Journal
LITHOS
Volume 248, Issue -, Pages 80-93Publisher
ELSEVIER
DOI: 10.1016/j.lithos.2016.01.009
Keywords
Monzodioritic-granodioritic intrusions; In situ plagioclase Sr isotopes; Magma mixing; Tongling
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Funding
- Natural Science Foundation of China [41272067, 41530206]
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The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle in a back-arc extensional regime. The principal geochemical signatures of these Mesozoic rocks include a high-K calc-alkaline affinity, high values of Mg#, high Sr-Ba abundances, high Sr/Y and La/Yb ratios, epsilon(Nd)(t) = -13.1 to -9.0, and I-sr = 0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and amphibole, (2) the Sr-87/Sr-86 ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (3) the negative correlations between whole-rock Nd and Sr isotopic ratios, and (4) the significant differences in the values of 410) (-9.5 to -26) within different zircons from the same intrusion. (C) 2016 Elsevier B.V. All rights reserved.
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