Chronological and Geochemical Study of the Cenozoic Potassic Felsic Igneous Rocks in Western Yunnan, SE Tibet: Implications for their Tectonic Mechanisms

Abstract

Whether there is a relationship between widespread Cenozoic igneous rocks and the activated Ailao Shan–Red River shear zone (ASRR) in western Yunnan, SE Tibet, remains highly controversial. New geochronological, and geochemical data derived from Cenozoic igneous rocks both within and far from the ASRR offers answers. Although these coeval felsic rocks (36.9–33.5 Ma) are enriched in large‐ion lithophile elements relative to high field strength elements, they also display some special geochemical features, such as high Y and Yb values of syenitic porphyries, which contrast with the high Sr and low Y contents of monzoporphyries and granitic porphyries. The syenitic porphyries exhibit geochemical characteristics similar to those of coeval mafic magmas, e.g., high K2O, Y, and Yb contents, indicating that the former were probably generated by fractional crystallization of the latter. However, the high Sr/Y (56.1–109) monzoporphyries and granitic porphyries, combined with their low MgO, and Cr (or Ni) contents, suggest that they were mainly derived from partial melting of a thickened mafic lower crust. Given that these Cenozoic magmatic events exhibiting planar distributions occurred outside of the activation of the ASRR (31–20 Ma), then they were not controlled by the latter. Instead, they were tied to convective removal of a thickened lower lithospheric mantle in western Yunnan during the Paleogene.

Geology and Geochemistry of K‐feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit, Yunnan, Southwest China: Implications for Gold Mineralization

“…Abundant igneous rocks with different ages are exposed in the Ailaoshan tectonic belt (Wang et al, 2001;Li et al, 2013;Liu et al, 2015;Tang et al, 2022). Late Proterozoic magmatic rocks, which mostly occur in the south of belt, are represented by hornblende gabbro with a zircon U-Pb age of 769 ± 7 Ma, granodiorite with a zircon U-Pb age of 761 ± 11 Ma, and diorite with a zircon U-Pb age of 773 ± 12 Ma (Qi et al, 2010;Zhang et al, 2011).…”

Petrogenesis and Physicochemical Conditions of Fertile Porphyry in Non‐arc Porphyry Mineralization: A Case from Habo Porphyry Cu‐Mo Deposits, SW China

“…Mafic magmas are predominantly basaltic lavas and lamprophyre dykes (Fig. 1b; Chung et al, 1998;Lu et al, 2015b), while the felsic rocks form small extrusive and intrusive porphyritic bodies, consisting of diverse lithologies such as porphyritic granite, granite porphyry, syenite porphyry and monzogranitic porphyry (Lu et al, 2013a;Hou et al, 2017;Zhou et al, 2019;Tang et al, 2021). These felsic rocks can host Cu-, Mo-, and Aumineralization (Lu et al, 2013b;Deng et al, 2014a, b;He et al, 2016;Hou et al, 2017;Bao, 2020;Yang et al, 2020Yang et al, , 2021Wang et al, 2021).…”

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 methods of dating used earlier were K-Ar or 40 Ar/ 39 Ar, using minerals biotite, K-feldspar, or hornblende, and then were the in-situ zircon uranium- lead method (Fig. 4; Table 2; Zhang et al, 1987;Zhang and Xie, 1997;Bi et al, 2005;Cheng et al, 2007;Lu et al, 2012;Sun et al, 2017;Yan et al, 2017Yan et al, , 2019Zhou et al, 2017;Li and Jiang, 2020;Tang et al, 2021;Huang et al, 2022). The K-Ar dating results have commonly shown a lower precision than those of zircon U-Pb methods, and the latter demonstrate that the YSC rocks were emplaced during a short timespan of 34-32 Ma from late Eocene to early Oligocene (Fig.…”

“…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).…”