rifted continental and oceanic crust. The basin of the Riiser-Larsen Sea was formed in the Early Jurassic under the action of the Karoo mantle plume. The intrusive complex, as a remote manifestation of the mantle plume, occurs along the inner boundary of the marginal rift. Opening of the ocean in the basin of Riiser-Larsen Sea started about 160 Ma ago and was characterized by rearrangement of plate motion and intense volcanic activity at the early stage. In the basin of the Cosmonauts, Cooperation, and Davis seas, the final stage of rifting was accompanied by the rise of the lithospheric mantle and by intrusive magmatism. The opening of the ocean started here 134 Ma ago. Emplacement of the Kerguelen plume resulted in jumping of ridges and detachment of continental crustal blocks from the Indian margin with the formation of the Kerguelen Plateau (microcontinent). The basin of the Mawson-d’Urville seas has evolved under conditions of long-term rifting since the Late Jurassic and is characterized by an extended zone of mantle unroofing. Breakup of the lithosphere between Australia and Antarctica developed asynchronously over a time interval of 95–65 Ma ago with propagation of MOR from the west eastward. The research was carried out using a great body of geophysical information (～140000 km of CDP seismic profiling, more than 250 stations of seismic refraction sounding, and more than 250000 km of magnetic and gravity profiles) obtained by expeditions from many countries over more than 30 years. 相似文献
12.
摘要：大陆造山带与沉积盆地之间具有十分密切的内在联系,空间上相互依存,物质上相互补偿,构造上相互作用,时间上同步演化。这些内在联系体现在统一的形成机制上:大陆造山带和沉积盆地是在大陆边缘俯冲板片脱水熔融和大陆内部地幔柱(枝)上隆的热动力作用下,地壳由盆向山侧向流动,导致盆山地壳物质发生循环运动。青藏高原与周边盆地的耦合作用十分典型。青藏高原不是印度板块与欧亚板块碰撞的结果,而是形成于下地壳流动驱动的板内盆山作用。青藏高原板内盆山耦合可分为两个阶段:(1)板内造山成盆阶段,表现为180～120 Ma→65～30 Ma→23～7 Ma从青藏高原北部和东部盆山系统→青藏高原中部盆山系统→青藏高原南部盆山系统有序迁移,以构造隆升、水平运动、地质作用和大规模板内金属成矿为特征;(2)均衡成山成盆阶段,表现为从36 Ma开始,青藏高原整体快速隆升和周边沉积盆地边缘坳陷带巨厚的磨拉石沉积,以36 Ma B.P.、25 Ma B.P.、18~12 Ma B.P.、 08 Ma B.P.和015 Ma B.P.等一系列脉动式快速隆升、垂直运动、地理作用和水系 环境变化为特征。大陆板内盆山构造演化经历从伸展构造向挤压构造的转换,伴随盆地主动作用转变成造山带主动作用。大陆下地壳流动和盆山耦合形成非安德森式的低角度拆离断层、波状起伏逆冲断层和异常共轭关系走滑断层。 相似文献
13.
造山带火山岩浆作用 总被引：9，自引：2，他引：9
造山带火山岩石学研究的主要目的在于重溯造山带的构造－岩浆演化历史。纵观我国到至全球的大陆造山带形成－演化历史，一个造山带往往经历了古大陆裂解，洋陆转换，陆块拼合，碰撞，陆内伸展－盆山耦合和新构造隆升（陆内造山）等众多不同的构造演化阶段，这些不同的构造演化阶段和不同的构造环境均有特定火山岩浆民之相伴。因此，我们可以根据造山带形成－演化不同阶段火山岩浆作用的特点来重溯造山带的的构造－岩浆演化历史，并进而从更大尺度上加以对比，探索全球动力学乃至比较行星学等重大学问题。本文对造山带火山岩石学研究中的一些重要问题进行了讨论和评述，这些问题包括有：板块内部火册浆活动，离散板块边界上的火山岩浆活动，会聚板块边缘的火山岩浆活动。 相似文献
14.
长江中下游庐枞火山岩盆地南侧钾质侵入岩带的成因 总被引：1，自引：0，他引：1
庐枞火山岩盆地南侧的钾质侵入岩带由正长岩-石英正长岩-正长花岗岩组成,以石英正长岩为主。它们的形成时间介于123"130 Ma之间,峰值约为126 Ma,其中正长岩和石英正长岩的形成时间稍早,而正长花岗岩的形成时间略晚。整个钾质侵入岩带的侵位时间晚于庐枞盆地内的橄榄玄粗质火山作用约4"7 Ma,也是长江中下游地区除最东段的宁镇地区外中生代最晚的岩浆活动产物之一。地球化学上,该钾质侵入岩带以高钾、富碱、富集Rb、Th、U、K等强不相容元素和轻稀土元素、亏损高场强元素Nb、Ta和Ti为特征。它们的母岩浆主要是由富集型上地幔部分熔融形成的,从正长岩经石英正长岩到正长花岗岩的演化主要受矿物的分离结晶作用控制,地壳物质同化所起的影响不大。但与同样来自富集型上地幔部分熔融的庐枞盆地内火山杂岩的母岩浆相比,前者的母岩浆来源深度可能更大些或其中包含了更多来自软流圈地幔的组分。两者的演化路径也完全不同,钾质侵入岩带的母岩浆除经历过高压下的分离结晶作用外,晚期在低压下还经历过长石为主,可能还有黑云母的分离结晶,甚至上地壳物质一定程度的混染作用;而盆地内火山杂岩的母岩浆低压下矿物的分离结晶作用及上地壳物质的混染都不明显。庐枞盆地南缘的富钾侵入岩与盆地内的火山杂岩一样,地球化学上都具有明显的大陆弧的特征,暗示它们的岩浆源区可能形成于俯冲带环境,意味着扬子地块北缘先前(推测为古元古代晚期)曾发生过俯冲作用,上地幔的交代富集可能就与这次的俯冲作用有关。 相似文献
15.
辉腾锡勒火山群位于内蒙古中部卓资县、察哈尔右翼中旗和后旗交界处的高山草原区。处于中国东部大同-阿尔山-诺敏河第四纪火山喷发带南段。火山群坐落在太古宙变质岩系、二叠纪花岗岩和新近纪汉诺坝玄武岩之上。平面上呈低洼的菱形台地，四周为山地，总面积约260km2。因上覆在汉诺坝玄武岩台地之上，故以往将其误归为新近纪汉诺坝玄武岩。火山群内发育近百座火山，大多数火山形貌保存基本完整。火山产物主要为一套碱性橄榄玄武岩，次为不同成因的火山碎屑物（岩）。碱性玄武岩覆盖在晚更新世坡积物和黄土之上。火山活动的时代主体为晚更新世，可进一步分为早、中、晚三期。早期为裂隙-中心式喷发，火口已剥蚀殆尽；中期主要形成"地池式"和玛珥式火山，火山形貌较完整，火口呈特征的圆形或椭圆形，大部分积水成湖，当地习称"九十九眼泉"或"海子"。晚期以熔浆的溢流为主，形成结构完整的盾片状火山。火山活动经历了沿裂隙的喷溢到中心式弱爆发、溢流-射汽岩浆爆发-溢流再到溅落堆积的演化过程。辉腾锡勒火山群是在新近纪汉诺坝玄武岩台地上新解体确定的第四纪火山群，这为研究蒙古高原南部地壳深部结构及其活动性提供了又一天然窗口，对了解新构造活动、环境及灾害预警研究都具有重要的理论和实际意义。 相似文献
16.
西昆仑阿什库勒火山群地质特征和活动分期 总被引：3，自引：2，他引：1
阿什库勒火山群作为青藏高原内最新期的北部昆仑火山群的典型代表,长期以来一直受到国内外地学界的广泛关注。我们通过对阿什库勒盆地火山区的野外地质地貌考察,研究了阿什库勒盆地内第四纪火山活动历史,完成了阿什库勒火山群重要火山锥体的1∶2000火山机构图。同时,对系统采集于不同火山机构和部位的20个火山岩样品进行了系列Ar-Ar同位素年代测试分析,获得了翔实的研究区不同火山岩石单元的绝对年龄数据。结合野外地质地貌考察结果,讨论了阿什库勒盆地的火山活动的第四纪时期活动历史,并将主要活动时期进一步划分为早更新世早期、早更新世中期、中更新世早期、中更新世晚期、晚更新世期和全新世期六期,取得了与前人有关该研究区火山活动历史和活动期次类似的划分方案,并补充了新的年代学证据。研究成果弥补了藏北高原西部由于恶劣工作环境而造成的第四纪火山学研究的不足。 相似文献
17.
老爷庙-额仁山一带发育3套性质不同的火山岩，通过对其岩石组合、岩相、古火山机构特征的详细观察及岩石学、岩石化学、地球化学的研究，晚泥盆世老爷庙组火山岩为玄武岩-安山岩组合，发育盾状和层状火山，属海相环境，为板块消减带岛弧型高铝玄武岩；晚石炭世-早二叠世哈尔加乌组火山岩为陆相火山岩，岩石组合为安山岩．英安岩-流纹岩，以爆发相为主，常形成破火山及锥状火山机构，为陆-陆碰撞造山期火山岩；早二叠世中晚期卡拉岗组火山岩为一套以酸性为主的陆相火山岩，喷溢相发育，常形成穹状古火山机构，岩石组合为英安岩-流纹岩，为造山期弛张期火山岩，3套火山岩为板块不同阶段的火山岩，从老爷庙组火山岩→哈尔加乌组火山岩→拉岗组火山岩，岩石向酸性演化，地壳成熟度愈来愈高，南混合壳转化为陆壳． 相似文献
18.
《Geodinamica Acta》2001,14(1-3):177-195
The east Anatolian plateau and the Lesser Caucasus are characterised and shaped by three major structures: (1) NW- and NE-trending dextral to sinistral active strike-slip faults, (2) N-S to NNW-trending fissures and /or Plio-Quaternary volcanoes, and (3) a 5-km thick, undeformed Plio-Quaternary continental volcano-sedimentary sequence accumulated in various strike-slip basins. In contrast to the situation in the east Anatolian plateau and the Lesser Caucasus, the Transcaucasus and the Great Caucasus are characterised by WNW-trending active thrust to reverse faults, folds, and 6-km thick, undeformed (except for the fault-bounded basin margins) continuous Oligocene-Quaternary molassic sequence accumulated in actively developing ramp basins. Hence, the neotectonic regime in the Great Caucasus and the Transcaucasus is compressional–contractional, and Oligocene-Quaternary in age; whereas it is compressional–extensional, and Plio-Quaternary in age in the east Anatolian plateau and the Lesser Caucasus.Middle and Upper Miocene volcano-sedimentary sequences are folded and thrust-to-reverse-faulted as a result of compressional–contractional tectonic regime accompanied by mostly calc-alkaline volcanic activity, whereas Middle Pliocene-Quaternary sequences, which rest with angular unconformity on the pre-Middle Pliocene rocks, are nearly flat-lying and dominated by strike-slip faulting accompanied by mostly alkali volcanic activity implying an inversion in tectonic regime. The strike-slip faults cut and displace dykes, reverse to thrust faults and fold axes of Late Miocene age up to maximum 7 km: hence these faults are younger than Late Miocene, i.e., these formed after Late Miocene. Therefore, the time period between late Serravalian (∼ 12 Ma) continent–continent collision of Arabian and Eurasian plates and the late Early Pliocene inversion in both the tectonic regime, basin type and deformation pattern (from folding and thrusting to strike-slip faulting) is here termed as the Transitional period.Orientation patterns of various neotectonic structures and focal mechanism solutions of recent earthquakes that occurred in the east Anatolian plateau and the Caucasus fit well with the N–S directed intracontinental convergence between the Arabian plate in the south and the Eurasian plate in the north lasting since Late Miocene or Early Pliocene in places. 相似文献
19.
《Journal of South American Earth Sciences》1999,12(1):33-49
Regional mapping (1:50,000) and U-Pb and K-Ar geochronology in the El Indio region refines the knowledge of the distribution, lithostratigraphy, and age of the sedimentary, volcanic, and intrusive rocks that comprise the regionally extensive Pastos Blancos Group which is equivalent to the Choiyoi Group of the Argentine Frontal Cordillera. The Pastos Blancos Group (which we elevate to Group status herein) includes at least two diachronous volcanic–sedimentary sequences: an older felsic volcanic and volcaniclastic unit, the Guanaco Sonso sequence, that is Permian in age, and a younger bimodal volcanic and volcaniclastic unit, the Los Tilos sequence that is Middle Triassic to Early Jurassic. Sedimentary rocks of the Los Tilos sequence are transitional upward into the overlying Early to Middle Jurassic shallow marine limestones of the Lautaro Formation.Intrusions that make up the regionally extensive Permian to Early Jurassic plutons of the Chollay and Elqui-Limarı́ batholiths that were previously mapped as a single plutonic association, the Ingaguás Complex, include in the El Indio region at least three discrete intrusive units. These include: Early Permian (280–270 Ma) biotite granites, Early to Middle Triassic (242–238 Ma) silica-rich leucocratic granites and rhyolitic porphyries that made up the bulk of the Chollay Batholith, and a younger Late Triassic–Early Jurassic unit (221–200 Ma) of mainly intrusive rhyolitic porphyries, extrusive domes, and subordinate mafic intrusions and both felsic and mafic dikes, which are coeval with volcanic rocks of the Los Tilos sequence.Our data show that latest Paleozoic to Early Jurassic intrusive, volcanic, and sedimentary rocks in the El Indio region of the High Andes of Chile between 29–30°S likely formed during extension driven processes after the cessation of Carboniferous–Early Permian subduction along the western edge of Gondwana. These processes began by Late Permian time, but instead of recording a single and protracted magmatic event, as has been previously suggested, rocks that belong to the Pastos Blancos Group and the Ingaguás Intrusive Complex record at least three discrete periods of silicic to bimodal magmatism which occurred during the Middle Permian to Early Jurassic interval. 相似文献
20.
V. D. Chekhovich S. A. Palandzhyan A. N. Sukhov A. V. Egorkin V. N. Ben’yamovsky 《Geotectonics》2008,42(1):48-63
The northeastern segment of the Late Cretaceous suprasubduction Okhotsk-Chukotka volcanic belt is not an analogue of Andean-type continental margin. During its formation, the belt was separated from the Paleopacific by a complexly built assembly that comprised the Central Koryak continental block and the Essoveem volcanic arc at its margin. Various types of independent terrigenous sedimentary basins were formed in the Late Cretaceous and Early Paleogene at the subsided portion of the microcontinent and its slope. The Uchkhichkhil-type basin was characterized by deposition of polymictic clastic sediments produced during erosion of the volcanic arc and pyroclastic material derived from active volcanic centers of this arc that extended along the microcontinent margin that faced the Okhotsk-Chukotka volcanic belt. The deposition of quartz-feldspathic flyschoid sequences as products of scouring of sialic basement of the continental block was inherent to the Ukelayat type of sedimentation. The closure of the minor oceanic basin that separated the Asian margin from microcontinent in the late Campanian resulted in the cessation of subduction-related activity of the Okhotsk-Chukotka volcanic belt and the Essoveem arc and initiated the formation of the Late Cretaceous accretionary margin of Asia. The deep structure of the central Koryak Highland deduced from the results of seismic surveying with the earthquake converted-wave method has corroborated the geotectonic interpretation. 相似文献