西藏羌塘中部冈玛错－双湖蓝片岩带及其构造意义     

胡克  李才  程立人  洪裕荣 《吉林大学学报(地球科学版)》1995,(3)

冈玛错－双湖蓝片岩带将羌塘地区一分为二，其南例为冈瓦纳型碳酸盐岩　拉斑玄武岩区，北侧为欧亚大陆型碳酸盐岩－碎屑岩区。根据蓝片岩的地质特征和年代学研究，高压变质作用发生在二叠纪－三叠纪早期，是在区域绿片岩相基础上继承发生的。该蓝片岩带标志晚古生代时冈瓦纳与欧亚大陆的分界线。  相似文献   

Structural and metamorphic evolution of the phengite‐bearing schists of the northern Adula Nappe (Central Alps,Switzerland)     

F. Zulbati 《Geological Journal》2008,43(1):33-57

Phengite‐bearing schists of the northern Adula Nappe experienced a polymetamorphic and polycyclic evolution that was associated with five deformation episodes. Evidence of a pre‐Alpine metamorphic event is preserved within garnet cores of some amphibole‐bearing schists. The D1 and D2 deformation episodes are recorded by S1 and S2 foliations preserved only within metre‐scale domains of low‐D3 strain. S1 is a relict foliation. Blueschist‐facies conditions at 565 ± 10°C and 11.5 ± 1.5 kbar were attained during D2 and were associated with the development of isoclinal folding and an S2 foliation. The D3 episode took place at 665 ± 50°C and 11.5 ± 2.1 kbar and was responsible for the development of a transpositive S3 foliation. The D4 episode took place at T < 550 ± 10°C and was associated with the development of a discrete S4 foliation and S‐C structures. The D5 episode is recorded by sub‐vertical metre‐scale open folds or centimetre‐scale kinks. The structural and metamorphic evolution described here indicates that the northern and central parts of the Adula Nappe were distinct continental crustal fragments and were brought together under amphibolite‐facies conditions. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Fingerprints of forearc element mobility in blueschist-facies metaconglomerates,Catalina Schist,California     

Natalie E. Sievers  Joanne Tenore  Gray E. Bebout 《International Geology Review》2017,59(5-6):741-752

ABSTRACT

Metaconglomerates in the lawsonite–blueschist facies unit of the Catalina Schist (California) contain gabbroic and dioritic clasts exhibiting evidence for extensive metasomatism during high-P/T metamorphism. We performed whole-rock and in situ analyses of these metaconglomerate clasts to better constrain the composition of infiltrating fluids and to elucidate the history of chemical alteration. Petrographic evidence for this alteration includes replacements of plagioclase by phengite and sodic amphibole rims developed on igneous hornblende. These observations regarding mineral replacement are reinforced by corresponding shifts in chemical compositions. Relative to compositions of presumed protoliths, whole-rock compositions of the metaconglomerate clasts show enrichments in elements that are relatively mobile in aqueous fluids (LILE: K, Rb, Cs, and Ba; Li, B, N), and elevated δ¹⁵N, and show depletions in Ca and Sr. Electron and ion microprobe data, and analyses of mineral separates, show that phengite and sodic amphibole are enriched in LILE and Li and B, respectively, relative to the igneous phases they have replaced. Oxygen and C isotope compositions of finely disseminated calcite in the clasts, and of calcite in veins cross-cutting or mantling the clasts, are consistent with crystallization from fluids previously equilibrated with metasedimentary rocks within the same unit. The same fluids are implicated as the source for the Li, B, N, and LILE enrichments. These metaconglomerate clasts provide unique records of forearc metasomatism due to the presumed extremely low and well-constrained concentrations of fluid-mobile elements in their protoliths and the previously published, larger-scale fluid–rock context into which the observed metasomatic changes can be placed.  相似文献   

中国东北黑龙江杂岩体蓝闪石片岩岩石学研究(英文)   总被引：1，自引：0，他引：1  

N I Volkova  李有柱 《地球科学与环境学报》2010,32(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   

西藏羌塘中部绒马地区石榴蓝闪片岩变质演化过程的视剖面模拟及其意义   总被引：3，自引：0，他引：3       下载免费PDF全文

刘焰  吕永增 《地学前缘》2011,18(2):100-115

藏北羌塘地体中部产出一变质杂岩带,因其地貌突起,将羌塘地体一分为二,故常称其为羌中隆起带。虽然在该变质杂岩带中先后识别出蓝片岩、榴辉岩等变质岩,但对该变质杂岩带演化过程的认识却存在截然不同的观点,一种观点认为该变质杂岩带是原位的古特提斯板块缝合带的标志;另一观点则针锋相对,认为该变质杂岩带系外来的、底辟上升的杂岩带,不能作为古板块缝合带的证据。在该变质杂岩带中部的绒马乡,石榴蓝闪片岩呈大小不一的岩片和/或透镜体产出于石榴石多硅白云母石英片岩内,主要由石榴石变斑晶和由蓝闪石、绿泥石、白云母、绿帘石、石英、钠长石、金红石/钛铁矿、磷灰石、黑云母等矿物构成的基质组成。石榴石变斑晶粒径达2 mm,具典型的生长环带：核部富锰,锰铝榴石分子摩尔分数可达22%,至边部,铁铝榴石和镁铝榴石分子含量显著升高,而锰铝榴石分子含量则快速下降。石榴石变斑晶内部包体发育,可再细分为两类,一类包体产出于核部,包括被解释为硬柱石假象的细粒钠云母,绿帘石所构成的细粒板状集合体和细粒富铁蓝闪石、石英及金红石等包体;另一类包体则为数量较少的自形大颗粒绿帘石包体,产出于石榴石边部,在其内部还有细粒蓝闪石、金红石与石英等包体产出。基质中的角闪石可识别出3期：核部为富铁的蓝闪石,幔部为贫铁的蓝闪石,最外部为冻蓝闪石。基质中的绿帘石和绿泥石常为自形,绿帘石内常见细粒蓝闪石、石英、金红石等包体,而绿泥石边部常有黑云母的冠状体。在PEXPLE程序计算的p T视剖面图中,石榴石核部形成的p T条件为20 GPa、470 ℃,对应硬柱石榴辉岩相,而石榴石边部形成的p T条件为17~18 GPa、530~540 ℃,对应绿帘石榴辉岩相。岩相学观察与p T视剖面模拟研究充分反映了绒马地区石榴蓝闪片岩分别经历了硬柱石榴辉岩相、绿帘石榴辉岩相和近等温快速降压的退变质等变质过程,系冷洋壳快速俯冲与折返的产物,因此,文中支持该变质杂岩带为原位古特提斯板块缝合带的观点。硬柱石转变为绿帘石时,在俯冲通道中释放了大量的流体。T O视剖面研究进一步表明这种矿物相转变只发生于高氧逸度条件下,暗示所释放的流体可能也是高氧逸度流体。该高氧逸度流体可交代上覆地幔楔,并诱发后者发生部分熔融作用形成高氧逸度岩浆,如果这一推测是合理的,则羌塘地块内部应该存在斑岩型铜金矿床。 关键词：羌塘地体; 石榴蓝闪片岩; 视剖面模拟; 富氧流体  相似文献