Research Article Fluid-Present Partial Melting of Paleoproterozoic Okbang Amphibolite in the Yeongnam Massif, Korea

GeoScienceWorld Lithosphere Volume 2020, Article ID 8854615, 26 pages https://doi.org/10.2113/2020/8854615

Yuyoung Lee 1,2 and Moonsup Cho3

1Research Center for Geochronology and Isotope Analysis, Korea Basic Science Institute, Cheongju 28119, Republic of Korea 2Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea 3Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju 28644, Republic of Korea

Correspondence should be addressed to Yuyoung Lee; [email protected]

Received 24 April 2019; Revised 11 December 2019; Accepted 18 May 2020; Published 1 September 2020

Academic Editor: Sarah M. Roeske

The waning stage of a long-lived collisional orogeny is commonly governed by an extensional regime in association with high-temperature metamorphism, anatexis, and magmatism. Such a late-orogenic process is well-recorded in the Okbang amphibolite, Yeongnam Massif, Korea, where thin layers or irregular patches of tonalitic leucosomes are widespread particularly in association with ductile shear zones. Various microstructures including interstitial felsic phases and former melt patches indicate that leucosomes are the product of partial melting. These leucosomes are aligned en echelon and contain large (up to ~2 cm) grains fl of peritectic hornblende, suggesting synkinematic uid-present anatexis. The leucosomes are enriched in Na2O and Sr contents compared to the amphibolite but depleted in rare earth and high field-strength elements. P - T conditions of the anatexis were estimated at 4.6–5.2 kbar and 650–730°C, respectively, based on hornblende-plagioclase geothermobarometry. Sensitive high-resolution ion microprobe U-Pb analyses of zircon from an amphibolite and a leucosome sample yielded weighted mean 207Pb/206Pb ages of 1866 ± 4 Ma and 1862 ± 2 Ma, which are interpreted as the times for magmatic crystallization and subsequent anatexis of mafic protolith, respectively. The latter is consistent with the time of partial melting determined from a migmatitic gneiss and a biotite-sillimanite gneiss at 1861 ± 4 Ma and 1860 ± 9 Ma, respectively. The leucosomes are transected by an undeformed pegmatitic dyke dated at 1852 ± 3 Ma; by this time, extensional ductile shearing ε ð Þ has ceased. Initial Hf t values of zircon from the amphibolite range from 4.2 to 6.0, suggesting juvenile derivation of basaltic ε ð Þ – melt from the mantle. In contrast, lower Hf t values ( 0.1 to 3.5) in leucosome zircons indicate a mixing of crust-derived melt. Taken together, the Okbang amphibolite has experienced synkinematic fluid-present melting during the waning stage of Paleoproterozoic hot orogenesis prevalent in the Yeongnam Massif as well as the North China Craton.

1. Introduction of the continental crust as well as substantial variation in the crustal strength (e.g., [18–21]). Many previous field- Partial melting of amphibolites at middle-lower crustal based studies have focused on the dehydration melting of depths commonly takes place in response to the dehydration amphibolites [2, 5, 22] but much less on the fluid-present of amphibole (e.g., [1–5]) or the influx of externally derived melting, although the latter is one of the key melt-forming hydrous fluid (e.g., [6–9]). This anatexis accounts for the processes in the middle to lower crust during orogenesis [1, widespread occurrence of tonalitic and trondhjemitic melts 6, 7, 9, 23, 24]. Nevertheless, fluid-present melting, resulting in orogenic belts [10–15], and the migration of these melts in a volume decrease in host rocks, is associated with plate provides the mechanism for crustal reworking to yield margin tectonic structures such as crustal-scale shear zones residual granulites or restites in the continental crust (e.g., or regional thrusting that may lead to extensional collapse [16, 17]). Thus, melt formation and migration are two and exhumation of an orogenic belt [25–27]. Thus, both principal processes responsible for chemical differentiation fluid-present and fluid-absent melting processes are

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important for understanding the melt formation, migration scale. On the other hand, the metasedimentary rocks are to drainage, and crustal rheology during orogenesis [27]. mainly composed of interbedded pelitic and psammopelitic The Okbang amphibolite in the Yeongnam Massif, Korea gneisses together with a lesser amount of quartzite. In particu- (Figure 1) contains abundant tonalitic leucosomes with a lar, the metapelitic rocks define high dT/dP, Buchan metamor- variety of microstructures and provides a natural laboratory phic zones progressing from cordierite through sillimanite to for investigating the processes involved in fluid-present melt- garnet zones; the latter two zones are associated with wide- ing and melt migration. Based on the whole-rock geochemis- spread anatexis typified by the occurrence of abundant (up try and multigrain zircon U-Pb age, previous workers [28, to ~20 vol.% on the outcrop) cordierite-bearing leucosomes 29] suggested that the protolith of amphibolites formed in a and leucogranites [34, 35, 41]. The country rocks hosting the rift-related setting at ~1.92 Ga, but these authors failed to rec- Okbang amphibolite are strongly deformed, particularly in ognize partial melting in the amphibolite. In order to assess the vicinity of lithologic boundaries (Figures 3(a) and 3(b)). the role of fluid-present melting, we investigated a suite of Extensional (C′) shear bands typically occur as sets of closely amphibolites, neosomes, and host gneisses (for the general spaced ductile shear zones at millimeter to centimeter scales, terminology of migmatites; we followed the recommendation accompanied by partial melting and leucosome formation. of Sawyer [8]) to determine field relationships, bulk-rock Synkinematic melting and melt segregation may be accounted geochemistry, and zircon U-Pb ages using a sensitive high- for in the context of an extensional tectonic regime prevalent resolution ion microprobe (SHRIMP). In addition, the Lu- during the Paleoproterozoic in the southern Yeongnam Massif Hf isotopic compositions of zircon were analyzed to unravel [31, 33]. Whole-rock geochemical analyses revealed the rift- the crust-mantle interaction during the formation of felsic related, enriched mid-ocean ridge basalt (E-MORB) composi- melts in the amphibolite. Our results, combined with avail- tion of amphibolite [28], and the U-Pb zircon dating based able data, provide further insight into ~1.87–1.85 Ga tectono- on multigrain thermal-ionization mass spectrometry analysis magmatism in the Korean Peninsula and its linkage to the yielded a discordant date of 1918 ± 10 Ma [29]. In addition, prolonged Paleoproterozoic orogenesis of the North China precise SHRIMP U-Pb zircon age constraints are available for Craton [30–33]. the Buncheon granitic gneiss, i.e., magmatic crystallization at 1966 ± 16 Ma and subsequent metamorphism at 1862 ± 4 Ma 2. Geological Background [35, 42]. The latter is associated with late orogenic event which is widespread in the entire Korean Peninsula, including the The Korean Peninsula consists of three major Precambrian Yeongnam Massif [30, 36]. massifs (Nangrim, Gyeonggi, and Yeongnam) adjoined by the Gyeonggi Marginal Belt ([30], Figure 1(a)). The Yeong- 3. Field Relationships nam Massif is a polymetamorphic terrain bounded to the north by the Ogcheon Belt and unconformably overlain to the south- The Okbang amphibolite occurs as elongate lenses ranging in east by thick volcanic-sedimentary sequences of the Cretaceous widths from ~20 to 400 m that are stretched and folded on a Gyeongsang Basin. This massif is primarily composed of quart- map scale (Figure 2). Various lines of evidence for partial zofeldspathic gneiss, migmatitic gneiss, porphyroblastic gneiss, melting are present on the outcrops, and metatexitic amphib- andgraniticgneisstogetherwithlesseramountsofamphibolite olites are predominant (Figures 3 and 4; [8]). Penetrative fi and calc-silicate rocks [34]. Igneous protoliths of gneisses were foliations (S1) in the amphibolite are occasionally de ned largely emplaced at ~2.0–1.9 Ga in an arc-related environment by preferred orientation of hornblende neoblasts and layer- and subsequently affected by upper amphibolite to lower gran- parallel leucosomes; their attitudes are consistent with those ulite facies metamorphism at ~1.9–1.85 Ga (Figure 1(b); [30, measured in the Buncheon and metasedimentary gneisses 31, 33, 35, 36]). The latter event is associated with widespread generally striking northeast and dipping moderately to the partial melting to produce abundant leucosomes and garnet- northwest (Figure 2). Both stretching and mineral (horn- bearing leucogranites and perhaps best exemplified by the blende) lineations mostly plunge to the north. Towards the granulite-facies aureole around 1.87–1.86 Ga anorthosite-man- boundary with the Buncheon granitic gneiss, the amphibo- gerite-charnockite-granite (AMCG) suite in the southern lites are progressively deformed to yield high-strain zones Yeongnan Massif (Figure 1(a); [32, 33]). P - T conditions where leucosomes are highly stretched and isoclinally folded. of migmatitic gneisses in the Yeongnam Massif are estimated The metasedimentary rocks also contain abundant granitic at 4–6 kbar and 750–850°C, based on conventional geother- leucosomes and garnet–tourmaline-bearing leucogranites, mobarometry and phase equilibria modeling [30, 33, 34]. but the Buncheon granitic gneiss is lacking in melt-related Similar high-temperature tectonothermal events have been features probably owing to the limited amount of fluid. well-documented in the North China Craton at 2.0–1.8 Ga, Tonalitic leucosomes in the amphibolite are generally including the Trans-North China Orogen where high thermal aligned parallel to the foliation but locally occur as discordant gradients were attained during accretionary–collisional or patchy segregations (Figure 3(c)). Some layer-parallel leu- orogenesis [37–39]. cosomes are deflected into the interboudin partition to yield The Okbang amphibolite, the focus of this study, occurs the “collapse” structure [43]. The proportion of leucosomes as planar bodies along the boundary between the Buncheon on many amphibolite outcrops is generally in the range granitic gneiss and metasedimentary rocks (Figure 2; [40]). of ~20–30 vol.% but rarely reaches up to ~40 vol.%. More- The Buncheon gneiss typically contains augens of megacrys- over, these estimates significantly vary on individual outcrops, tic K-feldspar and is penetratively deformed on an outcrop ranging from <5to~30 vol.% over a distance of a few tens of

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North China Craton (b) 129° 30′ (a) Nangrim N Massif 0 100 km

Gyeonggi Imjingang Massif Belt East Sea Gyeonggi (Sea of Japan) (1)1853±15 Ma Marginal Belt (b) (3) (3)1975±16 Ma 1867±6 Ma Gyeongsang Ogcheon Basin (3) Sulu Belt 37° 10′ 1985±14 Ma Belt Yeongnam (3) Tan-Lu fault Japan 1864±11 Ma South China Craton Massif

Paleozoic-Cretaceous (3)1966±15 Ma sedimentary rocks East Sea Mesozoic granitoids

Leucogranite Okbang amphibolite (2)1959±28 Ma Figure 2 Icheonri granitic gneiss 36° 50′ (3)1980±22 Ma (2)1892±27 Ma Hongjesa granitic gneiss (2)1990±5 Ma Pyeonghae gneiss (2) 1861±4 Ma Buncheon granitic gneiss 0 N 10 (2)1848±5 Ma Metasedimentary rocks km 129° 00′ 129° 30′

Figure 1: (a) Simplified tectonic province map of East Asia (modified after [137]). The area shown in solid box is enlarged in (b). The red star indicates the location of the Sancheong-Hadong AMCG (anorthosite-mangerite-charnockite-granite) suite. (b) Geological map of the northeastern Yeongnam Massif showing the compilation of available geochronologic data (modified after [35]). SHRIMP zircon U-Pb ages representing igneous and metamorphic events in basement gneisses are shown in red and blue, respectively, together with references: (1) Lee et al. [138], (2) Kim et al. [42], and (3) Kim et al. [35].

meters. In situ leucosomes have diffuse boundaries with volu- minerals and represent a rare example of pegmatite-type metrically minor melanosomes enriched in hornblende tungsten ore worldwide [46]. (Figure 3(d)). The leucosomes, either concordant or discordant, are interconnected with each other, and often concen- 4. Petrography trated along the axial plane of mesoscopic folds and within the interboudin partition of amphibolite, suggesting synkine- The Okbang amphibolites are medium to coarse-grained and matic formation of melts (Figures 3(c), 3(e), 3(f), 4(a), and primarily consist of hornblende, plagioclase, biotite, and 4(b); [44]). On the other hand, poikilitic megacrysts of horn- quartz together with small amounts of ilmenite and magne- blende (up to 2 cm) are common in the leucosomes where tite. Zircon and apatite occur as accessory phases. Micro- melanosomes are generally lacking (Figure 4(c)). We interpret structures with straight grain boundaries and ~120° triple that these megacrysts represent peritectic hornblende-rich junctions are characteristic (Figure 5(a)), and prismatic segregations interconnected with tonalitic leucosome pools grains of hornblende are often aligned parallel to a weak foli- or layers (Figures 4(d) and 4(e)). ation. The hornblende grains are mostly subhedral, rarely The cessation of synkinematic melting was followed by exceed 1.5 mm in the maximum dimension, and commonly the intrusion of discordant pegmatitic dykes and pods. The contain rounded inclusions of quartz and rare plagioclase. pegmatitic bodies range from a few centimeters to ~3m in Plagioclase is generally stubby, subhedral to anhedral, and width, lack penetrative deformation, and often transect the less than 1.0 mm in size (Figure 5(a)). The majority of plagio- stringers of leucosomes aligned subparallel to the foliation clase grains are compositionally zoned and show undulose in amphibolite (Figure 4(f)). The margins of pegmatites often extinctions and/or deformation twins. Quartz grains are also contain alteration bands. In particular, tungsten ore deposits subhedral to anhedral and less than 0.5 mm in size and show are associated with pegmatites and attributed to metasomatic undulose extinction. In particular, interstitial quartz fills the reactions of the amphibolite with tungsten-bearing alkaline space among rounded grains of hornblende and plagioclase melts [40, 45]. The Okbang ores containing ~70% WO3 (Figures 5(b) and 5(c)); this microstructure is indicative of consist of scheelite, wolframite, fluorite, and minor sulfide dissolution at high temperatures [8]. Biotite uncommonly

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N (a) 129° 15′ N 0 12 km 1852±3 Ma (UJ03-3) 36° 70′ 1861±4 Ma (WN-1) Foliation 1860±9 Ma (n = 22) Lineation (WN-2) (n = 6) A 1981±2 Ma (BCG-1) 1866±4 Ma Mesozoic granitoids (UJ03) Paleozoic sedimentary rocks 1862±2 Ma A′ (OB-01L) 36° 60′ 129° 15′ Okbang amphibolite (b) NNW SSE 900 High-strain zone Buncheon granitic gneiss 750 600 Metasedimentary rocks 450 Granitic Migmatitic Shear zone 300 metasedimentary

Elevation (m) Elevation gneiss 150 rocks Foliation and lineation AA′ Sample locations for 0 500 1000 1500 2000 2500 SHRIMP dating Distance (m)

Figure 2: (a) Geological map of the Okbang area, enlarged from Figure 1 (modiﬁed after [60]). The analyzed samples are shown together with the SHRIMP U-Pb zircon ages. Foliations (n =22) and lineations (n =6) measured in the shear zone are plotted on the stereogram of lower-hemisphere, equal-area projection (inset ﬁgure). A-A’ denotes the location of cross-section. (b) Schematic cross-section across the normal-sense shear zone involving the sill-like amphibolite.

occurs as subhedral, medium-grained (up to 5 mm in size) Interstitial or vermicular quartz uncommonly occurs along poikiloblasts, containing small inclusions of hornblende and the grain boundaries of hornblende; such microstructures plagioclase together with interstitial quartz (Figure 5(d)). Thin are interpreted to represent the pseudomorph after former films of quartz develop to mantle the rounded grains of horn- melts or the reaction product between hornblende and blende and plagioclase in contact with biotite (Figure 5(e)); residual melt [8, 49]. such microstructures are diagnostic of the former presence of in situ melts [47]. 5. Mineral and Bulk-Rock Compositions The leucosomes in amphibolites primarily consist of plagioclase and quartz; both phases commonly reach ~90 vol.%. 5.1. Analytical Methods. Major element compositions of Mafic phases are represented by poikilitic hornblende con- calcic amphibole and plagioclase were determined using a taining inclusions of plagioclase, quartz, and rare biotite JEOL JXA-8100 electron microprobe at Gyeongsang (Figure 5(f)). Plagioclase grains are mostly subhedral and National University, Korea, with an accelerating voltage of locally form framework structures with interstitial quartz 15 kV and a beam current of 10 nA. The beam diameter aggregates (Figure 5(g)); such a microstructure is interpreted was typically 5 μm, but a wider beam of 10 μm was used for to denote the presence of former melts crystallized into the analyzing feldspars to minimize the loss of Na. Analytical leucosome [48]. In addition, equant plagioclase grains together errors are generally less than 2%. Data acquisition and with irregular morphology of quartz suggest minor influence of reduction were performed using the ZAF (Z, atomic number; postsolidification strain [8]. Hornblende-rich segregations A, X-ray absorption; and F, secondary fluorescence effects) consist of megacrystic hornblende (up to ~1.5 cm in the maxi- calculation for the matrix correction. Representative analyses mum dimension) together with medium-grained plagioclase for amphibole and plagioclase are given in Tables 1 and 2. and quartz. Representative samples of amphibolite, leucosome, mela- The melanosomes are generally enriched in hornblende nosome, and hornblende segregation were analyzed for together with minor plagioclase and quartz. Hornblende is major and trace elements in order to determine geochemical subhedral to anhedral and commonly contains quartz inclu- variations during the melting. Samples were crushed to sions; its grain size ranges from a few millimeters to ~2 cm, sig- millimeter-sized fragments and then ground in a tungsten nificantly greater than that of the amphibolite (Figure 5(h)). carbide ring mill to powders less than 125 μm in size. Major

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SSE NNW

(a) (b)

Leucosome

Melanosome

(e) (f)

Figure 3: Outcrop photographs of the gneisses and migmatitic amphibolites. (a) Highly deformed Buncheon granitic gneiss showing augen-like feldspars mantled by fine-grained biotite aggregates. (b) Diatexitic metasedimentary gneiss containing granitic leucosomes and ellipsoidal psammitic schollens. Pen for scale is 14 cm long. (c) Layer-parallel and discordant leucosomes in the amphibolite, which appear to be continuous. The collapse structure (circle) in which the layers are “sucked” into interboudin partitions reflects the melt loss at this site. (d) In situ leucosome associated with hornblende-rich melanosome. (e) Tonalitic leucosomes developing at dilational sites (triangles) in conjunction with other leucosomes subparallel to the foliation. (f) Strongly attenuated leucosomes in association with mafic layers which are locally folded and boudinaged.

elements were determined on the fused lithium tetraborate 5.2. Mineral Chemistries and P-T Conditions (Li2B4O7) glass beads using a Panalytical Axios Advanced wavelength dispersive X-ray ﬂuorescence spectrometry 5.2.1. Calcic Amphibole. The analyzed amphiboles are mostly – (XRF) at Activation Laboratories (Actlabs), Canada. Trace magnesiohornblende with an Si value of 6.93 7.27 a.p.f.u. X ½ ð Þ and rare-earth elements were measured using a PerkinElmer (atoms per formula unit) and Mg = Mg/ Mg + Fetotal of Sciex ELAN 9000 inductively coupled plasma-mass spec- 0.51–0.60, according to the nomenclature of Leake et al. trometry (ICP-MS) at the Actlabs. Analytical uncertainties [50]; those from the segregation domain (Figure 4(e)) lie are in the range of 1–3%. Representative compositions of in the ﬁeld of ferrohornblende with lower Si (6.53–6.66 X – amphibolite, leucosome, melanosome, and hornblende a.p.f.u.) and Mg (0.39 0.42; Figure DR1). These segregation are listed in Table 3. hornblendes are mostly homogenous, although the

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SSE NNW SSE Amphibolite NNW

Leucosome

S 1 10 cm (a) (b) SSE NNW Hornblende-rich segregation

Hornblende segregation S1

Pegmatite

(e) (f)

Figure 4: Outcrop photographs and a sketch of migmatitic amphibolites. (a) Leucosomes generally oriented parallel to major foliation and concentrated at boudin necks or along conjugate extensional shear bands. (b) Line drawing of (a); leucosome melts accommodated along the ﬂ ﬂ shear band as well as the foliation (S1). The lack of melanosomes is indicative of uid- uxed melting. (c) Poikilitic hornblende megacrysts of leucosome in the absence of melanosome. (d, e) Hornblende-rich segregation, inferred to be residual after melt extraction. (f) Undeformed pegmatitic patches or dykes transecting thin leucosome layers subparallel to penetrative foliation (S1) of amphibolite. Metasomatic alteration bands are present at the margin of pegmatitic dyke.

hornblende cores in the amphibolite could be slightly lower in the amphibolite, plagioclase grains are commonly zoned, with X – – Mg (0.51 0.60) but higher in Ti content (0.07 0.13 a.p.f.u.) the An content decreasing towards the rim (Figure DR2). than those of the rims (0.55–0.60 and 0.04–0.11 a.p.f.u., The rim compositions are compatible with those of the respectively). leucosome, probably reﬂecting the reequilibration during the cooling. Plagioclase grains of the leucosome are mostly 5.2.2. Plagioclase. The analyzed compositions of plagioclase homogeneous and contain less An than those of the show distinctive compositional ranges (Figure DR2); the melanosome (Figure DR2). Such a relationship is consistent anorthitecontentsinamphiboliteareintherangeofAn47–57, with the anatectic origin of leucosomes [51, 52]. It is further intermediate between those of melanosome (An52–59)and noted that An content (An30–55) of plagioclase inclusions leucosome (An43–47). On the other hand, the orthoclase within large biotite poikiloblasts is the most variable among contents are highly variable and range from Or4 to Or25.In the analyzed grains.

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500 �m 250 �m

(a) (b)

(e)

200 �m 500 �m

100 �m 500 �m

(e) (f)

500 �m 500 �m

(g) (h)

Figure 5: Representative photomicrographs showing various microstructures in migmatitic amphibolites. (a) Granoblastic texture consisting of fine-grained hornblende and plagioclase. (b) Quartz-filled melt pools interstitial to the corroded grains of hornblende and plagioclase. (c) Former melt films represented by quartz grains tapering along the hornblende-hornblende boundaries. Note the rounded and resorbed nature of hornblende. (d) A large skeletal poikiloblast of rare biotite in amphibolite containing many inclusions of rounded hornblende and plagioclase. The area shown in a box is enlarged in (e). (e) Multiphase inclusion assemblage within biotite. Rounded grains of hornblende and plagioclase are mantled by interstitial quartz. (f) Poikilitic hornblende containing rounded plagioclase and quartz in tonalitic leucosome. (g) Felsic domain of the same leucosome shown in (f), represented by the framework of plagioclase and quartz in the matrix of fine-grained quartz. (h) Hornblende-rich melanosome showing the vermicular shape of interstitial quartz. Images (a), (b), (c), (e), and (g) are from cross-polarized light; (d), (f), and (h) from plane-polarized light. Abbreviations: Bt: biotite; Hbl: hornblende; Pl: plagioclase; and Qz: quartz.

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Table 1: Representative analyses of amphiboles.

Hornblende Amphibolite Melanosome Leucosome accumulation OBA-02A OBA-02A OBA-02A OBA-02A OBA-02A OBA-02A UJ-03 UJ-03 UJ-03 OBA-04m OB-01L OBA-03 § Incl .inBt Matrix Matrix Matrix Matrix core Matrix core Matrix core Matrix rim Matrix rim Matrix rim Matrix core Matrix rim average average average average (n =8) (n =7) (n =9) (n =7)

SiO2 46.61 46.81 46.77 47.07 48.53 46.88 46.93 48.20 47.08 47.32 46.95 42.41

TiO2 1.10 1.08 0.98 0.79 0.37 0.94 1.11 0.71 0.83 0.59 0.81 0.48

Al2O3 8.34 8.47 8.41 8.56 7.18 8.36 8.16 7.58 8.23 7.90 8.81 10.81 ∗ FeO 15.24 15.17 15.47 14.70 14.04 14.91 15.37 14.19 15.00 16.20 15.01 19.49 MnO 0.33 0.36 0.38 0.23 0.30 0.32 0.30 0.30 0.31 0.31 0.33 0.42 MgO 10.72 10.83 10.68 10.84 11.65 10.63 10.84 11.26 10.94 10.34 10.56 7.48 CaO 11.52 11.44 11.50 11.89 12.03 11.59 11.31 11.94 11.66 11.45 11.68 11.47

Na2O 0.99 0.96 0.89 0.91 0.78 1.04 1.04 0.79 0.93 0.81 0.86 1.61

K2O 0.57 0.63 0.56 0.45 0.24 0.56 0.60 0.44 0.51 0.47 0.55 1.41 F 0.00 0.00 0.26 0.00 0.08 0.11 0.19 0.08 0.17 0.11 0.08 1.09 Cl 0.04 0.04 0.07 0.07 0.06 0.03 0.05 0.05 0.05 0.06 0.05 0.04 O = F, Cl -0.01 -0.01 -0.12 -0.01 -0.05 -0.05 -0.09 -0.04 -0.08 -0.06 -0.04 -0.47 Total 95.45 95.78 95.83 95.50 95.21 95.31 95.81 95.49 95.63 95.51 95.65 96.24 Cations per 23 oxygens (O, F, and Cl) Si 7.02 7.02 7.02 7.22 7.27 7.08 7.04 7.22 7.07 7.13 7.05 6.62 Ti 0.13 0.12 0.11 0.08 0.04 0.11 0.13 0.08 0.09 0.07 0.09 0.06 Al 1.48 1.50 1.49 1.34 1.27 1.49 1.44 1.34 1.46 1.40 1.56 1.99 Fe3+ 0.10 0.15 0.19 0.00 0.00 0.00 0.17 0.00 0.08 0.19 0.03 0.06 Fe2+ 1.82 1.75 1.76 1.78 1.76 1.88 1.76 1.78 1.80 1.86 1.86 2.48 Mn 0.04 0.05 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.06 Mg 2.41 2.42 2.39 2.51 2.60 2.39 2.42 2.51 2.45 2.32 2.37 1.74 Ca 1.86 1.84 1.85 1.92 1.93 1.87 1.82 1.92 1.88 1.85 1.88 1.92 Na 0.29 0.28 0.26 0.23 0.23 0.31 0.30 0.23 0.27 0.24 0.25 0.49 K 0.11 0.12 0.11 0.08 0.05 0.11 0.11 0.08 0.10 0.09 0.11 0.28 F 0.00 0.00 0.13 0.00 0.04 0.06 0.09 0.04 0.04 0.03 0.02 0.27 Cl 0.01 0.01 0.02 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.00 Total 15.26 15.25 15.36 15.25 15.24 15.34 15.34 15.24 15.29 15.21 15.26 15.96 Mg/ðÞ Mg + Fe 0.56 0.56 0.55 0.57 0.60 0.56 0.56 0.59 0.58 0.56 0.56 0.41 Lithosphere § Note: Mineral abbreviation: Bt: biotite. ∗Total Fe as FeO. Fe3+ and Fe2+ calculated on the basis of 13 cations excluding Ca, Na, and K. Incl. = inclusion. Lithosphere 9

Table 2: Representative analyses of plagioclase.

Amphibolite Leucosome Melanosome UJ-03 OBA-02A UJ-03 ∗ OB-01L OBA-04m (Incl . in Bt) Core average Rim average Average Core Core Core Rim Rim Rim Core Rim Core Rim (n =8) (n =10) ðÞn =5

SiO2 53.67 54.96 55.33 54.67 58.33 59.07 53.17 54.81 54.31 57.36 56.12 56.17 53.21

Al2O3 28.97 27.82 27.79 27.71 25.75 25.51 29.33 28.02 28.40 26.32 27.57 27.48 29.52 CaO 11.76 10.49 10.54 10.49 7.77 7.33 11.92 10.23 11.12 8.53 9.76 9.65 11.77

Na2O 5.11 5.78 5.87 5.67 7.56 7.59 4.68 5.64 5.45 6.94 6.13 6.18 4.92

K2O 0.03 0.05 0.09 0.06 0.04 0.04 0.05 0.04 0.04 0.05 0.06 0.06 0.04 Total 99.54 99.09 99.62 98.60 99.45 99.54 99.14 98.74 99.31 99.20 99.64 99.55 99.46 Cations per 8 oxygens Si 2.44 2.50 2.50 2.50 2.62 2.65 2.42 2.50 2.47 2.59 2.53 2.53 2.42 Al 1.55 1.49 1.48 1.49 1.37 1.35 1.57 1.50 1.52 1.40 1.47 1.46 1.58 Ca 0.57 0.51 0.51 0.51 0.37 0.35 0.58 0.50 0.54 0.41 0.47 0.47 0.57 Na 0.45 0.51 0.52 0.50 0.66 0.66 0.41 0.50 0.48 0.61 0.54 0.54 0.43 K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 5.01 5.01 5.01 5.01 5.02 5.01 4.99 5.00 5.01 5.01 5.00 5.01 5.01 An 0.56 0.50 0.50 0.50 0.36 0.35 0.58 0.50 0.53 0.40 0.47 0.46 0.57 Ab 0.44 0.50 0.50 0.50 0.64 0.65 0.41 0.50 0.47 0.59 0.53 0.54 0.43 Or 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ∗ Note: Mineral abbreviation: Bt: biotite. Incl.: inclusion. An = Ca/M, Ab = Na/M, and Or = K/M, where M=ðCa + Na + KÞ.

P T ½ ð ∗Þ – 5.2.3. - Conditions. The Okbang amphibolite has garnet- number = Mg/ Mg + Fe and TiO2 content are 0.2 0.5 free assemblages of high variance, hampering any attempt and 0.6–2.0 wt.%, respectively. Their compositions mostly for precise determination of P-T conditions. Nevertheless, belong to gabbro and gabbroic diorite in the total alkali we estimated the P - T conditions using the hornblende–pla- vs. silica diagram [61] and are plotted in the tholeiitic field gioclase geothermometer [53, 54] in combination with the on the AFM diagram [62]. In contrast, leucosomes are – – hornblende plagioclase quartz geobarometer governed by rich in silica (>70 wt.% SiO2) and weakly metaluminous A : – : – a net-transfer reaction, tremolite + tschermakite + 2 albite = ( /CNK = 0 80 0 98); their Na2O (3.0 3.6 wt.%) contents – 2 pargasite + 8 quartz [55]. The result using the compositions are higher than K2O (0.2 0.5 wt.%). Relative to amphibolites, P T – of hornblende-plagioclase cores gives the - range of 4.6 leucosomes are enriched in SiO2,Al2O3, and Na2O contents – ° ∗ 5.2 kbar and 650 730 C (Figure DR3), which is consistent but depleted in TiO2,Fe2O3 , MgO, and CaO (Table 3). with P - T conditions of previous studies determined from Major element concentrations of leucosomes are similar to cordierite-bearing metapelitic assemblages in the northern those of melts derived from wet melting of amphibolites Yeongnam Massif [34, 41]. Our P - T estimates are also and dioritic rocks (Figure 6; [15, 23]). Melanosomes have fi ∗ consistent with those of wet solidus in ma c rocks based similar TiO2, CaO, and K2O but higher Fe2O3 +MgO on the pseudosection modeling [56] or experimental abundances compared to amphibolites (Figure 6). calibrations [11, 14, 57, 58]. In contrast, dehydration melting The compositions of leucosomes fall into the tonalite of amphibole occurs at temperatures higher than ~850°C, field on normative An-Ab-Or diagram (Figure 7) and are yielding anhydrous peritectic phases such as orthopyroxene compatible with those of partial melts experimentally pro- or clinopyroxene [13, 14, 56, 59]. Such anhydrous minerals duced by fluid-present melting of tholeiitic basalt [63]. Our are absent in the Okbang amphibolite, whereas hornblende leucosome compositions are also comparable to those of melt ubiquitously occurs in the leucosome. Hence, we conclude patches derived from the fluid-present melting of amphibo- that tonalitic leucosomes in the amphibolite were produced lites in the Gyeonggi Massif and western Shandong Province, by fluid-present melting at midcrustal conditions. China (6; [24]). In contrast, a series of phase equilibria modeling with a minimal amount of fluid suggests that the fi 5.3. Whole-Rock Geochemistry partial melting of ma c rocks yields granitic melts at relatively low temperatures (Figure 7; [13]). Thus, fluid- 5.3.1. Major and Trace Elements. The amphibolites, deficient open-system melting cannot account for tonalitic leucosomes, and melanosomes generally show linear melts of the Okbang amphibolite. relationships in major element contents (Figure 6). The On the primitive mantle-normalized spider diagram, the compositions of three amphibolites together with those of amphibolites are characterized by negative Nb-Ta anomalies, previous studies [28, 60] are in the range of 48–53 wt.% together with weak Zr, Hf, and Ti anomalies (Figure 8(a)). – – SiO2, 12.2 14.7 wt.% Al2O3, and 6.8 11.8 wt.% CaO; the Mg Hornblende-free leucosomes are enriched in Sr compared

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Table 3: Representative whole-rock analyses of migmatitic amphibolites.

Hornblende Amphibolite Melanosome Leucosome segregation OB-01P OB-02P UJ03 OBA-04m OBA-05m OB-01L OB-02L OB-03L OBA-05L OBA-03 Major elements (wt.%)

SiO2 51.38 51.15 51.38 50.40 45.20 75.41 75.61 72.65 76.39 42.16 TiO2 0.75 0.78 0.68 0.42 0.90 0.09 0.01 0.02 0.04 0.34

Al2O3 13.81 13.90 14.27 7.42 11.22 13.66 15.09 14.29 13.74 10.55

 Fe2O3 12.87 12.96 12.26 17.10 21.06 1.53 0.10 0.33 0.65 15.37 MnO 0.20 0.19 0.20 0.27 0.56 0.03 0.00 0.01 0.02 0.28 MgO 7.51 7.25 7.34 10.27 8.16 0.88 0.06 0.18 0.24 5.13 CaO 10.90 11.16 10.58 11.00 10.40 5.32 5.34 6.82 4.56 18.37

Na2O 1.76 1.55 2.20 0.72 1.57 2.95 3.31 3.04 3.63 1.52

K2O 0.31 0.45 0.50 0.42 0.77 0.16 0.17 0.51 0.40 1.05

P2O5 0.07 0.07 0.06 0.03 0.06 0.02 0.21 0.26 0.01 0.04 § LOI 0.56 0.84 0.78 0.76 0.64 0.34 0.35 1.51 0.87 4.77 Total 100.12 100.30 100.25 98.81 100.54 100.39 100.25 99.62 100.55 99.58 Mg# 0.37 0.36 0.37 0.38 0.28 0.37 0.38 0.35 0.27 0.25 Trace elements (ppm) V 284.00 281.00 269.00 174.00 447.00 32.00 5.00 5.00 12.00 327.00 Cr 90.00 80.00 170.00 90.00 30.00 30.00 20.00 20.00 20.00 30.00 Co 73.00 68.00 70.00 69.00 72.00 132.00 75.00 71.00 142.00 106.00 Ni 80.00 80.00 100.00 100.00 100.00 20.00 20.00 20.00 20.00 260.00 Cu 90.00 200.00 20.00 20.00 10.00 10.00 10.00 10.00 10.00 10.00 Zn 80.00 90.00 90.00 130.00 380.00 30.00 30.00 30.00 30.00 250.00 Ga 15.00 15.00 15.00 12.00 20.00 11.00 14.00 12.00 11.00 21.00 Sn 2.00 2.00 11.00 14.00 161.00 2.00 1.00 1.00 5.00 53.00 Cs 0.50 0.80 0.90 0.50 1.80 0.50 1.10 2.40 1.80 1.50 Rb 12.00 13.00 13.00 9.00 41.00 5.00 7.00 36.00 44.00 43.00 Ba 25.00 31.00 20.00 10.00 34.00 17.00 34.00 51.00 28.00 49.00 Th 0.60 1.00 0.20 0.50 0.40 0.20 0.30 0.50 0.10 0.50 U 0.20 0.20 0.50 0.70 0.60 0.40 0.80 1.20 0.10 0.70 Nb 2.00 2.00 2.00 2.00 4.00 1.00 1.00 1.00 1.00 8.00 Ta 0.10 0.10 0.30 0.60 0.70 0.20 0.10 0.10 0.10 0.70 Pb 5.00 5.00 10.00 5.00 7.00 12.00 11.00 14.00 19.00 7.00 Sr 91.00 101.00 79.00 15.00 31.00 109.00 152.00 117.00 145.00 51.00 Pb 305.49 305.49 261.85 130.93 261.85 87.28 916.48 1134.69 43.64 174.57 Nd 6.00 6.40 8.20 5.40 13.40 2.30 1.20 1.80 0.60 14.50 Hf 1.10 1.30 1.10 0.90 1.50 0.40 0.30 0.30 0.20 1.10 Zr 44.00 48.00 42.00 27.00 43.00 17.00 10.00 11.00 11.00 23.00 Ti 3000.00 3120.00 2720.00 1680.00 3600.00 360.00 40.00 80.00 160.00 1360.00 Y 17.00 17.00 19.00 16.00 40.00 5.00 1.00 2.00 1.00 76.00 Rare earth elements (ppm) La 3.70 4.20 5.30 4.00 6.70 2.10 2.40 2.80 2.90 4.40 Ce 8.70 9.40 13.20 9.30 18.60 4.10 3.50 4.80 2.90 15.90 Pr 1.26 1.33 1.84 1.24 2.82 0.53 0.32 0.52 0.16 2.74 Nd 6.00 6.40 8.20 5.40 13.40 2.30 1.20 1.80 0.60 14.50 Sm 2.00 2.00 2.50 1.60 4.30 0.70 0.30 0.50 0.20 6.50 Eu 0.69 0.73 0.70 0.54 1.12 0.40 0.42 0.39 0.45 0.77 Gd 2.50 2.60 2.90 2.10 5.40 0.90 0.30 0.50 0.20 9.80

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Table 3: Continued.

Hornblende Amphibolite Melanosome Leucosome segregation OB-01P OB-02P UJ03 OBA-04m OBA-05m OB-01L OB-02L OB-03L OBA-05L OBA-03 Tb 0.50 0.50 0.50 0.40 1.10 0.20 0.10 0.10 0.10 2.10 Dy 3.00 3.20 3.40 2.50 6.90 1.00 0.20 0.40 0.20 13.50 Ho 0.60 0.60 0.70 0.50 1.40 0.20 0.10 0.10 0.10 2.40 Er 1.80 1.80 1.90 1.60 3.90 0.50 0.10 0.20 0.10 6.40 Tm 0.27 0.27 0.28 0.24 0.61 0.07 0.05 0.05 0.05 0.97 Yb 1.80 1.80 1.80 1.60 4.00 0.50 0.10 0.10 0.10 6.70 Lu 0.29 0.29 0.28 0.26 0.62 0.07 0.01 0.01 0.01 1.03 ∗ Eu/Eu 0.94 0.98 0.79 0.90 0.71 1.54 4.28 2.38 6.88 0.29

1.39 1.58 1.99 1.69 1.13 2.84 16.22 18.92 19.60 0.44 La(N)/Yb(N)

 § Total Fe as Fe2O3. LOI: loss on ignition.

to the amphibolite, but depleted in Rb; in contrast, (UJ03), leucosome (OB-01L), pegmatitic dyke (UJ03-3), hornblende-bearing leucosomes are enriched in Rb. High Buncheon granitic gneiss (BCG-1), migmatitic gneiss (WN-1), Sr/Rb in the former indicates the prevalence of feldspar over and biotite-sillimanite gneiss (WN-2); the latter two are from mica participating in the melting reaction [64]. High field- the metasedimentary rock unit (Figure 2). Conventional heavy strength elements (HFSE) such as Zr, Hf, and Ti are generally liquid and hand picking techniques were used for the separa- enriched in melanosomes and hornblende-rich segregations tion, and zircon grains were mounted on a 25.4 mm epoxy disk compared to amphibolites, suggesting the accumulation of together with FC1 zircon standard (1099 Ma; [68]). The mount accessory phases in restites during melt extraction. In con- was ground and polished to expose the approximate centers of trast, the leucosomes have the lowest HFSE concentrations zircon grains. Cathodoluminescence (CL) images of individual and are depleted in other trace elements such as Y, Sn, V, grains were obtained using a JEOL JSM 6380 scanning elec- Cr, and Ni, which are generally partitioned into ferromagne- tron microscope at the School of Earth and Environmental sian minerals (Table 3). Sciences, Seoul National University. In situ U-Pb zircon ages were obtained using a SHRIMP housed at the Korea Basic Sci- 5.3.2. Rare Earth Elements. The analyzed amphibolites ence Institute (KBSI). The analytical protocol for zircon fol- yielded a relatively flat REE pattern at ~10–20 times lows routine procedures described by Williams [69]. All chondrite, with a slight LREE enrichment (Figure 8(b); – isotopes were acquired using a negative ion oxygen (O ) La /Sm =1:16 – 1:33) and small negative Eu anomalies 2 N N beam. The primary oxygen beam was 4–6 nA in intensity ½ðEu/Eu ∗Þ =Eu /√½ðSm Þ/ðGd Þ =0:79 – 0:98. Such a N N N N and ~25 μm in diameter. The measured Pb/U and Pb/Th result is consistent with that of previous studies, suggesting ratios were corrected using the reference zircon FC1. The that protolith of the amphibolite was a tholeiitic basalt abundances of U, Th, and Pb were normalized to the value (Figure 8(b); [28]). The leucosomes are typified by fraction- – (U = 238 ppm) of standard zircon SL13. The common Pb con- ated REE patterns with (La/Yb)N of 2.84 19.60 and positive 204 Eu anomalies (Eu/Eu ∗ =1:54 – 6:88; Figure 8(b)). The tributions were corrected using the measured Pb amount latter, together with the Sr enrichment (Table 3), is compat- and the model common Pb composition [70]. The Squid 2 ible with the plagioclase accumulation (Figure 5(g)). In and Isoplot/Ex softwares [71, 72] were used for the age calcu- contrast, hornblende segregations are characterized by lation and data evaluation, respectively. Individual spot analy- 207 206 σ slightly convex-upward middle REE and pronounced nega- ses and weighted mean Pb/ Pb ages are quoted at 1 and σ fi tive Eu anomaly (Eu/Eu ∗ =0:29); both of which are diag- 2 con dence levels, respectively. Analyses with large uncer- nostic of hornblende crystals precipitating from tonalitic tainty (>10%) and discordance (>5%) were discarded in the melt [65, 66]. Hence, the segregation is best interpreted as age calculation. hornblende-rich restite that has trapped a small amount of After completing the U-Pb analyses, the same zircon melt [67]. Melanosomes, similar to the amphibolite, yielded amounts were used for in situ Hf analyses employing a Nu relatively flat REE patterns and weak negative Eu anomalies Plasma II MC-ICPMS combined with a 193 nm ArF excimer (Eu/Eu ∗ =0:71 – 0:90; Figure 8(b)). laser ablation system housed at the KBSI. Hf isotopic compositions of zircon were measured on top of the U-Pb analytical 6. U-Pb and Hf Isotopic Compositions of Zircon pit (Figures 9(a)–9(c)). The ablation time for each analysis was ~60 s, with a 5 Hz repetition rate, and the beam diameter was 6.1. Analytical Methods. Zircon grains for the U-Pb isotopic ~50 μm. Lu and Yb isotopic compositions, employed for analyses were separated from six samples: amphibolite the correction of mass bias and isobaric interference, were

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18 2.0

16 1.6 14

12 1.2 3 2 O 2 TiO Al 10 0.8

8 0.4 6

4 0 40 50 60 70 80 40 50 60 70 80 (a) (b) 30 20

18 25 16

20 14

+ MgO 15 ⁎ 3 CaO 10 O 2

Fe 10 8 6 5 4

0 0 40 50 60 70 80 40 50 60 70 80 (c) (d) 4.0 1.6

3.5 1.4

3.0 1.2

2.5 1.0 O O 2 2.0 2 0.8 K Na 1.5 0.6

1.0 0.4

0.5 0.2

0 0 40 50 60 70 80 40 50 60 70 80 SiO2 (wt.%) SiO2 (wt.%) Amphibolite Hbl segregation Leucosome Amphibolite Melanosome (Chang et al. 1993; Arakawa et al. 2003) (e) (f)

Figure 6: Major element compositions of amphibolites, melanosomes, leucosomes, and a hornblende (Hbl) segregation, plotted in the Harker diagram. Also shown are the compositions of amphibolites reported by Chang et al. [60] and Arakawa et al. [28]. The short- [23] and ﬁ ﬁ long-dashed [15] elds denote the compositions of leucosomes derived from H2O-present melting of ma c igneous rocks.

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Winther (1996) Lee and Cho (2013) Yakymchuk et al. (2019)

1000°c

Tonalite

Granodiorite Granite Solidus (~800°c) Stuck and Diener, 2018

Trondhjemite Ab Or Amphibolite + Hbl segregation Leucosome Amphibolite Melanosome (Chang et al. 1993; Arakawa et al. 2003)

Figure 7: Normative An-Ab-Or diagram for the analyzed compositions of amphibolites, leucosomes, melanosomes, and a hornblende (Hbl) segregation. Also shown are the compositional ﬁelds of experimental [63] and natural [6, 24] melts produced by the ﬂuid-present melting of amphibolite. Four arrows denote the relative changes in modal proportions of An, Ab, and Or with decreasing temperature for the dehydration melting of several amphibolites [13]. An = 100 ∗ Ca/ðNa + K + CaÞ, Ab = 100 ∗ Na/ðNa + K + CaÞ, Or = 100 ∗ K/ðNa + K + Ca Þ, An: anorthite; Ab: albite; and Or: orthoclase.

adopted from Vervoort et al. [73] and Chu et al. [74], shape with aspect ratios ranging from 1 to 1.5 (Figure 9(a)). respectively. Isobaric interference-corrected 176Hf/177Hf ratios Most grains have broad-banded or irregular CL zoning and were exponentially normalized to 179Hf/177Hf = 0:7325 [75]. are devoid of an overgrowth rim. Uranium concentrations Zircon 91500 and FC1 were used as standards with recom- and Th/U ratios of zircon range from 172 to 335 ppm and mended 176Hf/177Hf ratios of 0:282306 ± 8 and 0:282184 ± 0.16 to 0.34, respectively, corroborating an igneous origin 16,respectively[76,77].The176Lu/177Hf and 176Yb/177Hf ([84]; Table DR1). A few zircon grains develop thin dark- ratios were calculated after Iizuka and Hirata [78] and CL rims which are apparently homogeneous without pores used for estimating initial 176Hf/177Hf isotopic ratios and or inclusions (<30 μm; Figure 9(a)), suggesting that these ½ðε Þ ½ð176 177 Þ rims have overgrown primary zircons during the melt corresponding initial epsilon Hf Hf = Hf/ Hf sample /ð176Hf/177HfÞ – 1 ×104 values and Hf model ages. crystallization [85]. The U contents of zircon rims are in chondrite the range of 205–2431 ppm, and their Th/U ratios vary Analytical results were monitored on 176Yb/177Hf and 176 177 from 0.07 to 0.23. Twelve spot analyses of magmatic Lu/ Hf ratios in order to check isobaric interferences from 207 206 ε ð Þ zircons yielded a weighted mean Pb/ Pb age of 1866 ± Yb and Lu, respectively. Initial Hf t values and model ages : T 176 : 4Ma (MSWD = 0 58; Figure 10(a)), whereas three analyses ( DM1) were calculated using a Lu decay constant of 1 865 : −11 −1 of dark-CL rims gave 1861 ± 3 Ma (MSWD = 0 27; ×10 y [79] together with depleted mantle Figure 10(a)). The latter is interpreted as the time of zircon 176 177 : 176 177 : ( Lu/ Hf = 0 0384, Hf/ Hf = 0 28325) and chondritic precipitation from the melt. 176 177 : 176 177 : ( Lu/ Hf = 0 0332, Hf/ Hf = 0 282772) values of Zircons from the tonalitic leucosome (OB-01L) are ﬃ Gri n et al. [80] and Blichert-Toft and Albarède [81], respec- ~100–200 μm in size and have subhedral to anhedral with T tively. Two-stage model ages ( DM2) were calculated with ref- aspect ratios ranging from 1.5 to 2.5 (Figure 9(b)). They have erence to the parameters suggested for lower crust irregular or broad-banded zoning with dark-CL cores and (176Lu/177Hf = 0:0187; [82]) and depleted mantle oscillatory-zoned or structureless overgrowth rims; the cores (176Lu/177Hf = 0:0384; [83]). contain high U, reaching up to 4548 ppm (Table DR1). Th/U ratios of the rims are limited to the range of 0.04–0.06 6.2. Zircon Morphologies and U-Pb Ages. Zircon grains from (Table DR1). The weighted mean 207Pb/206Pb age of twelve the amphibolite (UJ03) are ~50–200 μm in size and stubby in rims, excluding three analyses possibly aﬀected by Pb loss or

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1000

100

1 Sample/primitive mantle

0.1

0.01 Rb Ba T U Nb Ta K La Ce Pr Sr P Nd Hf Zr Ti Dy Y Yb Lu (a) 100

Hbl-bearing Sample/chondrite 1

0.1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Amphibolite Hbl segregation Leucosome Amphibolite Melanosome (Arakawa et al., 2003). (b)

Figure 8: (a) Primitive mantle-normalized [139] trace element and (b) Chondrite-normalized [140] rare earth element (REE) diagrams of the analyzed samples. Gray ﬁelds represent the compositional ranges of the Okbang amphibolite, based on Arakawa et al. [28]. Hbl: hornblende.

inherited core component, is 1862 ± 2 Ma (MSWD = 0:96; of crystallization. Many zircon analyses show a slightly Figure 10(b)), corresponding to the time of melt crystallization. reverse discordance which is attributable to the site- Zircon grains from undeformed pegmatitic dyke (UJ03-3) specificmatrixeffect on damaged, metamict, and high-U are euhedral or subhedral and relatively large (up to ~500 μm; zircons with unsupported radiogenic Pb [87]. Nevertheless, Figure 9(c)). Their aspect ratios range from ~1.5 to 3.0. Most the 207Pb/206Pb ages estimated from reverse discordant grains show homogeneous CL features with high U contents analyses are consistent with concordant ages [88]. (2382–8938 ppm), and their Th/U ratios are below 0.01 Zircon grains from the granitic gneiss (BCG-1) are (Table DR1). These high-U zircons generally yield older ~50–200 μm in size and euhedral to anhedral with aspect than true 206Pb/238U ages owing to the machine-induced ratios of 1.0–2.5 (Figure 9(d)). Their CL images are often bias related to metamictization of grains, but the 207Pb/206Pb homogeneous or reveal broad-banded and oscillatory ages are unaffected by high-U bias [86]. The weighted mean zones. Zircon grains contain mineral inclusions such as 207Pb/206Pb age of five grains, excluding two spot analyses quartz and thorite associated with some pores, probably affected by possible inheritance or Pb loss, is 1852 ± 5 Ma resulting from fluid-induced recrystallization [89]. The (MSWD = 2:5; Figure 10(c)) which is interpreted as the time analyzed magmatic zircons have variable U contents

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Amphibolite (UJ03) 1864±7 Ma 1865±7 Ma 1862±7 Ma 1869±7 Ma

4.7 4.9 6.0 5.0

1862±2 Ma

(a)

Leucosome (OB-01L) 1874±4 Ma 1858±4 Ma 1859±4 Ma 1860±4 Ma

1.8 0.5 0.6 1.7

(b) Pegmatitic dyke (UJ03-3) 1855±3 Ma 1851±3 Ma 1857±2 Ma 1850±2 Ma

–3.5 –2.9 –4.7 –2.8

1900±5 Ma 1983±4 Ma 1975±5 Ma (d)

Migmatitic gneiss (WN-1) 1858±5 Ma 1859±5 Ma 1863±6 Ma

2664±20 Ma 2500±20 Ma 1862±5 Ma 2692±19 Ma (e) Biotite-sillimanite gneiss (WN-2) 2562±21 Ma 2300±7 Ma 2366±4 Ma

1856±8 Ma

2486±4 Ma (f)

Figure 9: Representative cathodoluminescence images of zircon grains from six analyzed samples: (a) UJ03, (b) OB-01L, (c) UJ03-3, (d) 207 206 ε ð Þ BCG-1, (e) WN-1, and (f) WN-2. The Pb/ Pb age and Hf t value of individual analytical spots, denoted by solid and dotted circles, respectively, are given. Scale bar is 100 μm. (967–4673 ppm) and Th/U ratios (0.17–0.41; Table DR1). Th/U ratios of 0.04–0.05. The recrystallized domains In contrast, recrystallized domains have low Th (38–127) yielded 207Pb/206Pb dates varying from 1953 ± 4 Ma to and moderate U (1102–3024 ppm) contents, yielding low 1900 ± 5 Ma (Figure 10(d)) and were excluded for further

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0.120 0.119 Amphibolite (UJ03) Leucosome (OB-01L)

0.118 1920 Core: Weighted mean Pb-Pb age (n = 12) 0.117 1866 ± 4 Ma (MSWD = 0.58) 1900 0.116 0.115

Pb 1880 1880 206 0.114

Pb/ 1860

207 0.113 1840 0.112 1840

0.111 1820 0.110 Rim: Weighted mean Pb-Pb age (n = 3) Weighted mean Pb-Pb age (n = 12) 1861 ± 3 Ma (MSWD = 0.27) 1800 1862 ± 2 Ma (MSWD = 0.96) 1800 0.108 0.109 2.7 2.8 2.9 3.0 3.1 2.6 2.7 2.8 2.9 3.0 3.1 3.2 (a) (b)

0.116 Pegmatitic dyke (UJ03-3) Granitic gneiss (BCG-1) 0.14 0.115 1880 Inherited core

0.114 2150 1860

Pb 0.13

206 0.113 Weighted mean Pb-Pb age (n = 12) 1981 ± 2 Ma Pb/ 2050 (MSWD = 0.68) 207 1840 0.112 0.12 1950 1820 0.111 Low T/U Weighted mean Pb-Pb age (n = 5) grains 1852 ± 5 Ma (MSWD = 2.5) 1850 0.110 0.11 2.6 2.8 3.0 3.2 3.4 2.2 2.6 3.0 3.4 3.8 (c) (d)

0.21 0.24 Migmatitic gneiss (WN-1) Biotite-sillimanite gneiss (WN-2) 2800 3000 0.19 0.20 0.17 2600 Inherited cores

Pb Inherited cores

206 2600

Pb/ 0.15 2400 0.16 207

2200 0.13 2200 2000 0.12 1800 0.11 Weighted mean Pb-Pb age (n = 8) 1800 Weighted mean Pb-Pb age (n = 2) 1861 ± 4 Ma (MSWD = 0.51) 1860 ± 9 Ma (MSWD = 0.39) 0.09 0.08 1.6 2.0 2.4 2.8 3.2 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 238U/206Pb 238U/206Pb (e) (f)

Figure 10: Tera-Wasserburg diagrams for the U-Pb zircon data of the analyzed samples. Dotted ellipses denote the spot analyses discarded for calculating the weighted mean age. The uncertainty in each spot analysis is shown as 1σ. MSWD: mean square of weighted deviates.

consideration. Excluding these six analyses, twelve spot Zircon grains from the migmatitic gneiss (WN-1) are analyses of magmatic zircons yielded a weighted mean typically ~70–200 μm in size with aspect ratios ranging from 207Pb/206Pb age of 1981 ± 2 Ma (MSWD = 0:68; Figure 10(d)) 1.5 to 2.0 (Figure 9(e)). The inherited cores are commonly which is interpreted as the time of magmatic crystallization. oscillatory zoned and overgrown by homogeneous or weakly

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Depleted mantle

10 North China Craton

5 2.0 Ga

(t) CHUR 0 Hf �

–5 2.5 Ga 177 Hf = 0.015 176 Lu/

–10

3.0 Ga –15 1500 1700 1900 2100 2300 2500 Age (Ma)

Amphibolite (UJ03) Pegmatite (UJ03-3) Leucosome (OB-01L) Kim et al. (2014), Lee et al. (2017)

Figure 207 206 ε ð Þ 11: Pb/ Pb age vs. Hf t plot of zircons from three analyzed samples of amphibolite, leucosome, and pegmatite. Zircon U-Pb ages ε ð Þ and Hf t values available from Paleoproterozoic gneisses of the Yeongnam Massif [32, 35] are also shown in gray diamonds. Gray envelope ε ð Þ represents the ranges in U-Pb ages and Hf t values of zircons compiled from igneous rocks of the North China Craton, including the Damiao gabbro-anorthosite suite [129–134]. Evolutionary path of the depleted mantle is based on 176Hf/177Hf and 176Lu/177Hf values of ﬃ ε ð Þ ﬃ Gri n et al. [83]. Three Hf t evolutionary paths at 3.0, 2.5, and 2.0 Ga were calculated using the Hf isotopic data of Gri n et al. [80]. CHUR: chondritic uniform reservoir.

zoned, dark-CL rims; such a microstructure is typical for meta- shown in Figure 11. Initial 176Hf/177Hf ratios of zircons from morphic overgrowth (e.g., [30, 90]). The inherited cores yielded the amphibolite (UJ03) are in the range of 0.281723– 207 206 ε ð Þ Pb/ Pb dates varying from 2717 ± 9 Ma to 2092 ± 4 Ma 0.281787, and their Hf t values range from 4.2 to 6.0, (Figure 10(e)). Th/U ratios of the cores range from 0.13 to when calculated using the weighted mean 207Pb/206Pb age. 1.03 except for one spot analysis, whereas those of the rims Depleted-mantle model ages and two-stage Hf model ages are are smaller than 0.01, suggesting metamorphic origin (e.g., in the range of 2.10–2.03 Ga and 2.22–2.13 Ga, respectively [84, 91]). Eight analyses of the rim yielded a weighted mean (Table DR2). In contrast, zircons from the leucosome (OB- 207Pb/206Pb age of 1861 ± 4 Ma (MSWD = 0:51;Figure10(e)) 01 L) have initial 176Hf/177Hf ratios (0.281629–0.281716) ε ð Þ – consistent with the time of leucosome crystallization. and Hf t values ( 0.1 to 3.5) smaller than those of UJ03. Zircons from the biotite-sillimanite gneiss (WN-2) are These leucosome zircons have depleted-mantle model ages typically ~100–200 μm in size with aspect ratios of 1.5–3.5 and two-stage Hf model ages of 2.27–2.14 Ga and 2.50– (Figure 9(f)). The inherited cores of zircon reveal oscillatory 2.29 Ga, respectively. Initial 176Hf/177Hf ratios of zircon from or patchy zoning and are rarely overgrown by homogeneous the pegmatitic dyke (UJ03-3) are in the range of 0.281544– 207 206 ε ð Þ – – dark-CL rims. The inherited cores yielded Pb/ Pb 0.281639, corresponding to Hf t values of 4.7 to 2.8, dates widely varying from 2700 ± 7 Ma to 2019 ± 5 Ma and reflect old crustal component inherited from the – – ε ð Þ (Figure 10(f)), suggesting that the depositional age of sed- metasedimentary host ( 11.9 to 6.1 Hf t ; [35]). Depleted- imentary protolith is younger than ~2.02 Ga. Th/U ratios mantle model ages and two-stage Hf model ages of of the cores range from 0.09 to 1.28 except for one analysis, pegmatite are in the range of 2.46–2.41 Ga and 2.75–2.64 Ga, whereas those of the rims are less than 0.01 (Table DR1). The respectively (Table DR2). weighted mean 207Pb/206Pb age of two rims, excluding one analysis affected by Pb loss, is 1860 ± 9 Ma (MSWD = 0:39; 7. Discussion Figure 10(f)). These results are consistent with those of fl migmatitic gneiss. 7.1. Evidence for Fluid-Present Melting. The H2O- uxed melting of mafic rocks is a fundamental process in the orogenic belt 6.3. Zircon Hf Isotopic Compositions. Hafnium isotopic com- where the development of crustal-scale shear zones or the positions of the analyzed zircons are listed in Table DR2 and underplating of arc-related magmas may lead to the

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infiltration of aqueous fluid into heated crust [26, 27]. The (Figures 5(b) and 5(c)). This melting episode is coeval with Okbang amphibolite, a product of mafic magmatism associ- the anatexis in leucosomes dated at 1862 ± 2 Ma. In addition, ated with the Paleoproterozoic orogeny in the Yeongnam the overgrowth rims of zircon in migmatitic gneiss and Massif [28, 29, 31], reveals various lines of evidence for biotite-sillimanite gneiss yielded weighted mean 207Pb/206Pb fl H2O- uxed melting associated with ductile deformation ages of 1861 ± 4 Ma and 1860 ± 9 Ma, respectively, coeval (Figures 2 and 3). Firstly, the leucosomes are typified by the with the melt crystallization in leucosomes (e.g., [101– presence of poikilitic hornblende megacrysts containing 103]). Such a timeline for partial melting and melt crystalliza- bleb-like inclusions of plagioclase, quartz, and rare biotite tion is consistent with that determined from the southern (Figure 4(c); [23]) in the absence of anhydrous peritectic Yeongnam Massif, where anorthositic-gabbroic magmatism phases. Such microstructural relationship is accounted for by and partial melting are well constrained at ~1.87–1.86 Ga fl fi an H2O- uxed melting reaction: hornblende1 + plagioclase + [33]. In particular, ma c rocks of the AMCG suite were quartz ± biotite + H2O = hornblende2 +melt. emplaced diachronously at 1870 ± 2 Ma and 1861 ± 6 Ma, This reaction is consistent with the melt-producing reac- respectively [32]. In contrast to migmatitic gneisses, the tion of Lappin and Hollister [92] and generally accompanied fingerprint of ~1.86 Ga anatexis is lacking in the Buncheon by a net decrease in volume with negative dP/dT slope [26, granitic gneiss, except for an array of apparently concordant 93]. In particular, negative reaction volume may lead to ten- zircons ranging from ~1.95 to 1.90 Ga (Figure 10(d)); similar sional microcracking that could facilitate local melt accumu- features were also documented by Kim et al. [42]. This scatter lation (Figure 3(e); [94]). Secondly, the occurrence of quartz in zircon ages is attributed to the relatively dry nature of the interstitial to the rounded grains of hornblende and plagio- Buncheon gneiss during the ~1.86 Ga melting event, yielding clase (Figure 5(b)–5(e)) corroborates the presence of excess incomplete Pb loss or thermal annealing of zircons crystal- fl uid during the melting because an increase in the H2O con- lized at 1981 ± 2 Ma. Thus, we suggest that the igneous tent of incipient melt may reduce the wetting angle [95, 96]. protolith of amphibolite was emplaced at ~1866 Ma and sub- Finally, hornblende-rich melanosomes or restites are volu- sequently metamorphosed at ~1862 Ma to yield partial melts metrically minor and locally present as narrow slivers along in the presence of excess fluid. Regional ductile deformation the leucosome margin (Figures 3(d) and 3(e)). These mela- likely ceased by 1852 ± 3 Ma, corresponding to the crystalli- fl nosomes are attributed to an H2O- uxed melting because zation age of pegmatitic dyke. Taken together, the protolith hornblende occurs as a peritectic phase in the absence of of the amphibolite was emplaced, solidified, and then affected other mafic phases (e.g., [25–27]). In addition, experimental by synkinematic fluid-present melting during a relatively studies suggest that peritectic amphiboles are stable for melt- short time interval at the terminal stage of a Paleoproterozoic fi ing in the ma c rocks, with a minimum H2O amount of hot orogeny. ~4 wt.% at 2 kbar or ~2.5 wt.% at 8 kbar [97, 98]. Gardien et al. [99] also reported that the addition of H2O into the melt 7.3. Petrogenesis of Tonalitic Leucosome. Tonalitic leuco- has stabilized the amphibole solid-solution. Thus, the pre- somes produced by partial melting of mafic igneous rocks dominance of peritectic hornblende in leucosomes is attrib- are common in high-temperature orogens, and such an ana- uted to the presence of external aqueous fluid during the texis may facilitate the segregation of newly formed felsic melting. Progressive dehydration of metaturbiditic sequences melts into the upper crust, significantly contributing to hosting the Okbang amphibolite might be responsible for the crustal differentiation [5, 27, 104]. Experimental studies supply of free aqueous fluids necessary for melting [34, 100]. (e.g., [11, 14, 15, 58, 105]) and phase equilibrium modeling Further studies are needed for a better comprehension of (e.g., [13, 56, 106, 107]) suggested that melt production in fluid sources for the melting. mafic rocks is a continuous process and melt compositions vary from granitic to dioritic, depending on temperature, 7.2. Timing of Mafic Magmatism and Fluid-Present Melting. bulk composition, and the presence of excess fluid. Beard Multiple episodes of zircon crystallization in amphibolites and Lofgren [15] experimentally investigated the dehydra- and associated leucosomes permit us to constrain the times tion melting of amphibolite at 800–1000°C and 1–6 kbar that of mafic magmatism and high-temperature metamorphism, yielded granodioritic to trondhjemitic melts and restitic respectively. A variety of field relationships, including diffuse assemblages of clinopyroxene+orthopyroxene+plagioclase – boundaries between the leucosome and host amphibolite +Fe Ti oxides; in contrast, H2O-saturated melting yielded (Figure 3(c)) and petrographic continuity between boudin peraluminous, low-Fe melts together with amphibole-rich, necks and layer-parallel leucosomes (Figures 3(e) and 4(a)), plagioclase-poor residues. The latter is compatible with our suggest that synkinematic melting is associated with the seg- petrographic observation (Figures 3 and 4) and Fe-poor, regation of tonalitic melt. These leucosomes are subsequently Ca-rich, and aluminous composition of tonalitic leucosomes transected by undeformed pegmatitic dykes (Figure 4(f)). (Figure 6). Based on thermodynamic modeling of open- The zircon cores and rims from the amphibolite yielded system melting in amphibolites, Stuck and Diener [13] sug- the weighted mean 207Pb/206Pb ages of 1866 ± 4 Ma and gested that the compositions of melts produced by horn- 1861 ± 3 Ma, respectively, which are best interpreted as the blende breakdown progressively change from tonalite– times for magmatic emplacement and subsequent metamor- trondhjemite to granite fields with a decreasing temperature phism, respectively. The development of overgrowth rims in the An-Ab-Or diagram (Figure 7). This result, however, may be attributed to in situ melting of the amphibolite, as is in marked contrast to the tonalitic composition of leuco- evidenced by the presence of melt-related microstructures some in the Okbang amphibolite (Figure 7).

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The leucosome may not always represent primary melt in the amphibolite further suggest that its parental magma is compositions because they are readily modified by fractional most likely derived from juvenile mantle-derived source, crystallization and/or melt loss. In particular, plagioclase frac- confirming the previous result based on enriched midocean ε ð Þ tionation is one of key factors for controlling melt compositions ridge basalt geochemistry and positive bulk-rock Nd t [24]. The REE patterns of the analyzed leucosomes show posi- values [28, 29]. ð ∗Þ : – : tive Eu anomalies [ Eu/Eu N =154 6 88;Figure8(b)], indicating that plagioclase with high Eu partitioning coefficient 7.4. Implications for Tectonic Evolution of the Yeongnam [108] has played a significant role during melt crystallization, Massif. Orogenesis in the continental crust generally com- locally yielding plagioclase-rich leucosomes (Figure 5(g)). Nev- prises two stages: initial crustal thickening and subsequent ertheless, limited scatters in Th, U, Hf, and Zr concentrations gravitational collapse of the thickened crust [27, 118, 119]. may reflect the retention of U-bearing minerals such as zircon During the latter extensional stage, upwelling asthenosphere during melt crystallization [22]. In addition, the majority of leu- may serve as a heat source for high-temperature metamor- cosomes within the amphibolite are apparently confined to the phism and anatexis (e.g., [120–122]). Such a linkage could amphibolite source area, and they show a limited range of tona- be represented by close association of mafic magmatism litic compositions (Figure 7). Thus, the compositions of tonali- with the granulite-facies metamorphism in the Yeongnam tic leucosomes in the Okbang amphibolite probably represent Massif, as illustrated in a conceptual geodynamic model those of initial melts although melt extraction and migration of Figure 12 [31]; arc-related magmatism and collisional are locally facilitated by regional deformation coeval with the orogeny at ~2.0–1.87 Ga are followed by late-orogenic mafic melting event (e.g., [109]). magmatism and regional metamorphism at ~1.87–1.85 Ga Based on the geochemical data of tonalite and amphibo- [30, 31, 33, 34]. The protracted orogenic history of the lite, Yakymchuk et al. [24] recently suggested that the fluid- Yeongnam Massif is compatible with that of the North China present melting of amphibolite generally produced tonalitic Craton [37, 123]. In particular, the tectonothermal event at leucosome as initial melt, and the paucity of K-feldspar and ~1.87–1.85 Ga is most likely linked to late-orogenic biotite in mafic source rocks is a critical factor for controlling amalgamation between the Paleoproterozoic Korean arc melt composition. This type of melting is operative in the and the North China Craton, ultimately leading to the forma- Okbang amphibolite where K-feldspar is generally lacking. tion of the Columbia/Nuna supercontinent [30]. Recently, In contrast, Stuck and Diener [13] suggested that initial soli- Lee et al. [33] suggested that high-temperature low-pressure dus melting of amphibolite, accompanied by the biotite metamorphism is associated with midcrustal emplacement breakdown, generally produced K-rich granitic melts, but of the AMCG magma at ~1.87–1.86 Ga during an extensional the hornblende dehydration at higher temperatures yielded regime in the southern Yeongnam Massif. Such a tectonother- granodioritic to tonalitic melts. These results are corrobo- mal event is consistent with that found in the Okbang amphib- rated by a progressive change in melt compositions of meta- olite and host metasedimentary rocks ([28, 34, 41]; this study). mafic rocks in the Ivrea Zone [110]. The variability in melt Our study further revealed that the Okbang amphibolite has composition, however, is inconsistent with tonalitic melt experienced fluid-present melting shortly after its protolith compositions prevalent for the fluid-present melting of mafic emplacement, suggesting that the late-orogenic process in rocks, including the Okbang amphibolite (Figure 7). the Yeongnam Massif has culminated at ~1862 Ma. Thus, we The pathway of external fluid is another key element for conclude that the entire massif has concurrently experienced fl understanding the process of H2O- uxed melting in the oro- widespread magmatism and high-temperature metamor- genic belt. Regional faults or shear zones commonly play a phism at ~1.87–1.86 Ga during the waning stage of Paleopro- major role as fluid channels during fluid-present melting in terozoic hot orogenesis (Figure 9(c); [33, 124]). migmatite complexes [25, 26, 111–113]. In the Okbang Fluid-present melting of mafic crustal fragment in the amphibolite, the amount of leucosomes apparently increases Yeongnam Massif ([33]; this study) sheds light on the late- towards ductile shear zones, suggesting that high-strain zones orogenic evolution of Paleoproterozoic Korean arc situated afforded pathways for transporting aqueous fluid and melt along the trailing edge of the North China Craton [30, 124]. (Figures 3 and 4). Synkinematic fluid-induced melting is cor- In particular, such a melting at upper amphibolite-facies con- roborated by the leucosome distribution typified by a network dition may produce a large amount of melt to be retained in of one or more sets of extensional shear bands and boudin host rocks because of negative volume change of the melt- necks (Figures 3(e), 4(a), and 4(b); [44, 109]). On the other forming reaction [26]. The presence of partially molten rocks hand, open-system melting induced by an ingress of external should result in the weakening of orogenic hinterland to fluid or melt could be recorded in the Hf isotopic compositions trigger the onset of extensional tectonics [125]. Thus, fluid- 176 177 ε ð Þ of zircon [114, 115]. Hf/ Hf ratios and Hf t values of zir- present melting in the Okbang amphibolite is most likely con in the leucosome are lower and more variable than those in linked to the late-orogenic extensional event at ~1.86 Ga the amphibolite (Figure 11; Table DR2), suggesting that the prevalent in the Yeongnam Massif [31, 33]. influx of external Hf component in migrated melts is The Hf isotopic data of zircon are useful for deciphering significant in the leucosome [116, 117]. Thus, Hf isotopic tectonic processes involved in the growth and recycling of values in the leucosome are interpreted to reflect the continental crust [126]. At the onset of supercontinent contribution of external melts derived from the surrounding assembly, subduction-related processes may lead to the ε ð Þ metasedimentary rocks whose Hf t values are in the range generation of juvenile magmas with enhanced radiogenic – – ε ð Þ ff of 11.9 to 6.1 [35]. Positive zircon Hf t values (4.2 to 6.0) Hf signature, a ected by the mixing of variable proportion

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(a)(a)

((b)b)

GGabbroicabbroic magmagmamaa

AsthenosphericAsthenospheric upweupwellinglling

(c)

Figure 12: The schematic tectonic model for the Paleoproterozoic orogeny in the Yeongnam Massif (modified after [31]). Three major tectonothermal episodes include (a) arc-related magmatism possibly associated with the back-arc rifting at ~2.0–1.9 Ga; (b) crustal-thickening collisional orogeny at ~1.9–1.87 Ga; and (c) late-orogenic magmatism and high-temperature metamorphism at ~1.87–1.85 Ga. The gabbroic-anorthositic magma is most likely a product of asthenospheric upwelling during the waning stage of prolonged hot orogenesis. ε ð Þ fl of recycled crustal materials [127]. During back-arc closure, The decrease in Hf t with time most likely re ects the crustal thickening and reworking dominate to yield negative increase in contribution of crustal recycling during the ε ð Þ – Hf t of magmatic zircons. On the other hand, orogenic col- magma generation and ascent [135]. Moreover, ~1.9 1.8 Ga lapse following the crustal accretion could be associated with zircons in the North China Craton, including the Yeongnam ε ð Þ – mantle upwelling to yield juvenile Hf isotopic signatures Massif, are characterized by a large Hf t spread ( 17.0 to ε ð Þ [128]. Such a scenario for geodynamic evolution from sub- 9.0; Figure 11) but many zircons have positive Hf t values, duction to accretion is compatible with the variation in Hf suggesting a significant influx of mantle-derived juvenile ε ð Þ ε ð Þ isotopic signatures of the Yeongnam Massif: Hf t values magmas. Such an Hf t excursion is attributed to the at ~2.0–1.9 Ga range from –12.0 to –1.0 except for one zir- emplacement of late- to postorogenic juvenile magmas, repre- con, whereas those at ~1.9–1.85 Ga from –8.0 to 6.0 sented by the AMCG suites [31, 131, 136]. Taken together, the (Figure 11; [31, 35]). Positive values in the latter are indica- geodynamic and tectonic evolution of the Yeongnam Massif is tive of juvenile mafic magmas generated in an extensional closely linked to the Paleoproterozoic terrane assembly in the setting, as revealed by the Okbang amphibolite as well as North China Craton, typified by prolonged accretionary–col- the Sancheong-Hadong AMCG suite [31]. In addition, zircon lisional orogenesis in association with final assembly of the ε ð Þ Hf t values of basement gneisses in the Yeongnam Massif Columbia/Nuna supercontinent [37, 123, 126]. generally decrease with time at ~2.5–2.0 Ga. These variations during the Paleoproterozoic are consistent with the overall 8. Conclusions ε ð Þ variation in zircon U-Pb ages and Hf t values recorded in igneous rocks of the North China Craton, including the The Okbang amphibolite in the Yeongnam Massif provides Damiao gabbro-anorthosite suite (Figure 11; [129–134]). an excellent opportunity for understanding the fluid-

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present melting of mafic rocks and the role of fluid during the Supplementary Materials evolution of high-temperature terranes at the periphery of the North China Craton. The partial melting of amphibolitic Supplementary 1. Table DR1: Results of SHRIMP Zircon protolith occurred at ~650–730°C and 4.6–5.2 kbar in the U-Pb analyses. fl presence of externally derived uid, particularly along a shear Supplementary 2. Table DR2: Summary of Lu-Hf isotopic zone, and yielded tonalitic leucosomes containing peritectic data. hornblende megacrysts. The leucosomes are commonly dis- tributed along axial plane of folds and within the interboudin Supplementary 3. Figure DR1: Classification of the analyzed partition of amphibolite, suggesting a synkinematic melting. amphiboles. Hornblende compositions plotted on the classi- Various microstructures including melt pockets and intersti- fication diagram of Leake et al. [49]. Bt: biotite. Figure DR2: tial melts with rounded grains of hornblende or plagioclase in Anorthite vs. orthoclase contents of plagioclase. Anorthite neosomes are indicative of in situ partial melting and melt (An) vs. orthoclase (Or) diagram of plagioclase. An = 100 ∗ crystallization. Our high-precision SHRIMP U-Pb zircon Ca/ðNa+K+CaÞand Or = 100 ∗ K/ðNa + K + CaÞ. Figure ages indicate that high-temperature metamorphism and ana- DR3: P - T conditions and phase equilibria relevant to partial texis of the amphibolite occurred at ~1861 Ma shortly after melting of the Okbang amphibolite. A diagram showing the P T its formation at ~1866 Ma. Such a timeline for partial melting - condition of the Okbang amphibolite estimated from is consistent with 1862 ± 2 Ma crystallization of the leuco- the hornblende-plagioclase-quartz assemblage. Also shown some and 1862–1861 Ma zircon overgrowth in migmatitic are two melting curves, 1 and 2, experimentally determined and biotite-sillimanite gneisses. The terminal phase of this by Piwinskii (1968) and Patiño-Douce and Beard (1995), P Tfi melting episode is constrained by the intrusion of tungsten respectively. Purple lines (3) depict the - eld of each ore-bearing pegmatites at ~1852 Ma. All of these results are lithology, varying from amphibolite to hornblende-bearing consistent with tectonothermal episodes at ~1.87–1.85 Ga granulite, calculated for natural amphibolite [55]. Hbl: horn- recorded throughout the Yeongnam Massif (Figure 12; [30, blende; Cpx: clinopyroxene; Opx: orthopyroxene; Pl: plagio- ε ð Þ clase; Qz: quartz; Liq: liquid; and V: volatile. 33]). Finally, the Okbang amphibolite has positive Hf t of zircon, 4.2–6.0, suggesting that the parental magma was derived from a mantle source. Together with the Hf isotopic References data available in the literature, the generation of such mafic [1] E. Hansen, L. Johansson, J. Andersson et al., “Partial melting magmas as well as high-temperature metamorphism in the in amphibolites in a deep section of the Sveconorwegian Yeongnam Massif is compatible with the late-orogenic exten- Orogen, SW Sweden,” Lithos, vol. 236-237, pp. 27–45, 2015. sional phase of prolonged hot orogenesis, linked to the Paleo- [2] T. H. D. Hartel and D. R. M. Pattison, “Genesis of the Kapus- proterozoic crustal buildup of the eastern North China kasing (Ontario) migmatitic mafic granulites by dehydration Craton. melting of amphibolite: the importance of quartz to reaction progress,” Journal of Metamorphic Geology, vol. 14, no. 5, pp. 591–611, 1996. Data Availability [3] B. E. Kunz, T. E. Johnson, R. W. White, and C. Redler, “Partial melting of metabasic rocks in Val Strona di Omegna, All data generated or analyzed during this study are included Ivrea Zone, northern Italy,” Lithos, vol. 190-191, pp. 1–12, in this published article (and its supplementary information 2014. fi les). [4] A. B. Thompson, “Dehydration melting of pelitic rocks and ” the generation of H2O-undersaturated granitic liquids, American Journal of Science, vol. 282, no. 10, pp. 1567– Conflicts of Interest 1595, 1982. [5] M. L. Williams, S. Hanmer, C. Kopf, and M. Darrach, “Syn- The authors declare that they have no conflicts of interest. tectonic generation and segregation of tonalitic melts from amphibolite dikes in the lower crust, Striding-Athabasca mylonite zone, northern Saskatchewan,” Journal of Geophys- Acknowledgments ical Research, vol. 100, no. B8, pp. 15717–15734, 1995. [6] Y. Lee and M. Cho, “Fluid-present disequilibrium melting in We thank C. Yakymchuk, an anonymous reviewer, and the Neoarchean arc-related migmatites of Daeijak Island, west- editor S. Roeske for insightful and constructive comments ern Gyeonggi Massif, Korea,” Lithos, vol. 179, pp. 249–262, that significantly improved the quality of this manuscript. 2013. We also acknowledge the help of K. Yi and Y.-J. Jeong for [7] X. Li, M. Niu, C. Yakymchuk, Z. Yan, C. Fu, and Q. Zhao, the SHRIMP and LA-MC-ICPMS analyses, respectively. This “Anatexis of former arc magmatic rocks during oceanic research was supported by the National Research Foundation subduction: A case study from the North Wulan gneiss 2016R1A6A3A01008112 and 2019R1F1A1055852 and the complex,” Gondwana Research, vol. 61, pp. 128–149, 2018. Basic Research Project (18-3111-1) of the Korea Institute of [8] E. W. Sawyer, Atlas of Migmatites, vol. 9, Canadian Mineral- Geoscience and Mineral Resources (KIGAM) funded by the ogist Special Publications, Ottawa, Canada, 2008. Ministry of Science and ICT (Information, communication, [9] A. C. Storkey, J. Herman, M. Hand, and I. S. Buick, “Using in and technology) to Y. Lee. situ trace-element determinations to monitor partial-melting

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processes in metabasites,” Journal of Petrology, vol. 46, no. 6, [25] E. W. Sawyer, “Migmatites formed by water-fluxed partial pp. 1283–1308, 2005. melting of a leucogranodiorite protolith: microstructures in [10] R. P. Rapp and E. B. Watson, “Dehydration melting of meta- the residual rocks and source of the fluid,” Lithos, vol. 116, basalt at 8–32 kbar: implications for continental growth and no. 3-4, pp. 273–286, 2010. crust-mantle recycling,” Journal of Petrology, vol. 36, no. 4, [26] R. F. Weinberg and P. Hasalová, “Water-fluxed melting of the pp. 891–931, 1995. continental crust: a review,” Lithos, vol. 212-215, pp. 158– [11] T. Rushmer, “Partial melting of two amphibolites: contrast- 188, 2015. ing experimental results under fluid-absent conditions,” [27] M. Brown, “Granite: from genesis to emplacement,” Geological Contributions to Mineralogy and Petrology, vol. 107, no. 1, Society of America Bulletin,vol.125,no.7-8,pp.1079–1113, pp. 41–59, 1991. 2013. [12] R. S. Selbekk and K. P. Skjerlie, “Petrogenesis of the anortho- [28] Y. Arakawa, K.-H. Park, N.-H. Kim, Y.-S. Song, and site dyke swarm of Tromso, North Norway: experimental H. Amakawa, “Geochemistry and tectonic implications of evidence for hydrous anatexis of an alkaline mafic complex,” Proterozoic amphibolites in the northeastern part of the Journal of Petrology, vol. 43, no. 6, pp. 943–962, 2002. Yeongnam massif, South Korea,” The Island Arc, vol. 12, [13] T. J. Stuck and J. F. A. Diener, “Mineral equilibria constraints no. 2, pp. 180–189, 2003. on open-system melting in metamafic compositions,” Journal [29] H.-W. Chang, A. Turek, and C.-B. Kim, “U-Pb zircon geochro- of Metamorphic Geology, vol. 36, no. 2, pp. 255–281, 2018. nology and Sm-Nd-Pb isotopic constraint for Precambrian plu- [14] M. B. Wolf and P. J. Wyllie, “Dehydration-melting of tonic rocks in the northeastern part of Ryeongnam massif, amphibolite at 10 kbar: the effects of temperature and time,” Korea,” Geochemical Journal,vol.37,no.4,pp.471–491, 2003. Contributions to Mineralogy and Petrology, vol. 115, no. 4, [30] M. Cho, Y. Lee, T. Kim, W. Cheong, Y. Kim, and S. R. Lee, pp. 369–383, 1994. “Tectonic evolution of Precambrian basement massifs and [15] J. S. Beard and G. E. Lofgren, “Dehydration melting and an adjoining fold-and-thrust belt (Gyeonggi Marginal Belt) water-saturated melting of basaltic and andesitic greenstones Korea: an overview:,” Geosciences Journal, vol. 21, no. 6, and amphibolites at 1, 3, and 6, 9 kb,” Journal of Petrology, pp. 845–865, 2017. vol. 32, no. 2, pp. 365–401, 1991. [31] Y. Lee, M. Cho, W. Cheong, and K. Yi, “A massif-type (~1.86 [16] M. Brown and T. Rushmer, Evolution and Differentiation Ga) anorthosite complex in the Yeongnam Massif, Korea: of the Continental Crust, Cambridge University Press, late-orogenic emplacement associated with the mantle Cambridge, UK, 2006. delamination in the North China Craton,” Terra Nova, – [17] M. B. Wolf and P. J. Wyllie, “Garnet growth during Amphibo- vol. 26, no. 5, pp. 408 416, 2014. lite Anatexis: Implications of a garnetiferous restite,” Journal of [32] Y. Lee, M. Cho, and K. Yi, “In situ U-Pb and Lu-Hf isotopic Geology,vol.101,no.3,pp.357–373, 1993. studies of zircons from the Sancheong- Hadong AMCG suite, [18] J. F. A. Diener and Å. Fagereng, “The influence of melting Yeongnam Massif, Korea: implications for the petrogenesis of ∼ ” and melt drainage on crustal rheology during orogenesis,” 1.86 Ga massif-type anorthosite, Journal of Asian Earth – Journal of Geophysical Research: Solid Earth, vol. 119, no. 8, Sciences, vol. 138, pp. 629 646, 2017. pp. 6193–6210, 2014. [33] Y. Lee, M. Cho, W. Cheong, and K. Yi, “Prolonged high-tem- ∼ [19] C. L. Rosenberg and M. R. Handy, “Experimental deforma- perature, low-pressure metamorphism associated with 1.86 tion of partially melted granite revisited: implications for Ga Sancheong-Hadong anorthosite in the Yeongnam Massif, the continental crust,” Journal of Metamorphic Geology, Korea: Paleoproterozoic hot orogenesis in the North China ” – vol. 23, no. 1, pp. 19–28, 2005. Craton, Precambrian Research, vol. 307, pp. 175 200, 2018. “ [20] M. Sandiford, S. McLaren, and N. Neumann, “Long-term ther- [34] J. Kim and M. Cho, Low-pressure metamorphism and leu- mal consequences of the redistribution of heat-producing ele- cogranite magmatism, northeastern Yeongnam Massif, ” ments associated with large-scale granitic complexes,” Journal Korea: implication for Paleoproterozoic crustal evolution, – of Metamorphic Geology,vol.20,no.1,pp.87–98, 2002. Precambrian Research, vol. 122, no. 1-4, pp. 235 251, 2003. “ [21] D. L. Whitney, C. Teyssier, A. K. Fayon, M. A. Hamilton, and [35] N. Kim, C. S. Cheong, K. Yi et al., Zircon U-Pb geochrono- M. Heizler, “Tectonic controls on metamorphism, partial logical and Hf isotopic constraints on the Precambrian melting, and intrusion: timing and duration of regional meta- crustal evolution of the north-eastern Yeongnam Massif, ” – morphism and magmatism in the Niğde Massif, Turkey,” Korea, Precambrian Research, vol. 242, pp. 1 21, 2014. Tectonophysics, vol. 376, no. 1-2, pp. 37–60, 2003. [36] S. R. Lee and K. Cho, “Precambrian crustal evolution of the ” [22] T. E. Johnson, S. Fischer, R. W. White, M. Brown, and H. R. Korean Peninsula, Journal of Petrological Society of Korea, – Rollinson, “Archaean intracrustal differentiation from partial vol. 21, no. 2, pp. 89 112, 2012. melting of Metagabbro–Field and geochemical evidence from [37] P. Peng, X. Wang, B. F. Windley, J. Guo, M. Zhai, and Y. Li, the central region of the Lewisian complex, NW Scotland,” “Spatial distribution of ~ 1950-1800 Ma metamorphic events Journal of Petrology,vol.53,no.10,pp.2115–2138, 2012. in the North China Craton: implications for tectonic subdivi- ” – [23] T. Slagstad, R. A. Jamieson, and N. G. Culshaw, “Formation, sion of the craton, Lithos, vol. 202-203, pp. 250 266, 2014. crystallization, and migration of melt in the mid-orogenic [38] G. C. Zhao, P. A. Cawood, S. Z. Li et al., “Amalgamation of crust, Muskoka domain migmatites, Grenville Province, the North China Craton: key issues and discussion,” Precam- Ontario,” Journal of Petrology,vol.46,no.5,pp.893–919, 2005. brian Research, vol. 222-223, pp. 55–76, 2012. [24] C. Yakymchuk, W. Zhao, Y. Wan, S. Lin, and F. J. Longstaffe, [39] L.-G. Zhou, M. G. Zhai, J. S. Lu et al., “Paleoproterozoic meta- “Fluid-present anatexis of Neoarchean tonalite and amphib- morphism of high-grade granulite facies rocks in the North olite in the Western Shandong Province,” Lithos, vol. 326- China Craton: study advances, questions and new issues,” 327, pp. 110–124, 2019. Precambrian Research, vol. 303, pp. 520–547, 2017.

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2020/8854615/5293682/8854615.pdf by guest on 01 October 2021 Lithosphere 23

[40] S. M. Lee, “Geology and ore deposits at the Okbang scheelite to garnet-free natural assemblages,” American Mineralogist, mine, north Gyeongsang Province, Korea,” Journal of the vol. 92, no. 4, pp. 491–502, 2007. Geological Society of Korea, vol. 3, pp. 1–19, 1967. [56] R. M. Palin, R. W. White, E. C. R. Green, J. F. A. Diener, [41] W. S. Cheong and K. C. Na, “Origin and evolution of leuco- R. Powell, and T. J. B. Holland, “High-grade metamor- granites of NE Yeongnam Massif from Samcheok area, phism and partial melting of basic and intermediate Korea,” Journal of the Petrological Society of Korea, vol. 17, rocks,” Journal of Metamorphic Geology, vol. 34, no. 9, pp. 16–35, 2008. pp. 871–892, 2016. [42] N. Kim, C.-S. Cheong, K.-H. Park, J. Kim, and Y.-S. Song, [57] W. G. Ernst and J. Liu, “Experimental phase-equilibrium “Crustal evolution of northeastern Yeongnam Massif, Korea, study of Al- and Ti-contents of calcic amphibole in MORB revealed by SHRIMP U-Pb zircon geochronology and geo- – a semiquantitative thermobarometer,” American Mineralo- chemistry,” Gondwana Research, vol. 21, no. 4, pp. 865–875, gist, vol. 83, no. 9-10, pp. 952–969, 1998. 2012. [58] R. P. Rapp, E. B. Watson, and C. F. Miller, “Partial melting of [43] N. Marchildon and M. Brown, “Grain-scale melt distribution amphibolites/eclogite and the origin of Archean trondhje- in two contact aureole rocks: implications for controls on mites and tonalities,” Precambrian Research, vol. 51, pp. 1– melt localization and deformation,” Journal of Metamorphic 25, 1991. Geology, vol. 20, no. 4, pp. 381–396, 2002. [59] A. E. Patiño Douce and J. S. Beard, “Dehydration-melting of [44] R. F. Weinberg and G. Mark, “Magma migration, folding, and biotite gneiss and quartz amphibolite from 3 to 15 kbar,” disaggregation of migmatites in the Karakoram shear zone, Journal of Petrology, vol. 36, no. 3, pp. 707–738, 1995. Ladakh, NW India,” Geological Society of America Bulletin, [60] H.-W. Chang, D.-H. Lee, and K.-H. Park, “Magmatism and vol. 120, no. 7-8, pp. 994–1009, 2008. metamorphism of the Proterozoic in the Northeastern part [45] H.-I. Park and S. M. Lee, “Tin, tungsten mineralization in of Korea: petrologic and geochemical characteristics of the Bongwha-Uljin area,” Journal of the Korean Institute of Okbang amphibolites,” Journal of the Korean Institute Min- Mining Geology, vol. 17, pp. 1–15, 1984. ing Geology, vol. 26, pp. 489–498, 1993. [46] A. B. T. Werner, W. D. Sinclair, and E. B. Amey, Interna- [61] R. W. Le Maitre, P. Bateman, A. Dudek et al., A Classification tional strategic mineral issues summary report–tungsten, of Igneous Rocks and Glossary of Terms, Blackwell, Oxford, Geological Survey Circular 903-O, U.S, 2014. UK, 1989. [47] E. W. Sawyer, “Criteria for the recognition of partial melting,” [62] T. N. Irvine and W. R. A. Baragar, “A guide to the chemical Physics and Chemistry of the Earth (A), vol. 24, no. 3, pp. 269– classification of the common volcanic rocks,” Canadian 279, 1999. Journal of Earth Sciences, vol. 8, no. 5, pp. 523–548, 1971. [48] R. H. Vernon and W. J. Collins, “Igneous microstructures in [63] K. T. Winther, “An experimentally based model for the origin migmatites,” Geology, vol. 16, no. 12, pp. 1126–1129, 1988. of tonalitic and trondhjemitic melts,” Chemical Geology, [49] M. B. Holness and E. W. Sawyer, “On the pseudomorph- vol. 127, no. 1-3, pp. 43–59, 1996. ing of melt-filled pores during the crystallization of [64] A. E. Patiño Douce and N. Harris, “Experimental constraints migmatites,” Journal of Petrology, vol. 49, no. 7, on Himalayan Anatexis,” Journal of Petrology, vol. 39, no. 4, pp. 1343–1363, 2008. pp. 689–710, 1998. [50] B. E. Leake, A. R. Woolley, C. E. S. Arps et al., “Nomenclature [65] M. Marks, R. Halama, T. Wenzel, and G. Markl, “Trace of amphiboles; report of the subcommittee on amphiboles of element variations in clinopyroxene and amphibole from the International Mineralogical Association, Commission on alkaline to peralkaline syenites and granites: implications New Minerals and Mineral Names,” Canadian Mineralogist, for mineral-melt trace-element partitioning,” Chemical vol. 35, pp. 219–246, 1997. Geology, vol. 211, no. 3-4, pp. 185–215, 2004. [51] W. Johannes, “Metastable melting in granite and related sys- [66] T. W. Sisson, “Hornblende-melt trace-element partitioning tems,” in Migmatites, melting and metamorphism, M. P. Ath- measured by ion microprobe,” Chemical Geology, vol. 117, erton and C. D. Gribble, Eds., pp. 27–36, Nantwich, England, no. 1-4, pp. 331–344, 1994. 1983. [67] H. Reichardt and R. F. Weinberg, “Hornblende chemistry in [52] D. L. Whitney and A. J. Irving, “Origin of K-poor leuco- meta- and diatexites and its retention in the source of leucogra- somes in a metasedimentary migmatite complex by nites: an example from the Karakoram shear zone, NW India,” ultrametamorphism, syn-metamorphic magmatism and Journal of Petrology,vol.53,no.6,pp.1287–1318, 2012. subsolidus processes,” Lithos, vol. 32, no. 3-4, pp. 173–192, [68] J. B. Paces and J. D. Miller Jr., “Precise U-Pb ages of Duluth 1994. complex and related mafic intrusions, Northeastern Minne- [53] J. Dale, T. J. B. Holland, and R. Powell, “Hornblende-garnet- sota: geochronological insights to physical, petrogenetic, plagioclase thermobarometry: a natural assemblage calibra- paleomagmetic, and tectonomagmatic processes associated tion of the thermodynamics of hornblende,” Contributions with the 1.1 Ga midcontinent rift system,” Journal of to Mineralogy and Petrology, vol. 140, no. 3, pp. 353–362, Geophysical Research, vol. 98, pp. 13991–14013, 1993. 2000. [69] I. S. Williams, “U-Th-Pb geochronology by ion microprobe,” [54] T. J. B. Holland and J. D. Blundy, “Non-ideal interactions in in Applications of microanalytical techniques to understand- calcic amphiboles and their bearing on amphibole- ing mineralizing processes, M. A. McKibben, W. C. Shanks plagioclase thermometry,” Contributions to Mineralogy and III, and W. I. Rindley, Eds., vol. 7, pp. 1–35, Reviews in Petrology, vol. 116, no. 4, pp. 433–447, 1994. Economic Geology, 1998. [55] S. Bhadra and A. Bhattacharya, “The barometer tremolite + [70] J. S. Stacey and J. D. Kramers, “Approximation of terrestrial tschermakite + 2 albite = 2 pargasite + 8 quartz: constraints lead isotope evolution by a two-stage model,” Earth and from experimental data at unit silica activity, with application Planetary Science Letters, vol. 26, no. 2, pp. 207–221, 1975.

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2020/8854615/5293682/8854615.pdf by guest on 01 October 2021 24 Lithosphere

[71] K. R. Ludwig, User’s Manual for Isoplot 3.6: A Geochronolog- [87] A. C. McLaren, J. D. Fitz Gerald, and I. S. Williams, “The ical Toolkit for Microsoft Excel, Berkeley geochronology microstructure of zircon and its influence on the age determi- center special publication, Berkeley, 2008. nation from Pb/U isotopic ratios measured by ion micro- [72] K. R. Ludwig, SQUID 2: A User’s Manual, Berkeley Geochro- probe,” Geochimica et Cosmochimica Acta, vol. 58, no. 2, nology Center Special Publication, Berkeley, 2009. pp. 993–1005, 1994. [73] J. D. Vervoort, P. J. Patchett, U. Söderlund, and M. Baker, [88] A. P. Nutman, H. Hagiya, and S. Maruyama, “SHRIMP U-Pb “Isotopic composition of Yb and the determination of Lu single zircon geochronology of a Proterozoic mafic dyke concentrations and Lu/Hf ratios by isotope dilution using Isukasia, southern West Greenland,” Geological Society of MC-ICPMS,” Geochemistry, Geophysics, Geosystems, vol. 5, Denmark Bulletin, vol. 42, pp. 17–22, 1995. no. 11, article Q11002, 2004. [89] W. T. Chen and M.-F. Zhou, “Hydrothermal alteration of [74] N. C. Chu, R. N. Taylor, V. Chavagnac, R. W. Nesbitt, magmatic zircon related to NaCl-rich brines: diffusion- M. Boella, and J. A. Milton, “Hf isotope ratio analysis using reaction and dissolution-reprecipitation processes,” American multi-collector inductively coupled plasma mass spectrome- Journal of Science,vol.317,no.2,pp.177–215, 2017. try: an evaluation of isobaric interference corrections,” Jour- [90] R. J. M. Taylor, C. L. Kirkland, and C. Clark, “Accessories nal of Analytical Atomic Spectrometry, vol. 17, no. 12, after the facts: constraining the timing, duration and condi- pp. 1567–1574, 2002. tions of high-temperature metamorphic processes,” Lithos, [75] P. J. Patchett, O. Kouvo, C. E. Hedge, and M. Tatsumoto, vol. 264, pp. 239–257, 2016. “Evolution of continental crust and mantle heterogeneity: [91] C. Yakymchuk, C. K. Kirkland, and C. Clark, “Th/U ratios in evidence from Hf isotopes,” Contributions to Mineralogy metamorphic zircon,” Journal of Metamorphic Geology, and Petrology, vol. 78, pp. 279–297, 1982. vol. 36, no. 6, pp. 715–737, 2018. [76] J. Woodhead and J. Hergt, “A preliminary appraisal of seven [92] A. R. Lappin and L. S. Hollister, “Partial melting in the natural zircon reference materials for in situ Hf isotope central gneiss complex near Prince Rupert, British Colum- determination,” Geostandards and Geoanalytical Research, bia,” American Journal of Science, vol. 280, no. 6, pp. 518– vol. 29, no. 2, pp. 183–195, 2005. 545, 1980. [77] J. Woodhead, J. Hergt, M. Shelley, S. Eggins, and R. Kimp, [93] J. D. Clemens and G. T. R. Droop, “Fluids, P-T paths and the “Zircon Hf-isotope analysis with an excimer laser, depth fates of anatectic melts in the Earth's crust,” Lithos, vol. 44, profiling, ablation of complex geometries, and concomitant no. 1-2, pp. 21–36, 1998. age estimation,” Chemical Geology, vol. 209, no. 1-2, [94] M. Brown, “Melt extraction from the lower continental crust pp. 121–135, 2004. of orogens: the field evidence,” in Evolution and Differentia- [78] T. Iizuka and T. Hirata, “Improvements of precision and tion of the Continental Crust, M. Brown and T. Rushmer, accuracy in in situ Hf isotope microanalysis of zircon using Eds., pp. 331–383, Cambridge University Press, Cambridge, the laser ablation-MC-ICPMS technique,” Chemical Geology, 2006. vol. 220, no. 1-2, pp. 121–137, 2005. [95] D. Laporte, “Wetting behavior of partial melts during crustal [79] E. Scherer, C. Münker, and K. Mezger, “Calibration of the anatexis: the distribution of hydrous silicic melts in polycrys- lutetium-hafnium clock,” Science, vol. 293, no. 5530, talline aggregates of quartz,” Contributions to Mineralogy and pp. 683–687, 2001. Petrology, vol. 116, no. 4, pp. 486–499, 1994. [80] W. L. Griffin, X. Wang, S. E. Jackson et al., “Zircon chemistry [96] E. W. Sawyer, “Melt segregation in the continental crust: dis- and magma genesis, SE China: in-situ analysis of Hf isotopes, tribution and movement of melt in anatectic rocks,” Journal Tonglu and Pingtan Igneous Complexes,” Lithos, vol. 61, of Metamorphic Geology, vol. 19, no. 3, pp. 291–309, 2001. pp. 237–269, 2002. [97] M. T. Naney, “Phase equilibria of rock-forming ferromagne- [81] J. Blichert-Toft and F. Albarède, “The Lu-Hf isotope geo- sian silicates in granitic systems,” American Journal of chemistry of chondrites and the evolution of the mantle- Science, vol. 283, no. 10, pp. 993–1033, 1983. crust system,” Earth and Planetary Science Letters, vol. 148, [98] M. T. Naney and S. E. Swanson, “The effect of Fe and Mg on no. 1-2, pp. 243–258, 1997. crystallization in granitic systems,” American Mineralogist, [82] R. L. Rudnick and S. Gao, “Composition of the continental vol. 65, pp. 639–653, 1980. crust,” in The Crust: Treatise in Geochemistry, Volume 3,R. [99] V. Gardien, A. B. Thompson, and P. Ulmer, “Melting of L. Rudnick, Ed., pp. 1–64, Elsevier, Oxford, 2003. biotite + plagioclase + quartz gneisses: the role of H2Oin [83] W. L. Griffin, N. J. Pearson, E. A. Belousova et al., “The Hf the stability of amphibole,” Journal of Petrology, vol. 41, isotope composition of cratonic mantle: LAM-MC-ICPMS no. 5, pp. 651–666, 2000. analysis of zircon megacrysts in kimberlites,” Geochimica et [100] R. W. White, N. E. Pomroy, and R. Powell, “An in situ Cosmochimica Acta, vol. 64, no. 1, pp. 133–147, 2000. metatexite-diatexite transition in upper amphibolite facies [84] D. Rubatto, “Zircon: the metamorphic mineral,” Reviews in rocks from Broken Hill, Australia,” Journal of Metamorphic Mineralogy and Geochemistry, vol. 83, no. 1, pp. 261–295, 2017. Geology, vol. 23, no. 7, pp. 579–602, 2005. [85] T. Geisler, U. Schaltegger, and F. Tomaschek, “Re-equilibra- [101] D. E. Kelsey, C. Clark, and M. Hand, “Thermobarometric tion of zircon in aqueous fluids and melts,” Elements, vol. 3, modelling of zircon and monazite growth in melt-bearing no. 1, pp. 43–50, 2007. systems: examples using model metapelitic and metapsam- [86] I. S. Williams and J. M. Hergt, “U–Pb dating of Tasmanian mitic granulites,” Journal of Metamorphic Geology, vol. 26, dolerites: a cautionary tale of SHRIMP analysis of high-U zir- no. 2, pp. 199–212, 2008. con,” Beyond 2000: new frontiers in isotope geoscience, Lorne, [102] M. J. Kohn, S. L. Corrie, and C. Markley, “The fall and rise of 2000, Abstracts and Proceedings, J. D. Woodhead, J. M. Hergt, metamorphic zircon,” American Mineralogist, vol. 100, no. 4, and W. P. Noble, Eds., pp. 185–188, 2000. pp. 897–908, 2015.

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2020/8854615/5293682/8854615.pdf by guest on 01 October 2021 Lithosphere 25

[103] C. Yakymchuk and M. Brown, “Behaviour of zircon and terrane with emphasis on Paleozoic low-δ18O magmatism,” monazite during crustal melting,” Journal of the Geological Geological Society of America Bulletin, vol. 130, no. 1-2, Society, vol. 171, no. 4, pp. 465–479, 2014. pp. 139–153, 2017. [104] E. W. Sawyer, “Disequilibrium melting and the rate of melt- [118] J. F. Dewey, “Extensional collapse of orogens,” Tectonics, residuum separation during migmatization of mafic rocks vol. 7, pp. 1123–1139, 1984. from the Grenville Front, Quebec,” Journal of Petrology, [119] O. Vanderhaeghe and C. Teyssier, “Partial melting and flow vol. 32, no. 4, pp. 701–738, 1991. of orogens,” Tectonophysics, vol. 342, no. 3-4, pp. 451–472, [105] T. W. Sisson, K. Ratajeski, W. B. Hankins, and A. F. Glazner, 2001. “Voluminous granitic magmas from common basaltic [120] W. J. Collins, “Hot orogens, tectonic switching, and creation sources,” Contributions to Mineralogy and Petrology, vol. 148, of continental crust,” Geology, vol. 30, no. 6, pp. 535–538, no. 6, pp. 635–661, 2005. 2002. [106] E. C. R. Green, R. W. White, J. F. A. Diener, R. Powell, T. J. B. [121] M. E. S. D. Giustina, M. M. Pimentel, C. F. F. Filho, and M. H. Holland, and R. M. Palin, “Activity-composition relations for B. Maia de Hollanda, “Dating coeval mafic magmatism and the calculation of partial melting equilibria in metabasic ultrahigh temperature metamorphism in the Anapolis- rocks,” Journal of Metamorphic Geology, vol. 34, no. 9, Itauçu Complex, Central Brazil,” Lithos, vol. 124, no. 1-2, pp. 845–869, 2016. pp. 82–102, 2011. [107] C. Yakymchuk, C. Clark, and R. W. White, “Phase relations, [122] R. Schuster and K. Stüwe, “Permian metamorphic event in reaction sequences and petrochronology,” Reviews in Miner- the Alps,” Geology, vol. 36, no. 8, pp. 141–603, 2008. – alogy and Geochemistry, vol. 83, no. 1, pp. 13 53, 2017. [123] L. Tang and M. Santosh, “Neoarchean-Paleoproterozoic terrane [108] M. Wilke and H. Behrens, “The dependence of the parti- assembly and Wilson cycle in the North China Craton: an tioning of iron and europium between plagioclase and overview from the central segment of the Trans-North China hydrous tonalitic melt on oxygen fugacity,” Contributions Orogen,” Earth-Science Reviews,vol.182,pp.1–27, 2018. – to Mineralogy and Petrology, vol. 137, no. 1-2, pp. 102 [124] Y. Zou, M. Zhai, M. Santosh et al., “Contrasting _P-T-t_ 114, 1999. paths from a Paleoproterozoic metamorphic orogen: petrol- [109] M. Brown, F. J. Korhonen, and C. S. Siddoway, “Organizing ogy, phase equilibria, zircon and monazite geochronology of melt flow through the crust,” Elements, vol. 7, no. 4, metapelites from the Jiao-Liao-Ji belt, North China Craton,” pp. 261–266, 2011. Precambrian Research, vol. 311, pp. 74–97, 2018. [110] B. E. Kunz and R. W. White, “Phase equilibrium modelling of [125] M. Finch, P. Hasalová, R. F. Weinberg, and M. C. Fanning, the amphibolite to granulite facies transition in metabasic “Switch from thrusting to normal shearing in the Zanskar rocks (Ivrea Zone, NW Italy),” Journal of Metamorphic shear zone, NW Himalaya: implications for channel flow,” Geology, vol. 37, no. 7, pp. 935–950, 2019. Geological Society of America Bulletin, vol. 126, no. 7-8, [111] M. García-Arias, L. Guillermo Corretgé, C. Fernández, and pp. 892–924, 2014. A. Castro, “Water-present melting in the middle crust: the [126] C. J. Hawkesworth, B. Dhuime, A. B. Pietranik, P. A. Cawood, case of the Ollo de Sapo gneiss in the Iberian Massif (Spain),” A. I. S. Kemp, and C. D. Storey, “The generation and Chemical Geology, vol. 419, pp. 176–191, 2015. evolution of the continental crust,” Journal of the Geological [112] P. Hasalová, P. Štipská, R. Powell, K. Schulman, V. Janoušek, Society, vol. 167, no. 2, pp. 229 –248, 2010. and O. Lexa, “Transforming mylonitic metagranite by open- [127] G. Hagen-Peter and J. Cottle, “Evaluating the relative roles of system interactions during melt flow,” Journal of Metamor- crustal growth versus reworking through continental arc phic Geology, vol. 26, pp. 55–80, 2008. magmatism: a case study from the Ross orogen, Antarctica,” [113] I. Milord, E. W. Sawyer, and M. Brown, “Formation of diatex- Gondwana Research, vol. 55, pp. 153–166, 2018. ite migmatite and granite magma during anatexis of semi- [128] C. L. Kirkland, R. H. Smithies, C. V. Spaggiari et al., “Protero- pelitic metasedimentary rocks: an example from St. Malo, zoic crustal evolution of the Eucla basement, Australia: impli- France,” Journal of Petrology, vol. 42, no. 3, pp. 487–505, cations for destruction of oceanic crust during emergence of 2001. Nuna,” Lithos, vol. 278-281, pp. 427–444, 2017. [114] A. I. S. Kemp, C. J. Hawkesworth, G. L. Foster et al., “Mag- [129] Y. Geng, L. Du, and L. Ren, “Growth and reworking of the matic and crustal differentiation history of granitic rocks early Precambrian continental crust in the North China from Hf-O isotopes in zircon,” Science, vol. 315, no. 5814, Craton: constraints from zircon Hf isotopes,” Gondwana pp. 980–983, 2007. Research, vol. 21, no. 2-3, pp. 517–529, 2012. [115] X.-L. Wang, J.-C. Zhou, Y.-S. Wan et al., “Magmatic evolu- [130] X.-L. Jia, M.-G. Zhai, W.-J. Xiao et al., “Late Neoarchean to tion and crustal recycling for Neoproterozoic strongly peralu- early Paleoproterozoic tectonic evolution of the southern minous granitoids from southern China: Hf and O isotopes North China Craton: evidence from geochemistry, zircon geo- in zircon,” Earth and Planetary Science Letters, vol. 366, chronology and Hf isotopes of felsic gneisses from the Taihua pp. 71–82, 2013. complex,” Precambrian Research, vol. 326, pp. 222–239, 2019. [116] Y.-B. Wu, Y.-F. Zheng, S.-B. Zhang, Z.-F. Zhao, F.-Y. Wu, [131] X. Teng and M. Santosh, “A long-lived magma chamber in and X.-M. Liu, “Zircon U-Pb ages and Hf isotope composi- the Paleoproterozoic North China Craton: evidence from tions of migmatite from the North Dabie terrane in China: the Damiao gabbro-anorthosite suite,” Precambrian constraints on partial melting,” Journal of Metamorphic Geol- Research, vol. 256, pp. 79–101, 2015. – ogy, vol. 25, no. 9, pp. 991 1009, 2007. [132] C. Wang, Y. Lu, X. He, Q. Wang, and J. Zhang, “The Paleo- [117] S.-H. Yang, Y.-J. Zhao, X.-C. Liu, L. Li, and Y.-B. Wu, “Track- proterozoic diorite dykes in the southern margin of the North ing partial melting and protolith nature by zircon U-Pb and China Craton: insight into rift-related magmatism,” Precam- Hf-O isotope compositions of migmatites in the North Dabie brian research, vol. 277, pp. 26–46, 2016.

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2020/8854615/5293682/8854615.pdf by guest on 01 October 2021 26 Lithosphere

[133] X. Wang, W. Zhu, M. Luo, X. Ren, and X. Cui, “Approxi- mately 1.78 Ga maﬁc dykes in the Lüliang complex, North China Craton: zircon ages and Lu-Hf isotopes, geochemistry, and implications,” Geochemistry, Geophysics, Geosystems, vol. 15, no. 8, pp. 3123–3144, 2014. [134] J. Zhao, C. Zhang, X. Guo, and X. Liu, “The late- Paleoproterozoic I- and A-type granites in Luliang Complex, North China Craton: new evidence on post-collisional extension of Trans-North China Orogen,” Precambrian Research, vol. 318, pp. 70–88, 2018. [135] W. J. Collins, E. A. Belousova, A. I. Kemp, and J. B. Murphy, “Two contrasting Phanerozoic orogenic systems revealed by hafnium isotope data,” Nature Geoscience, vol. 4, no. 5, pp. 333–337, 2011. [136] J. F. Liu, J. Y. Li, J. F. Qu, Z. C. Hu, Q. W. Feng, and C. L. Guo, “Late Paleoproterozoic tectonic setting of the northern margin of the North China Craton: constraints from the geochronology and geochemistry of the mangerites in the Longhua and Jianping areas,” Precambrian Research, vol. 272, pp. 57–77, 2016. [137] M. Cho, K. Min, and H. Kim, “Geology of the 2018 Winter Olympic site Pyeongchang, Korea:,” International Geology Review, vol. 60, no. 3, pp. 267–287, 2018. [138] S.-G. Lee, Y. Asahara, T. Tanaka et al., “La-Ce and Sm-Nd isotopic systematics of early Proterozoic leucogranite with tetrad REE pattern,” Chemical Geology, vol. 276, no. 3-4, pp. 360–373, 2010. [139] S. R. Taylor and S. M. McLennan, The continental crust: its composition and evolution, Blackwell, Oxford, 1985. [140] S.-S. Sun and W. F. McDonough, “Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes,” Geological Society Special Publication, vol. 42, no. 1, pp. 313–345, 1989.

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