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Geochemistry and Petrogenesis of the Tongshankou and Yinzu Adakitic Intrusive Rocks and the Associated Porphyry Copper‐Molybdenum Mineralization in Southeast Hubei, East China
Author(s) -
Wang Qiang,
Zhao ZhenHua,
Bao ZhiWei,
Xu JiFeng,
Liu Wei,
Li ChaoFeng,
Bai ZhengHua,
Xiong XiaoLin
Publication year - 2004
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.2004.tb00195.x
Subject(s) - geochemistry , geology , adakite , partial melting , petrogenesis , mineralization (soil science) , plagioclase , pluton , crust , oceanic crust , petrology , basalt , subduction , quartz , tectonics , soil science , paleontology , soil water
. The late Jurassic Tongshankou and Yinzu plutons in southeast Hubei have been investigated for their contrasting metal mineralization features. The former is closely associated with porphyry Cu‐Mo mineralization, while the latter is barren of metal mineralization, althouth both are located very close to each other. The Tongshankou granodiorite porphyries and the Yinzu granodiorites are geochemically similar to adakites, e.g., high Al 2 O 3 and Sr contents and La/Yb and Sr/Y ratios, enriched in Na 2 O, depleted in Y and Yb, very weak Eu anomalies and positive Sr anomalies. However, different geochemi‐cal characteristics exist between the two plutons: the Tongshankou adakitic rocks (1) are relatively enriched in SiO 2 , K 2 O, MgO, Cr, Ni, and Sr and depleted in Y and Yb; (2) have higher degree REE differentiation; (3) have positive Eu anomalies in contrast with very weak negative or unclear Eu anomalies in the Yinzu rocks; and (4) isotopically have relatively higher eP Nd(t) values (‐5.19 to ‐5.38) and lower initial 87 Sr/ 86 Sr ratios (0.7060 to 0.7062), while the Yinzu adakitic rocks have relatively lower eP Nd(t) values (‐7.22 to ‐8.67) and higher initial 87 Sr/ 86 Sr ratios (0.7065 to 0.7074). The trace element and isotopic data demonstrate that the Tongshankou adakitic rocks were most probably originated from partial melting of delaminated lower crust with garnet being the main residual mineral whereas little or no plagioclase in the source. On the contrary, the Yinzu adakitic rocks were likely derived from partial melting of thickened lower crust, with residual garnet and a small quantity of plagioclase and hornblende in the source. Interactions between the adakitic magmas and mantle peridotites possibly took place during the ascent of the Tongshankou adakitic magmas through the mantle, considering that MgO, Cr, and Ni contents and eP Nd(t) values of the adakitic magmas were possibly elevated and initial 87 Sr/ 86 Sr ratios were possibly lowered due to the contamination of mantle peridotites. In addition, the Fe 2 O 3 of the adakitic magmas was likely released into the mantle and the oxygen fugacities (ƒ o2 ) of the latter were obviously possibly raised, which made metallic sulfide in the mantle oxidized and the chalcophile elements such as Cu were incorporated into the adakitic magmas. The ascent of the adakitic magmas enriched in Cu and Mo will lead to the formation of porphyry Cu‐Mo deposit. Nevertheless, the Yinzu adakitic magmas were possibly lack of metallogenetic materials due to not interacting with mantle peridotite, and thus unfavorable to metal mineralization.