豫西太山庙花岗岩体特征与多金属矿产的关系

经从岩石学、矿物学、地球化学等方面对燕山期太山庙花岗岩体详细研究,认为该岩体侵入为一重要构造热事件,控制着区内多个多金属矿床的形成与规模。本文着重探讨和阐述太山庙花岗岩体特征及其对周边矿床的控矿关系。     

Tectonic setting and petrogenesis of the Çelebi granitoid, (Kırıkkale-Turkey) and comparison with world skarn granitoids

Many studies have shown systematic correlations between the composition of plutons worldwide and the metal content of associated skarns. This is the first report of similar correlations between the composition of Çelebi granitoid and skarns of the Çelebi district in Central Anatolia, Turkey. The Çelebi district is well known for its polymetallic Fe–W and Cu vein ores. These are hosted by calcic skarn zones. Both exoskarns (pyroxene–garnet) and endoskarns (epidote–pyroxene) occur in the district formed mainly along the granitoid contacts and along the fractures within the marble. Based on mineralogy, petrology and geochemistry, two different igneous rocks were recognized in the Çelebi granitoid, referred to as leucocratic (felsic) and mesocratic (intermediate) Çelebi granitoid. The leucocratic Çelebi occurs as dominant rock type, and is classified as granite. The mesocratic Çelebi is not widespread and is classified as adamellite, tonalite, quartz monzonite and quartz monzodiorite. The mesocratic Çelebi has I-type characteristics, and have subalkaline, calc-alkaline and metaluminous characteristics like most worldwide skarn granitoids.A post-collisional tectonic setting is proposed on the basis of field evidence, the relative timing of intrusions with respect to metamorphic and obducted ophiolitic rocks and trace element geochemistry. The high abundance of La and Ce and the enrichment of V in mafic components suggest that Çelebi granitoids are formed by partial melting of mantle rocks, but have been contaminated by interaction with continental crust involving possible magma mixing processes (i.e. mixing of coexisting felsic and mafic magmas). In the district, the mesocratic type and mafic microgranular enclaves (MME) mainly within leucocratic type represent a mafic underplating magma that was mixed with and/or injected into felsic magma of the leucocratic type.The present study shows that Fe mineralization is associated with mesocratic Çelebi type, whereas W mineralization is associated with leucocratic type. Mesocratic Çelebi granitoid is significantly different from the worldwide average of plutons associated with Fe skarns. In particular, MgO vs. SiO₂, FeOt+CaO+Na₂O/K₂O vs. SiO₂, Fe₂O₃/Fe₂O₃+FeO vs. SiO₂ and V vs. Ni vary from typical values (are lower than values typical for plutons associated with Fe skarns) for plutons associated with Fe skarns. Instead, it resembles the geochemical characteristics of plutons associated with worldwide Cu and possibly Au skarns. This suggests new exploration possibilities for copper and gold in the Çelebi district.     

华北地台和秦岭—大别—苏鲁造山带的中生代花岗岩与深部地球动力学过程

近年来的研究证实 ,华北地台和大别—苏鲁造山带的中生代花岗岩与同时代的镁铁质超镁铁质岩有类似的Sr、Nd同位素特点 ,许多花岗岩和火山岩还具有类似埃达克岩的地球化学性质。在此基础上 ,根据现已积累的大量Sr、Nd同位素资料 ,从整个华北地台岩石圈的角度论证了中生代岩石圈地幔富集的性质、富集地幔发生的时代及其形成机制 ,进而探讨了岩浆活动的动力学机制 ,指出本区岩石圈富集地幔的形成是在Pangea超大陆裂解时岩石圈大规模拆沉减薄 ,被拆沉的太古宙古老地壳重循环进入地幔改变了地幔成分所致 ,说明超大陆裂解、岩石圈大规模拆沉减薄和富集地幔形成之间有密切的成因联系 ,超大陆裂解伴随着大陆地壳生长和消亡 (重循环 )的大体平衡。结合全球地震层析资料 ,进一步探讨了由俯冲大洋残片转化的下地壳同古老克拉通地壳物质在花岗岩源区中的重要意义。     

Absence of Archean basement in the South Kunlun Block: Nd-Sr-O isotopic evidence from granitoids

Abstract   The West Kunlun mountain range along the northwestern margin of the Tibetan Plateau is crucial in understanding the early tectonic history of the region. It can be divided into the North and South Kunlun Blocks, of which the former is considered to be part of the Tarim Craton, whereas consensus was not reached on the nature and origin of the South Kunlun Block. Samples were collected from the 471 Ma Yirba Pluton, the 405 Ma North Kudi Pluton and the 214 Ma Arkarz Shan Intrusive Complex. These granitoids cover approximately 60% of the Kudi area in the South Kunlun Block. Sr, Nd, and O isotope compositions preclude significant involvement of mantle-derived magma in the genesis of these granitoids; therefore, they can be used to decipher the nature of lower–mid crust in the area. All samples give Mesoproterozoic Nd model ages (1.1–1.5 Ga) similar to those of the exposed metamorphic complex of this block but significantly different from those of the basement of the North Kunlun Block (2.8 Ga). This indicates that the South Kunlun Block does not have an Archean basement, and, thus, does not support the microcontinent model that suggests the South Kunlun Block was a microcontinent once separated from and later collided back with the North Kunlun Block.     

Characterisation of the Dabla Granitoids, North Khetri Copper Belt, Rajasthan, India: Evidence of Bimodal Anorogenic Felsic Magmatism

The Palaeoproterozoic Dabla granitoid pluton of the North Khetri Copper Belt is located to the east of a NNE-SSW trending lineament with numerous albite-rich intrusives, the intraplate ‘albitite line’. The Dabla pluton is essentially made up of calcic amphibole-bearing granitoids, displaying a concentric bimodal distribution of alkali-feldspar granites, comprising a microcline-albite granite and an albite-granite. The dominant rock type is pink-coloured granite, which is characterised by quartz, microcline, albite and hastingsitic hornblende, and occurs in the marginal parts of the pluton. The volumetrically subordinate albite-granite in the central part of the pluton is invariably white in colour, non-foliated and is mainly composed of quartz, albite and amphibole of actinolite to ferro-actinolite composition. The albite-granite is characterised by low K₂O (0.06-0.09%), Rb (<5 ppm) and Ba (<20 ppm), high Na₂O (7.19-7.36%) and high Na/K ratios (122.4-185.2) as compared to the granite. These rocks are not subjected to any metamorphic overprint, especially the albite-granite, which shows pristine abundances of major and trace elements. The rocks are highly evolved as reflected in their high SiO₂ (72 to 78%) contents and high DI (89.5-97) values. The Dabla granitoids are characterised by similar REE and spider patterns, displaying LREE enriched slopes, flat HREE profiles and strong negative Sr, P, Ti and Eu anomalies suggesting their comagmatic nature. Nevertheless, the granite is relatively more fractionated [(La/Yb)_N = 3.89-8.19] and show higher REE abundances (466-673 ppm) as compared to the albite-granite [(La/Yb)_N = 1.97-2.96; REE = 220-277 ppm]. Distinctive features of these rocks are their low Ca (0.21-1.53%), Mg (<0.02-0.19%), Al (11.84-12.96%) and Sr (12-46 ppm) abundances, high Zr (155-631 ppm), Y (67-156 ppm), Nb (14-91 ppm), and Ga (20-31 ppm) concentrations and high Fe*-number, high Ga/Al ratio and high agpaitic index (AI) values. These features, coupled with their ferroan, alkaline and metaluminous nature, are typical of within-plate aluminous A-type granites. The geochemical data further indicate that the Dabla magma was generated at fairly high temperature, apparently in an upper mantle region, under relatively low H₂O activities and reduced conditions and emplaced at a shallow depth in an extensional tectonic environment.     

Important Geological Factors Controlling the Formation of Gold Deposits in East China

The major gold deposits in east China are characterized by their occurrence in pre-Cambrian host metamorphic rocks,restriction in some specific stratigraphic-structural terranes,tendentious localization in ductile or ductile-brittle shear zones,association with the syntexis type granitoids,and significant remobilization,superimposition and enrichment by the later stage Mesozoic tectono-magmatic activities.     

华北南部地区——古生界构造演化及其油气远景

华北南部地区的地质演化与华北其他地区一样，经历了结晶基底形成，中一晚元古代台内裂谷发育、古生代稳定地台沉积和中一新生代活化等发展过程。但本区受秦岭褶皱带构造活动的强列影响。因而具有相对独特的构造演化特征和油气控制条件。早寒武世中期，古秦岭海槽伸展扩张，沉积了一套全区广泛分布的以碳酸盐岩为主夹泥页岩的地层；晚寒武世开始，古秦岭海槽向北俯冲挤压，在本区南部出现一个平行于海槽的大陆边缘隆起；中奥陶世发生     

Isotope provinces, mechanisms of generation and sources of the continental crust in the Central Asian mobile belt: geological and isotopic evidence

The available geological, geochronological and isotopic data on the felsic magmatic and related rocks from South Siberia, Transbaikalia and Mongolia are summarized to improve our understanding of the mechanisms and processes of the Phanerozoic crustal growth in the Central Asian mobile belt (CAMB). The following isotope provinces have been recognised: ‘Precambrian’ (T_DM=3.3–2.9 and 2.5–0.9 Ga) at the microcontinental blocks, ‘Caledonian’ (T_DM=1.1–0.55 Ga), ‘Hercynian’ (T_DM=0.8–0.5 Ma) and ‘Indosinian’ (T_DM=0.3 Ga) that coincide with coeval tectonic zones and formed at 570–475, 420–320 and 310–220 Ma. Continental crust of the microcontinents is underlain by, or intermixed with, ‘juvenile’ crust as evidenced by its isotopic heterogeneity. The continental crust of the Caledonian, Hercynian and Indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments. The crustal growth in the CAMB had episodic character and important crust-forming events took place in the Phanerozoic. Formation of the CAMB was connected with break up of the Rodinia supercontinent in consequence of creation of the South-Pacific hot superplume. Intraplate magmatism preceding and accompanying permanently other magmatic activity in the CAMB was caused by influence of the long-term South-Pacific plume or the Asian plume damping since the Devonian.     

Integrated approach of using ASTER-derived emissivity and pixel temperature for delineating different granitoids – a case study in parts of Dharwar Craton,India

We have delineated different granitoids based on variation in emissivity and relative surface temperature recorded in thermal bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor of EO-1 satellite. In this regard, we have used emissivity normalization algorithm to derive broadband emissivity from thermal bands of ASTER sensor to delineate different lithounits of the granitoid family. We have compared emissivity and radiance image composites in terms of delineation of different granitoids. We have also used false colour composite (FCC) image derived using two emissivity bands and temperature (derived using emissivity normalisation method) bands to delineate different granitoids. We could differentiate different granitoids in the three-dimensional (3D) data space of ASTER-derived emissivity bands (second and third bands) and temperature bands. Based on the analysis of 3D scatter plot, we also proposed a ternary diagram of emissivity and temperature, which can be used to delineate different granitoids.     

西准噶尔成矿带晚古生代花岗岩类岩浆活动及其构造意义

中亚造山带是晚古生代地壳显著生长与大规模成矿的重要地区。本文采集了中亚造山带西部的西准噶尔成矿带哈图-别鲁阿嘎希及其附近地区11个岩体共33件花岗岩类样品,对其开展了岩石地球化学与同位素示踪等研究,厘定了该地区晚古生代岩浆活动的特点与大地构造环境,并与哈萨克斯坦境内的巴尔喀什成矿带晚古生代岩浆活动进行了对比。研究表明,哈图地区晚石炭世花岗岩类主要为后碰撞伸展构造环境的A型花岗岩类,别鲁阿嘎希等地区存在洋内俯冲与岛弧环境的埃达克岩,显示了西准噶尔晚古生代构造环境时空变化的复杂性。该地区花岗岩类εNd(t)值较高(+4.62~+7.53)、εSr(t)值为(-57.61~+18.21),具有中亚造山带花岗岩类的共同特征,为古生代增生的新生陆壳,其源区与亏损地幔组分具有亲缘关系,这与巴尔喀什成矿带东段的花岗岩类具有一致性。花岗岩的~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb比值范围分别为18.2776~19.1677、15.5260~15.5796和38.2080~39.0821,为造山带花岗岩类。