宽坪岩群斜长角闪岩Sm-Nd同位素年龄

北秦岭豫西马驹口地区宽坪岩群中的斜长角闪岩原岩为基性侵入岩（ 辉长岩） ,其全岩的Ｓｍ－Ｎｄ 同位素等时线年龄为７４７－７２±４３Ｍａ,钕同位素初始比值为εＮｄ（ｔ） ＝ － ０．１ ,表明该基性侵入岩形成于晚元古代晚期,岩石来源于亏损的上地幔源区,但岩浆在形成和侵位过程中遭受不同程度的地壳物质成分的混染。     

The clew bay group: A displaced terrane of highland border group rocks (Cambro-ordovician) in Northwest Ireland

Marine turbidites, tuffs, black mudstones and conglomerates of the Cambro-Ordovician Clew Bay Group, were deposited in the E–W elongate transtensional Clew Bay Graben that is centred on Clew Bay, NW Ireland. The group is characterized by extensive sedimentary deformation and mass movement on slides; olistostromes, autoclastic breccias and course proximal turbidites are interbedded with apparently less disturbed but often overturned sediments. The Clew Bay Group lies structurally above serpentinized dunite/harzburgite breccias, schistose carbonate peridotites, and other basic and ultrabasic igneous rocks that have ophiolitic geochemical affinities; the sediments may have been in part deposited upon oceanic crust. Ophiolites and sediments that now rest on the Clew Bay Thrust abut Silurian shallow water strata in which the main tectonothermal history, associated with sinistral transcurrent faulting along the thrust zone, is dated at about 410 Ma. The sole thrust dips northward and coalesces with a major deep structure along the Fair Head-Clew Bay Line (FCL) that is the western continuation of the Highland Border Fault of Scotland. Blueschist relics in the Dalradian immediately to the north of the FCL indicate that subduction was active early in the history of the late Cambrian–early Ordovician Grampian orogeny. The Clew Bay Thrust was a sinistral, transpressional shear zone late in its history, but it probably originated as an obduction complex. The Clew Bay Group cannot be traced into sedimentary, metamorphic or structural continuity with the adjacent Dalradian to the north or Ordovician and Silurian rocks in the South Mayo Trough to the south. It should be considered as a distinct terrane (Clew bay Terrane) or a subterrane of Highland Border-type rocks along the southern margin of the Grampian Terrane.     

Comparing the Upper Triassic Deep-sea Flysch of theShannan Terrane with the Coeval Shallow Shelf Sediments ofthe Tethys Himalaya,Southern Tibet

The provenance and paleogeography of the Upper Triassic deep-sea flysch Langjiexue Group(LG) of the Shannan Terrane in the northeastern Himalaya orogen, south of Yarlung Zangbo, have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000 s. Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation(QF) in shallow shelf sediments of the Tethys Himalaya, the previous viewpoints on the basin and tectonics of the LG have been recently rejected. We compared the two units of the Upper Triassic, and our results reveal a number of differences,discrepancies, and inconsistencies in the debate, raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG. It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units.     

龙首山地块的归属问题：来自地壳结构和中—新元古代地层的证据

为了弄清楚龙首山地块的归属问题,对龙首山地块地壳结构和地层特征进行研究,发现龙首山地块具有由结晶基底和沉积盖层组成的双层地壳结构。该地块结晶基底由龙首山群组成,龙首山群岩性主要为一套条带状、眼球状混合岩夹斜长角闪岩、花岗质片麻岩、黑云斜长片麻岩等,普遍经历了角闪岩相区域变质作用。龙首山地块缺失长城系、青白口系和南华系,下部沉积盖层由蓟县系墩子沟群和震旦系顶部的烧火筒沟组构成。墩子沟群经历了埋藏变质作用,粉砂岩具千枚状构造,砂岩有一定程度的重结晶,地层层理保存完整。烧火筒沟组上部为含砾千枚岩、粉砂质千枚岩,下部为冰碛砾岩,冰碛砾岩总与寒武系含磷层相伴出现。地壳整体结构与华北克拉通基本特征相同,而扬子克拉通具有结晶基底、褶皱基底和沉积盖层3层地壳结构,与华北克拉通和龙首山地块迥异。因此,龙首山地块应归属于华北克拉通。     

保山地体寒武纪基性火山岩及其大地构造意义

保山地体位于青藏高原东南缘。有关保山地体的岩浆作用研究大多集中在中生代及新生代,针对古生代岩浆作用的讨论较少。对云南省保山邦迈地区蒲满哨群中变质基性岩的锆石U-Pb年代学、地球化学及Sm-Nd同位素组成进行了研究。这些变质基性岩可分为2组:一组为斜长角闪岩,另一组为黑云斜长角闪岩。锆石U-Pb测年结果表明,斜长角闪岩的形成时代为536.7Ma,黑云斜长角闪岩的形成时代为532.0Ma。地球化学特征显示,斜长角闪岩的原岩为玄武安山岩,黑云斜长角闪岩的原岩为碱性玄武岩。稀土和微量元素配分曲线及多种构造环境判别图解显示,二者分别具有富集型大洋中脊玄武岩和洋岛玄武岩的地球化学特征。结合区域大地构造背景认为,保山地体邦迈变质基性岩为洋脊俯冲的产物。在新元古末期—早古生代,保山地体与拉萨地体、喜马拉雅地体等类似,皆位于冈瓦纳大陆边缘,且共同经历了增生造山过程。     

中天山南缘艾尔宾山志留纪侵入岩地球化学特征及地质意义

中天山南缘艾尔宾山地区岩浆活动的产物可能记录着南天山洋盆与伊犁中天山板块的活动,对解决南天山洋盆的俯冲问题具有重要意义。本文对中天山南缘艾尔宾山志留纪花岗岩进行了系统的岩石学、地球化学及同位素年代学研究。对4件样品的LA-ICP-MS锆石U-Pb定年结果表明,该岩体的形成时代为志留纪;研究区岩石具有准铝质高钾钙碱性系列岩石特征,为I型花岗岩,岩浆来源可能为下地壳的部分熔融;在稀土元素球粒陨石标准化分布图上,表现为强烈的右倾近平行的曲线簇。大离子亲石元素Rb、Ba、K等明显富集;高场强元素Nb、Ta、Ti、P等强烈亏损,表现出岛弧岩浆岩的地球化学特征。综合分析认为志留纪侵入岩为火山弧花岗岩,是与洋壳俯冲作用有关的产物。     

三江北段晚三叠世构造-岩浆作用和几个相关的科学问题

中国西南三江北段的松潘-甘孜褶皱带和义敦地体以强烈的晚三叠世构造-岩浆活动为特征.松潘-甘孜褶皱带的岩浆活动主要发生在228～190 Ma(峰期时代为约210 Ma),略晚于义敦地体的岩浆活动(236～200 Ma,峰期时代为约216 Ma).金沙江洋可能经历了西向和东向的双向俯冲,于晚二叠世末—早三叠世初闭合,甘孜-...     

Tectonic setting of the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt,NW India and its implication on correlation with the East African Orogen in the Gondwana assembly

Granulites are developed in various tectonic settings and during different geological periods, and have been used for continental correlation within supercontinent models. In this context the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt of northwestern India are significant. The granulites occur as shear zone bounded lensoidal bodies within low-grade rocks of the South Delhi Terrane and comprise pelitic and calcareous granulites, a gabbro-norite-basic granulite suite and multiple phases of granites of the Ambaji suite. The granulites have undergone three major phases of folding and shearing. The F₁ and F₂ folds are coaxial along NE-SW axis, and F₃ folds are developed across the former along NW-SE axis. Thus, various types of interference patterns are produced. The granulite facies metamorphism is marked by a spinel–cordierite–garnet–sillimanite–quartz assemblage with melt phase and is synkinematic to the F₁ phase of folding. The peak thermobarometric condition is set at ≥850 °C and 5.5–6.8 kb. The granulites have been exhumed through thrusting along multiple ductile shear zones during syn- to post-F₂ folding. Late-stage shearing has produced cataclasites and pseudotachylites. Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb dating of zircon from pelitic granulites and synkinematically emplaced granites indicate that: (1) the sedimentary succession of the South Delhi Terrane was deposited between 1240 and 860 Ma with detritus derived from magmatic sources with ages between 1620 and 1240 Ma; (2) folding and granulite metamorphism have taken place between ca. 860 and 800 Ma, and exhumation at around ca. 800–760 Ma; and (3) the last phase of granitic activity occurred at ca. 759 Ma. This shows, for the first time, that the granulites of the South Delhi Terrane are much younger than those of the Sandmata Granulite Complex of the northern part of the Aravalli Mobile Belt, the Saussar granulites of the Central India Mobile Belt and the Eastern Ghats Mobile Belt. Instead, they show similarities to the Neoproterozoic granulites of the Circum Indian Orogens that include the East African Orogen (East Africa and Madagascar), the Southern Granulite Terrane of India and much of Sri Lanka. We suggest that the South Delhi Basin probably marks a trace of the proto-Mozambique Ocean in NW India within Gondwana, that closed when the Marwar Craton, arc fragments (Bemarivo Belt in Madagascar and the Seychelles) and components of the Arabian-Nubian Shield collided with the Aravalli-Bundelkhand Protocontinent at ca. 850–750 Ma.     

Avalonian and Cadomian terranes in North Dobrogea,Romania

The North Dobrogea orogen is a collage of dismembered terrane fragments between the Moesian platform and East European craton (Baltica). It records Alpine and Variscan deformation, magmatism and metamorphism. Its basement comprises three metamorphic complexes (Boclugea, Megina and Orliga) that are separated by tectonic boundaries. Detrital zircon U/Pb ages suggest the Boclugea and Orliga complexes represent two peri-Gondwanan terranes of Avalonian and Cadomian affinities, respectively. The new data clarify the original relationships between the North Dobrogea terranes, and Baltica and Moesia platform.     

北大别北东地区榴辉岩温度条件分析

北大别榴辉岩温度条件的精确评价直接涉及到北大别变质单元性质的判定.由于榴辉岩温度分类方案的不同,以及温度估算时温度计选择和绿辉石Fe2+校正方法不同的影响,导致北大别榴辉岩温度评价和分类归属具有较大的不确定性.为此,本研究应用5个不同的温度计和4种不同的绿辉石Fe2+校正方法,评价了北大别北东地区榴辉岩的温度条件.研究显示,当应用Kogh (2000)的Grt-Cpx Fe-Mg温度计和设定绿辉石的铁为Fe3+/Fe2+=1∶1时,温度计算较为合理:P标定=3.5 GPa,温度范围为600～740℃或P标定=5.0GPa,温度范围为670～ 810℃.参照Carswell (1990)的温度分类,北大别榴辉岩应属于中温类型.但结合此次榴辉岩的地质特征、岩相学和矿物成分分析,以及前人的研究资料,北大别榴辉岩与中大别和南大别榴辉岩有明显的差异,其可能是在相对高温的条件下形成的.