Two Paleoproterozoic strongly peraluminous granitic plutons (Nonggeori and Naedeokri granites) at the northeastern part of Yeongnam Massif, Korea: Geochemical and isotopic constraints in East Asian crustal formation history

Abstract

In the northeastern Yeongnam Massif of South Korea, voluminous granitoids were emplaced from Mesozoic to Paleoproterozoic period. Nonggeori (NG) and Naedeokri (ND) granites are known as two of Paleo- to Meso-proterozoic plutons in the northeastern margin of the Yeongnam Massif. They occur as stocks intruding Precambrian metasediments at the Taebaek area in northeastern part of South Korea. Pegmatites occur at adjoining areas either near or between NG and ND granites. The pegmatites have experienced tin mineralization. The NG and ND granites consist of quartz, plagioclase, K-feldspar, biotite and muscovite. The accessory minerals are tourmaline, zircon, apatite, chlorite and calcite. The mineral assemblages and major chemical compositions of the two granites are very similar. Geochemically, the NG and ND granites are strongly peraluminous, with a molar ratio of A/CNK from 1.13 to 1.46 for NG and ND granites and 1.12 to 1.34 for pegmatites. In the chondrite-normalized diagrams, the NG and ND granites have characteristics of LREE-enriched, HREE-depleted patterns and large negative Eu anomalies. However, the pegmatite shows two types of the REE pattern. One is flattened type with highly negative Eu anomalies, the other is slightly LREE enriched with strong positive Eu anomalies. Trace element characteristics of NG, ND granites and pegmatites are generally compatible with those of syn-collisonal granite rather than volcanic arc granite. The granites show Sm–Nd whole rock age of 1865 ± 120 Ma with ɛ Nd (1.87 Ga) = −7.0, suggesting light-REE enriched continental like feature. Based on the initial ɛ Nd value and trace element geochemistry, the NG and ND granites apparently were originated from remelting (or recycling) of crustal materials. However, ultimately, the protolith of NG, ND granites including neighbor pegmatites was derived from depleted mantle sources, which are related with those that had been involved in producing East Asian crust such as the basement of the Sino-Korean Craton during the Archean. Particularly, the Precambrian granitoids from the Yeongnam Massif may provide critical evidence for unraveling Precambrian plate tectonics and crustal evolution in East Asia including Japanese islands.