U–Pb, trace element and Lu–Hf properties of unique dissolution–reprecipitation zircon from UHP eclogite in SW Sulu terrane, eastern China
U–Pb, trace element and Lu–Hf properties of unique dissolution–reprecipitation zircon from UHP eclogite in SW Sulu terrane, eastern China
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DOI：
10.1016/j.gr.2011.11.007
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发表时间：
2012-07
影响因子：
6.1
通讯作者：
Fulai Liu;A. Gerdes;Pinghua Liu
中科院分区：
文献类型：
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作者：
Fulai Liu;A. Gerdes;Pinghua Liu
利用激光拉曼和阴极发光成像结合微量元素分析和U-Pb、Lu-Hf同位素数据，首次在苏鲁超高压地体西南部CCSD-MH孔含QTZ和Phe的榴辉岩中发现了一种独特的溶解-再沉淀锆石。部分溶解锆石的残留继承域具有岩浆特征，保存了Cpx+Pl+Qtz+Ap的矿物包裹体。而新形成的锆石在继承(岩浆)域的裂隙周围或沿裂隙结晶，含有典型的超高压变质作用的CoE+GRT+OMP+Phe+AP的矿物包裹体。此外，在含柯石英的锆石区域中发现了原生流体包裹体，其特征为单一的H2O相或CO2-H2O相，表明在超高压条件下存在流体。强溶继承(岩浆)锆石SHRIMP206Pb/238U年龄为782~588 Ma，上交点年龄为780±14 Ma。新的重结晶或变质锆石获得了一致的三叠纪超高压年龄，其加权平均值为229.2±2.3 Ma。锆石微量元素、Hf同位素组成和矿物包裹体将苏鲁榴辉岩原岩划分为中基性-镁铁质新元古代火成岩，中三叠世俯冲到地幔深处，经历了超高压变质作用。继承(岩浆)锆石的年轻εHf(780 Ma)值为+7.4±2.9，表明中新元古代亏损地幔对大别-苏鲁超高压地体具有显著的输入作用。新的超高压锆石具有较低的Lu/Hf、Th/U和明显高于继承(岩浆)锆石的176Hf/177Hf比值，这与超高压变质过程中Lu-Hf系统重结晶和分馏的形成相一致。
A unique dissolution–reprecipitation zircon has been identified for the first time in a Qtz- and Phe-bearing eclogite from the drill hole CCSD-MH, southwestern Sulu UHP terrane by using laser Raman and cathodoluminescence (CL) imaging combined with trace-element analyses and U–Pb and Lu–Hf isotope data. Relic inherited domains of partially dissolved zircon show magmatic features and preserve mineral inclusions of Cpx+Pl+Qtz+Ap. Whereas newly formed zircons crystallized around or along cracks of the inherited (magmatic) domains and contain mineral inclusions of Coe+Grt+Omp+Phe+Ap typical for UHP metamorphism. In addition, primary fluid inclusions were identified in the coesite-bearing zircon domains, characterized by a single H2O-phase or CO2–H2O-phase, indicating the presence of fluids during UHP conditions. Strongly dissolved inherited (magmatic) zircons yielded SHRIMP206Pb/238U ages of 782–588Ma with an upper intercept age of 780±14Ma. New recrystallized or metamorphic zircons yielded consistent Triassic UHP ages around 238–225Ma with a weighted mean of 229.2±2.3Ma. Zircon trace element and Hf isotope compositions and mineral inclusions classify the protolith of the Sulu eclogite as an intermediate to mafic Neoproterozoic igneous rock, which was subducted to mantle depth and experienced UHP metamorphism in Middle Triassic times. The juvenile εHf(780Ma)value of+7.4±2.9 in inherited (magmatic) zircon points to a significant input from the depleted mantle to the Dabie–Sulu UHP terrane during Middle Neoproterozoic. New UHP zircon domains have low Lu/Hf, Th/U and significantly higher176Hf/177Hf ratios than the inherited (magmatic) zircons, consistent with formation during recrystallization and fractionation of the Lu–Hf system during UHP metamorphism.