Petrogenesis of the Early Cretaceous Aolunhua Adakitic Monzogranite Porphyries, Southern Great Xing’an Range, NE China: Implication for Geodynamic Setting of Mo Mineralization

Abstract

This paper reports on whole-rock major- and trace-elemental and Sr–Nd isotopic compositions of the Aolunhua adakitic monzogranite porphyries from the Xilamulun district in the southern Great Xing’an Range, Northeast (NE) China. The high-K calc-alkaline Aolunhua monzogranite porphyries are characterized by high Sr/Y ratios (34.59–91.02), Sr (362–809 ppm), and low Y contents (7.66–10.5 ppm), respectively. These rocks also show slightly enriched Sr and Nd isotopes ((87Sr/86Sr)i = 0.7051–0.7058; εNd(t) = −2.98–0.92), with young two-stage model ages (T2DM = 0.84–1.16 Ga). Such a signature indicates that these rocks were most likely formed by partial melting of juvenile mafic lower crust. Based on equilibrium melting and batch-melting equations, we performed incompatible trace elements modeling. Low FeOT/(FeOT + MgO) values indirectly reflect these adakitic rocks were derived from an oxidizing source related to magnesian granitoids. The decreasing content of TiO2, Fe2O3, Nb/Ta ratio, and moderately negative Eu anomalies suggest that minimal fractionation of Fe–Ti oxides and plagioclase may have occurred in their evolutionary history. The result shows that the Aolunhua adakitic porphyries and coeval adakitic intrusive rocks in this area had not experienced extensive fractional crystallization and were derived from 20%–40% partial melting of lower continental crust, which was composed of ~25%–40% and 5%–20% garnet-bearing amphibolite, respectively. Integrating with rock assemblages and regional tectonic evolutionary history in this regime, high (Sm/Yb)SN (SN—source normalized data, normalized to mafic lower continental crust with Yb = 1.5 ppm and Sm/Yb = 1.87 for continental adakite) and low YbSN ratios suggest that these rocks were generated in an extensional environment related to lithospheric delamination without crustal thickening. The collision between North China and Siberian cratons around 160 Ma blocked the westward movement of the lithosphere as a result of the subduction of Pacific plate, which then led to lithospheric delamination induced by asthenospheric upwelling and underplating. Subsequently, partial melting of mafic lower crust caused by mantle upwelling resulted in the Early Cretaceous magmatic activities of adakitic rocks and associated Mo mineralization in the southern Great Xing’an Range.

Geochemistry and petrogenesis of Syrostan granitoid intrusions in the Southern Urals

“…6b) [39]. The pronounced negative anomalies of Nb in the figure confirm the participation of the continental crust in the magmatic processes [40][41][42]. The ratios Nb/Ta (8-16) < 17 point at the existence of melts of the depleted mantle, which also follows from the behavior of P and Ti relative to the primitive mantle composition (see fig.…”

“…5e). Furthermore, the ratios of the elements detected in the samples are: Rb/Ba (0.05-0.70); Rb/Sr (0.1-0.05); Nb/Ta (8-16); Nb/La (0.6-0.3); Nb/Ce (0.4-0.2); Th/Ta (3.5-8.5) and Zr/Hf (38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52).…”

Petrogenesis, W metallogenic and tectonic implications of granitic intrusions in the southern Great Xing’an Range W belt, NE China: insights from the Narenwula Complex

“…However, this model was later abandoned because late Mesozoic magmatism in the Great Xing'an Range (GXR) lasted for a relatively long period of time (40 Ma), distinguishing it from the short-lived intense period of magmatic eruption expected to result from a mantle plume (Wu et al 2011). More recent studies have suggested a genetic relationship between the late Mesozoic magmatism in NE China and the subduction of the PPO (Ji et al 2019;Li, S. Z. et al 2019;Suo et al 2019;He et al 2020;Sun et al 2020;Wei et al 2020;Jing et al 2021). However, this scenario can be precluded because (1) late Mesozoic SGB magmatism likely occurred far from (> 2000 km) the PPO subduction front, whereas the maximum extent of the PPO plate subduction is evaluated as 1300 km (Wan et al 2019); (2) seismological studies suggest that back-arc extension led by the PPO subduction did not reach the late Mesozoic SGB ; and (3) during Late Jurassic time, igneous rocks were mainly distributed in the GXR and absent in other regions of NE China, indicating that the PPO plate was rotating and undergoing oblique subduction beneath the Eurasian continent during this time (Maruyama et al 1997;Xu, W. L. et al 2013).…”

“…However, the overprinting of the Palaeo-Asian Ocean (PAO), Mongol-Okhotsk Ocean (MOO) and Palaeo-Pacific Ocean (PPO) tectonic regimes had significant influence on the SGB during late Mesozoic time, which has led to disagreements on the interpretation of the deep geodynamic processes and limited our understanding of regional W-related granitic magmatism and W mineralization. Several models have been proposed for the SGB tectonic setting during late Mesozoic time, including (a) upwelling of a mantle plume (Wang, T. et al 2015), (b) post-orogenic gravitational collapse and/or subductioninduced back-arc extension related to the closure of the MOO (Wang, Z. H. et al 2015;Fritzell et al 2016;Guan et al 2018;Ji et al 2018Ji et al , 2020Han et al 2021;Shi et al 2020;Wei et al 2021), (c) arc/back-arc extension and asthenosphere upwelling induced by subduction of the PPO (Ji et al 2019;Li, S. Z. et al 2019;Suo et al 2019;He et al 2020;Sun et al 2020;Wei et al 2020;Jing et al 2021), and (d) compositional effects resulting from the closure of the MOO and subduction of the PPO (Ouyang et al 2015;Liu, C. F. et al 2017;Liu et al 2020;Pang et al 2020;Zhang, C. et al 2020;Mi et al 2021). Additionally, although researchers generally agree that the disappearance of the PAO occurred along the Solonker-Xar Moron-Changchun Fault (SXCF), the closure time of the PAO remains ambiguous (Liu, Y. J. et al 2017).…”