Petrogenesis and geochemistry of circa 2.5 Ga granitoids in the Zanhuang Massif: Implications for magmatic source and Neoarchean metamorphism of the North China Craton

Abstract
The tectonic framework of the North China Craton (NCC) during late Archean to
early Paleoproterozoic (circa 2.5 Ga) is still lacking comprehensive understanding due
to subsequent strong deformation and metamorphic overprinting events. Circa 2.5 Ga
magmatic and metamorphic activities are widely spread throughout the NCC, which
can be used as an efficient target to better understand the tectonic evolution at this
period. In this study, based on a detailed field, structural, geochemical,
geochronological and Sm-Nd isotopic study, we focus our work on the Haozhuang
granitoids in the Zanhuang Massif located at the eastern margin of the Central
Orogenic Belt of the NCC. The granitoids mainly include undeformed pegmatite and
granodiorite. One pegmatite and two granodiorite samples yield zircon 207Pb/206Pb
ages of 2513 ± 29 Ma, 2511 ± 36 Ma and 2528 ± 18 Ma, respectively. The
granodiorites show metaluminous and shoshonitic to high-K calc-alkaline series
characteristics with A-type granite affinity. The circa 2.5 Ga granodiorites have
highly negative εNd(t) values (–29.22 ~ –33.12) and TDM model ages between 2671 Ma
and 3151 Ma. This work shows clearly, from whole-rock major and trace elements
and Sm–Nd isotopic studies, that the Haozhuang granodiorites were derived from
partial melting of old and thickened TTG crust rather than mantle sources, and formed
in a subduction-related tectonic setting. With geochemical comparison studies to other
similar-aged granitic rocks in the Zanhuang Massif, we suggest that these granitic
rocks possibly have a certain correlation during the magma evolution. Coupled with
our previous geochemical and isotopic studies on circa 2.5 Ga mafic dike swarms, we
propose that the similar-aged granitic rocks and mafic dike swarms were produced by
an east-dipping subduction polarity reversal event following an arc-continent collision
between the Fuping/Wutai island arc and Eastern Block of the NCC above a
west-dipping slab. The east-dipping subduction resulted in partial melting of the
enriched lithospheric mantle, firstly forming the circa 2.5 Ga mafic dikes inducing the
widespread circa 2.5 Ga metamorphism in the Central Orogenic Belt and the Eastern
Block, and then the parental magma of these mafic dike swarms heated the old and
thickened TTG crust causing the formation of similar-aged granitic rocks at a later
stage.