کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
11024693 | 1701088 | 2018 | 13 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Subducted Mg-rich carbonates into the deep mantle wedge
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
علوم زمین و سیاره ای (عمومی)
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چکیده انگلیسی
Recent studies have concluded that subducted calcium (Ca-) rich carbonates could be dissolved in slab-derived aqueous fluids and transported upwards into the shallow mantle wedge (75-120 km), while magnesium (Mg-) rich carbonates could be delivered to a greater depth (i.e., the mantle transition zone, â¼410 km), melted, and recycled into the convective upper mantle. However, it remains unknown whether or not Mg-rich carbonates can be transferred to the deep mantle wedge (>â¼120 km) by subduction-zone fluids, which, if true, is important for tracing deep carbon. In this paper, we report a comprehensive mineralogical, geochemical, stable (Mg and O) and radiogenic isotopic (zircon U-Pb) study of garnet clinopyroxenites from the Maowu ultra-mafic massif (a slice of the mantle wedge) in the Dabie orogeny, Central China. Whole-rock and mineral trace elemental features and zircon U-Pb ages reveal evidence of mantle wedge metasomatism by a slab-derived melt or supercritical fluid from the subducted rutile-bearing eclogitic Paleo-Tethys oceanic crust, in addition to subsequent metamorphism occurring during the Triassic collision between the South and North China blocks. Combined with the results of previous works, the high Th/U ratios of both whole rocks and metasomatized zircons with no oscillatory zoning lead us to infer that a supercritical liquid rather than a melt was the metasomatic agent during oceanic subduction at peak conditions (5.3-6.3 GPa and â¼800â°C, 160-190 km). Abundant carbonate mineral inclusions (including calcite, dolomite and magnesite) and the high δ18OVSMOW values of the metasomatized zircons (up to 12.2â°) indicate that sedimentary carbonates were leached by the supercritical fluid. Furthermore, whole-rock δ26Mg values (â0.99â° to â0.65â°) that are lower than normal mantle values (â0.25±0.07â°) imply that the incorporated carbonates contain not only calcites but also a certain amount of dolomites (approximately 1-10 wt.% of the metasomatic supercritical liquid). The dissolved Mg-rich carbonates in the slab-derived supercritical liquid could effectively modify the Mg isotope composition of the deep mantle wedge. Our study represents a critical step towards achieving a broad understanding of the behaviours of recycled carbonate during slab subduction.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 503, 1 December 2018, Pages 118-130
Journal: Earth and Planetary Science Letters - Volume 503, 1 December 2018, Pages 118-130
نویسندگان
Ji Shen, Shu-Guang Li, Shui-Jiong Wang, Fang-Zhen Teng, Qiu-Li Li, Yong-Sheng Liu,