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지질학회지 제 56권 제 6호, p. 727-735, (2020년 12월)J. Geol. Soc. Korea, v. 56, no. 6, p. 727-735, (December 2020)DOI http://dx.doi.org/10.14770/jgsk.2020.56.6.727ISSN 0435-4036 (Print)ISSN 2288-7377 (Online)북 콘툼 터레인 I-형 및 S-형 화강암의 저어콘 우라늄-납 연령:중부 베트남에서의 후기 고생대-중생대 화성작용의 의의Nguyen Quoc Hung․Ngo Xuan Thanh‡․Vu Anh DaoHanoi University of Mining and Geology요 약인도차이나 육괴의 주요 지구조체 중 하나인 북 콘툼 터레인은 베트남 중부에 위치해 있으며, 다수의 신원생대-신생대 화산암-심성암 복합체로 이루어져 있다. 이 지역의 페름기-트라이아스기 화강암과 화강섬록암은 I형과 S-형 화강암의 지구화학 친화성을 모두 가진다. 북 컨툼 터레인에서 사장석, 정장석, 석영, 흑운모와 소량의 각섬석으로 구성된 시료(QN-791)와 석영, 사장석, 정장석, 흑운모와 소량의 백운모로 구성된 시료(QN-750)를 채취하였다. 이 시료들에서 산출하는 각섬석과 백운모는 각각 이 시료들이 I-형과 S-형 화강암 기원임을 제시한다. 이 대표적 두 시료로부터 추출한 저어콘 결정들을 다검출기 레이저 삭박 유도결합플라즈마를 이용하여우라늄-납 연령을 측정하였으며, 이로부터 I-형과 S-형 화강암의 정치시기가 각각 262.0 1.3 Ma (2σ)와 243.3 1.0 Ma (2σ)임을 밝혔다. 우리의 지구연대학적 자료는 서 인도차이나 지괴에서의 후기 고생대 화성작용과 함께 컨툼 터레인의 후기 고생대 화성작용이 아마도 석탄기부터 시작된 대륙 호 환경과 관련되어 있으며 베트남중부에서 일어난 중생대 초기 대륙지각 중첩 작용의 증거를 제공한다.주요어: 저어콘, 화강암질암, 컨툼 터레인, Ben Giang-Que Son 복합체, 인도차이나 육괴Nguyen Quoc Hung, Ngo Xuan Thanh and Vu Anh Dao, 2020, U-Pb ages of zircon from I- and S-type granitesfrom northern Kon Tum terrane: Implications for late Paleozoic - Mesozoic magmatism in CentralVietnam. Journal of the Geological Society of Korea. v. 56, no. 6, p. 727-735ABSTRACT: The northern Kon Tum terrane in central Vietnam, one of the most key tectonic terranes of theIndochina block, consists of numerous volcano-plutonic complexes of the Neoproterozoic to Cenozoic ages.Permo-Triassic granites and granodiorite in the terrane have both I- and S-type geochemical affinities. Two graniticsamples collected from the northern Kon Tum terrane show mineral assemblages of plagioclase, K-feldspar, quartz,biotite, and minor hornblende (Sample QN-791) and quartz, plagioclase, K-feldspar, biotite, and minor muscovite(Sample QN-750). The presence of minor hornblende and muscovite in the samples may suggest their I- and S-typeorigin, respectively. Multicollector Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (MCLA-ICP-MS) zircon U-Pb ages from two representative samples revealed the emplacement of the I- and S-typegranites at 262.0 1.3 Ma (2σ), and at 243.3 1.0 Ma (2σ), respectively. Our geochronological data provide anevidence for late Paleozoic magmatism in the Kon Tum terrane along the western Indochina block that probablycorresponded to a Carboniferous continental arc and early Mesozoic crustal thickening evolution in CentralVietnam.Key words: Zircon, granitoids, Kon Tum terrane, Ben Giang-Que Son complex, Indochina block(Nguyen Quoc Hung, Ngo Xuan Thanh and Vu Anh Dao, Hanoi University of Mining and Geology, N18 Duc Thang,Bac Tu Liem, Hanoi, Vietnam)1. IntroductionIn Central Vietnam, the Tam Ky-Phuoc Son‡Suture Zone (TPSZ) is extended from the TamKy to Phuoc Son areas (Vietnam) over a distanceof 100 km (Fig. 1a; e.g., Tran et al., 2014). TheCorresponding author: 84-978-224-246, E-mail: [email protected]

728Nguyen Quoc Hung․Ngo Xuan Thanh․Vu Anh Daosuture zone is considered to represent either anEarly Paleozoic ocean separating the Truong Sonterrane in the north from the Kon Tum terrane inthe south (Lepvrier et al., 2008; Tran et al., 2014; Nguyenet al., 2019). Along the TPSZ in Vietnam, numerous lenticular-shaped, metamorphosed peridotites(dunite and harzburgite), cumulate gabbros-pyroxenites, gabbros, and plagiogranites occur in afew meters to several kilometers in length, andhave been considered as an ophiolitic complex(e.g., Izokh et al., 2006; Pham et al., 2006). In thesouthern TPSZ, the Kon Tum terrane is locatedat the northeastern part of the Indochina terrane(Fig. 1a), and is composed of magmatic and metamorphic rocks (Tran and Vu, 2011). OrdovicianSilurian (e.g., Nagy et al., 2001; Usuki et al., 2009;Nguyen et al., 2019) and Permian-Triassic (e.g.Lepvrier et al., 2004; Osanai et al., 2004; Nakanoet al., 2007, 2013; Dinh, 2011) ages were obtainedfrom metamorphic and granitic rocks from theKon Tum terrane. The magmatic and metamorphicevent is attributed to the microcontinental collision tectonics in Asia (e.g., Osanai et al., 2004),but it is still controversial whether the timing ofthe collision is Ordovician-Silurian (e.g., Maluskiet al., 2005; Tran et al., 2014; Nguyen et al., 2019)or Permian-Triassic (e.g., Nagy et al., 2001; Lan etal., 2003; Osanai et al., 2004; Nakano et al., 2013).The Permian-Triassic granitoid complex in thenorthern Kon Tum terrane is composed of granite and granodiorite with both I- and S-type geochemical affinities (Tran and Vu, 2011). Threemain granitic complexes have been classified: theI-type Ben Giang-Que Son, and S-type Hai Van andVan Canh. Although the Permo-Triassic metamorphic events have been reported (Osanai etal., 2004; Nakano et al., 2007, 2013; Bui et al., 2020),its corresponding magmatic records are rare (Tranand Vu, 2011). In this study, we report the petrology and zircon U-Pb ages of two granitoidsamples each from the Ben Giang-Que Son andHai Van complexes in the northern Kon TumFig. 1. (a) Simplified tectonic map of Southeast Asia (after Metcalfe, 2013; Metcalfe et al., 2017; SMSZ: Song MaSuture Zone, TPSZ: Tam Ky - Phuoc Son Suture Zone). (b) Simplified geological map of the northern Kon Tumterrane (Central Vietnam) showing distribution of the Tam Ky-Phuoc Son Suture Zone and lithology. Sample localities are also shown.

북 콘툼 터레인 I-형 및 S-형 화강암의 저어콘 우라늄-납 연령: 중부 베트남에서의 후기 고생대-중생대 화성작용의 의의 729terrane. Our results contribute to a better understanding of Permo - Triassic magmatism withinthe Indochina block.2. Geological settingThe Kon Tum terrane was formerly considered as the Precambrian core of the Indochinablock (Hutchison, 1989; Tran and Vu, 2011; Metcalfeet al., 2017). However, the late Archean signaturewas only recorded in a Nd model age of 2.7 Gafor a pelitic granulite of continental crust origin (Lanet al., 2003). The Kon Tum terrane is subdividedinto three litho-tectonic units: the Kham Duc,Ngoc Linh, and Kan Nack complexes southwards(Tran and Vu, 2011). The Kham Duc unit in thenorthern part consists of metapelite, metapsammite,and amphibolite of greenschist- to amphibolite-facies.Ultramafic and gabbroic rocks occur locally aslenticular shape in the unit, and recorded the ophiolitic geochemical affinity (Izokh et al., 2006). TheNgoc Linh and Ka Nack units are composed offelsic mylonite, pelitic gneiss, and mafic granulite(Nakano et al., 2007). High temperature (HT) toultra-high temperature (UHT) metamorphic rockswere reported with coeval migmatites (e.g., Osanaiet al., 2004; Nakano et al., 2007, 2013). Investigationon the metamorphic ages using the zircon andmonazite U-Pb chronometers, and the biotite andmuscovite K-Ar and Ar-Ar chronometers revealedat least two metamorphic events: the Ordovician- Silurian (ca. 430-460 Ma; e.g., Nakano et al., 2013;Bui et al., 2020) and the Permian-Triassic (ca. 240-260Ma; e.g., Osanai et al., 2004; Nakano et al., 2007;Bui et al., 2020).The early Paleozoic dioritic-granodioritic-plagiograniticintrusions are locally distributed in the northernKon Tum terrane, and are classified as the TraBong, Dieng Bong, Chu Lai complexes (Fig. 1b).In general, these rocks belong to peraluminous,calc-alkaline series with enrichment in large-ionlithophile-elements (LILEs) and depletion in high-field-strength-elements (HFSEs, e.g. Nb, Ta) (e.g.,Tran and Vu, 2011), which is interpreted as arc-relatedmagmatism within the Kon Tum terrane (e.g., Tranet al., 2014; Gardner et al., 2017; Nguyen et al.,2019). The Dieng Bong complex has geochemicalcharacteristics of island-arc magma with ca. 500-520Ma emplacement ages (Nguyen et al., 2019). Thelate Paleozoic to early Mesozoic magmatic intrusions are locally exposed in the northern KonTum terrane, and are mainly grouped as the BenGiang-Que Son, Hai Van, and Van Canh complexes (Tran and Vu, 2011). In general, the BenGiang-Que Son complex is composed of diorite,granodiorite to granite, and leucogranitic dikes.The K-Ar ages of biotite from these rocks are inthe range ca. 232 - 269 Ma. Rare geochemical dataof this complex show that the rocks are depletedin HFSE such as Nb, Ta, Ti, and are enriched inTh, U, Cs, which is similar to the modern arc-related magma worldwide (Tran and Vu, 2011).The Hai Van and Van Canh consist of porphyritic granitoids such as granodiorite, granite, andgranosyenite dikes. Petrological and geochemicalcharacteristics of these rocks were suggested asS-type granite formed by a crust-thickening eventwithin the Indochina block (Tran and Vu, 2011).The U-Pb isotopic analyses of six representativesamples from the Hai Van complex by the LA-ICP-MSshow that granites formed at ca. 224-242 Ma (Phamet al., 2015). Only a few K-Ar ages of muscovitefrom the Van Canh complex were reported to beca. 140-191 Ma (Tran and Vu, 2011).3. Sample collection, analytical procedure andresult3.1 Sample collection and petrographyIn this study, two representative hornblendeand muscovite-bearing granitic samples were collectedfrom the TPSZ (Fig. 1b). Sample QN-791 was collected in a rock quarry of the Ben Giang-Que Soncomplex. In the field, the rocks are exposed in a

730Nguyen Quoc Hung․Ngo Xuan Thanh․Vu Anh Daolarge massif of granodiorite in brown color (Fig.2a). Sample QN-750 was collected in a white graniteblock exposed in about 15 m width along the KhamDuc complex. Field investigation suggest theboundary between this granite and the KhamDuc amphibolite is intrusive origin (Fig. 2b).The rock-forming minerals of sample QN-791are plagioclase, K-feldspar, quartz, biotite, andminor hornblende (Fig. 2c). Plagioclase is subhedral, and is slightly altered to sericite in its rimsand cleavages. Hornblende and biotite are mostly anhedral and altered, and biotite is slightlyoriented. Accessory minerals include magnetite,pyrite, ilmenite, apatite, sphene, and zircon. SampleQN-750 is composed of quartz, plagioclase, K-feldspar,biotite, and minor muscovite (Fig. 2d). Plagioclaseis subhedral, and is highly altered to sericite. Biotiteis subhedral, and is partly altered to chlorite.Accessory minerals include magnetite, pyrite, ilmenite, apatite, sphene, and zircon.3.2 Zircon U-Pb isotopic age datingZircon grains were separated by a conventionalmethod, and then were mounted in epoxy resinprior to polishing to expose the interior of thecrystals. Cathodoluminescence (CL) images weretaken to examine zircon morphology, internaltextures, and further to guide spot selection during the U-Pb analyses. The U-Pb dating of zirconwas conducted using MC-LA-ICP-MS housed atKorea Basic Science Institute. Zircon 91500 wasused as an internal standard for the U-Pb dating.Time-dependent drifts of U-Th-Pb isotopic ratioswere corrected using linear interpolation (withtime) for every eight analyses according to thevariations of standard zircon. U-Th-Pb isotopicFig. 2. (a) Outcrop photograph of a granodioritic block within the Ben Giang - Que Son complex (sample QN-791).(b) Outcrop photograph showing the occurrence of the white granite intruded the Kham Duc complex (sampleQN-750). (c and d) Photomicrographs showing the representative minerals of the granodioritic sample (QN-791)and granitic sample (QN-750), respectively (Qtz: quartz, Kfs: K-feldspar, Pl: plagioclase, Bt: biotite; Ms: muscovite,Hbl: hornblende).

북 콘툼 터레인 I-형 및 S-형 화강암의 저어콘 우라늄-납 연령: 중부 베트남에서의 후기 고생대-중생대 화성작용의 의의 731

732Nguyen Quoc Hung․Ngo Xuan Thanh․Vu Anh Daoratios for zircon 91500 are from Wiedenbeck et al.(1995). Uncertainty of preferred values for the internal standard 91500 was propagated to the ultimate results of the samples. In order to monitorthe external uncertainties of measurements, azircon standard GJ-1 was analyzed. Eight meas206238urements yielded a weighted mean Pb/ Uage of 607 3 Ma, which is in agreement withthe recommended age of 608.5 0.4 Ma withinuncertainty (Jackson et al., 2004). During theanalyses, the spot size of the laser beam was 20 μm in diameter. The detailed analytical procedureis similar to that described by Lee et al. (2018).Common Pb correction followed the procedureof Andersen (2002). Concordia plots and weighted mean calculations were carried out using thesoftware Isoplot/EX (Ludwig, 2008). Analyticalresults are listed in Table 1.Zircons grains from samples QN-791 and QN-750are 150-200 μm and 120-250 μm in the longest dimension, respectively. They have morphologiesvariable from subhedral to euhedral, and lengthto-width ratios of 2:1 to 4:1 (Fig. 3a, 3b). The majority of these grains is devoid of inherited zircon cores in the sample QN-791, but a few zircons contain inherited cores in a rounded shape.Moreover, most of the zircon grains show welldeveloped oscillatory zoning throughout theirCL images, indicative of their magmatic origin.Twenty-two zircon U-Pb isotopic analyses arewithin 10 % discordance, and their Th/U ratiosare over 0.13 (Table 1). All data points on TeraWasserburg Concordia diagrams are located onor close to the U-Pb Concordia, suggesting littlePb loss after zircon crystallization (Fig. 3). Tenconcordant analyses from sample QN791 yielded206238a weighted mean Pb/ U age of 262.0 1.3 Ma(2σ) (MSWD 1.03, Fig. 4a). Eleven analyses within 10 % discordance from sample QN-750 gave a206238weighted mean Pb/ U age of 243.3 1.0 Ma (2σ) (MSWD 0.20, Fig. 4b).4. Discussion and conclusionsWithin the Kon Tum terrane, two main magmatic events were recognized: (1) the early Paleozoicsubduction and collision between the Truong Sonand Kon Tum terranes, forming both I- and S-typefoliated granites, during the Cambro-OrdovicianCaledonian orogeny (e.g., Nguyen et al., 2019; Tranet al., 2020); and (2) the late Paleozoic-early MesozoicIndosinian orogeny (e.g., Tran and Vu, 2011; Tranet al., 2020). Granitoids in the latter orogeny arewidely exposed in the Kon Tum terrane (e.g., Dinhet al., 2011; Ngo et al., 2011, 2014, 2016; Tran andVu, 2011; Tran et al., 2020), but tectonic model inassociation with their petrogeneses is attributedeither to the Permo-Triassic subduction/collisionFig. 3. Representative cathodoluminescence (CL) images of zircons and U-Pb Concordia diagrams of the analyzedsamples.

북 콘툼 터레인 I-형 및 S-형 화강암의 저어콘 우라늄-납 연령: 중부 베트남에서의 후기 고생대-중생대 화성작용의 의의 733of the South China block underneath the Indochinablock (e.g., Ngo et al., 2016) or to the late CarboniferousTriassic subduction/collision of the Sibumasu blockunderneath the Indochina block (e.g., Metcalfe etal., 2017).The Ben Giang- Que Son magmatic complexin the Kon Tum terrane has two magmatic phases: the phase 1 is represented by small dioritic,quartz-dioritic blocks within the main lithologyof the phase 2 that are composed of granodioriteand hornblende-bearing granites. The geochemistryand zircon U-Pb ages of the dioritic rocks reported by Pham et al. (2015) resulted in theircalc-alkaline origin and early Ordovician (479 3Ma) emplacement. Based on the results, the authors attributed petrogenesis of the complex tothe result of the Caledonian orogeny. However,the occurrence of phase 1 (diorite) within the mainlithology of phase 2 (granodiorite) in the Ben Giang- Que Son magmatic complex suggests that thediorites are xenoliths representing for earlier magmatism within the Kon Tum terrane (Fig. 2a).206238The Pb/ U mean age of 262.0 1.3 Ma fromthe granodioritic sample (QN-791) in this studyis consistent with ages reported by Dinh (2011)and Tran et al. (2020) (LA-ICP MS U-Pb ages ofzircon) from the granite and granodiorite of theBen Giang-Que Son complex in the northernKon Tum terrane, which range from 261 2 Ma to306 2 Ma. These igneous rocks show typical island arc to active continental margin geochemicalsignatures such as high LILE enrichment relativeto HFSE, and high LREE relative to low HREE(Tran et al., 2020), suggesting the existence of active margin during the Carboniferous-Permianwithin the Kon Tum terrane. The CarboniferousEarly Permian volcanic rocks of andesites, dacites, and basalts with continental arc affinitywere also reported in the western and southernpart of the Indochina block (e.g., 330-349 Ma andesitic, rhyolitic and tuffaceous rocks, ca. 315 Mabasalts and andesites (Qian et al., 2019), and 288-295Ma granite (Zaw et al., 2014) in Laos; 278-301 Magranitoids (Tran and Vu, 2020) in Cambodia andThai Land). The magmatic events are relativelyolder than those reported in North Central Vietnamwhere most of the ages are middle to late Permian(ca. 270-252 Ma). The tectonic setting of middleto late Permian granitoids in the Kon Tum terrane is still unclear, and it is thus considered thatthe Ben Giang-Que Son complex in the Kon Tumterrane may be a part of the Carboniferous-Permiansuites distributed in Vietnam, Laos, Thailand, andCambodia, which probably resulted from subduction event of the Sibumasu underneath theIndochina blocks (e.g., Metcalfe, 2013; Metcalfe etal., 2017).Undeformed, muscovite-bearing S-type granite sample QN-750 in the study intruded theKham Duc amphibolite, and its crystallizationage based on the zircon U-Pb dating was 243.3 1.0Ma. This age is identical to those of S-type gran-Fig. 4. Diagrams showing weighted mean ages of the analyzed samples.

734Nguyen Quoc Hung․Ngo Xuan Thanh․Vu Anh Daoite (ca. 242-224 Ma) in the Hai Van complex(Pham et al., 2015), and the U-Th-Pb chemicalages of monazite (ca. 240-260 Ma) from metamorphic rocks in the Kon Tum terrane (Osanai etal., 2004; Nakano et al., 2007; Bui et al., 2020).Pham et al. (2015) suggested that the geochemicalcharacteristics of the Hai Van granite has geochemical characteristics of S-type granite formedfrom partial melting of crustal materials. Duringmiddle to late Triassic, collision of the Indochinablock to the South China blocks in the north (e.g.,Tran et al., 2008) and to the Sibumasu block inthe west (e.g., Metcalfe, 2013; Metcalfe et al., 2017)had caused highly crust-thickening within theIndochina block that resulted crustal partial melting to form S-type granites and metamorphic rockswithin the Indochina block (e.g., Tran et al., 2008).Thus, the middle to late Triassic S-type granitemay originated from the latest stage of crustalthickening during the Indosinian orogeny.AcknowledgementWe thank the Korean authorities to contributethe U-Pb age analyses. The reviewers have greatly allowed the improvement of this manuscript.This research was performed for the ResearchProject number B2017-MDA-14DT funded by theMinistry of Education and Training of Vietnam.REFERENCESAndersen, T., 2002, Correction of common lead in U-Pb204analyses that do no report Pb. Chemical Geology,192, 59-79.Bui, V.T.S., Osanai, Y., Nakano, N., Adachi, T., Kitano, I.and Owada, M., 2020, Timing of high-grade metamorphism in the Kon Tum Massif, Vietnam: Constraintsfrom zircon-monazite multi-geochronology and traceelements geochemistry of zircon-monazite-garnet.Journal of Asian Earth Sciences, 187, 104084, https://doi.org/10.1016/j.jseaes.2019.104084.Dinh, S.Q., 2011, Petrographic characteristics and zirconU-Pb geochronology of granitoid rocks in the southernBến Giằng, Quảng Nam province. Journal of Sicenceand Technology Development, 14, 17-30.Gardner, C.J., Graham, I.T., Belousova, E., Booth, G.W.and Greig, A., 2017, Evidence for Ordovician subduction-related magmatism in the Truong Son terrane,SE Laos: implications for Gondwana evolution and porphyry Cu exploration potential in SE Asia. GondwanaResearch, 44, 139-156, , C.S., 1989, Geological Evolution of South-EastAsia. Oxford Science Publications, 368 p.Izokh, A.E., Tran, T.H., Ngo, T.P. and Tran, Q.H., 2006,Ophiolite ultramafic-mafic associations in the northernstructure of the Kon Tumblock (central Vietnam). J.Geol. Hanoi, 28, 20-26.Jackson, S.E., Pearson, N.J., Griffin, W.L. and Belousova,E.A., 2004, The application of laser ablation-inductivelycoupled plasma-mass spectrometry to in situ U-Pb zircon geochronology. Chemical geology, 211, 47-69.Lan, C.Y., Chung, S.L., Tran, V.L., Lo, C.H., Lee, T.Y.,Mertzman, S.A. and Shen, J.J.S., 2003, Geochemicaland Sr-Nd isotopic constraints from the Kon Tum massif, central Vietnamonthe crustal evolution of the Indochinablock. Precambrian Research, 122, 7-27, https://doi.org/10.1016/S0301-9268(02)00205-X.Lee, T.H., Park, K.H. and Yi, K., 2018, Nature and evolution of the Cretaceous basins in the eastern margin ofEurasia: A case study of the Gyeongsang Basin, SEKorea. Journal of Asian Earth Sciences, 166, 19-31,doi:10.1016/j.jseaes.2018.07.004.Lepvrier, C., Maluski, H., Vu, V.T., Leyreloup, A., Phan,T.T. and Nguyen, V.V., 2004, The Early Triassic Indosinianorogeny in Vietnam (Truong Son Belt and KontumMassif); implications for the geodynamic evolution ofIndochina. Tectonophysics, 393, 87-118.Lepvrier, C., Van Vuong, N., Maluski, H., Thi, P.T. and VanVu, T., 2008, Indosinian tectonics in Vietnam. ComptesRendus Geoscience, 340, 94-111, https://doi.org/10.1016/j.crte.2007.10.005.Ludwig, K.R., 2008, Isoplot/Ex 3.70. A GeochronologicalToolkit for Microsoft Excel. Berkeley GeochronologicalCenter, Berkely, Special publication 4, 76 p.Maluski, H., Lepvrier, C., Leyreloup, A., Van Tich, V. and4039Thi, P.T.M., 2005, Ar- Ar geochronology of the charnockites and granulites of the Kan Nack complex, KonTum Massif, Vietnam. Journal of Asian Earth Sciences,25, 653-677.Metcalfe, I., 2013, Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys. Journal of Asian Earth Sciences, 66, 1-33.Metcalfe, I., Henderson, C.M. and Wakita, K., 2017, LowerPermian conodonts from Palaeo-Tethys ocean platestratigraphy in the Chiang Mai-Chiang Rai suture zone,

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/HVZFO2 VPD) VOH / HP9 VBO5IBOIBOE7V" OI%BP 6 1CBHF TPG[ JSDPOGSPN* BOE 4 UZQFHSBOJUFT . Multicollector Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (MC LA-ICP-MS) zircon U-Pb ages from two representative samp les revealed the emplacement of the I- and S-type granites at 262.0 1.3 Ma (2 M ), and at 243.3 1.0 Ma (2 M .