Eclogitic metapelites in the western segment of the north Qaidam Mountains: Evidence on “in situ” relationship between eclogite and its country rock |
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| Authors: | Zhang Jianxin Meng Fancong and Yang Jingsui |
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| Institution: | (1) Chinese Academy of Geological Sciences, Institute of Geology, 100037 Beijing, China |
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| Abstract: | 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+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± 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°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (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”. |
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| Keywords: | eclogitic metapelites in situ tectonic emplacement |
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