Zoned Zircon from Eclogite Lenses in Marbles from the Dabie‐Sulu UHP Terrane, China: A Clear Record of Ultra‐deep Subduction and Fast Exhumation
Zoned Zircon from Eclogite Lenses in Marbles from the Dabie‐Sulu UHP Terrane, China: A Clear Record of Ultra‐deep Subduction and Fast Exhumation
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DOI：
10.1111/j.1755-6724.2007.tb00945.x
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发表时间：
2007-04
期刊：
影响因子：
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通讯作者：
Liu Fulai;A. Gerdes;P. Robinson;Xue Huaimin;Ye Jianguo
中科院分区：
文献类型：
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作者：
Liu Fulai;A. Gerdes;P. Robinson;Xue Huaimin;Ye Jianguo
翻译后摘要：从大别-苏禄超压（UHP）的大理石榴辉岩透镜体深俯冲Meta沉积岩。这些岩石中的锆石已被用来限制俯冲过程中的超高压和超高压变质作用以及后来折返过程中的退变质作用的年龄。继承（碎屑）和变质锆石的透射光显微镜，阴极发光（CL）成像，微量元素含量和矿物包裹体的基础上区分。矿物包裹体的分布与变质锆石的CL成像相结合，可以将锆石带（域）与不同的变质阶段联系起来。域1由圆形、椭圆形和纺锤形核组成，具有暗发光图像，并含有石英榴辉岩相矿物包裹体组合，表明在T = 571-668°C和P = 1.7 - 2.02 GPa的高压（HP）变质条件下形成。结构域2总是围绕结构域1或以具有白色发光图像的圆形和细长的核心出现。含有柯石英榴辉岩相矿物包裹体组合，表明其形成于T = 782-849°C，P > 5.5GPa的超高压变质条件下。具有灰色发光图像的结构域3总是围绕结构域2，并且作为最外面的锆石边缘出现。以低压矿物包裹体组合为特征，与T = 600-710°C、P = 0.7 - 1.2 GPa的区域角闪岩相退变质作用有关。三个变质锆石域具有不同的时代;大别山样品H1的SHRIMP年龄为245 ± 4 Ma，域1为235 ± 3 Ma，域3为215 ± 6 Ma，而苏鲁山样品H2的SHRIMP年龄为244 ± 4 Ma，域2为233 ± 4 Ma，域3为214 ± 5 Ma，分别这些带的平均年龄表明，俯冲到超高压深度发生在10-11 Ma和折返的岩石发生在一个时期的19-20 Ma。因此，从155公里到160公里深的地幔深度的俯冲发生在大约9.5-10.5公里/Ma的速率，而从160公里深到-30公里深的地壳底部的折返发生在大约6.5公里/Ma的速率。我们提出了一个模型，这些岩石涉及大陆边缘岩石圈的深俯冲，然后在地幔深处的超高压板片断裂后，由浮力驱动的超快折返。
Abstract: Eclogite lenses in marbles from the Dabie‐Sulu ultrahigh‐pressure (UHP) terrane are deeply subducted meta‐sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited (detrital) and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence (CL) imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones (domains) to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark‐luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high‐pressure (HP) metamorphic conditions of T = 571–668°C and P = 1.7‐2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white‐luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782–849°C and P > 5.5 GPa. Domain 3, with gray‐luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low‐pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600–710°C and P = 0.7‐1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215 ± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10–11 Ma and exhumation of the rocks occurred over a period of 19–20 Ma. Thus, subduction from ∼ 55 km to > 160 km deep mantle depth took place at rates of approximately 9.5–10.5 km/Ma and exhumation from depths >160 km to the base of the crust at −30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin Iithosphere followed by ultrafast exhumation driven by buoyancy forces after break‐off of the UHP slab deep within the mantle.