Neoarchean to Paleoproterozoic tectonothermal evolution of the North China Craton: Constraints from geological mapping and Th-U-Pb geochronology of zircon, titanite and monazite in Zanhuang Massif

Abstract

The North China Craton (NCC) consists of Neoarchean to Paleoproterozoic basement, with rare Eo-Paleoarchean crustal relicts. However, the Precambrian tectonothermal evolution of the Central Orogenic Belt (COB) of the NCC is still hotly debated. In this contribution, we present new results of field-based litho-structural analysis, Th-U-Pb geochronology of accessory minerals including zircon, titanite and monazite from paragneiss and marble in a passive margin sequence in the Zanhuang Massif of the COB. Field studies show that two generations of deformation events occurred in the Zanhuang Massif. The earlier deformation is widely distributed in the entire Zanhuang Massif and developed with a top-to-SE shear sense resulting in foliation of the micaschist, metavolcanic rock, marble and paragneiss. The latter deformation is locally occurred in the central Zanhuang Massif and developed with a top-to-SW shear sense represented by the faulting and folding events which are similar to the fold-and-thrust structures of accretionary wedge during the formation of Zanhuang mélange. Zircons from paragneiss yield single-peak age populations with mean ages of 2.52 and 2.51 Ga, and a metamorphic age of 1.84 Ga. Zircon ages from marble are divided into four groups including a main peak of 2.54 Ga, two older groups of 2.77–2.82 and 2.60–2.70 Ga, and a younger metamorphic age of 1.81 Ga. Titanites from paragneiss and marble yield mean metamorphic ages between 1.94 and 1.88 Ga, representing an earlier thermal event. Monazites from paragneiss yield an isochron age of 1.80 Ga, representing a later thermal event. Based on our new litho-structural observations and geochronological data, coupled with previous studies, we suggest that the paragneiss and marble from the marble-siliciclastic unit represent the passive margin sequence, and were mainly deposited at 2.51–2.50 Ga. In addition, the Zanhuang Massif has experienced two tectonothermal events at ca. 1.94–1.88 Ga and ca. 1.83–1.80 Ga, which are widely distributed in the entire NCC, but gradually become weaker from north to south.