Zircon U-Pb geochronological and Hf isotopic constraints on the Precambrian crustal evolution of the north-eastern Yeongnam Massif, Korea

Precambrian Research 242 (2014) 1–21

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Zircon U-Pb geochronological and Hf isotopic constraints on the Precambrian crustal evolution of the north-eastern Yeongnam Massif, Korea Namhoon Kim a , Chang-sik Cheong a,b,∗ , Keewook Yi a , Yong-Sun Song c , Kye-Hun Park c , Jian-zhen Geng d , Huai-kun Li d a

Division of Earth and Environmental Sciences, Korea Basic Science Institute, Chungbuk 363-883, Republic of Korea Graduate School of Analytical Science and Technology, Chungnam National University, 99 Daehangno, Yuseong-gu, Daejeon 305-764, Republic of Korea c Department of Earth Environmental Sciences, Pukyong National University, Pusan 608-737, Republic of Korea d Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China b

a r t i c l e

i n f o

Article history: Received 25 September 2013 Received in revised form 11 December 2013 Accepted 12 December 2013 Available online 20 December 2013 Keywords: Yeongnam Massif Zircon U-Pb age Hf isotopes Crustal formation

a b s t r a c t In situ U-Pb dating and Hf isotopic analyses were conducted on zircons extracted from Paleoproterozoic metasedimentary rocks and peraluminous (meta)granitoids in the north-eastern Yeongnam Massif, Korea. Combined with previous results, analyses from detrital zircons from the metasedimentary rocks yield a predominant age population of ca. 2.5 Ga with subordinate clusters at ca. 2.7, 2.3, and 2.1 Ga, and minor points older than 2.8 Ga. The detrital zircons frequently have textureless rims that were overgrown at ca. 2.03–1.85 Ga, indicating post-depositional thermal overprints associated with the intrusion of neighbouring granitoids and metamorphism. The (meta)granitoids are divided into three lithologic groups of banded or augen biotite gneisses (group I: Pyeonghae and Buncheon gneiss), massive cordierite or two mica granitic gneisses (group II: Icheonri and Hongjesa granitic gneiss), and a garnet-bearing leucogranite (group III: Imwon leucogranite). The best estimates of the timing of the emplacement of the first two groups are indistinguishable within their error ranges; 1980 ± 22 Ma (Pyeonghae gneiss), 1966 ± 15 Ma (Buncheon gneiss), 1985 ± 14 Ma (Icheonri granitic gneiss), and 1975 ± 16 Ma (Hongjesa granitic gneiss). The upper intercept discordia ages of ca. 1.86 Ga indicated by the metamorphic overgrowth rims of zircons from the Buncheon gneiss and the Icheonri granitic gneiss agree with the emplacement age of the Imwon leucogranite (1867 ± 6 Ma). A close genetic link between the (meta)granitoids and metasedimentary rocks is demonstrated by the comparable age pattern of inherited zircon cores in the former with that of detrital zircons in the latter. The lower intercept ages of zircons indicate repeated Pb loss events in the Neoproterozoic to Paleozoic, although their exact tectonic meaning is still unclear. Most zircons have negative εHf values corresponding to two-stage Hf model ages (T2DM ) from 3.4 to 2.7 Ga, demonstrating Neoarchaean to Paleoproterozoic reworking of the Paleo- to Neoarchaean crust. Zircons from group I metagranitoids display a narrow T2DM range (2.74 ± 0.09 Ga). The Neoarchaean Hf model ages are also reduced by high-εHf zircons from the metasedimentary rocks and group II metagranitoids (T2DM = ca. 2.75 Ga), and most zircons from the Imwon leucogranite (T2DM = 2.62 ± 0.06 Ga). The protoliths of group I metagranitoids are considered to be I-type granites that was derived by infracrustal melting at depth. In contrast, the scattered Hf model ages of zircons from group II metagranitoids are suggestive of crystallisation from heterogeneous S-type magmas derived from the partial melting of supracrustal rocks. It is concluded that the Neoarchaean Era (ca. 2.75–2.62 Ga) marks the most important stage of crustal formation in the north-eastern Yeongnam Massif. The Paleoproterozoic (ca. 2.50–1.98 Ga) magmas from which the zircons crystallised were principally a product of crustal reworking. These Hf isotopic features generally match those reported for zircons from the North China Craton and the eastern part of the Cathaysia Block in the South China Craton, but the zircon ages determined here do not allow an indisputable correlation of the north-eastern Yeongnam Massif with Paleoproterozoic terranes in eastern China. © 2013 Elsevier B.V. All rights reserved.

∗ Corresponding author at: Division of Earth and Environmental Sciences, Korea Basic Science Institute, 162 Yeongudanji-ro, Ochang-eup, Cheongwon-gun, Chungbuk 363-883, Republic of Korea. Tel.: +82 43 240 5170; fax: +82 43 240 5319. E-mail address: [email protected] (C.-s. Cheong). 0301-9268/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.precamres.2013.12.008

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N. Kim et al. / Precambrian Research 242 (2014) 1–21

1. Introduction It is generally accepted that Archaean–Proterozoic continental blocks in East Asia were amalgamated along a number of orogenic belts such as the Trans-North China Orogen between the Eastern and Western Blocks of the North China Craton (NCC), the Jiao-LiaoJi Belt between the Longgang Block in eastern China and Nangrim Massif in North Korea, the Qinling-Dabie-Sulu Belt between the North and South China Cratons, and the Jiangnan Belt between the Yangtze and Cathaysia Blocks of the South China Craton (SCC) (Zheng et al., 2013 and references therein) (Fig. 1). There is still much controversy regarding the precise subdivision of the tectonic blocks, and how and when the micro-continental blocks were assembled and dispersed, as described in recent synoptic reviews of the crustal evolution of the NCC (Faure et al., 2007; Kusky and Santosh, 2009; Zhai and Santosh, 2011; Zhao et al., 2012) and the SCC (Xu et al., 2007; Yao et al., 2012; Zhang and Zheng, 2013). The combination of zircon U-Pb dating and Hf isotopic analyses on these blocks has made it easier to discuss these issues, and has provided evidence for episodic growth and recycling of the Archaean–Proterozoic continental crust (Wu et al., 2005, 2008; Zhang et al., 2006, 2013; Yang et al., 2008, 2012; Yu et al., 2009, 2012, 2013; Jiang et al., 2010; Ying et al., 2011; Geng et al., 2012; Liu et al., 2012; Sun et al., 2012; Wang et al., 2012a,b; Yao et al., 2012). Precambrian high-grade basement and supracrustal rocks are widespread in the Korean Peninsula, which lies at the present far eastern margin of the Asian continent. The peninsula comprises three Precambrian (mainly Paleoproterozoic) blocks (Nangrim, Gyeonggi, and Yeongnam Massifs) that are intervened by Neoproterozoic to Paleozoic fold-and-thrust belts (Imjingang and Okcheon Belts) (Fig. 1). The available isotopic data indicate that these massifs have experienced complicated magmatic and metamorphic episodes since at least the Neoarchaean (Lan et al., 1995; Turek and Kim, 1996; Kim et al., 1999, 2012b, 2013b; Cheong et al., 2000, 2004; Chang et al., 2003; Kim and Cho, 2003; Lee et al., 2003a,b, 2007, 2010a,b; Sagong et al., 2003; Zhao et al., 2006; Wu et al., 2007a,b; Cho et al., 2008). Although the massifs may provide first-hand information on some key issues regarding the tectonic architecture of East Asia, such as the nature and continuation of the orogenic belts, a general consensus about their linkage and correlation with the Chinese blocks has not been achieved. This study presents the results of detailed sensitive high resolution ion microprobe (SHRIMP) U-Pb and laser ablationmulti collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) Hf isotopic analyses of zircons collected from Paleoproterozoic metasedimentary and (meta)granitoid rocks in the north-eastern Yeongnam Massif. The main aims of the study are: (1) to refine the geochronological framework of crustal evolution in the north-eastern Yeongnam Massif, and (2) to determine the timing of continental formation and recycling in this region, and the source characteristics of the granitoids by using Hf isotopes of zircons that have crystallised since the Paleoarchean. The zircon data also have implications for the correlation of the north-eastern Yeongnam Massif with Chinese terranes.

2. Geological setting and sample collection The Yeongnam Massif is a Paleoproterozoic metamorphic terrane that is northwestwardly bounded to the Okcheon Belt, an intra-plate rift composed mainly of Neoproterozoic metavolcanic rocks and Paleozoic metasedimentary sequences (Cho and Kim, 2005; Park et al., 2011; Cho et al., 2013). Its south-eastern margin is unconformably overlain by, or in fault contact with Cretaceous volcano-sedimentary rocks formed within the Gyeongsang backarc

basin (Choi et al., 2002; Chough and Sohn, 2010). Orthogneisses are predominant over paragneisses in the massif, especially in the south-western part that is referred to as the Jirisan complex. The peak metamorphic condition has reached the granulite facies (≥800 ◦ C, 6 kbar) both in the Jirisan complex (Song, 1999) and the north-eastern part of the massif (Kim and Cho, 2003; Cheong and Na, 2008), but the P–T–t paths are poorly understood. Although previous whole-rock Nd and zircon Hf isotopic analyses indicated Archaean model ages (Lan et al., 1995; Cheong et al., 2000, 2004; Lee et al., 2007), there are still no data for basement rocks older than 2.5 Ga within the massif (Lee and Cho, 2012 and references therein). The north-eastern Yeongnam Massif comprises Paleoproterozoic stratigraphic units including metasedimentary rocks and (meta)granitoids, and Phanerozoic cover rocks and granitoid plutons (Fig. 2). The metasedimentary rocks are traditionally referred to as the Yuli (the western part) and Wonnam (the eastern part) Groups and the Hosanri (the north-eastern part) Formation. They are similarly composed of banded gneiss, mica schist, quartz-mica schist, mica-sillimanite schist, quartzite, migmatite and marble. The preferred occurrence of migmatite in the eastern area implies a local difference in the metamorphic grade. Metapelitic and metapsammitic sections alternate with a width of a few to ten centimetres, and are intruded by granitic gneisses and amphibolites along the major foliation which consists mainly of biotite and prismatic or fibrous sillimanite. The metapelite comprises quartz, biotite, garnet and sillimanite with subordinate cordierite, plagioclase, microcline, muscovite, chlorite and zircon. Centimetre-sized garnet porphyroblasts commonly have a poikiloblastic texture with quartz, biotite, plagioclase, and/or fibrous sillimanite inclusions. Cordierite polysynthetic or complex twins are occasionally altered to pinnite. Quartz and feldspar-rich lenticular bands or patches in the metapelite represent leucosomes that developed by partial melting. The alternating metapsammitic section is composed of dominant quartzofeldspathic layers containing minor biotite and garnet, and subordinate lenticular or boudinage quartzite. The migmatite occurs as metatexite to diatexite, and displays stromatic to schollen structures. It is composed of quartz, plagioclase, Kfeldspar, biotite, muscovite, sillimanite, cordierite and garnet with minor amounts of staurolite, apatite and zircon. The deposition time of metasedimentary rocks in the Yuli Group and the southern part of the Wonnam Group was confirmed to be Paleoproterozoic (2.2–2.0 Ga) by LA-ICPMS (Lee et al., 2011) and SHRIMP (Kim et al., 2012b) zircon analyses. Two samples of quartz schist (YN804-4) and migmatite (YN821) were collected from the Hosanri Formation, and a quartzite (YN908b) sample was taken from the Wonnam Group (Fig. 2). The Precambrian (meta)granitoids occurring in the northeastern Yeongnam Massif are invariably peraluminous (Cheong et al., 2004, 2006; Cheong and Na, 2008). They can be divided into three lithologic groups. The first group is coarse-grained banded or augen biotite gneisses that are distributed in the southern part, and referred to as Pyeonghae and Buncheon gneiss. The two gneisses are typically composed of quartz, microcline, plagioclase and biotite with minor muscovite, chlorite, hornblende, zircon and garnet. Kfeldspar porphyroblasts are commonly elongated parallel to the major foliation defined by biotite, forming augens or ribbons with a length of a few to several tens of centimetres. Their whole-rock Pb-Pb and zircon U-Pb ages are reported to be 1990–1920 Ma (Park et al., 1993; Chang et al., 2003; Kim et al., 2012b). Two samples were collected from the Pyeonghae (YN902) and Buncheon (YN906) gneisses (Fig. 2). The second group is composed of massive cordierite or two mica granitic gneisses distributed in the northern part of the study area, referred to as the Icheonri and Hongjesa granitic gneiss. The Icheonri granitic gneiss consists of quartz, plagioclase, K-feldspar

N. Kim et al. / Precambrian Research 242 (2014) 1–21

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Fig. 1. The distribution of Precambrian rocks in the Korean peninsula (Lee and Cho, 2012). Subdivided geotectonic provinces are separated by dashed lines. The inset shows the tectonic architecture of East Asia (Zheng et al., 2013). (1) Yinshan Block, (2) Khondalite Belt, (3) Ordos Block, (4) Trans-North China Orogen, (5) Longgang Block, (6) Jiao-Liao-Ji Belt, (7) Qinling-Dabie-Sulu Belt, (8) Yangtze Block, (9) Jiangnan Belt, and (10) Cathaysia Block.

and biotite with minor amounts of garnet, cordierite and sillimanite. Sillimanite and cordierite are characteristic metamorphic minerals in the gneisses in the western part, whereas garnet is prominent in the eastern part. Xenoliths of metasedimentary rocks and amphibolites commonly occur as schlieren. The Hongjesa granitic gneiss is characterised by the occurrence of bluish grey K-feldspar, which is generally massive but is well-foliated when in contact with the metasedimentary rocks. The primary mineral constituents are quartz, plagioclase and K-feldspar with minor amounts of biotite, muscovite, tourmaline, titanite and ilmenite. Biotite is the predominant mafic mineral in the central part, whereas biotite and muscovite are prominent in the margin. The emplacement age of the Hongjesa granitic gneiss is reported to be 2013 ± 30 Ma (LA-ICPMS zircon U-Pb, Lee et al., 2010a). Samples YN806 and YN810h were collected from the Icheonri granitic gneiss, and YN229 and YN230a were taken from the Hongjesa granitic gneiss (Fig. 2). The third group is a massive garnet-bearing leucogranite, referred to as the Imwon leucogranite. It is partly pegmatitic and xenoliths mainly composed of schists occasionally occur where it makes contact with the Hosanri Formation. The mineral

constituents consist of quartz, microcline, orthoclase and plagioclase, with subordinate muscovite, biotite, sillimanite, garnet, zircon and monazite. Garnet is prominent in the coarse-grained sections. Lee et al. (2010b) reported SHRIMP zircon U-Pb ages of 1859–1853 Ma for leucogranite samples collected from the eastern coastal area. Two samples (YN801 and 1016-7) were collected from the central and southern parts of the granite body (Fig. 2).

3. Analytical methods Zircon concentrates were extracted using density and magnetic techniques and were finally handpicked under a binocular microscope. Microscopic observation and SHRIMP analyses were carried out at the Korea Basic Science Institute. Back-scattered electron (BSE) and cathodoluminescence (CL) images of the separated zircon grains mounted together with zircon standards, FC1 (for calibrating U-Th-Pb ratios; 1099 Ma; Paces and Miller, 1993) and SL13 (for calibrating U concentrations; U = 238 ppm), were viewed using a scanning electron microscope (JEOL JSM-6610LV). SHRIMP U-Pb dating mostly followed the analytical protocols

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N. Kim et al. / Precambrian Research 242 (2014) 1–21

Fig. 2. Geologic map of the north-eastern Yeongnam Massif (modified after Cheong et al., 2006; Kim et al., 2012b) and the sampling locations. (1) YN804-4, (2) YN821, (3) YN908b, (4) YN902, (5) YN906, (6) YN806, (7) YN810h, (8) YN229, YN230a, (9) YN801, and (10) 1016-7.

of Williams (1998). Typically five-scan cycles were used for determining the ages. Ion-beam spot sizes were approximately 25 ␮m in diameter. The common Pb corrections were made from 204 Pb counts and the model isotopic composition of Stacey and Kramers (1975). The matrix effect was corrected for highU (>2500 ppm) zircons by assuming a systematic 2%/1000 ppm increase of apparent 206 Pb/238 U ratios (Williams and Hergt, 2000). Ages and concordia diagrams were produced using the Squid 2.50 and Isoplot 3.71 programs of Ludwig (2008, 2009). Individual spot ages were reported on the basis of 204 Pb-corrected 207 Pb/206 Pb ratios. Errors associated with individual data points were quoted at the 1 level, and weighted mean ages were reported at the 2 confidence level. Zircon Hf isotopic compositions were analysed for the dated zircon spots or new spots within the same CL domains, using a Neptune MC-ICPMS combined with an ArF excimer laser ablation system (New Wave Research) at the Tianjin Institute of Geology and Mineral Resources. The laser ablation system includes a short pulse width (<4 ns) excimer laser operated at 193 nm with an energy density of ∼15 J/cm2 . The spot was approximately 50 ␮m in diameter. Details of the operational parameters are described in Cheong et al. (2013). The Yb and Lu isotopic compositions used for the correction of mass bias and isobaric interference were adopted from Vervoort et al. (2004) and Chu et al. (2002), respectively. The isobaric interference-corrected 176 Hf/177 Hf ratios were exponentially normalised to 179 Hf/177 Hf = 0.7325 (Patchett et al., 1981). The 176 Lu/177 Hf and 176 Yb/177 Hf ratios were calculated following Iizuka

and Hirata (2005). Initial epsilon Hf values were calculated using a 176 Lu decay constant of 1.865 × 10−11 y−1 (Scherer et al., 2001) and chondritic values suggested by Blichert-Toft and Albarade (1997). For calculation of Hf model ages, the Lu-Hf isotopic composition of depleted mantle was adopted from Griffin et al. (2000). During the sample analysis, FC1 and GJ1 standard zircons yielded average 176 Hf/177 Hf ratios of 0.282146 ± 0.000037 (n = 24, 1 s.d., recommended value = 0.282184 ± 0.000016; Woodhead and Hergt, 2005) and 0.281999 ± 0.000028 (n = 28, 1 s.d., recommended value = 0.282003 ± 0.000018; Gerdes and Zeh, 2006), respectively. 4. Results 4.1. Zircon U-Pb ages Representative CL and BSE images of the analysed zircons are shown in Fig. 3. The SHRIMP U-Th-Pb data are listed in Table 1, and displayed graphically in Tera-Wasserburg diagrams in Fig. 4. 4.1.1. Metasedimentary rocks Zircons from a quartz schist (sample YN804-4) in the Hosanri Formation are transparent, brown to dark brown, and rounded to subrounded. The grains range from 80 to 210 ␮m in length, with aspect ratios (width:length) less than 1:2.5. They often contain biotite and quartz inclusions. Many grains contain rounded or subhedral cores showing oscillatory, undulous, and convolute zoning (Fig. 3). The thickened and blurred oscillatory zoning often

N. Kim et al. / Precambrian Research 242 (2014) 1–21

5

Table 1 SHRIMP zircon U-Th-Pb isotopic composition. Spota

206

Pbc (%)b

U (ppm)

Th (ppm)

206

Pb* /238 Uc

±%

207

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

YN804-4 1.1 2.1 2.2 3.1 3.2mt 4.2 5.1mt 5.2mt 6.1 6.2 7.1 7.2mt 8.1 8.2 9.1 9.2mt 10.2r 11.2r 12.1 12.2r 13.1 13.2mt 14.1 14.2mt 15.1 15.2 16.2mt 17.1 17.2 18.1 19.1 20.1 20.2 21.1 22.1 23.1mt 24.1mt 25.1 25.2 26.1 27.2mt 28.1mt

0.40 0.13 0.03 4.02 0.09 1.28 2.02 0.19 0.17 – 0.40 0.09 0.47 0.76 8.25 1.57 – 0.13 0.01 0.47 – 0.90 0.04 0.59 – – 0.39 0.05 0.05 0.03 0.56 0.20 0.05 0.01 – 2.51 1.47 0.16 0.88 0.09 0.43 0.04

494 864 396 406 1152 298 1338 1126 59 310 358 661 199 774 363 1495 356 427 294 193 125 675 75 1346 121 607 984 382 377 165 1198 469 84 143 251 1032 1118 379 410 381 698 540

171 393 67 165 57 182 69 53 54 121 181 10 103 242 230 199 42 323 315 119 44 130 26 540 102 314 573 496 273 86 582 218 46 48 102 35 203 683 46 201 8 50

0.319 0.219 0.315 0.457 0.184 0.411 0.135 0.161 0.469 0.408 0.442 0.211 0.402 0.254 0.286 0.095 0.361 0.345 0.411 0.350 0.430 0.253 0.697 0.192 0.465 0.422 0.202 0.465 0.391 0.507 0.335 0.287 0.396 0.415 0.520 0.171 0.168 0.371 0.219 0.352 0.156 0.338

1.0 0.9 1.7 1.0 1.1 1.8 1.3 1.5 1.9 1.1 1.1 1.0 1.2 1.0 1.1 1.1 1.2 1.1 1.1 1.3 2.3 1.1 5.0 2.8 1.5 1.0 0.9 1.5 1.0 1.3 1.4 3.1 2.9 1.3 1.7 1.2 0.9 1.0 1.0 1.5 0.9 1.0

0.146 0.142 0.143 0.162 0.111 0.147 0.092 0.097 0.162 0.154 0.166 0.111 0.153 0.137 0.142 0.081 0.130 0.126 0.147 0.131 0.160 0.117 0.344 0.109 0.160 0.151 0.110 0.158 0.156 0.180 0.254 0.149 0.149 0.144 0.193 0.107 0.107 0.153 0.131 0.157 0.107 0.121

0.5 0.4 1.6 0.4 6.6 1.8 1.8 3.7 1.2 1.4 1.2 0.7 1.6 1.0 1.5 3.5 2.1 0.6 1.2 2.0 1.7 0.8 4.9 0.9 0.9 0.8 0.6 0.4 0.4 0.6 0.7 1.9 1.2 0.8 1.1 1.8 2.5 1.1 1.7 1.3 0.8 0.5

+26 +48 +25 +3 +43 +5 +48 +41 – +9 +7 +35 +10 +37 +32 +54 +6 +7 +4 +9 +7 +27 +10 +40 – +5 +38 −1 +14 – +48 +34 +9 +2 +3 +45 +46 +17 +44 +23 +50 +6

2302 2255 2260 2479 1814 2317 1471 1558 2472 2388 2518 1814 2383 2194 2252 1225 2102 2037 2306 2105 2453 1912 3681 1791 2454 2361 1804 2439 2409 2654 3213 2335 2331 2282 2768 1744 1750 2382 2113 2428 1755 1971

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

8 7 27 6 121 31 34 69 20 23 20 13 27 17 25 69 37 10 20 35 29 15 74 16 15 14 11 7 7 9 11 32 20 14 18 33 45 19 30 22 14 9

YN821 1.1 2.1r 3.1r 4.1 5.1 6.1 7.1 8.1 9.1 10.1 11.1 12.1mt 12.2mt 13.1r 13.2mt

0.01 0.13 2.44 – 0.10 0.13 0.39 0.44 – – – 0.81 0.42 6.94 0.74

357 736 487 137 366 94 484 396 176 202 312 723 530 776 546

683 330 327 130 162 43 463 325 90 117 177 181 38 473 36

0.482 0.301 0.256 0.443 0.296 0.406 0.319 0.380 0.381 0.399 0.418 0.250 0.371 0.160 0.335

2.2 2.3 2.2 2.4 2.6 2.5 2.2 2.2 2.3 2.3 2.2 2.2 3.3 2.2 2.2

0.166 0.121 0.117 0.159 0.133 0.136 0.145 0.150 0.130 0.133 0.135 0.112 0.112 0.117 0.113

0.4 0.9 1.2 0.7 0.6 1.1 0.6 2.1 0.7 0.7 0.5 1.0 0.9 2.0 0.8

−1 +16 +26 +4 +25 −1 +25 +13 +1 −2 −5 +24 −13 +54 −1

2519 1969 1917 2447 2136 2173 2293 2342 2094 2132 2159 1833 1836 1918 1852

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

7 15 22 11 10 20 10 37 13 12 9 18 16 35 14

YN908b 1.2 2.1 2.2r 3.1 3.2 4.1 5.1 6.1mt 7.1 7.2 8.1 8.2mt 9.1 9.2 10.1

0.01 – 0.05 0.02 0.08 – – 0.26 1.25 0.01 – – 0.06 0.13 –

1579 199 316 273 108 325 41 26 293 997 2043 1159 144 56 579

126 25 140 152 22 195 44 0.1 317 177 1282 3 48 16 89

0.549 0.464 0.356 0.497 0.437 0.470 0.503 0.358 0.469 0.460 0.512 0.371 0.520 0.471 0.498

1.5 1.8 1.7 1.7 2.0 1.7 2.7 3.2 1.8 1.5 1.5 1.5 1.9 2.6 1.6

0.175 0.183 0.132 0.166 0.162 0.164 0.185 0.117 0.166 0.165 0.165 0.125 0.184 0.161 0.176

0.2 0.8 0.9 0.6 1.2 0.6 1.9 5.2 1.2 0.3 0.2 0.4 0.9 2.2 0.4

−10 +10 +9 −4 +7 +1 +3 −4 +2 +3 −8 – – −1 +1

2602 2678 2121 2519 2474 2495 2694 1915 2518 2503 2503 2029 2693 2468 2617

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

4 14 16 10 21 10 31 94 20 6 4 7 15 38 7

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N. Kim et al. / Precambrian Research 242 (2014) 1–21

Table 1 (Continued) Spota

206

Pbc (%)b

U (ppm)

Th (ppm)

206

Pb* /238 Uc

±%

207

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

10.2r 11.1r 11.2r 12.1 13.1 14.1 15.1 15.2 16.1 16.2r 17.1r 17.2r 18.1 19.1 19.2 20.1 20.2 21.1 21.2 22.1r 22.2r 23.1 23.2r 24.1mt 24.2 25.1r 25.2r 26.1

0.45 0.09 – 0.46 0.01 0.04 0.04 – 0.12 – – 0.15 – 0.20 0.07 0.02 – 0.21 0.05 0.13 0.03 0.04 0.18 0.02 0.09 – 0.04 –

411 1040 116 1180 117 231 82 111 79 386 436 197 326 585 233 590 54 47 668 186 897 557 307 996 262 119 618 1026

93 358 49 1097 116 24 67 85 127 64 156 186 136 482 37 319 43 24 14 46 76 93 78 29 50 46 10 131

0.621 0.448 0.396 0.492 0.493 0.462 0.475 0.416 0.467 0.543 0.349 0.413 0.506 0.575 0.463 0.558 0.472 0.562 0.528 0.406 0.421 0.445 0.385 0.352 0.482 0.376 0.430 0.472

4.4 1.5 2.0 1.5 1.9 1.7 1.7 1.6 1.8 4.0 1.0 1.6 1.1 1.6 1.2 0.8 2.1 2.3 0.9 1.3 0.8 0.9 1.1 0.8 1.1 1.6 0.8 0.8

0.133 0.153 0.140 0.165 0.164 0.158 0.164 0.160 0.160 0.120 0.125 0.121 0.167 0.162 0.157 0.179 0.165 0.185 0.181 0.133 0.131 0.158 0.128 0.125 0.163 0.141 0.135 0.161

1.4 0.4 1.3 2.0 1.0 0.8 2.3 1.5 1.4 1.9 0.8 1.9 1.1 0.5 3.1 0.6 1.8 1.9 1.0 1.0 0.5 0.5 0.9 0.8 0.8 1.7 0.9 0.3

−58 – +4 −4 −4 −1 – +10 −1 −53 +6 −16 −5 −23 −1 −10 +1 −8 −3 −3 −9 +3 −2 +5 −3 +9 −8 −1

2133 2376 2231 2505 2493 2440 2495 2453 2461 1961 2034 1968 2528 2477 2428 2644 2503 2697 2659 2133 2109 2434 2072 2026 2484 2236 2164 2463

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

24 6 23 34 16 13 39 25 24 33 13 33 18 8 53 9 30 32 16 18 8 9 16 14 13 29 16 6

YN902 1.1mm 1.2mm 2.1mm 2.2mm 3.1mm 3.2mm 4.1i 4.2mm 5.1mm 5.2mm 6.1mm 6.2mm 7.1mm 8.1i 8.2mm 9.1mm 10.1mm 10.2mm 11.1mm 12.1mm 13.1mm 14.1i 14.2mm 15.1i 15.2mm 16.1mm 16.2mm 17.1mm 17.2mm 18.1mm 20.1mm 21.1i 21.2mm 22.1mm 22.2mm 23.2mm 24.1mm 25.1mm 26.1i 27.1mm

0.90 0.35 0.07 0.94 0.12 0.55 0.26 0.03 0.02 0.21 0.01 1.93 0.25 0.01 0.26 – – 0.09 0.10 0.09 0.08 0.93 1.41 0.07 – 0.09 0.34 0.20 0.55 3.05 0.10 – 0.07 0.34 0.02 0.03 5.63 0.14 – 0.19

914 741 246 806 296 445 334 284 342 536 393 840 479 254 482 321 233 259 423 418 397 66 1570 169 454 480 648 588 617 373 244 198 407 391 319 215 683 327 471 302

235 111 86 102 123 168 124 97 76 118 93 180 105 136 68 79 99 84 89 135 59 24 115 124 80 73 74 125 94 75 99 138 115 44 86 82 226 118 428 99

0.102 0.121 0.305 0.156 0.239 0.164 0.243 0.269 0.216 0.160 0.197 0.112 0.222 0.356 0.256 0.267 0.296 0.256 0.325 0.149 0.250 0.424 0.133 0.409 0.230 0.215 0.131 0.241 0.204 0.298 0.314 0.308 0.215 0.192 0.298 0.334 0.131 0.280 0.117 0.281

1.2 1.3 1.4 1.3 1.4 1.3 1.8 1.4 2.2 1.3 1.3 1.2 1.3 1.4 3.0 1.3 1.4 0.9 1.7 0.8 0.8 1.6 1.1 1.1 0.8 0.8 0.7 0.7 0.7 0.8 1.0 1.0 0.8 0.8 0.9 1.0 0.8 0.9 0.8 0.9

0.104 0.094 0.118 0.108 0.116 0.109 0.146 0.118 0.115 0.109 0.115 0.095 0.116 0.158 0.112 0.119 0.121 0.118 0.119 0.109 0.118 0.209 0.094 0.158 0.115 0.118 0.102 0.118 0.112 0.120 0.120 0.157 0.115 0.111 0.120 0.120 0.104 0.117 0.130 0.117

1.2 1.2 0.9 1.1 1.0 1.2 0.8 0.9 0.9 1.0 0.9 2.5 0.8 1.0 1.6 0.8 0.9 1.2 0.8 1.0 0.7 1.4 2.9 0.9 0.8 0.8 1.1 0.6 0.8 1.4 0.9 0.8 0.9 1.1 0.8 1.0 3.9 0.9 1.1 0.9

+66 +54 +12 +51 +30 +49 +43 +23 +36 +49 +42 +58 +35 +22 +22 +24 +17 +26 +8 +53 +28 +25 +49 +11 +32 +38 +55 +31 +38 +16 +11 +33 +36 +41 +16 +6 +56 +18 +70 +19

1695 1501 1925 1772 1899 1790 2301 1924 1883 1776 1881 1525 1893 2435 1831 1934 1971 1924 1944 1776 1931 2896 1501 2430 1881 1926 1658 1926 1840 1959 1950 2426 1873 1812 1963 1959 1693 1904 2104 1909

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

23 23 17 21 18 23 14 17 16 19 16 47 15 17 29 15 15 21 14 19 13 22 55 15 14 13 20 12 15 25 17 14 16 20 14 17 72 15 19 17

YN906 1.1i 1.2mm 2.1mt 2.2mm 3.1mt 3.2mm

– 0.63 2.11 0.81 – 1.97

181 908 3663 689 759 1110

152 290 272 284 82 250

0.485 0.339 0.243 0.336 0.347 0.289

1.3 0.7 0.6 0.8 0.8 0.7

0.167 0.120 0.104 0.119 0.114 0.115

0.7 0.5 0.4 0.6 0.6 0.5

−1 +4 +20 +4 −3 +15

2524 1950 1705 1944 1871 1884

± ± ± ± ± ±

12 9 7 12 11 9

N. Kim et al. / Precambrian Research 242 (2014) 1–21

7

Table 1 (Continued) Spota

206

Pbc (%)b

U (ppm)

Th (ppm)

206

Pb* /238 Uc

±%

207

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

4.1mm 4.2mm 5.1mt 5.2mm 6.1i 6.2mm 7.1mt 7.2mm 8.1mm 9.1i 9.2mm 10.1i 10.2mm 11.1mm 11.2mt 12.2mt 12.3mm 13.1i 13.2mm 14.1i 14.2mm 15.1i 15.2i 16.1i 16.2mm 17.1i 17.2mm

0.90 1.69 1.69 2.40 1.20 1.10 2.98 3.38 0.74 3.47 2.58 – 0.85 1.66 3.29 2.09 – 1.08 0.03 – 0.65 – – 0.78 2.28 0.01 –

803 1355 3681 2783 131 991 4813 1911 879 1058 1348 173 738 1141 2750 2361 523 87 664 158 857 189 245 340 1338 88 896

371 459 139 375 64 184 349 334 756 546 176 124 235 345 282 271 166 85 227 75 231 75 87 168 155 60 231

0.339 0.297 0.265 0.259 0.426 0.323 0.149 0.222 0.336 0.460 0.263 0.476 0.339 0.309 0.188 0.250 0.371 0.446 0.357 0.497 0.339 0.507 0.517 0.635 0.263 0.470 0.368

0.8 0.7 0.6 0.6 1.5 0.7 0.9 1.8 0.7 0.7 0.7 1.2 0.8 0.7 0.6 0.6 0.8 1.7 0.8 1.2 1.3 1.2 1.0 1.0 0.7 1.6 0.7

0.120 0.115 0.108 0.110 0.152 0.118 0.086 0.107 0.119 0.183 0.114 0.156 0.121 0.118 0.096 0.107 0.121 0.159 0.121 0.169 0.119 0.173 0.182 0.251 0.112 0.161 0.121

0.6 0.5 0.3 0.4 1.4 0.5 0.7 0.6 0.5 0.3 0.4 0.9 0.5 0.9 1.4 0.4 0.6 2.3 0.6 0.8 0.9 1.9 1.3 0.8 0.4 1.4 0.4

+4 +12 +16 +20 +4 +7 +35 +29 +4 +11 +22 −5 +5 +11 +31 +19 −3 +3 – −3 +4 −3 −1 +1 +20 −1 −3

1955 1875 1759 1804 2371 1925 1333 1755 1941 2679 1867 2416 1975 1920 1553 1742 1974 2445 1966 2547 1947 2586 2674 3194 1825 2466 1969

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

11 9 6 7 24 10 14 10 9 5 8 15 9 17 27 7 11 40 10 14 16 32 22 12 8 23 8

YN806 1.1i 1.2mt 2.1i 2.2mt 3.1i 3.2mt 4.1i 4.2mt 5.1i 5.2mt 6.1i 6.2mt 7.1i 7.2mt 8.1mm 8.2mt 9.1i 9.2mt 10.1i 10.2mt 11.1i 11.2mt 12.1i 12.2mt 13.1i 13.2mt 14.1r 14.2mt 15.1i 15.2mt 16.1i 16.2mt 17.1i 17.2r 18.1i 19.1i 20.1mm 21.1i 22.1i 23.1i 25.1i 26.1mm 27.1i 28.1i 29.1i 30.1mm 31.1i

0.11 0.12 0.14 – 0.03 0.53 0.04 1.51 0.47 0.09 – 1.04 0.14 0.05 0.27 2.10 0.23 0.41 0.12 – – 0.38 0.03 1.12 0.05 0.66 – – 0.44 0.09 0.07 0.01 0.11 0.36 0.02 0.01 0.02 0.10 0.07 0.24 0.08 0.25 0.09 0.25 0.08 0.12 0.11

164 953 134 956 477 1323 238 1247 63 949 165 1261 119 1039 56 1522 146 1210 134 1027 170 1029 336 1216 98 2040 378 1050 109 907 227 906 202 67 218 174 371 109 257 182 344 239 219 360 191 331 507

186 37 61 33 278 46 127 43 71 16 67 41 70 22 175 47 82 50 151 24 118 34 391 49 57 37 30 40 68 51 178 39 74 13 92 96 233 52 188 90 39 189 147 227 123 98 260

0.433 0.325 0.476 0.344 0.508 0.244 0.546 0.241 0.408 0.332 0.481 0.244 0.452 0.286 0.349 0.213 0.455 0.259 0.465 0.338 0.407 0.310 0.465 0.263 0.484 0.262 0.318 0.342 0.426 0.349 0.482 0.343 0.529 0.314 0.457 0.462 0.344 0.476 0.477 0.418 0.344 0.358 0.473 0.422 0.485 0.361 0.571

1.5 1.2 1.6 1.2 1.3 1.3 1.4 1.3 2.0 1.2 1.5 1.3 1.6 1.2 3.2 1.3 1.6 1.2 1.6 1.2 1.5 1.2 1.3 1.5 1.6 1.2 1.3 1.2 1.6 1.2 1.4 1.2 1.0 1.6 1.0 1.1 0.8 1.3 0.9 1.2 0.8 0.9 1.0 0.8 1.1 0.9 0.8

0.151 0.114 0.163 0.114 0.170 0.112 0.185 0.110 0.138 0.115 0.164 0.110 0.165 0.113 0.123 0.107 0.164 0.109 0.157 0.115 0.159 0.113 0.161 0.113 0.164 0.105 0.119 0.113 0.162 0.114 0.162 0.114 0.183 0.119 0.165 0.167 0.122 0.176 0.164 0.155 0.139 0.122 0.167 0.149 0.164 0.123 0.212

0.7 0.4 0.7 0.4 0.3 0.5 0.5 0.9 2.5 0.4 0.6 0.9 0.9 0.4 1.9 0.9 0.8 0.7 0.7 0.3 0.7 0.4 0.4 1.6 1.5 1.2 0.5 0.3 0.9 0.4 0.5 0.3 0.5 1.9 0.6 1.0 0.6 0.8 0.5 1.8 0.5 0.8 0.6 0.5 0.6 1.0 0.6

+2 +3 −1 −3 −5 +26 −5 +25 – +2 −1 +24 +5 +14 +4 +31 +4 +19 −2 – +12 +7 – +20 −3 +14 +10 −2 +9 −4 −3 −2 −3 +10 +4 +4 +4 +5 −1 +7 +16 +1 +1 +3 −3 +1 –

2355 1865 2488 1860 2553 1829 2698 1805 2200 1876 2502 1801 2511 1844 1998 1744 2498 1790 2428 1883 2440 1854 2465 1841 2493 1718 1945 1856 2477 1857 2475 1864 2683 1936 2504 2531 1982 2613 2500 2400 2219 1983 2529 2338 2495 1996 2921

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

12 7 12 7 6 9 8 16 43 7 11 16 15 8 33 17 13 12 12 6 11 7 7 28 25 22 8 6 16 7 8 6 9 35 10 17 10 13 8 30 9 14 9 9 10 17 10

8

N. Kim et al. / Precambrian Research 242 (2014) 1–21

Table 1 (Continued) Spota

206

Pbc (%)b

U (ppm)

Th (ppm)

206

Pb* /238 Uc

±%

207

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

YN810h 1.1i 1.2mt 2.1i 2.2mt 3.1i 3.2mt 4.1i 4.2mm 5.1i 5.2i 6.1i 8.1i 8.2mt 9.1i 9.2mt 10.1i 10.2mt 11.1i 11.2mt 12.1i 12.2i 13.1i 13.2mt 14.1i 14.2i 14.3mm 15.1i 15.2mt 16.1i 16.2mt 17.1mm 18.1i 19.1mm 20.1mt 21.1i 22.1i 23.1i 24.1i 25.1i 26.1i 27.1i 28.1i 29.1i 30.1i 31.1i 32.1i 33.1i 34.1 35.1i 36.1i 37.1i 38.1i 39.1i

0.09 0.03 0.06 – 0.05 – 0.08 0.04 0.03 – – 0.03 0.07 0.11 0.80 – 0.05 – 0.36 0.06 – 0.18 0.38 – – 0.02 0.82 0.26 0.02 0.01 1.02 0.42 0.19 0.06 – 0.05 0.12 – – – 0.10 0.05 0.43 0.05 0.13 0.11 0.05 0.05 0.16 0.08 0.18 0.05 –

166 1610 228 738 202 919 226 528 128 702 411 110 1477 144 1281 335 1902 37 1010 115 558 179 1215 445 179 888 392 816 171 938 365 292 631 972 54 67 126 175 251 134 770 198 269 640 72 143 193 109 242 97 138 484 98

100 18 260 16 154 23 62 21 97 73 214 49 13 115 25 247 16 19 15 72 57 208 39 264 91 36 40 21 116 14 36 91 47 12 22 37 54 48 257 103 54 15 90 87 59 78 120 33 34 78 63 561 49

0.393 0.226 0.729 0.349 0.512 0.340 0.451 0.328 0.501 0.283 0.825 0.515 0.204 0.464 0.237 0.475 0.186 0.544 0.262 0.452 0.350 0.399 0.221 0.488 0.507 0.268 0.301 0.254 0.443 0.251 0.280 0.410 0.306 0.224 0.373 0.467 0.428 0.342 0.391 0.395 0.272 0.398 0.337 0.272 0.448 0.463 0.460 0.396 0.368 0.399 0.371 0.379 0.447

1.3 0.8 1.2 0.9 1.2 0.9 1.1 0.9 1.3 0.9 1.0 1.4 0.8 1.3 0.8 1.0 0.8 2.2 0.9 1.4 0.9 1.2 0.8 1.9 2.2 1.8 1.4 1.8 2.0 1.5 1.5 1.4 2.8 1.3 2.3 2.1 1.7 1.6 1.5 1.7 1.3 2.1 3.4 1.4 2.1 1.7 1.6 1.8 1.5 1.8 1.7 1.4 1.8

0.134 0.107 0.306 0.114 0.179 0.114 0.165 0.120 0.163 0.125 0.383 0.167 0.106 0.153 0.109 0.174 0.106 0.180 0.110 0.157 0.126 0.130 0.109 0.178 0.177 0.117 0.141 0.110 0.162 0.112 0.121 0.150 0.117 0.108 0.128 0.160 0.158 0.143 0.136 0.155 0.130 0.143 0.133 0.146 0.167 0.181 0.174 0.143 0.128 0.125 0.128 0.161 0.146

1.6 0.4 0.3 0.4 0.5 0.3 1.2 0.5 1.9 0.5 1.9 2.2 0.4 1.6 0.6 0.4 0.3 2.2 0.5 0.8 0.4 0.8 0.5 0.6 0.9 0.7 0.7 0.9 1.7 0.6 1.4 0.8 1.0 0.6 3.1 1.4 1.0 1.1 0.7 1.0 0.8 0.8 1.6 1.0 2.5 0.9 2.4 1.4 0.9 1.6 1.8 0.5 1.3

+1 +28 −1 −4 −1 −1 +5 +7 −6 +23 −1 −7 +34 −4 +25 +4 +40 −7 +18 +1 +6 −3 +30 +3 −1 +22 +27 +21 +6 +24 +21 +6 +12 +29 +2 −1 +7 +19 +2 +13 +29 +5 +14 +36 +6 +10 +7 +6 +3 −8 +2 +19 −5

2153 1755 3499 1860 2645 1867 2507 1953 2489 2028 3845 2530 1737 2377 1776 2598 1736 2655 1793 2420 2049 2102 1778 2633 2622 1912 2236 1804 2481 1832 1964 2342 1918 1774 2075 2455 2436 2267 2173 2402 2094 2263 2135 2299 2525 2666 2599 2264 2077 2023 2077 2466 2294

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

28 7 5 7 8 6 21 8 32 9 28 37 7 27 10 7 6 36 9 13 8 14 9 9 16 12 12 17 28 11 25 14 18 11 55 23 18 18 12 17 13 14 28 18 43 14 40 25 16 28 31 8 22

YN229 1.1i 1.2mm 2.1mm 2.2mm 3.1mm 3.2mm 4.1mm 4.2mm 5.1i 5.2mm 6.1mm 6.2mm 7.2mm 8.2mm 9.1mm 9.2mm 10.1mm 10.2mm 11.1mm 11.2mm 12.1mm

0.16 0.42 0.09 1.66 1.00 0.42 1.56 0.19 – 0.35 – 1.49 1.41 0.17 0.46 – 0.63 0.06 0.10 0.23 0.52

261 913 312 1908 796 858 1463 741 61 417 333 1418 1015 438 743 409 225 452 433 603 1781

70 63 66 29 52 55 54 35 38 97 106 47 100 122 160 124 66 66 82 77 342

0.366 0.197 0.333 0.077 0.213 0.194 0.165 0.179 0.484 0.303 0.361 0.120 0.143 0.312 0.254 0.312 0.354 0.310 0.355 0.295 0.144

1.5 1.3 1.4 1.2 2.4 2.9 1.3 1.3 2.2 1.4 1.4 2.8 1.5 1.4 1.3 1.4 1.5 1.4 1.4 1.3 1.2

0.173 0.106 0.122 0.077 0.114 0.109 0.103 0.107 0.164 0.119 0.122 0.085 0.101 0.121 0.113 0.119 0.120 0.118 0.122 0.117 0.104

0.6 1.4 0.7 5.2 1.1 1.5 5.6 0.7 1.3 0.8 0.6 3.2 1.8 0.7 1.4 0.6 1.1 0.7 0.6 0.8 0.6

+26 +36 +8 +59 +36 +39 +44 +43 −2 +14 – +47 +51 +13 +24 +11 – +11 +1 +15 +52

2589 1725 1986 1109 1862 1776 1672 1757 2494 1947 1987 1321 1645 1971 1851 1941 1950 1927 1980 1918 1688

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

10 26 13 103 21 26 103 14 22 14 11 61 34 13 25 11 20 12 11 14 12

N. Kim et al. / Precambrian Research 242 (2014) 1–21

9

Table 1 (Continued) Spota

206

Pbc (%)b

U (ppm)

Th (ppm)

206

Pb* /238 Uc

±%

207

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

12.2mm 13.1mm 14.2mm 15.1i 15.2mm

0.07 0.66 0.71 – –

926 362 639 141 271

74 115 46 64 78

0.246 0.337 0.217 0.390 0.366

1.3 1.9 1.8 1.8 1.5

0.115 0.122 0.107 0.128 0.120

0.6 0.9 1.6 1.1 0.8

+27 +7 +31 −2 −3

1877 1985 1755 2077 1960

± ± ± ± ±

10 16 29 19 14

YN230a 1.1i 1.2mm 2.1i 2.2mm 3.1mm 4.1mm 5.1mm 6.1mm 7.1mm 8.1i 9.1mm 9.2mm 10.1i 10.2mm 11.1i 11.2mm 12.1mm 13.1i 14.1mm 14.2mm 15.1i 15.2mm 16.1i 17.1mm 17.2mm 19.1i 19.2mm

– 0.32 0.43 2.25 1.13 0.02 0.76 0.84 0.19 – 1.09 1.46 – 0.40 – 0.33 0.51 0.29 3.99 0.85 0.11 1.33 0.10 3.98 1.64 0.83 0.13

264 810 136 941 838 526 1010 1178 807 186 1370 1338 40 879 82 1094 743 313 1031 817 296 1395 810 390 822 182 615

161 8 52 7 210 130 126 38 221 162 471 12 32 10 38 7 175 155 180 19 59 12 376 210 8 96 28

0.390 0.193 0.414 0.186 0.213 0.219 0.190 0.145 0.231 0.453 0.147 0.149 0.459 0.196 0.550 0.176 0.230 0.459 0.200 0.223 0.422 0.170 0.279 0.336 0.171 0.380 0.264

1.7 2.4 2.0 1.4 1.8 1.5 1.4 2.5 1.4 1.8 1.4 1.4 3.7 2.1 3.1 1.2 1.7 1.3 2.7 1.2 1.3 1.2 1.6 1.4 1.2 1.5 1.2

0.136 0.105 0.157 0.101 0.105 0.112 0.106 0.090 0.108 0.146 0.090 0.090 0.151 0.102 0.182 0.099 0.109 0.158 0.111 0.107 0.152 0.091 0.153 0.120 0.103 0.135 0.110

0.7 2.2 1.8 1.3 3.8 0.7 0.9 1.2 0.7 0.7 3.9 2.9 7.6 1.1 1.6 0.6 0.7 0.5 8.2 0.8 0.5 2.6 0.4 3.3 1.9 1.2 0.6

+3 +36 +9 +36 +30 +34 +38 +42 +26 −5 +41 +40 −4 +34 −7 +38 +27 – +38 +29 +5 +32 +38 +5 +43 +4 +18

2178 1706 2419 1650 1709 1839 1729 1428 1764 2305 1433 1418 2356 1666 2674 1614 1777 2437 1808 1756 2363 1441 2385 1954 1687 2159 1804

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

13 40 31 24 70 13 17 23 12 13 75 56 129 20 26 11 12 9 149 15 9 49 7 58 35 21 11

YN801 1.1i 1.2mm 2.1i 2.2mm 3.1i 3.2mm 4.1i 4.2mm 5.1i 5.2mm 6.2mm 7.1mm 7.2mm 8.1i 9.1i 9.2mm 10.1i 10.2mm 11.1i 12.1i 12.2mm 13.1i 13.2mm 14.1i 15.1i 15.2mm 16.1i 16.2mm 17.1i 17.2mm 18.1i 18.2mm

0.01 2.39 0.03 1.80 – 0.28 0.08 4.07 – 0.20 1.39 0.62 1.84 – – 0.69 – 1.86 – 0.08 1.51 0.02 1.26 0.12 0.62 4.60 – 0.67 0.05 1.49 0.59 0.82

780 4154 102 2311 100 1465 86 708 238 867 1953 2044 1594 141 379 1676 261 1961 241 524 3235 811 1055 2993 310 3421 355 1766 1194 2472 502 1087

399 80 92 14 59 110 70 25 176 8 99 95 84 80 181 21 162 36 163 216 64 410 16 138 239 26 348 861 687 20 251 54

0.392 0.114 0.499 0.156 0.470 0.159 0.501 0.231 0.480 0.194 0.168 0.136 0.193 0.391 0.370 0.173 0.388 0.163 0.497 0.360 0.137 0.388 0.201 0.210 0.412 0.104 0.292 0.064 0.273 0.140 0.418 0.225

0.9 0.7 1.8 0.7 1.9 0.7 2.0 2.2 1.3 1.2 1.0 0.7 0.7 1.5 1.0 0.8 1.2 0.7 1.2 1.0 0.7 0.9 0.9 0.7 1.2 1.3 1.1 0.8 0.8 1.6 1.4 0.8

0.187 0.084 0.162 0.099 0.164 0.104 0.170 0.110 0.164 0.112 0.095 0.098 0.104 0.130 0.125 0.099 0.136 0.092 0.170 0.126 0.092 0.163 0.109 0.145 0.147 0.084 0.131 0.070 0.121 0.096 0.148 0.112

0.4 1.1 1.1 1.9 3.7 0.7 2.8 4.4 0.7 0.7 1.9 1.0 1.2 1.1 1.4 0.9 0.7 1.1 0.6 0.6 1.5 0.4 1.2 0.3 0.9 1.7 0.8 2.0 0.4 0.9 0.6 1.4

+25 +49 −7 +45 – +47 −3 +28 −1 +41 +37 +51 +36 −1 – +39 +3 +37 −2 +3 +46 +18 +37 +51 +5 +53 +25 +59 +24 +48 +3 +31

2717 1296 2478 1611 2494 1704 2554 1804 2501 1827 1529 1580 1698 2103 2032 1599 2176 1471 2554 2040 1465 2489 1777 2290 2313 1288 2112 938 1976 1544 2318 1826

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

6 22 19 35 62 13 47 80 11 13 35 19 23 19 25 16 13 21 10 11 28 7 23 6 16 33 14 42 8 17 11 25

1016-7 1.1mm 2.1mm 3.1mm 4.1mm 5.1mm 6.1mm 7.1mm 8.1mm

0.10 – 0.02 0.02 – – – 0.01

2537 1609 1833 4399 3337 3337 4483 2400

64 6 27 36 92 139 159 34

0.285 0.333 0.358 0.212 0.254 0.222 0.188 0.296

1.4 1.4 1.4 1.3 1.3 2.0 1.3 1.4

0.111 0.114 0.114 0.109 0.111 0.109 0.106 0.112

0.3 0.4 0.3 0.3 0.3 1.2 0.7 0.4

+13 +3 −5 +30 +21 +29 +37 +10

1614 1851 1975 1241 1458 1292 1110 1672

± ± ± ± ± ± ± ±

6 7 6 5 5 21 12 7

10

N. Kim et al. / Precambrian Research 242 (2014) 1–21

Table 1 (Continued) Spota 9.1mm 10.1mm 11.1i 12.1mm 13.1mm 14.1mm 15.1mm 16.1mm 17.1mm 18.1mm 19.1mm 20.1mm 21.1mm

206

Pbc (%)b

– – 0.01 0.01 0.01 0.02 0.03 0.03 0.03 0.01 – – 0.01

U (ppm) 1075 2433 752 3190 2618 9479 7749 3657 3941 2738 3121 2595 11,867

Th (ppm)

206

Pb* /238 Uc

9 40 277 83 48 282 223 142 117 72 87 50 321

0.337 0.347 0.407 0.256 0.272 0.244 0.160 0.217 0.210 0.256 0.232 0.248 0.135

a

i, inherited core; mm, magmatic zone; mt, metamorphic zone; r, recystallised zone.

b

Common lead fraction. “*” means radiogenic fraction. 207 Pb/206 Pb discordance.

c d

observed in outer bands (Fig. 3) is probably a remnant of primary magmatic texture modified during subsequent solid-state recrystallisation (Pidgeon, 1992; Hoskin and Black, 2000). Textureless dark overgrowth rims are frequently developed around the cores

±%

207

1.4 1.4 1.5 1.4 1.4 1.6 1.3 1.3 1.4 1.4 1.4 1.4 1.3

0.113 0.114 0.131 0.108 0.112 0.112 0.099 0.109 0.109 0.111 0.111 0.111 0.102

Pb* /206 Pb* c

±%

Dis. (%)d

Date (Ma)

0.5 0.3 0.5 1.1 0.3 1.5 0.2 0.3 0.4 0.7 0.3 0.6 0.2

+2 −3 −1 +18 +17 +14 +37 +30 +32 +21 +28 +24 +44

1874 1921 2202 1472 1553 1406 958 1268 1228 1469 1343 1426 818

± ± ± ± ± ± ± ± ± ± ± ± ±

8 5 8 20 6 28 4 5 6 12 6 11 4

(Fig. 3). Bright and blurred oscillatory zoning is partially exhibited in the rim. A few grains are entirely composed of a textureless domain that produces a dark CL emission. Irregular or radial cracks developed in some grains crosscut internal domains. Even

Fig. 3. Representative CL (samples YN804-4–YN801) and BSE (sample 1016-7) zircon images. Small ellipses and large circles represent the locations of the points for SHRIMP dating and LA-MC-ICPMS Hf analysis, respectively. The 207 Pb/206 Pb spot date (Ma) and εHf (t) values are given with the locations. All scale bars are 50 ␮m in length.

N. Kim et al. / Precambrian Research 242 (2014) 1–21

11

Fig. 4. Zircon concordia diagrams. Numbers on tick marks of the concordia curve are in Ma. Error ellipses are at the 1 level. Symbols: open ellipses, detrital grains and inherited cores; closed ellipses, magmatic oscillatory zones; light-grey ellipses, metamorphic zones; dashed ellipses, recrystallised zones. Solid and dashed lines respectively represent the discordia arrays formed by inherited and magmatic domains, and by metamorphic domains. Some Meso- and Paleoarchean data points of detrital grains from sample YN804-4, and inherited cores from samples YN906 and YN810h are not shown due to reduction in the y-scale for clarity.

though most core data are discordant, a few concordant (≤10% discordance, unless otherwise stated) data indicate an age span from 3.7 to 2.3 Ga, with an early Paleoproterozoic cluster (Fig. 4). Note that two Meso- to Paleoarchean points are not shown in Fig. 4 due to reduction in the y-scale for clarity. The textureless dark CL domains have relatively low Th/U ratios (<0.2 except for two points) and form a discordia line with the upper and lower intercepts at 1979 ± 32 and 365 ± 54 Ma, respectively (n = 10, MSWD = 2.5) (Fig. 4). The Paleozoic lower intercept age is also indicated by ca. 2.5–2.3 Ga detrital zircons. Some data (dashed circles in Fig. 4) from the thickened and blurred primary zones plot around the 2.1 Ga point of the concordia. Zircons from a migmatite (sample YN821) in the Hosanri Formation are transparent, yellow to pale-brown and rounded to subrounded. They are relatively small crystals (50–60 ␮m in length) with aspect ratios from 1:1 to 1:2. Rounded or subhedral cores show oscillatory, unzoned, banded, and sector zoning (Fig. 3). They are often surrounded by narrow textureless rims. The core data are somewhat discordant in general, but a few concordant points display an age range from 2.5 to 2.1 Ga (Fig. 4). Three data points showing thickened oscillatory zoning are highly discordant. The textureless rims have a relatively low Th/U ratio (0.07–0.26), from which one concordant point yields 1852 ± 14 Ma. Zircons from a quartzite (sample YN908b) in the Wonnam Group are transparent, pale-brown rounded to subrounded crystals with a length of 50–180 ␮m. They are mostly equant but some are prismatic (aspect ratio up to 1:4) with rounded crystal faces. Rounded to subhedral cores display oscillatory, banded, and convolute zoning, or rarely textureless dark CL emission (Fig. 3). They are sometimes resorbed by textureless dark overgrowth rims. Some 207 Pb-206 Pb

grains have thickened and blurred primary zones. The core data are mostly concordant, indicating two age populations at 2491 ± 23 Ma (n = 16) and 2684 ± 16 Ma (n = 5) (Fig. 4). Three data points for the dark CL domains with low Th/U ratios (0.003–0.03) are concordant, yielding a weighted mean of 2027 ± 13 Ma (MSWD = 0.74). Mostly discordant data from the thickened and blurred zones plot between the fields of the cores and the overgrowth rims (Fig. 4). 4.1.2. (Meta)granitoids 4.1.2.1. Group I. Zircons from the Pyeonghae gneiss (sample YN902) are translucent, milky to pale-brown, euhedral to subhedral prismatic grains with a length from 100 to 250 ␮m and have aspect ratios varying from 1:1.7 to 1:3.7. They dominantly exhibit well-developed oscillatory zoning typical of magmatic origin (Vavra, 1990) (Fig. 3). Some grains have rounded, subhedral or euhedral inherited cores that display oscillatory, banded, and convolute zoning (Fig. 3). Thin (<20 ␮m) textureless overgrowth rims are present in some grains but were not analysed here. A number of irregular or radial cracks, filled with quartz, K-feldspar, plagioclase and uraninite inclusions, are commonly developed towards the inner CL domains. Most zircons yield highly discordant results on the U-Pb diagram (Fig. 4). The Th/U ratios of the magmatic zones (0.08–0.44) are generally lower than those of the inherited cores (0.37–0.94). The magmatic zones display a discordia line with the upper and lower intercepts at 1980 ± 22 Ma and 296 ± 38 Ma, respectively (n = 34, MSWD = 4.8) (Fig. 4). Five analysis points from the inherited cores yield a discordia line with an upper intercept of 2449 ± 74 Ma and a lower intercept of 250 ± 100 Ma (MSWD = 5.8). We interpret that the protolith of the Pyeonghae gneiss intruded at 1980 ± 22 Ma and then experienced a Paleozoic Pb loss.

12

N. Kim et al. / Precambrian Research 242 (2014) 1–21

Translucent pale-brown to brown zircons from the Buncheon gneiss (sample YN906) are mostly euhedral, long and prismatic (aspect ratios up to 1:5) crystals reaching a length up to 400 ␮m. CL images of these zircons revealed three different textural domains: inherited cores, magmatic oscillatory zones, and textureless rims (Fig. 3). As in zircons from the Pyeonghae gneiss, micro-cracks generally penetrate towards the inner domains, often forming new CL zones along crystal faces (Fig. 3). Mostly concordant inherited core data yield ages ranging from 2679 to 2371 Ma. One data point indicates an early Mesoarchaean (3194 Ma) inheritance (not shown in Fig. 4). In contrast, data for the magmatic zones are mostly discordant, displaying a discordia line with an upper intercept of 1966 ± 15 Ma and a latest Precambrian lower intercept (618 ± 68 Ma) (n = 15, MSWD = 2.5) (Fig. 4). The textureless dark CL domains have distinctly low Th/U ratios (0.04–0.12) and define a discordia with the upper and lower intercepts at 1856 ± 13 Ma and 572 ± 27 Ma, respectively (n = 6, MSWD = 0.51). We interpret that the protolith of the Buncheon gneiss intruded at 1966 ± 15 Ma, and then experienced Paleoproterozoic metamorphism and Neoproterozoic Pb loss. 4.1.2.2. Group II. Zircon grains from the Icheonri granitic gneiss (sample YN806) are mostly transparent, brown, long and prismatic (aspect ratio = 1:2 to 1:4). Most grains contain rounded and subhedral inherited cores displaying oscillatory, banded, sector, and convolute zoning. Parts of the original oscillatory zoning are blurred (Fig. 3). Some of the cores have curved domain boundaries, suggesting thermal events after crystallisation. Data for the cores mostly plot on the concordia, indicating ages ranging from 2.9 to 2.2 Ga. Their Th/U ratios vary considerably from 0.12 to 1.20. A mid-Paleoproterozoic age (1985 ± 14 Ma) is calculated from four concordant data points (Fig. 4). Two slightly younger data points with low Th/U ratios (0.08 and 0.2) are obtained from the blurred oscillatory zones. Textureless dark CL rims displaying very low Th/U ratios (0.02–0.06) yield a discordia line with the upper and lower intercepts at 1864 ± 11 Ma and 298 ± 110 Ma, respectively (n = 16, MSWD = 4.2) (Fig. 4). Zircons from another Icheonri granite sample (YN810h) have similar morphological and textural characteristics to the zircons from sample YN806 (Fig. 3). They also display similar age populations of the cores, ranging from the late Archaean to the early Proterozoic. An Eoarchean (3845 Ma) inheritance is indicated by one point (not shown in Fig. 4). Four discordant points of the youngest core group yield an intercept age at 1964 ± 25 Ma, reproducing the zircon core age of sample YN806 within error. The textureless dark CL rims yield an upper intercept of 1855 ± 19 Ma and a lower intercept of 301 ± 56 Ma (n = 11, MWSD = 3.4) (Fig. 4), which are also comparable to the discordia ages of the same CL domain in zircons from sample YN806. Considering the error range, the best age estimate for the emplacement of the Icheonri granitic gneiss is the youngest core age of 1985 ± 14 Ma. The inherited zircons experienced metamorphism at ca. 1.86 Ga, and then the metamorphic rims lost radiogenic lead during the Paleozoic. Zircon grains from the Hongjesa granitic gneiss (sample YN229) are mostly prismatic with aspect ratios ranging from 1:2 to 1:4. They are translucent, grey or brown in colour, and 100 to 200 ␮m in length. CL images revealed three textural domains: inherited cores, magmatic oscillatory zones, and thin overgrowth rims (Fig. 3). Rounded or prismatic inherited cores typically display oscillatory or convolute zoning, but sometimes occur as unzoned patches. The magmatic zones have a relatively weak contrast between the bright and dark CL domains. Many quartz, plagioclase, K-feldspar, and monazite inclusions are present in this domain. Two concordant data of the inherited cores plot around the 2.5 and 2.1 Ga points. Most data from the magmatic zones are discordant, forming a discordia line with the upper and lower intercepts at 1975 ± 16 and

373 ± 36 Ma, respectively (n = 23, MSWD = 2.8) (Fig. 4). Zircons from another Hongjesa granitic gneiss sample (YN230a) have a similar morphology and internal texture to those from sample YN229 (Fig. 3). Most inherited cores yield concordant ages ranging from 2.7 to 2.2 Ga. Data for the magmatic zones are highly discordant, yielding a discordia forming the upper and lower intercepts at 1940 ± 63 and 522 ± 85 Ma, respectively (n = 18, MSWD = 4.4) (Fig. 4). We interpret these data to indicate that the best age estimate for the emplacement of the protolith of the Hongjesa granitic gneiss is 1975 ± 16 Ma defined by sample YN229. Zircons from the magmatic zones experienced Paleozoic Pb loss.

4.1.2.3. Group III. Zircons from the Imwon leucogranite (sample YN801) have a highly variable morphology. They consist of mixtures of transparent or translucent, colourless, milky, pale-brown, and dark brown equant or prismatic grains exhibiting rounded, subrounded, or euhedral crystal faces. Two distinct domains of inherited cores and a textureless weak luminescence zone were identified by CL observation. The inherited cores contain oscillatory, banded, convoluted, and homogeneous zones (Fig. 3) and commonly have quartz and plagioclase inclusions. The irregular or radial cracks are developed in some grains. Data from the inherited cores are mostly concordant, yielding ages from 2.6 to 2.0 Ga with a cluster at ca. 2.5 Ga. The weak CL rims contain tiny inclusions of plagioclase, K-feldspar, quartz and titanite. Such rims have relatively low Th/U ratios (<0.08 except for one point) and form a discordia line with an upper intercept of 1862 ± 100 Ma and a lower intercept of 356 ± 75 Ma (n = 16, MSWD = 19) (Fig. 4). Zircons from another Imwon leucogranite sample (1016-7) are also variable in morphology. They consist of mixtures of translucent, colourless, brown, grey grains with aspect ratios from 1:1 to 1:4. Many grains contain quartz, K-feldspar, plagioclase, monazite and uraninite inclusions. Due to the weak CL intensity of these grains, we used BSE images to observe their internal texture. BSE images revealed various different internal textures such as unzoned, heterogeneous patches and oscillatory and convolute zoning (Fig. 3). Inherited cores displaying homogeneous or convolute zoning are contained in some grains. One concordant point has a ca. 2.1 Ga inheritance. The weak CL rims have highly variable U contents (1075–11,867 ppm) and their Th/U ratios are very low (0.004–0.043). The discordia line formed by the rims yields the upper and lower intercepts at 1866 ± 19 and 300 ± 45 Ma, respectively (n = 20, MSWD = 11.6) (Fig. 4). The weighted mean of four concordant (<5% 207 Pb-206 Pb discordance) points is 1867 ± 6 Ma (n = 4, MSWD = 1.15), which represents the best estimate for the emplacement age of the Imwon leucogranite. As described above, investigated zircons displayed diverse morphologies and complicated internal textures. However, careful CL and BSE observations combined with Th/U analyses made it possible to distinguish detrital, inherited, magmatic and metamorphic domains in the zircons. Our zircon data indicate that there is quite a consistent tendency for metamorphic zones to have the lower Th/U ratio than magmatic zones, although a widely cited Th/U value of less than 0.1 for metamorphic zircon (Rubatto, 2002) may not always a valid discriminant. The U-Pb data obtained from the thickened and blurred oscillatory zones are excluded from further discussions because their original U-Pb isotopic compositions are commonly disturbed but not completely reset during the solid-state recrystallisation, resulting in the measurement of mixed isotopic ages (Hoskin and Black, 2000). Additionally, it is notable that the 207 Pb-206 Pb discordances of the magmatic and metamorphic zircons tend to be positively correlated with their U concentrations. This may indicate that the metamictisation of the zircon crystal lattice promoted the loss of radiogenic lead during the superimposed geologic events that are represented by the lower intercepts of the discordia lines.

N. Kim et al. / Precambrian Research 242 (2014) 1–21

13

Table 2 LA-MC-ICPMS zircon Lu-Yb-Hf isotopic composition. Spota

2 SE

εHf (t)

TDM (Ma)

T2DM (Ma)

0.04153 0.02174 0.01396 0.02865 0.03271 0.02159 0.01634 0.01468 0.01528 0.04690 0.03680 0.08830 0.02619 0.02923

0.00029 0.00005 0.00020 0.00032 0.00014 0.00003 0.00027 0.00001 0.00005 0.00174 0.00049 0.00133 0.00003 0.00005

−14.9 −8.2 3.0 −3.4 0.1 0.6 13.0 3.8 0.4 −3.8 −4.0 −2.0 −13.1 −11.9

3365 2965 2670 2954 2642 2749 3344 2625 2674 2910 3098 2718 3531 2820

3715 3230 2753 3131 2778 2871 3203 2697 2805 3093 3275 2872 3845 3160

0.000032 0.000003 0.000002

0.03032 0.03645 0.02831

0.00090 0.00027 0.00013

−2.6 5.8 −9.6

2632 2242 2863

2816 2299 3159

0.000633 0.000655 0.000159 0.001187 0.000435 0.001392 0.000382 0.000572 0.000886 0.000537

0.000002 0.000006 0.000001 0.000015 0.000004 0.000014 0.000002 0.000003 0.000013 0.000002

0.02328 0.02568 0.00299 0.04277 0.01423 0.05096 0.01122 0.01912 0.03707 0.02399

0.00006 0.00012 0.00002 0.00075 0.00016 0.00046 0.00008 0.00012 0.00051 0.00011

−15.8 −6.7 −6.1 −5.4 −1.8 −4.3 2.0 −2.9 −1.0 1.8

3400 3230 2631 3037 2851 2988 2728 3044 3020 2686

3772 3449 2889 3238 3010 3173 2827 3208 3150 2790

0.000016 0.000018 0.000016 0.000013 0.000013 0.000019 0.000019 0.000016 0.000018 0.000015 0.000016

0.001124 0.001257 0.001345 0.000499 0.001253 0.001418 0.000921 0.001290 0.001011 0.001168 0.000807

0.000012 0.000006 0.000006 0.000001 0.000011 0.000004 0.000003 0.000005 0.000002 0.000015 0.000010

0.04192 0.04292 0.04796 0.01835 0.03860 0.05510 0.03621 0.04662 0.03578 0.04095 0.02856

0.00032 0.00037 0.00037 0.00009 0.00035 0.00034 0.00015 0.00009 0.00010 0.00048 0.00034

−5.8 −2.5 −6.8 −12.2 −4.5 −4.7 −5.9 −2.1 −2.6 −3.6 −6.0

2595 2470 2635 3226 2545 2558 2593 2455 2469 2510 2596

2836 2660 2887 3548 2763 2778 2838 2638 2663 2717 2844

0.281320 0.281463 0.281514 0.281496 0.281521 0.281279 0.281514 0.281456 0.281354 0.281520 0.281468 0.281268 0.281440 0.281339 0.281482 0.281239 0.280824 0.281310 0.281485

0.000016 0.000015 0.000013 0.000015 0.000013 0.000016 0.000015 0.000018 0.000020 0.000014 0.000011 0.000014 0.000012 0.000017 0.000014 0.000015 0.000018 0.000017 0.000019

0.000730 0.000857 0.001250 0.001020 0.001730 0.000606 0.000921 0.001652 0.001089 0.000754 0.001147 0.000462 0.000665 0.001546 0.000840 0.000671 0.001941 0.000659 0.000959

0.000008 0.000003 0.000003 0.000006 0.000012 0.000012 0.000001 0.000027 0.000007 0.000002 0.000002 0.000003 0.000003 0.000022 0.000001 0.000001 0.000005 0.000005 0.000003

0.02532 0.03188 0.04679 0.03795 0.05455 0.02007 0.03197 0.06168 0.04054 0.02686 0.04121 0.01567 0.02308 0.05318 0.03122 0.02400 0.08262 0.02602 0.03679

0.00038 0.00012 0.00032 0.00045 0.00050 0.00039 0.00015 0.00080 0.00006 0.00011 0.00014 0.00008 0.00015 0.00084 0.00007 0.00010 0.00011 0.00022 0.00011

4.0 −3.6 −2.3 −2.6 −5.1 −0.7 −1.9 −4.9 2.2 −1.4 −6.2 0.8 −4.2 3.8 −2.9 4.6 −1.1 2.5 −3.0

2678 2493 2449 2459 2470 2725 2428 2556 2657 2409 2506 2731 2513 2711 2466 2784 3455 2688 2470

2741 2705 2635 2654 2697 2871 2613 2775 2752 2588 2760 2850 2736 2773 2668 2829 3549 2778 2671

0.281442 0.281486 0.281351 0.281340 0.281164 0.281248 0.281282 0.281295 0.281422 0.281132

0.000015 0.000013 0.000017 0.000021 0.000016 0.000015 0.000017 0.000016 0.000015 0.000019

0.001226 0.000528 0.001151 0.001662 0.000516 0.000483 0.000708 0.000361 0.000490 0.000911

0.000011 0.000003 0.000007 0.000009 0.000003 0.0000004 0.000007 0.000002 0.000002 0.000003

0.04601 0.01917 0.04602 0.05943 0.01897 0.01842 0.02648 0.01130 0.01628 0.03012

0.00037 0.00013 0.00026 0.00017 0.00012 0.00002 0.00031 0.00007 0.00005 0.00008

3.8 −6.5 3.6 3.8 2.8 −5.4 2.2 −8.5 −4.6 −5.1

2546 2512 2667 2718 2874 2759 2729 2688 2439 2947

2620 2780 2737 2779 2947 2991 2822 2983 2678 3154

176

Hf/177 Hf

2 SE

176

Lu/177 Hf

2 SE

176

YN804-4 3.1 4.2 6.1 7.1 12.1 13.1 14.1 15.1 15.2 17.1 18.1 21.1 22.1 28.1mt

0.280829 0.281103 0.281311 0.281117 0.281352 0.281260 0.280805 0.281343 0.281307 0.281173 0.281021 0.281365 0.280676 0.281219

0.000021 0.000021 0.000018 0.000020 0.000024 0.000022 0.000021 0.000021 0.000016 0.000025 0.000022 0.000022 0.000018 0.000018

0.001025 0.000625 0.000423 0.000746 0.000818 0.000562 0.000399 0.000392 0.000406 0.001153 0.000924 0.002156 0.000588 0.000791

0.000007 0.000001 0.000008 0.000009 0.000004 0.0000004 0.000008 0.000001 0.000001 0.000040 0.000011 0.000036 0.000001 0.000002

YN821 6.1 9.1 10.1

0.281363 0.281658 0.281186

0.000020 0.000019 0.000016

0.000886 0.001116 0.000763

YN908b 4.1 5.1 6.1mt 7.1 9.2 12.1 13.1 20.1 21.1 23.1

0.280777 0.280906 0.281327 0.281082 0.281177 0.281129 0.281266 0.281041 0.281076 0.281305

0.000015 0.000015 0.000013 0.000015 0.000014 0.000015 0.000015 0.000017 0.000018 0.000023

YN902 2.1mm 10.1mm 11.1mm 15.1i 15.2mm 18.1mm 20.1mm 22.2mm 23.2mm 25.1mm 27.1mm

0.281402 0.281499 0.281383 0.280900 0.281445 0.281443 0.281393 0.281512 0.281488 0.281466 0.281385

YN906 1.1i 2.2mm 4.1mm 4.2mm 5.1mt 6.1i 6.2mm 8.1mm 10.1i 10.2mm 12.2mt 13.1i 13.2mm 14.1i 14.2mm 15.2i 16.1i 17.1i 17.2mm YN806 1.1i 1.2mt 2.1i 3.1i 4.1i 5.1i 6.1i 8.1mm 9.2mt 10.1i

Yb/177 Hf

14

N. Kim et al. / Precambrian Research 242 (2014) 1–21

Table 2 (Continued) Spota

176

Hf/177 Hf

2 SE

176

Lu/177 Hf

2 SE

176

Yb/177 Hf

2 SE

εHf (t)

TDM (Ma)

T2DM (Ma)

10.2mt 11.2mt 13.1i 13.2mt 15.2mt 20.1mm 22.1i 26.1mm 27.1i 28.1i 29.1i 30.1mm 31.1i

0.281446 0.281478 0.281374 0.281442 0.281442 0.281468 0.281098 0.281658 0.280920 0.281054 0.281045 0.281463 0.280986

0.000013 0.000014 0.000015 0.000013 0.000015 0.000018 0.000022 0.000021 0.000014 0.000017 0.000015 0.000017 0.000015

0.000515 0.000581 0.000491 0.000787 0.000461 0.001280 0.001129 0.002106 0.000546 0.000718 0.001082 0.001045 0.000926

0.000005 0.000005 0.000001 0.000007 0.000001 0.000003 0.000014 0.000006 0.000004 0.000002 0.000017 0.000004 0.000001

0.01853 0.01930 0.01565 0.02601 0.01755 0.05103 0.04334 0.07949 0.01963 0.02625 0.03743 0.03694 0.03230

0.00012 0.00010 0.00002 0.00016 0.00002 0.00016 0.00053 0.00023 0.00015 0.00008 0.00056 0.00010 0.00007

−6.9 −6.1 5.7 −5.2 −6.1 −3.6 −5.1 2.1 −9.8 −9.6 −7.0 −3.4 0.7

2527 2498 2589 2468 2496 2514 3010 2302 3203 3037 3079 2505 3146

2801 2759 2629 2712 2759 2718 3210 2415 3482 3321 3308 2710 3235

YN810h 1.1i 3.1i 3.2mt 4.1i 5.1i 6.1i 8.1i 9.1i 10.1i 11.1i 12.1i 13.1i 14.1i 14.3mm 16.1i 18.1i 19.1mm 20.1mt 21.1i 23.1i 25.1i 33.1i 34.1i 37.1i 39.1i

0.281437 0.281260 0.281485 0.281365 0.281353 0.280202 0.281351 0.281341 0.281163 0.281262 0.280999 0.281271 0.281174 0.281277 0.281288 0.280979 0.281063 0.281191 0.281241 0.281354 0.281361 0.281042 0.281320 0.281485 0.281253

0.000021 0.000019 0.000015 0.000018 0.000018 0.000018 0.000017 0.000016 0.000019 0.000021 0.000019 0.000022 0.000017 0.000016 0.000015 0.000016 0.000016 0.000022 0.000023 0.000023 0.000020 0.000015 0.000018 0.000018 0.000020

0.000501 0.000874 0.000262 0.000822 0.000740 0.000668 0.001016 0.000633 0.001159 0.000705 0.000460 0.000624 0.001451 0.000869 0.000646 0.000408 0.000690 0.000831 0.000437 0.001010 0.001099 0.000281 0.000862 0.000564 0.000636

0.000001 0.000026 0.000001 0.000002 0.000005 0.000001 0.000001 0.000007 0.000007 0.000003 0.000001 0.000001 0.000011 0.000004 0.000001 0.000001 0.000001 0.000003 0.000004 0.000001 0.000008 0.000002 0.000004 0.000003 0.000001

0.02173 0.03681 0.01321 0.03715 0.02976 0.02724 0.04019 0.02328 0.04342 0.02819 0.01968 0.02955 0.05110 0.02638 0.02411 0.01977 0.03045 0.03877 0.02025 0.04645 0.05004 0.01116 0.03290 0.01851 0.02265

0.00004 0.00108 0.00003 0.00010 0.00027 0.00004 0.00004 0.00024 0.00019 0.00005 0.00006 0.00011 0.00046 0.00009 0.00010 0.00004 0.00005 0.00025 0.00015 0.00003 0.00051 0.00010 0.00025 0.00011 0.00007

0.2 4.4 −4.5 5.1 4.4 −5.4 4.8 1.6 −0.7 5.0 −9.3 −7.0 0.0 −10.3 2.1 −11.7 −17.6 −15.7 −8.5 2.8 −3.0 −3.4 −2.0 0.1 −3.4

2505 2771 2426 2624 2635 4166 2656 2644 2924 2756 3091 2737 2931 2747 2717 3113 3023 2861 2765 2653 2649 3019 2688 2445 2763

2651 2821 2668 2672 2695 4297 2707 2753 3051 2797 3370 2998 3044 3062 2813 3436 3455 3266 3054 2739 2837 3197 2858 2597 2956

YN229 2.1mm 5.1i 6.1mm 9.1mm 9.2mm 10.1mm 10.2mm 11.1mm 13.1mm 15.2mm

0.281508 0.281372 0.281431 0.281409 0.281435 0.281441 0.281440 0.281448 0.281424 0.281440

0.000018 0.000018 0.000016 0.000013 0.000016 0.000014 0.000015 0.000016 0.000014 0.000014

0.001237 0.000912 0.001026 0.001040 0.001008 0.000876 0.000724 0.001097 0.001017 0.000801

0.000010 0.000001 0.000001 0.000004 0.000004 0.000003 0.000002 0.000002 0.000003 0.000003

0.05774 0.03669 0.04731 0.03993 0.03862 0.03463 0.02784 0.04277 0.03671 0.02897

0.00023 0.00014 0.00012 0.00023 0.00013 0.00008 0.00007 0.00014 0.00008 0.00006

−2.3 4.9 −4.7 −5.5 −4.6 −4.2 −4.0 −4.2 −5.0 −4.1

2457 2620 2548 2579 2542 2525 2516 2529 2558 2520

2643 2671 2774 2817 2766 2746 2736 2747 2788 2741

YN230a 1.1i 2.1i 8.1i 10.1i 11.1i 13.1i 15.1i 17.1mm

0.281454 0.281272 0.281247 0.281341 0.280949 0.281249 0.281198 0.281431

0.000019 0.000017 0.000018 0.000018 0.000015 0.000018 0.000011 0.000016

0.001085 0.000831 0.001293 0.000277 0.000551 0.000791 0.000481 0.001026

0.000007 0.000002 0.000005 0.000002 0.000001 0.000004 0.000006 0.000003

0.03985 0.02869 0.05335 0.00927 0.02054 0.03027 0.01504 0.03630

0.00040 0.00013 0.00035 0.00006 0.00007 0.00018 0.00023 0.00015

0.5 −0.2 −4.4 1.7 −5.5 −0.6 −3.5 −5.5

2521 2751 2819 2620 3164 2780 2825 2548

2655 2884 3017 2732 3367 2918 3018 2788

YN801 2.1i 3.1i 4.1i 8.1i 9.1i 11.1i 15.1i

0.281311 0.281352 0.281167 0.281468 0.281501 0.281143 0.281441

0.000018 0.000016 0.000015 0.000013 0.000014 0.000019 0.000013

0.000787 0.000591 0.000702 0.000557 0.000854 0.001633 0.001347

0.000016 0.000003 0.000007 0.000001 0.000003 0.000014 0.000007

0.03117 0.02202 0.02707 0.02031 0.03128 0.06015 0.04744

0.00081 0.00002 0.00038 0.00005 0.00036 0.00069 0.00032

2.6 4.7 −0.7 0.0 −0.8 −3.2 2.6

2696 2627 2884 2468 2442 2988 2555

2784 2681 3019 2619 2607 3150 2648

1016-7 2.1mm 3.1mm 5.1mm 6.1mm 7.1mm 8.1mm

0.281497 0.281521 0.281516 0.281503 0.281501 0.281498

0.000008 0.000009 0.000009 0.000009 0.000010 0.000008

0.000381 0.000647 0.000143 0.000119 0.000145 0.000387

0.000007 0.000008 0.000001 0.000003 0.0000001 0.000014

0.01651 0.02635 0.00753 0.00542 0.00727 0.01321

0.00032 0.00062 0.00008 0.00009 0.00003 0.00047

−4.0 −3.5 −3.0 −3.5 −3.5 −3.9

2417 2401 2377 2393 2397 2415

2648 2621 2595 2619 2624 2646

N. Kim et al. / Precambrian Research 242 (2014) 1–21

15

Table 2 (Continued) Spota 9.1mm 10.1mm 14.1mm 16.1mm 21.1mm a

176

Hf/177 Hf

0.281514 0.281502 0.281533 0.281550 0.281538

2 SE

176

Lu/177 Hf

0.000006 0.000009 0.000011 0.000010 0.000011

0.000230 0.000169 0.000208 0.000100 0.000391

2 SE

176

Yb/177 Hf

0.000002 0.000002 0.000003 0.000001 0.000012

0.00711 0.00672 0.01368 0.00630 0.02356

2 SE 0.00009 0.00004 0.00015 0.00007 0.00075

εHf (t) −3.2 −3.5 −2.5 −1.8 −2.6

TDM (Ma)

T2DM (Ma)

2385 2397 2358 2329 2363

2606 2624 2567 2528 2571

i, inherited core; mm, magmatic zone; mt, metamorphic zone.

4.2. Zircon Hf isotopes The zircon Lu-Yb-Hf isotopic data are presented in Table 2, and plotted on 176 Hf/177 Hf vs. 176 Lu/177 Hf diagrams in Fig. 5. The LuYb-Hf analyses were made on concordant spots or discordant spots whose ages were well defined by the discordia line. The 176 Yb/177 Hf ratios of the analysed zircons are positively correlated with their 176 Lu/177 Hf ratios (176 Yb/177 Hf = 37.8 × 176 Lu/177 Hf, R2 = 0.95). The two-stage Hf model ages (T2DM ) in Table 2 were calculated by assuming that the crustal source of zircon had the same Lu/Hf ratio as the average continental crust (=0.0116; Rudnick and Gao, 2005). In reality, the single-stage Hf model age (TDM ) of zircon only marginally represents the correct crustal residence time of the source especially when the interval between the separation of the source crust from the mantle and the internal crustal melting (and crystallisation of zircon) is sufficiently long.

4.2.1. Metasedimentary rocks The 176 Hf/177 Hf and 176 Lu/177 Hf ratios of detrital zircons from sample YN804-4 (quartz schist) range from 0.280676 to 0.281365 and 0.000392 to 0.002156, respectively, yielding a TDM between 2.63 and 3.53 Ga, and a T2DM between 2.70 and 3.85 Ga. Two spots of detrital zircons from sample YN821 (migmatite) have comparable 176 Hf/177 Hf (0.281186 and 0.281363) and 176 Lu/177 Hf

(0.000763 and 0.000886) ratios to those from sample YN804-4, but one spot has the higher 176 Hf/177 Hf (0.281658) and 176 Lu/177 Hf (0.001116) ratios. Detrital zircons from sample YN908b (quartzite) display similar 176 Hf/177 Hf (0.280777–0.281305) and 176 Lu/177 Hf (0.000382–0.001392) ratios to those from the other two metasedimentary samples. 176 Hf/177 Hf and 176 Lu/177 Hf ratios and Hf model ages from the metamorphic zones of zircons from samples YN804-4 and YN908b are in the same range as for the detrital zircons (Fig. 5). The initial εHf values of detrital zircons are variable (−15.8 to +13.0) but are predominantly negative (16 of 25 data). The highest εHf (t) value is recorded in a spot of YN804-4 zircon that has an Eoarchean (3681 Ma) inheritance. Two metamorphic zones of the zircons also display negative εHf (t) values (−11.9 and −6.1).

4.2.2. (Meta)granitoids 4.2.2.1. Group I. Magmatic zircons from group I exhibit slight variations in 176 Hf/177 Hf and 176 Lu/177 Hf ratios (Fig. 5). The 176 Hf/177 Hf (0.281383–0.281512) and 176 Lu/177 Hf (0.000807–0.001418) ratios of sample YN902 (Pyeonghae gneiss) yield a restricted TDM (2.46–2.64 Ga) and T2DM (2.64–2.89 Ga). When calculated at the crystallisation age (1980 Ma), they all display negative εHf values (−6.8 to −2.1). An early Paleoproterozoic (2449 Ma) inherited core has a negative εHf (t) (−12.2) and an older TDM (3226 Ma). Magmatic zircons from sample YN906 (Buncheon

Fig. 5. Plots of zircon 176 Hf/177 Hf versus 176 Lu/177 Hf ratios. Reference lines representing single-stage Hf model ages of 4, 3, and 2 Ga are also shown. Open circles represent detrital grains and inherited cores. Closed and grey circles represent magmatic and metamorphic zones, respectively.

16

N. Kim et al. / Precambrian Research 242 (2014) 1–21

gneiss) have similar εHf (t) and Hf model ages to those from sample YN902. Inherited zircons from sample YN906 crystallised in the Archaean–Proterozoic transition period (2.67–2.37 Ga) yield mostly positive εHf (t) values (−0.7 to +4.6) and a narrow range of Hf model ages (TDM = 2.66–2.78 Ga, T2DM = 2.74–2.87 Ga). A Mesoarchaean (3194 Ma) inherited core displays a negative εHf (t) (−1.1) and an older TDM (3.46 Ga). Two data points from metamorphic zones yield negative εHf (t) values (−5.1 and −6.2 at 1856 Ma) and TDM (2.47 and 2.51 Ga) older than their metamorphic ages. 4.2.2.2. Group II. As described earlier, most analysed zircons from the Icheonri granitic gneiss (samples YN806 and YN810h) are inherited in origin. The 176 Hf/177 Hf and 176 Lu/177 Hf ratios of these inherited cores range from 0.280202 to 0.281485 and 0.000281 to 0.001662, respectively, which yield a TDM from 2.45 to 4.17 Ga and a T2DM from 2.60 to 4.30 Ga. Their εHf (t) values are variable (−11.7 to +5.7). The youngest group of magmatic zircons from the Icheonri granitic gneiss has dominantly negative εHf (t) (−17.6 to +2.1) and TDM (2.30–3.02 Ga) older than their crystallisation age (1985 ± 14 Ma). Most metamorphic zones of zircons display little variation in their 176 Hf/177 Hf ratio (0.281422–0.281486), εHf (t) (−6.9 to −4.5), and TDM (2.43–2.53 Ga). A metamorphic spot from sample YN810h yields a significantly negative εHf (t) (−15.7) and a latest Mesoarchaean TDM (2.86 Ga). Overall, inherited zircons from the Hongjesa granitic gneiss (samples YN229 and YN230a) have similar 176 Hf/177 Hf (0.280949–0.281454) and 176 Lu/177 Hf (0.000277–0.001293) ratios (Fig. 5), TDM (2.52–3.16 Ga), T2DM (2.66–3.37 Ga), and εHf (t) (−5.5 to +4.9) to those from the Icheonri granitic gneiss. Magmatic zircons representing the protolith age of the Hongjesa granitic gneiss (1975 ± 16 Ma) display restricted ranges in their Hf model ages (TDM = 2.46–2.58 Ga, T2DM = 2.64–2.82 Ga) and εHf (t) (−5.5 to −2.3). 4.2.2.3. Group III. The 176 Hf/177 Hf and 176 Lu/177 Hf ratios of inherited cores from sample YN801 range from 0.281143 to 0.281501 and 0.000557 to 0.001633, respectively, yielding a TDM from 2.44 to 2.99 Ga, and a T2DM from 2.61 to 3.15 Ga. Their initial εHf (t) values are in the range of −3.2 to +4.7. The magmatic zircons from sample 1016-7, defining the emplacement age of the Imwon leucogranite (1867 ± 6 Ma), display slight variations in 176 Hf/177 Hf 176 Lu/177 Hf the (0.281497–0.281550) and (0.000100–0.000647) ratios, TDM (2.33–2.42 Ga), T2DM (2.53–2.65 Ga), and εHf (t) (−4.0 to −1.8). 5. Discussion 5.1. Refined geochronological framework of crustal evolution When our results are combined with data previously reported by Kim et al. (2012b), zircons from the Hosanri Formation and the Wonnam Group display age patterns comparable with each other. Sixty-eight concordant data points of detrital zircons from the two units yield a prominent peak at 2493 ± 25 Ma (n = 23), together with subordinate populations at 2325 ± 14 Ma (n = 7), 2679 ± 19 Ma (n = 6) and ca. 2.2–2.1 Ga, and some Archaean points on the probability density plot (Fig. 6). The youngest population of detrital zircons constrains the upper boundary of the timing of sedimentation. As the lower limit of sedimentation age is constrained by the intrusion age of the granitoids, it can be concluded that the metasedimentary rocks in the Hosanri Formation and the Wonnam Group were deposited sometime between ca. 2.1 and 1.98 Ga. This span is overlapped with the sedimentation age of the westward Yuli Group (2.18–2.01 Ga) as recently suggested by LA-ICPMS zircon analyses (Lee et al., 2011). The occurrence of zircons with ages of ca. 2.8, 3.5, and 3.7 Ga supports the contribution of Archaean components to the metasedimentary rocks, which was previously

suggested by whole-rock Nd data (Cheong et al., 2000, 2004). Etype MORB affinities of the amphibolites, which occur as a sill-like body or inclusions within the metasedimentary sequences in the study area (Arakawa et al., 2003) imply a back-arc setting related to the subduction that occurred prior to 1.98 Ga. Group I and II metagranitoids showed indistinguishable ages of magmatic zircons within error; 1980 ± 22 Ma (Pyeonghae gneiss), 1966 ± 15 Ma (Buncheon gneiss), 1985 ± 14 Ma (Icheonri granitic gneiss) and 1975 ± 16 Ma (Hongjesa granitic gneiss) (Fig. 4). The ca. 1.98 Ga magmatism that produced the protoliths of the Buncheon gneiss and the lithologically similar Pyeonghae gneiss may have occurred in association with subduction, because previous wholerock data for the Buncheon gneiss demonstrated geochemical arc affinities, such as the enrichment of large-ion-lithophile-elements and the depletion of high-field-strength-elements (Kim et al., 2012b). The slightly older SHRIMP zircon age of 1990 ± 5 Ma reported previously for the Buncheon gneiss (Kim et al., 2012b) may indicate a prolonged subduction and arc magmatism. Our SHRIMP zircon age for the Imwon leucogranite (1867 ± 6 Ma) agrees with previous data (1859–1853 Ma; Lee et al., 2010b). Leucogranites commonly occur in continental collision zones (Harris et al., 1986), but the tectonic environment of the Imwon leucogranite is still unclear considering the lack of evidence for crustal thickening in the north-eastern Yeongnam Massif (Kim and Cho, 2003) and transitional trace element composition of the Imwon leucogranite straddling between the volcanic arc granite and syn-collisional granite fields (Lee et al., 2010b). It is notable that the age pattern of inherited zircon cores from the (meta)granitoids exactly mimics that of detrital zircons from the metasedimentary rocks. Ninety-one concordant data points for inherited zircon cores yield a prominent peak at 2499 ± 22 Ma (n = 27), and subordinate populations at 2676 ± 13 Ma (n = 7), 2325 ± 15 Ma (n = 6), and 2074 ± 7 Ma (n = 6), together with some Archaean points on the probability density plot (Fig. 6). This resemblance strongly indicates a close genetic link between the (meta)granitoids and the metasedimentary rocks in the northeastern Yeongnam Massif. Such inference supports a previously suggested hypothesis that the Icheonri granitic gneiss was derived from the partial melting of metasedimentary rocks in the Hosanri Formation and the fractional crystallisation of plagioclase, which was based on the major and trace element modelling (Cheong et al., 2006). Combining the data from this study and Kim et al. (2012b) indicates that zircons in the metasedimentary rocks overgrew at ca. 2.0–1.98 and 1.89–1.85 Ga (Fig. 6). It is reasonable to relate the former and latter age spans to the emplacement of the protoliths of groups I and II metagranitoids, and the regional metamorphism and associated intrusion of the Imwon leucogranite, respectively. The 1.89–1.85 Ga event is a prominent metamorphic imprint recorded not only in the Yeongnam Massif but also in the Gyeonggi and Nangrim Massifs (Kim et al., 2012b and references therein), and is probably related to the contemporaneous global tectonic event, i.e. the formation of the Columbia supercontinent (Zhao et al., 2002, 2004). The Neoproterozoic–Paleozoic Pb loss was indicated by the lower intercept ages formed by discordant zircon data, ranging from 618 ± 68 to 250 ± 100 Ma. Comparable Pb loss ages were reduced from various zircon domains in the same rock specimen. For example, the lower intercept age yielded by sample YN804-4 (quartz schist in the Hosanri Formation) is consistent for the metamorphic zones (365 ± 54 Ma) and the inherited cores (ca. 380 Ma). This level of consistency is confirmed by zircon data from sample YN906 (Buncheon gneiss: metamorphic zones, 572 ± 27 Ma; magmatic zones, 618 ± 68 Ma), and sample YN902 (Pyeonghae gneiss: inherited cores, 250 ± 100 Ma; magmatic zones, 296 ± 38 Ma) (Fig. 4). The lower intercept age is

N. Kim et al. / Precambrian Research 242 (2014) 1–21

17

Fig. 6. A graphic summary of the refined geochronological scheme for the evolution of the north-eastern Yeongnam Massif based on SHRIMP zircon ages of the present study and Kim et al. (2012b). Closed circles represent magmatic events. Metamorphic and Pb loss events are represented by grey circles. Grey bands indicate geologic events that were recorded reproducibly.

also found to be reproducible in data from different samples from the Icheonri granitic gneiss (YN806, 298 ± 110 Ma; YN810h, 301 ± 56 Ma) and the Imwon leucogranite (YN801, 356 ± 75 Ma; 1016-7, 300 ± 45 Ma), although it should also be noted that two Hongjesa granitic gneiss samples record different ages (YN229, 373 ± 36 Ma; YN230a, 522 ± 85 Ma). These ages have relatively large errors mainly due to the lack of concordant points near the lower intercepts. However, when considering the reproducibility, it is evident that the Archaean–Paleoproterozoic zircons analysed in this study experienced complicated Pb loss events at ca. 620–570 and 380–300 Ma (Fig. 6). This is not compatible with the conventional idea that the Korean peninsula was magmatically and tectonically calm during the Paleozoic (Lee, 1987), but does conform with U-Pb ages indicating Paleozoic magmatism and metamorphism in the northern Gyeongsang Basin and the Okcheon Belt (Cheong et al., 2003; Yi et al., 2012; Lee et al., 2013), and Neoproterozoic to Paleozoic SHRIMP ages of detrital zircons from the south-western Gyeonggi Massif, the Okcheon Belt, and the eastern Yeongnam Massif (Cho et al., 2010, 2013; Cheong et al., 2011; Park et al., 2011; Kim et al., 2012a, 2013a). The Cambro-Ordovician Choson Supergroup resting unconformably upon the basement of the Yeongnam Massif (Chough et al., 2000) was deposited between the older Neoproterozoic and the younger Paleozoic events constrained here. More data are required to fully understand the nature of Neoproterozoic–Paleozoic events that occurred on the Korean peninsula.

5.2. Zircon Hf isotopic constraints Initial εHf values of the zircons are plotted against their crystallisation and metamorphic growth ages in Fig. 7. Also shown in Fig. 7 are histograms of T2DM for the zircons. As shown in Fig. 7, the detrital zircon data display a highly dispersed pattern, resulting in a diverse range of Hf model ages (T2DM = 2.30–3.85 Ga). However, it is noted that all data points, except one with the highest εHf value (+13.0) plot below the model evolution curve of the depleted mantle, indicating that the magmas from which the zircons crystallised were derived mainly from the melting of pre-existing crustal rocks. The majority of high-εHf data at a given crystallisation age span younger than 2.5 Ga form a linear array that intersects the depleted mantle curve at ca. 2.75 Ga. The slope of this linear array (=0.0175, R2 = 0.78) broadly corresponds to the typical Hf isotopic evolution of the continental crust. For example, a plot of the evolution of the average continental crust with a 176 Lu/177 Hf of 0.0116 (Rudnick and Gao, 2005) forms a slope of 0.0146. We contend that the source melt of detrital zircons comprised mixtures of crustal materials that originally separated from the mantle in the Neoarchaean (ca. 2.75 Ga) and the earlier era. The point plotted above the depleted mantle curve may reflect the heterogeneity of the source mantle reservoir. It has been shown that the 176 Hf/177 Hf ratios of mid-oceanic ridge basalts are not uniform. For Pacific MORBs, the present 176 Hf/177 Hf ratio is reported to range from 0.283130 ± 5 to 0.283294 ± 6 (Chauvel

18

N. Kim et al. / Precambrian Research 242 (2014) 1–21

Fig. 7. (Left) Plots of zircon εHf versus the crystallisation and overgrowth ages. The evolutionary path of the depleted mantle is based on 176 Hf/177 Hf and 176 Lu/177 Hf ratios from Griffin et al. (2000). The dashed lines projected from the depleted mantle curve are ␧Hf evolutionary paths of model crustal reservoirs that separated from the mantle at 3.4 and 2.7 Ga with a 176 Lu/177 Hf ratio of average continental crust (=0.0116; Rudnick and Gao, 2005). CHUR denotes the chondritic uniform reservoir. Symbols are the same as in Fig. 5. (Right) Histograms of zircon T2DM for detrital, inherited, and magmatic zones (filled squares) and metamorphic zones (grey squares).

and Blichert-Toft, 2001), which yields an εHf value (+12.7 to +18.5) different from the assumed value of +16.9 (Griffin et al., 2000). Zircons from group I metagranitoids have contrasting εHf – crystallisation age paths when compared to those from the metasedimentary rocks (Fig. 7). The majority of magmatic and inherited zircons from the Pyeonghae and Buncheon gneiss yield a coherent array that intersects the depleted mantle curve at ca. 2.75 Ga (T2DM = 2.74 ± 0.09 Ga, 1 s.d.). The crustal residence time of ca. 2.75 Ga fits nicely with that reduced by the high-εHf zircons from the metasedimentary rocks. Hf isotopic compositions from two spots of metamorphic zircon rims from the Buncheon gneiss

sample YN906 follow the evolutionary path formed by magmatic and inherited zircons, indicating no adjustment of Hf isotopic composition during the metamorphic event. All these observations suggest that most zircons in the group I metagranitoids crystallised or overgrew in the same crustal protolith separated from the mantle at ca. 2.75 Ga. Conversely, zircons from the group II metagranitoids display a highly scattered pattern on the εHf –age plot (Fig. 7), as indicated by the detrital zircons from the metasedimentary rocks. Most zircon data are bracketed by model evolution lines of crustal reservoirs that separated from the mantle at 3.4 and 2.7 Ga. Therefore it is

N. Kim et al. / Precambrian Research 242 (2014) 1–21

evident that they crystallised from heterogeneous magmas derived from the partial melting of source materials with a diverse εHf and crustal residence age. The difference in the zircon Hf evolutionary path between group I and II metagranitoids could be attributed to selective melting of infracrustal and supracrustal materials that produced I and S-type (White and Chappell, 1977) granites, respectively. The protoliths of group I metagranitoids are considered to be I-type granites derived primarily from the partial melting of igneous rocks that solidified at depth. The internal melting of these protoliths has produced zircons with various crystallisation ages but virtually uniform crustal residence ages. In contrast, the protoliths of group II metagranitoids were possibly S-type granites that originated from supracrustal rocks formed at the surface. These supracrustal protoliths contained zircons diverse in their model ages as well as crystallisation ages. This interpretation is supported by the selective occurrence of hornblende in group I and cordierite and muscovite in group II metagranitoids. It is also notable that zircons from group I contain less inherited cores than zircons from group II, which is possibly related to the difference in magma temperature (Chappell et al., 1998; Miller et al., 2003). The significance of Neoarchaean crustal formation is also confirmed by zircon data from the Imwon leucogranite. Five out of seven inherited core data points from sample YN801, together with all of the magmatic zircon data from sample 1016-7 form an evolutionary path that separated from the mantle in the Neoarchaean (T2DM = 2.62 ± 0.06 Ga, 1 s.d.) (Fig. 7). We conclude that the Neoarchaean Era (ca. 2.75–2.62 Ga) marks the most important stage of crustal formation in the north-eastern Yeongnam Massif. The magmas from which the ca. 2.50–1.98 Ga zircons crystallised were derived principally from the reworking of pre-existing crustal materials. 5.3. Implications for the correlation with Chinese blocks The correlation of Korean Precambrian massifs with Chinese cratons remains controversial. This has led to the generation of diverse, often mutually exclusive tectonic models on the eastward extension of northeast-trending orogenic belts in China through Korea and Japan (Yin and Nie, 1993; Ernst and Liou, 1995; Ree et al., 1996; Zhang, 1997; Ishiwatari and Tsujimori, 2003; Ernst et al., 2007; Oh and Kusky, 2007; Kwon et al., 2009; Yu et al., 2009). As stated above, our zircon Lu-Hf isotopic data indicate that juvenile crustal formation in the north-eastern Yeongnam Massif occurred largely in the Neoarchaean (ca. 2.75–2.62 Ga), and the magmas formed in the period ca. 2.50–1.98 Ga were derived principally from crustal recycling. Geng et al. (2012) synthesised a large database of zircon Hf isotopes and concluded that the new growth of continental crust in the NCC occurred exclusively at ca. 2.7 Ga. They further indicated that the widespread 2.5 Ga rocks in the NCC are basically a reworking product of pre-existing crustal materials. The significance of ca. 2.75 Ga (based on crustal 176 Lu/177 Hf of 0.0116) formation of juvenile crust was also indicated by zircon Hf isotopic data for Paleoproterozoic granitoids in the Wuyishan terrane, eastern Cathaysia Block (Yu et al., 2009). These Hf isotopic features agree well with our findings for the north-eastern Yeongnam Massif. The ca. 2.5 Ga tonalite-trondhjemite-granodiorite (TTG) gneisses comprise more than 80% of the total exposure of the basement in the Eastern Block of the NCC (Zhao and Cawood, 2012 and references therein). Although basement rocks of this age have not been reported in the Yeongnam Massif, our data demonstrate that the ca. 2.5 Ga rocks were widespread in the source region of the Paleoproterozoic metasedimentary and metagranitoid rocks in the north-eastern part of the massif (Fig. 6). However, it should also be noted that the ca. 1.98 Ga peraluminous arc-related magmatism constrained by our zircon data has not been clearly identified from the Paleoproterozoic terranes

19

in eastern China. The Jiao-Liao-Ji Belt in the Eastern Block of the NCC consists largely of greenschist to lower amphibolites facies volcanosedimentary successions and associated monzogranitic gneisses and potassic granitoids emplaced at 2176–2143 and 1875–1843 Ma, respectively (Li and Zhao, 2007). The S- and A-type granites in the Wuyishan terrane intruded at 1888–1855 Ma (Yu et al., 2009). Furthermore, the repeated Neoproterozoic–Paleozoic disturbances indicated by our zircon data are in marked contrast to the consistent Triassic (ca. 230 Ma) lower intercept ages displayed by the zircon data of the Wuyishan granitoids (Yu et al., 2009). The ca. 1.86 Ga metamorphism and magmatism recorded in the northeastern Yeongnam Massif (Lee et al., 2005; this study), as well as in the two Chinese terranes, may be a global event related to the formation of the Columbia supercontinent (Zhao et al., 2002, 2004) and thus cannot be a decisive parameter used in the correlation between Archaean–Paleoproterozoic terranes. The discrepancies of zircon crystallisation and Pb loss ages do not definitely allow the correlation between the north-eastern Yeongnam Massif and Paleoproterozoic terranes in eastern China. Further studies are demanding to elucidate this issue.

6. Conclusions Our zircon age data establish a geochronological scheme of the north-eastern Yeongnam Massif consisting of: (1) Middle Paleoproterozoic (ca. 2.1–1.98 Ga) sedimentation of source materials that formed predominantly at ca. 2.5 Ga, and subordinately at 2.7, 2.3, and 2.1 Ga, presumably in backarc regions, (2) ca. 1.98 Ga peraluminous arc-related magmatism that produced the protoliths of group I (Pyeonghae and Buncheon gneiss) and group II (Icheonri and Hongjesa granitic gneiss) metagranitoids, (3) ca. 1.86 Ga metamorphism and associated intrusion of a leucogranite in an arc- or collisionrelated environment, and (4) multiple Neoproterozoic–Paleozoic (ca. 620–570 and 380–300 Ma) Pb loss events. A close genetic link between the metasedimentary rocks and the (meta)granitoids is indicated by the reproducible age patterns of detrital and inherited zircons. The Lu-Hf isotopic data of most zircon data plot below the depleted mantle evolution curve on the εHf –crystallisation age diagram, indicating that the magmas from which the zircons crystallised were derived mainly from the melting of pre-existing crustal rocks. Considering the systematic array of zircon Hf isotope data, the protoliths of group I metagranitoids may be I-type granites derived from the partial melting of infracrustal rocks that solidified at depth. By contrast, the scattered pattern of zircon data from group II metagranitoids is indicative of an S-type origin sourced by supracrustal rocks. The Hf model ages narrowly constrained by magmatic and inherited zircons from group I and III (meta)granitoids, and the high-εHf zircons from the metasedimentary rocks and group II metagranitoids suggest that the Neoarchaean Era (ca. 2.75–2.62 Ga) marks the most important stage of crustal formation in the north-eastern Yeongnam Massif. The Paleoproterozoic (ca. 2.50–1.98 Ga) magmas were derived principally by crustal recycling. These Hf isotopic features generally agree with those reported for zircons from the NCC and eastern Cathaysia Block, but the zircon ages determined here leave uncertainties regarding the correlation of the north-eastern Yeongnam Massif with Paleoproterozoic terranes in eastern China.

Acknowledgements This study was supported by KBSI grants (G33200 and T33621) and KBSI visiting scholar programme to Y.-S. Song and K.-H. Park. We are grateful for constructive comments of the anonymous reviewers.

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