کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
9531956 1638788 2005 26 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Two contrasting eclogite cooling histories, North Qaidam HP/UHP terrane, western China: Petrological and isotopic constraints
کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
Two contrasting eclogite cooling histories, North Qaidam HP/UHP terrane, western China: Petrological and isotopic constraints
چکیده انگلیسی
Felsic gneisses near Yuka, western North Qaidam Mountains (NQD), and (60 km SE) near Xitieshan, central NQD, enclose eclogite-bearing mafic boudins. Inclusions in prograde-zoned garnets from a Yuka eclogite record pre-eclogite facies conditions of 12.1 ± 2.1 kbar, 603 ± 36 °C. The phengite-bearing matrix assemblage records peak conditions near or in the coesite stability field (23-28 kbar, 600-730 °C), but no coesite or coesite pseudomorphs have been found. Amphibolitized eclogite in the boudin margin records retrograde conditions of 10.9 ± 1.2 kbar, 630 ± 44 °C. Garnets from the Xitieshan eclogite lack prograde inclusions and compositional zoning. The bimineralic matrix assemblage records minimum eclogite-facies conditions of > 14 kbar, 730-830 °C. Symplectites of plagioclase and clinopyroxene record early retrograde conditions of 10-14 kbar, 750-865 °C. Positive εNd values from two Yuka and five Xitieshan eclogites indicate a depleted mantle source, consistent with formation of the eclogite protoliths in a continental rift or incipient oceanic basin setting. A Sm-Nd WR-Grt-Cpx isochron age of 435 ± 49 Ma obtained from one Xitieshan eclogite represents a cooling age. Zircon U-Pb TIMS and SHRIMP geochronology, combined with CL and inclusion analysis indicates a magmatic protolith age of ca. 750-800 Ma, and eclogite-facies zircon growth at 486-488 Ma. For the Yuka eclogite, exhumation to lower-crustal depths occurred before 477 ± 8 Ma (amphibole 40Ar-39Ar), and a 466 ± 5 Ma phengite 40Ar-39Ar age indicates an average cooling rate of 13-19 °C/Ma. In contrast, the 407 ± 4 Ma amphibole 40Ar-39Ar age from the Xitieshan eclogite indicates a much slower cooling rate of 3-4 °C/Ma. HP/UHP rocks of similar age 200 km SE near Dulan, eastern NQD, and in the Altun Mountains on the NW side of the Altyn Tagh fault suggest that the Altun, Yuka, Xitieshan, and Dulan localities are part of the same early Paleozoic HP/UHP metamorphic belt.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volume 84, Issues 1–2, September 2005, Pages 51-76
نویسندگان
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