Petrogenesis of the Mesozoic intrusive rocks in the Tongling area,Anhui Province,China and their constraint on geodynamic process |
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Authors: | Email author" target="_blank">Qiang?WangEmail author Jifeng?Xu Zhenhua?Zhao Xiaolin?Xiong Zhiwei?Bao |
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Affiliation: | Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China |
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Abstract: | Petrology, element and isotopic geochemistry of the Mesozoic intrusive rocks in the Tongling area were systematically investigated
in this study. The intrusive rocks can be divided into two groups, one contains shoshonitic rocks with SiO2 ⩽ 55%, the other consists mainly of high-potassic calc-alkaline rocks with SiO2 > 55%. The shoshonitic rocks (SiO2 ⩽ 55%) were generated by the fractional crystallization of the primary basaltic magma sourced from an enriched mantle, then
the evolved basaltic magma likely experienced low-degree contamination with the lower crust materials when they ascended.
On the other hand, although the intrusive rocks with SiO2 > 55% show most elemental geochemical characteristics similar to an adakite, such as high Na2O, AI2O3, Sr contents, high Sr/Y and La/Yb ratios, they have isotopic compositions much different from an adakite, such as low σNd(t)
(-9.16—16.55) and high (87Sr/86Sr), (0.7068—0.7105), and some of them show relatively high Y and Yb contents than those of an adakite. We propose that the
intrusive rocks with SiO2 > 55% were most probably produced by mixing of the mantle-derived basaltic magma and adakite-like magma derived from the
melting of basaltic lower crust that was heated by the underplating mantle-derived shoshonitic magmas. The delamination of
lower crust likely took place after or during the formation of these adakite-like rocks in the Tongling area. |
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Keywords: | magma mixing adakite underplating delamination shoshonite Tongling |
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