Episodic growth of zircon in UHP orthogneisses from the North Dabie Terrane of east‐central China: implications for crustal architecture of a collisional orogen
Episodic growth of zircon in UHP orthogneisses from the North Dabie Terrane of east‐central China: implications for crustal architecture of a collisional orogen
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DOI：
10.1111/j.1525-1314.2010.00902.x
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发表时间：
2010-12
影响因子：
3.4
通讯作者：
Z. Xie;J.‐F. Chen;Ying Cui
中科院分区：
文献类型：
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作者：
Z. Xie;J.‐F. Chen;Ying Cui
对北大别地体的三个正片麻岩样品（NDT）进行了锆石U-Pb定年，以重建其形成和演化历史，以及三叠纪俯冲和折返后大别造山带的地壳结构。 SHRIMP 锆石 U-Pb 定年与背散射电子 (BSE) 成像和激光拉曼光谱测定相结合，可以准确识别原岩形成期间锆石生长以及俯冲/折返和碰撞后变质作用期间过度生长的核心、地幔和边缘结构。对于未变生化的继承岩心的残余振荡分带场，获得了 760-730 Ma 的一致 U-Pb 年龄和 >0.4 的高 Th/U 比率。这些特征表明这些年龄代表了罗迪尼亚分裂期间岩浆原岩形成的时间。变生化核心周围生长茂盛的地幔域是干净的，几乎没有矿物包裹体（例如石英、石榴石和磷灰石）。地幔域的 Th/U 比率较低，为 0.719，与 CDT 中的超高压正片麻岩获得的值相似。结论是，与 CDT 一样，NDT 产生的幕式锆石生长的正片麻岩也应该是大陆深俯冲后挖出的切片的一部分。然而，与白垩纪岩浆作用之前的CDT相比，本研究中的正片麻岩埋藏在造山地壳中的埋藏位置较低。因此，NDT 的正片麻岩受到了白垩纪岩浆作用的影响，而 CDT 的正片麻岩则没有受到影响。
Zircon U‐Pb dating of three orthogneiss samples from the North Dabie terrane (NDT) is undertaken in order to reconstruct their formation and evolutionary histories, and also the crustal architecture of the Dabie orogen after Triassic subduction and exhumation. SHRIMP zircon U‐Pb dating, in combination with back scattered electron (BSE) imaging and Laser Raman spectrometry, provides accurate identification of the core, mantle and rim structure for zircon growth during protolith formation and overgrowth during subduction/exhumation and post‐collisional metamorphism. Concordant U‐Pb ages of 760–730 Ma and high Th/U ratios of >0.4 are obtained for relict oscillatory zoning fields of inherited cores that were not metamictized. These features suggest that these ages represent the time of magmatic protolith formation during the breakup of Rodinia. The overgrown mantle domains around the metamictized cores are clean with few mineral inclusions (e.g. quartz, garnet and apatite). Mantle domains have low Th/U ratios of 0.719, similar to the values obtained from UHP orthogneisses in the CDT. It is concluded that, as with the CDT, the orthogneisses with episodic zircon growths from the NDT should also be a part of the exhumed slice following the continental deep subduction. However, the orthogneisses in this study were buried at a lower level in the orogenic crust compared with those of the CDT prior to the Cretaceous magmatism. Therefore, the orthogneisses from the NDT were affected by the Cretaceous magmatism whereas the CDT orthogneisses were not affected.