| 再论蛇绿岩中豆荚状铬铁矿的成因——质疑岩石/熔体反应成矿说 |
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| 引用本文： | 鲍佩声.再论蛇绿岩中豆荚状铬铁矿的成因——质疑岩石/熔体反应成矿说[J].地质通报,2009,28(12):1941-1961. |
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| 作者姓名： | 鲍佩声 |
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| 作者单位： | 中国地质科学院地质研究所,北京,100037 |
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| 基金项目： | 中国地质调查局项目，中石化项目 |
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| 摘 要： | 着重论述了蛇绿岩地幔橄榄岩中豆荚状铬铁矿的成因，并对现今盛行的岩石/熔体反应成矿说提出了质疑。世界含铬铁矿的地幔橄榄岩均显示上部偏基性、下部偏酸性的垂直熔融分带，与蛇绿岩堆晶岩中上部偏酸性、下部偏基性的岩浆分异垂直层序恰恰相反。豆荚状铬铁矿与熔融剖面上部的纯橄岩或纯橄岩-方辉辉橄岩杂岩带紧密伴生。豆荚状铬铁矿是原始地幔岩高度熔融再造的产物，高铬型铬铁矿与PPG型蛇绿岩伴生，形成于岛弧或弧前盆地环境；高铝型铬铁矿与PTG型蛇绿岩伴生，形成于扩张脊（MOR）或弧后盆地环境。玻安岩（boninite）与高铬型豆荚状铬铁矿无成因关系，铬铁矿（或富铬矿浆）的形成反而为boninite提供了其形成所需的残余地幔；高铝型铬铁矿不是地幔橄榄岩/拉斑玄武质熔体反应形成的，而是富铬矿浆与基性熔体发生再平衡的产物。豆荚状铬铁矿中超高压矿物包体的出现为其地幔深部成因提供了佐证，而boninite形成于浅部较低压的条件；豆荚状铬铁矿中富集强相容元素IPGE（Os、Ir、Ru）合金，boninite富集不相容元素PPGE (Pt、Pd)硫（砷）化物, 而亏损IPGE，显示其形成较晚。因此，boninite与铬铁矿无生因关系，两者均受岛弧（或弧前盆地）环境的制约而在空间上相伴产出。
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| 关 键 词： | 豆荚状铬铁矿 蛇绿岩 地幔橄榄岩 高度熔融再造 玻安岩 |
Further discussion on the genesis of the podiform chromite deposits in the ophiolites-questioning about the rock/ melt interaction metallogeny |
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| BAO Pei-sheng.Further discussion on the genesis of the podiform chromite deposits in the ophiolites-questioning about the rock/ melt interaction metallogeny[J].Geologcal Bulletin OF China,2009,28(12):1941-1961. |
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| Authors: | BAO Pei-sheng |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | The author has emphatically discussed the genesis of the podiform chromite deposits in the ophiolites and thus questions the widespread rock/melt interaction metallogeny. The mantle peridotites-bearing chromite deposits in the world also exhibit a vertical zoning of melting, with more basic material in the upper part and more acid material in the lower part, being opposite to vertical zoning of magmatic differentiation with more acid material in the upper part and more basic material in the lower part. The podiform chromite deposits are closely associated with the dunite or dunite-harzburgite complex belts in the upper part of melting profile. The podiform chromite deposits are products formed by highly partial melting and reconstitution of primary peridotites. The Cr-rich chromite deposits belong to PPG ophiolite series and form in island arc (or fore-arc basin) and Al-rich one are associated with PTG ophiolite series and form in MOR or(back-arc basin). A residue depleted mantle was left after the formation of Cr-rich podiform chromite deposit, which is needed to form the boninite. So, there is no genetic relationship between the chromte and boninite. The Al-rich podiform chromite deposits are products formed by re-equilibrium between the Cr-rich ore magma and basic melt and are not formed by interaction between the tholeiitic melt and peridotite. The occurrence of the UHP mineral inclusions in the chromite ores suggests a deeper mantle genesis for the podiform chromite deposits, but the boninite is segregated in the lower pressure (<10km). The podiform chromite deposits are rich in strong compatible elements IPGE (Os, Ir, Ru) alloys during partial melting, in contrast the boninites are rich in incompatible elements PPGE (Pt, Pd) surfide (arsenite) representing a later magmatic segregation. Obviously, there is no any genetic relationship between the boninite and Cr-rich podiform chromite deposit, and they are also controlled by island arc (or fore-arc) tectonic environment and thus only occur together spatially. |
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| Keywords: | podiform chromite deposit ophiolite mantle peridotite highly partial melting and reconstitution boninite |
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