Geochronology and petrogenesis of the granites in Malanyu Anticline in eastern North China Block

Abstract

Widespread Mesozoic magmatism and intracontinental deformation is recorded in the North China Block (NCB), but few studies have considered the link between the emplacement of the granite and deformation. The Malanyu Anticline is a large-scale east-trending fold exposed in the eastern part of NCB and is intruded by many plutons. Whole rock geochemistry, LA-ICP-MS zircon U–Pb ages, Sr–Nd isotopic composition, as well as zircon Hf isotopic data for eight granitic bodies in the anticline have been studied in detail and are reported in this contribution. Fourteen zircon LA-ICP-MS U-Pb ages have been obtained ranging from ca. 218 to 126 Ma spanning the Triassic to Cretaceous, with a major population at ca. 220–160 Ma. This age range is different from rest of the Mesozoic igneous rocks in NCB, indicating the emplacement of the granites in the anticline was structurally controlled, although the regional tectonic setting during the Mesozoic played an important role in magmatism in the region. All of the granites in the Malanyu Anticline are enriched in light Rare Earth Elements relative to heavy Rare Earth Elements, and have similar trace elements patterns, with depletions in Ba, Nb, Sr, P and Ti, and enrichments in Rb, Th, U, K, La, Ce, Sm and Tb. The Triassic to Jurassic granites' two-stage depleted mantle Nd model (T2DM) ages are both Paleoproterozoic, with similar εNd(t) values and two-stage depleted mantle Nd model ages. Their in-situ zircon two-stage depleted mantle Hf model ages (tDM2) range from ca. 2861 to 1406 Ma. Integrated with the Sr-Nd-Hf data from previous studies, the Triassic Dushan Granite in the study area has high Sr and low Y assays derived from the partial melting of Archean TTGs in the lower crust with a minor contribution from a depleted mantle source. The emplacement was during a post-collisional setting following the closure of the Paleo-Asian Ocean along the Suolun Suture in the north. The emplacement of most of the Jurassic granites involved the superimposition of the initial subduction of the Paleo-Pacific Ocean plate beneath NCB, while the emplacement of the minor Jurassic and Cretaceous granites are probably related to the partial melting of the Precambrian crust due to widespread extensional tectonics at the northern margin of the NCB.