云开造山带条带-眼球状(环斑)强过铝花岗岩的岩石地球化学、年代及成因

云开造山带广泛出露的条带-眼球状(环斑)花岗质岩石及紫苏花岗岩岩石地球化学和离子探针(SHRIMP)定年的研究表明,绝大多数为强过铝(SP)高钾钙碱性-钙碱性花岗岩,并且是高温俯冲-碰撞后构造环境形成的强过铝(SP)高钾钙碱性-钙碱性花岗岩。高钾钙碱性条带状黑云二长花岗岩、眼球状(环斑)黑云二长花岗岩到钙碱性紫苏花岗闪长岩(闪长岩)和片麻状含榴黑云二长花岗岩形成时代逐渐变新,岩浆结晶锆石SHRIMP年龄由(465±10)Ma、(467±10)Ma变为(435±11)Ma、(413±8)Ma,侵入辉长岩的Sm-Nd矿物-岩石等时线年龄为(392±53)Ma,并主要形成于俯冲-碰撞转换为碰撞后底侵-伸展的构造环境,其中紫苏花岗闪长岩(闪长岩)和片麻状含榴黑云二长花岗岩具A型花岗岩地球化学特征,侵入辉长岩的形成则标志俯冲-碰撞造山作用的结束和大陆伸展作用环境的开始。条带-眼球状(环斑)花岗岩及紫苏花岗岩中尽管存在四堡期(格林威尔)造山事件的重要信息,但它们应代表加里东期扬子板块向华夏板块俯冲-碰撞后拆沉-底侵-伸展作用构造环境岩浆岩活动的产物,并且经历了印支期的挤压抬升和伸展揭顶作用。     

苏鲁造山带岩浆岩的锆石U Pb定年及构造意义

锆石U-Pb定年和地球化学分析结果显示,苏鲁造山带南缘连云港锦屏山片麻状花岗岩形成于(806.0±14.0)Ma,海州群云台组变质火山岩形成于(800.8±7.8)Ma,张八岭隆起的张八岭群西冷组变质火山岩形成于(751.6±7.1)Ma和(767.0±15.0)Ma.这些岩浆岩总体上具有高钾钙碱性系列、右倾型REE(Rare Earth Elements)模式、Nb、Ta、Sr、P和Ti强烈亏损、中等负铕异常、重稀土弱到中等亏损、低Sr、高Yb等特点,与浙闽型岩浆岩反映的区域伸展环境和下地壳部分熔融是一致的.这次构造岩浆活动820～740Ma,是晋宁期主碰撞造山后Rodinia超大陆裂解和岩石圈减薄演化的记录.     

贺兰山地区黄旗口花岗岩体地质特征、成因类型与构造环境探讨

贺兰山地区黄旗口花岗岩体呈岩基状产出,岩体具不甚明显的岩相分带现象.岩石类型复杂,以黑云母英云闪长岩、二云母英云闪长岩为主,二云母花岗岩、二云母二长花岗岩次之,蚀变较强烈.岩石化学成分总体呈中酸性,岩浆分异强烈.化学类型属钙性一钙碱性岩系,具壳源型（S）花岗岩特征.综合分析表明,贺兰山地区黄旗口花岗岩体成因类型属S型花岗岩,形成于大陆碰撞造山环境,具有汇聚、离散、扩张的强力就位特点,形成时代厘定为中元古代长城纪（晋宁期）.     

江南隆起（九岭）多阶段构造演化的花岗岩记录

以江南隆起九岭花岗岩体为研究对象,应用激光剥蚀等离子体质谱(LA-ICP-MS)锆石U-Pb定年技术,得到该花岗岩侵入年龄为853～811Ma.自晋宁期以来,九岭地区依次经历了加里东、印支及燕山等多阶段构造演化.通过花岗岩地球化学及构造图解分析,可知江南隆起九岭多阶段构造演化环境各不相同.晋宁期(929-810 Ma)花岗岩体落入岛弧与碰撞的过渡环境;而加里东期(439-411 Ma)花岗岩体具板内汇聚环境特点;燕山期(158-118 Ma)花岗岩形成于同碰撞兼火山弧构造环境.     

西藏冈底斯西部地区花岗岩锆石U-Pb年龄及其地质意义

对西藏冈底斯西部措勤县打加错地区粗粒二长花岗岩、中粒二长花岗岩、花岗岩进行LA-ICP-MS锆石U-Pb法定年、锆石同位素组成、主量元素测定,获得年龄值分别为(43.5±1.5)Ma、(44.2±2.6)Ma及(44.2±1.7)Ma,结合区域岩浆侵位规律,根据侵入岩地质特征、岩石学、同位素年代学、岩石化学等特征,将研究区出露的花岗岩划分为喜山早期侵入岩,属冈底斯-念青唐古拉中酸性杂岩带南亚带重要组成部分之一。其物质来源与上地壳变质泥岩的部分熔融有关,所形成的构造环境与区域构造背景息息相关,是始新世末喜马拉雅陆块同冈底斯陆块碰撞,陆-陆碰撞造山结束后相对松弛阶段的产物,构造环境同碰撞花岗岩。     

大兴安岭北部晋宁期片麻杂岩的地球化学特征及地质意义

大兴安岭北部阿龙山地区发育一套元古代凤水山片麻杂岩(Pt2Fgn),岩石类型以花岗质片麻岩为主,原岩属于一套钙碱性的中酸性花岗岩系列,以高SiO2、高碱(Na2O K2O)、高REE,具强烈的负Eu异常.其K-Ar稀释法年龄为920.95±32.7 Ma,表明为晋宁期岩浆事件的产物.岩石学岩石地球化学特征表明具岩浆成因特点,形成于同碰撞构造环境.     

西秦岭光头山花岗岩锆石U-Pb年代学及其地质意义

光头山花岗岩体出露于勉略缝合带北侧, 主要由英云闪长岩和二长花岗岩组成。英云闪长岩表现为片麻状构造, 局部英云闪长岩糜棱岩化形成花岗质糜棱岩。而二长花岗岩在糜棱岩带形成之后侵位, 含有少量的石榴石,弱的片麻状到块状构造。LA-ICPMS 锆石原位U-Pb同位素定年结果表明, 光头山岩体为两个阶段侵位, 糜棱岩化英云闪长岩( 样品GT18-01)的侵位结晶年龄是221±6Ma, 而二长花岗岩(样品GT11-01)的结晶年龄是199±4Ma,代表了晚期二长花岗岩形成的时代。结合区域构造背景和前人研究的地球化学特征, 早期的英云闪长岩可能在勉略洋盆闭合前的岛弧发育阶段侵位, 代表了洋壳俯冲的弧岩浆活动的产物。然后扬子地台与秦岭微陆块拼合, 形成勉略缝合带。约199Ma秦岭主造山期同碰撞岩浆活动形成了晚期(石榴石)二长花岗岩。因此, 勉略洋盆闭合和勉略缝合带形成时期大约为221～199Ma 。     

辽南梁屯-矿洞沟古元古代岩体LA-ICP-MS锆石U-Pb年龄及岩石地球化学特征

辽南梁屯-矿洞沟古元古代岩体包括坎子岩体、卧龙泉岩体、学校后街岩体与梁屯岩体,岩性分别为中细粒二长花岗岩、中细粒似斑状黑云母二长花岗岩、细粒黑云母二长花岗岩、细粒正长岩。学校后街岩体与梁屯岩体LA-ICP-MS锆石U-Pb年龄加权平均值为1 887.2±5.4 Ma、1 883.9±2.6 Ma,为古元古代。从坎子岩体到梁屯岩体岩石化学体现了一个偏铝-过铝型,钙碱性-碱性的演化序列,K及Mg O含量逐渐增高,富集大离子亲石元素K、Rb、Ba、Sr,亏损高场强元素Nb、Ta、Zr、Hf,稀土元素配分模式右倾,属具有负铕异常的轻稀土富集、重稀土亏损型。结合相关构造环境分析,古元古代岩体在辽河岩群沉积完成后存在着一个活动大陆边缘-碰撞造山-造山晚期,岩石类型由I型-S型-A型的演化过程。     

浅议宁夏西华山——南华山海原群的变形变质作用特征

海原群为一套绿帘角闪岩相的区域变质岩系,基本属总体有序,局部无序的变质地层。其主体变质作用为区域变质作用和韧性动力变质作用,发生时代为中元古代晚期（四堡期）一晚元古代中期（晋宁期）,加里东构遗运动使海原群发生了叠加区域变质作用。海原群变形变质构造演化及动力过程可划分为三个阶段。     

华北板块北缘中段中元古代晚期花岗岩类特征及其构造意义

华北板块北缘出露的中元古代晚期花岗岩主要为黑云母花岗岩和二长花岗岩,化学上富SiO₂和K₂O, 贫FeO、CaO、MgO和TiO₂,A/CNK平均大于1.1,具过铝质花岗岩特征。微量元素Nb、Sr、P、Ti相对亏损,而Rb、K、Ta、Nd相对富集;轻重稀土较强分馏,其(La/Yb)_N=6.61～64.31,负铕异常明显,具有碰撞成因S型花岗岩特征。花岗岩呈东西向带状展布,并与北侧白乃庙（白乃庙群）和阜新旧庙（魏家沟岩群）中元古代古岛弧链及开原蛇绿混杂岩带平行,这表明该区中元古代晚期存在一个强烈的俯冲碰撞造山过程,这一碰撞造山事件为华北板块在Rodinia超大陆的拼合模式提供了最基本的制约条件。     

Fission track age of granite batholith from Southern Tibet:implications for the plateau uplift

Fission track (FT) ages of apatite and zircon from four granite batholiths from Lhasa and Shannan areas are measured.The FT ages of apatite range from 3.2±8.3 Ma, corresponding to the uplift rates of 0.12±0.20 mm·a~(-1) during this period. The upliftheight is 580m, showing that there is not large-scale rapid uplifting in southern Tibet from 3.2 to 8.3 Ma. The zircon FT ages of Lhasabatholith are 25.9±1.7 and 32.7±2.8 Ma, yielding an uplift rate of 0.08 mm·a~(-1) between 26 and 33 Ma. Combining this work withother studies, it is suggested that the average uplift rate in southern Tibet is low from the time of collision between India and Asian conti-nents to ～3Ma. The uplift of Tibetan Plateau seems to have finished in multi-stage processes with varied rates.     

U-Pb zircon dating constraints on formation time of Qilian high-grade metamorphic rock and its tectonic implications

In order to constrain the formation time of high-grade metamorphic rocks in the Qilian Mountains, U-Pb zircon dating was carried out by using LA-ICPMS technique for a paragneiss of the Hualong Group in the Qilian Mountains basement series and a weakly foliated granite that intruds into the Hualong Group. Zircons from the paragneiss consist dominantly of detrital magma zircons with round or sub-round shape. They have 207Pb/206Pb ages mostly ranging from 880 to 900 Ma, with a weighted mean age of 891 ±9 Ma, which is interpreted as the magma crystallization age of its igneous provenance and can be taken as a lower age limit for the Hualong Group. Magma crystallization age for the weak-foliated granite is 875±8 Ma, which can be taken as an upper age limit for the Hualong Group. Accordingly, the formation time of the Hualong Group is constrained at sometime between 875 and 891 Ma. A few zir- cons from both paragneiss and weak-foliated granite display old inherited ages of 1000 to 1700 Ma and young metamorphic ages of Early Paleozoic. The zircon age distribution pattern confirms that the Qilian Mountains and the northern margin of Qaidam Basin had a united basement, with geotectonic affinity to the Yangtze Block. The results also reveal that sediments of the Hualong Group formed by rapid accumulation due to rapid crustal uplift-erosion. This process may result from intensive Neoproterozoic orogenesis due to assembly of the suppercontinent Rodinia.     

内蒙古东部索伦二叠纪哲斯组碎屑锆石U-Pb年龄及其大地构造意义

内蒙古索伦地区位于贺根山-黑河断裂和西拉木伦河-长春-延吉断裂之间,该区发育巨厚的二叠系哲斯组地层。研究其年代学特征对确定该区大地构造背景具有重要的指示意义。哲斯组50颗碎屑锆石镜下具有典型岩浆锆石特征,年代学记录表现为4个峰值:(1)[(270±2)～(335±4)]Ma,峰期年龄为(272±2)Ma,与该区晚古生代岩浆活动一致;(2)[(363±3)～(429±3)]Ma,峰期年龄为(382±4)Ma,暗示其物源来自于松辽地块及其周边地区的加里东期岩浆事件;(3)[(507±5)～(555±6)]Ma,峰期年龄为(515±3)Ma,与东北地区各地块的泛非期变质基底年龄一致;(4)少量前寒武纪年龄分别为(847±7)Ma、(923±7)Ma、(1 342±14)Ma、(2 040±13)Ma,表明东北地区存在元古宙的结晶基底。上述碎屑锆石的年代学研究表明,以泛非期和新元古事件年龄为代表,说明研究区哲斯组的物源应来源于东北地区的变质基底,其中年轻一组谐和年龄(270±2)Ma限定了哲斯组的沉积下限为晚二叠世。由于哲斯组的物源均来自于东北地区的变质基底,推测华北和西伯利亚板块的缝合位置在西拉木伦河-长春-延吉一线。     

U-Pb zircon age of the foliated garnet-bearing granites in western Dabie Mountains, Central China

U-Pb zircon dating on two foliated garnet-bearing granite samples in the western Dabie ultra-high-pressure (UHP) metamorphic unit yields concordant ages of (234±4) Ma and (227±5) Ma, respectively. These ages, following the UHP peak metamorphism, represent the magma emplacement ages for the foliated garnet-bearing granites. This, for the first time, shows that there are the Triassic granites in the Dabie Mountains. The foliated garnet-bearing granites resemble A-type granite in geochemical characteristics, indicating that they were formed in extensional geodynamic setting. The magma formation reflects a reheating event in the Dabie orogenic belt and it enhances the transfer of tectonic regime from collision into extension and promotes the rapid exhumation into lower crust for the UHP metamorphic rocks.     

Ore-forming event and geodynamic setting of molybdenum deposit at Wenquan in Gansu Province, Western Qinling

The Wenquan molybdenum deposit is associated with a Triassic granite in this area. The Wenquan granite is enriched in LILE and LREE, poor in HFSE, and has significantly higher contents of alkali （K2O＋Na2O） and Sr, Ba than those of the island arc volcanic rocks. These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series. Studies of major elements, trace elements, REEs and chronology of the Wenquan pluton show that, in the geodynamic transition stage of continent-continent convergence to extension, the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma, and the Wenquan pluton was formed by mixing of the two magmas. Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma, and an Re-Os isochron age of 214.4±7.1 Ma. These ages are close to K-Ar ages （223 to 226 Ma） and a SHRIMP zircon U-Pb age （223±7 Ma） for the Wenquan granite within the error range, but relatively younger. This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion, and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt （QOB） after continental collision between the North China Block （NCB） and the South China Block （SCB）. This process is also corresponding to the geological events of metamorphism and deformation in South Qinling, closure of the Mian-Lue oceanic basin, and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks. The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered significant crustal thickening and exhumation of subducted slab. In the late Triassic, the tectonic setting was transformed to the transition stage from collision to extension. Materials from the asthenospheric mantle would ascend into the root of the lower crust, which could induce partial melting of the lower crust and generate Mo-enriched granitic magma. The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization. The Mo deposits in the QOB are mainly formed in two episodes, namely 220± Ma and 140± Ma. The two episodes of metallogenesis were developed in the tectonic transition settings from compression to extension, but they were in the different stages of the tectonic evolution. The occurrence of the Wenquan Mo-bearing pluton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB. Therefore, it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.     

华北板块北缘中段新太古代的陆-陆碰撞事件: 来自合教S型花岗岩的证据

通过对内蒙古达茂旗合教地区具有明显构造意义的新太古代S型花岗岩的主量元素、微量元素及SHRIMP锆石U-Pb年代学的研究, 为揭示华北板块北缘新太古代末的构造环境提供了进一步的证据。合教花岗岩的主量元素特征表明它是高分异的强过铝 S 型花岗岩; 其里特曼指数 σ为0. 54 ～0. 57, 属于低钾钙碱性岩石。稀土元素总量为 243. 8 ～427. 1 μg/ g。球粒陨石标准化分配模式显示 LREE 相对富集, HREE 相对亏损; ( La/ Yb)_N为 14. 88～18. 18, Eu 具有较大的负异常( Eu*/ Eu = 0. 31 ～0. 65); 模式图总体呈一右倾的海鸥型。微量元素显示Nb, Ta, Zr, Hf, Ti 等高场强元素相对亏损。合教花岗岩的微量元素组成表明其来源于正常厚度的大陆地壳, 形成于低压高温的后碰撞环境, 相当于澳大利亚拉克伦造山带的S型花岗岩。合教花岗岩的SHRIMP锆石U-Pb年龄为2556±8Ma, 属于新太古代晚期。合教强过铝 S型花岗岩反映在新太古代晚期华北板块北缘中段可能发生了一次陆-陆碰撞事件, 也表明固阳地区同时期的赞岐岩可能形成于后碰撞环境而非板片消减带。     

Zircon SHRIMP dating of granite from Qaidamshan, NW China

Zircon SHRIMP dating from Qaidamshan granite shows that the granite age is 446 Ma, similar to that of eclogite in the UHP belt. We think that both granite and eclogite may be formed at different stages during tectonic evolution of this area. Together with other studies we suggested that the collision of ocean and continent plates may occur at the early Caledonian in this area, forming the eclogite, and the collision of continent and continent plates at the late Caledonian, forming the Qaidamshan granite with the zircon SHRIMP age of 446 Ma.     

恒山－五台地区同位素年代学与地质事件演化格架的认识

近10年在恒山和五台地区所获得的大量同位素年代学资料,统计发现恒山杂岩的同位素年龄峰值比五台杂岩大致要年轻20 Ma, 这与恒山－五台地区为岛弧根带－岛弧关系的推论相符合。综合各种不同的同位素测年结果按不同的地质体,进行了图解分析,将恒山－五台地区早前寒武纪的地质演化划分为3个大的阶段：2.70～2.60 Ga,早期演化（洋壳形成？）;2.55～2.52 Ga(?,最晚不晚于2.45 Ga),东西陆块俯冲碰撞阶段;2.50～1.75 Ga,早期盖层演化阶段。最后一个阶段有可以根据不同时段内研究区主要事件的不同,将2.50～1.75 Ga的演化分为5个时期。1）2.50～2.30 Ga表现为间歇性大陆溢流玄武岩的活动期;2）2.30～2.20 Ga华北较稳定沉降期,基本以接受沉积为主;3）2.20～2.10 Ga,构造活化期,五台地区主要有伸展非造山花岗岩（大洼梁花岗岩）的形成;4）2.10～1.85Ga阶段,地幔柱活动期？ 5）1.86～1.75 Ga,大规模基性岩墙形成期陆块裂解。     

Ages and tectonic significance of the collision-related granite porphyries in the Lhunzhub Basin, Tibet, China

The Paleocene collision-related granite porphyries are identified for the first time along the western margin of the Lhunzhub Basin, Tibet. SHRIMP U-Pb zircon analysis indicates that the granite porphyries were emplaced at 58.7±1.1 Ma (MSWD = 0.79) during the Indo-Asian continental collision. The granite porphyries are peraluminous and high in K, belonging to the calc-alkaline to high-K calc-alkaline series. They are relatively enriched in LILE, Th and LREE and depletion in Ba, Nb, P and Ti, characterized by LREE-enriched patterns with slightly to moderately negative Eu anomalies. These Paleocene granite porphyries are interpreted as the products generated by partial melting of the pre-existing arc crustal rocks caused by the increase of pressures and temperatures during the crustal shortening at the early stages of the Indo-Asian continental collision since 65 Ma. Despite inherited geochemical features and tectonic settings of the arc protoliths, they are significantly different from the volcanic rocks of the Dianzhong Formation within the Linzizong Group and the Miocene granite por- phyries in the Gangdise belt.