Coexisting different types of zoned garnet in kyanite-quartz eclogites from the Sanbagawa metamorphic belt: Evidence of deformation-induced lithological mixing during prograde metamorphism
Coexisting different types of zoned garnet in kyanite-quartz eclogites from the Sanbagawa metamorphic belt: Evidence of deformation-induced lithological mixing during prograde metamorphism
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三波川变质带蓝晶石-石英榴辉岩中共存不同类型的分区石榴石：顺变质作用过程中变形引起的岩性混合的证据
DOI：
10.1111/iar.12274
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发表时间：
2018
期刊：
影响因子：
1.5
通讯作者：
Huang Shuaimin
中科院分区：
文献类型：
--
作者：
Enami Masaki;Kimura Jun-Ichi;Tsuboi Motohiro;Kouketsu Yui;Nagaya Takayoshi;Huang Shuaimin
四国中部别志地区三坝川石英榴辉岩中的石榴石颗粒普遍表现出由核和幔/缘组成的分带模式，分别形成于榴辉岩的两个退变质阶段和随后的绿帘-角闪岩相变质作用阶段。石英榴辉岩中的石榴子石颗粒根据其芯部的成分趋势可分为四种类型（I、II、III和IV）。I型石榴石是最常见的，有时与其他类型的石榴石在薄切片中共存。I型岩芯形成于榴辉岩相阶段，由绿帘石和蓝晶石组成。II型和III型内核分别在进积早期阶段在不含绿帘石和含蓝晶石的榴辉岩以及不含绿帘石和蓝晶石的榴辉岩的不同全岩成分中结晶。IV型内核可能形成于前榴辉岩相阶段。II、III和IV类的内核在不同的俯冲变质作用和/或全岩成分的P-T条件下形成，与I类的内核并列，可能是由于俯冲榴辉岩相阶段不同点的岩石构造混合。它们经历了以下共同的生长历史：（1）榴辉岩相变质后期的连续晶体生长，形成了I型核的边缘和II、III、IV型核的外核，（2）在折返和水化阶段，部分核被再吸收;（iii）在绿帘石-角闪岩相的逆冲变质作用中形成地幔带。在某些三八川变质岩中，在等化学条件下可能没有进行过变质反应，至少在手标本尺度上是这样。这种解释表明，在某些情况下，由机械混合和流体辅助扩散传质促进的物质相互作用可能会影响高压变质岩的矿物反应和共生。
Garnet grains in Sanbagawa quartz eclogites from the Besshi region, central Shikoku commonly show a zoning pattern consisting of core and mantle/rim that formed during two prograde stages of eclogite and subsequent epidote–amphibolite facies metamorphism, respectively. Garnet grains in the quartz eclogites are grouped into four types (I, II, III, and IV) according to the compositional trends of their cores. Type I garnet is most common and sometimes coexists with other types of garnet in a thin section. Type I core formed with epidote and kyanite during the prograde eclogite facies stage. The inner cores of types II and III crystallized within different whole‐rock compositions of epidote‐free and kyanite‐bearing eclogite and epidote‐ and kyanite‐free eclogite at the earlier prograde stage, respectively. The inner core of type IV probably formed during the pre‐eclogite facies stage. The inner cores of types II, III, and IV, which formed under different P–T conditions of prograde metamorphism and/or whole‐rock compositions, were juxtaposed with the core of type I, probably due to tectonic mixing of rocks at various points during the prograde eclogite facies stage. After these processes, they have shared the following same growth history: (i) successive crystal growth during the later stage of prograde eclogite facies metamorphism that formed the margin of the type I core and the outer cores of types II, III, and IV; (ii) partial resorption of the core during exhumation and hydration stage; and (iii) subsequent formation of mantle zones during prograde metamorphism of the epidote–amphibolite facies. The prograde metamorphic reactions may not have progressed under an isochemical condition in some Sanbagawa metamorphic rocks, at least at the hand specimen scale. This interpretation suggests that, in some cases, material interaction promoted by mechanical mixing and fluid‐assisted diffusive mass transfer probably influences mineral reactions and paragenesis of high‐pressure metamorphic rocks.