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首页> 外文期刊>Contributions to Mineralogy and Petrology >Omphacite breakdown reactions and relation to eclogite exhumation rates
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Omphacite breakdown reactions and relation to eclogite exhumation rates

机译：辉石分解反应及其与榴辉石发掘率的关系

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Clinopyroxene + plagioclase (+ - Hbl + - Qtz) symplectites after omphacite are widely cited as evidence for prior eclogite-facies or high-pressure (HP) metamor-phism. Precursor omphacite compositions of retrograde eclogites, used for reconstructing retrograde P-T paths, are commonly estimated by reintegrating symplectite phases with the assumption that the symplectite-forming reactions were isochemical. Comparisons of broadbeam symplectite compositions to adjacent unreacted pyroxene from various symplectites after clinopyroxene from the Appalachian Blue Ridge (ABR) and Western Gneiss Region (WGR) suggest that the symplectite forming reactions are largely isochemical. Endmember calculations based on reintegrated symplectite compositions from the ABR and WGR suggest that a minor Ca-Eskola (CaEs) component (X_(C_aE_s) = 0.04-0.15) was present in precursor HP clinopyroxene. WGR symplectites consist of fine-grained (approx 1 mu m-scale), vermicular intergrowths of PI + Cpx II + - Hbl that occur at grain boundaries or internally. ABR symplectites contain coarser (approx10 mu m-scale) planar lamellae and rods of P1 + Cpx II + Qtz + Hbl within clinopyroxene cores. The contrasting textures correlate with decompression and cooling rate, and degree of overstepping of the retrograde reaction (lamellar: slow, erosionally controlled exhumation with slow/low overstepping; fine-grained, grainboundary symplectite: rapid, tectonic exhumation with rapid/high overstepping). Variations in X_(C_aE_s), X_(jd), and X_(C_aT_s) of precursor HP omphacite are related to the symplectic mineral assemblages that result from decompression. Quartz-normative symplectities indicate quartz-producing retrograde reactions (e.g., breakdown of precursor CaEs); quartz-free symplectities (e.g., diopside + plagioclase after omphacite) indicate quartz-consuming reactions (jd, CaTs breakdown) outpaced quartz-producing reactions.
机译：辉石岩后的斜辉石+斜长石（+-Hbl +-Qtz）的共晶被广泛引用为以前的榴辉岩相或高压（HP）变质作用的证据。用于逆行P-T路径重构的逆向榴辉岩的前体辉绿岩成分通常是通过重新合成手榴石相来估算的，前提是假定形成的手榴石反应是等化学的。比较来自阿巴拉契亚蓝岭（ABR）和西部片麻岩地区（WGR）的次生辉石之后，宽束叠石组成与相邻的未反应的辉石。根据来自ABR和WGR的重新整合的脚手架组成的端构件计算表明，前体HP斜py中存在少量Ca-Eskola（CaEs）组分（X_（C_aE_s）= 0.04-0.15）。 WGR交折物由细粒（约1微米级）的PI + Cpx II +-Hbl的蠕虫共生体在晶界或内部产生。 ABR共沸石包含较粗的（约10微米尺度）平面薄片，并在斜辉石岩心内含有P1 + Cpx II + Qtz + Hbl杆。对比的质地与减压和冷却速度以及逆行反应的超步程度相关（薄层：缓慢，侵蚀控制的发掘，缓慢/低超步;细粒，晶界共生物：快速，构造发掘，具有快速/高超步）。前体HP绿辉石的X_（C_aE_s），X_（jd）和X_（C_aT_s）的变化与减压产生的辛矿物组合有关。石英规范的对立性表明产生石英的逆行反应（例如，前体CaE的分解）。无石英的对映体（例如，辉绿岩后的透辉石+斜长石）表明消耗石英的反应（jd，CaTs分解）超过了产生石英的反应。

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