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A genetic linkage between subduction- and collision-related porphyry Cu deposits in continental collision zonesZengqian Hou1,2*, Zhiming Yang1, Yongjun Lu2, Anthony Kemp2, Yuanchuan Zheng3, Qiuyun Li1, Juxing Tang4, Zhusen Yang4, and Lianfeng Duan1

1Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, P.R. China2 Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), University of Western Australia, Perth, WA 6009, Australia

3China University of Geosciences (Beijing), Beijing 100082, P.R. China4Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, P.R. China

ABSTRACTThe genesis of continental collision-related porphyry Cu deposits (PCDs) remains contro-

versial. The most common hypothesis links their genesis with magmas derived from subduc-tion-modified arc lithosphere. However, it is unclear whether a genetic linkage exists between collision- and subduction-related PCDs. Here, we studied Jurassic subduction-related Cu-Au and Miocene collision-related Cu-Mo porphyry deposits in south Tibet. The Jurassic PCDs occur only in the western segment of the Jurassic arc, which has depleted mantle-like isotopic compositions [e.g., (87Sr/86Sr)i = 0.7041–0.7048; eNd(t) as high as 7.5, and eHf(t) as high as 18]. By contrast, no Jurassic PCDs have been found in the eastern arc segment, which is isotopically less juvenile [e.g., (87Sr/86Sr)i = 0.7041–0.7063, eNd(t) < 4.5, and eHf(t) ≤ 12]. These results imply that incorporation of crustal components during underplating of Jurassic magma induced copper accumulation as sulfides at the base of the eastern Jurassic arc, inhibiting PCD formation at this time. Miocene PCDs are spatially confined to the Jurassic arc, and the giant Miocene PCDs cluster in its eastern segment where no Jurassic PCDs occur. This suggests that the arc segment barren for subduction-related PCDs could be fertile for collision-related PCDs. Mio-cene ore-forming porphyries have young Hf model ages and Sr-Nd-Hf isotopic compositions overlapping with those of the Jurassic rocks in the eastern segment, whereas contemporane-ous barren porphyries outside the Jurassic arc have abundant zircon inheritance and crust-like Sr-Nd-Hf isotopic compositions. These data suggest that remelting of the lower crustal sulfide-bearing Cu-rich Jurassic cumulates, triggered by Cenozoic crustal thickening and/or subsequent slab break-off, led to the formation of giant Miocene PCDs. The spatial overlap and complementary metal endowment between subduction- and collision-related magmas may be used to evaluate the mineral potential for such deposits in other orogenic belts.

INTRODUCTIONMost porphyry Cu deposits (PCDs) form in

magmatic arcs worldwide and are associated with hydrous (>4 wt% H2O) calc-alkaline magmas, derived from an asthenospheric mantle wedge metasomatized by slab fluids (Richards, 2003). Subduction processes are thought to ultimately cause enrichment of metals (Cu, Au) and S (Grif-fin et al., 2013) and the relatively high oxygen fugacity (fO2

) and high H2O contents in arc mag-mas (Kelley and Cottrell, 2009) that are critical to the formation of PCDs. Recently, such PCDs have been found in collisional zones such as that in Tibet, where they are associated with post-col-lisional magmas emplaced as isolated complexes within the Jurassic–Cretaceous magmatic arcs (Hou et al., 2004). These magmas are thought to derive by remelting of a thickened juvenile mafic lower crust (Hou et al., 2004) resulting from pre-vious arc magmatism (Richards, 2009; Hou et al., 2009; Li et al., 2011) with subduction-associated PCDs (Tafti et al., 2009). This model implies a spatial relationship between subduction- and

collision-related PCDs, but it is unclear whether a genetic linkage exists.

Here, we report new geological, geochemi-cal, and isotopic data for Jurassic subduction- and Miocene collision-related PCDs in southern Tibet. Our new evidence suggests that remelting of sulfide-bearing, lower crustal cumulates of former arc magmas associated with subduction-related PCDs could produce giant collision-related PCDs.

SUBDUCTION- AND COLLISION-RELATED PCDS IN SOUTH TIBET

The India-Asia continental collision zone was built on a complex tectonic collage of terranes accreted onto the southern margin of the Asian continent since the Mesozoic (Fig. 1A; Yin and Harrison, 2000). The Lhasa terrane, bounded by the Meso-Tethyan Bangong-Nujiang suture and the Neo-Tethyan Indus-Yarlung Zangbo suture (Fig. 1A), is composed of Precambrian crystal-line basement and Paleozoic–Mesozoic shallow marine clastic strata. Northward subduction of the Neo-Tethyan Ocean beneath the Lhasa ter-rane formed the Jurassic–Cretaceous volcano-plutonic arcs (Fig. 1B; Chu et al., 2006). The

India-Asia collision during the Cenozoic pro-duced a 1500-km-long trans-Himalayan Mio-cene igneous belt along the southern margin of the Lhasa terrane (Miller et al., 1999), and led to crustal thickening (as much as 80 km) in south Lhasa (Chung et al., 2009).

Porphyry-type mineralization in the Lhasa terrane is linked to two distinct magmatic suites. These are the Jurassic arc suites asso-ciated with Cu-Au deposits (e.g., Xiongcun, Laze, and Zemoduola; Tafti et al., 2009), and the Miocene post-collisional suites associated with Cu-Mo deposits (e.g., Qulong, Jiama, Tinggong, and Chongjiang; Hou et al., 2009). Numerous 184–158 Ma granitoids and associ-ated Jurassic volcanic rocks form a 600-km-long Jurassic arc (JA) (Geng et al., 2005), onto which a >1000-km-long Cretaceous arc was subsequently superimposed (Fig. 1). This Jurassic arc is divided by a north-south–ori-ented rift into a western segment (WSJA) and an eastern segment (ESJA), which are domi-nated by diorite intrusions with andesites, and granitic intrusions with basalt and dacite, respectively. The giant Xiongcun PCD (219.8 Mt Cu resources averaging 0.43% Cu and 0.61 g/t Au; Tafti et al., 2009) with Re-Os molybe-denite age of 173 ± 5 Ma (Tang et al., 2010) is associated with a Jurassic quartz diorite porphyry in the WSJA (Fig. 1B). No Jurassic PCDs have been found in the ESJA (Fig. 1B).

The Miocene post-collisional magmas occur as isolated stocks of porphyritic monzogranite and minor granodiorite and granite. The miner-alized porphyries developed in the Jurassic arc, whereas contemporaneous barren ones were emplaced outside the arc (Fig. 1B). All porphy-ries have zircon U-Pb ages of 26–13 Ma with a peak at 16 Ma (Hou et al., 2013a), and the asso-ciated PCDs have molybdenite Re-Os ages of 17–14 Ma (Hou et al., 2009), postdating subduc-tion-related Jurassic PCDs by at least 150 m.y.

The Miocene PCDs show a close spatial rela-tionship with the Jurassic arc (Fig. 1B), despite being separated by a time interval of ~170–130 m.y. For example, the giant Qulong deposit (1420 Mt at 0.5% Cu and 0.03% Mo; Yang et al., 2009) is partly hosted by Jurassic dacitic lavas. The giant Jiama deposit is only 2 km from the nearest outcrop of Jurassic volcanic succes-*E-mail: houzengqian@126.com

GEOLOGY, March 2015; v. 43; no. 3; p. 247–250; Data Repository item 2015088 | doi:10.1130/G36362.1 | Published online 5 February 2015

© 2015 Geological Society of America. Gold Open Access: This paper is published under the terms of the CC-BY license.

248 www.gsapubs.org | Volume 43 | Number 3 | GEOLOGY

sions (Fig. 1B). Other PCDs are ~20–50 km away from Jurassic magmatic rocks (Fig. 1B). Importantly, the coeval Miocene porphyry intru-sions emplaced outside of the Jurassic arc are all barren (Fig. 1B).

GEOCHEMICAL AND ISOTOPIC CHARACTERISTICS

Thirty-two key samples from the PCDs and relevant magmatic rocks in south Tibet were analyzed for major and trace element chemistry and bulk-rock Sr-Nd and zircon Hf isotopic com-positions (Tables DR1–DR3 in the GSA Data Repository1). These data, combined with previ-ously published results, are presented in Figure 2 and in Figures DR1–DR3 in the Data Repository.

The Jurassic arc rocks are mainly calc-alka-line, and are characterized by enrichment in large-ion lithophile elements (LILE; e.g., Rb, Ba, Sr) and depletion in high field strength ele-ments (HFSE; e.g., Nb, Ta, P, Ti) with flat heavy rare earth element (HREE) patterns (Fig. DR1), thus showing typical subduction-related geo-chemical features (Hawkesworth et al., 1993). However, the Sr-Nd-Hf isotopic compositions of rocks from the western and eastern segments are distinct. Arc rocks from the WSJA have (87Sr/86Sr)i varying from 0.7041 to 0.7048, eNd(t) from +5.5 to +7.5, and zircon eHf(t) between +11 and +18 (Fig. 2). Those from the ESJA have higher (87Sr/86Sr)i, from 0.7041 to 0.7063, and lower eNd(t) (+1.5 to +4.5; Fig. 2) with variable zircon eHf(t) of +1 to +12 (Wei, 2014).

The Miocene Cu-Mo–related porphyries are mainly high-K calc-alkaline to shoshonitic (Hou et al., 2004) with enrichment in LILE (e.g., Rb, Ba, Sr) and depletion in HFSE (e.g., Nb, Ta, P, Ti), similar to the Jurassic rocks (Fig. DR1). These porphyries have large isotopic variations with (87Sr/86Sr)t = 15Ma from 0.7048 to 0.7062, eNd(t

= 15Ma) from -4.8 to +2.2, and zircon eHf(t) from +2 to +12 (Fig. 2). In contrast, the barren Miocene porphyries have higher (87Sr/86Sr)t = 15Ma (0.7063–0.7101) and lower eNd(t = 15Ma) (-8.1 to -3.1) and zircon eHf(t) (-8 to +5; Fig. 2). In addition, these barren porphyries yield relatively old crustal Hf model ages (average ca. 1100 Ma) and have abundant inherited zircons ranging in age from 30 Ma to 2680 Ma (Table DR3; Fig. DR2).

Compared with the Jurassic rocks, the Mio-cene Cu-Mo–related porphyries have higher light REE and LILE contents, and lower HREE and HFSE contents with steeper HREE patterns (Fig. DR1). They have Sr-Nd isotopic composi-tions partly overlapping with those of the Juras-sic rocks and plot along a two-component mix-ing array between Jurassic basalt and old lower crust in Tibet (Fig. 2A). Their zircon Hf isotopic

LhasaBR

IYZS

90 92 9429

30

JMLKENMCJ TGDZK

XC NMB

ML LinzhiNMQ

SNM

LZHYGR

TBC

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Fig.1bQiangtang

Songpan-Ganzi

QaidamTarim

88

80 90

28

32

36

Himalaya

0 50 100km

LZZD

YareMayum

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KathmanduThimphu

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(B)

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Miocene barren porphyry

Jurassic intrusion

Jurassic arc volcanic rock

Ophiolitc melange

Suture zone

Yadong-Gulu Rift (YGR)large, 0.5 ≤ Cu < 5 Mt

Jurassic porphyryCu-Au deposit

giant, Au ≥ 100 t

Miocene porphyryCu-Mo deposits

large, 50 ≤ Au ≤ 100 t

giant, Cu ≥ 5 Mt

small, Cu < 0.5 Mt

Jurassic ArcLhasa Terrane

(Jurassic arc cumulates)

Ɛ Hf(t)

Depleted mantle

CHUR

(B)

176Lu/177Hf = 0.022

Jurassic dacite (eastern segment)

Juvenile mafic lower crust

Mafic lower crust

0.2 Ga arc crust

Jurassic basalt (eastern segment)

Nd(

t) (1

5 M

a)

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60%

10%

5%

-12

-8

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0

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Jurassic Cu-Au-related porphyry (195~175 Ma)Jurassic intrusion (western segment)Jurassic intrusion (eastern segment)Miocene Cu-Mo-related porphyry (17-15 Ma)Miocene barren porphyry (26-14 Ma)End member of mixing curve (YB5-1)

(A)MORB

Lower crust [ ( 87Sr/86Sr)i =0.7100,ε Nd(t) = -22 ]

Upper crust (Amdo orthogneiss)50%

40%

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Ɛ

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Figure 1. A: Tectonic framework of Tibetan plateau (after Zhu et al., 2008). JSS—Jinsha suture; BNS—Bangonghu-Nujiang suture; IYZS—Indus-Yarlung Zangbo suture. B: Geo-logical map of Lhasa terrane showing distribution of Jurassic, Cretaceous, and Miocene magmatic rocks and associated porphyry Cu deposits (PCDs). Jurassic arc is delineated by outcrops of Jurassic intrusive and volcanic rocks. SNM—Shiquanhe-Nam Tso mélange. Jurassic PCDs: XC—Xiongcun; LZ—Laze; ZD—Zemoduola. Miocene PCDs: BR—Bairong; CJ—Chongjiang; TG—Tinggong; NM—Nanmu; LKE—Lakang’e; QL—Qulong; JM—Jiama. Jurassic intrusive rocks: XC—Xiongcun; TBC—Tangbaicun; DZK—Dazhuka; NMB—Ni Mu Bridge; QL—Qulong; JC—Jiacha; ML—Milin. Miocene barren stock: Yare, Mayum (in A); NMQ—Nanmuqie; LZH—Linzhi.

Figure 2. Sr-Nd-Hf isotopic compositions of Jurassic and Miocene rocks in south Tibet. A: Bulk-rock (87Sr/86Sr)i versus eNd(t). Black curve with ticks represents two-component mixing model between melt derived from mafic underplate (as isoto-pically approximated by Ju-rassic basalt sample YB5-1 from Zhu et al. [2008]) and old lower crust in Tibet (Miller et al., 1999). All data are recalculated to 15 Ma and listed in Table DR2 (see footnote 1), and only the least-altered samples with 87Rb/86Sr < 1 are plotted. Mio-cene ore-related porphyries plot on mixing line, whereas barren porphyries shift to-ward upper crust (e.g., Amdo orthogneiss). MORB—mid-oceanic ridge basalt. B: Zir-con eHf(t) values versus U-Pb age. Dashed lines represent evolution trend of Jurassic Cu-Au–related porphyries (0.2 Ga arc crust) in western segment of Jurassic arc and least-contaminated Jurassic basalts and granitic rocks in eastern segment, assum-ing that unexposed comple-mentary mafic cumulates to these rocks have Lu/Hf ratio similar to that of global mafic lower crust (176Lu/177Hf ratio ~0.022). Gray band shows that majority of Miocene ore-related porphyries could derive by re-melting hydrous cumulates of Jurassic arc magmas, isotopically equivalent to Jurassic rocks in eastern segment. Data are listed in Table DR3. CHUR—chondritic uniform reservoir.

1GSA Data Repository item 2015088, Tables DR1–DR3 and Figures DR1–DR3, is available online at www.geosociety.org/pubs/ft2015.htm, or on request from editing@geosociety.org or Documents Secre-tary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.

GEOLOGY | Volume 43 | Number 3 | www.gsapubs.org 249

compositions plot within the inferred evolution trend of the Jurassic rocks from the ESJA on plot of eHf(t) versus age (Fig. 2B).

REMELTING OF JURASSIC MAFIC UNDERPLATE

Geochemical and isotope data suggest that the WSJA arc rocks associated with the sub-duction-related PCDs derive from subduction-modified asthenospheric mantle (Fig. 2; Fig. DR1; Chu et al., 2006). However, the ESJA barren rocks show Sr-Nd isotopic departure from the depleted mantle toward the crust (Fig. 2), indicating the involvement of old crustal components (<15 vol%), consistent with old Hf model ages for these rocks (ca. 700–1500 Ma; Table DR3A).

The Miocene barren porphyries outside the Jurassic arc have crust-like Sr-Nd-Hf isotopic signatures and abundant zircon inheritance, consistent with a source dominated by old con-tinental crust (Fig. 2). By contrast, the Miocene Cu-Mo–related porphyries are free of inherited zircons, and have relatively “depleted” isoto-pic compositions and younger Hf model ages (average 800 Ma), suggesting a juvenile source (Hou et al., 2004, 2013a).

Importantly, the Miocene Cu-Mo–related porphyries are spatially confined to the Juras-sic arc (Fig. 1B), and have overlapping Sr-Nd isotopic compositions with those of the Juras-sic rocks from the ESJA (Fig. 2A). The zircon Hf data of the mineralized Miocene porphyries also lie within the evolution trend of the Juras-sic rocks from the ESJA (Fig. 2B). These obser-vations are consistent with derivation of these ore-related Miocene porphyries by remelting of the juvenile mafic rocks underplated during the Jurassic magmatism. The trend to lower eNd(t) shown by some ore-related porphyries could reflect mixing with lesser amounts (5%–30%) of old lower crust (Fig. 2A). The remelting sce-nario is also supported by the subduction-like features of the Miocene ore-related porphyries (such as Nb-Ta negative anomaly), which were inherited from the Jurassic arc magmas (Rich-ards, 2009). In addition, the Miocene Cu-Mo–related porphyries have higher Sr/Y ratios (23–186) and higher (La/Yb)N ratios (11–47) than the Jurassic rocks, showing geochemical affinity with adakite (Hou et al., 2004). This suggests that remelting of the Jurassic cumulates took place in a thickened crust (>50–55 km) within the amphibole and garnet stability field (Rapp and Watson, 1995), consistent with Cenozoic collision-induced crustal thickening in south Tibet (Yin and Harrison, 2000). Pronounced crustal thickening at 45–30 Ma (Chung et al., 2009) and subsequent slab break-off (or tearing) starting at 25 Ma (Hou et al., 2004) triggered this remelting as isotherms rebounded and/or hot asthenospheric melts infiltrated the litho-sphere (Richards, 2009).

CONTROLS ON METAL ENDOWMENTThe lack of Miocene PCDs outside of the

Jurassic arc suggests that there are no sulfide-bearing Jurassic cumulates to remelt there. In contrast, localization of Miocene PCDs within the Jurassic arc implies that metal-rich Jurassic cumulates could release Cu into the Miocene porphyry systems (Lee et al.., 2012). This is sup-ported by the east-west spatial variation in the average eHf(t) values of magmatic zircons from the Jurassic and Miocene magmatic rocks (Fig. DR3). The average zircon eHf(t) values of the Jurassic rocks decrease significantly from the WSJA (average +16) to the ESJA (average +6), suggesting distinct intra-crustal magmatic pro-cesses along the arc. High fO2

of the arc magma in the WSJA, evidenced by appearance of mag-matic anhydrite in the Xiongcun host porphyry (Tang et al., 2010), suppressed the formation of significant amounts of Cu-rich sulfides (e.g., Richards, 2009), which led to Cu enrichment in the evolving magma, thus forming the Juras-sic PCDs (Fig. 3). By contrast, incorporation of older crust by the ESJA basaltic rock, indicated by the lower and variable zircon eHf(t) (+1 to +12), may be responsible for lowering magmatic fO2

(e.g., Ripley and Li, 2013), thus inducing sulfide saturation (Tomkins et al., 2012) and sequester-ing Cu-rich sulfides (Nadeau et al., 2010) in the Jurassic lower-crustal arc cumulates (Fig. 3). The complementary metal endowment of the Jurassic and Miocene magmatic suites (Fig. 1) suggests

that enrichment of Cu in the juvenile mafic lower crust, though inhibiting the Jurassic PCD forma-tion, could have provided abundant metals for the Miocene giant PCDs by breakdown of the host sulfides during post-collisional melting.

IMPLICATIONS FOR EXPLORATIONOur study highlights a spatial overlap and

genetic linkage between giant collision-related PCDs and non-economic volcano-plutonic arcs. This is applicable to other orogenic belts, where former arc magmatism left sulfide-bearing metal-rich cumulates at the base of the crust (e.g., Lee et al., 2012), which provided abundant metals and S for post-subduction or collision-related PCDs during later remelting (e.g., Richards, 2009). Typical examples include: the Miocene post-collisional Kerman porphyry Cu belt, occur-ring within a non-economic Eocene magmatic arc in Iran (Shafiei et al., 2009); the Cretaceous giant PCDs, developed along the Mesozoic Qin-ling orogen in central China (Dong et al., 2011); and the Jurassic giant Dexing PCD, formed on a Mesozoic intra-continental orogen in east China (Hou et al., 2013b). Therefore, the spatial overlap and complementary metal endowment between subduction- and collision-related porphyry suites could be used for predicting PCD occurrence and assessing the mineralization potential of other tectonically composite orogens.

Our data also demonstrate that in a given magmatic suite the PCDs are associated with

Upper crust (UC)

Mantle lit

hosphereMantle lithosphere

Moho Remelting

Asthenosphereupwelling

Leucogranite

Normal faultIY

ZS UCJurassic

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of former arc magmas

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Sulfide-deficient cumulates

Miocene barren porphyry

subduction-related PCD

Collision-related PCD

Sulfide-bearing cumulates

of former arc magmas

Continental

Indian

W

E

W

E

Crust

Figure 3. Schematic illustration of genetic linkage between subduction- and collision-related porphyry Cu deposits (PCDs). Underplating and crystallization of Jurassic arc magmas in lower crust form hydrous cumulates, in which accumulation of Cu sulfides depends on redox state of arc magmas. High oxygen fugacity (fO2

) suppresses formation of significant amounts of Cu-rich sulfide in cumulates, leading to Cu enrichment in evolving magma and generation of subduction-related PCDs. Decreasing fO2

caused by magma-crust interaction leads to Cu enrichment in cumulates, thus providing metal source for younger, collision-related Cu-Mo porphyry systems. Collision-induced crustal thickening leads to prograde metamorphism of juvenile mafic lower crust (cumulates), and upwelling of asthenosphere related to slab tear-ing or/and breaking off (Hou et al., 2004) triggers remelting of Cu sulfide-bearing cumulates, leading to formation of Miocene collision-related porphyry Cu deposits. Black arrow shows underthrusting direction of the Indian continent. IYZS—Indus-Yarlung Zangbo suture.

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the isotopically “primitive” magmas with high bulk-rock eNd and zircon eHf values (Figs. 2 and 3). Hf isotopes might, therefore, be an impor-tant tool for assessing the metallogenic fertility of porphyry magmas (Fig. DR3). We suggest that systematic zircon eHf measurement could be effective in identifying the most prospective areas during regional targeting of PCDs.

ACKNOWLEDGMENTSThis work was funded by National Basic Research

Program of China (2011CB403104), IGCP/SIDA-600, National Science Foundation of China (41221061, 41320104004, and 41273051), and the Ministry of Land and Resources of China (201011011). We thank Chris Hawkesworth, Jeremy Richards, Rui Wang, and two anonymous reviewers for their constructive comments. This is contribution 383 from the CCFS and the Innovation Center of Continental Tectonics, Northwest University (China).

REFERENCES CITEDChu, M.F., Chung, S.L., Song, B., Liu, D., O’Reilly,

S.Y., Pearson, N.J., Ji, J., and Wen, D.J., 2006, Zircon U-Pb and Hf isotope constraints on the Mesozoic tectonics and crustal evolution of southern Tibet: Geology, v. 34, p. 745–748, doi:10.1130/G22725.1.

Chung, S.-L., Chu, M.-F., Ji, J.Q., O’Reilly, S.Y., Pearson, N.J., Liu, D.Y., Lee, T.-Y., and Lo, C.-H., 2009, The nature and timing of crustal thickening in Southern Tibet: Geochemical and zircon Hf isotopic constraints from post-collisional adakites: Tectonophysics, v. 477, p. 36–48, doi:10.1016/j.tecto.2009.08.008.

Dong, Y.-P., Zhang, G.-W., Neubauer, F., Liu, X.-M., Genser, J., and Christoph Hauzenberger, C., 2011, Tectonic evolution of the Qinling oro-gen, China: Review and synthesis: Journal of Asian Earth Sciences, v. 41, p. 213–237, doi: 10.1016/j.jseaes.2011.03.002.

Geng, Q.R., Pan, G.T., Jin, Z.M., Wang, L.Q., Zhu, D.C., and Liao, Z.L., 2005, Geochemistry and genesis of the Yeba volcanic rocks in the Gangdese magmatic arc, Tibet [in Chinese with English abstract]: Earth Science Journal of China University of Geosciences, v. 30, p. 747–760.

Griffin, W.L., Begg, G.C., and O’Reilly, S.Y., 2013, Continental-root control on the genesis of mag-matic ore deposits: Nature Geoscience, v. 6, p. 905–910, doi:10.1038/ngeo1954.

Hawkesworth, C.J., Gallagher, K., Hergt, J.M., and McDermott, F., 1993, Mantle and slab contri-butions in arc magmas: Annual Review of Earth and Planetary Sciences, v. 21, p. 175–204, doi:10.1146/annurev.ea.21.050193.001135.

Hou, Z.Q., Gao, Y.F., Qu, X.M., Rui, Z.Y., and Mo, X.X., 2004, Origin of adakitic intrusives gener-ated during mid-Miocene east–west extension

in southern Tibet: Earth and Planetary Science Letters, v. 220, p. 139–155, doi:10.1016 /S0012 -821X(04)00007-X.

Hou, Z.Q., Yang, Z.M., Qu, X.M., Meng, X.J., Li, Z.Q., Beaudoin, G., Rui, Z., Gao, Y., and Zaw, K., 2009, The Miocene Gangdese porphyry copper belt generated during post-collisional extension in the Tibetan orogen: Ore Geol-ogy Reviews, v. 36, p. 25–51, doi:10.1016/j .oregeorev .2008.09.006.

Hou, Z.Q., Zheng, Y.C., Yang, Z.M., Rui, Z.Y., Zhao, Z.D., Qu, X.M., Jiang, S.H., and Sun, Q.Z., 2013a, Contribution of mantle compo-nents within juvenile lower-crust to collisional zone porphyry Cu systems in Tibet: Minera-lium Deposita, v. 48, p. 173–192, doi:10.1007 /s00126 -012 -0415-6.

Hou, Z.Q., Pan, X.F., Li, Q.Y., Yang, Z.M., and Song, Y.C., 2013b, The giant Dexing porphyry Cu–Mo–Au deposit in east China: Product of melt-ing of juvenile lower crust in an intracontinen-tal setting: Mineralium Deposita, doi:10.1007 /s00126 -013-0472-5.

Kelley, K.A., and Cottrell, E., 2009, Water and the oxi-dation state of subduction zone magmas: Science, v. 325, p. 605–607, doi:10.1126 /science .1174156.

Lee, C.-T.A., Luffi, P., Chin, E.J., Bouchet, R., Das-gup tam, R., Morton, D.M., Roux, V.L., Yin, Q.Z., and Jin, D., 2012, Copper systematics in arc magmas and implications for crust-mantle differentiation: Science, v. 336, p. 64–68, doi: 10.1126 /science.1217313.

Li, J.X., Qin, K.Z., Li, G.M., Xiao, B., Chen, L., and Zhao, J.X., 2011, Post-collisional ore-bearing adakitic porphyries from Gangdese porphyry copper belt, southern Tibet: Melting of thick-ened juvenile arc lower crust: Lithos, v. 126, p. 265–277, doi:10.1016/j.lithos.2011.07.018.

Miller, C., Schuster, R., Klotzli, U., Frank, W., and Grasemann, B., 1999, Post-collisional potassic and ultrapotassic magmatism in SW Tibet: Geo-chemical and Sr-Nd-Pb-O isotopic constraints for mantle source characteristics and petrogen-esis: Journal of Petrology, v. 40, p. 1399–1424, doi:10.1093/petroj/40.9.1399.

Nadeau, O., Williams-Jones, A.E., and Stix, J., 2010, Sulphide magma as a source of metals in arc-related magmatic hydrothermal ore fluids: Nature Geo science, v. 3, p. 501–505, doi: 10.1038 /ngeo899.

Rapp, R.P., and Watson, E.B., 1995, Dehydration melting of metabasalt at 8–32 kbar: Implica-tions for continental growth and crust–mantle recycling: Journal of Petrology, v. 36, p. 891–931, doi:10.1093/petrology/36.4.891.

Richards, J.P., 2003, Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation: Economic Geology and the Bulletin of the Soci-ety of Economic Geologists, v. 98, p. 1515–1533, doi:10.2113/gsecongeo.98.8.1515.

Richards, J.P., 2009, Postsubduction porphyry Cu-Au and epithermal Au deposits: Products of remelt-

ing of subduction-modified lithosphere: Geol-ogy, v. 37, p. 247–250, doi:10.1130/G25451A.1.

Ripley, E.M., and Li, C., 2013, Sulfide saturation in mafic magmas: Is external sulfur required for magmatic Ni-Cu-(PGE) ore genesis?: Economic Geology and the Bulletin of the Society of Eco-nomic Geologists, v. 108, p. 45–58, doi:10.2113 /econgeo.108.1.45.

Shafiei, B., Haschke, M., and Shahabpour, J., 2009, Recycling of orogenic arc crust triggers por-phyry Cu mineralization in Kerman Cenozoic arc rocks, southeastern Iran: Mineralium Depos-ita, v. 44, p. 265–283, doi:10.1007/s00126-008 -0216-0.

Tafti, R., Mortensen, J.K., Lang, J.R., Rebagliati, M., and Oliver, J., 2009, Jurassic U-Pb and Re-Os ages for the newly discovered Xietongmen Cu-Au porphyry district, Tibet, PRC: Implica-tions for metallogenic epochs in the southern Gangdese belt: Economic Geology and the Bulle-tin of the Society of Economic Geologists, v. 104, p. 127–136, doi:10.2113 /gsecongeo .104.1.127.

Tang, J.X., Li, F., Li, Z., Zhang, L., Deng, Q., Lang, X., Huang, Y., Yao, X., and Wang, Y., 2010, Time limit for formation of main geological bodies in Xiongcun copper-gold deposit, Xietong-men County, Tibet: Evidence from zircon U-Pb ages and Re-Os age of molybdenite [in Chinese with English abstract]: Mineral Deposits, v. 29, p. 461–475.

Tomkins, A.G., Rebryna, K.C., Weinberg, R.F., and Schaefer, B.F., 2012, Magmatic sulfide forma-tion by reduction of oxidized arc basalt: Journal of Petrology, v. 53, p. 1537–1567, doi:10.1093 /petrology/egs025.

Wei, Y.-Q., 2014, The geochronology, geochemistry and petrogenesis of the volcanic rocks of Yeba Formation, southern Tibet [unpublished Ph.D. thesis]: Beijing, China University of Geosci-ences, 66 p.

Yang, Z.M., Hou, Z.Q., White, N.C., Chang, Z., Li, Z., and Song, Y., 2009, Geology of the post-collisional porphyry copper-molybdenum deposit at Qulong, Tibet: Ore Geology Reviews, v. 36, p. 133–159, doi:10.1016/j .oregeorev .2009.03.003.

Yin, A., and Harrison, T.M., 2000, Geologic evolu-tion of the Himalayan-Tibetan orogen: Annual Review of Earth and Planetary Sciences, v. 28, p. 211–280, doi:10.1146/annurev.earth.28.1.211.

Zhu, D.C., Pan, G.T., Chun, S.L., Liao, Z.L., Wang, L.Q., and Li, G.M., 2008, SHRIMP zircon age and geochemical constraints on the origin of Early Jurassic volcanic rocks from the Yeba Formation, southern Gangdese in south Tibet: International Geology Review, v. 50, p. 442–471, doi:10.2747/0020-6814.50.5.442.

Manuscript received 17 October 2014 Revised manuscript received 21 December 2014 Manuscript accepted 12 January 2015

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