The possible subduction of continental material to depths greater than 200 km
The possible subduction of continental material to depths greater than 200 km
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DOI：
10.1038/35037566
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发表时间：
2000-10
期刊：
影响因子：
64.8
通讯作者：
K. Ye;B. Cong;Danian Ye
中科院分区：
文献类型：
--
作者：
K. Ye;B. Cong;Danian Ye
确定大陆岩石圈可以在会聚的板块边界俯冲到地幔中的深度，对于理解超级大陆的长期增长以及塑造这种边缘的动态过程非常重要。最近在区域超高压变质岩中发现的柯石英和钻石表明，大陆物质可以俯冲到至少120 公里的深度。)，根据几次间接观测，推断了造山超高压带中石榴石橄榄岩的俯冲深度为150-300 Km。但在天然超高压变质壳岩中，由于广泛的晚期重结晶作用和缺乏合适的压力指示器，用常规矿物学和岩石学方法很难直接追踪到大陆俯冲到这样的深度。然而，根据实验工作预测，辉石的固态溶解应发生在深度大于150 Km的石榴石中。本文报道了中国苏鲁超高压变质带洋口榴辉岩中石榴石中高含量的单斜辉石、金红石和磷灰石出溶的观测结果。我们将这些数据解释为俯冲大陆物质中辉石固溶体高压形成的结果。在这些样品中观察到的Na2O浓度和八面体硅的合适条件在大于200 公里的深度满足。
Determining the depth to which continental lithosphere can be subducted into the mantle at convergent plate boundaries is of importance for understanding the long-term growth of supercontinents as well as the dynamic processes that shape such margins. Recent discoveries of coesite and diamond in regional ultrahigh-pressure (UHP) metamorphic rocks has demonstrated that continental material can be subducted to depths of at least 120 km (ref. ), and subduction to depths of 150–300 km has been inferred from garnet peridotites in orogenic UHP belts based on several indirect observations,,,. But continental subduction to such depths is difficult to trace directly in natural UHP metamorphic crustal rocks by conventional mineralogical and petrological methods because of extensive late-stage recrystallization and the lack of a suitable pressure indicator. It has been predicted from experimental work, however, that solid-state dissolution of pyroxene should occur in garnet at depths greater than 150 km (refs ,,). Here we report the observation of high concentrations of clinopyroxene, rutile and apatite exsolutions in garnet within eclogites from Yangkou in the Sulu UHP metamorphic belt, China. We interpret these data as resulting from the high-pressure formation of pyroxene solid solutions in subducted continental material. Appropriate conditions for the Na2O concentrations and octahedral silicon observed in these samples are met at depths greater than 200 km.