affinity to the South China block, and the Yeong- nam massif to the North China block. This idea
provided a principal background for later tectonic interpretations of the Korean peninsula by Cluzel
et al. 1991 and Yin and Nie 1993. Cluzel et al. 1991 suggested that the Gyeonggi massif and the
Ogcheon belt of South China affinity have been juxtaposed with the Yeongnam massif of North
China affinity as a result of Triassic dextral dis- placement of the order of 200 km along the
Honam shear zone. Yin and Nie 1993 adopted Cluzel et al. 1991’s idea and further proposed an
indentation model for explaining the diachronic nature of the Chinese collision belt and develop-
ment of the Tan-lu and Honam fault systems. If Kobayashi 1966’s scheme is valid, it is expected
that the two massifs are different in terms of isotopic signatures and ages of crustal formation
and tectono-metamorphic events, considering a presumed distinction between the North and
South China blocks Ma and Wu, 1981; Jahn et al., 1990; Zhang et al., 1997; Chen and Jahn,
1998.
In this study, we address this problem by Pb and Nd isotope data. First, we present Pb – Pb
ages and Nd isotopic data of basement rocks from the Pyeonghae area, northeastern Yeong-
nam massif Fig. 1B. Using the Pb and Nd isotope data of this study and previous works, we
compare geochronology and isotopic characteris- tics between the Gyeonggi and Yeongnam mas-
sifs. Second, we compare Nd isotopic signatures of Korean basement rocks with those of Chinese
blocks on the basis of compiled data set, and discuss their tectonic implications for the hypoth-
esis of continuation of the Chinese collision belt to the Korean peninsula.
2. Geologic setting
The Korean peninsula can be divided into seven major tectonic provinces: i.e. from northwest to
southeast, the Precambrian Nangrim massif, the Paleozoic Pyeongnam basin, the Paleozoic Imjin-
gang belt, the Precambrian Gyeonggi massif, the late Precambrian to Paleozoic Ogcheon belt, the
Precambrian Yeongnam massif, and the Creta- ceous Gyeongsang basin Fig. 1A. The Gyeonggi
and Yeongnam massifs constitute the Precam- brian basement in the southern Korean peninsula,
and consist primarily of high-grade gneisses and schists. The Gyeonggi massif is bounded by nor-
mal faults with the Imjingang belt to the north Ree et al., 1996 and with the Ogcheon belt to
the south Kwon et al., 1995; Ree et al., 1995. The boundary between the Yeongnam massif and
the Ogcheon belt is a dextral strike-slip ductile shear zone called the Honam shear zone Yanai et
al., 1985; Cluzel et al., 1991, which is overlain unconformably by the Gyeongsang basin. How-
ever, many parts of the tectonic boundaries are obscured by extensive intrusions of Mesozoic
granites. The two belts comprise highly deformed meta-volcanosedimentary sequences which experi-
enced Barrovian metamorphism during Permian- Triassic time Adachi et al., 1996; Ree et al.,
1996. The Ogcheon belt is considered to have developed in a failed intracontinental rift setting
during early Paleozoic time and therefore cannot be a suture zone Chough, 1981; Cluzel et al.,
1991. Recently, Lee et al. 1998 reported a late Precambrian age for a metavolcanic rock in the
Ogcheon belt. Ree et al. 1996 showed from structural, metamorphic and geochronological
studies that the Imjingang belt is a possible candi- date for the suture zone extending from the
Sulu belt in China. The Gyeongsang basin is covered
with volcano-sedimentary
sequences the Gyeongsang supergroup and basement rocks
are rarely exposed. Previous age data for the formation and meta-
morphism of basement rocks in the Gyeonggi and Yeongnam massifs are mainly concentrated in the
early Proterozoic ca. 2.2 – 1.8 Ga. However, an upper intercept age of U-Pb zircon Turek and
Kim, 1996 and some Nd model ages Lan et al., 1995 indicate the presence of Archean basement
rocks in South Korea.
In the Pyeonghae area of northeastern Yeong- nam massif Fig. 1C, the Precambrian rocks are
divided into the Wonnam group of metasedimen- tary rocks and the Pyeonghae gneiss of metaig-
neous rocks on the basis of lithology and field occurrence, with the latter intruding the former
Kim et al., 1963. They are unconformably over-
lain by Phanerozoic sedimentary rocks, and are locally intruded by Cretaceous granitic rocks in
the southern part of the area. The Wonnam group, the oldest unit in the study area, is mainly
composed of mica schists, garnet-mica schists, biotite gneisses, quartzite, and aplitic gneisses to-
gether with subordinate calcsilicates and amphi- bolites. The Pyeonghae gneiss comprises mainly
well-foliated biotite gneisses and aplitic gneisses, showing augen and banded structures. In the fel-
sic interlayer, K-feldspar porphyroblasts about 2 cm in length are commonly observed. Kim et al.
1991 suggested an upper amphibolite facies metamorphic condition for the Pyeonghae gneiss,
but quantitative estimates of temperature and pressure are not available yet. No geochronologi-
cal data have been reported for the Precambrian rocks in the Pyeonghae area.
3. Samples and experimental procedures
