Crustal control on the redox state of granitoid magmas: tectonic implications from the granitoid and metallogenic provinces in the circum-Japan Sea Region

Abstract

Felsic magmatism has occurred over a large region of East Asia since Jurassic times and has provided important mineral resources such as tin, tungsten, base metals and gold. The circum-Japan Sea region preserves various geological records of active continental margins, including Jurassic to Early Tertiary magmatic arcs and subduction zones and pre-Jurassic continental basements, which were separated by the opening of the Japan Sea during the Miocene. The felsic magmatism in this region shows a wide variation in terms of redox state and related mineralisation, encompassing east–west contrasts around the Pacific Ocean. A review of granitoids and associated ore deposits in this region indicates that the character of the crust, sedimentary versus igneous, is an essential factor to control the redox state, and a tectonic setting may be an additional factor in some cases.The reduced-type granitoids, characterised by tin mineralisation, were generated in carbonbearing sedimentary crust which was composed mainly of accretionary complex material and not influenced by previous magmatism. Involvement of sedimentary materials is corroborated by oxygen, sulphur and strontium isotope data. The oxidised-type granitoids, characterised by gold or molybdenum mineralisation, were generated in igneous crust which was depleted in reducing agents as a result of previous magmatism. Granitoid magmatism in a given area tends to become more oxidised with time.Jurassic accretionary complexes in East Asia are thought to have been largely displaced from the original place of accretion and stacked up against the northeastern margin in the Khingan and Sikhote–Alin Mountains. This region, dominated by sedimentary crust, was subsequently subjected to Cretaceous felsic magmatism and converted to a large province of reduced-type granitoids and tin–tungsten mineralisation. Diverse geodynamic processes, including the change of the arc-trench system, the creation and collapse of the back-arc basin and the collision of continents, may have prepared many favourable sites for the generation of reduced-type granitoids in northeast Asia. These processes may have resulted in a remarkable contrast with the Pacific margin of North America, where repeated arc magmatism during the Mesozoic formed granitoid batholiths of the oxidised-type.The granitoid types may also be controlled by the tectonic setting and mode of magma emplacement. In the northern Kitakami area of Northeast Japan, Early Cretaceous episodic magmatism occurred in a Jurassic accretionary complex, and formed the oxidised-type granitoids accompanied by submarine bimodal volcanism associated with kuroko mineralisation. Granitoids of fissure-filling type emplaced under extensional environments may be oxidised, irrespective of basement geology, because of insignificant crustal input.

Lermontovskoe Tungsten Skarn Deposit: the Oldest Mineralization in the Sikhote-Alin Orogen, Far East Russia

“…No significant tin mineralization is associated with them (Sato et al, 2004b). The East Sikhote-Alin Volcano-Plutonic Belt along the Japan Sea coast ( Fig.…”

“…The igneous regions within Russia are divided into two belts: the Khingan-Okhotsk Belt and Sikhote-Alin Belt (Sato et al, 2002). These two belts are considered to be juxtaposed arcs with different geotectonic histories, showing an unusually broad distribution of igneous rocks (Sato et al, 2004b).…”

“…Both the redox state of the Cretaceous to Paleogene felsic magmatism and character of associated mineralization show a systematic regional variation with the pre-Cretaceous basement geology (Sato et al, 2004b). Cretaceous reduced-type granitoids and volcanic rocks are widely distributed in the Khingan-Okhotsk Belt and major part of the Sikhote-Alin Belt, and are accompanied by tin and tungsten mineralization.…”

“…These two regions of oxidized igneous rocks accompanied by gold mineralization are characterized by earlier intense magmatism; Paleozoic in the Khanka massif and Cretaceous in the 258 RESOURCE GEOLOGY : K. SATO, S. M. RODIONOV and A. A. BRUBLEVSKY Sato et al (2002Sato et al ( , 2004b. The Zhuravlevka terrane in Sikhote-Alin is composed mainly of Early Cretaceous turbidites (e.g., Khanchuk et al, 1996), and is included in the Jurassic-Early Cretaceous accretionary complexes in this map.…”

“…The East Sikhote-Alin Volcano-Plutonic Belt is thought to be a northern extension of the San-in Belt of Southwest Japan; both are characterized by the Paleogene oxidized-type magmatism (Sato et al, 2004b East Sikhote-Alin Volcano-Plutonic Belt. These correlations between the redox state of felsic magmatism and history of magmatism are also recognized in the Japanese Islands, and are considered to be related to the involvement of carbonaceous materials in sedimentary rocks acting as reducing agents (Sato et al, 2004b).…”