塔里木二叠纪基性-中性-酸性岩浆岩的年代学及其地质意义

塔里木西部柯坪地区出露的早二叠纪玄武岩与盆地内其他地区广泛分布的玄武岩共同构成一个面积约0.25Mkm²的溢流玄武岩省。巴楚地区出露的早二叠纪辉绿岩、正长岩、石英正长岩与石英正长斑岩等多种岩浆岩构成了连续的基性-中性-酸性岩浆序列。野外露头观察表明,巴楚麻扎尔塔格地区的基性-中性-酸性岩浆岩为近同时侵位。柯坪塔格开派兹雷克组顶部层位玄武岩的锆石SHRIMP U-Pb年龄为279.0±4.5Ma, 该年龄值可限定该区二叠纪溢流玄武岩喷发的最晚时限。巴楚麻扎尔塔格石英正长斑岩脉的锆石SHRIMP U-Pb年龄为273.0±3.7Ma, 与前人测定的巴楚辉绿岩脉和正长岩的锆石年龄在误差范围内一致,表明巴楚地区的基性-中性-酸性岩浆岩为近同时侵位,时间在275Ma左右。综合已发表的塔里木二叠纪岩浆岩高精度年代数据,本文提出：整个塔里木大火成岩省岩浆作用的持续时间约为20Myrs; 291~287Ma喷发的巨量溢流玄武岩可能构成塔里木大火成岩省的主体,是地幔柱头部熔融的直接产物; 283~272Ma侵位的巴楚、一间房和塔北地区的其它类型岩浆岩体积较小,为塔里木大火成岩省晚期岩浆作用的产物。     

Fractionation,hybridisation and magma-mixing in the Kialineq centre East Greenland

The igneous rocks of the Kialineq centre on the coast of East Greenland at 67°N include a number of quartz syenite and granite plutons intruded 35my BP. These are subvolcanic bodies emplaced by cauldron subsidence and with ring-dike and bell-jar form. Associated with the major intrusions is an extensive acid-basic mixed magma complex. Two-liquid structures, chilling of basic against acid magma, pillows of basic in acid, and net-veining of basic by acid magma, are superbly displayed. The basic magma was of a transitional or alkaline type and underwent varying degrees of fractionation in a regime of repeated intrusions and diverse chambers. Heterogeneous hybrid rocks intermediate between basalt and quartz syenite are strongly developed and were formed by repeated mechanical mixing of contrasting magmas. The energy for this mixing probably came in the main from cauldron-block subsidence. The quartz syenite magma, which itself fractionated towards granite, has initial ⁸⁷Sr/⁸⁶Sr ratios the same as the basic magma and is itself believed to be a fractionation product of alkali basalt magma.     

Structural setting, hydrothermal alteration, and gold mineralisation at the Archaean syenite-hosted Jupiter deposit, Yilgarn Craton, Western Australia

The Jupiter gold deposit in the northeastern Eastern Goldfields Province of the Yilgarn Craton of Western Australia is hosted in greenschist facies metamorphosed tholeiitic basalt, quartz–alkali-feldspar syenite, and quartz–feldspar porphyry. Syenite intrudes basalt as irregularly shaped dykes which radiate from a larger stock, whereas at least three E–W and NE–SW striking quartz–feldspar porphyries intrude both syenite and basalt. Brittle–ductile shear zones are shallow-dipping, NW to NE striking, or are steep-dipping to the south and west. Quartz ± carbonate veins that host gold at Jupiter occur in all lithologies and are divided into: (1) veins that are restricted to the shear zones, (2) discrete veins that are subparallel to shear zone-hosted veins, and (3) stockwork veins that form a network of randomly oriented microfractures in syenite wallrock proximal to shallow-dipping shear zones. The gold-bearing veins comprise mainly quartz, calcite, ankerite, and albite, with minor sericite, pyrite, chalcopyrite, galena, sphalerite, molybdenite, telluride minerals, and gold. Proximal hydrothermal alteration zones to the mineralised veins comprise quartz, calcite, ankerite, albite, and sericite. High gold grades (>2 g/t Au) occur mainly in syenite and in the hanging walls to shallow-dipping shear zones in syenite where there is a greater density of mineralised stockwork veins. The Jupiter deposit has structural and hydrothermal alteration styles that are similar to both granitoid-hosted, but post-magmatic Archaean lode-gold deposits in the Yilgarn Craton and intrusion-related, syn-magmatic, syenite-hosted gold deposits in the Superior Province of Canada. Based on field observations and petrologic data, the Jupiter deposit is considered to be a post-magmatic Archaean lode-gold deposit rather than a syn-intrusion deposit. Received: 5 January 1999 / Accepted: 24 December 1999     

塔里木盆地二叠纪火成岩的同位素年代学

在分区概述了塔里木盆地二叠纪火山一沉积地层的划分和对比的基础上,本文报道了2件玄武岩样品、2件辉长岩样品、1件辉绿岩样品、1件正长岩样品、1件英安斑岩样品和1件花岗闪长岩样品的锆石U-Pb法定年,表明强烈的火成活动发生在早二叠世（玄武岩定年294 Ma,287 Ma）,可延续到中二叠世（辉长岩定年265 Ma）.空间上,火山活动的中心位于巴楚一柯坪地区.玄武岩喷发可分为2个旋回,分别称南闸组和阿恰群中（火山岩）段;前者伴有英安斑岩（285 Ma）喷发和辉长岩（283.1 Ma）、辉绿岩（283 Ma）侵入,正长岩（281.7 Ma）则代表了区域上岩浆分异的晚期阶段.巴楚及邻近地区辉绿岩规律的北西走向指示了区域拉张应力场方向为北东一南西向.Ar-Ar法测年未获得理想的坪年龄值,仍支持了二叠纪早期发生过热事件的认识.     

赣东北前寒武纪岩浆混合作用岩带的发现及其地质意义

在总结新近发现的赣北前寒武纪岩浆混合岩带地质特征的基础上,从地质学、岩相学和同位素地球化学的角度,论证了发生于这一特殊地质时期和地质背景下的岩浆混合作用。文中将该作用形成的岩浆混合杂岩体有效地分解为：（１） 偏酸性端员的岩浆岩（ 角闪石英正长岩、石英正长岩） ;（２） 基性端员岩浆岩（ 玄武玢岩、玄武安山玢岩） 和（３） 岩浆混合岩,后者又可分为非均一岩浆混合岩和均一岩浆混合岩（ 如石英二长闪长岩） 。阐明该岩浆混合作用是新元古期我国东南地区江南古洋向扬子古陆俯冲消减这一构造演化的重要物质表现;示踪该地区于中元古期（１４８ ～１８５ Ｇａ） 经历了一次与全球范围一致的壳 幔分离事件和新元古期（０８５ Ｇａ） 亏损地幔与大洋沉积物在源区混合的事件;确认该地区前寒武纪的岩浆混合作用和岩浆侵入作用实际上是一个连续的岩浆作用序列,并且两者受近南北向挤压的同一应力场条件所制约     

江西广丰早白垩世中晚期盆地火山-侵入杂岩活动序列确认及地质意义

江西广丰早白垩世盆地座落在124.51±11.9Ma(Rb-Sr等时线)石溪组火山岩系之上,是一个由湖进到湖退、具完整2级层序的湖相盆地;盆地湖进期沉积岩中穿插有斑岩岩脉群(正长斑岩、花岗斑岩),Rb-Sr等时线年龄为110.83±3.16Ma,U-Pb不一致曲线下交点105.4±1.3Ma,盆地最大湖面时期伴有碱性玄武岩的溢出,K-Ar年龄为100～104Ma,盆地湖退时期伴有亚碱性拉斑玄武岩溢出,K-Ar年龄为98～103Ma。同位素年代学无法区分其早晚,但野外迭置关系及沉积岩序可判别出早晚,这就构成了伴随盆地形成过程的火山-侵入杂岩活动序列,即中酸性岩脉→碱性玄武岩→拉斑岩武岩,该序列对探索该区早白垩中晚期拉张盆地的成因机制具有启迪意义。     

Geology of Pulikonda and Dancherla alkaline complexes,Andhra Pradesh

Geological studies on saturated to oversaturated and subsolvus aegirine-riebeckite syenite bodies of the Pulikonda alkaline complex and Dancherla alkaline complex were carried out. The REE distribution of the Dancherla syenite shows a high fractionation between LREE and HREE. The absence of Eu anomaly suggests source from garnet peridotite. The Pulikonda syenite shows moderate fractionation between LREE and HREE as reflected by enrichment of HREE and moderate enrichment of LREE. The negative Eu anomaly indicates role of plagioclase fractionation.Three distinct co-eval primary magmas i.e. mafic syenite-, felsic syenite- and alkali basalt magmas — all derived from low-degrees of partial melting of mantle differentiates and enriched metasomatised lower crust played a major role in the genesis and emplacement of the syenites into overlying crust along deep seated regional scale trans-lithospheric strike-slip faults and shear zones following immediately after late-Archaean calc-alkaline arc magmatism at different time-space episodes i.e. initially at craton margin and later on into the thickened interior of the Eastern Dharwar craton. The ductile sheared and folded Pulikonda alkaline complex was evolved dominantly from the magmas derived from partial melting of lower crust and minor juvenile magmas from mantle. Differentiation and fractionation by liquid immiscibility of mafic magma and commingling-mixing of intermediate and felsic magmas followed by fractionational crystallisation under extensional tectonics during waning stages of calc-alkaline arc magmatism nearer to the craton margin were attributed as the main processes for the genesis of Pulikonda syenite complex. Commingling and limited mixing of independent mantle derived mafic and felsic syenitic magmas and accompanying fractionation resulting into soda rich and potash rich syenite variants was tentatively deduced mechanism for the origin of Dancherla, Danduvaripalle, Reddypalle syenites and other bodies belonging to Dancherla alkaline complex at the craton interior. The Peddavaduguru syenite was formed by differentiation of alkali mafic magma (gabbro to diorite) and it’s simultaneous mingling with fractionated felsic syenitic magma under incipient rift. Vannedoddi and Yeguvapalli syenites were derived due to desilicification and accompanying alkali feldspar mestasomatism of younger potash rich granites along Guntakal-Gooty fault and along Singanamala shear zone respectively.     

A likely reason for the appearance of the Daly Gap in magmatic series of large igneous provinces: Geological and petrological evidence

The problem of the Daly Gap is considered for the example of bimodal basalt–trachyte series and their intrusive analogs (layered syenite–gabbro intrusions). It is shown that the gap is not controlled by the processes of crystallization differentiation or liquid immiscibility in intermediate chambers of igneous systems (intrusive chambers) and has a primary nature. We interpret its origin as from the existence of two independent types of melts from the materials of head parts of the same mantle plumes. These are mid-alkali Fe–Ti basalt, products of its adiabatic melting, and trachyte, which is the result of incongruent melting of the material of the upper cool rims of plumes under the influence of fluids percolating from the underlying zone of adiabatic melting.

     

Petrology of Igneous Rocks in Northern Golpayegan, Iran

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The petrogenetic interrelationship of Wajilitag complex components in the early Permian Tarim large igneous province,NW China

ABSTRACT

The Permian Tarim large igneous province (TLIP) is located in the Tarim basin, NW China. Although the flood basalt of the TLIP has been intensively studied, other igneous components within TLIP have not yet been sufficiently investigated. The Wajilitag igneous complex is outcropped with a rather limited exposure by regional tectonic uplift. However, various igneous rocks, both mafic–ultramafic and syenitic, can be observed as either intrusions or extrusions in this area. It is an ideal location for studying the magmatic evolution of different components within the TLIP. We systematically examine the geological, geochronological, and geochemical characteristics of the Wajilitag complex, to further constrain the petrogenesis of each component and their interrelationships, as well as the implications to the petrogenetic model of TLIP. The igneous rocks in Wajilitag complex can be classified into two series based on their geochemical features: Series A and Series B. Series A are more alkalic, more trace element enriched and more isotopically depleted than Series B. Series A includes nephelinite, aegirine–nepheline syenite (ANS), and syenite porphyry (SP), whereas the Series B consists of clinopyroxenite, gabbro, diorite, hornblende-bearing syenite (HS), and quartz syenite (QSN). Dolerites can either belong to Series A or Series B depend on its geochemistry. Kimberlitic rocks are independent of the Wajilitag complex geologically, geochemically, and geochronogically. The temporal sequences of Wajilitag complex would be clinopyroxenite→gabbro→ diorite/syenite→nephelinite. The dolerite can be emplaced later than the syenite but can extend to an earlier period. In contrast to the Tarim basalts, the Wajilitag complex belongs to the second stage of magmatism in the TLIP. The mantle source for the Tarim basalts, the Series B and Series A gradually changed from SCLM-dominated to plume-dominated component.     

Two A—type Syenite—Granite Belts in Anhui

There exist two parallel A-type syenite-granite belts on both banks of the Yangtze River in Anhui Province: one is the Dalongshan-Chengshan-Huangmeijian belt on the north bank and the other is the Huayuangong-Maotan-Banshiling belt on the south bank. Both of them consist of syenite, quartz-syenite and alkali feldspar granite, which were formed at about 125 Ma ago and are enriched in alkalies and high-field-strength elements but depleted in water, with the total alkali accounting for 9–12%. and H₂O⁺ only for 0.50%. The Ga× 10⁻⁴/Al ratio is as high as 2.7 to 3.8 for granite. They were formed in the extension stage of ancient rifting. So they are considered to be the A-type syenite-granite belts. Granites in the two belts resulted from a syenite magma by an AFC mechanism while the magma was derived from alkali basalt magma through the fractional-crystallization-dominated AFC mechanism. Financially supported by the National Eighth-Five-Year Science and Technology Breakthrough Project No. 85-901-03-04.     

Crust-mantle interaction in the evolution of the Ilímaussaq Complex, South Greenland: Nd isotopic studies

Sm-Nd isotopic compositions were determined for the peralkaline Ilímaussaq Complex of the Gardar Province of southern Greenland. The majority of the samples in the agpaitic and augite syenitic units have near chondritic initial _Nd(≈ 0), whereas a few samples trend towards _Nd values as low as − 6 at the time of intrusion (1143 Ma). This latter value, from a sample taken from the margin of the complex, lying on the evolutionary trend for Ketilidian country-rock granitoids, suggests that large-scale contamination took place only at the margins of the complex. The similarity of the Nd isotopic compositions of the augite syenite and agpaitic units suggests that their parental magmas were derived from the same reservoir. A comparison of the Nd with existing Sr and Hf isotopic data for the complex suggests an origin by combined assimilation fractionation processes. Assimilation-fractional crystallization modeling of the isotopic compositions indicates that the Ilímaussaq magmas could have formed through fractional crystallization of a basaltic melt while assimilating granitic crust. The model requires initially higher assimilation rates from basalt to augite syenite composition with subsequent decreasing assimilation rates from augite syenite to agpaitic compositions. Alkali granites, which formed after the intrusion of the augite syenites, have isotopic compositions intermediate between those of the augite syenites and the surrounding Ketilidian basement. This implies even greater amounts of assimilation and is interpreted as evidence for an origin through fractionation of a basaltic or augite syenite magma with concurrent assimilation of Ketilidian crust.     

“康滇地轴”北段花岗岩岩浆类型及其含矿性

康滇地轴位于扬子地台西部边缘,是我国著名的南北向构造带。在其北段广泛分布着不同时代、不同类型的花岗岩,沿安宁河深断裂和金河—箐河深断裂构成了南北向花岗岩带。这些花岗岩可分为两大类。一、陆壳重熔S型花岗岩,二、上地幔基性岩浆分异的Ⅰ型花岗岩。它们在时空分布、岩石化学性质、含矿性和成岩机理等方面都备具不同的     

Isotopic Geochronology of the Xianghongdian Alkaline Complex, Northern Margin of the Dabie Mountains, China

To the north of the Qinling-Dabie orogen there exists a Mesozoic (K1) granite-syenite belt called the Beihuaiyang granite-syenite belt, in which the Xianghongdian alkaline complex outcrops in the Devonian Foziling schist and also intruded into the slightly earlier volcanic rocks. This alkaline complex is composed of syenite, alkaline syenite and nepheline syenite, but the nepheline syenite occurs inside the alkaline syenite in the pod-like, irregular, lenticular or layered shape. Researches on the petrogenesis of the alkaline complex and the relationship between the alkaline syenite and the nepheline syenite must rely on precise isotopic ages. Previous researches have reported iso-topic dating results merely by the 40Ar/39Ar method on hornblende and biotite separated from the alkaline syenite and nepheline syenite. In view of this, the authors have made fairly detailed isotopic geochronological studies of the alkaline syenite and nepheline syenite by using Rb-Sr isochron for the whole rock and minerals,     

赛马-柏林川碱性杂岩常量组分变异的分离结晶制约

赛马－柏林川碱性杂岩体为侵位于古元古宙与新元古宙之间的缓倾斜岩席状岩体,缓倾的张裂隙制约了分异岩浆的侵位和含矿溶液的流通,交代富集的上地幔产生的富碱岩浆与富集的地壳产生的岩浆以不同比例混合,形成了正长质岩浆和霞石正长质岩浆。含地壳组分较高的正长质岩浆,受富钙辉石、角闪石和镁质较高黑云母的结晶分离制约向硅酸过饱和方向演化;霞石正长质岩浆受富钙辉石—霓辉石、白榴石、含Ｆｅ较高黑云母、黑榴石的分离结晶制约发生分异。稀土元素矿床是霞石正长质岩浆分异残余熔体的产物,侵位于岩体最高层位。     

Magmatic evolution and rare earth element enrichment of Saima alkaline complex,Liaoning, ChinaSCIEI北大核心CSCD

赛马碱性杂岩体位于我国辽东半岛,是一个典型的铀-铌和稀土多金属矿化杂岩体,富含重稀土,其复杂的演化过程和稀土元素富集机制仍没有得到有效约束。本文对该碱性杂岩体中角闪辉石正长岩、正长岩、黑云正长岩、云霓霞石正长岩和异霞正长岩5类岩石及锆石的元素地球化学特征进行了系统研究,并开展了特征矿物包裹体的显微岩相学研究,旨在限定杂岩体母岩浆的演化路径,揭示稀土元素的富集机制。研究结果显示,赛马碱性杂岩体的母岩浆经历了由钾质碱性(角闪辉石正长岩、正长岩和黑云正长岩),到钾质过碱性(云霓霞石正长岩),向钠质过碱性(异霞正长岩)的充分演化。在演化过程中赛马碱性杂岩体母岩浆的体系状态发生了明显变化,碱性岩浆演化受流体不饱和的纯岩浆体系的控制,而过碱性岩浆岩则形成于流体过饱和的岩浆体系,且异霞正长岩母岩浆流体的饱和程度明显高于云霓霞石正长岩的母岩浆。研究还显示,钾质碱性岩浆稀土元素的地球化学行为主要受控于磷灰石等矿物的分离结晶,而成矿的钠质过碱性岩浆稀土、锆和铌等元素的富集成矿则主要受富CO_(2)的高盐度岩浆热液的控制。     

西藏冈底斯南缘雄村铜金矿床成矿斑岩厘定及其锆石U-Pb和黑云母Ar-Ar年龄分析

雄村特大型斑岩铜金矿床主要以细脉浸染状产于强烈蚀变岩石中,赋矿岩石原岩成因类型存在争议。本文对多个赋矿蚀变岩石作了系统光薄片显微鉴定,在多个蚀变较弱的矿化样品中发现赋矿岩石具斑状结构,其基质主要为钾长石,斑晶主要为斜长石、钾长石及少量石英,显示石英正长斑岩及二长斑岩(少量)矿物组成特征。结合前人工作,可以认为雄村铜金矿床赋矿岩石为正长斑岩、火山岩及少量二长斑岩。正长斑岩发育斑岩铜金矿床成矿早期常见的钾硅化蚀变及磁铁矿化蚀变,锆石具高的Ce4+/Ce3+比值(334~3084,平均值为1169),显示高氧逸度岩浆特征,和世界斑岩铜金矿床成矿岩体一致;这表明石英正长斑岩为雄村铜金矿床成矿岩体。石英正长斑岩锆石LA-ICP-MS U-Pb年龄为173.7±2.1Ma(MSWD=0.23),石英正长斑岩钾化阶段形成的黑云母40Ar/39Ar坪年龄为48.3±0.9Ma(MSWD=1.58),远小于锆石U-Pb年龄却与矿区东北部始新世花岗岩基的年龄一致,显示Ar-Ar年龄受后期地质事件影响而发生重置。通过上述研究,可以认为雄村铜金矿床为与石英正长斑岩有关的斑岩型矿床,形成时代约173Ma,和新特提斯洋洋壳向北俯冲诱发的岩浆事件有关,矿区内云母受后期地质事件影响重置,不能记录其形成时代。     

湖北观子山硬玉钙霞正长岩初步研究

观子山侵入体从岩体中心到边部，由硬玉钙霞正长岩、硬玉正长岩和黑云角闪正长岩组成。本文着重讨论硬玉钙霞正长岩的岩石学、矿物学、岩石化学、REE的地球化学、时代及岩石成因。据Rb-Sr等时线测定，其年令值为306Ma，说明它形成于海西期。根据产状、FeO/MgO,^δSr/^δSr（i）、REE分配模式以及形成硬玉的压力温度条件，足以证明硬玉钙霞正长岩的成因与上地幔物质有关。     

Petrogenesis of syenites at a rifted continental margin: origin,contamination and interaction of alkaline mafic and felsic magmas in the Astrophyllite Bay Complex,East Greenland

The Astrophyllite Bay Complex in East Greenland (part of the Palaeogene North Atlantic Igneous Province) consists of an alkaline diorite plug, with detached trachyandesitic pillows, surrounded by co-magmatic syenite that was emplaced into Archaean basement. The diorite intrusion has yielded a 47.11 ± 0.68 Ma Rb-Sr isochron age. Saw-cut profiles through pillow-syenite-gneiss sections have been taken to resolve close spatial elemental and isotopic (Sr-Nd-Hf-Pb-O) variations. The diorite and syenite formed from alkaline basaltic, mantle-derived, melts with complex histories of prolonged assimilation and fractional crystallisation. Each evolved to different extents in separate magma chambers during the establishment of new plumbing systems in the Kangerlussuaq area. The diorite is dominated by lower crustal, granulite facies contamination, whereas the syenite shows evidence for greater degrees of upper crustal amphibolite facies contamination, indicating stalling and fractionation of magmas at different levels within the crust. The syenite and diorite magmas were subsequently emplaced as separate pulses into the basement gneisses at Astrophyllite Bay giving rise to superimposed local contamination trends between pillow/syenite and syenite/gneiss, respectively.     

广东从化石岭碱性杂岩的岩石学特征及其地质意义

对广东从化石岭碱性杂岩体进行了１：１万地质调查和填图,并进行了详细的岩石力学研究。其结果表明：杂岩体由霞石角闪石正长岩、角闪石正长岩、墨云母正长岩等岩性组成,为Ａ－型花岗岩的分异结晶作用所形成,产于板内引张构造环境,与深大断裂有关。岩体本身已构成霞石正长岩矿床,具有较高的工业利用和经济价值。