SHRIMP U-Pb Dating of Zircons of a Dark Eclogite and aGarnet-bearing Gneissic Granitic Rock from Bixiling, EasternDabie Area, Anhui Province: Isotope Chronological Evidenceof Neoproterozoic UHP Metamorphism

The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approxim     

沙沟街地区原划秦岭群中解体出一套TTG岩系

通过对沙沟街地区商丹构造带北部原划秦岭群进行 1∶ 5万区调填图 ,从前人划分的副变质片麻岩中解体出一套变质中酸性古侵入体 - TTG岩系。划分和圈定出 5个片麻岩体 ,归并为 2个片麻杂岩 ,建立了老安子沟片麻岩套 ,并从岩石、地球化学等方面综合进行了探讨。     

延边小西南岔富金铜矿田燕山晚期花岗杂岩的锆石SHRIMP U-Pb年龄及其地质意义

首次对延边小西南岔富金铜矿床矿田内产出的燕山晚期花岗杂岩进行了系统的锆石SHRIMPU-Pb年龄测定,获得中细粒黑云母二长花岗岩、中细粒黑云母花岗闪长岩和似斑状角闪花岗闪长岩的3组锆石谐和年龄数据,分别为98.4~109.0Ma〔加权平均值为(104.6±2.5)Ma,n=10,MSWD=0.71,置信度0.70〕、98.3~108.3Ma〔加权平均值为(106.7±1.6)Ma,n=12〕和104.4~118.8Ma〔加权平均值为(111.7±2.8)Ma,n=12〕,指示它们的岩浆侵位时限在112~104Ma之间,相对侵位时序为似斑状角闪花岗闪长岩、中细粒黑云母花岗闪长岩到中细粒黑云母二长花岗岩;考虑到它们在成矿元素和地质上与矿化的密切程度以及控(容)矿断裂的张扭性特征,进而确定大规模的金铜矿化应发生在似斑状角闪花岗闪长岩、中细粒黑云母花岗闪长岩、中细粒黑云母二长花岗岩形成之后,闪长玢岩之前,或在104.6~102.1Ma之间,成矿环境应处于早白垩世晚期伊泽奈崎板块向古亚洲大陆边缘俯冲消亡、中国东部大陆边缘燕山造山期末的走滑、伸展构造转换过程。     

Mineralogy and geochemistry of Nb-, Ta-, Sn-, U-, Th-, and Zr-bearing granitic rocks from Abu Rusheid shear zones,South Eastern Desert,Egypt

Granite-hosted,Nb-,Ta-,Sn-,U-,Th-,and Zr(Hf)-bearing mineralization from the Abu Rusheid shear zones occurs about 97 km southwest of the town of Marsa Alam,South Eastern Desert,Egypt.The SSE-trending brittle-ductile Abu Rusheid shear zones crosscut the peralkalic granitic gneisses and cataclastic to mylonitic rocks(mylonite,protomlyonite,and ultramylonite).The northern shear zone varies in width from 1 to 3 m with a strike length of >500 m,and the southern shear zone is 0.5 to 8 m wide and >1 km long.These shear zones locally host less altered lamprophyre and locally sheared granitic aplite-pegmatite dykes.The rare-metal minerals,identified from the peralkalic granitic gneisses and cataclastic to mylonitic rocks are associated with muscovite,chlorite,quartz,fluorite,pyrite,magnetite,and rare biotite that are restricted to the Abu Rusheid shear zones;these are columbite-tantalite and pyrochlore(var.betafite) in the northern shear zone and ferrocolumbite in the southern shear zone.Cassiterite occurs as inclusions in the columbite-tantalite minerals.U-and Th-minerals(uraninite,thorite,uranothorite,ishikawaite,and cheralite) and Hf-rich zircon coexist.Magmatic(?) zircon contains numerous inclusions of rutile,fluorite,U-Th and REE minerals,such as uranothorite,cheralite,monazite,and xenotime.Compositional variations in Ta/(Ta+Nb) and Mn/(Mn+Fe) in columbite range from 0.07-0.42 and 0.04-0.33,respectively,and Hf contents in zircon from 1.92-6.46 of the two mineralized shear zones reflect the extreme degree of magmatic fractionation.Four samples of peralkalic granitic gneisses and cataclastic to mylonitic rocks from the southern shear zone have very low TiO2(0.02 wt%-0.04 wt%),Sr [(15-20)×10-6],and Ba [(47-78)×10-6],with high Fe2O3T(0.94 wt%-1.99 wt%),CaO(0.14 wt%-1.16 wt%),alkalis(9.2 wt%-10.1 wt%),Rb [(369-805)×10-6],Zr [(1033-2261)×10-6],Nb [(371-913)×10-6],U [(51-108)×10-6],Th [(36-110)×10-6],Ta [(38-108)×10-6],Pb [(39-364)×10-6],Zn [(21-424)×10-6],Y [(8-304)×10-6],Hf [(29-157)×10-6],and ∑REE [(64-304)×10-6],especially HREE [(46-167)×10-6].Three samples from the northern shear zone also have very low TiO2(0.03 wt%),Sr [(11-16)×10-6],and Ba [(38-47)×10-6],with high Fe2O3T(1.97 wt%-2.91 wt%),CaO(0.49 wt%-1.01 wt%),alkalis(7.2 wt%-8.3 wt%),Rb [(932-978)×10-6],Zr [(1707-1953)×10-6],Nb [(853-981)×10-6],Ta [(100-112)×10-6],U [(120-752)×10-6],Th [(121-164)×10-6],Pb [(260-2198)×10-6],Zn [(483-1140)×10-6],Y [(8-304)×10-6],Hf [(67-106)×10-6],and ∑REE [(110-231)×10-6],especially HREE [(91-177)×10-6].The very high Rb/Sr(57.5-88.9),and low Zr/Hf(16.9-25.6),Nb/Ta(7.7-9.8),and Th/U(0.21-1.01) are consistent with very frac-tionated fluorine-bearing granitic rocks that were altered and sheared.The field evidence,textural relations,and compositions of the ore minerals suggest that the main mineralizing event was magmatic(629+/-5 Ma,CHIME monazite),with later hydrothermal alteration and local remobilization of the high-field-strength elements.     

福建泉州笔架山花岗瓷石矿地质特征及成因分析

泉州笔架山花岗瓷石矿贮存于钾长花岗岩中心柏和花岗斑岩中,矿石化学成分高硅、富、碱、贫铁镁。矿体埋藏浅、质优、规模大、易采易选易加工。开发利用远景看好。     

与花岗质岩浆系统有关的石英脉型钨矿和斑岩型铜矿成矿流体特征比较

文中对比了与S型花岗岩有关的石英脉型钨矿和与I型（及少数A型）花岗岩类有关的斑岩型铜矿床的成矿流体特征。它们的共同点在于成矿流体都由岩浆流体演化而来,在后期逐渐有大气降水的加入。差异性在于：（1）石英脉型钨矿成矿流体主要属于中—中高温、中—中低盐度的NaCl-H2O±CO2体系,而斑岩型铜矿属于中高-高温、高盐度的Na...     

Identification of the Early Jurassic mylonitic granitic pluton and tectonic implications in Namling area,southern Tibet

A number of studies revealed that the Gangdese magmatic belt of southern Tibet was closely related to the northward subduction of the Neo-Tethys oceanic lithosphere and Indo-Asian collision.However,pre-Cretaceous magmatism is still poorly constrained in the Gangdese magmatic belt,southern Tibet.Here,we conducted systematically geochronology and geochemistry studies on a newly-identified granitic pluton in the middle Gangdese magmatic belt(Namling area),southern Tibet.Zircon SHRIMPⅡU-Pb dating for one representative sample gives a weighted age of 184.2±1.8 Ma(MSWD=±1.11),corresponding to emplacement and crystallization age of the granitic pluton in the Early Jurassic(Pliensbachian).High SiO2(68.9-72.1 wt.%)contents and intermediate Mg#values(35-38)together suggest that the newly-identified granitic pluton was probably formed by partial melting of crustal material with minor injection of mantle-derived magma,precluding an origin from melting of metasedimentary rocks that are characterized by low Mg#and high zirconδ^18O values(>8‰).Geochemically,the newly-identified granitic pluton belongs to typical I-type granitic affinity,whereas this is inconsistent with aluminium saturation index(ASI=A/CNK ratios)and geochemical signatures.This suggests that zircon oxygen isotopes(4.30‰-5.28‰)and mineral features(lacking Al-rich minerals)are reliable indicators for discriminating granitic origin.Significantly depleted whole-rock Sr-Nd-Hf isotopic compositions and zirconεHf(t)values indicate that the granitic pluton was derived from partial melting of depleted arc-type lavas.In addition,the granitic pluton shows zirconδ^18O values ranging from 4.30‰to 5.28‰(with a mean value of 4.77‰)that are consistent with mantle-derived zircon values(5.3‰±0.6‰)within the uncertainties,indicating that the granitic pluton might have experienced weak short-living high-temperature hydrous fluid-rock interaction.Combined with the Sr-Nd-Hf-O isotopes and geochemical signatures,we propose that the newly-identified granitic pluton was originated from partial melting of depleted mafic lower crust,and experienced only negligible wall-rock contamination during ascent.Integrated with published data,we also propose that the initial subduction of the Neo-Tethys oceanic lithosphere occurred no later than the Pliensbachian of the Early Jurassic.     

东昆仑东段三叠纪岩浆混合作用:以香加南山花岗岩基为例

香加南山花岗岩基位于东昆仑造山带东段,岩基主要岩石类型为花岗闪长岩。千瓦大桥-加鲁河一带花岗岩体为香加南山岩基的重要组成部分。香加南山花岗岩基含大量暗色微粒包体,包体中捕掳晶丰富。千瓦大桥-加鲁河一带花岗岩体寄主岩中斜长石和暗色微粒包体中捕掳晶斜长石具正常环带,An值震荡变化,角闪石和黑云母Mg O含量和Mg#值较低,具壳源特征;暗色微粒包体中基质斜长石具核边结构,核部和边部An值存在间断,角闪石和黑云母Mg O含量和Mg#值较高,具幔源特征。LA-ICP-MS锆石U-Pb同位素定年结果显示千瓦大桥花岗闪长岩、暗色微粒包体和加鲁河辉长岩的结晶年龄分别为251.0±1.9Ma、252.8±3.0Ma和221.4±3.3Ma。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(HFSE),具较低的Mg#和Nb/Ta比值;从千瓦大桥到加鲁河花岗闪长岩呈现出由准铝质中钾钙碱性系列向准铝-弱过铝质中钾-高钾钙碱性系列演化;暗色微粒包体和加鲁河辉长岩轻重稀土元素分异程度相对较低,具较高的Mg#和Nb/Ta比值。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩分别为古特提斯演化俯冲阶段和后碰撞阶段幔源岩浆底侵新生地壳使其部分熔融产物。镁铁质岩浆注入长英质岩浆的混合作用形成了暗色微粒包体。岩浆混合过程中,如果岩浆不完全混合,混合岩浆中混入物质除了长英质岩浆的残留岩浆和捕掳晶,还应该有镁铁质岩浆与长英质岩浆之间的元素梯度差导致的物质扩散;如果岩浆为近完全混合,混合岩浆近似为镁铁质岩浆和长英质岩浆以一定比例二元混合。东昆仑东段晚古生代-早中生代幔源岩浆对花岗质岩浆的影响是一个持续的过程,从俯冲阶段早期流体交代地幔熔融,到俯冲阶段后期板片断离,然后同碰撞阶段板片断离的持续影响,再到后碰撞阶段加厚地壳的拆沉作用,由于地球动力学体制不同,导致幔源岩浆影响的大小和特征不同。     

南阿尔金尤努斯萨依花岗质高压麻粒岩的发现及其地质意义

南阿尔金尤努斯萨依地区首次发现一套高压麻粒岩相特征矿物组合的含蓝晶石石榴子石的花岗质片麻岩,其矿物组合为Grt+Ky+Per(+Ksp)+Ru+Q。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物组合稳定域及三元长石温度计等,确定其早期变质温压条件为T=970～1010℃,P=23. 2～25. 3kbar,达到了榴辉岩相变质条件。同时,根据岩相学观察获得的矿物共生组合与矿物变质显微结构以及P-T视剖面图,可识别出该岩石在早期变质之后还经历了以矿物组合Grt+Ky+Per(+Ksp)+Pl+Ru+Q为代表的麻粒岩相、以及Grt+Ky+Ksp+Pl+Bi+Ru+Ilm+Q为代表的麻粒岩-高角闪岩相和以Ky+Ksp+Pl+Q+Bi+Mu+Ru+Ilm为代表的角闪岩相三期退变质作用,它们共同构成了一个顺时针型降温降压的退变质P-T演化轨迹,指示出与大陆俯冲-深俯冲相关的高压变质事件和俯冲碰撞后的折返事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析表明,该高压岩石峰期变质年龄497. 8±2. 7Ma,与南阿尔金地区已发现的高压-超高压岩石的峰期变质时代完全一致,表明它们应属同一变质岩带;其原岩形成时代为900. 2±4. 1Ma,与南阿尔金已报道的正变质的高压-超高压岩石原岩的形成时代基本一致,指示它们可能具有相同的原岩属性。这套花岗质高压麻粒岩的确定为进一步约束南阿尔金早古生代高压-超高压变质岩带的时空分布规律提供了新的限定。     

海南岛西部戈枕含金剪切带花岗质糜棱岩中锆石SHRIMP U-Pb年代学及其地质意义

海南岛西部的中元古代抱板群混合岩主要沿北东向戈枕剪切带展布,近年来的研究逐渐揭示混合岩的原岩为花岗质岩石,是遭受强烈剪切作用改造的糜棱岩。本文选择土外山金矿的花岗质糜棱岩和不磨金矿的糜棱岩化花岗岩进行锆石SHRIMP U-Pb年代学测试,3件样品的锆石SHRIMP U-Pb谐和线年龄值分别为1439.1±8.4Ma(样品13JC-8-1,MSWD=0.85,n=14)、1436.9±8.3Ma(样品13JC-41,MSWD=0.54,n=10)和1448±13Ma(样品BM-3,MSWD=0.56,n=10),代表其原岩的侵位时代。结合研究区已有的研究成果,本文认为海南岛西部花岗质岩类和沿戈枕剪切带出露的糜棱岩原岩结晶年龄为~1450Ma,之后于~1400Ma经历一期构造-热变质事件;海南岛应为华夏地块的一部分,在Rodinia超大陆聚合前,华夏地块(包括海南岛,至少包括海南岛北西部)最有可能位于劳伦大陆南缘的西南延伸部分,华夏地块(包括海南岛)所经历的格林威尔造山事件可能较扬子板块偏早。