后碰撞花岗岩类的多样性及其构造环境判别的复杂性

造山带中普遍存在着相当数量的后碰撞花岗岩类。它们在时间上晚于碰撞事件形成,在空间上可以不受构造单元的严格控制,而是可以跨构造单元分布,有时可以侵入在蛇绿岩之中。后碰撞花岗岩类的主元素特征属于中—高钾钙碱性系列和钾玄岩系列,但以钙碱性系列为主。按照MISA分类,后碰撞花岗岩类可以有I、S和A等3种类型,有的造山带以发育I型花岗岩类为主,而另一些造山带可以广泛发育S型花岗岩,而碱性A型花岗岩并不是在每个造山带都会出现。在微量元素构造环境判别图解上,后碰撞花岗岩类可以落在多种构造环境的区域。因此,仅仅依靠花岗岩类构造环境的地球化学判别图解会得出似是而非的结果。文中强调时空分布特征及区域地质构造的全面分析可能是厘定后碰撞花岗岩类最重要的依据,而在区域地质研究基础上的高精度锆石U-Pb年代学研究能够建立区域构造演化的年代学框架,进而准确地限定后碰撞花岗岩类岩浆活动的时限。     

西秦岭与赛什塘铜矿床有关的花岗质岩石岩浆源区特征及大地构造背景探讨

西秦岭赛什塘铜矿区内出露的三叠纪花岗质岩石有闪长玢岩、石英闪长岩、石英闪长玢岩、花岗斑岩和石英斑岩,其岩浆源区与形成构造环境可为古特提斯洋演化和区域成矿作用研究提供证据。岩石地球化学特征共同表明,这些花岗质岩石属于准铝质钙碱性-高钾钙碱性系列,为I型花岗岩;Mg#值变化较大(39~68),LREE富集,HREE亏损,(La/Yb)N比值介于8.50~22.9,具有Eu负异常,δEu介于0.28~0.78,同时富集大离子亲石元素Cs、Rb、K、Pb,亏损高场强元素Nb、Ta、Ti,呈现出与典型俯冲作用密切相关岛弧花岗岩相一致地球化学特征。石英闪长玢岩和石英斑岩SHRIMP锆石U-Pb年龄分别为219.0±2.3Ma和220.0±2.0Ma,锆石εHf(t)分别为-4.5~-2.1和-2.5~+1.0,对应二阶段模式年龄分别为1392~1544Ma和1190~1415Ma。结合前人对西秦岭三叠纪花岗岩以及其南侧阿尼玛卿蛇绿混杂带研究成果,本文认为赛什塘铜矿区花岗质岩石与西秦岭同时期花岗岩形成于与古特提斯洋向北俯冲密切相关的大陆边缘弧环境,其岩浆源区为中元古代下地壳变基性岩,且岩浆可能受到地幔物质混染。     

Gold-hosting high Ba-Sr granitoids in the Xincheng gold deposit,Jiaodong Peninsula,East China: Petrogenesis and tectonic setting

The Xincheng deposit is the only large gold deposit with a proven reserve of >200 t gold hosted by the Early Cretaceous granitoids in northwest Jiaodong Peninsula, East China. The granitoids hosting this ore deposit comprise an inner medium- to fine-grained quartz monzonite and an outer medium- to coarse-grained monzogranite with distinctive K-feldspar megacrysts. LA–ICP–MS zircon dating yields U–Pb ages of 128 ± 1 to 132 ± 1 Ma and 127 ± 2 to 129 ± 1 Ma, for the quartz monzonite and the monzogranite, respectively. The Early Cretaceous ages obtained in our study are comparable with the 126–130 Ma age range reported for the Guojialing granitic suite. The monzogranites, typical high Ba–Sr granites, possess high SiO₂ (70.89–73.35%), K₂O (3.85–4.32%), total alkalis (K₂O + Na₂O = 8.08–8.68%), Sr (634–888 ppm), Ba (1395–2111 ppm) and LREE (59.43–145.88), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (114–297) and (La/Yb)_N (20–79) ratios. They have low MgO (0.23–0.62%), Cr (0.4–8.33 ppm) and Ni (0.47–2.92 ppm) contents. The typical high Ba–Sr signatures of the outer acidic monzogranites are also shared by the inner intermediate-acidic quartz monzonites, with a relatively higher abundance of these elements. The plagioclases in the quartz monzonites and monzogranites are oligoclase–andesine with An contents of 11.7–44.5%, and oligoclase with An contents of 12.9–29.3%, respectively, which both show the reverse zoning texture. The quartz monzonites have zircon ε_Hf(t) values of −21.3 to −13.9 (average −18.7), which are less negative and show larger variations than those of the monzogranites (ε_Hf(t) = −24.7 to −18.1, average −19.5). Detailed elemental, mineralogical and isotopic data suggest that the high Ba–Sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane accompanied by crustal assimilation, with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma, and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma. In combination with previous investigations, we suggest subduction of the paleo-Pacific slab beneath the North China Craton (NCC) and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high Ba–Sr granites.     

Age and tectonic setting of granitoid gneisses in the Eastern Desert of Egypt and south-west Sinai

Strongly deformed and locally migmatized gneisses occur at several places in the southern Eastern Desert of Egypt and in Sinai and have variously been interpreted as a basement to Pan-african (900 to 600 Ma) supracrustal and intrusive assemblages. A suite of grabbroic to granitic gneisses was investigated in the Hafafit area, which constitutes an I-type calc-alkaline intrusive assemblage whose chemistry suggests emplacement along an active continental margin and whose granitoid members can be correlated with the so-called Older Granites of Egypt.²⁰⁷Pb/²⁰⁶Pb single zircon evaporation from three samples of the Hafafit gneisses yielded protolith emplacement ages between 677 ± 9 and 700 ± 12 Ma and document granitoid activity over a period of about 23 Ma. A migmatitic granitic gneiss from Wadi Bitan, south-west of Ras Banas, has a zircon age of 704 ± 8 Ma, and its protolith was apparently generated during the same intrusive event as the granitoids at Hafafit. Single zircons from a dioritic gneiss from Wadi Feiran in south-west Sinai suggest emplacement of the protolith at 796 ± 6 Ma and this is comparable with ages for granitoids in north-east Sinai and southern Israel. None of the above gneisses is derived from remelting of older continental crust, but they are interpreted as reflecting subduction-related calc-alkaline magmatism during early Pan-african magmatic arc formation.     

长江源各拉丹冬花岗岩体的基本特征及其构造属性

在区域地质调查基础上,对各拉丹冬花岗岩的岩石化学、构造环境等进行了研究.该花岗岩体以硅、碱含量较高和高钾、低铝为特征,轻稀土富集,Eu负异常较明显,δ18O值为8.18‰~9.01‰,属正常δ18O花岗岩,副矿物组合为磁铁矿-榍石-磷灰石型.花岗岩体40 Ma的单颗粒锆石U-Pb年龄值,说明其时代应属喜马拉雅期.运用Pearce微量元素构造环境判别图解及R1-R2图解判别,各拉丹冬花岗岩属同碰撞花岗岩.     

Age and tectonic setting of the first orogenic gold deposit discovered in the Yanbian Region,NE China

The Yangjingou gold deposit in Jilin Province lies 11 km south of the large-scale Xiaoxinancha gold–copper deposit. Yangjingou orebodies are structurally controlled fault- or fracture-related auriferous quartz veins. This type of mineralization is significantly different from that of the Xiaoxinancha porphyry gold–copper deposit, and has mineral assemblages and fluid inclusion compositions typical of orogenic gold deposits. We suggest that the Yangjingou deposit is the first orogenic gold deposit discovered in the Yanbian area, even in all of NE China. Here, we present new isotopic dating and trace element analysis of the ore-hosting monzogranite and auriferous quartz veins within the deposit, in order to determine the age and tectonic setting of metallogenesis, and the geological conditions controlling gold mineralization. LA-ICP-MS U–Pb dating of zircons separated from the monzogranite yielded an age of 262.3 ± 1.3 Ma, indicating intrusion during the late Permian. Hydrothermal muscovite from auriferous quartz veins yielded a ⁴⁰Ar/³⁹Ar plateau age of 241.57 ± 1.2 Ma, indicating that gold mineralization occurred at 241 Ma. Trace element and REE compositions of the monzogranite and auriferous quartz veins are both indicative of the formation from a region of the upper mantle that previously underwent crustal contamination. Geochronological analysis indicates that the diagenesis and mineralization resulting in the Yangjingou gold deposit occurred during the late Permian–Early Triassic. The tectonic evolution of the region and comparison of this deposit with other mineralizing events indicate that the orebody formed during orogenesis associated with collision between the North China and Siberian cratons.     

北秦岭老君山和秦岭梁环斑结构花岗岩及构造环境——一种可能的造山带型环斑花岗岩

老君山和秦岭梁岩体产于秦岭造山带商丹缝合带北侧,其岩石普遍发育环斑结构,表现为碱性长石巨晶多为卵球状,有些发育斜长石外壳,有些不发育。这不同于一般花岗岩局部出现的具斜长石外壳自形碱性长石巨晶结构。在地球化学上,该岩石显示I—A型花岗岩过渡特点。区域背景、构造被动定位特点和地球化学综合分析表明,它们可能定位于后碰撞或后造山环境。这些特征与典型的元古代克拉通非造山环境中的环斑花岗岩既有相似之处,也有一定差异,而与巴西造山带中环斑花岗岩较为相似。本文认为,它们不是一般的斑状花岗岩,而是最近注意研究的环斑结构花岗岩,有可能是一种造山带型环斑花岗岩,即产于造山带中的非典型环斑花岗岩。     

华南东段加里东期花岗岩类形成构造背景探讨

根据近年对区域地质调查取得的认识和前人的研究成果,研究了华南东段加里东期花岗岩类的地质产状、分布规律、形成时代以及Nd、Sr同位素特征;结合研究区超镁铁质-镁铁质岩及火山岩的形成时代、震旦纪—奥陶纪的沉积环境、加里东期构造事件的构造变形特征,对加里东期花岗岩类的形成背景进行了探讨。结果表明,加里东期花岗岩类形成于410～460Ma,大部分岩体属于S型花岗岩,岩浆来源于地壳物质的部分熔融;极少数为I型花岗岩,有幔源物质参与。研究区在早古生代不存在与俯冲有关的弧火山岩,也不存在大面积的早古生代I型花岗岩,震旦纪—奥陶纪地层主要形成于浅海环境。研究提出,加里东期花岗岩类主体形成于板内构造环境。     

新疆卡特巴阿苏金铜矿床地质特征及构造环境

新疆卡特巴阿苏金铜矿床位于新疆西天山那拉提构造带的北缘,主要赋存于晚泥盆世二长花岗岩之中。推测富矿二长花岗岩形成于俯冲-碰撞-造山的构造环境,可能是以下动力过程的产物:伊犁中天山南缘地壳解体,地幔物质强烈加入形成的新生南天山洋壳,向北沿那拉提构造带俯冲,部分熔融后在碰撞-造山晚期于晚泥盆世侵入,且与海西运动早期的地质事件关系密切。成矿年龄推测为二叠纪,与成岩年龄相差约91Ma,所以成矿物质应该不是来源于二长花岗岩。从成矿构造与矿体关系及矿石结构构造特征来看该矿受到断裂和节理裂隙系统的联合控制,且在成矿期经历了一次先挤后张的地质构造事件。结合区域构造演化,推测此次地质构造事件应该与二叠纪塔里木地台北缘一带发生的裂谷引张作用有关。     

Age and evolution of scheelite-hosting rocks in the Felbertal deposit (Eastern Alps): U-Pb geochronology of zircon and titanite

U-Pb isotope analyses of zircon and titanite extracted from different rocks of the Felbertal scheelite deposit yield the following information: (1) An age of 593±22 Ma (2) is obtained for zircon crystallization in the scheelite-bearing matrix of an eruption breccia in the western ore field. (2) Discordant zircons from an elongated, up to 8 m thick scheelite-rich quartzite body in the eastern ore field give an upper intercept age of 544±5 Ma. This quartzite contains a laminated, fine-grained scheelite mineralization. (3) Zircons from a small granitoid intrusion of the western ore field reveal an age of 336±16 Ma, and concordant titanites document an age of 282±2 Ma for Variscan amphibolite facies metamorphism. Both events, granitoid intrusion and later metamorphism caused ore re-mobilization, including the formation of yellowish fluorescent (molybdo-) scheelite porphyroblasts. (4) For a narrow lamprop-1hyric dike in the western ore field, a concordant titanite age of 283±7 Ma is obtained. This age is identical with the titanites from the amphibolite facies metamorphic intrusion. Tiny scheelite grains were tapped by the dike from pre-existing scheelite mineralizations in the truncated host rocks. (5) Alpine metamorphism at 31±4 Ma did not exceed lowermost amphibolite facies conditions, and it caused scheelite re-mobilization on a minor scale only, producing bluish fluorescent porphyroblasts in quartz veinlets and veins, as well as bluish fluorescent scheelite rims around older scheelite grains. Moreover, crosscutting Alpine fissure fillings show bluish fluorescent, inclusion-free scheelite. (6) The preservation of Variscan titanites, the absence of Alpine titanite growth, and the large degree of Variscan scheelite re-mobilization demonstrate that amphibolite facies metamorphism in the Felbertal area has a Variscan age. This result clearly documents Variscan tectono-metamorphism to be the dominant event, instead of the hitherto surmised Alpine metamorphism. This multi-stage evolution of the Felbertal ore bodies corroborates the view that tungsten deposits are conditioned by several succeeding thermal events, leading to a series of stages that ultimately produce high-grade scheelite concentrations. These high-grade ores predominately occur along shear zones of different age, accompanied by the formation of large volumes of low-grade scheelite mineralizations along host rock foliations and quartz veinlets and veins.     

Age and tectonic setting of the Kengurak-Sergachi gabbro-anorthosite massif (the Selenga-Stanovoi superterrane,southern frame of the Siberian craton)

The results of geochemical and geochronological study of the Kengurak-Sergachi gabbroanorthosite massif in the Selenga-Stanovoi superterrane, southern frame of the Siberian craton, are presented. According to geochemical peculiarities, the massif rocks are close to the autonomous “massif-type anorthosite.” The massif age corresponds to 1866 ± 6 Ma based on the results of U-Pb zircon dating. The Kengurak-Sergachi massif was intruded most likely in post-collision epoch concurrently to formation of the South Siberian giant post-collision magmatic belt (1.87–1.84 Ga) extending along the southwestern flank of the Siberian craton.     

内蒙古白乃庙铜金矿床的成矿时代和成矿构造背景

内蒙古白乃庙铜金钼矿床位于华北板块北缘的中亚造山带的温都尔庙加里东期增生带内,其成矿时间、成因类型和构造环境一直存在分歧.为确定成矿时间,作者运用高精度单颗粒激光熔融氩氩法对含矿石英脉中的黑云母和白云母矿物进行了年龄测定.获得黑云母样品22点40Ar/39Ar等时线年龄为396±2 Ma(MSWD=20),白云母样品23点40Ar/39Ar等时线年龄为358±2 Ma(MSWD=11),确证矿床形成于泥盆纪.矿区斑岩等岩浆岩类侵位年龄为428～466 Ma,早于成矿年龄至少40 Ma;赋矿地层白乃庙群形成于1130Ma左右,早于成矿时间约700Ma.如此大的年龄差表明白乃庙矿床不是斑岩型或海底喷流沉积型矿床,而是通过矿床地质和流体包裹体研究所确定的造山型铜金矿床.白乃庙矿床的成矿年龄与赋矿地层白乃庙群的峰期变质作用年龄(384.5±6Ma)基本一致,也与晚志留世-泥盆纪时温都尔庙增生岩浆弧与华北克拉通北缘的碰撞拼贴时间吻合,因此认为白乃庙铜金矿床形成于碰撞造山体制,是世界首例造山型铜矿床.     

小兴安岭-张广才岭成矿带福安堡钼矿区花岗岩类的岩石成因和构造背景:元素地球化学、锆石U-Pb年龄和Sr-Nd-Hf同位素约束

小兴安岭-张广才岭成矿带位于华北克拉通北缘东北段、中亚造山带东南段和西环太平洋外带交汇部位,经历了多期次的叠加改造运动,使得该区成为研究大陆造山带地质构造演化、地质构造域转换以及构造作用叠合成矿的理想区域.本文选择小兴安岭-张广才岭成矿带南段的福安堡钼矿区的二长花岗岩和花岗闪长岩进行岩石学、LA-ICP-MS锆石U-P...     

西藏达金砾岩的沉积时代、物源及构造背景

达金砾岩出露于西藏阿里地区冈仁波齐峰南麓,因其地层中发现深海有孔虫化石而受到广泛关注,然而由于达金砾岩的沉积时代不确定,对其沉积的大地构造背景也没有统一的认识。本文中,根据最年轻的碎屑锆石U-Pb年龄限定达金砾岩的最大沉积时代为渐新世末-中新世初(24~27Ma)。综合野外观察,砂岩碎屑统计和碎屑锆石U-Pb年龄分析,本文认为达金砾岩的底部和顶部地层中碎屑物质直接来源于北侧的冈底斯弧,而其中部地层中碎屑物质(包括有孔虫化石)应再旋回自西侧的弧前盆地错江顶群地层。达金砾岩与上覆的冈底斯砾岩连续沉积,且其沉积时代,源区分析结果都与冈底斯砾岩一致,因此本文认为达金砾岩应隶属于冈底斯砾岩。达金砾岩地层变形较弱,产状近乎水平,应沉积于拉张应力背景下,可能与渐新世末-中新世初俯冲的印度板片的"折返"和"断离"有关。     

Kuranakh complex diabases in the western part of the Aldan-Stanovoi Shield: Age and tectonic setting

The age of Kuranakh Complex diabases in the western part of the Aldan-Stanovoi Shield determined by the zircon U-Pb method is virtually identical to that of basic rocks in the Chinei stratified pluton and granites in the Kodar Complex. Thus, it is possible to suggest that they form a unified bimodal magmatic association and belong to the South Siberian postcollision magmatic belt, which extends along the southwestern framing of the Siberian Craton for more than 2500 km from the Yenisei mountain range to the Aldan-Stanovoi Shield. The occurrence of the diabase dike swarms in magmatic associations of this belt testifies to formation under lithospheric extension conditions.     

新疆东天山觉罗塔格地区花岗岩类年代学、构造背景及其成矿作用研究

东天山觉罗塔格地区岩浆岩非常发育,以花岗岩类分布最为广泛,对其研究还较为薄弱。本文对觉罗塔格地区主要的花岗岩类岩体系统开展了地质特征研究并进行了同位素精确测年,报道了区内16个主要花岗岩类岩体的锆石LA-ICPMS U-Pb年龄：镜儿泉岩体376.9±3.1Ma、西凤山岩体349.0±3.4Ma、石英滩岩体342±11Ma、长条山岩体337.4±2.8Ma、天目岩体320.2±3.1Ma、百灵山岩体317.7±3.7Ma、白石泉岩体303±18Ma、迪坎岩体288.0±2.5Ma、黄山岩体288±17Ma、白山东岩体284.5±4.5Ma、管道岩体284.1±5.8Ma、红石岩体282.7±4.2Ma、陇东岩体276.2±2.5Ma、多头山岩体271.7±5.5Ma、双岔沟岩体252.4±2.9Ma、土墩岩体246.2±2.6Ma,上述定年结果为研究区岩浆活动与区域构造演化及深部过程的关系研究提供了可靠的年代学支持。结合前人已有的部分年代学成果认为,觉罗塔格地区花岗岩类的形成年龄分布在386~230Ma之间,岩浆活动可分为晚泥盆世(386.5~369.5Ma)、早石炭世(349~330Ma)、晚石炭世-晚二叠世(320~252Ma)、早中三叠世(246~230Ma)等4个阶段。前3个阶段岩浆活动具有持续时间逐渐变长、岩浆活动逐渐加剧的特点,并在第三阶段达到顶峰,而第四阶段岩浆活动则明显变弱。花岗岩类岩浆活动在时空分布上表现为,自哈尔里克-大南湖岛弧带→阿奇山-雅满岛弧带→康古尔-黄山韧性剪切带,岩体侵位由早到晚; 自研究区东部→中西部→沿韧性剪切带,岩体侵位由老到新。结合区域构造演化研究成果认为,觉罗塔格地区花岗质岩浆活动与区域构造演化具有很强的耦合关系,花岗岩类在前碰撞阶段、主碰撞阶段、后碰撞阶段、板内阶段等4个构造演化阶段均有发育,与花岗岩类在时间分布上的4个阶段完全对应,其中尤以后碰撞构造演化阶段花岗岩类的分布最广泛、岩浆活动最强烈。觉罗塔格地区与4个阶段花岗岩类有关的成矿作用由早到晚具有无明显矿化→斑岩型铜矿、火山岩型铁矿→韧性剪切带型金矿、夕卡岩型银(铜)矿→斑岩-石英脉型钼矿的演化特点,其中以对应于主碰撞阶段的斑岩型铜矿和后碰撞阶段的韧性剪切带型金矿最为发育。本文系统阐述了东天山觉罗塔格地区中酸性岩体的时空格架、与区域构造演化的耦合、与成矿作用的关系,为北疆地区晚古生代特别是后碰撞背景下的岩浆演化及其成矿关系的研究提供了有力支持。