中大别腹地榴辉岩锆石U-Pb年龄及其类型归属  

Zircon U-Pb geochronology and typological classification of eclogites in the hinterland of the central Dabie

作　　者：徐旭峰 石永红[2] 林伟[3] 冀文斌 

机构地区：[1]江苏地质调查研究院,南京210000 [2]合肥工业大学资环学院,合肥230009 [3]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2013年第5期1559-1572,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272073);国家"973"项目(2009CB825008)联合资助

摘　　要：根据对黄岗-牛凸岭地区榴辉岩样品JS249和JS250的岩相学研究表明,该地区榴辉岩具有明显的高压变质特征,石榴石中包含大量的早期矿物,成分环带显著,其峰期矿物组合主要为Grt+Omp+Phn+Rt+Qtz+Ep+Ky,角闪岩相退变矿物主要为Di+Mg-Hbl+Ab+Prg+Bt。对样品JS249和JS250温压条件进行计算,样品JS249为T=594±61℃,P=2.58±0.27GPa;样品JS250为T=616±56℃,P=2.14±0.14GPa。同时利用LA-ICPMS以及激光拉曼对这两个样品进行锆石U-Pb年代学研究和锆石包裹体分析,结果显示样品JS249锆石包体主要为角闪石、长石等退变矿物,其加权平均年龄为217.3±3.5Ma,该组年龄代表了角闪岩相退变质年龄;样品JS250锆石包含了石榴石、金红石、绿辉石等峰期矿物包体,其加权平均年龄为235.2±4.2Ma,该年龄应为峰期变质年龄。综合榴辉岩的岩石学、热力学和年代学的研究表明,黄岗-牛凸岭地区应属于低温高压单元,与南大别变质块体类似。According to the petrological analysis for eclogites of JS249 and JS250, the eclogites in Huanggang-Niutuling area have a clear characteristic of high-pressure metamorphism, garnets with zoning of compositions contain inclusions of earlier stage, the main mineral assemblage of peak metamorphic is Grt ＋ Omp ＋ Phn ＋ Rt ＋ Qtz ＋ Ep ＋ Ky, meanwhile the main mineral assemblage of amphibolite-faeies metamorphic is Di ＋ Mg-Hbl ＋ Ab ＋ Prg ＋ Bt. The resuh of P-T conditions from eclogites of JS249 and JS250 shows that, T = 594± 61℃ and P = 2. 58 ± 0. 27GPa are for JS249, T = 616 ±56℃ and P = 2. 14 ± 0. 14GPa are for JS250. LA-ICPMS zircon U-Pb geochronology and laser Raman spectroscopy of inclusions are determined for these two samples, the results show that, the inclusions of JS249 are amphibole, feldspar and other retrograde minerals with U-Pb age of 217.3 ±3.5Ma, which is timing the age of amphibolite-facies metamorphism. The inclusions of JS250 are garnet, rutile, omphacite and other peak-metamorphism minerals; the weighted average age is 235.2± 4. 2Ma, which is the age of peak metamorphism. Combined of petrology, thermodynamic and zircon U-Pb geochronology, Huanggang-Niutuling unit should be belong to lower-temperature and high-pressure unit, similar to the south Dabie Terrane.

关 键 词：中大别腹地 锆石U-PB年龄 低温高压榴辉岩 峰期变质P-T条件 

分 类 号：P588.348[天文地球—岩石学] P597.3[天文地球—地质学]