Geochemical evolution of the Late Carboniferous to Early Permian igneous rocks from the Baolidao magmatic belt, eastern Central Asian Orogenic Belt

Abstract

The Late Palaeozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB) and the genesis of magmatic rocks in the terrane have been topics of debate for decades. We have tried to understand the processes involved in the evolution of the Late Palaeozoic Baolidao belt and magma generation by compiling data from more than 200 samples along with new age estimates and geochemical data. Spinel stability field melting of the subduction hydrated juvenile depleted mantle (DM) is the dominant mafic magma generating process. The crustal granitoids from the Late Carboniferous suite (320 ~ 300 Ma) and the Early Permian suite (300 ~ 280 Ma) have contrasting characteristics. The Late Carboniferous suite is characterized by lower crustal AFC process at hornblende‐dominated and plagioclase‐free pressure, which resulted in considerable growth of continental crust, while the Early Permian suite is characterized by low pressure partial melting (plagioclase stable in residue) of a thinned juvenile crust. The process of the extension of hydrous mantle coupled with crustal thinning from the Late Carboniferous to Early Permian can be used to explain the chemical and petrogenetic features of the Late Palaeozoic magmatism along the Baolidao belt. We propose that lithosphere‐scale extension should have been a key process in the tectonic evolution of the eastern CAOB during the Late Palaeozoic.

Depositional age and genesis of the host strata of the Shuangjianzishan Ag–Pb–Zn deposit: Implications for the Late Carboniferous magmatic–hydrothermal activities and tectonic evolution of the eastern central Asia orogenic belt

“…However, the redistribution of alkalies in the Shuangjianzishan slates is clear when evaluated using these triangular diagrams. The trend of all Shuangjianzishan data, together with one datum from a tuff from the Benbatu Formation reported in Gong et al (2020), does not terminate at the A-CN line of the A-CN-K diagram where natural groundwater compositions lie (Fig. 13).…”

“…Lava flows and volcaniclastic strata are unevenly distributed throughout this formation. The zircon U-Pb age of a tuff layer from the Benbatu Formation is 322.7 ± 2.4 Ma (Gong et al, 2020). The basal conglomerate of the Benbatu Formation represents a regional unconformity, which covers the underlying metamorphic basement (Bao et al, 2006).…”

“…The limestone strata's deposition time in the Amushan Formation is constrained by fusulinids, ranging from Gzhelian to Sakmarian (Yan et al, 2019). The early Permian Dashizhai Formation is composed mainly of volcanic and volcaniclastic strata (Zhang et al, 2008), which are characterized by a bimodal distribution of SiO 2 abundance, with dominant rhyolite and dacite and subordinate basalt and local andesite (Shao, 1991;Zhang et al, 2008;Gong et al, 2020). In later times, the middle Permian Zhesi Formation, famous for its Zhesi fauna, was deposited as shallow marine limestone and sandstone (e.g., Wang et al, 2004).…”

“…However, recent geochronological data have shown that these stratigraphic units are somehow diachronous, especially the Upper Carboniferous to lower Permian system. As summarized in Gong et al (2020), volcanic strata previously mapped as the Dashizhai Formation yielded Late Carboniferous ages in places. For example, the basalt strata from the Daqing pasture were mapped as the Dashizhai Formation in BGMRIM (1991) and other literature (e.g., RGSTNM, 1987).…”

“…Besides their unevaluated significance in metallogeny, the Late Paleozoic strata bear remarkable significance in the tectonic evolution of the CAOB. Whether the CAOB was an active subduction zone (e.g., Xiao et al, 2003;Xiao et al, 2015;Zhang et al, 2015aZhang et al, , 2015bSong et al, 2015;Li et al, 2015Li et al, , 2018Li et al, , 2019Li et al, , 2020Zhou et al, 2016;Eizenhöfer et al, 2015aEizenhöfer et al, , 2015bJiang and Zhu, 2020;Yang et al, 2020) or was rifted during the Late Paleozoic (Shao, 1991;Xu et al, 2013Xu et al, , 2018Shao et al, 2014Shao et al, , 2015Gong et al, 2018Gong et al, , 2020 has been hotly debated for decades. An important aspect of this discrepancy is the contradicting interpretation of how the Upper Paleozoic sediments were deposited.…”