Occurrence and field relationships of ultrahigh-pressure metagranitoid and coesite eclogite in the Su-Lu terrane, eastern China
Occurrence and field relationships of ultrahigh-pressure metagranitoid and coesite eclogite in the Su-Lu terrane, eastern China
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DOI：
10.1144/gsjgs.154.1.0045
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发表时间：
1997-01
影响因子：
2.7
通讯作者：
S. Wallis;A. Ishiwatari;T. Hirajima;K. Ye;J. Guo;D. Nakamura;T. Kato;M. Zhai;M. Enami
中科院分区：
文献类型：
--
作者：
S. Wallis;A. Ishiwatari;T. Hirajima;K. Ye;J. Guo;D. Nakamura;T. Kato;M. Zhai;M. Enami
在区域发育的角闪岩相苏鲁正片麻岩中，有一个50×100 m2的露头，柯石英榴辉岩与变花岗岩伴生。变质花岗岩和基性岩之间的原生侵入关系和大量化学分析表明，它们共同代表了一个复合火成岩体，随后强烈变形和变质。金红石、钠辉石、冠状石榴石和柯石英后可能的假晶的存在都表明变质花岗岩中的变质压力非常高。这是第一次记录到欧洲阿尔卑斯山以外的超高压（UHP）变质花岗岩。超高压变质花岗岩类的存在表明，岩石的低密度并不一定阻止俯冲到地幔深处。即使在峰变质条件下，这里报道的超高压复合火成岩体的体积密度也小于地幔。因此，浮力可能对这一部分的早期挖掘起了重要作用。苏鲁地区其他柯石英榴辉岩的露头也可能最初与低密度花岗岩类一起沿着变质。
Coesite eclogite is associated with metagranitoid in a 50×100 m2 outcrop within the regionally developed amphibolite-facies Su-Lu orthogneiss. Primary intrusive relationships between the metagranitoid and basic rocks and bulk-chemistry analyses show that together they represent a composite igneous body that has subsequently been strongly deformed and metamorphosed. The presence of rutile, sodie pyroxene, corona garnet, and possible pseudomorphs after coesite all suggest very high pressures of metamorphism in the metagranitoid. This is the first documented occurrence of ultrahigh-pressure (UHP) metagranitoid outside of the European Alps. The existence of UHP metagranitoid shows that low density of rocks does not necessarily prevent subduction to mantle depths. Even at peak metamorphic conditions the UHP composite igneous body reported here would have a bulk density less than the mantle. Buoyancy forces may, therefore, have been important in the early exhumation of this unit. Other outcrops of coesite eclogite in the Su-Lu region may also have been originally metamorphosed along with low-density granitoid rocks.