是岩浆侵入还是构造侵位?——湖北两郧随枣镁铁岩带野外调查纪实   总被引：2，自引：0，他引：2  

王荃  刘雪亚 《地质论评》2010,56(3):329-338

湖北省武当山—随州—枣阳一线存在一呈北西西走向的镁铁质岩浆岩带,长约390km,宽40～100km。其中超镁铁质岩14处,超镁铁质、镁铁质杂岩21处,镁铁质岩250处,出露面积689km2。自上世纪开展1∶20万区调工作迄今,已出版的成果资料一致认为,这些岩体是镁铁质岩浆沿深大断裂侵入而成。笔者等于2005年随机选择了丹江口和随州境内两条地质调查路线,在实地详细观察了35个大小不一的岩体,证实该岩浆岩带的岩体都不是镁铁质岩浆就地侵入形成,而是众多外来的镁铁质岩块与武当山群和随县群浅变质浊积岩共同构成的混杂岩带。这一论断的具体根据为:邻接岩块的围岩普遍不存在热变质;围岩的纹理、层理及韵律层理均有完好保留;岩块边部并无冷凝边及结晶变细现象;岩块内部的相带及条带状构造与岩块的外形无关,并可常见造岩矿物之结晶条带被接触界面斜截;岩块中穿插有不规则状石英脉体及斜长花岗岩脉,但二者从不侵入围岩,这表明,岩块形成时代早于围岩;一些大、中型岩体都不是单一侵入体,而是许多中、小型岩块的集合体;在岩块内部从来未见到围岩捕虏体。从岩块的岩石化学分析结果看出,调查区内的镁铁质岩均属拉斑玄武岩系列,相当于蛇绿岩套中的堆积杂岩,是古洋脊或边缘海盆扩张脊的产物。据此可以断定,此混杂岩带所在的武当山—大悟山地体,具有增生楔的属性。  相似文献   

东昆仑都兰可可沙地区镁铁-超镁铁质杂岩的发现及其LA-ICP-MS锆石U-Pb年龄   总被引：12，自引：0，他引：12       下载免费PDF全文

冯建赟裴先治  于书伦丁仨平  李瑞保孙 雨张亚峰  李佐臣陈有炘张晓飞  陈国超 《中国地质》2010,37(1):28-38

东昆仑地区是在经历晋宁、加里东、海西、印支等多期构造旋回之后形成的一个复合大陆造山带,其中包括多条重要的构造缝合带。近来,在东昆仑地区东段清水泉以西约15km的可可沙及其以南地区进行1∶5万区域地质调查的过程中,发现了一套镁铁-超镁铁质杂岩。对该镁铁-超镁铁质杂岩中的辉长岩进行LA-ICP-MS锆石U-Pb同位素测年,获得(509.4±6.8)Ma(MSWD=1.4)的同位素年龄。该年龄与东昆中断裂附近的清水泉蛇绿岩的时代可以很好地对应起来,这为清水泉蛇绿岩带向西的延伸方向及东昆仑地区东段早古生代的构造演化提供了新的年代学证据。  相似文献   

The Cansiwang Melange of Southeast Bohol (Central Philippines): Origin and tectonic implications     

Joel V. De Jesus  Graciano P. Yumul  JR    Decibel V. Faustino 《Island Arc》2000,9(4):565-574

Abstract The Cansiwang Melange underlies the Southeast Bohol Ophiolite Complex (SEBOC) and is composed mainly of sheared ophiolite-derived blocks such as harzburgites, microgabbros, basalts and cherts in a pervasive serpentinite matrix. Available field, as well as geophysical evidence show that this melange unit is not diapiric, nor does it have a sedimentary origin considering that it lacks slump and flow structures. A tectonic origin for the Cansiwang Melange is favored in view of the numerous thrust faults, which cut across the exposures, as well as the tectonic contacts that the melange has with the overlying and underlying formations. The presence of the Cansiwang Melange in between the SEBOC and the Alicia Schist provides evidence that the amphibolite of the Alicia Schist do not correspond to the metamorphic sole of SEBOC. Similar to what is recognized in the Josephine Ophiolite, this suggests a 'cold' emplacement of the ophiolite over the Alicia Schist. The Cansiwang Melange represents an accretionary prism product which marks the location of an ancient subduction zone in what is now Central Philippines.  相似文献   

甘孜-理塘构造带泥盆系的深水沉积   总被引：8，自引：0，他引：8  

张世涛  冯庆来  王义昭 《地质科技情报》2000,19(3):17-20

甘孜－理塘构造带由大面积为三叠系地层覆盖而难以对其下覆的地层进行研究,导致了了们对甘孜－理塘构造带的构造演化认识产生很大分歧。通过对劳改皮沉积混杂岩体的地层学、生物学,沉积学和岩石化学等方面的研究,认为甘孜－理塘构造带三叠系盖层之下可能存在大面积的泥盆系、甚至上古生界的深水沉积。进而得出甘孜－理塘洋的演化历史应该向前推移到早泥盆世,而不是通常所说的晚二叠世,同时指出,沉积混杂岩是研究隐伏基底的重要  相似文献   

THE ROCK ASSOCIATION IN JINSHAJIANG MELANGE BELT     

Lin Shiliang 《地学前缘》2000,(Z1)

THE ROCK ASSOCIATION IN JINSHAJIANG MELANGE BELT  相似文献   

YAMDROK MELANGE,SOUTH TIBET     

Liu Jianbing  J.C.Aitchison  Badengzhu  A.M.Davis  S.V.Ziabrev  Luo Hui  I.McDermid 《地学前缘》2000,(Z1)

YAMDROK MELANGE,SOUTH TIBET  相似文献   

Rb–Sr and Sm–Nd isotopic systematics of the Hayachine–Miyamori ophiolitic complex: Melt generation process in the mantle wedge beneath an Ordovician island arc     

Masako Yoshikawa  Kazuhito Ozawa   《Gondwana Research》2007,11(1-2):234

The Hayachine–Miyamori (HM) ophiolitic complex in the Kitakami Mountains, northeastern Japan consists of ultramafic tectonite and cumulate members. The most fertile lherzolites have mineral and trace element compositions similar to those of abyssal peridotites. They show 350–430 Ma Nd depleted mantle model ages, which are within the range of the K–Ar emplacement ages obtained from intrusive gabbroic rocks, suggesting a partial melting event just before the emplacement. The measured ¹⁴³Nd/¹⁴⁴Nd ratio of clinopyroxene in the tectonite peridotites shows positive correlation with ¹⁴⁷Sm/¹⁴⁴Nd and decreases with increasing refractoriness, which cannot be explained by a simple melting and melt extraction to a various extent followed by radiogenic ingrowth. It clearly suggests influx of a melt/fluid enriched in highly incompatible trace elements during melting. Time corrected isotopic compositions of the HM complex exhibit a clear island arc signature with uniform initial isotopic ratio (⁸⁷Sr/⁸⁶Sr = 0.7035–0.7041, ε_Nd = + 7.8–+ 5.0). Application of an open-system melting model to the observed trace element abundances in clinopyroxene suggests influx of three distinct agents to the HM mantle with the following characteristics: (1) moderate enrichment in highly incompatible elements with negative anomalies of Sr and Zr; (2) extensive enrichment of highly incompatible elements with positive Sr and negative Zr anomalies; and (3) extensive enrichment of highly incompatible elements with positive anomalies of Sr and Zr. These characteristics cover a variety of slab-derived components proposed in the literatures, suggesting the agents responsible for the open-system melting in the HM ophiolite might represent full spectrum of slab-derived components from back-arc to fore-arc regions of the Ordovician island arc system.  相似文献   

内蒙古杜尔基构造混杂岩物质组成及构造属性研究     

金松 《地质学报》2020,94(8):2227-2242

杜尔基构造混杂岩是一套由"基质"和"岩块"构成的混杂堆积地质体。通过岩石学、岩石地球化学特征研究,查明其"基质"主要为一套强变形浅变质的海相碎屑岩,局部具有复理石沉积建造的特点,形成于活动大陆边缘构造环境;"岩块"岩石类型为辉石角闪岩、角闪石岩、玄武岩、辉绿岩、闪长岩,其中玄武岩、辉绿岩具有低Ti、高Mg和Al的特点,为一套富钠贫钾岩系,具有洋中脊和岛弧拉斑玄武岩的双重构造属性,形成于洋内初始俯冲背景下的弧前构造环境,属"外来岩块";闪长岩SiO_2均值53.41%, MgO均值5.57%,Mg~#均值51,FeO/MgO均值1.08,属镁闪长岩(MA),相比玄武岩、辉绿岩更加富集Ti、Ta、亏损Nb,形成于俯冲消减背景下活动大陆边缘构造环境,与基质大地构造环境基本一致,应属"原地岩块"。通过对杜尔基构造混杂岩的物质组成及其构造属性的研究,结合其各组成物质的同位素年龄信息、区域地质背景及区域构造演化史研究成果,认为杜尔基构造混杂岩可能反映了晚石炭世洋内俯冲-早二叠世洋陆俯冲-中二叠世洋盆关闭的过程。  相似文献   

托莫尔日特蛇绿混杂岩带地质特征及其构造意义     

韩英善  彭琛 《青海国土经略》2000,(1)

托莫尔日特蛇绿混杂岩带是柴北缘早古生代蛇绿混杂岩带东段的重要组成部分,亦是整个柴北缘地区各蛇绿混杂单元组合、出露较为齐全的地段之一,其中放射虫硅质岩在蛇绿混杂岩带中首次发现。托莫尔日特蛇绿混杂岩岩石学、岩石化学、地球化学等特征表明,其具有大洋中脊向岛弧蛇绿岩过渡的特点。  相似文献   

High pressure garnet amphibolites in ophiolitic mélange from the Changning-Menglian suture zone,southeast Tibetan Plateau: P-T-t path and tectonic implication     

《China Geology》2021,4(1):95-110

The garnet amphibolites from the newly identified Wanhe ophiolitic mélange in the Changning-Menglian suture zone (CMSZ) provide a probe to elucidate the evolution of the Triassic Palaeo-Tethys. An integrated petrologic, phase equilibria modeling and geochronological study of the garnet amphibolites, southeast Tibetan Plateau, shows that the garnet amphibolites have a peak mineral assemblage of garnet, glaucophane, lawsonite, chlorite, rutile, phengite and quartz, and a clockwise P-T path with a prograde segment from blueschist-facies to eclogite-facies with a peak-metamorphic P-T conditions of 2000–2100 MPa and 495 –515°C, indicating a cold geothermal gradient of about 240 –260°C/GPa. Theretrograde metamorphic P-T path is characterized by nearly isothermal decompression to lower amphibolite-facies and subsequent cooling to greenschist-facies. The metamorphic zircons have fractionated HREE patterns and significant negative Eu anomalies, and therefore the obtained zircon U-Pb age of 231 ± 1.5 Ma is interpreted to be the timing of the amphibolite facies metamorphism occurrence. The present study probably indicates that the garnet amphibolites in the Wanhe ophiolitic mélange was the retrograded high-pressure eclogite-facies blueschist, instead of the previously proposed eclogites, and the garnet amphibolites recorded the subduction and exhumation process of the Palaeo-Tethys Oceanic crust in the Triassic.©2021 China Geology Editorial Office.  相似文献