Petrogenesis and tectonic significance of Early Paleozoic magmatism in the northern margin of the Qilian block, northeastern Tibetan Plateau

Abstract

Abundant Early Paleozoic magmatism is preserved in northern Tibet and has important implications for continental crustal growth in response to continental collisions. To better constrain the evolution of the northern margin of the Tibetan Plateau and the resulting closure of the North Qilian Ocean, we conducted an integrated investigation involving U-Th-Pb zircon geochronology, whole-rock geochemistry, and syntheses of existing data sets across the North Qilian orogenic belt. Zircon U-Pb dating indicates that the Early Paleozoic intrusive rocks in the study area can be divided into two stages: 460-480 Ma and 440 Ma. The 478-480 Ma meta gabbro-diorite samples belong to the calc-alkaline series and show a fractional crystallization trend in the Harker diagrams. These samples have relatively high La/Nb (2.08-3.26) and low La/Ba (0.05-0.06) ratios, indicating a subduction-modified continental-lithospheric mantle source. The 460-480 Ma meta-granite samples are I-type and classified as high-K calc-alkaline series. Both the meta gabbro-diorite and meta-granite samples are characterized by negative Nb, Ta, and Ti anomalies and enriched LILEs, and showing arc signatures that may be related to the southward subduction of the North Qilian oceanic crust. The 441 Ma hornblende syenite samples have high contents of alkalis (K 2 O +Na 2 O = 7.80%-12.07%) and belong to the alkaline series, suggesting an extensional geological setting. The 440 Ma syenogranite samples are classified as high Ba-Sr granites and belong to the shoshonitic series. The syenogranite samples were most likely generated by partial melting of lithospheric mantle that had been metasomatized by slab-derived fluids, and mixed by the crust derived granitic magmas during the ascent of the magma. Both the hornblende syenite (441 Ma) and the syenogranite (440 Ma) samples were emplaced in a postcollisional tectonic setting associated with the closure process of the North Qilian Ocean.

Experimental Investigations on Mechanical Properties of Consolidated Samples for Collapse Columns under Seepage-Stress Coupling Effects

“…The initial height of the consolidated specimen after preconsolidation was about 105 mm. The standard specimen size was determined as ϕ50 mm × 100 mm after grinding and cutting [26], and the test sample is shown in Figure 6.…”

Punctuated Orogeny During the Assembly of Asia: Tectonostratigraphic Evolution of the North China Craton and the Qilian Shan From the Paleoproterozoic to Early Paleozoic

“…A Cambrian-middle Ordovician Qilian arc sequence developed along the northern margin of the Qaidam, which suggests a south-dipping subduction of the Qilian oceanic crust (C. F. Liu et al, 2019;C. Wu et al, 2016aC.…”

“…Silurian-Devonian plutonic intrusions along the southern margin of the Longshou Shan may be syn-to postcollisional after the closure of the Qilian Ocean occurred at ca. 445-440 Ma (e.g., C. F. Liu et al, 2019;Zuza et al, 2018) (Figure 14e). Alternatively, early Paleozoic plutons in the Longshou Shan may be evidence for bivergent subduction of the Qilian Ocean (e.g., X. H. Chen et al, 2019;B.…”

Petrogenesis and tectonic evolution of the Palaeozoic to Mesozoic Niuxinshan granitoids in the North Qilian orogen,NWChina

“…The Qilian orogen in the northeastern Tibetan Plateau hosts abundant granitoids (Figure 1a) (Li et al, 2018;Liu, Wu, Song, Liu, & Zhang, 2019;Yang et al, 2015), the formation of which were correlated to the subduction of the Proto-Tethyan Ocean and subsequent accretion of arc crust and proto-margin of the North China Craton (Song et al, 2013). The Early Palaeozoic granitoids in the Qilian orogen have also been considered to be related to the subduction of the North Qilian Ocean during the Early Palaeozoic (Li et al, 2016;Peng et al, 2017;Wu et al, 2011;Zhang, Li, Pan, & Song, 2018), and several previous studies have been carried out on these rocks (Xiao et al, 2009;Zhang et al, 2012;Song et al, 2006Song et al, , 2013Wang et al, 2017).…”