Search

In view of the importance of mafic dyke swarms and their contribution to current scientific problems relating to South China, herein, we present the findings of studies on twenty–five representative mafic dykes cropping out in Hunan Province and Guangxi Zhuang Autonomous Region, within the southern Wuling Mountain gravity lineament, China. These results include new zircon LA‐ICP‐MS U‐Pb age, whole rock geochemical, Sr‐Nd‐Pb isotopic, and zircon Hf isotopic data for these dykes. The dykes formed between 131.5 ± 1.2 and 121.6 ± 1.1 Ma, and have typical doleritic textures. They fall into the alkaline and shoshonitic series, are enriched in light rare earth elements (LREE), some large ion lithophile elements (LILE; e.g., Rb, Ba, and Sr), Th, U, and Pb, and are depleted in Nb, Ta, Hf, and Ti. Moreover, the dolerites have high initial 87Sr/86Sr ratios (0.7055–0.7057), negative ∊Nd(t) and zircon ∊Hf(t) values (–14.8 to –11.9, –30.4 to –14.9), and relatively constant initial Pb isotopic ratios (that are EM1‐like, 16.77–16.94, 15.43–15.47, and 36.84–36.92 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively). These results indicate that the dykes were likely derived from magma generated through low‐degree partial melting (1.0%–10%) of an EM1‐like garnet–lherzolite mantle source. The parental magmas fractionated olivine, clinopyroxene, plagioclase, and Ti‐bearing phases with negligible crustal contamination, during ascent and dyke emplacement. Several possible models have been proposed to explain the origin of Mesozoic magmatism along the Wuling Mountain gravity lineament. Herein we propose a reasonable model for the origin of these mafic dykes, involving the collision between the paleo‐Pacific Plate and South China, which led to subsequent lithospheric extension and asthenosphere upwelling, resulting in partial melting the underlying mantle lithosphere in the Early Cretaceous, to form the parental magmas to the WMGL mafic dykes, as studied. [ABSTRACT FROM AUTHOR]

This work reports an important episode of extensional, mafic magmatism that impacted the North China Craton (NCC) during the Permo-Triassic and influenced the evolution of this Craton. We sampled 30 representative mafic dykes cropping out in eastern NCC, within the Hebei Province, China. New zircon LA-ICP-MS U–Pb ages, geochemical, and Sr–Nd–Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9 ± 1.3 and 263.9 ± 2.6 Ma. The mafic rocks fall into the alkaline and calc-alkaline series. They are enriched in light rare earth elements, some large ion lithophile elements (e.g., Rb, Ba, and Sr), K, and Pb, and depleted in Nb, Ta, and Ti. The dykes have high initial 87Sr/86Sr ratios (0.7034–0.7178), negative εNd (t) values (−2.2 to −5.9), and relatively constant initial Pb isotopic ratios, that are EM1-like: (206Pb/204Pb)i = 16.39–16.74, (207Pb/204Pb)i = 15.22–15.24, and (208Pb/204Pb)i = 36.66–36.86, respectively. Our results indicate that the Hebei Province dolerites were likely derived from magma generated through low-medium degree partial melting (3.0–20%) of an EM1-like garnet-lherzolite mantle source. The parental magmas fractionated olivine, clinopyroxene, and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement. Since the possible influence of subduction of the Yangtze Plate has been excluded, we propose a model for the origin of the investigated mafic rocks, involving the Permian collision between the Siberian Block and the NCC. The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision. [ABSTRACT FROM AUTHOR]

As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strike-slip fault is present, the Altyn Orogenic belt (AOB) has become an important focus for research. Magmatic rocks are widely distributed across the AOB. However, many investigations have focused primarily on Paleozoic igneous rocks; discussion of Mesozoic related igneous activity is often ignored. Here we present the result of studies of representative diorite and granite rocks outcropping in the AOB, within the Xinjiang Uygur Autonomous Region, South Altyn, China. We present new zircon LA-ICP-MS U–Pb age, geochemical, and Sr–Nd–Pb–Hf isotopic data for these sample suites, identifying them as typical igneous rocks formed between 238 ± 1.5 and 238.8 ± 1.1 Ma. The rocks that we studied fall into the alkaline series, also enriched in light rare earth elements (LREE), some large ion lithophile elements (LILE; e.g., Rb, Ba, Sr, and K), Pb, Th and U, and depleted in heavy rare earth elements (HREE), Nb, Ta, Hf, and Ti. The granite and diorite have high initial 87Sr/86Sr ratios (0.7062–0.7114), negative εNd (t) values (− 8.8 to − 11.3), εHf (t) values (− 8.7 to − 18.7), and relatively constant Pb isotopic ratios ((206Pb/204Pb)i = 6.74–17.884, (207Pb/204Pb)i = 15.51–15.58, and (208Pb/204Pb)i = 35.36–38.04), respectively. This suggests that the magmas parental to these rocks were generated from the partial melting of the ancient crust. The parental magmas to these rocks experienced a degree of fractionation of plagioclase, K-feldspar, and hornblende, possibly during rapid magma ascent. Based on these studies, we propose a reasonable model for the origin of the investigated rocks from the Xinjiang Uygur Autonomous Region of South Altyn, which involves crustal thickening, lithospheric extension, and asthenosphere upwelling, that induced crustal melting. [ABSTRACT FROM AUTHOR]