西藏中北部双湖地区蓝片岩带及其构造涵义   总被引：50，自引：2，他引：48  

鲍佩声  李才 《地质学报》1999,73(4):302-314,T001

西藏中北部的蓝片岩岩块断续出露长达３００ｋｍ,东起西亚尔岗双湖及其以西的恰格勒拉,经纳岩,角木日,冈塘错,果干加年山,玛依岗日,西至冈玛错一带,除恰勒拉及果干加年山的蓝片岩早年有简要报导外,其余均为李才等近年的新发现,蓝片岩的原岩主要为冈瓦纳大陆北缘晚石炭世一早二叠世裂谷型（裂陷槽）沉积－火山岩系,包括基性火山岩（或火山碎屑岩）泥质砂岩,泥质灰岩等,尚有少量基性煌斑岩,高压低温变质矿物主要为青铝闪  相似文献   

中国蓝片岩中闪石族矿物的研究     

Ye Huiwen 《吉林大学学报(地球科学版)》1990,(2)

本文对中国篮片岩中间石族矿物进行了综合研究,可将它们分为三个亚族:碱性问石亚族;钠钙闪石亚族;钙质闪石亚族。碱性闪石亚族再按Fe 、Mg、Al的比值,后二者按Si的含量划分为矿物种。编制了闪石成分分类图。碱性闪石的光学性质、红外吸收光谱和x射线衍射数据,与其它两个亚族有明显差异,但各亚族内特征基本相似。利用多色性和延性特征鉴别碱性问石各矿物种较为准确,并发现青铝闪石的多色性公式应为Ng-紫色、Nm-深蓝色、Np-浅黄色,与前人描述不一致。  相似文献   

蓝片岩与绿片岩共存:龙江岩系构造演化的新证据     

张兴洲  张元厚 《吉林大学学报(地球科学版)》1991,(3)

本文从岩石及矿物的变质—变形关系和化学成分研究证明,龙江岩系①中蓝片岩与绿片岩的共存不是单一变质事件的产物,而是构造变动和不连续变质作用叠加的结果。早期蓝片岩形成在一种高压低温,高氧逸度环境。后经构造变动,转变为地热梯度较高的变形环境中,遭受韧性变形和以增温为主的绿片岩相变质作用的叠加。其间,钠质闪石向钠钙质闪石的转变,代表一种不连续的增温事件,而钠钙质闪石向钙质闪石的转变反映一种连续的增温过程。  相似文献   

陕甘川交界区碧口群的变质作用及其地质意义   总被引：4，自引：1，他引：4  

魏春景 《地质学报》1994,68(3):241-254

碧口群由一套中晚元古代的变质双峰式火山岩及复理石型深积岩组成，其变质作用分为蓝片岩相和绿片岩相。据其野外分布及白云母ｂ０值的变化可分成Ａ、Ｂ、Ｃ三个变质带。蓝片岩相以钠质闪石＋绿帘石共生为特征，在Ａ带的大面积绿片岩中呈条带或残片状分布。对区内的角闪石、绿泥石、绿帘石及白云母等矿物及其间的交代关系研究表明蓝片岩和绿片岩并非同一物理化学条件下的产物。蓝片岩相的温度为３００－４００℃，压力为０．５－０．  相似文献   

The effect of ductile deformation on the kinetics and mechanisms of the aragonite-calcite transformation   总被引：2，自引：0，他引：2  

ELEANOUR SNOW  RICHARD A. YUND 《Journal of Metamorphic Geology》1987,5(2):141-153

Abstract The effect of ductile deformation (dislocation creep) on the kinetics of the aragonite-calcite transformation has been studied at 1 atm (330° C and 360° C) and 900-1500 MPa (500° C) using undeformed and either previously or simultaneously deformed samples (500° C and a strain rate of 10^-6 s). Deformation enhances the rate of the transformation of calcite to aragonite, but decreases the rate of transformation of aragonite to calcite. The difference results from a dependence of transformation rate on grain size, coupled with a difference in the accommodation mechanisms, climb versus recry-stallization, of these minerals during dislocation creep. Dislocation climb is relatively easy in calcite and thus plastic strain results in high dislocation densities without significant grain size reduction. The rate of transformation to aragonite is enhanced primarily because of the increase in nucleation sites at dislocations and subgrain boundaries. In aragonite, on the other hand, dislocation climb is difficult and thus plastic strain produces extensive dynamic recry-stallization resulting in a substantial grain size reduction. The transformation of aragonite is inhibited because the increase in calcite nucleation sites at dislocations and/or new grain boundaries is more than offset by the inability of calcite to grow across high angle grain boundaries. Thus the net effect of ductile deformation by dislocation creep on the kinetics of polymorphic phase transformations depends on the details of the accommodation mechanism.  相似文献   

再论塔里木北缘阿克苏蓝片岩的时代和成因环境:来自锆石U-Pb年龄、Hf同位素的新证据   总被引：11，自引：9，他引：2  

张健  张传林  李怀坤  叶现韬  耿建珍  周红英 《岩石学报》2014,30(11):3357-3365

阿克苏蓝片岩和基性岩墙形成时代和构造背景对认识塔里木地块前寒武纪构造演化以及新元古代超大陆重建具有重要意义.本文通过对含蓝片岩的阿克苏群中变质碎屑岩和侵入阿克苏群的基性岩墙的锆石U-Pb定年及Hf同位素分析表明,(长石)石英片岩中碎屑锆石出现2个明显的统计峰值,较老一组锆石²⁰⁷Pb/²⁰⁶Pb的表面年龄集中在~1.9Ga,并有少量太古代的年龄信息;另一组较年轻锆石²⁰⁶Pb/²³⁸U表面年龄峰值为~820Ma,代表阿克苏群的最大沉积年龄.侵入阿克苏群的基性岩墙锆石U-Pb年龄为~760Ma.阿克苏蓝片岩相变质的时间被严格限定在820~760Ma区间内.碎屑锆石Hf同位素地壳模式年龄峰值出现在2.2~2.3Ga,2.6Ga和3.2~3.3Ga.综合本次工作及前人研究成果,表明阿克苏蓝片岩地体是塔里木早前寒武纪基底之上发育起来的大陆边缘岩浆弧.  相似文献   

Graphite‐schist blocks in the Franciscan Mélange,San Simeon,California: Evidence of high‐P metamorphism          下载免费PDF全文

E. Ukar  M. Cloos 《Journal of Metamorphic Geology》2016,34(3):191-208

The seacliff exposure at San Simeon, California, contains graphite‐schist blocks in a shale‐matrix, an undocumented lithology within the Franciscan mélange. Thirty graphite‐schist blocks were studied to discover all the varieties in this classic locality of mélange. Based on their mineralogical assemblage and composition, and textural characteristics the graphite‐schists in San Simeon are subdivided into two main types (Type I and II) with two subdivisions each (A and B). Type IA and IIA blocks are the most abundant. Type IA graphite‐schists are siltstone/fine greywacke‐like, preserve sedimentary textures, and lack lawsonite. Type IB graphite‐schists are mineralogical and texturally similar to Type IA schists, but are finer grained siltstone and shale. Type IIA graphite‐schists are compositionally layered and contain quartz‐ and albite‐rich layers and dark graphite‐ and intergrown mica/chlorite‐rich layers. Nine out of the 15 Type IIA blocks contain lawsonite. Two Type IIA blocks also contain aragonite (+calcite) in veins. Type IIB graphite‐schists are mostly composed of quartz and minor graphite, intergrown chlorite and white mica, and white mica pseudomorphs after lawsonite. The phengite content of mica in Type IIA blocks is higher than that of mica in Type IA graphite‐schists, confirming they were metamorphosed under high‐P/low‐T conditions. Type IA blocks were recrystallized between 200 and 250 °C at <~3 kbar; whereas, Type IIA blocks were metamorphosed under higher pressure conditions, probably at 250–300 °C and 3–5 kbar. Most likely both types of graphite‐schists were derived from a similar layered siltstone/fine greywacke/shale protolith. Organic matter‐rich sediments deposited in the trench axis were subducted along with oceanic crust during Franciscan subduction. Type I graphite‐schists were subducted to depths <10 km, whereas Type II graphite‐schists were subducted to depths ~15 km where they were underplated under high‐P conditions. The graphitic metasedimentary rocks were juxtaposed with mafic lithologies from the subducted oceanic crust that were metamorphosed to blueschist facies and retrograded to greenstone as they returned to the surface in the subduction channel shear zone.  相似文献   

Phase equilibria modelling of blueschist and eclogite from the Sanbagawa metamorphic belt of southwest Japan reveals along‐strike consistency in tectonothermal architecture          下载免费PDF全文

O. M. Weller  S. R. Wallis  M. Aoya  T. Nagaya 《Journal of Metamorphic Geology》2015,33(6):579-596

The Sanbagawa metamorphic belt of southwest Japan is one of the type localities of subduction‐related high‐P metamorphism. However, variable pressure–temperature (P–T) paths and metabasic assemblages have been reported for eclogite units in the region, leading to uncertainty about the subduction zone paleo‐thermal structure and associated tectonometamorphic conditions. To analyse this variation, phase equilibria modelling was applied to the three main high‐P metabasic rock types documented in the region – glaucophane eclogite, barroisite eclogite and garnet blueschist – with modelling performed over a range of P, T, bulk rock H₂O and bulk rock ferric iron conditions using thermocalc . All samples are calculated to share a common steep prograde P–T path to similar peak conditions of ～16–20 kbar and 560–610 °C. The results establish that regional assemblage variation is systematic, with the alternation in peak amphibole phase due to peak conditions overlapping the glaucophane–barroisite solvus, and bulk composition effects stabilizing blueschist v. eclogite facies assemblages at similar P–T conditions. Furthermore, the results reveal that a steep prograde P–T path is common to all eclogite units in the Sanbagawa belt, indicating that metamorphic conditions were consistent along strike. All localities are compatible with predictions made by a ridge approach model, which attributes eclogite facies metamorphism and exhumation of the Sanbagawa belt to the approach of a spreading ridge.  相似文献   

Metamorphic and tectonic evolution of a structurally continuous blueschist‐to‐Barrovian terrane,Sivrihisar Massif,Turkey     

D. L. WHITNEY  C. TEYSSIER  E. TORAMAN  N. C. A. SEATON  A. K. FAYON 《Journal of Metamorphic Geology》2011,29(2):193-212

Metamorphic terranes comprised of blueschist facies and regional metamorphic (Barrovian) rocks in apparent structural continuity may represent subduction complexes that were partially overprinted during syn‐ to post‐subduction heating or may be comprised of unrelated tectonic slices. An excellent example of a composite blueschist‐to‐Barrovian terrane is the southern Sivrihisar Massif, Turkey. Late Cretaceous blueschist facies rocks are dominated by marble characterized by rod‐shaped calcite pseudomorphs after aragonite and interlayered with blueschist that contains eclogite and quartzite pods. Barrovian rocks, which have ⁴⁰Ar/³⁹Ar white mica ages that are >20 Myr younger than those of the blueschists, are also dominated by marble, but rod‐shaped calcite has been progressively recrystallized into massive marble within a ～200‐m transition zone. Barrovian marble is interlayered with quartzite and schist in which isograds are closely spaced and metamorphic conditions range from chlorite to sillimanite zone over ～1 km present‐day structural thickness. Andalusite, kyanite and prismatic sillimanite are present in muscovite‐rich quartzite; in one location, all three are in the same rock. Andalusite pre‐dates Barrovian metamorphism, kyanite is both pre‐ and syn‐Barrovian and sillimanite is entirely Barrovian. Muscovite with phengitic cores and relict kyanite in quartzite below the staurolite‐in isograd are evidence for pre‐Barrovian subduction metamorphism preserved at the low‐T end of the Barrovian domain; above the staurolite isograd, all evidence for subduction metamorphism has been erased. Some regional metamorphism may have occurred during exhumation, as indicated by syn‐kinematic high‐T minerals defining the fabric of L‐tectonite. Quartz microstructures in lineated quartzite reveal a strong constrictional fabric that may have formed in a transtensional bend in the plate boundary. Transtension accounts for the closely spaced isograds and development of a strong constrictional fabric during exhumation.  相似文献   

Constraining P–T conditions during thrusting of a higher pressure unit over a lower pressure one (Gran Paradiso,Western Alps)          下载免费PDF全文

P. Manzotti  P. Pitra  J. Langlade  M. Ballèvre 《Journal of Metamorphic Geology》2015,33(9):981-1002

Identifying higher pressure units overlying lower pressure ones is a first order argument to determine the presence of large‐scale thrusting. For the first time, petrology is used to quantify the pressure difference between two stacked units in the Western Alps. In the Gran Paradiso Massif, the Money unit crops out as a tectonic window below the Gran Paradiso unit. The reconstruction of the Alpine evolution of these two units and the history of their tectonic contact has been achieved using a multidisciplinary approach that combines meso‐ and microstructural analysis and pseudosection calculations. In both units, four stages of deformation and metamorphism have been identified. Stage 1 reflects the phase of continental crust subduction and P–T conditions of ~18–20 kbar, 480–520 °C and of ~13–18 kbar, 500–530 °C have been estimated for the Gran Paradiso and the Money units respectively. This yields a maximum difference of ~20 km in the depth reached by these two units during the early Alpine history. Thrusting of the Gran Paradiso unit over the Money unit (stage 2) led to the development of the main foliation and occurred in the high‐P part of the albite stability field at P–T conditions of ~12.5–14.5 kbar and 530–560 °C, identical in both units. The thrust contact was folded during stage 3 together with the entire Money unit, and then both units were exhumed together (stage 4). During this polyphase evolution, detrital garnet has been partially dissolved, while the earliest Na‐bearing phases (glaucophane, paragonite) have been overprinted by the low‐P mineral associations. The uncertainties on derived pressures between the two units are unfortunately larger than hoped, and this is attributed to the muscovite solid‐solution model not incorporating a pyrophyllite component.  相似文献