| 柴北缘锡铁山一带榴辉岩的岩石学特征及其退变PT轨迹 |
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| 引用本文： | 张聪,张立飞,张贵宾,宋述光.柴北缘锡铁山一带榴辉岩的岩石学特征及其退变PT轨迹[J].岩石学报,2009,25(9):2247-2259. |
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| 作者姓名： | 张聪 张立飞 张贵宾 宋述光 |
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| 作者单位： | 北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京,100871 |
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| 基金项目： | 国家自然科学基金，国家973项目(2009CB825007)资助成果 |
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| 摘 要： | 柴北缘锡铁山地区榴辉岩以透镜体的形式存在于花岗质片麻岩和副变质片麻岩中.根据矿物组合的不同,可以分为多硅白云母榴辉岩和角闪石榴辉岩.在多硅白云母榴辉岩中首次发现了柯石英假象.利用榴辉岩中Grt-Cpx-Phn矿物温压计.结合绿辉石中存在柯石英假象包体的现象,得到锡铁山榴辉岩的峰期温压条件为751～791℃,2.71～3.17GPa,证明了锡铁山地区与柴北缘其他地块一样,也经历了超高压变质作用.通过PT视剖面图计算了榴辉岩退变的PT轨迹具有2个阶段演化特征：即先等温降压,然后再降温降压的PT轨迹.详细的岩石学研究探讨了榴辉岩在退变过程中,各矿物的成分和结构的改变过程.石榴石在等温降压过程中成分变化不大,而在角闪石出现后,其边部镁铝榴石含量明显降低,进而形成了韭闪石+斜长石的冠状体.绿辉石在水饱和状态下经过贫硬玉化改造,而后形成了Di+Ab+Amp的后生合晶.多硅白云母分解形成白云母+黑云母及少量石英及钾长石的组合.角闪石随着温压条件的降低由钠钙质闪石逐渐向钙质闪石转化.
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| 关 键 词： | 柴北缘 锡铁山 榴辉岩 PT视剖面图 退变PT轨迹 |
| 收稿时间： | 2008/12/12 0:00:00 |
| 修稿时间： | 2009/3/17 0:00:00 |
Petrology and calculation of retrograde PT path of eclogites from Xitieshan, North Qaidam, China |
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| ZHANG Cong,ZHANG LiFei,ZHANG GuiBin and SONG ShuGuang.Petrology and calculation of retrograde PT path of eclogites from Xitieshan, North Qaidam, China[J].Acta Petrologica Sinica,2009,25(9):2247-2259. |
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| Authors: | ZHANG Cong ZHANG LiFei ZHANG GuiBin and SONG ShuGuang |
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| Institution: | Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, Peking University, Beijing 100871, China;Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, Peking University, Beijing 100871, China;Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, Peking University, Beijing 100871, China;Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, Peking University, Beijing 100871, China |
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| Abstract: | Eclogite from Xitieshan area occurs as lenses within granitic gneiss and pelitic gneiss. According to the characteristic minerals, these eclogites can be divided into two types, i. e. , phengite eclogite and hornblend eclogtie. Coesite pseudomorph inclusion in omphacite is found in the phengite eclogite. Using garnet-omphacite-phengite geothermobarometer, the peak P-T conditions of Xitieshan eclogites are P = 2.71 ～ 3. 17GPa and T = 751 ～ 791℃ which is consistent with the presence of coesite pseudomorph inclusion in omphacite. Therefore, we infer that some of eclogites in Xitieshan have undergone VHP metamorphism as the other blocks such as Dulan eclogites in North Qadam. Based on the PT pseudosections calculation by the Thriak/Domino programme, two stages of retrograde metamorphic evolution have been simulated, i. e. , the early isothermal decompression process followed by a late process of decreasing temperature and pressure. The mineral compositions and texture changed a lot during retrograde metamorphic evolution. The composition of garnet made little changes during the ITD (Isothermal Decompression) process, however, pyrope contents decreased obviously in the rim of the garnet when amphibole appeared, and then formed the pargasite + plagioclace coronas around garnet. Jadeide contents of omphacite decreased in the presents of active fluid during retrograde metamorphism. The appearance of Di + Ab + Amp symplectites around omphacite indicated a fluid absent condition. Phengite decomposed into the assemblage of muscovites + biotites and a little K-feldspar + quartz. Amphibole changed from magnesiokatophorite to pargasite, which indicated a transform from calcic-sodic to calcic amphibole. |
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| Keywords: | North Qaidam Xitieshan Eclogite PT pseudosection Retrograde PT paths |
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