Paleo-mantle wedge preserved in the Sambagawa high-pressure metamorphic belt and the thickness of forearc continental crust
Paleo-mantle wedge preserved in the Sambagawa high-pressure metamorphic belt and the thickness of forearc continental crust
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DOI：
10.1130/g33834.1
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发表时间：
2013-04
期刊：
影响因子：
5.8
通讯作者：
M. Aoya;S. Endo;T. Mizukami;S. Wallis
中科院分区：
文献类型：
--
作者：
M. Aoya;S. Endo;T. Mizukami;S. Wallis
俯冲型高压变质带中的超镁铁岩有两种可能的成因：（1）来自俯冲板片或下盘;（2）来自上盘地幔楔。根据对23 × 30 km 2的典型高压变质带--日本西南部三钵川带的野外研究，对该带中超镁铁质岩体的成因进行了评价。橄榄岩和/或蛇纹岩体在该带的高压部分很常见，但在低压部分（高压带）没有发现。如果超镁铁岩起源于下盘，则它们应与俯冲物质一起变质，其分布与变质压力无关。地幔岩石局限于高压区的分布是超镁铁岩块体幔楔成因的有力证据。地幔岩周围俯冲变质沉积物的存在表明，俯冲板片可以在构造上携带和运输大量的上盘物质到地球表面。超镁铁岩首次出现在石榴子石带内，其峰值变质压力为8.0-9.5 kbar，对应深度（30-35 km）代表白垩纪Sambagawa俯冲带弧前陆壳的厚度。
There are two possible origins for ultramafic rocks in subduction-type high-pressure metamorphic terranes: (1) they are derived from the subducted slab or footwall, or (2) they are derived from the mantle wedge in the hanging wall. The origin of ultramafic rock bodies in a classic high-pressure metamorphic belt, the Sambagawa belt of southwest Japan, is assessed based on wide-ranging field studies covering an area of 23 × 30 km 2 and corresponding to metamorphic pressures of 5–25 kbar. Peridotite and/or serpentinite bodies are common in the higher pressure part of the belt, but no occurrence is known in the low-pressure part (the chlorite zone). If the ultramafic rocks originated in the footwall, they should be metamorphosed together with the subducted material and their distribution should not show any correlation with metamorphic pressure. The restricted distribution of mantle rocks to the high-pressure part is strong evidence for a mantle-wedge origin of the ultramafic blocks. The presence of subducted metasediments surrounding the mantle rocks indicates that the subducted slab can tectonically entrain and transport substantial amount of hanging-wall material to the Earth’s surface. The first appearance of ultramafics occurs within the garnet zone, which has a peak metamorphic pressure of 8.0–9.5 kbar, and the corresponding depth (∼30–35 km) represents the thickness of the forearc continental crust in the Cretaceous Sambagawa subduction zone.