Petrogenesis of Granite complex in the Jiudingshan porphyry Cu‐Mo Deposit, Western Yunnan: Constraints from Geochronology, Geochemistry and Sr‐Nd‐Hf Isotopes

Abstract

This paper aims to reveal the magma evolution and petrogenesis of Jiudingshan granite complex by geochronology, geochemistry and Sr-Nd-Hf isotopes, which is different with the previously reported result (Guo et al, 2009, and references therein ). Geological backgroundThe Jiudingshan Cu-Mo deposit hosted by the granite complex was located between the NW JingshajiangAilaoshan fault and NNE Chenghai -Binchuan fault in the middle of the Sanjiang metallogenic belt, western Yunnan, and formed by the continental collision during the Himalaya epoch. Five magma series can be recognized in the field: porphyritic granite, orthophyre, granite porphyry, alkali feldspar granite and lamprophyre. Results The whole rock geochemical compositionsThese samples contain 61.37 -74.98 wt% SiO2, 1.15 -5.2 wt% Na2O, and 3.35 -8.92 wt% K2O, and fall in high -K calcalkaline or shoshonitic field defined by the SiO2 vs K2O diagram. They have MgO and Mg # (molar 100× MgO / (MgO + FeOT)) of 0.66 -1.63 wt% and 25 -45, respectively. The calculated A/CNK values (molar Al 2 O 3 / (CaO + Na 2 O + K 2 O)) are 0.84-1.04, indicating a metaluminous composition. They exhibit subparallel chondrite-normalized REE patterns, characterized by strong fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) without obvious Eu anomaly. Samples are rich in large-ionlithophile elements (LILE) but depleted in high-fieldstrength elements (HFSE) and displaying strong Nb-Ta-Ti negative anomalies. Zircon U-Pb geochronology and Hf isotopeZircon U and Th contents range from 354 to 1,657 ppm and 148 to 915 ppm, respectively, corresponding to Th/U values of 0.20 -0.54, which supports a magmatic origin of these zircon. Ten LA-ICP-MS single spot analyses on 10 zircon grains of each porphyritic granite, orthophyre and granite porphyry yield similar concordant U-Pb ages and weighted mean 206 Pb/ 238 U ages of 34.9±2.0 Ma, 34.6±0.7 Ma and 34.7±0.6Ma, respectively. Thus, ~35 Ma can be considered as the crystallization age of the Jiudingshan granite complex.Ten in situ Hf isotopic analyses were made on 10 zircon grains of each rock that had been previously studied for LA-ICP-MS geochronology. Both ɛHf (t) values and the Hf model ages are calculated using the zircon crystallization age. The results show that these zircons

Petrogenesis of the Late Eocene to Early Oligocene Yao'an Shoshonitic Complex, Southeastern Tibet: Partial Melting of an Ancient Continental Lithospheric Mantle beneath the Yangtze Block

“…The rocks of each stage of the YSC have been intensively sampled and analyzed for bulk geochemistry and geochronology or thermochronology (Bi et al, 2005;Guo et al, 2005;Lu et al, 2012;Xu et al, 2016;Sun et al, 2017;Yan et al, 2017Yan et al, , 2018Yan et al, , 2019Zhou et al, 2017;Li and Jiang, 2020;Tang et al, 2021;Huang et al, 2022). The zircons from a few samples have been analyzed for Hf-O isotopics as well.…”

“…The chondrite-normalized rare earth element (REE) patterns of the YSC rocks are right-dipping with variable, high (La/Yb) N ratios ranging from 21 to 247 (the subscript Data from Table 1 and literature (Bi et al, 2005;Guo et al, 2005;Cheng et al, 2007;Lu et al, 2013bLu et al, , 2015Xu et al, 2016;Sun, 2017;Sun et al, 2017;Yan et al, 2018;Yang H et al, 2020;Tang et al, 2021).…”

“…Some researchers considered that these rocks derived from an enriched lithospheric mantle that had been metasomatized by subduction-derived fluids and subsequent fractional crystallization of the mantlederived mafic magmas (Bi et al, 2005;Guo et al, 2005;Lu et al, 2013b). By contrast, other researchers suggested that these rocks were likely formed by different degrees of mixing between a mantle-derived mafic magma and a crust-derived felsic magma (e.g., Yan et al, 2018Yan et al, , 2019.…”

“…The Yao'an Shoshonitic complex (YSC, seeing Section Petrogenesis of the Late Eocene to Early Oligocene Yao'an Shoshonitic Complex, Southeastern Tibet: Partial Melting of an Ancient Continental Lithospheric Mantle beneath the Yangtze Block 5.2 for definitions) is an important part of the potassic igneous rocks along the southeastern margin of the Tibetan Plateau. Surveying the literature reveals the following two characteristics of YSC: 1) highly enriched whole-rock Nd and zircon Hf isotopic compositions and related old Nd and Hf model ages (Bi et al, 2005;Guo et al, 2005;Lu et al, 2013bLu et al, , 2015Yan et al, 2018;Huang et al, 2022); and 2) a total lack of inherited zircons (Lu et al, 2013b). In addition, the Laojiezi Pb-Ag and Baimaju Au (-Cu) polymetallic deposits were formed by volcanism of the YSC (Bi et al, 2001(Bi et al, , 2004Jiang et al, 2018;Yang H et al, 2020).…”