The big mantle wedge and decratonic gold deposits

Abstract

The Circum-Pacific subduction zone is a famous gold metallogenic domain in the world, with two important gold metallogenic provinces, the North China Craton and Nevada, which are related to the destruction of the North China Craton and the Wyoming Craton, respectively. Their ore-forming fluids were possibly derived from the stagnant slab in the mantle transition zone. The oceanic lithospheric mantle usually contains serpentine layers up to thousands of meters thick. During plate subduction, serpentine is dehydrated at depths of <200 km and transformed into high-pressure hydrous minerals, known as Phases A to E, which carries water to the depth of >300 km. The overlying big mantle wedge is hydrated during the breakdown of these hydrous facies in the mantle transition zone. The dehydration of the subducted slab in the big mantle wedge releases sulfur-rich fluid, which extracts gold and other chalcophile elements in the surrounding rocks, forming gold-rich fluid. Because the cratonic geotherm is lower than the water-saturated solidus line of lherzolite, the fluid cannot trigger partial melting. Instead, it induces metasomatism and forms pargasite and other water-bearing minerals when it migrates upward to depths of less than 100 km in the cratonic lithospheric mantle, resulting in a water-and gold-rich weak layer. During the destruction of craton, the weak layer is destabilized, releasing gold-bearing fluids that accelerate the destruction. The ore-forming fluids migrate along the shallow weak zone and are accumulated at shallow depths, and subsequently escape along deep faults during major tectonic events, leading to explosive gold mineralization. The ore-forming fluids are rich in ferrous iron, which releases hydrogen at low pressure through iron hydrolysis. Therefore, decratonic gold deposits are often reduced deposits.

Origin, Accretion, and Reworking of Continents

“…10.1029/2019RG000689 formation of lithospheric properties from a refractory, enriched mantle to a fertile, depleted mantle (Tang et al, 2021, and references therein), formation of large oil and gas reservoirs, and explosive gold mineralization (Zhu et al, 2015(Zhu et al, , 2017Zhu & Sun, 2021). Compared with other cratons globally, the NCC is the best example of craton destruction.…”

“…The following processes mark craton destruction: the extensive volcanic eruption and granitic emplacement (Ma & Xu, 2021, and references therein), intensive lithospheric extension, thinning, crustal deformation, and rift-basin formation, all of which indicate that the cratonic lithosphere has been destabilized (Zhu et al, 2020, and references therein). Notably, the destruction of a craton is also accompanied by the trans-formation of lithospheric properties from a refractory, enriched mantle to a fertile, depleted mantle (Tang et al, 2021, and references therein), formation of large oil and gas reservoirs, and explosive gold mineralization (Zhu et al, 2015(Zhu et al, , 2017Zhu & Sun, 2021). Compared with other cratons globally, the NCC is the best example of craton destruction.…”

“…The eastern part of the NCC has undergone complicated geological processes since the Mesozoic, and the nature of the subcontinental lithospheric mantle changed fundamentally from cratonic to oceanic-like, accompanying the thinning and reactivation of the crust (Tang et al, 2021;Wu et al, 2008Wu et al, , 2014F. Y. Wu et al, 2019;Xu, 2001;Yang et al, 2018;Zhang, 2005;Zheng et al, 2018;Zhu & Sun, 2021;Zhu & Xu, 2019;Zhu, Xu, et al, 2012;Zhu, Yang, & Wu, 2012;Zhu et al, 2011Zhu et al, , 20172020). However, what kind of geodynamic mechanisms caused the reworking and even destruction of an ancient continent is still debated.…”

Application of the AMT Method to Gold Deposits: A Case Study in the Qinling Metallogenic Belt of North China Craton

“…Tectonic regime transformation and crustal activation appeared in the NCC during Mesozoic, and the thinning of the lithosphere and the appearance of voluminous crust-derived granites were the main characteristics [28]. Previous studies have shown that the destruction of the craton and the Mesozoic magmatism in eastern North China are closely related to the subduction of the paleo-Pacific plate [29][30][31]. Since the Early Jurassic, the paleo-Pacific plate has changed from a low-angle subduction to a high-angle subduction, accompanied by the retreat of the subduction zone, which induced strong destruction in the eastern part of the NCC.…”

“…Minerals 2021, 11, x FOR PEER REVIEW 3 of 14 in eastern North China are closely related to the subduction of the paleo-Pacific plate [29][30][31]. Since the Early Jurassic, the paleo-Pacific plate has changed from a low-angle subduction to a high-angle subduction, accompanied by the retreat of the subduction zone, which induced strong destruction in the eastern part of the NCC.…”