中天山巴仑台地区变形花岗岩类LA-ICP-MS-U-Pb年代学及其构造意义

本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS-U-Pb年代学研究。中天山北缘花岗质片麻岩中岩浆锆石结晶年龄为630.0±5.0 Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3 Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世。中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2 Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3 Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期。研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底。     

冈底斯东段古新世朱拉岩体LA-ICP-MS锆石U-Pb定年和岩石地球化学特征

朱拉岩体位于冈底斯带东部,主要由黑云母二长花岗岩组成,其中发育闪长质包体,二者呈渐变过渡关系。3件寄主岩石LA-ICP-MS锆石U-Pb年龄加权平均值分别为64.6Ma±0.8Ma、64.3Ma±0.8Ma和63.9Ma±0.5Ma,含776Ma的继承岩浆锆石。1件闪长质包体样品年龄加权平均值为66.1Ma±0.3Ma。闪长质包体低Si,中Mg(Mg﹟平均41.1),属铝质高钾钙碱性系列,Nb/Ta值为22,Sr/Y值为3.69,稀土元素分馏较低,LREE/HREE平均值为1.92,Eu强烈亏损,富集大离子亲石元素(Rb、K、U、Th),亏损高场强元素(Nb、Ta、Sr、Ti),暗示岩浆成分主要为幔源。寄主岩石富Si、K,贫P,属铝质—偏铝质钙碱性—高钾钙碱性系列,Nb/Ta值15.9,富集大离子亲石元素(Rb、K、Th),亏损高场强元素(Nb、Ta、Ba、P、Ti),具有活动陆缘钙碱性岩系的微量元素分布特征。寄主岩石与闪长质包体具有密切的成生联系,闪长岩形成于富集俯冲带组分的地幔熔体,在上升过程中混染了一定量的壳源物质结晶分异产物,寄主岩石则为底侵作用产生的大量壳源熔体与少量幔源熔体混合并发生一定程度分离结晶后的产物。结合前人的研究成果,认为古新世朱拉岩体与雅鲁藏布江大洋的向北消减有关。     

内蒙古二连浩特北部阿仁绍布地区晚石炭世花岗岩Sr-Yb分类及其成因

对分布在内蒙古二连浩特北部阿仁绍布地区的晚石炭世花岗岩类,依据Sr、Yb含量,划分为低Sr高Yb型、极低Sr高Yb型和低Sr低Yb型花岗岩3种类型。低Sr高Yb型花岗岩类相对低Si、富Al,Na2O>K2O,稀土元素分馏中等,有或无负Eu异常,Sr含量低,平均为183×10-6,Ba含量较高,平均585×10-6,Y含量高,平均30.06×10-6,Rb/Sr比值较低,平均0.97;极低Sr高Yb型花岗岩富Si、REE,低Al、Sr、Ba,高的Rb/Sr比值(平均为7.47),具明显的负Eu异常等;低Sr低Yb型花岗岩富Si,贫Al、Ca、Mg,重稀土元素(Y、Yb)含量低,Y含量在(7.26～10.6)×10-6之间,平均9.76×10-6,Yb含量在(1.04～1.89)×10-6之间,平均1.44×10-6,δEu=0.64～0.94,具弱负Eu异常,微量元素Ba含量高,Rb/Sr比值低。3种类型的花岗岩类过铝指数(A/CNK)多小于1.0,说明它们均源自变质火成岩的部分熔融。由于源区的深度不同(pT条件不同)和残留的主要矿物相不同,它们的岩石地球化学特征存在差异。极低Sr高Yb型花岗岩形成深度最浅(中上地壳),熔融残留相以斜长石为主;低Sr高Yb型花岗岩类形成于中下地壳,熔融残留相为斜长石和辉石;低Sr低Yb型花岗岩形成深度最深,推测可能形成于加厚下地壳(>40km)底部,熔融残留相为石榴子石、斜长石和角闪石。     

Zircon U–Pb Dating and Geochemistry of the Linong Granitoid and Its Relationship to Cu Mineralization in the Yangla Copper Deposit,Yunnan, China

The Yangla copper deposit (Cu reserves: 1.2 Mt) in the Jinshajiang–Lancangjiang–Nujiang region in China is spatially associated with the Linong granitoid. Zircon U–Pb dating shows the granitoid formed at 234.1 ± 1.2 to 235.6 ± 1.2 Ma, and the KT2 ore body of the deposit yields a molybdenite Re–Os model age of 230.9 ± 3.2 Ma. The ages of mineralization and crystallization of the granitoid are identical within the measurement uncertainties, suggesting the Yangla deposit is genitically related to the Indosinian Linong granitoid.     

Petrogenesis of the ü?kap?l? Granitoid and its Mafic Enclaves in Elmal? Area (Ni?de, Central Anatolia, Turkey)

The Late Cretaceous ükapili Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Ni de area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The ükapili Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The ükapili Granitoid has calcalkaline and peraluminous (A/CNK= 1.0-1.3) geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios ((La/Lu) N = 3-33), and has negative Ba, Ta, Nb and Eu anomalies, resembling those of collision granitoids. The ükapili Granitoid has relatively high 87Sr/86Sr (i) ratios (0.711189-0.716061) and low εNd (t) values (-5.13 to -7.13), confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs (K, Rb) and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the ükapili granitoid is H-(hybrid) type, post-collision granitoid developed by mixing/mingling processes between crustal melts and mantle-derived mafic magmas.     

南秦岭张家坝岩体和新院岩体地球化学特征及其形成环境

南秦岭中生代张家坝岩体和新院岩体的LILE相对富集、HFSE贫化,高钾、富Sr（（498—623）×10^-6）、低Y（（5．57～24）×10^-6）和Yb（（0．52～2．13）×10^-6）,Eu异常微弱,显示了地壳增厚背景下下部地壳物质部分熔融所形成的高钾钙碱性花岗岩特征。岩体内的包体中出现长宽比很高的针状磷灰石,且边缘发育冷凝边结构,包体与寄主岩间存在明显的成分间断,并构成了两个不同的岩浆演化趋势和它们所具有的不同稀土特征,证明它们为来自两个不同源区岩浆混合的产物,同时指示秦岭地区中生代时期发生了一次壳幔混合作用和重要的地壳垂向增生事件。     

花岗岩研究与大陆动力学

花岗岩是大陆地壳的主要物质组成之一 ,蕴含着探索大陆动力学的重要信息。成因研究特别是混合成因研究可以提供探索大陆结构、生长及壳幔相互作用演化的信息 ;花岗岩形成演化揭示了构造动力学演化、大陆动力学演化及壳幔相互作用演化的某些特点 ;岩浆上升、迁移是大陆内部能量传播、物质迁移和调整的一种形式 ;岩浆的聚集及岩体生产方式与大陆块体运动学、动力学密切相关 ;岩体定时、定位对大陆块体时空定位提供了限制条件 ;变形岩体可作为区域应变标志体和时间标志体 ,研究大陆的变形 ,并有助于古老块体早期构造的解析。这些研究涉及到大陆的形成、演化、内部物质再分配、热动力效应和构造变动等动力学等问题 ,是花岗岩研究与大陆动力学研究的结合点。     

中俄阿尔泰山中生代花岗岩与稀有金属矿床的初步对比分析

中国阿尔泰山和俄罗斯阿尔泰山均属于阿尔泰山脉的组成部分,地理上互相连接,地质上具有相似的古生代演化历史,同样都发育中生代花岗岩及伴生的稀有金属矿床。中国阿尔泰山和俄罗斯阿尔泰山的中生代花岗岩及其稀有金属矿床既表现出一定的相似性,也存在一定的差别。两地与稀有金属矿床有关的中生代花岗岩主要为S型花岗岩,属于非造山花岗岩类,但在俄罗斯阿尔泰山发育以岩珠和岩脉型钨-钼、锂-钽为主的稀有金属矿床,时限为晚三叠世和早侏罗世,而中国阿尔泰山则发育以花岗伟晶岩脉型锂-铍-铌-钽为主的稀有金属矿床,时限从晚三叠世到晚侏罗世。这些花岗岩具有相似的Sr- Nd同位素特征,但~(87)Sr/~(86)Sr初始比值变化很大,可能是岩浆-流体作用的结果,而变化较小的ε_(Nd)(t)值与富集地幔来源的岩浆基本相当,或者可以解释为幔源岩浆与地壳物质混合的结果。     

湘南中生代花岗质岩石成岩成矿的时限

位于南岭中段的湘南地区,中生代花岗质岩石广泛分布;该区W、Sn、Pb、Zn、Mo、Bi等金属矿床密集产出,很多钨、锡矿床达到大型、超大型规模,且找矿潜力巨大,构成一个世界级的有色金属矿集区。最近大量的同位素年代学研究表明,南岭中段钨、锡、铅锌等金属的成矿是一个爆发性、区域性的地质事件,成矿时间高度集中,成矿时限主要在150~160 Ma之间,与该区主要花岗岩的成岩时间相当吻合;对单个钨、锡矿床而言,其矿区的成岩、成矿存在着一种准同期性,即成矿与矿区花岗岩的成岩基本上是同时的、或稍晚于花岗岩的成岩作用。因此,该区中生代的花岗岩与钨锡成矿作用具有明显的时、空联系。南岭中段花岗岩大规模的侵入和钨、锡等金属的爆发性成矿均形成于一种岩石圈伸展减薄、地壳拉张的构造环境,可能与华南中生代第二幕岩石圈伸展事件密切相关。     

Dehydration melting of micas in the Chilka Lake Khondalites: The link between the metapelites and granitoids

Garnet-sillimanite gneisses, locally known as khondalites, occur abundantly in the Chilka Lake granulite terrane belonging to the Eastern Ghats Proterozoic belt of India. Though their chemistry has been modified by partial melting, it is evident that the majority of these rocks are metapelitic, with some tending to be metapsammitic. Five petrographically distinct groups are present within the khondalites of which the most abundant group is characteristically low in Mg:Fe ratios — the main chemical discriminant separating the five groups. The variations in Mg:Fe ratios of the garnets, biotites, cordierites, orthopyroxenes and spinels from the metapelites are compatible with those in the bulk rocks. A suite of granitoids containing garnet, K-feldspar, plagioclase and quartz, commonly referred to as leptynites in Indian granulite terranes, are interlayered with khondalites on the scale of exposures; in a few spots, the intercalated layers are thin. The peraluminous character of the leptynites and presence of sillimanite trails within garnets in some of them suggest derivation of leptynites by partial melting of khondalites. Here we examine this connection in the light of results derived from dehydration melting experiments of micas in pelitic and psammitic rocks. The plots of leptynites of different chemical compositions in a (MgO + FeO)-Na₂O-K₂O projection match the composition of liquids derived by biotite and muscovite dehydration melting, when corrected for co-products of melting reactions constrained by mass balance and modal considerations. The melt components of the leptynites describe four clusters in the M-N-K diagram. One of them matches melts produced dominantly by muscovite dehydration melting, while three clusters correspond to melting of biotite. The relative disposition of the clusters suggests two trends, which can be correlated with different paths that pelitic and psammitic protoliths are expected to generate during dehydration melting. Thus the leptynites evidently represent granitoids which were produced by dehydration melting in metapelites of different compositions. The contents of Ti, Y, Nb, Zr and Th in several leptynites indicate departures from equilibrium melt compositions, and entrainment of restites is considered to be the main causative factor. Disequilibrium in terms of major elements is illustrated by leucosomes within migmatites developed in a group of metapelites. But the discrete leptynites that have been compared with experimental melts approach equilibrium melt compositions closely.