Eclogitic metapelites in the western segment of the north Qaidam Mountains: Evidence on in situ relationship between ecl
In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites.Their typical mineral assemblages are garnet + kyanite + chloritoid + phengite + quartz + rutile.Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ Chll + Cldl+ Phel ± Stl + Qtz; (2) Grt+Ky +Phell±Cldll +Qtz; and (3) Grt + Cldlll + Chlll + Phelll +Stll + ky + Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry,P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22℃ (prograde stage); P=2.3-3.1GPa, T=615-700℃(peak stage); and P =1.22 ± 0.26GPa, T=581± 20℃ (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred.In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is "in situ" rather than "tectonic emplacement".
作 者： ZHANG Jianxin MENG Fancong YANG Jingsui 作者单位： Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 刊 名： 中国科学D辑（英文版） SCI 英文刊名： SCIENCE IN CHINA SERIES D 年，卷(期)： 2004 47(12) 分类号： P5 关键词： eclogitic metapelites in situ tectonic emplacement