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1.
赣南龙南地区余田群玄武岩SHRIMP锆石U-Pb年龄及其地质意义 总被引:1,自引:2,他引:1
江西南部余田群由双峰式火山岩组成,分布在近EW向展布的三南-寻乌断裂带的临江、东坑、白面石、菖蒲等火山盆地之中。SHRIMP锆石U-Pb定年结果显示:东坑盆地余田群最下部玄武岩的年龄为194.4Ma±2.0Ma,菖蒲盆地余田群最上部玄武岩的年龄为191.9Ma±2.2Ma。这2个年龄结果,一方面指示余田群的地质时代属早侏罗世早期,另一方面说明玄武岩和长英质火山岩的年龄一致,且与剖面层序吻合,属典型的双峰式火山岩组合。余田群双峰式火山岩地质时代的厘定,为江西南部早侏罗世早期处于拉张构造环境提供了年代学证据。同时,菖蒲盆地玄武岩中存在2571~2225Ma残留锆石或捕获锆石,为江西南部可能存在新太古代晚期—古元古代的基底提供了旁证。 相似文献
2.
中国东南部晚白垩世早期广泛发育红色沉积岩系,沉积岩系底部常见玄武岩夹层,但赣南-粤北的长塘、仁居、寻乌盆地以长英质火山岩为主体,底部也夹有玄武岩层,构成“大量流纹岩-少量玄武岩”的双峰式组合。SHRIMP锆石U-Pb年龄表明,长塘、仁居盆地流纹岩和寻乌盆地碎斑熔岩的锆石206Pb/238U年龄分别为96.8Ma±1.4Ma、95.5Ma±1.3Ma、96.7Ma±1.1Ma,属晚白垩世早期。鉴于版石盆地火山岩系为长英质火山岩组合,且中部凝灰岩和上部流纹岩SHRIMP锆石U-Pb年龄分别为142.5Ma±1.3Ma和131.4Ma±1.3Ma,地质时代属早白垩世早期,长塘、仁居和寻乌盆地的火山岩系不能与版石盆地的火山岩系对比。赣南-粤北长塘、仁居和寻乌盆地长英质火山岩地质时代的确认,证实余姚-丽水-政和-大浦-莲花山断裂以东和以西“大量流纹岩-少量玄武岩”构成的不对称双峰式组合具有不同的地质时代,显示出东早西晚的特征,这对于研究中国东南部中生代岩浆活动和构造演化具有重要意义。 相似文献
3.
内蒙古达茂旗北部闪长岩锆石SHRIMP U-Pb、角闪石~(40)Ar/~(39)Ar年代学及其地质意义 总被引:1,自引:0,他引:1
内蒙古达茂旗北部的早古生代闪长岩侵入体产于包尔汉图-白乃庙岛弧带的西部,采用SHRIMP锆石U-Pb定年及角闪石40Ar/39Ar测年对其进行了精确的年代学研究。两件闪长岩样品分别获得的SHRIMP锆石U-Pb年龄为453±3Ma和446.8±5.3Ma,角闪石40Ar/39Ar坪年龄为459.2±2.4Ma和442.9±4.2Ma。这为研究该时期弧岩浆作用提供了新的年代学证据,并表明该岩浆侵位后,经历了结晶并快速冷却的过程,可能揭示了本区岛弧带和华北板块碰撞的构造意义。 相似文献
4.
湘南荷花坪锡多金属矿床成矿年代研究 总被引:1,自引:1,他引:0
荷花坪锡多金属矿床是本世纪初在南岭中段湘南地区新发现的一个大型矿床,区内的锡多金属矿化产在王仙岭岩体东南内、外接触带,已发现有Ⅰ、Ⅱ、Ⅲ和Ⅳ号4个主要锡多金属矿体。其中,Ⅰ、Ⅱ和Ⅳ号矿体由早期矽卡岩型和晚期蚀变碎裂岩型矿石组成,Ⅲ号矿体则由独立产出的蚀变碎裂岩型矿石组成,且包含有部分碎裂花岗斑岩。以往研究已对Ⅳ号矿体中的矽卡岩型矿石和Ⅲ号矿体中含矿斑岩脉分别采用辉钼矿Re-Os法和锆石SHRIMP U-Pb法进行了测年,获得的年龄分别为224.0±1.9Ma和142±2Ma。本文补充了晚期蚀变碎裂岩型矿石的~(40)Ar/~(39)Ar测年,结果显示,Ⅱ号矿体中蚀变碎裂岩型矿石白云母样品和石英样品的坪年龄分别为151.88±1.58Ma和155.39±7.04Ma;Ⅳ号矿体中蚀变碎裂岩型矿石石英样品的坪年龄为156.94±1.64Ma。结合前人研究资料综合分析,认为荷花坪矿区存在印支晚期(224Ma)、燕山早期(151~156Ma)和燕山晚期(142Ma)三期成矿作用,分别与区内印支期中粗粒含电气石黑云母花岗岩、燕山早期中粗粒黑云母花岗岩和燕山晚期花岗斑岩脉有关,不同期成岩、成矿作用的构造环境均为岩石圈的拉张伸展。湘南地区印支期(205~224Ma)基性岩浆活动及荷花坪矿床印支期成岩、成矿过程中均有幔源物质的参与,它们共同指示南岭地区中生代构造体制的转换或岩石圈伸展减薄可能始于印支主期(230~244Ma)之后的224Ma左右,即晚三叠世。 相似文献
5.
蚌埠淮光“混合花岗闪长岩”的形成时代及源区:锆石SHRIMP U-Pb地质年代学证据 总被引:34,自引:1,他引:34
对蚌埠淮光花岗闪长岩的岩相学和锆石阴极发光图象研究表明,淮光"混合花岗闪长岩"为岩浆结晶作用的产物,岩石形成后受到了应力作用的改造.锆石SHRIMP U-Pb定年结果和岩浆锆石的SHRIMP U-Pb年龄显示淮光花岗闪长岩形成于130.0±2.0 Ma;大多数继承锆石的年龄集中在1 800~1 900 Ma、2 300~2 517 Ma和3 443 Ma,这意味着淮光花岗闪长岩的母岩浆起源于华北地块基底的部分熔融.早白垩世(130 Ma左右)的岩浆作用是引起继承锆石和碎屑锆石Pb丢失的重要原因,同时也是华北地块东部岩石圈减薄的最重要时期.130 Ma左右的岩浆作用和岩石圈减薄应与太平洋板块的俯冲相联系. 相似文献
6.
西拉沐伦钼矿带半拉山斑岩钼矿床花岗斑岩锆石SHRIMP U-Pb测年及其地质意义 总被引:6,自引:0,他引:6
半拉山斑岩钼矿床是大兴安岭南段中生代西拉沐伦钼矿带中重要的钼矿床之一。矿床产于晚侏罗世火山岩中,矿区发育中生代侵入杂岩,侵入岩主要包括花岗闪长岩、闪长岩及花岗斑岩。矿床形成与侵入杂岩岩浆演化晚期岩浆活动有关。花岗斑岩锆石SHRIMP U-Pb定年表明,与成矿有关的晚期花岗斑岩侵位于(132.1±1.8) Ma。这表明,半拉山钼矿化发生在早白垩世,形成于中国东部岩石圈减薄构造环境。结合已有资料分析,认为大兴安岭南段除铅锌银铁铜等矿床之外,在白垩纪发生过重要的钼矿成矿作用,与白垩纪花岗斑岩有关的钼矿化是今后重要的找矿方向。 相似文献
7.
铜陵地区高钾钙碱性系列侵入岩锆石U-Pb年代学及其地质意义 总被引:6,自引:0,他引:6
铜陵地区高钾钙碱性系列侵入岩主要岩石类型为石英二长闪长(玢)岩、花岗闪长(斑)岩,其次为辉长闪长岩。本文报道该系列侵入岩最新锆石U-Pb定年结果及岩石地球化学数据。结果表明,南洪冲和沙滩脚花岗闪长岩、新桥头花岗闪长斑岩、缪家石英二长闪长玢岩的SHRIMP锆石U-Pb年龄分别为(138.8±1.3)Ma、(144.1±1.2)Ma、(147.2±1.5)Ma和(142.8±1.6)Ma,沙滩脚岩体和缪家岩体的LA-ICPMS锆石U-Pb年龄分别为(144.1±1.5)Ma、(143.2±1.3)Ma,与SHRIMP定年结果一致。一般来说,区内具有斑状结构的岩石,其年龄大于同类无斑状结构的岩石,但狮子山矿田的南洪冲花岗闪长岩年龄比区域上其他的同类岩石偏小,可能反映了区域上此类岩浆具有多次活动的特点。铜陵地区岩浆侵位的大致顺序为花岗闪长斑岩/第一次花岗闪长岩→辉长闪长岩/第一次辉石二长闪长岩→石英二长闪长玢岩/石英二长闪长岩→第二次花岗闪长岩→第二次辉石二长闪长岩。本区高钾钙碱性系列岩浆侵入活动是中国东部晚侏罗-早白垩世期间岩浆事件的组成部分,反映了中国东部区域构造由晚侏罗世的挤压转变为早白垩世的伸展环境。 相似文献
8.
9.
江西南部余田群由双峰式火山岩组成,分布在近EW向展布的三南-寻乌断裂带的临江、东坑、白面石、菖蒲等火山盆地之中。SHRIMP锆石U-Pb定年结果显示:东坑盆地余田群最下部玄武岩的年龄为194.4Ma±2.0Ma,菖蒲盆地余田群最上部玄武岩的年龄为191.9Ma±2.2Ma。这2个年龄结果,一方面指示余田群的地质时代属早侏罗世早期,另一方面说明玄武岩和长英质火山岩的年龄一致,且与剖面层序吻合,属典型的双峰式火山岩组合。余田群双峰式火山岩地质时代的厘定,为江西南部早侏罗世早期处于拉张构造环境提供了年代学证据。同时,菖蒲盆地玄武岩中存在2571~2225Ma残留锆石或捕获锆石,为江西南部可能存在新太古代晚期—古元古代的基底提供了旁证。 相似文献
10.
赣南-粤北地区晚白垩世早期长英质火山岩SHRIMP锆石U-Pb年龄及其地质意义 总被引:1,自引:0,他引:1
中国东南部晚白垩世早期广泛发育红色沉积岩系,沉积岩系底部常见玄武岩夹层,但赣南-粤北的长塘、仁居、寻乌盆地以长英质火山岩为主体,底部也夹有玄武岩层,构成"大量流纹岩-少量玄武岩"的双峰式组合。SHRIMP锆石U-Pb年龄表明,长塘、仁居盆地流纹岩和寻乌盆地碎斑熔岩的锆石206Pb/238U年龄分别为96.8Ma±1.4Ma、95.5Ma±1.3Ma、96.7Ma±1.1Ma,属晚白垩世早期。鉴于版石盆地火山岩系为长英质火山岩组合,且中部凝灰岩和上部流纹岩SHRIMP锆石U-Pb年龄分别为142.5Ma±1.3Ma和131.4Ma±1.3Ma,地质时代属早白垩世早期,长塘、仁居和寻乌盆地的火山岩系不能与版石盆地的火山岩系对比。赣南-粤北长塘、仁居和寻乌盆地长英质火山岩地质时代的确认,证实余姚-丽水-政和-大浦-莲花山断裂以东和以西"大量流纹岩-少量玄武岩"构成的不对称双峰式组合具有不同的地质时代,显示出东早西晚的特征,这对于研究中国东南部中生代岩浆活动和构造演化具有重要意义。 相似文献
11.
江西冷水坑矿区构造-岩浆活动的年代学约束 总被引:3,自引:3,他引:3
江西省冷水坑矿区火成岩-构造演化一直缺少系统的年代学制约.作者运用LA-ICP-MS锆石U-Pb和40Ar/39Ar测年技术,对冷水坑矿区两套火山岩地层(打鼓顶组和鹅湖岭组)、含矿花岗斑岩和主推覆断层F2进行了年代学测试,结果表明,打鼓顶组流纹质含角砾熔结凝灰岩形成于160.8±1.9Ma,鹅湖岭组合角砾熔结凝灰岩则具有间歇性和多期喷发特点,其最初活动时间为159Ma,而主体形成于146.6±2.2Ma;矿区含矿花岗斑岩与打鼓顶组、鹅湖岭组几乎同期形成,年龄介于163.6 ±2.1Ma~154.3±3.0Ma之间;研究区构造活动起始时间不晚于加里东期,推覆断层F2中保留有40Ar/39Ar年龄为398.5±2.6Ma的构造活动痕迹,中生代重新复活,导致震旦系叠覆于鹅湖岭组之上,年龄晚于146.6Ma,可能对含矿斑岩体起破坏作用. 相似文献
12.
New radiometric dating of the dykes from the Hurd Peninsula, Livingston Island, South Shetland Islands 总被引:1,自引:0,他引:1
Fifteen new K–Ar ages in the range of 79–31 Ma are partially confirmed by three 40Ar/39Ar plateaus and isochron data of 64.9±0.4, 55.5±0.1 and 52.8±0.6 Ma. The new geochronological data reveal a much more detailed picture of the subduction imprint in the Hurd Peninsula. Using cutting relationships, the dyke emplacement history is divided into four episodes. The Late Cretaceous–Paleocene dykes in the range of 80–60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of subduction of the proto-Pacific oceanic crust. The Early Eocene dykes (56–52 Ma) fill the gap in volcanic activity 70–50 Ma ago. They are the only magmatic event manifested at this time in the region. The 45–42 Ma dykes may be related to the intrusion of the Barnard Point tonalite. Three samples of Oligocene age appear to represent the last igneous activities on the Hurd Peninsula prior to the opening of the Bransfield Strait. 相似文献
13.
河北承德铁马哈叭沁超贫铁矿床的成因与成矿时代 总被引:3,自引:1,他引:3
河北承德一带基性-超基性岩中的超贫铁矿石(全铁TFe含量<20%)资源在河北的铁精矿产量中占有重要地位,其中以铁马哈叭沁超贫铁矿床贡献最大。本研究以铁马哈叭沁岩体中的超贫铁矿石即钒钛磁铁矿化的角闪石岩中的角闪石为研究对象,通过电子探针分析和40Ar/39Ar测年,结合野外地质特征,探讨了超贫铁矿床的成矿时代及矿床成因。野外和岩相学特征表明,铁马哈叭沁超贫铁矿床为岩浆晚期分异型铁矿床。电子探针分析表明,角闪石岩中角闪石主量元素变化范围较小,具有富Ca、富Mg、富Na、贫K的特征,属于韭闪石和镁绿钙闪石。角闪石成因矿物学研究表明,角闪石岩主要为幔源成因,并受到了地壳物质的混染。角闪石岩中角闪石单矿物的40Ar/39Ar年龄为379~401 Ma,表明成岩成矿时代为泥盆纪,形成于白乃庙岛弧与华北克拉通北缘发生弧-陆碰撞后的伸展阶段。 相似文献
14.
滇西腾冲更新世粗面安山岩Ar-Ar年代学、地球化学特征及其构造意义 总被引:1,自引:1,他引:0
腾冲芒棒地区广泛发育新近纪以来的火山岩,本文首次对该区粗面安山岩进行的高精度40Ar/39Ar同位素定年,其坪年龄分别为2.1±0.1Ma和2.0±0.1Ma,代表其喷溢时代为早更新世。岩石地球化学特征研究显示,粗面安山岩属高钾钙碱性系列,富集大离子亲石元素、亏损高场强元素,具有弧火山岩与大陆板内火山岩的双重属性,推测其形成于后造山环境。综合研究表明,腾冲地块更新世火山岩的形成与印度-欧亚板块俯冲-碰撞造山隆升后的伸展垮塌、富集地幔部分熔融作用密切相关,而印支陆块向东南逃逸以及腾冲弧形走滑断裂带(龙川江断裂带、大盈江断裂带)的活化促使了该期火山岩的喷发与侵位。 相似文献
15.
An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show 40Ar/39Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in 40Ar/39Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified 40Ar/39Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These 40Ar/39Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of 40Ar/39Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles. 相似文献
16.
At the Sandpiper gold deposit in the Tanami region of northern Australia sericite is intimately intergrown with arsenopyrite in gold-bearing quartz veins and breccias, suggesting sericite crystallisation synchronous with gold-bearing fluid flow. This ore-stage sericite yields a 40Ar/39Ar plateau age of 1785 ± 32 Ma (2σ including both analytical and systematic uncertainties). Recalculation using revised and more precise values for the 40K decay constants and the age of the Fish Canyon Sanidine standard shifts the age to 1794 ±12 Ma (2σ including all known uncertainties). Given the possibility of post-mineralisation isotopic resetting this age can be conservatively interpreted as a minimum constraint on the timing of gold deposition although, given local geological relationships and estimates for the argon retentivity of white mica, we consider complete isotopic resetting to be unlikely. The preferred interpretation is, therefore, that the sericite 40Ar/39Ar age indicates the timing of gold mineralisation. Thesericite age accords with a limited dataset of 207Pb/206Pb xenotime ages of ca 1800 Ma from other gold deposits in the Tanami region, interpreted as mineralisation ages. The agreement between independently derived ages from several gold deposits lends support for a widespread gold-mineralising event at ca 1800 Ma in the Tanami region. 相似文献
17.
《International Geology Review》2012,54(8):1007-1019
Сharoitite consists of gem-quality mineral charoite and subordinate quartz, aegirine, K-feldspar, tinaksite, canasite, and some other minerals. This rock type is known only from one locality in the world associated with the Early Cretaceous (131.3 ± 2.4 Ma, K–Ar age) Malyy Murun syenite massif, Siberia, Russia. Although charoitite mineralogy is well known, there is disagreement whether it reflects metasomatic or magmatic activity. In order to understand when the charoitites formed we attempted to date it by 40Ar/39Ar incremental step-heating and laser ablation techniques. Our results show that the fibrous structure of water-bearing charoite does not retain radiogenic argon. Laser ablation 40Ar/39Ar for K-feldspar and tinaksite from the charoitite yielded several age clusters even from the same mineral grain. The oldest cluster of 134.1 ± 2.9 Ma for the K-feldspar agrees with the age of the Malyy Murun syenites. The youngest age of 113.3 ± 3.4 Ma for charoitite K-feldspar overlaps with the youngest of published K–Ar ages (112 ± 5 Ma) for one K-feldspar sample of the Malyy Murun syenite. Tinaksite is characterized by a similar spread of ages (from 133.0 ± 3 Ma to 115.7 ± 4.3 Ma) within a single grain. We suggest that charoitites originated due to the interaction of metasomatic agents derived from the Malyy Murun magma and country rocks. Timing of magma emplacement and charoitite crystallization is reflected by the older cluster of ages, whereas the younger ages are due to a secondary process. 相似文献
18.
Mrio Neto C. Araújo Paulo M. Vasconcelos Fernando C. Alves da Silva Emanuel F. Jardim de S Jaziel M. S 《Journal of South American Earth Sciences》2005,19(4):445-460
40Ar/39Ar geochronology of muscovite and biotite grains genetically related to gold and Be–Ta–Li pegmatites from the Seridó Belt (Borborema province, NE Brazil) yield well-defined, reliable plateau ages. This information, combined with data about paragenetic and field relationships, reveals Cambro-Ordovician mineralization ages (520 and 500–506 Ma) for the orogenic gold deposits in the Seridó Belt. Biotite ages of 525±2 Ma, which represent the mean weighted results of the incremental heating analysis of six biotite single crystals, record the time of pegmatite emplacement and reactivation of Brasiliano/Pan-African strike-slip shear zones. These results, along with previous structural evolution studies, suggest that shear zones formed during the Brasiliano/Pan-African event were reactivated in the Upper Cambrian–Lower Ordovician. Mineralization occurs late in the history of the orogen. 相似文献
19.
Mark Quigley Yu Liangjun Liu Xiaohan Christopher J.L. Wilson Mike Sandiford David Phillips 《Tectonophysics》2006,421(3-4):269-297
Structural and thermochronological studies of the Kampa Dome provide constraints on timing and mechanisms of gneiss dome formation in southern Tibet. The core of Kampa Dome contains the Kampa Granite, a Cambrian orthogneiss that was deformed under high temperature (sub-solidus) conditions during Himalayan orogenesis. The Kampa Granite is intruded by syn-tectonic leucogranite dikes and sills of probable Oligocene to Miocene age. Overlying Paleozoic to Mesozoic metasedimentary rocks decrease in peak metamorphic grade from kyanite + staurolite grade at the base of the sequence to unmetamorphosed at the top. The Kampa Shear Zone traverses the Kampa Granite — metasediment contact and contains evidence for high-temperature to low-temperature ductile deformation and brittle faulting. The shear zone is interpreted to represent an exhumed portion of the South Tibetan Detachment System. Biotite and muscovite 40Ar/39Ar thermochronology from the metasedimentary sequence yields disturbed spectra with 14.22 ± 0.18 to 15.54 ± 0.39 Ma cooling ages and concordant spectra with 14.64 ± 0.15 to 14.68 ± 0.07 Ma cooling ages. Petrographic investigations suggest disturbed samples are associated with excess argon, intracrystalline deformation, mineral and fluid inclusions and/or chloritization that led to variations in argon systematics. We conclude that the entire metasedimentary sequence cooled rapidly through mica closure temperatures at 14.6 Ma. The Kampa Granite yields the youngest biotite 40Ar/39Ar ages of 13.7 Ma immediately below the granite–metasediment contact. We suggest that this age variation reflects either varying mica closure temperatures, re-heating of the Kampa Granite biotites above closure temperatures between 14.6 Ma and 13.7 Ma, or juxtaposition of rocks with different thermal histories. Our data do not corroborate the “inverse” mica cooling gradient observed in adjacent North Himalayan gneiss domes. Instead, we infer that mica cooling occurred in response to exhumation and conduction related to top-to-north normal faulting in the overlying sequence, top-to-south thrusting at depth, and coeval surface denudation. 相似文献
20.
In situ UV-laser ablation 40Ar/39Ar geochronological and geochemical data, together with rock and mineral compositional data, have been determined from pseudotachylyte and surrounding mylonitic gneiss associated with the UHP whiteschists of the Dora Maira Massif, Italy. Several generations of fresh pseudotachylyte occur as irregular veins up to a few cm thick both parallel and at high angles to the foliation. Whole rock XRF data collected from representative lithologies of mylonitic gneiss are uniformly consistent with a mildly alkalic granitic protolith. Minimal compositional variation is observed between the pseudotachylyte and its surrounding mylonitic gneiss. The pseudotachylyte contains newly crystallized grains of biotite and K-feldspar in a matrix of glass with partially fused grains of quartz, zircon, apatite, and titanite. Electron microprobe analyses of the glass show significant compositional variation that is probably strongly influenced by micrometer-scale changes in mineralogy. UV-laser ablation ICP-MS traverses across the mylonitic gneiss–pseudotachylyte contact are consistent with cataclastic communition of REE carriers such as epidote, monazite, allanite, zircon, and apatite before melting as an efficient mechanism of REE homogenization in the pseudotachylyte. The 40Ar/39Ar data from one band of pseudotachylyte indicate formation at 20.1 ± 0.5 Ma, when the mylonitic gneisses were already in a near surface position. The variable effects of top-to-the-west shear deformation within outcrops of the coesite-bearing unit are reflected in localized zones of protomylonite, cataclasite, ultracataclasite, and pseudotachylyte. Preservation of several generations of pseudotachylyte suggests that seismic events may have played a significant role in triggering late unroofing of the UHP rocks. It is speculated that deeper crustal seismic events potentially played a role in the unroofing of the UHP rocks at earlier stages in their exhumation history. 相似文献