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中文摘要：
浒湾高压变质带位于大别造山带的西北部，是研究秦岭-大别-苏鲁造山带演化过程和时间的关键地区。我们对产于该高压变质带的三个榴辉岩样品进行了LA-ICPMS锆石U-Pb定年、微量元素和Hf同位素组成分析，以限定榴辉岩相变质作用及原岩形成的时间和原岩性质。苏家河榴辉岩中的变质锆石颗粒具低Th／U值、弱的Eu负异常、较平坦的重稀土（HREE）配分模式，以及低的176Lu／177Hf值。表明这些锆石形成过程中有石榴子石的存在而缺乏斜长石，因此形成于榴辉岩相变质条件。Ti含量温度计计算表明，这些变质锆石的形成温度约为655℃和638℃，与在榴辉岩相变质作用温度条件下形成一致，206Pb／238U年龄加权平均结果为309士4Ma（2a），代表了榴辉岩相变质作用时间的最佳估计值。胡家湾变质锆石可能形成于前进变质作用阶段，206Pb／238U年龄加权平均值为312±11Ma（2σ），这一结果在误差范围内与苏家河的年龄结果一致。锆石U—Pb年龄和微量元素分析结果表明，榴辉岩核部的锆石属岩浆型，年龄为406±5～420±7Ma（20），表明原岩晚于中古生代华北与秦岭地体的碰撞时间。三个榴辉岩样品的锆石颗粒εHf（t）值的变化范围较大（-4．9～21．3）。变质锆石与岩浆锆石的Hf同位素的变化范围相近，少数变质增生边部锆石与核部残留岩浆锆石给出较一致的Hf同位素组成，表明变质增生锆石可能是原岩岩浆锆石溶解再结晶作用的结果，因此保留了原岩的初始Hf同位素组成。高的εHt（t）值表明它们的原岩来自亏损的地幔源区，可能是古特提斯洋壳；而低εHf（t）值则归因于地壳混染作用。少量继承核锆石的出现表明榴辉岩的原岩形成过程中有古老地壳物质的加入。浒湾地区一些榴辉岩具明显的来自扬子板块大陆地壳的年代学和地球化学特征。该区古生代的洋壳?
英文摘要：
The Huwan high-pressure （HP） metamorphic zone, located in the northwestern Dabie Mountains, is a key region in which to investigate the processes and timing of continental growth in the Qinling-Dabie-Sulu orogenic belt. Three eclogite samples, two from Sujiahe and one from Hujiawan in this zone, were selected for in situ LA- ICPMS U-Pb dating and trace element and Hf isotope analysis of zircon, in order to constrain the timing of eclogite- facies metamorphism and nature and ages of the protoliths. Metamorphic zircon crystals in the Sujiahe eclogites are characterized by low Th/U ratios, small negative Eu anomaly, flat HREE patterns, and low 176Lu/177 H f ratios.These geochemical signatures suggest that the zircon crystallized in the presence of garnet and in the absence of pla- gioclase feldspar. Furthermore, temperatures of -655℃ and -638℃, calculated using the Ti content of zircon, are consistent with their formation during eclogite-facies metamorphism. The weighted mean 206pb/238U age of 309 ± Ma （2σ） for the zircon is the best estimate of the age of this metamorphic event in the Huwan shear zone, constraining earlier estimates that ranged from 420 to 220 Ma. Metamorphic zircon crystals from the Hujiawan eclogite sample most likely formed during prograde metamorphism, and yielded a 206Pb/238 U age of 312±11 Ma （2σ）,which is within analytical uncertainty of the results obtained for the two Sujiahe eclogite samples. U-Pb and trace element analyses of magmatic zircon cores in the three eclogite samples suggest almost coeval protolith crystalliza- tion ages of 406±5 to 420±7 Ma （20）. This indicates that intrusion of the protoliths postdated the middle Paleozo- ic collision of the North China Craton and the Qinling terrain. The zircon crystals in the three eclogite samples con tain a large variation of Era（t） values of -4.9 to 21.3. The metamorphic zircon overgrowths show the same range of εHr（t） values as those of the inherited magmatic crystal interiors. This suggests that the m
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