Geochronology and geochemistry of late Carboniferous–Middle Jurassic magmatism in the Helong area, NE China: Implications for the tectonic transition from the Paleo‐Asian oceanic to circum‐Pacific regime

Abstract

In this study, we present new U–Pb zircon ages and whole‐rock major and trace element data for the late Carboniferous–Middle Jurassic intrusive rocks in the Helong area, NE China. These data constrain the timing of tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime. U–Pb zircon dating indicates that the late Carboniferous–Middle Jurassic magmatic events in the Helong area can be subdivided into late Carboniferous, middle Permian, Early–Middle Triassic, Late Triassic, Early Jurassic, and early Middle Jurassic. The late Carboniferous granodiorites and middle Permian monzogranites belong to the calc‐alkaline series and have an affinity to I‐type granitoids, suggesting that they formed in a typical Andean‐type continental arc setting due to the southward subduction of the Paleo‐Asian oceanic plate beneath the NCC. The Middle Triassic granodiorites and monzogranites in the Helong area exhibit an affinity to adakitic rocks with their parental magma derived by the partial melting of thickened lower continental crust. The Late Triassic I‐type monzogranites and coeval ultramafic–mafic rocks constitute a bimodal igneous rock association, together with coeval A‐type granites and rhyolites, signifying an extensional environment. Combined with the absence of 240‐ to 225‐Ma sedimentation, the study area experienced a change from Early–Middle Triassic compression to Late Triassic extension related to the final closure of the Paleo‐Asian Ocean. The Early–early Middle Jurassic gabbros, diorites, granodiorites, and monzogranites are calc‐alkaline in nature and enriched in LREE and LILE but depleted in HREE and HFSE. Combined with the spatial variations in K contents of Early Jurassic igneous rocks in NE China from the continental margin to intracontinental region, and the presence of an Early Jurassic accretionary complex, we suggest that Early–early Middle Jurassic magmatism in the Helong area formed in an active continental margin setting related to the subduction of the Paleo‐Pacific Plate beneath Eurasia. We conclude that the tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime occurred in the Late Triassic–Early Jurassic.

Final-Stage Magmatic Record of Paleo-Asian Oceanic Subduction? Insights from Late Permian to Early Triassic Intrusive Rocks in the Yanbian Area, Easternmost Central Asian Orogenic Belt

“…However, these igneous rocks are classified as late Paleozoic based on K-Ar ages and lithostratigraphic relationships [36]. Thus, previous studies have shown that the voluminous igneous rocks include Late Permian-Cretaceous rocks [5,16,34,37,38]. Furthermore, according to their emplacement ages, the Late Permian-Triassic igneous rocks in study area could be divided into the three groups: (1) Late Permian, (2) Early Triassic, and (3) Middle Triassic [5,16,30,34,37].…”

“…Thus, previous studies have shown that the voluminous igneous rocks include Late Permian-Cretaceous rocks [5,16,34,37,38]. Furthermore, according to their emplacement ages, the Late Permian-Triassic igneous rocks in study area could be divided into the three groups: (1) Late Permian, (2) Early Triassic, and (3) Middle Triassic [5,16,30,34,37]. However, the poor exposure of The study area is to the east of Helong City, in the southern Yanbian area ( Figure 2B) and is located at the eastern segment of the CAOB.…”

“…It was formed by long-lived subduction, continental margin accretion, and continent-arc-continent collision due to the closure of the Paleo-Asian Ocean and is a key element for understanding the evolution of the eastern CAOB [4,[8][9][10][11][12][13]. Previous studies have suggested that the closure of the Paleo-Asian Ocean is a scissor-like closure process [4,11]; however, the precise timing of the final closure of the Paleo-Asian Ocean is controversial, and includes proposals for Middle to Late Devonian, Late Devonian to Early Carboniferous, Late Permian, Late Permian to Early Triassic, or even Middle to Late Triassic timing [4,5,10,11,[14][15][16][17]. Moreover, the location of final closure of the Paleo-Asian Ocean in NE China is still remaining controversial [4,15,17,18].…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…In the study undertaken by Tang, Li and Xu (, this issue), the authors present new U–Pb zircon ages and whole‐rock major and trace element data for the late Carboniferous–Middle Jurassic intrusive rocks in the Helong area, NE China. These data put a robust constraint of the timing of tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime on the Late Triassic‐Early Jurassic.…”

“…The mechanism by which PMMs develop in peridotites reveals that some podiform chromite in this area may also be xenoliths that formed after chromite was captured by ultramafic magmas in early times. In the study undertaken by Tang, Li and Xu (2020, this…”