Crustal reworking in the North China Craton at ~2.5 Ga: evidence from zircon U–Pb age, Hf isotope and whole rock geochemistry of the felsic volcano‐sedimentary rocks from the western Shandong Province

Abstract

The western Shandong Province (WSP) is one of the typical Neoarchaean granite–greenstone belts in the Eastern Block of the North China Craton (NCC) and is an important region to investigate the early Precambrian evolutionary history of the NCC. The Taishan association, consisting of a ~2.7 Ga komatiite–tholeiite sequence and a ~2.5 Ga felsic volcano‐sedimentary sequence, is the major lithological assemblage in the WSP. In the Qixingtai area, the felsic volcano‐sedimentary sequence, partly subjected to anatexis, is composed of hornblende gneiss, voluminous fine‐grained biotite gneiss and biotite plagioclase gneiss. SHRIMP zircon dating shows that the protolith of the biotite plagioclase gneiss formed after ca. 2.53 Ga. The tonalite intrusion into the volcanic protoliths of the fine‐grained biotite gneiss and biotite plagioclase gneiss occurred at 2.52 Ga. Our age data constrain the time of formation of the felsic volcano‐sedimentary sequence in the Taishan area as 2.53–2.52 Ga. The majority of zircons from the felsic volcano‐sedimentary rocks have intermediate εHf(t) values (−1.2 to +2.1). The whole rock Nd isotopes of the Taishan felsic volcano‐sedimentary rocks yield the εNd(t = 2522 Ma) values of +2.6 to −1.8 and TDM2 ages 3.03–2.68 Ga. These values indicate the pre‐existing crust was reworked at the end of the Neoarchaean (~2.5 Ga). The Taishan felsic volcano‐sedimentary rocks are rhyodacite–dacite and andesite in composition. These rocks and the tonalite display similar high SiO2 (65–72 wt.%) and low MgO (1–2 wt.%) content. In contrast, the minor andesites in the area have lower SiO2 (61–62 wt.%) and higher MgO (5.3–6.3 wt.%), suggesting more mantle contribution during their petrogenesis. However, the Mg‐rich andesites have identical rare earth element and multi‐element patterns with the rhyodacite–dacites and distinguish them from the Taishan sanukitoids. We suggest that the 2.53–2.52 Ga felsic volcanics of the Taishan association are the products of partial melting of a subducted oceanic crust. The andesites were produced by minor modification of the ascending tonalite–trondhjemite–granodiorite‐type magma by the mantle wedge. Our study indicates that (1) the tectonic regime of the WSP greenstone belt was dominated by an arc‐subduction system at ~2.52 Ga and (2) the 2.53–2.52 Ga felsic volcano‐sedimentary rocks and intrusive tonalite are the products of crustal reworking. The felsic volcano‐sedimentary sequence of the Taishan association and other ~2.5 Ga arc‐like assemblages in the NCC provide important clues to understand the nature of the tectonothermal events at the end of the Neoarchaean. Copyright © 2013 John Wiley & Sons, Ltd.

The genesis of Archean supracrustal rocks in the western Shandong Province of North China Craton: Constraints on regional crustal evolution

“…3k). The biotite leptite shows same occurrence as the hornblende leptite of upper Liuhang Formation and no sharp contact with the latter (Wang et al, 2013b). Following anatexis, the leucosome-rich biotite leptite progressively increases from west to east, and the metamorphic rocks show a marked coarsening of grain size.…”

“…It seems that the ~2.5 Ga supracrustal rocks recorded a changing process from magmatism to sedimentation in a stable basin of the WSP in the late of Neoarchean. Distinct from the high temperature magmas originated from mantle plume in the early Neoarchean, the ~2.5 Ga volcanics display negative anomalies in Nb, Ta and Ti contents and other geochemical affinities of calc-alkaline series (Wang et al, 2013b). It is known that the development of the calc-alkaline volcanism is associated with fluids, which could decrease the temperature of partial melting.…”

“…Moreover, the magmas originated from mantle plume and mantle wedge partial melting usually generate garnet and olivine residue in the sources. The ~2.5 Ga meta-volcanics of the Taishan Group show linear extension and the andesitic rocks show geochemical affinities of sanukitoids (Wang et al, 2013b). Although the calc-alkaline rocks could be generated from partial melting of mafic rocks of lower crust without arc system, the geological and geochemical features of the ~2.5 Ga Taishan volcanics can be better explained by arc-like magmatism.…”

“…In the Qixingtai area, the upper part of the Liuhang Formation is dominated by hornblende leptite, which is also intensely deformed near the contact with the lower basaltic sequence. Wang et al (2013b) proposed that the protolith of the hornblende-biotite leptite is related to andesitic-rhyolitic volcanics. The correlations of major elements of hornblendebiotite leptite indicate that they originated from a calcalkaline series of pyroclasts.…”

“…The North China Craton (NCC) is one of the oldest cratons in the world (Liu et al, 1992;Song et al, 1996;Wan et al, 2005b;Wu et al, 2008). Compared to North America, Western Austrilia and South Africa, the NCC is characterized by extensive ~2.5 Ga tectono-thermal events (Kröner et al, 1998;Zhao et al, 2002Zhao et al, , 2008Wilde et al, 2005;Shen et al, 2005;Wan et al, 2005aWan et al, , 2010Wan et al, , 2012aYang et al, 2008;Wang et al, 2009bWang et al, , 2010aWang et al, , 2013bNutman et al, 2011;Liu et al, 2012;Peng et al, 2012). The TTGs and granites formed at ~2.5 Ga compose near 80% of the Archean basement of the NCC (Zhao and Cawood, 2013).…”