中国蓝片岩带的分布及其构造意义     

代艳娟  曾普胜  麻菁  苟瑞涛  王聚杰 《地质力学学报》2015,21(3):426-437

在前人研究的基础上, 根据变质时代及产地将中国蓝片岩带划分为20个带, 选取不同时代典型蓝片岩带论述其特征(分布区域、大体规模、原岩特征、形成时代及矿物组合), 并对其地质成因进行分析。中国蓝片岩带生成方式复杂, 但均与俯冲消减作用有关, 且大多属B型俯冲消减; 部分地段叠加了A型俯冲的高压—超高压变质带(如阿尔金带、大别-苏北带、南迦巴瓦-密支那带等)。中国蓝片岩带在时代上可以分为元古代(晋宁期)、古生代(加里东—海西期)、中生代(印支—燕山期)和新生代(喜马拉雅期)4个时期, 每个时期蓝片岩带的形成大多与中国地体增生过程中洋盆的消减俯冲有关, 并在特定地段经历后期的陆内俯冲(高压—超高压俯冲)叠加影响。   相似文献   

Petrology and phase equilibrium of newly found eclogites from Kekesu Valley in eastern part of southwest Tianshan HP-UHP metamorphic belt, China, and its tectonic significance   总被引：2，自引：0，他引：2  

XIA Bin  ZHANG LiFei  XIA Yang 《中国科学:地球科学(英文版)》2014,57(1):117-131

Eclogites and omphacite-bearing blueschists have been newly found in the eastern segment of the southwest Tianshan orogenic belt,Xinjiang,northwest China.After detailed petrological study,three samples including one fresh eclogite TK003,one blueschist sample TK026-8 and one retrograded eclogite TK027,were selected for phase equilibrium modeling under NC(K)MnFMASHO(N2O-CaO-K2O-MnO-FeO-MgO-Al2O3-SiO2-H2O-O)system,by thermocalc 3.33 software.Composition analyses of garnets in these three samples show typical growth zoning with Xpy and Xgrs increasing,Xspss decreasing from core to rim.Pseudosection modeling of the garnet zonation reflects that the eclogites and blueschist experienced a similar P-T evolution trajectory,with a near iso-baric heating in the early stage,and reached eclogite facies metamorphic field with peak P-T regime of 480–515°C,2.00–2.30 GPa.Subsequently the rocks experienced an early iso-thermal decompression retrograde stage with P-T conditions of 515–519°C,1.78–1.93 GPa.Variations of mineralogy and modes of these rocks are probably due to different retrograde paths as a consequence of different bulk-rock composition,as well as a variation in fluid activity during exhumation.P-T calculation and a peak geothermal gradient of 6–7°C/km indicate HP rocks in the Kekesu Valley experienced cold subducted eclogite facies metamorphism.Thus a huge oceanic subduction eclogite facies metamorphic belt in southwest Tianshan has been recognized,extending from the Kekesu Valley in the east to the Muzhaerte Valley in the west for nearly200 km.However,UHP evidence has not been found in the Kekesu terrane,perhaps because the slab in east part of southwest Tianshan did not subduct into such a great depth.  相似文献   

P–T evolution and tectonic significance of lawsonite-bearing schists from the eastern segment of the southwestern Tianshan,China     

Bin Xia  Michael Brown  Lifei Zhang 《Journal of Metamorphic Geology》2020,38(9):935-962

Robust quantification of pressure (P)–temperature (T) paths for subduction-related HP/UHP metamorphic rocks is fundamental in recognizing spatial changes in both the depth of detachment from the down-going plate and the thermal evolution of convergent margin sutures in orogenic belts. Although the Chinese southwestern (SW) Tianshan is a well-known example of an accretionary metamorphic belt in which HP/UHP metabasites occur in voluminous host metasedimentary schists, information about the P–T evolution of these rocks in the eastern segment is limited, precluding a full understanding of the development of the belt as a whole. In this study at Kekesu in the eastern segment of the SW Tianshan, we use microstructural evidence and phase equilibrium modelling to quantify the peak and retrograde P–T conditions from two lawsonite-bearing micaschists and an enclosed garnet–epidote blueschist; for two of the samples we also constrain the late prograde P–T path. In the two micaschist samples, relics of prograde lawsonite are preserved in quartz inclusions in garnet, whereas in the metabasite, polymineralic aggregates included in garnet are interpreted as pseudomorphs after lawsonite. For garnet micaschist TK21, which is mainly composed of garnet, phengite/paragonite, albite, chlorite, quartz and relict lawsonite, with accessary rutile, titanite and ilmenite, the maximum P–T conditions for the peak stage are 18.0–19.0 kbar at 480–485°C. During initial exhumation, the retrograde P–T path passed through metamorphic conditions of 15.0–17.0 kbar at 460–500°C. For garnet–glaucophane micaschist TK33, which is mainly composed of garnet, glaucophane, phengite/paragonite, albite, chlorite, quartz, relict lawsonite and minor epidote, with accessary titanite, apatite, ilmenite and zircon, the maximum P conditions for the peak stage are >24.0 kbar at 400–500°C. During exhumation, the P–T path passed through metamorphic conditions of 17.5–18.5 kbar at 485–495°C and 14.0–17.5 kbar at 460–500°C. For garnet–epidote blueschist TK37, which is mainly composed of garnet, glaucophane, epidote, phengite, chlorite, albite and quartz, with accessary titanite, apatite, ilmenite, zircon and calcite, the prograde evolution passed through metamorphic conditions of ~20.0 kbar at ~445°C to P_max conditions of ~21.5 kbar at 450–460°C and T_max conditions of 19.5–21.0 kbar at 490–520°C. During exhumation, the rock passed through metamorphic conditions of 17.5–19.0 kbar at 475–500°C, before recording P–T conditions of <17.5 kbar at <500°C. These results demonstrate that maximum recorded pressures for individual samples vary by as much as 6 kbar in the eastern segment of the SW Tianshan, which may suggest exhumation from different depths in the subduction channel. Furthermore, the three samples record similar P–T paths from ~17.0 to 15.0 kbar, which suggests they were juxtaposed at a similar depth along the subduction interface. We compare our new results with published information from eclogites in the same area before considering the wider implications of these data for the orogenic development of the belt as a whole.  相似文献   

青藏高原羌塘中部高压变质带的研究进展及存在问题     

张修政  董永胜  王强  但卫 《地质通报》2018,37(8):1406-1416

羌塘中部高压变质带是目前青藏高原内部延伸规模最大的高压变质带,是理解特提斯演化的关键地质记录。高压变质带主要沿龙木措-双湖-澜沧江缝合带一线出露,主要由榴辉岩、蓝片岩、石榴子石多硅白云母片岩及少量高压麻粒岩组成。其中,榴辉岩主要出露于戈木、果干加年山、冈玛错、巴青及滇西的勐库地区,主要呈透镜状产于石榴子石多硅白云母片岩中。除巴青地区的榴辉岩外,其余地区榴辉岩的峰期变质温度较低且含有硬柱石及其假象,峰期变质条件位于硬柱石榴辉岩相稳定区域,是洋壳冷俯冲的产物。虽然对于戈木地区榴辉岩锆石成因仍有争议,但已有资料显示,羌塘中部高压变质带主体变质时代集中在晚三叠世,其相关高压变质岩石的折返可能与洋盆的闭合及随后的陆-陆碰撞相关。近期研究表明,羌塘中部可能存在二叠纪低温高压变质岩,折返于大洋俯冲阶段,可能与洋岛或海山的俯冲及引发的俯冲侵蚀作用相关。此外,羌塘香桃湖地区出露早古生代的基性高压麻粒岩,是冈瓦纳大陆北缘陆块拼贴的记录。因此,对羌塘中部高压变质带进行进一步系统的研究工作,对于深入理解冈瓦纳北缘构造演化及古特提斯的俯冲与闭合过程具有重要的意义。  相似文献   

滇西云龙漕涧地区高压片麻岩的发现及厘定     

黄亮  田素梅  张虎  熊波  王晓林  浦涛  杨仕潘  方雄 《岩石矿物学杂志》2021,40(4):747-756

笔者在滇西云龙县漕涧新发现了一套以黑云斜长片麻岩为主的变泥质岩石,其呈构造透镜体状产出,出露面积极小,中高级变质矿物发育,与围岩特征明显不同。岩相学研究表明,片麻岩保留有明显的俯冲-折返的矿物学记录,矿物世代具顺时针变质演化特征,其中还残存有蓝晶石+铝直闪石的共生矿物组合,对应的变质压力达1.0GPa以上。通过GBP平均温压计法计算得到岩石的变质温压范围为566～623℃和0.36～0.53 GPa;此外,片麻岩中还有少量的多硅白云母矿物,根据相平衡模拟p-T视剖面图及其硅原子数最大值为3.23的特点,推断其属蓝片岩类。综合研究认为,黑云斜长片麻岩属于高压变质岩(峰期变质压力最小约为1.60 GPa),为昌宁-孟连结合带的北段寻找高压变质岩提供了新的信息,并表明昌宁-孟连结合带为一条连续的高压-超高压变质带。  相似文献   

Geochemistry of eclogite‐ and blueschist‐facies rocks from the Bantimala Complex,South Sulawesi,Indonesia: Protolith origin and tectonic setting     

Adi Maulana  Andrew G. Christy  David J. Ellis  Akira Imai  Koichiro Watanabe 《Island Arc》2013,22(4):427-452

We present the first data on bulk‐rock major and trace element compositions for a suite of eclogite‐ and blueschist‐facies rocks from the Bantimala Complex, Indonesia, with the aim of better constraining the protolith origins and nature of the subducted crust. The eclogites can be classified into two groups: glaucophane‐rich eclogite and glaucophane‐free eclogite, whereas the blueschists are divided into albite–epidote glaucophanite and quartz–glaucophane schists. SiO₂ contents of the eclogites are 43.3–49.6 wt%, with Na₂O + K₂O contents 3.7–4.7 wt%. The blueschists show a wider range of compositions, with SiO₂ = 40.7–63.8 wt% and Na₂O + K₂O = 2.7–4.5 wt%. Trace element data suggest that the eclogite protoliths include both enriched and normal mid‐oceanic ridge basalt (E‐MORB and N‐MORB) and also gabbroic cumulates. The blueschists show more variation in protoliths, which include N‐MORB, Oceanic Island Basalt (OIB) and Island Arc Basalt (IAB). Plots of element concentrations against the immobile Zr show considerable mobility of large ion lithophiles but not of high field‐strength elements during high‐pressure metamorphism, and indicate that the high SiO₂ content of some blueschists is probably due to metasomatism by a LILE‐rich siliceous aqueous fluid. Strong correlations between K, Rb, Ba and Cs suggests that enrichment of these elements occurred by a single process. All the protoliths were subducted, metamorphosed to blueschist/eclogite‐facies and subsequently exhumed. It is noteworthy that the samples deduced to have come from thicker‐crust environments (OIB, IAB) were subducted to shallower depths (blueschist‐facies) than MORB‐derived samples, all except one of which reached eclogite‐facies conditions. The geochemical data of this study demonstrate the variety of ocean floor types that were subducted under the southeast margin of Sundaland in the late Jurassic period.  相似文献   

中国东北黑龙江杂岩体蓝闪石片岩岩石学研究     

N I Volkova  李有柱 《西安地质学院学报》2010,(2):111-119

黑龙江杂岩主要由蓝闪石片岩构成,蓝闪石片岩主要包括绿帘石、绿泥石、钠长石、钠质角闪石、多硅白云母和石英以及为数不多的榍石、钛铁矿和黑硬绿泥石。其中,钠质角闪石包括蓝闪石和镁质钠闪石。变质条件的压力（P）温度（T）评价条件为400－425℃和0.69－0.86 MPa,对应岩相为绿帘蓝闪石片岩相。黑龙江杂岩蓝闪石片岩的地球化学研究表明,其原岩是可与洋岛型（OIB）玄武岩和一些洋中脊型（E-MORB）玄武岩相对比的大洋玄武岩,这说明黑龙江杂岩蓝闪石片岩的玄武岩原岩是在海底山或者在大洋隆起条件下由富集源形成的;具有洋岛型玄武岩地球化学特征的变质玄武岩以及富锰的变质燧石、大理石、变质硬砂岩和蛇绿岩鳞片的加入证明黑龙江杂岩是消减—增生杂岩,它含有变形洋壳的碎块和在被改造的前震旦纪佳木斯岩体西边缘上形成于侏罗纪的增生楔岩石;黑龙江杂岩在原岩成分上可与活动大陆边缘许多增生的杂岩相当。  相似文献   

40Ar‐39Ar Geochronology and Tectonic Implications of the Blueschist from Northwestern Qiangtang,Northern Tibet,Western China     

TANG Xianchun  and ZHANG Kaijun 《《地质学报》英文版》2012,86(6):1471-1478

Blueschist exposed in the northwestern Qiangtang terrane, northern Tibet, western China (~84°30′ E, 34°24′ N), provides new constraints on the tectonic evolution of Qiangtang as well as northern Tibet. The blueschist represented by lawsonite- and glaucophane-bearing assemblages equilibrated at 375–400 °C and ~11 kbar. 40Ar-39Ar analysis on mineral separate from one blueschist sample yielded a well-defined plateau age of ~242 Ma. Geochemical studies show the blueschist is metamorphosed within-plate basalts. The high pressure-low temperature blueschist indicates a Triassic event of lithosphere subduction, and clearly represents an extension of the central Qiangtang metamorphic belt, and defines an in?situ suture between eastern and western Qiangtang.  相似文献   

P–T path of high-pressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains, NW China     

Gao  Klemd  Zhang  Wang  & Xiao 《Journal of Metamorphic Geology》1999,17(6):621-636

The Chinese western Tianshan high-pressure/low-temperature (HP–LT) metamorphic belt, which extends for about 200 km along the South Central Tianshan suture zone, is composed of mainly metabasic blueschists, eclogites and greenschist facies rocks. The metabasic blueschists occur as small discrete blocks, lenses, bands, laminae or thick beds in meta-sedimentary greenschist facies country rocks. Eclogites are intercalated within blueschist layers as lenses, laminae, thick beds or large massive blocks (up to 2 km² in plan view). Metabasic blueschists consist of mainly garnet, sodic amphibole, phengite, paragonite, clinozoisite, epidote, chlorite, albite, accessory titanite and ilmenite. Eclogites are predominantly composed of garnet, omphacite, sodic–calcic amphibole, clinozoisite, phengite, paragonite, quartz with accessory minerals such as rutile, titanite, ilmenite, calcite and apatite. Garnet in eclogite has a composition of 53–79 mol% almandine, 8.5–30 mol% grossular, 5–24 mol% pyrope and 0.6–13 mol% spessartine. Garnet in blueschists shows similar composition. Sodic amphiboles include glaucophane, ferro-glaucophane and crossite, whereas the sodic–calcic amphiboles mainly comprise barroisite and winchite. The jadeite content of omphacite varies from 35–54 mol%. Peak eclogite facies temperatures are estimated as 480–580 °C for a pressure range of 14–21 kbar. The conditions of pre-peak, epidote–blueschist facies metamorphism are estimated to be 350–450 °C and 8–12 kbar. All rock types have experienced a clockwise P–T path through pre-peak lawsonite/epidote-blueschist to eclogite facies conditions. The retrograde part of the P–T path is represented by the transition of epidote-blueschist to greenschist facies conditions. The P–T path indicates that the high-pressure rocks formed in a B-type subduction zone along the northern margin of the Palaeozoic South Tianshan ocean between the Tarim and Yili-central Tianshan plates.  相似文献   

Mineral isograds and metamorphic zones of the Anglesey blueschist belt, UK: implications for the metamorphic development of a Neoproterozoic subduction–accretion complex     

T. KAWAI  B. F. WINDLEY  M. TERABAYASHI  H. YAMAMOTO  S. MARUYAMA  Y. ISOZAKI 《Journal of Metamorphic Geology》2006,24(7):591-602

The 560–550 Ma blueschists and associated rocks in Anglesey, UK were derived from a subduction–accretion complex. The blueschist unit is divided into three mineral zones by two newly mapped metamorphic isograds; zone I sub-greenschist facies, (crossite isograd), zone II blueschist facies, (barroisite isograd), zone III epidote-amphibolite facies. The zones and isograds dip gently to the east, and decrease in metamorphic grade from the central high-pressure zone III to lower grade zones II and I to the west and east. The P – T conditions estimated from zoned amphibole indicate an anticlockwise P – T path following adjustment to a cold geotherm. This path is well preserved in the compositional zoning of Na–Ca amphibole that have a core of barroisite surrounded by a rim of crossite, although this is only locally developed. The sense of subduction was to the east and exhumation to the west, as indicated by the metamorphic isograds. The symmetrical arrangement of the metamorphic zones with the deepest high-pressure rocks in the middle suggests an isoclinal antiformal structure that formed by wedge extrusion during exhumation in the subduction zone.  相似文献