Trace element behavior and P–T–t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): implications for adakite genesis
Trace element behavior and P–T–t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): implications for adakite genesis
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DOI：
10.1016/j.lithos.2014.12.009
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发表时间：
2015-06
期刊：
影响因子：
3.5
通讯作者：
Guibin Zhang;Y. Niu;Shuguang Song;Lifei Zhang;Z. Tian;A. Christy;Lei Han
中科院分区：
文献类型：
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作者：
Guibin Zhang;Y. Niu;Shuguang Song;Lifei Zhang;Z. Tian;A. Christy;Lei Han
我们研究了超高压岩石折返过程中微量元素的行为和减压熔融的时间，柴北缘超高压变质带都兰地区南部一个露头中的熔融相（浅色体）、堆积相（石榴子石）和残余相（角闪榴辉岩）。两个不同的事件的部分熔融被确认。第一，无Grt的英云闪长-奥长闪长质浅色体熔体在424.0 ± 2.7Ma结晶，含较高的硅。石榴石生长在无色体熔体中，但分离出来形成石榴石堆积沿着与富钛相（金红石和钛铁矿），加强埃达克质签名的无色体。晚期含Gr的浅色体熔体，年龄为412.4 ± 2.9 Ma，横切石香肠和角闪岩化榴辉岩层。岩石地球化学和矿物地球化学研究证实了角闪榴辉岩与英云闪长-奥长质熔体的成因关系。角闪岩化榴辉岩中的锆石具有更老的原岩年龄（> 700 Ma），随后经历了榴辉岩相变质、退变质麻粒岩相叠加和部分熔融。通过相模拟和锆石定年计算，揭示了柴北缘俯冲带早古生代深俯冲陆壳折返和部分熔融的P-T-t演化轨迹。
We have studied trace element behavior and timing of decompression melting of UHP rocks during exhumation recorded in the magmatic products, i.e., the melt phase (leucosomes), cumulate (garnetite) and residue (amphibolitized eclogite) from a single outcrop in the south Dulan area, North Qaidam UHPM belt, NW China. Two distinct episodes of partial melting are recognized. First, Grt-free tonalitic–trondhjemitic leucosome melts with higher silica crystallized at 424.0 ± 2.7 Ma. Garnets grew in the leucosome melt but fractionated out to form garnetite cumulates along with Ti-rich phases (rutile and titanite), strengthening the adakitic signature of the leucosome. Later Grt-bearing leucosome melts with an age of 412.4 ± 2.9 Ma cross-cut boudins and layers of amphibolitized eclogite. Geochemical investigation of bulk-rocks and in situ minerals verifies the genetic relationship between the amphibolitized eclogite and the tonalitic–trondhjemitic melts. Zircons from the amphibolitized eclogite have older (> 700 Ma) protolith ages, with subsequent eclogite-facies metamorphism, retrograde granulite-facies overprinting and partial melting. Phase modeling and Zr-in-rutile thermometry calculations in combination with zircon geochronology reveal the evolutionP–T–t path for the exhumation and the partial melting of the deeply subducted continental crust at the North Qaidam subduction zone in the Early Paleozoic.