Implications based on the first SHRIMP U–Pb zircon dating on Precambrian granitoid rocks in North Korea

Abstract

Precambrian basement rocks in North Korea consist of supracrustals and granitoid rocks, of which the former comprise the late Archean Nangrim Group and the Paleoproterozoic Jungsan and Machollyong Groups, whereas the latter include four major types: grey TTG gneisses, garnet/sillimanite-bearing (S-type) granites, massive porphyritic granites, and hornblende-bearing granites. SHRIMP U–Pb zircon geochronology, combined with cathodoluminescence (CL) imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the Precambrian history of North Korea and its relations to North China. SHRIMP U–Pb zircon analyses on two grey gneiss samples (PO501 and K14) reveal that they were emplaced at 2538 ± 14 Ma and 2636 ± 49 Ma, respectively, and metamorphosed at 2462–2433 Ma. These data, for the first time, confirm the existence of late Archean rocks in the Korean Peninsula. Moreover, one grey gneiss sample (K14) contains several zircons with ages of 3.1–3.4 Ga, suggesting possible middle Archean crust in North Korea. Rocks with such ages are widely distributed in North China, implying that North China and North Korea have similar Archean basement. One grey gneiss sample (R53) yielded a SHRIMP zircon age of 1933 ± 12 Ma, indicating that some grey gneisses in North Korea formed during the Paleoproterozoic. Two garnet- and/or sillimanite-bearing S-type granite samples gave 207Pb/ 206Pb ages of 1908 ± 31 Ma and 1903 ± 49 Ma, interpreted to reflect the time of metamorphism of the Paleoproterozoic Jungsan and Machollyong Groups since these S-type granites are considered to be derived from the partial melting of pelitic rocks from these groups. The ∼ 1.9 Ga metamorphic event has also been revealed in Paleoproterozoic rocks in South Korea and North China. SHRIMP zircon data also show that massive porphyritic monzogranites in North Korea evolved over a protracted interval from 1865 Ma to 1843 Ma. Similar-aged porphyritic monzogranites are also found in North China and South Korea, and their origin is considered to be related to a post-tectonic extensional event of regional extent. The last phase of Precambrian magmatism recognized in North Korea is Grenvillian-aged, represented by the hornblende-bearing granite that yields a SHRIMP zircon age of 1195 ± 4 Ma, and is considered to be the source rock of the adjacent Yushulazi Group (North China) that contains numerous 1.1–1.2 Ga old detrital zircons.