Cretaceous Ridge Subduction Along the Lower Yangtze River Belt, Eastern China

Abstract

The Lower Yangtze river belt is one of the most important metallogenic belts in China. The mechanisms responsible for ore genesis and the formation of related Cretaceous igneous rocks, such as adakite, A-type granitoid, and Nb-enriched basalt, remain controversial. Mesozoic granitoids in the Lower Yangtze river belt were mostly formed in the Early Cretaceous (140-125 Ma), and three granitoid belts-the inner, the south, and the north-have been defined according to petrological and geochemical characteristics. Previously, based mainly on negative εNd and high initial Sr isotope values, the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust, both of which require crustal thickening. Mesozoic crustal thickening, however, is not supported by the development of extensional basins in the region. From the Late Jurassic to Cretaceous, eastern China was closely associated with subduction of the Pacific plate in the south and the Izanagi plate in the north. The midocean ridge (MOR) between these two plates was drifting toward and likely subducting under the Lower Yangtze river belt. A ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt. Partial melting of subducting young, hot oceanic slabs close to the ridge formed adakitic rocks. The negative εNd values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle, and/or crustal materials through AFC process. A slab window opened during ridge subduction as indicated by A-type granitoids in the center of the inner belt. Nb-enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths.

Destruction of the North China Craton Induced by Ridge Subductions

“…Three adakite belts have been recognized ( fig. 1), with ages of Ma (Early Cretaceous) along the LYRB (Xu 140 ‫ע‬ 5 et al 2002;Wang et al 2006;Ling et al 2009;Liu et al 2010a), Ma (Early Cretaceous) along 130 ‫ע‬ 5 the Shandong Peninsula and Xu-Huai region (Y. G. Xu et al 2004;W. L. Xu et al 2006aW.…”

The formation of Qulong adakites and their relationship with porphyry copper deposit: Geochemical constraints

“…Considering that porphyry Cu deposits are usually closely associated with adakites (Ling et al, 2009(Ling et al, , 2013bOyarzun et al, 2001;Sun et al, 2011Sun et al, , 2013, it is very important to study the origin and relationship of adakites with the Gangdese porphyry copper deposits.…”

Early Cretaceous potassic volcanic rocks in the Jiangnan Orogenic Belt, East China: Crustal melting in response to subduction of the Pacific–Izanagi ridge?

“…The origin of the Mesozoic adakitic rocks in eastern China did not require a thickened crust, except for those adakitic rocks from the continental collisional orogens (i.e., SuluDabie orogens, Ma et al, 2015). Instead, increasing evidence has been presented to support the view that the Mesozoic adakitic rocks in SE China were likely generated by melting of oceanic crust (Sun et al, 2007(Sun et al, , 2010Ling et al, 2009Ling et al, , 2011Liu et al, 2010).…”

“…A ridge subduction model has recently been proposed for the magmatism in the LYRB (Sun et al, 2007(Sun et al, , 2010Ling et al, 2009Ling et al, , 2011Li et al, 2011Li et al, , 2012. The movement direction of the Paleo-Pacific Plate changed several times since the Early Cretaceous (~140 Ma, Koppers et al, 2001;Sun et al, 2007).…”