Early Paleozoic convergence process in the southern Central Asia Orogenic Belt: constraints from the Late Ordovician fore-arc sedimentation in the central Beishan Orogenic Belt

The Early Paleozoic magmatism and sedimentation within the Beishan Orogenic Belt are crucial for understanding the Early Paleozoic accretionary orogeny along the southern margin of the Central Asian Orogenic Belt. The Hengluanshan Formation， characterized by tuffaceous lithic sandstone interbedded with dacitic and rhyolitic tuff， plays a pivotal role in reconstructing the Early Paleozoic convergence-accretion processes. Late Ordovician ages are constrained by a single peak age of 458 Ma for tuffaceous sandstone and a weighted average age of 448.5 ± 6.7 Ma for rhyolitic tuff. The dacitic tuffs exhibit characteristics akin to adakite， while the rhyolitic tuffs resemble typical arc magmatic rocks. When analyzed using the Th/Yb-Nb/Yb diagram， these volcanic rocks are indicative of a mature arc tectonic setting. The single peak age of the tuffaceous sandstones aligns closely with their sedimentary age， indicating that their source was predominantly contemporaneous volcanic rocks. The detrital zircon age cumulative proportion curve further suggests that the tuffaceous sandstones share characteristics with typical fore-arc sedimentation. Collectively， the Hengluanshan Formation is representative of fore-arc sedimentation. Integrating data from ophiolites， fore-arc sedimentation， and arc magmatic rocks， we propose a novel model for the Early Paleozoic convergence-accretion process in the central Beishan Orogenic Belt.