Lawsonite-bearing eclogites in the north Qilian and north Altyn Tagh: Evidence for cold subduction of oceanic crust
Lawsonite-bearing eclogites in the north Qilian and north Altyn Tagh: Evidence for cold subduction of oceanic crust
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DOI：
10.1007/s11434-006-1238-6
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发表时间：
2006-05
影响因子：
--
通讯作者：
Z. Jianxin;Meng Fancong
中科院分区：
文献类型：
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作者：
Z. Jianxin;Meng Fancong
根据岩相学和矿物化学，分别在北祁连（NQL）和北阿尔金（NAT）地区发现了含硬铝榴石的榴辉岩。硬石榴石与绿辉石、多硅白云石作为包裹体共存于石榴石中，表明榴辉岩相变质作用。估计平衡硬钠钙石-绿辉石-多硅白云母-石榴石峰组合的峰值变质条件为2.1-2.4 GPa和420-500°C，处于硬钠钙石榴辉岩相的稳定范围内。参考了 6-8 °C/km 的低地温，这与冷俯冲一致。 NQL和NAT地区均出现了含硬柱石榴辉岩，进一步证明NAT高压/低温变质带可能是被阿尔金塔格左旋滑断层偏移的NQL高压/低温变质带向西北延伸的部分。 NQL和NAT含硬钠长石榴辉岩是早古生代阿拉善地块和祁连地块碰撞前洋壳俯冲形成的。
Lawsonite-bearing eclogites are recognized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions in garnet, indicating eclogite-facies metamorphism. Peak metamorphic conditions for equilibrium lawsonite-omphacite-phengite-garnet peak assemblages are estimated to be 2.1–2.4 GPa and 420–500°C, which is in the stability field of lawsonite eclogite-facies. A low geotherm of 6–8 °C/km is referred, which is in consistent with a cold subduction. The occurrences of lawsonite-bearing eclogites in both NQL and NAT provide further evidence that the NAT HP/LT metamorphic belt is possibly the northwestward extension of the NQL HP/LT metamorphic belt offset by the Altyn Tagh left-lateral slip fault. The NQL and NAT lawsonite-bearing eclogites are formed by subduction of oceanic crust before collision of the Alashan and Qilian blocks in early Paleozoic.