Early Paleozoic crustal anatexis in the intraplate Wuyi-Yunkai orogen, South China
Early Paleozoic crustal anatexis in the intraplate Wuyi-Yunkai orogen, South China
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华南武夷-云开造山带板内早古生代地壳深熔
DOI：
10.1016/j.lithos.2013.04.024
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发表时间：
2013-08
期刊：
影响因子：
3.5
通讯作者：
Wong, Jean
中科院分区：
文献类型：
--
作者：
Zhao, Huan;Zhao, Huan;Wong, Jean;Wong, Jean
华南陆块武夷-云开板内造山带广泛发育早古生代角闪岩-麻粒岩相变质作用、地壳深熔作用和同时代岩浆作用。然而，麻粒岩相部分熔融的确切时间及其与造山作用的联系还没有得到很好的约束。本研究选取华夏地块云开隆起高州杂岩中的紫苏花岗岩、片麻状混合岩和富铝片麻岩（Grt-Sil-Bt片麻岩和Bt-Pl片麻岩）进行全岩常量元素和锆石U-Pb定年、微量元素和Lu-Hf同位素分析。高州杂岩经历了早古生代区域高温（高达850 °C）、低压-中压（4-7 kbar）变质作用，并伴有地壳深熔作用。云母熔体是由云母脱水而成的，如紫苏花岗岩中的黑云母+石英+斜长石=斜方辉石+钾长石+熔体，黑云母+石英+斜长石+硅线石=石榴子石+钾长石+熔体，Grt-Sil-Bt片麻岩中的白云母+石英+斜长石=硅线石+钾长石+熔体。紫苏花岗岩、片麻状混合岩和片麻岩为长英质，SiO2> 64%，过铝质，A/CNK > 1.0，反映原岩与沉积岩的亲合性。部分锆石显示出明显的核-环结构，其一致年龄主要在440-425 Ma左右，少数为2.8- 2.4Ga、1.5- 1.25Ga、1.2- 0.9Ga、850-540 Ma和460-450 Ma。440-425 Ma的颗粒自形、分带，从轻稀土元素到重稀土元素的斜率较陡，具有Ce正异常和Eu明显负异常，表明它们在熔体中重结晶。这些早古生代锆石的εHf（t）为负值（− 34.1 ~ − 1.5），TCRUST年龄更大（3.6-1.5 Ga），表明它们是由旧地壳物质（> 1.5 Ga）重熔形成的。年龄为2.8- 2.4Ga、1.6- 1.2Ga和1.2- 0.9Ga的锆石具有较高的εHf（t）值（高达+ 10.2-+ 15.2）。850-540 Ma锆石的εHf（t）值在+9.0到-24.0之间变化，TDM（亏损地幔Hf模式年龄）= 2.2-1.0 Ga，TCRUST（地壳Hf模式年龄）= 3.1-1.1 Ga。结合已发表的资料，我们认为华夏地块中含有3.6Ga的太古代物质，并经历了复杂的演化过程，包括2.7Ga、1.6- 1.2Ga和1.2- 0.9Ga的新生代物质的加入。旧地壳成分的改造主要发生在约850-750 Ma、750-540 Ma、460-450 Ma，在约440-425 Ma更为强烈。综合上述研究结果，认为云开紫苏花岗岩、片麻状混合岩和Bt-Pl片麻岩是早古生代高温热液地壳深熔作用的产物，而这一深熔作用可能是由华南陆块武夷-云开板内造山运动期间地壳缩短和增厚所触发的。
Early Paleozoic amphibolite- to granulite-facies metamorphism, crustal anatexis and coeval magmatism are extensively developed in the Wuyi–Yunkai intraplate orogen in the South China block. However, the exact timing of granulite-facies partial melting and its link with orogenesis have not been well constrained. In this study, the charnockites, gneissic migmatites and Al-rich gneisses (Grt–Sil–Bt gneiss and Bt–Pl gneiss) from the Gaozhou Complex of the Yunkai uplift in the Cathaysia block were selected for the analysis of whole-rock major elements and zircon U–Pb dating, trace elements and Lu–Hf isotopes. The Gaozhou Complex experienced early Paleozoic regional high-temperature (up to 850 °C), low- to medium-pressure (4–7 kbar) metamorphism accompanied by crustal anatexis. The melts were produced through the dehydration of mica, such as biotite + quartz + plagioclase = orthopyroxene + K-feldspar + melt and biotite + quartz + plagioclase + sillimanite = garnet + K-feldspar + melt in the charnockites, and muscovite + quartz + plagioclase = sillimanite + K-feldspar + melt in the Grt–Sil–Bt gneisses. The charnockites, gneissic migmatites and gneisses are felsic with SiO2> 64% and peraluminous with A/CNK > 1.0, reflecting protoliths with affinities to sedimentary rocks. Zircons from these rocks partly show clear core–rim structure and yield concordant ages mainly around 440–425 Ma, with minor groups at 2.8–2.4 Ga, 1.5–1.25 Ga, 1.2–0.9 Ga, 850–540 Ma and 460–450 Ma. The 440–425 Ma grains are euhedral, oscillatorily-zoned and have steep slopes from the LREE to the HREE with a positive Ce anomaly and clear negative Eu anomaly, suggesting they (re-) crystallized in the melts. These early Paleozoic zircons have negative εHf(t) (− 34.1 to − 1.5) and much older TCRUST(3.6–1.5 Ga), demonstrating they were formed by re-melting of old crustal materials (> 1.5 Ga). The zircons with ages of 2.8–2.4 Ga, 1.6–1.2 Ga and 1.2–0.9 Ga have relatively high εHf(t) values (up to + 10.2–+ 15.2). The 850–540 Ma zircons show variable εHf(t) values of + 9.0 to − 24.0 with TDM(depleted mantle Hf model ages) = 2.2–1.0 Ga and TCRUST(crustal Hf model ages) = 3.1–1.1 Ga. Combined with the published data, we suggest that the Cathaysia block contains Archean materials as old as 3.6 Ga and has had a complex evolution, including the addition of juvenile materials at ca 2.7 Ga, 1.6–1.2 Ga and 1.2–0.9 Ga. Reworking of old crustal components dominated at ca 850–750 Ma, 750–540 Ma, 460–450 Ma and more intensively at ca 440–425 Ma. Synthesizing the obtained results, we argue that the Yunkai charnockites, gneissic migmatites and Bt–Pl gneisses were formed due to the early Paleozoic high-T crustal anatexis, which may have been triggered by crustal shortening and thickening during the intraplate Wuyi–Yunkai orogeny in the South China block.
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影响因子：
--
作者：
Chuan-heng Zhang;Linzhi Gao;Zhenjie Wu;Xiaoying Shi;Q. Yan;Dajian Li
通讯作者：
Chuan-heng Zhang;Linzhi Gao;Zhenjie Wu;Xiaoying Shi;Q. Yan;Dajian Li
影响因子：
3.9
作者：
Groppo, Chiara;Rolfo, Franco;Indares, Aphrodite
通讯作者：
Indares, Aphrodite
影响因子：
3.8
作者：
Kang Chen;Shan Gao;Y. Wu;Jing‐Liang Guo;Zhaochu Hu;Yongsheng Liu;K. Zong;Zhengwei Liang;
通讯作者：
Kang Chen;Shan Gao;Y. Wu;Jing‐Liang Guo;Zhaochu Hu;Yongsheng Liu;K. Zong;Zhengwei Liang;
DOI：
--
发表时间：
2001
期刊：
--
影响因子：
--
作者：
N. Machado;A. Simonetti
通讯作者：
N. Machado;A. Simonetti
影响因子：
6.1
作者：
Yuejun Wang;W. Fan;Guowei Zhang;Yanhua Zhang
通讯作者：
Yuejun Wang;W. Fan;Guowei Zhang;Yanhua Zhang