作　　者： ; ; ; ; ; ; ;

机构地区： 南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室

出　　处： 《地质学报》 2011年第9期1420-1434,共15页

摘　　要： 前人对东天山海西期的构造-热事件作了大量研究,得出了许多方面的重要认识。东天山印支期的构造演化到底是海西期的延续,还是受控于另一构造域,至今仍不清楚。因此,印支期岩浆岩岩相学、地球化学和同位素地质学的综合研究,对阐明本区印支期的构造演化具有重要意义。产于中天山东段的尾亚石英闪长岩形成于印支早-中期。该岩石主要组成矿物为石英（10%~15%）、斜长石（An35-40,55%~60%）、钾长石（1%~10%）、黑云母（10%~15%）和角闪石（5%~10%）。岩石地球化学分析表明,尾亚石英闪长岩的SiO2含量介于62.40%~65.25%之间,其Al2O3含量（16.06%~16.90%）高,TiO2含量（0.70%~0.88%）低,Na2O/K2O〉1（1.26~1.75）,铝饱和指数（ASI）为0.91~0.93,具准铝质、高钾钙碱性岩系的特征。该岩石富集大离子亲石元素（LILE）Cs、Rb、Ba、K以及Pb和高场强元素（HFSE）U、Th以及Zr等,亏损高场强元素Nb;具有轻稀土（LREE）富集、重稀土（HREE）亏损以及轻、重稀土之间分异明显的特征。Sr、Nd和O同位素分析表明,尾亚石英闪长岩Sr和Nd初始值分别为0.70672~0.70879和0.512413~0.512441,氧同位素值（SMOW,‰）为8.64~8.73,其εNd（t）为1.64~2.16,Nd的模式年龄为0.79~0.80 Ga。这些特征表明,尾亚石英闪长岩既不是幔源岩浆直接分异的产物,也不是幔源岩浆与壳源的酸性岩浆在深部岩浆房混合的产物,而是由原生的下陆壳中-高钾的变质玄武岩在高温（1000~1100℃）和高压（1600~1800 MPa）条件下部分熔融的结果。作者认为,造成尾亚石英闪长岩成岩的动力和热力来源,归根结蒂,可能与古特提斯洋板块于晚二叠世到三叠纪向北俯冲诱发了本区陆内俯冲有关。本文研究结果表明,东天山印支期可能不是海西期的延续演化过程,而是已经受到古特提斯构造域的显著影响。 Voluminous cognition has resulted from intensive studies of the geology and Hercynian tectonic envents in the eastern Tianshan Mountains.To date,howeven,it has not been unknown whether the Indosinian tectonic evolution was a continuing episode of Hercynian orogeny or it was significantly controlled by other tectonic regimes.Hence integrated petrographic,geochemical and isotopic studies of the Indosinian magmatism are critical to understand the tectonic evolution of the eastern Tianshan Mountains in Triassic.The Weiya quartz diorite,occurring in the eastern segment of the Middle Tianshan Mountains,was formed in early-middle Indosinian.The rock is mainly composed of quartz（5%~10 %）,plagioclase（An 35-40,55%~60 %）,K-feldspar（1%~10 %）,biotite（10%~15 %） and hornblende（5%~10 %）.Geochemical study indicates that the Weiya quartz diorite is characterized by varing SiO2 contents（ranging from 62.40 % to 65.25 %）,higher Al2O3 conent（16.06~16.90 %）,and lower TiO2（0.70%~0.88 %）,with high ratios of Na2O/K2O（1.26~1.75） and aluminium saturation indices（ASI） of 0.91~0.93.These features suggest that it can be defined as high K calc-alkaline rocks.The rock is enriched in large ion lithopile elements（LILE） such as Cs,Rb,Ba,K and Pb and high field strength elements（HSFE） such as U,Th and Zr,depleted in HFSE such as Nb.All samples display similar chondrite-normalized REE patterns with enrichment in LREE,depletion in HREE,and significant fractionation（LaCN/YbCN=12.07~17.29） between LREE and HREE.Sr,Nd and O isotopic analyses show that the Weiya quartz diorite has an initial Sr and Nd values of 0.70672～0.70879和0.512413～0.512441,respectively,O isotope values of 8.64 ‰ to 8.73 ‰,εNd（t） values of 1.64~2.16,and an Nd model ages（TDM） of 0.79~0.80 Ga.All these features strongly indicate that the Weiya quartz diorite is derived from neither direct fractionation of mantle-derived magmas nor deep hybrid sources between mantle-derived magmas and crustal felsic melts,but a produc

关 键 词： 闪长岩 原生陆壳 陆内俯冲 印支期 尾亚 天山

领　　域： [天文地球] [天文地球]