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“三江”地区中甸弧普朗成矿斑岩地球化学特征及其成因
Geochemistry and petrogenesis of Pulang porphyries in Sanjiang region
投稿时间:2010-10-13  修订日期:2011-04-08
中文关键词:斑岩铜矿  Sr-Nd同位素  印支期  普朗  中甸弧
英文关键词:porphyry copper deposit  Sr-Nd isotope  Indosinian  Pulang  Zhongdian island arc
基金项目:国家重点基础研究发展规划973资助项目(2009CB421004)
作者单位
任江波 中国科学院广州地球化学研究所, 广东 广州 510640
中国科学院 研究生院, 北京 100039 
许继峰 中国科学院广州地球化学研究所, 广东 广州 510640 
陈建林 中国科学院广州地球化学研究所, 广东 广州 510640 
张世权 云南省地质调查院, 云南 大理 671000 
梁华英 中国科学院广州地球化学研究所, 广东 广州 510640 
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中文摘要:
      普朗斑岩铜矿床是中国西南“三江”地区新发现的具超大规模的印支期斑岩铜矿床,其成矿岩体的斑岩具有高的Sr含量(289×10-6~1 200×10-6,平均值为820×10-6)、Sr/Y(23~92)和La/Yb(平均值为16.4)比值和相对较高的MgO和Mg#值(>59),并富集大离子亲石元素和亏损高场强元素(Nb、Ta、Ti)等成分特征,这与形成于俯冲岛弧环境埃达克岩的地球化学组成相似,表明可能存在一个板片熔体在成岩和成矿过程中的贡献。同时高Th/Y、Ba/La、Rb/Sr和Ba/Sr比值,以及相对较高的(87Sr/86Sr)i同位素比值(0.705 60~0.705 74)和较低的εNd(t)(-2.85~-2.20),指示有一个富集组分参与了成矿斑岩的形成过程,这个富集组分可能是普朗地区的岛弧地壳基底物质,也可能是俯冲沉积物。岛弧地壳物质或俯冲沉积物、或两者与板片熔融的埃达克质熔体进行了一定程度的相互作用,导致成矿斑岩“混合”型地球化学的组成。初步提出,普朗斑岩铜矿床可能是在东侧的甘孜-理塘洋晚三叠世俯冲过程中形成的,俯冲作用在早期形成了具有岛弧成分特征的石英闪长玢岩,其后板片熔融形成的埃达克质熔体增加,并混合了一定数量的上覆地壳物质或沉积物,产生了更酸性的、并具有较高氧逸度的埃达克岩岩浆,上侵到普朗地区的地壳中形成成矿斑岩和相关的斑岩铜矿床。
英文摘要:
      Located in Zhongdian island arc belt in northwestern Yunnan Province, the Pulang superlarge porphyry copper deposit was formed in late Triassic during the westward subduction of the Ganzi-Litang ocean plate below Zhongdian microplate. The mineralized rocks of the Pulang porphyry copper deposit mainly include quartz dioritic porphyries and quartz monzonitic porphyries in a complex pluton, and economic ores are mainly preserved in the quartz monzonitic porphyries. The quartz dioritic porphyrites were intruded by later quartz monzonitic porphyries, but the two kinds of rocks display similar geochemical characteristics, such as similar REE patterns, incompatible trace element patterns and initial 87Sr/86Sr and 143Nd/144Nd ratios, suggesting that they were cogenetic products or were derived from similar sources. Geochemically, both kinds of rocks are akin to adakite, as evidenced by such characteristics as high Sr content (289×10-6~1 200×10-6), high La/Yb and Sr/Yb ratios, relatively high MgO and Mg# (>59), depleted Y and Yb, slightly negative Eu anomalies and positive Sr anomalies. Moreover, the radiogenic Sr [0.705 60<(87Sr/86Sr)i<0.705 74] and less radiogenic Nd [-2.85<εNd(t)<-2.20] isotopic characteristics, together with high Th/Y, Ba/La, Rb/Sr, and Ba/Sr trace elements ratios, imply that enriched source components were involved during the formation of the porphyries. This enriched source was probably derived from the basement of arc crust or subducted sediments, and then some mixing processes possibility occurred between adakitic magmas and melts from sediments and/or arc crustal materials. A comparison between the quartz dioritic porphyrites and quartz monzonitic porphyries suggests that the former have low SiO2 (>61.0%) and K2O (2.2%~4.4%), while the latter have high SiO2 (>65.9%) and K2O (3.5%~8.1%). Therefore, the authors hold that the Pulang porphyry copper deposit was probably related to the westward subduction of Ganzhi-Litang oceanic plate during late Triassic. At the early stage of subduction, the quartz dioritic porphyries with subduction-related origin were formed firstly, then increasing adakitic magmas of slab melting were mixed with melts from subducted sediments or arc materials, producing more acid and high oxygen fugacity adakitic magmas, which finally intruded the upper crust below Pulang and promoted the mineralization of the Pulang porphyry copper deposit at the shallow level.
任江波,许继峰,陈建林,张世权,梁华英,2011,“三江”地区中甸弧普朗成矿斑岩地球化学特征及其成因[J].岩石矿物学杂志,30(4):581~592.
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