Comment on Re-Os isotopes constrain the formation of the Emeishan Large Igneous Province
| 作者: |
RenDeng, S., H. Yanli, and H. Qshuai |
| 期刊名称: |
Acta Petrologica Sinica |
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2008 |
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24 |
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11 |
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| 页码: |
2515-2523 |
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| 摘要: |
Emeishan Large Igneous Province ( ELIP) in Southwest China is composed of major basalts, basaltic pyroclastic rocks with minor picrites, including komatiites in northwest Vietnam, and felsic rocks. Based on the "later veneer" theory of the earth formation, Re-Os isotopic systematics can trace different possible proposed mantle sources for ELIP, including subcontinental lithospheric mantle, asthenospheric mantle, and deep plume-related mantle sources. The basalts, picrites and komatiites yield distinct Os signatures in terms of Os-187/Os-188 and Os content. Both low- and high-Ti basalts have a radiogenic Os isotopic composition, the value of Os-187/Os-188 for low-Ti basalts ranging from 0.1371 and 1.403 with the Os content between 0.006 x 10(-9) and 0.400 x 10(-9), which were considered mainly derived from a mantle plume reservoir, while one high-Ti basalt with highest Os concentration (0.560 10(-9)) has unradiogenic Os isotopic signatures (Os-187/Os-188 value is low down 0.1271), suggesting that a subcontinental lithosphere mantle (SUM) component most likely contributed to the generation of these magmas, indicating the high-Ti basaltic magmas were most likely derived from a SCLM reservoir or were contaminated by a significant amount of lithospheric mantle material during plume-related magma ascent through the SCLM (Xu JF et al., 2007). Both pierites and komatiites have subehondritic Os isotopic signatures with Os-187/Os-188 initial values ranging from 0.1233 to 0.1266, and ranging from 0.1251 to 0.1261, respectively, indicating they originated from SCLM (Hanski et al., 2004; Chen et al., 2007). We demonstrate that the material source of ELIP mainly controlled by the mixing of crust and depleted mantle, such as Tethys oceanic mantle, including some SCLM, according to the two-end member mixing model using the Os content versus Os-187/Os-188 initial value, in which one high-Ti basalt with highest Os-187/Os-188 initial values and lowest Os content in both high-Ti and low-Ti basalts is used as crustal end member, the iron meteorite as enriched core end member, primitive upper mantle (PUM) as fertile one, abyssal peridotite as depleted mantle (DMM) one. In the mixing model diagrams, most ELIP samples, including basalts, picrites and komatiites, plot near the crust-DMM mixing line. And the Paleo-Tethys mantle has the same Os isotopic signature Lis the DMM suggesting that the ELIP may be controlled by the crust-mantle interaction during or after the closing of the Paleo-Tethys Ocean.
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