Phase transformations of continental crust during subduction and exhumation: Western Gneiss Region, Norway
Phase transformations of continental crust during subduction and exhumation: Western Gneiss Region, Norway
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俯冲和折返过程中大陆地壳的相变：挪威西部片麻岩地区
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
E. Baxter
中科院分区：
文献类型：
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作者：
E. Peterman;B. Hacker;E. Baxter
石英长岩是否在俯冲过程中转变为（U）HP矿物，并在折返时转变为低压矿物，仍然是与碰撞造山作用有关的更深刻的问题之一。来自挪威西部片麻岩地区的含石榴石石英长石片麻岩为回答这个问题提供了机会。这些片麻岩的高精度 Sm-Nd 石榴石地质年代学记录了石榴石的生长时间为 418 Ma 至 398 Ma。两个样品中的石榴石分带表明，在与俯冲相关的压力从 0.5 GPa 和 550 °C 增加到 1.7 GPa 和 700 °C 期间发生了生长。所有其他石榴石的分带表明，在减压期间，在 1.0-1.6 GPa 和 725-800 °C 的相当窄的 P-T 范围内发生了生长，可能伴随着熔化。如果这些样品构成了代表性的套件，（i）（U）HP石榴石的缺乏表明西部片麻岩地区的大多数石英长石片麻岩在俯冲过程中并未转变为榴辉岩相共生岩； (ii) 减压期间生长的大量石榴石表明，致密化的主要时期是在折返期间。俯冲过程中石英长岩的广泛亚稳定性与之前的研究结果有很大不同，这表明在板片出现正浮力之前，大陆地壳的俯冲作用相应较小。
Whether quartzofeldspathic rocks transform to (U)HP minerals during subduction - and back to low-pressure minerals upon exhumation - remains one of the more profound questions pertaining to collisional orogenesis. Garnet-bearing quartzofelds- pathic gneisses from the Western Gneiss Region, Norway provide an opportunity to answer this question. High-precision Sm-Nd garnet geochronology of these gneisses documents garnet growth from 418 to 398 Ma. Garnet zoning in two samples implies growth during subduction-related increase in pressure from 0.5 GPa and 550 � C to 1.7 GPa and 700 � C. Zoning in all other garnets suggests growth over rather narrow P-T ranges from 1.0-1.6 GPa and 725-800 � C during decompression, possibly accompanying melting. If these samples constitute a representative suite, (i) the dearth of (U)HP garnets suggests that most of the quartzofeldspathic gneisses in the Western Gneiss Region did not transform to eclogite-facies parageneses during subduction; (ii) the abundance of garnets grown during decompression indicates that the major period of densification was during exhumation. The widespread metastability of quartzofeldspathic rocks during subduction is substantially different from the findings of previous work and suggests commensu- rately less subduction of continental crust before the slab is positively buoyant.
影响因子：
4.2
作者：
Hacker, Bradley R.;Wallis, Simon R.;Gehrels, George
通讯作者：
Gehrels, George