A型花岗岩的研究进展及意义

A型花岗岩主要形成于伸展的构造背景中,是构造环境识别的重要岩石学标志之一。由于形成于特殊的构造背景和重要的地球动力学意义,A型花岗岩的研究一直得到广泛的关注,但是仍旧有许多问题(如命名、分类和成因等)在争论之中。本文从下面几个方面对A型花岗岩的研究现状进行了较系统的总结:(1)A型花岗岩的概念及特征;(2)A型花岗岩与高分异I、S型花岗岩的区别;(3)A型花岗岩的物质来源及成因模式;(4)A型花岗岩的实验岩石学成果;(5)A型花岗岩的分类;(6)A型花岗岩的构造背景及动力学意义。A型花岗岩在形成过程中斜长石、斜方辉石可能为主要的残留或分离结晶矿物相。除了传统的A1(非造山)、A2(后碰撞)分类外,"还原型"和"氧化型"的分类方案最近也受到广泛关注。     

湖北麻城市四道河地区面理化含榴花岗岩的成因

野外和室内研究结果表明,四道河地区面理化含榴花岗岩由古生代沉积岩变质而成。在元素地球化学特征上,具有与岩浆成因的碱性花岗岩一致的特点:高硅(SiO2=75.24%～77.23%)、富碱(Na2O+K2O=6.87%～8.84%)、低铝(Al2O3=11.00%～12.78%);富Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf等高场强元素;稀土元素含量较高(∑REE=101.08～180.1μg/g),轻稀土元素相对富集(LREE/HREE=3.1～6.8),铕有中等负异常(δEu=0.30～0.68);锆石成因类型及定年结果表明,老核(继承锆石)是异地多时代(元古代-古生代),其寄主岩的原岩是沉积岩,时代不会早于古生代。     

Archaean high-K granitoids produced by remelting of earlier Tonalite–Trondhjemite–Granodiorite (TTG) in the Sangmelima region of the Ntem complex of the Congo craton,southern Cameroon

We present a geochemical and isotopic study that, consistent with observed field relations, suggest Sangmelima late Archaean high-K granite was derived by partial melting of older Archaean TTG. The TTG formations are sodic-trondhjemitic, showing calcic and calc-alkalic trends and are metaluminous to peraluminous. High-K granites in contrast show a potassic calc-alkaline affinity that spans the calcic, calc-alkalic, alkali-calcic and alkalic compositions. The two rock groups (TTG and high-K granites) on the other hand are both ferroan and magnesian. They have a similar degree of fractionation for LREE but a different one for HREE. Nd model ages and Sr/Y ratios define Mesoarchaean and slab-mantle derived magma compositions respectively, with Nb and Ti anomalies indicating a subduction setting for the TTG. Major and trace element in addition to Sr and Nd isotopic compositions support field observations that indicate the derivation of the high-K granitic group from the partial melting of the older TTG equivalent at depth. Geochemical characteristics of the high-K granitic group are therefore inherited features from the TTG protolith and cannot be used for determining their tectonic setting. The heat budget required for TTG partial melting is ascribed to the upwelling of the mantle marked by a doleritic event of identical age as the generated high-K granite melts. The cause of this upwelling is related to linear delamination along mega-shear zones in an intracontinental setting.     

内蒙古查干诺尔铜矿区矿石特征及成因探讨

查干诺尔铜矿床产在西伯利亚板块和华北板块汇聚带附近,华力西晚期构造岩浆带内。成矿与早二叠世洋盆闭合,后碰撞高钾钙碱性花岗岩类岩浆演化晚期的钾质花岗岩有关。铜矿(化)体呈细脉浸染状产在钾质花岗岩的内外接触带内。铜矿石的主要金属矿物为黄铜矿、黄铁矿、闪锌矿、方铅矿等;化学组分以铜、钼、金、银、铅、锌为主。主要的矿化发生在热液期,围岩蚀变明显,有钾长石化、绢英岩化、高岭土化、青盘岩化等。铜矿形成在华力西晚期,属斑岩型铜矿床。     

新疆西准噶尔苏云河钼矿床含矿岩体地球化学和年代学

苏云河钼矿床位于新疆西准噶尔巴尔鲁克山西段,容矿岩石为二长花岗岩和二长花岗斑岩。这些花岗岩具有类似的地球化学特征:富集Rb、Th、U和LREE,相对亏损Ba、P、Ti,属于高钾钙碱性I型花岗岩系列,局部经历过强烈的分离结晶作用。LA-ICPMS锆石U-Pb定年结果显示苏云河钼矿区的成岩年龄为309.3~310.2 Ma,这表明与成矿有关的岩浆活动发生于晚石炭世。黑云母的Ti温度计表明Ⅰ号和Ⅲ号岩体的结晶温度相近,为695~728℃;而Ⅱ号岩体的结晶温度较低,为642~668℃。同时根据角闪石-斜长石压力计获得Ⅰ号和Ⅲ号岩体的结晶压力为(3.0~3.9)×108Pa。综合地球化学研究表明,苏云河钼矿区3个岩体均形成于岛弧环境。此外,以苏云河钼矿床为代表的巴尔鲁克山成矿带与哈萨克斯坦境内的巴尔喀什成矿带在岩石地球化学、成岩成矿时代等方面具有许多类似的特点,表明巴尔鲁克山成矿带可能是巴尔喀什成矿带在中国境内的延伸。     

秦祁结合部位宝鸡地区早泥盆世香泉A型正长花岗岩年龄、地球化学特征及其构造意义

对秦祁结合部位宝鸡地区香泉正长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究。结果显示,锆石~(206)Pb/~(238)Pb年龄加权平均值为410±5Ma(MSWD=0.20,n=18),限定该岩体的形成时代为早泥盆世。香泉正长花岗岩具有高硅(SiO_2=69.63%~73.94%)、富钾(K_2O=4.24%~4.88%,K_2O/Na_2O=1.23~1.44)、富铁(TFe_2O_3=2.10%~3.70%,TFe_2O_3/MgO=3.88~6.84)、低镁(MgO=0.31%~0.94%)、低磷(P_2O_5=0.08%~0.21%)的特征,属准铝质、高钾钙碱性系列。香泉正长花岗岩稀土元素含量较高(318×10~(-6)~499×10~(-6)),表现出明显的负Eu异常(δ Eu=0.37~0.46),富集Rb、Th、Zr、Sm、Ga(10000×Ga/Al=2.59~2.93)等微量元素,贫Ba、Nb、Ta、Sr,整体表现出A型花岗岩特征。结合区域资料认为,香泉正长花岗岩形成于造山后环境,为低压环境下长英质地壳物质部分熔融成因。     

哈密头苏泉哈尔欣巴A型花岗岩厘定

初步研究表明新疆哈密头苏泉地区哈尔欣巴花岗岩为A型花岗岩.该岩体富硅(SiO2=71.87%~76.80%)和碱(K2O+N2O=7.39%~8.94%),贫铁、锰、镁(FeOt 0.67%~2.04%;MnO 0.03%~0.06%;MgO 0.10%~0.61%),具较高FeOt/MgO比值,A/NKC=0.78~1.02,属准铝质花岗岩石.在微量元素和稀土元素组成上,岩石富Zr,Rb,Ce等不相容元素,亏损Ni,Co,Cr等元素.10000×Ga/Al为3.12~4.1,大于A型花岗岩下限值(2.6).在Zr,Ce,Nb,Y与10000×Ga/Al,及(Nb+Zr+Ce+Y)/(FeOt/MgO)、SiO2/( FeOt/MgO)图解中大多数点都落在A型花岗岩区域.在A1-A2构造环境判别图上显示后造山花岗岩特征.对头苏泉地区哈尔欣巴A型花岗岩的厘定,为研究该区地壳物质组成及构造演化具重要意义.     

朝鲜半岛平南盆地中元古代岩浆事件

朝鲜平南盆地翁津地区发育中元古代黄海群和同时期(称之为瓮津期)花岗岩,花岗岩体侵入于黄海群。本文采用锆石原位微区U-Pb定年技术,对黄海群中的酸性火山岩及花岗岩进行了年龄测试。获得的数据表明,黄海群中下部层位及上部层位的酸性火山岩分别在1235±5Ma和1203±7Ma喷发,由此说明黄海群的沉积时代应为中元古代,而不是传统上认为的古元古代;两个翁津期花岗岩体(翁津和黄衣山岩体)的侵位年龄分别为1251±22Ma和1248±13Ma,为中元古代花岗质岩浆活动的产物。上述1251~1203Ma年龄的获得,表明朝鲜半岛发育中元古代岩浆作用,从而明确朝鲜黄海裂谷与华北东缘裂谷在时间上具有同期性,同时也表明中国华北与朝鲜在中元古代具有类似的发展历史。     

新疆西准噶尔庙尔沟岩体的地球化学及年代学研究

新疆西准噶尔庙尔沟岩体侵入于早中石炭世海相火山-沉积建造中,主体由碱长花岗岩组成,局部分布有紫苏花岗岩和碱长花岗岩脉。碱长花岗岩及岩脉高硅、富碱、贫钙,里特曼指数(δ)=2.17~2.98,A/CNK=0.96~1.03,A/NK=1.08~1.13,为准铝质-弱过铝质高钾钙碱性花岗岩,其富集LILEs(Rb、U、K、Th),相对亏损HFSEs(Nb、Ta、P、Ti)和Ba、Sr等,以及强烈Eu负异常,过渡族地幔相容元素Cr、Ni含量低,U、Th、Pb等地壳富集元素含量较高。Sr、Nd同位素组成:(87Sr/86Sr)i=0.70370~0.70541,εNd(t)=+4.10~+6.79,tDM=0.57~0.99Ga。锆石LA-ICP-MS U-Pb定年研究获得锆石U-Pb年龄为309±1.4Ma,表明岩体碱长花岗岩的形成时代为晚石炭世。紫苏花岗岩的SiO 2含量为60.88%~62.06%,Al2O3含量为15.50%~15.72%,里特曼指数(δ)=2.59~2.77,A/CNK=0.86~0.88,A/NK=1.50~1.53,为准铝质钙碱性-高钾钙碱性过渡的花岗岩,相对富集LREE(Rb、U、K、Th),而亏损HREE(Nb、Ta、P、Ti)和Sr,以及较显著的Eu负异常,过渡族地幔相容元素Cr、Ni含量低,U、Th、Pb等地壳富集元素含量较高。Sr、Nd同位素组成:(87Sr/86Sr)i=0.70382~0.70388,εNd(t)=+6.67~+6.98,tDM=0.59~0.62Ga。锆石LA-ICP-MS U-Pb定年研究获得锆石U-Pb年龄为302.1±2.1Ma,表明岩体紫苏花岗岩的形成时代为晚石炭世。综合庙尔沟岩体的地质特征、地球化学特征、年代学和区域地质背景,认为庙尔沟岩体碱长花岗岩及岩脉为A2型花岗岩,紫苏花岗岩具有A型花岗岩的地球化学性质,且它们是可能来自同一个岩浆源区,属于西准噶尔后碰撞阶段的岩浆活动产物。     

Interaction of crustal and mantle materials,sources of trace elements during the formation and evolution of Early Paleozoic Li-rich granite-pegmatite systems in southeastern Tuva

We present new data on the age, composition, and environments of formation of granites of the Kystarys complex and the associated Li-rich rare-element pegmatites of the South Sangilen pegmatite belt including the large Tastyg lithium deposit. It has been established that they formed during the Early Paleozoic collisional orogeny in the Tuva-Mongolian massif at the Cambrian-Ordovician boundary. The granites of the Kystarys complex are moderately alkaline high-K rocks and are enriched in Zr, Nb, Y, and REE; therefore, they are classified as postcollisional, transitional to within-plate (A-type). The spodumene pegmatites of the South Sangilen pegmatite belt are similar to the above granites in age and isotopic and geochemical parameters, which suggests a paragenetic relationship between these rocks. Pegmatites form several pegmatite fields within the belt, which differ in trace-element signatures. In addition to predominant Li, Cs, and Ta, specific to all spodumene pegmatites (LCT family), pegmatites of two fields have high contents of Nb, Y, REE, and Zr, which are indicator elements of NYF family pegmatites. It has been established that the formation of spodumene pegmatites with combined LCT-NYF geochemical signatures was preceded by the intrusion of dikes of monzogabbro with the geochemical characteristics of OIB and of alkali aegirine granites and by the formation of associated metasomatites enriched in Zr, Nb, Y, and REE. Based on the geological, mineralogical, and geochemical data, we substantiate the hypothesis of the formation of Li-bearing granite-pegmatite melts from a mixed source resulted from the influence of fluids of an alkaline igneous complex of mantle genesis on the crustal protolith.