Poly-cyclic metamorphic evolution of eclogite: Evidence for multistage burial–exhumation cycling in a subduction channel
Poly-cyclic metamorphic evolution of eclogite: Evidence for multistage burial–exhumation cycling in a subduction channel
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榴辉岩的多旋变质演化：俯冲通道多阶段埋藏-折返循环的证据
DOI：
10.1093/petrology/egw002
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发表时间：
2016
影响因子：
3.9
通讯作者：
John Timm
中科院分区：
文献类型：
--
作者：
Li Ji-Lei;Klemd Reiner;Gao Jun;John Timm
超高压榴辉岩为俯冲带地幔深部变质作用提供了直接证据。纹理证据和压力-温度（P-T）路径重建提供了一个独特的机会，以限制地球动力学过程沿着板块界面。为了更好地了解俯冲通道的动力学，我们提出了一个详细的岩石学，岩石学和假剖面模拟研究的变质复杂的高压榴辉岩样品从构造块体的阿克亚兹（U）高压变质岩在中国天山。矿物化学变化和结构的不连续性表明，所有的主要阶段的岩石（石榴石，绿帘石，单斜辉石和角闪石）显示多个生长区兼容的多周期演化，包括两个埋藏-剥露周期。基于有效体相成分的热力学模拟得出的精确P-T路径表明，该榴辉岩经历了复杂的埋藏-剥露循环，具有两个P-T循环，表现为多相石榴子石的出现以及相互置换和再生长的角闪石。这表明，榴辉岩样品，这是一个遗迹的构造分离的洋壳，经历了两个埋葬-折返周期在俯冲通道的对流。这一自然现象与数值模拟研究相一致，数值模拟研究表明，在俯冲通道中的深俯冲洋壳预计会出现压力循环。榴辉岩样品的模拟折返过程对应于先前建议的Akeyazi（U）高压岩石的俯冲通道折返模型。
(Ultra-)high-pressure [(U)HP] eclogites provide direct evidence for metamorphic processes at mantle depths in subduction zones. Textural evidence and pressure–temperature (P–T) path reconstruction allow a unique opportunity to constrain the geodynamic processes along the plate interface. To better understand the dynamics of subduction channels, we present a detailed petrographical, petrological and pseudosection modeling study of a metamorphically complex HP eclogite sample from a tectonic block of the Akeyazi (U)HP metamorphic terrane in the Chinese Tianshan. Mineral chemical variations and textural discontinuities show that all the major phases of the rock (garnet, epidote, clinopyroxene and amphibole) display multiple growth zones compatible with a poly-cyclic evolution including two burial–exhumation cycles. The preciseP–Tpath derived from thermodynamic modeling based on effective bulk compositions suggests that the eclogite underwent complex burial–exhumation cycles with twoP–Tloops indicated by the occurrence of polyphase garnet and mutually replaced and regrown amphibole. It is suggested that the eclogite sample, which represents a relic of tectonically detached oceanic crust, underwent two burial–exhumation cycles during convective flow in a subduction channel. This natural occurrence is consistent with numerical simulation studies showing that pressure cycling is to be expected for deeply subducted oceanic crust in a subduction channel. The modeled exhumation process for the eclogite sample corresponds to a previously suggested subduction channel exhumation model for the Akeyazi (U)HP rocks.