Crustal evolution of ca. 1.9-1.85 Ga collisional orogen associated with the massif-type anorthosite in the Yeongnam Massif, Korea

English Abstract:

The North China Craton (NCC) including the Korean Peninsula has experienced episodic amalgamation and intracrustal reworking since its formation in the Archean. The Yeongnam Massif, Korea, situated at the eastern margin of the NCC, records prolonged crustal evolution characterized by an arc-related magmatism at ca. 2.0-1.9 Ga and subsequent collisional event at ca. 1.9-1.87 Ga, followed by a massif-type anorthositic magmatism at 1.86 Ga. An extensive occurrence of migmatites is well documented throughout this massif, but their temporal relationship and tectonic setting are poorly constrained. Zircon and baddeleyite grains separated from the anorthositic rocks were dated using a sensitive high-resolution ion microprobe (SHRIMP)¹. The weighted mean ²⁰⁷Pb/²⁰⁶Pb age of zircon from two anorthosites is 1862 ± 2 Ma, corroborated by the baddeleyite age of 1861 ± 14 Ma. On the other hand, the ages of hornblende gabbro and granitic gneiss are 1873 ± 4 Ma and 1875 ± 5 Ma, respectively. In contrast, zircon rims from mafic granulite and migmatitic gneiss yielded ages of 1860 ± 5 Ma and 1858 ± 4 Ma, respectively, implying that the granulite-facies metamorphism and anatexis are associated with the anorthosite emplacement. Our preliminary P–T–t analyses based on pseudosections and microstructures of garnet–sillimanite–cordierite–K-feldspar–plagioclase–ilmenite–melt-bearing aluminous migmatites suggest a peak metamorphic condition at 800–850 °C and 4–7 kbar, followed by a near-isobaric cooling with melt crystallization in the range of 700–750 °C and 4–6 kbar. These results together with available Re-Os data are compatible with ca. 1.9–1.85 Ga collisional orogeny prevalent in the NCC, and suggest that orogenesis was accompanied by the mantle delamination beneath the craton. Taken together, we suggest that the Yeongnam Massif has experienced a prolonged orogeny characterized by late-orogenic anorthositic magmatism.

[1] Lee et al. (2014) Terra Nova, 26, 408–416.