青藏高原东南缘点苍山-哀牢山杂岩带中片麻岩的变质演化及深熔作用特征

片麻岩是点苍山-哀牢山变质杂岩带最常见的岩石类型,主要由夕线石榴黑云二长片麻岩、石榴黑云斜长片麻岩以及含十字石蓝晶夕线石榴片麻岩所组成,其原岩的化学成分与华北克拉通典型孔兹岩系十分相似.岩相学、成因矿物学和变质反应性质研究以及温压条件估算结果表明,研究区片麻岩类岩石变质峰期的温压条件为T=700～770℃,P=0.5～0.8GPa,已达到或接近麻粒岩相变质,晚期退变质阶段的温压条件为T=600～650℃,P=0.35～0.45GPa.片麻岩变质演化的P-T轨迹具有顺时针型式.在麻粒岩相变质阶段,片麻岩类岩石普遍发生深熔作用,主要表现为含水矿物黑云母的脱水熔融和长英质矿物的部分熔融.该项研究对于进一步揭示青藏高原东南缘点苍山-哀牢山造山带的变质演化深熔作用机理及动力学过程具有重要的科学意义.     

吕梁界河口群变质岩石的构造指示:来自地球化学和同位素年代学的证据

华北中部造山带是华北克拉通内部一条重要的前寒武纪碰撞造山带,该造山带的形成经历了一个漫长而复杂的演化过程。吕梁变质杂岩位于造山带中段,阜平杂岩西南,是透视华北克拉通早前寒武纪构造-热演化的一个重要窗口。本文针对该地区的界河口(岩)群黑云斜长片麻岩和含榴斜长角闪岩开展了系统的野外地质调查、显微岩石学、地球化学和变质年代学研究。结果表明,界河口(岩)群黑云斜长片麻岩的原岩多为富铝富钾的变泥质岩石,其物源主要来自长英质火成岩,形成于有演化岛弧发育的活动大陆边缘构造背景;含榴斜长角闪岩的原岩多数是拉斑玄武岩,源区来自于富集地幔,形成于岛弧构造环境。显微岩相学研究显示,含榴夕线黑云斜长片麻岩和含榴斜长角闪岩中均保留了早期进变质、峰期变质和晚期退变质三个阶段的变质矿物组合,且石榴子石边部多发育明显的"白眼圈"反应结构。其中,含榴夕线黑云斜长片麻岩的峰期矿物组合包括石榴子石、黑云母、夕线石、斜长石、石英和少量钾长石等;含榴斜长角闪岩的峰期矿物组合主要由石榴子石、角闪石、斜长石、磁铁矿和石英等组成。前期研究表明,二者的变质演化均记录了类似的顺时针近等温降压型的变质作用P-T轨迹,其峰期变质条件分别为 750℃/ 7.0kbar和 750℃/ 6.3kbar。本文LA-ICP-MS锆石U-Pb年代学研究表明,含榴黑云斜长片麻岩中记录了1928～1920Ma和1882～1855Ma两组变质年龄。结合中部带前人研究成果,本文推断吕梁变质杂岩的区域变质事件与华北克拉通东、西部陆块间的碰撞造山作用有关,该地区与碰撞阶段同期的峰期变质作用发生在1928～1920Ma,而后于1882～1855Ma期间进入与快速构造隆升有关的退变质作用阶段。     

Constraints from phase equilibrium modeling and in -situ U-Pb dating of monazite.SCIEI北大核心CSCD

西秦岭天水北道地区位于西秦岭造山带北缘,地处秦岭造山带和祁连造山带的结合部位。近来,我们在该地区秦岭杂岩中识别出一套麻粒岩相岩石(石榴夕线黑云片麻岩),峰期矿物组合为石榴子石+钛铁矿+金红石+夕线石+钾长石+石英,相平衡模拟计算结果显示其峰期温压条件为P=1.02GPa,T=820℃,经历了进变质阶段以升温升压为特征,峰期之后以大致近等温降压为特征的顺时针P-T轨迹。独居石原位LA-ICP-MS U-Pb年代学结果显示石榴夕线黑云片麻岩经历了~421Ma、~388Ma和368~362Ma三期构造热事件。结合独居石的产出位置,我们推测421Ma代表了麻粒岩相变质作用的时代,这与天水花庙地区获得的麻粒岩峰期年龄一致;388Ma近似代表了峰期之后大致近等温降压至固相线附近的年龄;368~362Ma与区域韧性剪切作用的时代一致,可能记录了与新阳-元龙韧性剪切变形作用相关的热事件的时代。结合区域地质资料和本研究成果(矿物演化特征、顺时针的P-T演化轨迹和独居石原位定年结果),我们推测西秦岭造山带北缘天水北道地区的麻粒岩可能是早古生代陆-陆碰撞造山过程的产物。     

Cambrian metamorphism of the Qaidam block:Constraints from phase equilibrium modeling and monazite U-Pb datingSCIEI北大核心CSCD

柴达木地块位于青藏高原东北缘的祁连-阿尔金-昆仑早古生代造山系之中,它的西段出露一套(超)高温变质岩组合:变泥质岩、长英质片麻岩、基性麻粒岩、钙硅酸盐岩、含橄榄石大理岩及少量Mg-Al麻粒岩。本文以相平衡模拟和独居石U-Pb年代学为主要手段,限定柴西缘变泥质岩的变质作用P-T-t轨迹。变泥质岩记录了顺时针P-T轨迹,其中,压力峰期条件约为0.89GPa和800℃,温度峰期条件约为0.64GPa和825℃,退变质条件为0.58GPa和800℃至0.37±0.05GPa和702±50℃。变泥质岩的独居石U-Pb年龄集中在517~496Ma之间,三个样品的加权平均年龄分别为508±2Ma(MSWD=2.0)、506±1Ma(MSWD=1.7)、506±1Ma(MSWD=1.3)。本文将其解释为独居石的形成年龄,并认为独居石主要形成于退变质过程中的残留熔体结晶阶段(0.58GPa和800℃左右)。结合已有的工作可以得出,柴达木地块西段麻粒岩相变质作用具有顺时针P-T轨迹和1000~1300℃/GPa的峰期T/P值,并且在高温变质条件(>800℃)持续了超过30Myr。该类高T/P型变质作用最有可能发生在大型碰撞造山带内,可以与冈瓦纳大陆内部的晚泛非期的高T/P型变质作用对比,很可能是与冈瓦纳大陆最终拼合有关的晚泛非期造山事件的体现。     

造山带中成对出现的高压麻粒岩与榴辉岩及其地球动力学意义

在一些典型碰撞造山带中,高压麻粒岩与榴辉岩在空间和时间上密切相关,它们之间的关系对揭示碰撞造山带的造山过程和造山机制具有重要意义.本文以中国西部的南阿尔金、柴北缘及中部的北秦岭造山带为例,详细陈述了这3个地区榴辉岩和相关的高压麻粒岩的野外关系、变质演化和形成时代,目的是要建立大陆碰撞造山带中榴辉岩和相关高压麻粒岩形成的地球动力学背景模式.南阿尔金榴辉岩呈近东西向分布在江尕勒萨依,玉石矿沟一带,与含夕线石副片麻岩、花岗质片麻岩和少量大理岩构成榴辉岩一片麻岩单元,榴辉岩中含有柯石英假象,其峰期变质条件为P=2.8～3.0GPa,T=730～850℃,并在抬升过程中经历了角闪岩-麻粒岩相的叠加;大量年代学研究显示其峰期变质时代为485～500Ma.南阿尔金高压麻粒岩分布在巴什瓦克地区,包括高压基性麻粒岩和高压长英质麻粒岩,它们与超基性岩构成了一个大约5km宽的构造岩石单元,与周围角闪岩相的片麻岩为韧性剪切带接触.长英质麻粒岩和基性麻粒岩的峰期组合均具有蓝晶石和三元长石(已变成条纹长石),形成的温压条件为T=930～1020℃,P=1.8～2.5GPa,并在退变质过程中经历了中压麻粒岩相变质作用叠加.锆石SHRIMP测定显示巴什瓦克高压麻粒岩的峰期变质时代为493～497Ma.都兰地区的榴辉岩分布柴北缘HP-UHP变质带的东端,在榴辉岩和围岩副片麻岩中均发现有柯石英保存,形成的峰期温压条件为T=670～730℃和P=2.7～3.25GPa,退变质阶段经过了角闪岩相的叠加;榴辉岩相变质时代为420～450Mao都兰地区的高压麻粒岩分布在阿尔茨托山西部,高压麻粒岩包括基性麻粒岩长英质麻粒岩,基性麻粒岩的峰期矿物组合为Grt+Cpx+Pl±Ky±Zo+Rt±Qtz,长英质麻粒岩的峰期矿物组合为：Grt+Kf+Ky+Pl+Qtz.峰期变质条件为T=800～925℃,P=1.4～1.85GPa,退变质阶段经历了角闪岩-绿片岩的改造,高压麻粒岩的变质时代为420～450Ma.北秦岭榴辉岩分布在官坡-双槐树一带,榴辉岩的峰期变质组合为Grt+Omp±Phe+Qtz+Rt,所计算的峰期温压条件为T=680～770℃和P=2.25～2.65GPa,年代学数据显示榴辉岩的变质时代为500Ma左右.北秦岭高压麻粒岩分布在含榴辉岩单元的南侧松树沟一带,包括高压基性麻粒岩和高压长英质麻粒岩,与超基性岩在空间上密切伴生,高压麻粒岩的峰期温压条件为T=850～925℃,P=1.45～1.80GPa,锆石U-Pb年代学研究显示其峰期变质时代为485～507Ma.以上三个实例显示,出现在同一造山带、在空间上伴生的高压麻粒岩和榴辉岩有各自不同的变质演化历史,但榴辉岩中的榴辉岩相变质时代和相邻的高压麻粒岩中的高压麻粒岩相变质作用时代相同或相近,这种成对出现的榴辉岩和高压麻粒岩代表了它们同时形成在造山带中不同的构造环境中,即榴辉岩的形成于大陆俯冲带中,而高压麻粒岩可能形成在俯冲带之上增厚的大陆地壳根部.     

Determination of Early Paleozoic metamorphic event in the Longshan Complex and its geological implicationSCIEI北大核心CSCD

长期以来,陇山杂岩的归属问题一直存在争议。本文对出露于秦岭-祁连山结合部位的陇山杂岩中石榴黑云斜长片麻岩和石榴斜长角闪岩进行了详细的岩石学、P-T温压计算、独居石和榍石U-Pb年代学研究。通过详细的岩相学观察,石榴黑云斜长片麻岩的变质峰期矿物组合为石榴子石+黑云母+斜长石+石英;石榴斜长角闪岩中则识别出了以石榴子石+单斜辉石+角闪石+斜长石+石英为峰期的变质矿物组合。通过传统温压计计算,石榴黑云斜长片麻岩(样品21LS40)和石榴斜长角闪岩样品(样品21LS42-1)的峰期变质P-T条件分别为700℃、0.72GPa和710℃、0.74GPa。激光剥蚀电感耦合等离子体质谱(LA-ICP-MS) U-Pb数据表明,石榴黑云斜长片麻岩中独居石的206Pb/238U的加权平均年龄为407~435Ma。石榴斜长角闪岩中榍石的下交点年龄分别为410±7Ma、409±5Ma和426±10Ma,榍石中Zr含量温度计的计算结果分别为750℃、751℃和748℃(假定压力为0.7GPa)。本文从变质作用的角度出发,将陇山杂岩与秦岭杂岩进行温压条件和变质时代对比研究,认为陇山杂岩与东秦岭杂岩高压-超高压岩石的最后一期退变质作用和西秦岭天水地区的秦岭杂岩麻粒岩相变质作用类似,可能为北秦岭造山带的西延。     

喜马拉雅造山带中段亚东地区石榴角闪岩的成因：岩石学和锆石U- Pb年代学

喜马拉雅造山带中段出露的基性麻粒岩是理解印度大陆前喜马拉雅期演化历史和新生代碰撞造山作用的理想研究对象。本文对亚东多庆湖地区的石榴角闪岩进行了岩石学、全岩主微量元素地球化学和锆石U- Pb年代学研究,揭示了其原岩类型和新生代的变质作用过程。石榴角闪岩的原岩很可能为新元古代(~890 Ma)的玄武岩,具有E- MORB型岩石的地球化学特征。石榴角闪岩具有三期矿物组合：① 进变质矿物组合可能为石榴子石+角闪石+斜长石+钛铁矿+石英,即石榴子石核部及其中包裹体;② 峰期矿物组合为石榴子石+角闪石+斜长石+黑云母+石英,即石榴子石边部和基质矿物;③ 退变质矿物组合为角闪石+斜方辉石+斜长石+黑云母+石英,包括退变质域和石榴子石边部的后成合晶矿物。矿物温压计和相平衡模拟表明,石榴角闪岩进变质、峰期和退变质条件分别为609~621℃和0. 59~0. 65 GPa、805~845℃和0. 91~1. 04 GPa、825~840℃和0. 61~0. 68 GPa,经历了峰期高压麻粒岩相的变质作用。锆石U- Pb年代学研究表明,石榴角闪岩的峰期变质时间为34. 8~20. 3 Ma,退变质时间为18. 1~17. 7 Ma,可能经历了一个较长期的部分熔融过程。本文研究认为,亚东石榴角闪岩是印度板块向欧亚板块长期俯冲、地壳增厚成因的基性麻粒岩,原岩可能与Rodinia超大陆拼合相关;其以加热埋藏、近等温降压为特征的顺时针P- T轨迹指示了喜马拉雅造山带中段的大喜马拉雅岩系上部构造层位经历了长期持续的地壳增厚和高温麻粒岩相变质作用,以及早中新世(21~17 Ma)相对快速的减压抬升和随后(17 Ma之后)相对缓慢的折返至地表的演化过程。     

柴北缘都兰地区含石榴石、蓝晶石片麻岩的变质演化历史

在柴北缘超高压变质带东段,新识别出一个高压麻粒岩单元,其主要的岩石组合包括基性（长英质）高压麻粒岩、花岗质片麻岩、富铝质片麻岩（片岩）、石榴角闪岩和英云闪长岩。岩相学和变质反应序列、矿物化学和温压估算结果表明,蓝晶-石榴-黑云-二长片麻岩共经历了4阶段的变质演化：Ⅰ早期进变质阶段,以石榴石核部发育的黑云母、白云母、斜长石和石英等矿物包裹体为特征;Ⅱ峰期高压麻粒岩相阶段,矿物组合为石榴石+蓝晶石+条纹长石+斜长石+石英,金红石Zr温度计和GASP压力计限定其峰期温压条件为：t=800～840℃和p=1.4～1.6GPa;Ⅲ高角闪岩相退变质阶段,矿物组合为石榴石（边部）+黑云母+长石+石英;Ⅳ晚期低角闪岩相-绿片岩相退变质阶段,以蓝晶石周围出现的Ms+Pl±Zo和Mrg+Qtz±Ms±Pl后成合晶为特征。锆石LA-ICP-MSU-Pb定年结果指示高压麻粒岩相变质时代为431Ma。蓝晶-石榴-黑云-二长片麻岩具有顺时针的pt演化轨迹,与基性高压麻粒岩形成于相同的动力学过程。     

两条不同类型的HP/LT和UHP变质带对祁连-阿尔金早古生代造山作用的制约

在祁连-阿尔金造山带的南北两侧,分别出露有北祁连-北阿尔金HP/LT变质带和柴北缘-南阿尔金UHP变质带。北祁连-北阿尔金HP/LT变质带主要由蓝片岩、低温榴辉岩和高压变沉积岩所组成,榴辉岩形成的温压条件为420～570℃和2.0～2.5GPa,形成时代为510～440Ma。含硬柱石榴辉岩和含纤柱石高压变沉积岩的存在显示洋壳俯冲把大量水带到地幔深处。与HP/LT变质带伴生的早古生代蛇绿岩、俯冲增生杂岩、岛弧、弧后盆地等显示北祁连-北阿尔金为典型的早古生代增生造山带。柴北缘-南阿尔金UHP变质带由榴辉岩、石榴橄榄岩、高压麻粒岩及具有陆壳性质的正副片麻岩所组成,它们遭受了超高压变质作用(T700℃,P2.8GPa),UHP变质时代为500～420Ma,榴辉岩的原岩时代为750～850Ma,形成于新元古代的大陆裂谷环境。野外地质关系、岩石学及年代学研究显示柴北缘-南阿尔金HP-UHP变质带为大陆深俯冲作用的产物。在柴北缘-南阿尔金UHP变质带中,超高压榴辉岩和高压麻粒岩同时形成在不同的构造热环境中,构成大陆俯冲及碰撞造山带中的"双变质带",同时也显示柴北缘-南阿尔金造山带具有典型碰撞造山带的特征。祁连-阿尔金造山带南北两侧几乎同时发生增生造山作用和碰撞造山作用,构成由不同造山类型所组成的复合造山带。南北两侧的HP/LT变质带和UHP变质带以及可能存在的不同类型双变质带制约了祁连-阿尔金造山带早古生代的造山性质、造山类型以及造山机制。     

喜马拉雅造山带两种不同类型榴辉岩与印度大陆差异性俯冲

印度与亚洲大陆新生代碰撞-俯冲形成的喜马拉雅造山带核部由高压和超高压变质岩组成.超高压榴辉岩分布在喜马拉雅造山带西段,由石榴石、绿辉石、柯石英、多硅白云母、帘石、蓝晶石和金红石组成.超高压榴辉岩的峰期变质条件为2.6～2.8GPa和600～620℃,其经历了角闪岩相退变质作用和低程度熔融.超高压榴辉岩的进变质、峰期和退变质年龄分别为～50Ma、45～47Ma和35～40Ma,指示一个快速俯冲与快速折返过程.高压榴辉岩产出在喜马拉雅造山带中-东段,由石榴石、绿辉石、多硅白云母、石英和金红石组成.高压榴辉岩的峰期变质条件为>2.1GPa和>750℃,叠加了高温麻粒岩相退变质作用与强烈部分熔融.高压榴辉岩的峰期和退变质年龄可能分别是～38 Ma和14～17 Ma,很可能经历了一个缓慢俯冲与缓慢折返过程.喜马拉雅造山带两种不同类型榴辉岩的存在表明,印度与亚洲大陆约在51～53Ma碰撞后,印度大陆地壳的西北缘陡俯冲到了地幔深度,导致表壳岩石经历了超高压变质作用,而印度大陆地壳的东北缘平缓俯冲到亚洲大陆之下,导致表壳岩石经历了高压变质作用.     

The Olkhon metamorphic terrane in the Baikal region: An Early Paleozoic collage of Neoproterozoic active margin fragments

We report data from the Khadarta, Khoboi, and Orso metamorphic complexes of the Olkhon terrane in the western Baikal region. High-grade rocks in the three complexes may have been derived from active continental margin rocks (island arc–backarc basin system). The backarc basin history possibly began at 840–800 Ma, according to SHRIMP-II U-Pb zircon ages of the Orso gneiss. Many tectonic units in the Olkhon terrane belonged to the active margin of the Barguzin microcontinent which rifted off the Aldan province of the Siberian craton in the early Neoproterozoic. The accretion of the microcontinent to the craton was accompanied by high-grade metamorphism recorded in the Khadarta and Khoboi granulites. The 507 ± 8 Ma and 498 ± 7 Ma SHRIMP-II U-Pb zircon ages of the latter complexes, respectively, may refer to the earliest evolution stage of the Olkhon metamorphic terrane. New data for the Olkhon terrane agree well with the ages of other high-grade complexes along the southern Siberian craton (Slyudyanka, Kitoikin, Derba) and correspond to the initiation of the Central Asian orogen. With these data, the Olkhon metamorphic terrane has been interpreted as an Early Paleozoic collisional collage of fragments of the microcontinent’s Neoproterozoic active margin.     

Thermochronology of the Chernorud granulite zone,Ol’khon Region,Western Baikal area

Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to upper crustal levels. The process is subdivided into four discrete stages, which corresponded to metamorphism to the granulite facies (500–490 Ma), metamorphism to the amphibolite facies (470–460 Ma), metamorphism to at least the epidote-amphibolite facies (440–430 Ma), and postmetamorphic events (410–400 Ma). The earliest two stages likely corresponded to the tectonic stacking of the backarc basin in response to the collision of the Siberian continent with the Eravninskaya island arc or the Barguzin microcontinent, a process that ended with the extensive generation of synmetamorphic granites. During the third and fourth stages, the granulites of the Chernorud nappe were successively exposed during intense tectonic motions along large deformation zones (Primorskii fault, collision lineament, and Orso Complex). The comparison of the histories of active thermal events for Early Caledonian folded structures in the Central Asian Foldbelt indicates that active thermal events of equal duration are reconstructed for the following five widely spiced accretion-collision structures: the Chernorud granulite zone in the Ol’khon territory, the Slyudyanka crystalline complex in the southwestern Baikal area, the western Sangilen territory in southeastern Tuva, Derbinskii terrane in the Eastern Sayan, and the Bayankhongor ophiolite zone in central Mongolia. The dates obtained by various isotopic techniques are generally consistent with the four discrete stages identified in the Chernorud nappe, whereas the dates corresponding to the island-arc evolutionary stage were obtained only for the western Sangilen and Bayankhongor ophiolite zone.     

内蒙古锡林浩特岩群岩石学特征及变质温压条件

锡林浩特岩群出露于内蒙古锡林浩特市东南部,指原锡林郭勒杂岩中表壳岩部分,为一套片麻岩夹层状斜长角闪岩、磁铁石英岩和变粒岩等的变质岩组合。选取岩群中片麻岩及斜长角闪岩进行岩石学及岩相学分析,其中斜长角闪岩主要矿物组合为角闪石+斜长石;片麻岩样品中见夕线石+钾长石矿物组合,石榴子石具明显进变质环带,所以在计算其形成条件时选取了生长于峰期变质阶段的特定部位。运用角闪石斜长石、石榴子石黑云母矿物温压计分别估算锡林浩特岩群中准同时形成的变质基性火山岩及变质碎屑岩的变质温压区间。综合二者计算结果,得锡林浩特岩群峰期变质温压条件为660~707 ℃,0.5~0.6 GPa。变质达高角闪岩相。其变质年龄为1 000 Ma左右,推测锡林浩特岩群角闪岩相变质为中元古代末期锡林浩特微陆块与其他陆块碰撞的结果。     

Early Palaeozoic high‐pressure granulites from the Dunhuang block,northeastern Tarim Craton: constraints on continental collision in the southern Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary collages in the world, and records a prolonged sequence of subduction‐accretion and collision processes. The Tarim Craton is located at the southernmost margin of the CAOB. In this study, the discovery of early Palaeozoic high‐pressure (HP) granulites from the Dunhuang block in the northeastern Tarim Craton is reported, and these rocks are characterized through detailed petrological and geochronological studies. The peak mineral assemblage of the HP mafic granulite is garnet + clinopyroxene + plagioclase + quartz + rutile, which is overprinted by amphibolite facies retrograde metamorphic assemblages. The calculated P–T conditions of the peak metamorphism are ～1.4–1.7 GPa and ～800 °C. The retrograde P–T conditions are ～0.7 GPa and ～700 °C. The metamorphic zircon grains from the HP mafic granulite show homogeneous CL‐images, low Th/U ratios and flat HREE patterns and yield a weighted mean ²⁰⁶Pb/²³⁸U age of 444 ± 5 Ma. The metamorphic zircon grains from the associated kyanite‐bearing garnet gneiss and garnet‐mica schist show a similar ²⁰⁶Pb/²³⁸U age of 429 ± 3 and 435 ± 4 Ma, respectively. The c. 440–430 Ma age is interpreted to mark the timing of HP granulite facies metamorphism in the Dunhuang block. The results from this study suggest that the Dunhuang block experienced continental subduction prior to the early Palaeozoic collisional orogeny between the northeastern Tarim Craton and the southern CAOB, and the Dunhuang area could be considered as the southward extension of the CAOB. It is suggested that the continental collision in the eastern part involving the Dunhuang block of the southern CAOB may have occurred c. 120 Ma earlier than in the western part involving the Tianshan orogen.     

大别山石马地区石榴黑云片麻岩的Sm-Nd、K-Ar年龄及冷却速率

南大别地体中榴辉岩的围岩──石榴黑云片麻岩具有角闪岩相变质矿物组合,其变质温度为525℃,Sm-Nd矿物等时线年龄为(229±3)Ma.黑云母的K-Ar封闭温度为300℃,相应K-Ar年龄为(231±5)Ma.因此该片麻岩在230Ma左右从525℃迅速冷却到300℃以下。然而该区榴辉岩在印支期(221Ma)变质温度为700℃左右,直到134Ma才降至400-450℃。说明该区榴辉岩与该片麻岩具有不同的冷却史。它不支持榴辉岩是原地(in situ)成因的。     

First data on the age of rocks from the northern flank of the Olkhon terrane,western Baikal area

The metamorphic complexes in the northern part of the Olkhon terrane (Zunduk megazone), Central Asian Fold Belt, are studied. It is found that the age of gneiss–granites, which correspond to granites of type I formed within the active continental margin, is 800 ± 11 Ma, whereas the age of the protolith of epidote–muscovite–feldspar–quartz schist, which formed by metamorphic reworking of island-arc volcanic rocks, is 650–630 Ma. New results and those published earlier show that the structure of the Olkhon terrane contains traces of at least three stages of different ages when suprasubduction processes were manifested. The earliest episode (～850?800 Ma) occurred within the Panthalassa, and the subsequent ones (～650?620 and ～500 Ma) occurred in the Paleoasian Ocean. New data give us grounds to consider protoliths of the studied rocks from the northern flank of the Olkhon metamorphic terrane as products of convergence-related processes that took place within the limits of the paleooceans in the Late Precambrian, rather than in the Pleoproterozoic as was supposed earlier.     

Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: a non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane

Summary The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes over an area of about 15 km². The U–Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ∼1730 Ma, and the formation of amphibolite-facies assemblages in both metagabbro and granulite occurred at ∼340–460 Ma. Petrologic and geochronological data indicate that these various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies metamorphism at ∼1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation.     

五台山晚太古代碰撞造山带的变质作用演化

五台山晚太古代碰撞造山带的三个构造岩片组成，即南部构造岩片－弧前混杂岩带，中部构造岩片－岛弧系和北部构造岩片－弧后混杂岩带，其间以大型逆冲型韧性剪切带相拼合。对三个构造岩片的矿物共生组合及变质反应研究，确定其具有相似的造山型ＰＴｔ轨迹，变质早期对峰期明显的升温升压过程与地壳的拼合作用有关，变质峰期至晚期的近等温降压过程与地壳的纵向伸展作用相联系，三个构造岩片变质程度的差异是由于其所处的大地构造位置不同造成的。     

蚌埠隆起区石榴辉石岩变质P-T轨迹的构建

蚌埠隆起区位于华北克拉通东南缘,胶—辽—吉造山带的最南端,主体由五河杂岩组成。前人对该地区的研究主要集中于同位素年代学和变质温压条件研究,其中变质P-T条件研究结果差异较大,以压力变化最为显著,对峰期变质P-T条件缺乏统一认识。本文对蚌埠隆起区石榴辉石岩进行了大量的岩相学、矿物化学成分分析,表明该岩石记录了3期变质作用,其中S_-M1和S_-M2的矿物组合类似为Grt+Cpx+Opx+Amp+Pl+Ilm,S_-M3的矿物组合为Cpx+Amp+Pl+Grt （极边窄带）。结合变质温压条件分析和锆石U-Pb年代学分析,本次主要取得以下几点认识：1）石榴辉石岩WS047-1中记录的3期变质作用,温压条件分别为T_-M1 = 616 ℃～647 ℃、P_-M1 = 1.03～1.08 GPa,T_-M2 = 721 ℃～837 ℃、P_-M2 = 1.11～1.29 GPa和T_-M3 = 531 ℃～607 ℃、P_-M3 = 0.81～0.91 GPa,经历了由较高压力的角闪岩相→中-低麻粒岩相→角闪岩相的变质过程;2）据变质温压条件分析知,蚌埠隆起区具有顺时针的P-T轨迹特征,S_-M1→S_-M2和S_-M2→S_-M3分别为近等压升温和近等压降温的缓慢过程;3）石榴辉石岩锆石U-Pb年代学结果主要分为4组：1 839±13 Ma、1 925±31 Ma、2 041±55 Ma和2 762±14 Ma,其中峰值变质年代为1.93～1.84 Ga;4）结合温压条件和锆石U-Pb年代学分析结果,本文认为蚌埠隆起区的P-T轨迹与弗朗西斯科型俯冲或大陆碰撞环境的P-T轨迹较为类似,其应与1.93～1.84 Ga华北克拉通东、西陆块的碰撞拼合及胶—辽—吉造山带形成时限基本吻合。本次研究为深入理解华北克拉通的构造演化特征和蚌埠隆起区的变质作用及演化,提供了大量可靠的科学资料。