Emplacement mechanism of Linglong granitoid complex, Shandong Peninsula, China

The Linglong granitoid complex (LGC) is composed of four major plutonic units that intruded and cooled in the Middle Jurassic (170-155 Ma). Gravity-anomaly modeling indicates that the LGC is a sheet-like laccolith, less than 10 km thick, that dips shallowly below the surface toward the Tancheng-Lujiang (Tan-Lu) fault, a major lithospheric structure in Eastern China. Measurements of foliation in the field and measurements of planar and linear magnetic fabrics from the study of anisotropy of magnetic susceptibility in the LGC indicate that foliation is dominantly shallowly dipping and magnetic lineation is mainly parallel to the dip direction of the laccolith toward the Tan-Lu fault zone. The trend of lineations is consistent with flow of magma up the thrust to reach shallower levels. The magma of the LGC probably originated by crustal melting within the Tan-Lu fault zone and the emplacement of magma occurred along a shallowly-dipping thrust that drained the Tan-Lu fault zone, the mechanism of which is mainly dike-fed model.     

对华容地区地质构造特征的新认识

通过对华容地区特别是岩体中构造特征研究及构造应力场分析,认为该区小墨山、桃花山岩体均为无根岩体,是在本区燕山早、晚两期受到挤压变形过程中混合岩化作用及由江南断裂带由南向北的推覆作用引起的断裂变质和超变质作用的结果。这一研究成果为该区构造特征研究和找矿提供了新的思路,也为中扬子地块南缘油气勘探提供了新的线索。     

Forceful Emplacement of Granitic Plutons in an Extensional Tectonic Setting:Syn-kinematic Plutons in the Yagan-Onch Hayrhan Metamorphic Core Complex

It is generally considered that granitic plutons are forcefully emplaced in a compressional setting and permissively emplaced in an extensional setting. This paper, however, shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhan metamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by (1) concentric distribution of the rock units, (2) a strain pattern with strong strains on the margins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shortening of the host rocks within the aureole. The strain analysis for the host rocks shows that the host-rock ductile shortening, i.e. forceful emplacement, provides about 16-24% of the emplacement space for the present plutons. All these suggest that forceful emplacement occurs not only in a compressional tectonic setting, but also in an extensional setting. This study further demonstrates the significance of the multiple emplacement of granitic plutons and provi     

东蒙地区燕山期三类成矿岩体地质地球化学特征

根据东蒙地区广泛发育的中生代燕山期岩体的成矿特征，将其成矿岩体分成三种类型。它们分别是铜成矿岩体、铅锌成矿岩体和锡成矿岩体。通过对三种成矿岩体的岩石学、稀土元素和微量元素的分析研究，认为铜成矿岩体具有明显的幔源和壳源双重特征，为燕山早期岩浆演化的结果；锡成矿岩体为燕山晚期岩浆演化的产物，具有壳源特点；铅锌成矿岩体的地质特征处于铜成矿岩体和锡成矿岩体的过渡。     

广西姑婆山岩体侵位构造及侵位机制研究

本文从环形构造和线性构造特征、侵位断裂—岩墙、岩脉、定向构造和挤压变形构造、外接触带的褶皱构造、岩体的应变测量等方面,系统地对姑婆山花岗岩的侵位构造进行了研究,并得出了该岩体属“气球膨胀”的侵位机制。     

中国东部早白垩世岩浆作用的伸展构造性质——以辽东半岛南部饮马湾山岩体为例

饮马湾山岩体位于辽东半岛南部,侵位于辽南变质核杂岩之中。岩体主要由三种岩石组成,由外向里分别是片麻状花岗岩、斑状花岗岩和中细粒二长花岗岩类。其中片麻状花岗岩类主要岩石类型为石英二长闪长岩和花岗闪长岩,具有明显的片麻理构造,部分岩石具有明显的变形组构,其片麻理方向与变质核杂岩中拆离断层方向一致。似斑状花岗岩仅显示微弱片麻理,而细粒二长花岗岩则为明显的块状构造,表明该岩体为同伸展变形就位产物。锆石U-Pb同位素测定显示,该岩体不同岩相岩石具有大体一致的年龄,其形成于120～130Ma的早白垩世,而不是以前认为的三叠纪。该岩体岩石具有较大的地球化学成分变化范围,其中片麻状和似斑状岩石具有高Sr含量(>600ppm)、低Y、Yb含量、轻重稀土分馏强烈的特点;而细粒二长花岗岩则相对低Sr高Rb、低~(87)Rb/~(86)Sr比值。Sr-Nd同位素综合分析表明,饮马湾山花岗岩主要来源于下地壳,但较大的范围Mg~#、Sr、Nd同位素组成则表明可能有其它物质(如岩石圈地幔、新生地壳)参与成岩作用。上述研究充分地显示,我国东部早白垩世岩浆活动发育在伸展构造背景,并可能与岩石圈减薄存在密切的联系。     

Metamorphic Environments around the Cretaceous Kurihashi Pluton in the Kitakami Mountains, NE Japan: in Comparison to the Ganidake Pluton - Kamaishi Skarn Metasomatism

Abstract. Many granitic plutons of Early Cretaceous age are intruded on various scales in the Kitakami Mountains. The stock‐type Ganidake pluton accompanies enormous Fe‐Cu mineralization of the Kamaishi deposits, whereas the Kurihashi pluton accompanies less mineralization. To elucidate the cause of these differences, the metamorphic conditions and redox state of the contact metamorphic aureole around the Kurihashi pluton have been examined by the petrochemical study and gas analysis of the metamorphic rocks. A typical mineral assemblage in the pelitic rocks in the lowest‐grade part is biotite‐muscovite‐chlorite‐quartz‐plagio‐clase‐graphite, which occur more than 2 km away from the contact point with the Kurihashi pluton. Graphite disappears at the 1550 m point, and cordierite and garnet appear in the middle and highest‐grade parts, respectively. A typical mineral assemblage in the tuffaceous rocks in the lower‐grade part is chlorite‐actinolite‐biotite‐quartz‐plagioclase. Actinolite changes into hornblende near to the pluton. The CO₂/CH₄ ratios obtained in measurements by gas chromatography exceeds 100 in the pelitic rocks at the contact point with the pluton. The ratios decrease and become less than 0.1 with distance from the pluton. Equilibrium temperatures calculated from a garnet‐biotite pair in the pelitic rock and a hornblende‐plagioclase pair in the tuffaceous rock are 640d? and 681 d?C at the contact point, respectively. The log?o₂ values among these metamorphic aureoles estimated from the CO₂/CH₄ ratios are slightly lower than the FMQ‐buffer. Redox states of the contact metamorphic aureole are kept in an intermediate condition between oxidized magma of the Kurihashi pluton and graphite‐bearing pelitic country rocks. Judging from these metamorphic conditions around the Kurihashi pluton and from the re‐evaluation of the previous knowledge about contact metasomatism around the Ganidake pluton, the Kurihashi metamorphism has occurred at higher temperatures and dry conditions than the Ganidake metasomatism. These differences in the metamorphic conditions and presence or absence of a large limestone mass around the pluton might be the principal reasons why the Kurihashi pluton accompanies less mineralization and the Ganidake pluton accompanies gigantic Kamaishi skarn mineralization.     

广东河源白石冈岩体:一个高分异的I型花岗岩

广东河源白石冈岩体位于近东西向展布的佛冈花岗岩带的东端,主体岩性为中粗粒黑云母花岗岩,主要组成矿物为石英(25%～35%)、微纹长石(45%～50%)、斜长石(An=20～30,15%～20%)和黑云母(5%～10%)。锆石U-Pb定年结果表明其形成年龄为148.5±1.6Ma,属晚侏罗世岩浆活动的产物。化学成分上,该岩体铝弱过饱和,A/NKC值主要变化于1.0～1.1之间;富硅,富钾(K2O/Na2O=1.31～1.70),全碱含量中等偏低(K2O Na2O=7.44%～8.48%),碱铝指数(AKI值)为0.75～0.88,可归为高钾钙碱性岩系。微量和稀土元素组成上,岩体富Rb、Th、U、Pb和轻稀土,贫Ba、Sr、P、Ti,Rb/Sr比值高,K/Rb比值低,铕负异常显著(δEu=0.05～0.28),Nb、Ta、Zr、Hf等高场强元素含量及104×Ga/Al比值(2.43～3.26)较之典型A型花岗岩均偏低。岩体的εNd(t)值为-5.99～-7.51,TDM值偏低(1.42～1.54Ga),综合地球化学资料指示其应属高分异的I型花岗岩。结合对区域动力地质背景的全面分析,表明白石冈岩体形成于后造山的伸展引张环境,是由底侵的幔源基性岩浆及其诱发的长英质岩浆在深部岩浆房混合,并经高程度分离结晶的产物。     

Zircon SHRIMP Dating for the Weiya Pluton, Eastern Tianshan: Its Geological Implications

1 Introduction Voluminous literature has resulted from study of the geology and tectonic evironments of post-orogenic granitoids in eastern Tianshan (He et al., 1995; Han et al., 1997; Gu et al., 1999, 2001; Li et al., 2003; Chen et al., 2004). Previous contributions (Hu et al., 1997; Li et al., 2003) indicate that major events of continental collision in northern Xinjiang occurred around 300 Ma. Then, the tectonics converted from compression to extension, resulting in the uplifting of th…     

粤北下庄矿田帽峰岩体的岩石地球化学特征

从主元素、微量元素、稀土元素的四分组效应及结合已有的锶同位素比值等方面研究了帽峰岩体的岩石地球化学特征,研究结果表明:(1)帽峰岩体具有富铝、硅和碱,A/CNK平均值为1.2,A′为正值等主量元素特征,富含石榴石、白云母等过铝矿物,强烈的铕亏损(δEu=0.01～0.25)及基本上无轻重稀土分异的稀土元素配分特征等,表明帽峰岩体是强过铝花岗岩,其物质来源主要是壳源;与同区域其它岩体相比较低的锶同位素比值((87Sr/86Sr)i=0.7185)是伴随着区域伸展构造所带来的幔源流体成分叠加所导致的。(2)帽峰岩体具有较为典型的稀土元素四分组效应,较低的Y/Ho比值(<28)及Zr/Hf比值(7.52～24.75),岩体的锆石年龄老(207.6±3.2Ma),而白云母KAr年龄(141.2Ma)与区域地壳伸展年龄(140Ma)及铀矿体的形成时代(138Ma)相接近,且岩体中常见碳酸盐团块,因此帽峰岩体较为典型的稀土元素的四分组效应是伴随着区域伸展和铀成矿过程与重碳酸络合物有关的流体之间的相互作用形成的。