| 西藏冈底斯造山带几乎同时形成的两套埃达克岩为什么一套含矿一套不含矿？ |
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| 引用本文：.2010.A study of two groups of adakite almost simulteneously formed in Gangdese collisional orogen, Tibet: Why does one group contain copper mineralization and the other not? [J].Mineral Deposits,29(3):381~394 |
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| 基金项目:国家自然科学基金面上项目（编号：40773022） |
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| 中文摘要:野外地质调查结合锆石U-Pb年龄测定和岩石化学成分分析，发现西藏冈底斯碰撞造山带晚中新世发育两套埃达克岩。一套呈NS向岩墙产出，锆石U-Pb-LA-ICP-MS年龄为15.6～16.8 Ma，地球化学上以富Na2O、贫K2O、Sr/Y比值高为特点，不含矿；另一套呈岩株产出，锆石U-Pb SHRIMP年龄为14.0～15.3 Ma，地球化学上以富K2O、贫Na2O、Sr/Y比值低为特点，伴随着大规模的斑岩型铜钼矿化。两套埃达克岩都高度富集大离子不相容元素（LILE）Rb、Ba、Th、U、K、Sr、Pb，强烈亏损高场强元素（HFSE）Nb、Ta、Ti，反映出俯冲组分对岩浆源区的明显影响，具备岛弧岩浆作用的基本特征。比较而言，含矿埃达克岩更富集Rb、Th、U、K、Pb，而不含矿埃达克岩更富集Sr；不含矿埃达克岩的高场强元素Nb、Ta、Ti亏损更加强烈，Zr、Hf相对富集。两套埃达克岩都是形成于碰撞后地壳伸展的同一地球动力学背景下，其岩石地球化学差异主要与岩浆源区有关。研究表明，含矿埃达克岩的岩浆源区较浅,位于下地壳底部，参与岩浆作用的俯冲组分以沉积物熔体为主，岩浆的氧化性较强，并且经历了更多的分异过程。不含矿埃达克岩的岩浆源区较深，位于岩石圈地幔上部，参与源区岩浆作用的俯冲组分主要是板片流体，岩浆氧化性较低，岩浆分异过程较少。两套埃达克岩含矿与不含矿的原因包含了源区物质组成和岩浆生成条件两方面的差异。 |
| 中文关键词:地球化学 岩浆源区 含矿埃达克岩 不含矿埃达克岩 冈底斯碰撞造山带 西藏高原 |
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| A study of two groups of adakite almost simulteneously formed in Gangdese collisional orogen, Tibet: Why does one group contain copper mineralization and the other not? |
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| Abstract:Field investigations combined with zircon U-Pb dating and petro-geochemical analysis demonstrate that two groups of adakite were formed in the Gangdese collisional orogen of the Tibet plateau in late Miocene. One group occurs as NS-striking dykes with zircon U-Pb-LA-ICP-MS ages ranging from 15.6 Ma to 16.8 Ma and is geochemically characterized by high Na2O, Sr/Y and low K2O without copper mineralization. The other group occurs as small stocks with zircon U-Pb SHRIMP ages from 14.0 ～15.3 Ma and is geochemically characterized by high K2O, low Na2O, Sr/Y, and the association with large-scale porphyry copper mineralization. The two groups are both notably enriched with large ion lithosphile elements (LILE) Rb, Ba, Th, U, Sr, Pb and strongly depleted in high field strength elements (HFSE) Nb, Ta, Ti, suggesting the evident influence of subduction components on their magma sources. By comparison, the ore-bearing adakite has higher enrichment of Rb, Th, U, K, Pb, whereas the barren adakite is richer in Sr, Zr, Hf and more strongly depleted in Nb, Ta, Ti. As these two groups were formed under the same geodynamic environment of post-collisional crustal extension, their geochemical differences might be mainly attributed to magma sources. The present study reveals that the ore-bearing adakite had a shallower magma source at the bottom of the lower crust, the subduction components involved in the magmatic generation was dominate d by subducted sedimentary melt, and its magma was more oxidative and experienced higher differentiation. In contrast, the barren adakite had a deeper magma source in the upper part of the lithospheric mantle, the subduction components involved in its magmatic source contained more slab fluids, and its magma was less oxidative and experienced lower differentiation. |
| keywords:geochemistry, magma source, ore-bearing adakite, barren adakite, Gangdese collisional orogen, Tibet plateau |
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