Ridge subduction and island arc evolution in the Duobaoshan region during early Paleozoic: Insights from crustal thickness and lava geochemistry

Abstract

The Duobaoshan island arc contains early Paleozoic association of adakitic high-Mg andesite, Nb-enriched basalt, and porphyry Cu deposits, concurrently indicating the ridge subduction in the eastern Xing’an Massif. This study further understands the unique island arc setting through the mantle metasomatism, oxygen fugacity and crustal thickness based on the zircon U–Pb geochronologic and Hf isotopic data from the early Paleozoic igneous and sedimentary rocks, as well as the whole–rock geochemical and Sr–Nd–Hf isotopic data from the igneous rocks in the Duobaoshan region, Xing’an Massif. The early Paleozoic igneous rocks are typical arc–type with low (La/Yb)_N ratios (3.37–6.60), exhibiting highly depleted zircon Hf (ε_Hf(t) = +12.44∼+16.50) and whole–rock Sr–Nd–Hf isotopic data ((⁸⁷Sr/⁸⁶Sr)_i = 0.7036–0.7048; ε_Nd(t) = +4.76∼+8.17; ε_Hf(t) = +12.44∼+16.50), which were derived from the depleted mantle metasomatized mainly by slab fluid accompanied with the altered oceanic crust melt and pelagic sediment melt, and reflected the maturing process of the island arc. In addition, the Early Ordovician igneous rocks indicated the increase of mantle temperature and oxygen fugacity (ΔFMQ > 2) leading to the solubility of metallogenetic elements, and the thickening crust was also conducive to the mineralization. Then we further revealed the existence of a Precambrian basement of the Xing’an Massif based on the sedimentary rocks, the geochronology of which revealed the youngest ages of 504–478 Ma, yielding the age peaks at 771 Ma, ∼860 Ma, ∼950 Ma, and ∼1800 Ma ∼2500 Ma. In the meanwhile, the Hf isotopic data of 600–478 Ma detrital zircons show depleted to more enriched ε_Hf(t) values (–10.22 to +12.70) and a proximal depositional traits, indicating that majority of the Neoproterozoic and early Paleozoic detrital zircons migrated from the Duobaoshan region, Xing’an Massif.