Decompressional Anatexis in the Migmatite Core Complex of Northern Dabie Orogen, Eastern China: Petrological Evidence and Ti-In-Quartz Thermobarometry

Lithos 202–203 (2014) 227–236

Contents lists available at ScienceDirect

Lithos

journal homepage: www.elsevier.com/locate/lithos

Decompressional anatexis in the migmatite core complex of northern Dabie orogen, eastern China: Petrological evidence and Ti-in-quartz thermobarometry

Chao Zhang a,c,⁎, Francois Holtz a, Jürgen Koepke a, Jasper Berndt b, Changqian Ma c a Institut für Mineralogie, Leibniz Universität Hannover, Callinstr. 3, D-30167 Hannover, Germany b Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149 Münster, Germany c State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, 430074 Wuhan, China article info abstract

Article history: The voluminous diatexites in the Dabie orogen of eastern China indicate spectacular anatexis in the orogen base- Received 19 March 2014 ment before exhumation to shallow depths, but determination of the pressure–temperature (P–T) conditions for Accepted 10 May 2014 anatexis in the core complex is problematic because of the lack of suitable mineral assemblages in the diatexite Available online 2 June 2014 and of re-equilibrations during the retrograde stages. To overcome this problem, we studied an amphibolitic migmatite, which occurs as a raft in the diatexites of the central dome and has been partially melted at a very Keywords: low degree. In such rocks with low degree of melting, the microstructures still reveal the high temperature Exhumation – Migmatite melting reactions, and thus mineral analyses can be used to constrain anatectic P T conditions and interpret Anatexis the geochemical characteristics of partial melts. We demonstrate from petrological evidences that incongruent Amphibole partial melting of amphibole + plagioclase + quartz lead to the formation of clinopyroxene and silicate melt. Ti-in-quartz thermobarometer Trace element analyses of clinopyroxenes conﬁrm that they have been equilibrated with anatectic melts. Two Dabie orogen types of amphiboles can be identiﬁed, and the amphibole cores have high Al2O3 (N9.0 wt.%) and TiO2 (N1.5 wt.%) contents suggesting a nearly constant temperature of 850–850 °C with a pressure varying from 6

to 2 kbar. In contrast, the rims of some amphibole grains have low Al2O3 (b8.0 wt.%) and TiO2 (b1.2 wt.%) contents indicating temperatures lower than 750 °C at low pressures (b2 kbar). We propose two distinct phases in the tectonic evolution of the migmatite core complex in the northern Dabie orogen. The early-stage is a near- isothermal exhumation and the investigated rocks are characterized by a decompression from more than 20 km to ~6 km. Low degree partial melting in the infertile quartz-poor amphibolite occurs at low pressure during this exhumation phase. The second phase is characterized by a shallow (nearly isobaric) cooling stage. These two tectonic phases are recorded in quartz grains using Ti-in-quartz thermobarometry. The quartz in contact with or enclosed in clinopyroxene and plagioclase is characterized by Ti concentrations with an average value of ~50 ppm. These quartz grains have been equilibrated at high temperatures and pressures during the anatexis and were chemically isolated in Ti-poor phases during the low-pressure cooling phase. On the other hand, the quartz enclosed in amphibole has much higher Ti concentrations up to ~140 ppm which is the result of further incorporation of Ti released from the host mineral during the low pressure cooling. Diffusion modeling on one Ti concentration proﬁle in quartz enclosed in amphibole suggests fast cooling within 800–650 °C with a rate of ca. 0.2 °C/yr. This study demonstrates that the application of the Ti-in-quartz thermobarometer to lithol- ogies with low fertility may be extremely helpful to constrain anatectic P–T conditions and exhumation history of migmatized orogen basements. © 2014 Elsevier B.V. All rights reserved.

1. Introduction occurring by means of exhumation. Deep partial melting (anatexis) in the continental crust has a critical effect on weakening rocks and pro- Continental orogens generally evolve along a route well known moting deformation (Jamieson et al., 2011; Rosenberg and Handy, as the Wilson Cycle, which ends with intense thinning of orogens 2005), which ﬁnally cause architectural rebuilding, chemical differenti- ation and rapid exhumation of thick mountain belts (Rey et al., 2001). Such an anatexis-induced crustal evolution scenario may have been ⁎ Corresponding author at: Institut für Mineralogie, Leibniz Universität Hannover, in progress for the active Himalaya (Ganguly et al., 2000; Harris and Callinstr. 3, D-30167 Hannover, Germany. Tel.: +49 511 762 5517; fax: +49 511 762 3045. Massey, 1994; Harris et al., 2004) and may have played an important E-mail address: [email protected] (C. Zhang). role in the exhumation processes of numerous ancient continental

http://dx.doi.org/10.1016/j.lithos.2014.05.024 0024-4937/© 2014 Elsevier B.V. All rights reserved. 228 C. Zhang et al. / Lithos 202–203 (2014) 227–236 collision orogens, such as the Variscan orogen of central Europe (Brown 2. Geological background and Dallmeyer, 1996) and the Appalachian orogen of North America (Solar and Brown, 2001). To dissect the mechanisms controlling The Dabie orogen is a part of the Qinling-Tongbai-Dabie-Sulu orogen exhumation, structural evidence and thermodynamic modeling UHP-HP metamorphic terrane in eastern China. The exhumation of have merits for decoding the deformation and metamorphic paths the UHP rocks from N100 km depth to the upper crust was accom- (Schulmann et al., 2008; White et al., 2005), while petrological plished by multiple stages (Li et al., 2005; Wu and Zheng, 2013), while microstructures are of particular importance in recognizing anatexis the last exhumation stage at the Early Cretaceous has been suggested (Holness et al., 2011). to be dominated by crustal extension and doming (Hacker et al., 1995; The exhumation history of the Dabie orogen, namely the pressure– Ratschbacher et al., 2000). Furthermore, the Early Cretaceous tectonic temperature-time (P–T–t) path, has been widely investigated by phase extension has effected a large scale area of eastern China (Wu et al., equilibrium thermodynamics for the P–T paths (e.g. Cong et al., 1995; 2005), the driving force has been ascribed to upwelling of hot astheno- Wei et al., 1998; Zhang et al., 2009) and by isotopic thermochronologies spheric mantle (Huang et al., 2007; Jahn et al., 1999; Wang et al., 2007; for the T–t paths (e.g. Eide et al., 1994; Hacker et al., 2000; Li et al., 2000; Xie et al., 2011; Zhao et al., 2005) and/or associated with the northwest- Liu et al., 2010; Ratschbacher et al., 2000). These investigations, which ward subduction of the Paleo-Pacific Plate beneath East China (Li and Li, have been mainly performed on ultra high-pressure (UHP) and high- 2007; Zhang et al., 2011). pressure (HP) metamorphic rocks or their debris in sediment basins, Based on metamorphic grades, the Dabie orogen can be divided into revealed multiple cooling/exhumation stages with different cooling several petrotectonic units outlined by faults (Fig. 1)(You et al., 1996; rates for UHP-HP rocks [see views of Li et al. (2005), Wang et al. Zhang et al., 1996), which are the Northern Dabie high-temperature (2008) and Wu and Zheng (2013)]. Recently, partial melting of the metamorphic core complex, the Central Dabie medium-temperature UHP-HP rocks during exhumation at great depths (N20 kbar) in the UHP-HP metamorphic rocks, and the Southern Dabie low-temperature Dabie-Sulu orogenic belt has been evidenced by geochemical and petro- ultra high-pressure metamorphic rocks, and the Su-Song Unit (SSU) logical studies (Chen et al., 2013; Wang et al., 2013; Xu et al., 2013; Zhao of low-temperature UHP-HP metamorphic rocks. The core complex et al., 2012) and confirmed by high-pressure melting experiments dome in the Northern Dabie is characterized by extensive and intensive (Liu and Wu, 2013). migmatization (Faure et al., 1999) and is composed of an outer However, a late lithospheric extensional and orogenic doming at the metatexite zone and an inner diatexite zone (Fig. 1). Zircon U–Pb dating Cretaceous (Wang et al., 1998, 2011), which might finally brought the of leucosomes of grey diatexite (Wu et al., 2007) indicates that anatexis UHP-HP rocks to the near-surface level (Faure et al., 1999; Hacker of the orogenic basement occurred nearly simultaneously with et al., 1995), was poorly constrained for the P–T–t path and the the large-scale post-collisional granitoid plutonism at 145–120 Ma relevant information can hardly be derived from studies on eclogite- (Ma et al., 1998; Xu et al., 2007; Zhang et al., 2010). The voluminous facies rocks. Thermochronological studies on a large body of basement Early Cretaceous granitoids in the Dabie orogen can be divided into samples collected across the Dabie orogen provide important data two types based on distinct ages and geochemical features (He et al., on the final-stage low-temperature (b400 °C) exhumation processes 2011; Wang et al., 2007; Xu et al., 2007), including (1) the early-stage (e.g. Grimmer et al., 2003; Reiners et al., 2003), which however cannot (145–130 Ma) granitoids derived from orogenic root of the thickened constrain the high-temperature (N600 °C) migmatization-related crustal extensional processes in the core complex. It is also notable that many thermochronological approaches usually need to transfer isotopic closure temperatures to pressures by assuming P/T gradients and this approach may result in great uncertainties without well- constrained thermal-depth profile for a geological period (England and Molnar, 1990), because P/T gradients usually vary widely along the evolution path of an orogenic belt (England and Thompson, 1984; Thompson et al., 1987). Compared to studies on eclogites and low-temperature thermochronologies, thermodynamic researches on granulites from the migmatite core complex of the northern Dabie orogen (Chen et al., 1998, 2006) may provide information more closely associated with the P–T path of doming processes, and the results show that temperatures as high as 850–900 °C could have been reached during the last exhumation stage at pressures below 6 kbar. Such a high temperature would induce extensive anatexis in the basement rocks of the dome, as being proved by zircon dating for felsic migmatites (Wu et al., 2007), which in turn would promote further crustal extension and exhumation (Faure et al., 1999). However, granulites tend to be sluggish at lower P–T conditions after peak metamorphism, especially when they have been previously depleted in felsic components in earlier anatectic events. Therefore, although some P–T–t information about exhumation of the migmatite core complex of the northern Dabie orogen has been obtained from investigations on granulites, further studies are required to improve our understanding of the coupling between anatexis and exhumation during the Cretaceous crustal extension of the Dabie orogen. For this purpose, we present a mineralogical and geochemical study on an amphibolitic metatexite which is enclosed in diatexites of the central dome of the Northern Dabie. This rock type suffered low-degree partial melting along a decompressional path, and the results are used to Fig. 1. Geological sketch map of the Dabie orogen (modified after Faure et al., 1999). The – contain the P T conditions associated with low pressure anatexis and sample location is within the diatexite zone, near the center of the migmatite dome in exhumation. the Northern Dabie. C. Zhang et al. / Lithos 202–203 (2014) 227–236 229 crust and (2) the late-stage (130–115 Ma) granites sourced from 3.2. LA-ICP-MS shallower depths after orogenic collapse and crustal thinning. The diatexite zone in the Northern Dabie shows various morphol- Trace element concentrations in clinopyroxene and amphibole were ogies, while foliated leucosomes and co-deformed melanosomes are measured using a laser-ablation-inductively coupled plasma-mass spec- most abundant. However, some undeformed melanocratic rafts within trometry (LA-ICP-MS) at Institute of Mineralogy, University of Münster, the diatexite show sharp contacts with the surrounding migmatites Germany. The ablation system was a 193-nm excimer laser (UP193HE, (Fig. 2), indicating that these melanocratic rocks may have evolved as New Wave Research) and ablated particles were transported by helium a nearly closed system with little exchange with the silicate melts carrier gas and mixed with argon before entering an Element 2 formed in the grey diatexite. In this study, we focus on one of these (ThermoFisherScientific) single collector mass spectrometer. Laser spot melanocratic rafts which have very low degree of melting and thus diameter was 35 μm. A NIST 612 reference material was used as external can be used to constrain original anatexis reactions. standard, while the SiO2 concentrations determined by electron microprobe were used as internal standard (29Si) for quantification. Overall measurement time for one analysis was 60 s, with 20 s for background 3. Analytical methods and 40 s for peak signal. Raw data were reduced using GLITTER program (Griffin et al., 2008; Van Achterbergh et al., 2001). Average 1-sigma 3.1. Electron microprobe standard errors are generally believed to be better than 5% for element concentrations above 0.1 ppm. The major element composition of rock-forming minerals was determined using a Cameca SX100 electron microprobe at Institute of 4. Petrography and mineral composition Mineralogy, Leibniz University of Hannover, Germany. Standard mate- rials include wollastonite (Si and Ca), albite (Na), orthoclase (K), and The bulk composition of the sampled amphibolitic metatexite is synthetic Al2O3,TiO2,Fe2O3,MgOandMn3O4. A 15 kV acceleration close to that of an alkali-rich basalt (Supplementary Table 1), and the voltage was used for all analyses. Raw data were corrected using the mineral assemblage includes mainly amphibole (Amp, ~55%) and standard PAP procedures (Pouchou and Pichoir, 1991). For analyzing plagioclase (Plg, ~40%), as well as minor clinopyroxene (Cpx, ~1%), major elements of feldspar, pyroxene and amphibole, a focused beam quartz (Qtz, ~2%), alkali feldspar (Kfs, ~2%) and titanite (Ttn, ~1%). was used. For analyzing the trace elements (Ti, Al, K and Fe) in quartz, we used a high beam current of 150 nA and a long peak time of 360 s 4.1. Clinopyroxene as well as a background time of 180 s on both sides, and large PET as diffracting crystal for Ti. The detection limit of Ti is about 13 ppm and Cpx forms bands or chains around Qtz (Fig. 3A), or sometimes occurs the absolute uncertainty is about 11 ppm. Most analyses on quartz as rounded individual grains enclosing Qtz and prehnite (Prh) (Fig. 3B). were conducted with a 5-μm diameter beam. A few analyses were per- The Cpx throughout the sample has a homogenous diopside composi- formed with a 2-μm diameter or focused beam and the results indicate tion, with Mg# [100 × molar Mg/(Mg + Fe)] of 70.3 ± 1.3, Al2O3 and no systematic difference using different beam sizes. Analyses on a TiO2 contents of 1.41 ± 0.15 wt.% and of 0.15 ± 0.02 wt.%, respectively MM-3 (Mineral Mountains obsidian) glass using this setting (beam (Supplementary Table 2). Microscopic observations reveal that Cpx only size 2 μm) obtained 0.15 ± 0.01 (2σ)wt.%TiO2, which is consistent to occurs occasionally and that is mostly coexisting with Qtz. This textural the average value (0.14 ± 0.02 wt.%) reported in Nash (1992).We relationship is useful to interpret the melting reactions and the crystal- also measured the recently calibrated reference quartz (a smoky natural lization of phases from silicate melt, as discussed below (see also quartz from Shandong, China) by Audétat et al. (under review) using Section 4.4). As revealed by dehydration melting experiments of this setting (beam size 2 μm), the obtained Ti concentration of amphibole-bearing protoliths with and without Qtz, a protoliths 52 ± 3 ppm is consistent within error to the recommended value of containing Qtz is more fertile than without Qtz, and the former has a 57 ± 4 ppm (Audétat et al. under review). fluid-absent dehydration melting solidus temperature which is lower

Fig. 2. Photograph of grey diatexite and engulfed amphibolite metatexite raft in the central dome of the Northern Dabie. A: The grey diatexite is schlieren-nebulitic with syn-anatectic ﬂow fabrics. The dark amphibolite metatexite contains some ﬁne-grained leucosomes (see their compositions in Supplementary Table 1) observable at the lower part of the melanocratic raft. Some coarse-grained leucocratic veins across can be seen just below the notebook, and they are clearly intrusions from grey diatexite which cut across the amphibolite metatexite. The width of the notebook is 12 cm. Sample location is 30°57.086′N, 115°13.059′E, Yantianhe Town, Luotian County. B: A scan of thin section for a close view of the amphibolite metatexite. The major minerals are dark–green to brownish amphibole and colorless plagioclase. 230 C. Zhang et al. / Lithos 202–203 (2014) 227–236

Fig. 3. Microstructures in the amphibolite metatexite. A: Multiple coronal Cpx grains form a chain around Qtz and separates from outer Amp and Plg. The three enclosed-in-Cpx Qtz grains contact with each other at junction and form ca. 120° dihedral angle, indicating equilibrium crystallization. The harbor-shaped Amp contacting Cpx indicates reactions consuming Amp but generating Cpx. The numbers denote LA-ICP-MS analyses on Cpx and Amp (see Supplementary Table 5). B: Single rounded Cpx crystal forms at junction of three Amp grains, and encloses

Qtz, Prh and alkali Kfs. C: Dendritic Plg constrained by Amp boundaries coexists with rounded Ttn. A rounded rutile (Rut) is enclosed by Ttn, indicating that activity of TiO2 decreased from sub-solidus to anatectic condition. D: Plg occurs in a conduit-like morphology enclosed in Amp phenocryst and further includes rounded Qtz and Kfs. Kfs occurs as schlierens rimming Qtz or individual anhedral patches enclosed in Plg. A and B are photos under plane-polarized light; C and D are back-scattered electron (BSE) images. than the latter, all other conditions being similar (e.g. Rushmer, 1991). 4.2. Amphibole Therefore, we consider that the presence of Cpx only in the vicinity of Qtz is an indication for incongruent partial melting at preferred loca- The Amp forms the framework of the rock with subhedral and tions where primitive Qtz existed, and the melting can be expressed anhedral morphologies. Some Amp grains exhibit embayed boundaries by the reaction Amp + Plg + Qtz = Cpx + H2O-bearing melt. contacting with Plg and Cpx (Fig. 3), which suggests that local melting

Fig. 4. Figure showing two types of amphibole. A: Back-scattered electron image showing amphibole (Amp) rim overgrowth between the main body amphibole and peritectic clinopyroxene (Cpx). Compared to Amp Core (main part), Amp rim is characterized by weaker brightness under BSE, and lower Ti and Al concentrations. The boundary of Cpx is outlined by the dashed curve. B: P–T estimation based on Al2O3 and TiO2 contents in Amp (according to Ernst and Liu, 1998). C. Zhang et al. / Lithos 202–203 (2014) 227–236 231 reactions have partially consumed the Amp rims (Holness et al., 2011; 1000 Sawyer, 1999). Compositionally the Amp in the amphibolite metatexite leucosome varies from pargasite to edenite with a consistent CaO content of 11– modeled melt from Amp 12.5 wt.% (Supplementary Table 3), but can be divided into two groups, modeled melt from Cpx late stage granites i.e. the Amp-core (main part of the minerals) and the Amp-rim group. 100 early stage granitoids As shown in the BSE image of Fig. 4A, the Amp rims only occur as narrow overgrowths or along some boundaries between Cpx and Amp. The

Amp-core has much higher Al2O3 (N9.0 wt.%) and TiO2 (N1.5 wt.%) contents compared to the rim of some Amp grains which have lower 10 Al2O3 (b8.2 wt.%) and TiO2 (b1.2 wt.%) contents.

normalized to chondrite 4.3. Feldspar

Anhedral Plg grains usually occur as an interstitial phase surrounded 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu by Amp grains (Fig. 3 A) and occasionally they can enclose Qtz, Amp, Ttn and rutile (Rut) (Fig. 3C–D). Distinguishing igneous and metamorphic Fig. 5. Rare earth element (REE) patterns of modeled partial melts from amphibole and Plg from mineral composition is not possible in this case, since all clinopyroxene trace element compositions (Supplementary Table 5). Also shown for com- measured Plg grains of variable textures show consistent anorthite parison are a leucosome from the amphibolite metatexite (see Fig. 2 and Supplementary (An) molar proportion of ca. 0.3–0.4 (Supplementary Table 3). Kfs is Table 1), and the late stage granites and early stage granitoids (after Xu et al., 2007). The often observed as a thin layer between Plg and Qtz (Fig. 3D) and this chondrite composition for normalization is after Sun and McDonough (1989). It is notable texture is interpreted to be formed as a result of cooling, suggesting that all modeled melts and the leucosome have less depleted heavy REE, which is similar to that of the late stage granites (low-pressure origin) but different from that of early stage that high-temperature Plg had crystallized from K-bearing silicate granitoids (high-pressure origin). melt previously. heavy REE. A similar pattern is observed for melts modeled from Amp, 4.4. Quartz but the trace element concentration of the modeled melt has an overall higher concentration of REE (Fig. 5). We interpret that the difference be- Fig. 3A presents a typical occurrence of Qtz crystals located next to tween the modeled melt compositions most likely reﬂects disequilibri- Cpx crystals, where the Qtz boundaries form a dihedral angle of ca. um between the Amp and silicate melt. The Amp cores analyzed by 120° at the junction of three grains, which likely resulted from equilib- LA-ICP-MS correspond to the composition of minerals prior to anatexis rium crystallization from a silicate melt. The crystallization of Qtz im- which did not re-equilibrate with the partial melt. In contrast, the Cpx plies that the anatectic melt was nearly saturated with respect to SiO2 formed as a result of the melting reaction is expected to be in equilibri- and thus the melting degree should be extremely low (e.g. Beard and um with the silicate melt. This conclusion also implies that partial Lofgren, 1991). The textural observations indicate that other Qtz crys- melting only took place locally, involving phases close to the mineral tals may have a different origin (Fig. 3A). In particular, the tiny rounded interface, rather than being pervasive. Qtz grain enclosed in a single Cpx grain shown in Fig. 3Bislikelyan Previous studies on the Early Cretaceous granitoids in the Northern anatectic residue, and the presence of Prh and Kfs next to the Cpx may Dabie revealed two types with distinct ages and geochemical features result from the transformation of former hydrous Al2O3-rich minerals (He et al., 2011; Wang et al., 2007; Xu et al., 2007). The early stage gran- which crystallized from the anatectic melt. Similarly, we propose that itoids show much stronger depletion in heavy REE with high Sr/Y ratios the rounded single Qtz grains enclosed in Plg and Amp (Fig. 3D) may which likely corresponds to partial melting of orogenic root prior to the be interpreted as anatectic residue. Based on the microstructure Cretaceous extension, while the late stage granites show less depletion described above, we may divide Qtz into four groups, including in heavy REE which suggests much shallower melting depths after ex- (i) crystallization-type Qtz at the contact with Cpx, (ii) residue-type tensive thinning of the Dabie orogen (Ma et al., 2004; Xu et al., 2007). Qtz enclosed in Cpx, (iii) residue-type Qtz enclosed in Plg and When comparing these two felsic magma types with the melt composi- (iv) residue-type Qtz enclosed in Amp. tions modeled from Cpx, it can be noted that the generation and melting reaction of the late stage granites may be similar to that described in the 5. Evidence of partial melting from trace element compositions metatexite in this study. Thus, the later stage granitoids might be origi- nated from low-degree partial melting of amphibolitic protoliths at As indicated by the microstructures described above, partial melting shallow depths, likely b30 km, where garnet is not stable as a residual might have occurred via the reaction Amp + Plg + Qtz = Cpx + Melt. phase (e.g. Beard and Lofgren, 1991; Zhang et al., 2013) and thus the Here, we use the trace element concentrations of Cpx and Amp mea- partial melts are characterized by the absence of a strong depletion in sured by LA-ICP-MS to estimate the composition of partial melt, assum- heavy REE. ing equilibrium trace element distribution between Amp, Cpx formed by dehydration melting, and the partial melt. The partition coefﬁcients of trace elements between Amp, Cpx and silicate melt compiled by 6. Estimation of P–T conditions Bédard (2006) to model partial melting processes of metabasites have been applied. We then compare the modeled partial melt compositions 6.1. Al- and Ti-in-amphibole thermobarometry to leucosome veins sampled within the amphibolitic metatexite, in order to clarify the contribution of the partial melting in amphibolitic Amphibole composition has been widely used to constrain pressure metatexites. and temperature in both metamorphic and igneous rocks. Here we use As shown in the chondrite-normalized rare earth element (REE) the Al- and Ti-in-amphibole thermobarometer of Ernst and Liu (1998), diagram of Fig. 5, the modeled REE pattern of a melt in equilibrium which has been calibrated for calcic amphibole in metabasaltic rocks with Cpx is consistent with that of a leucosome sampled from the within 2–20 kbar and 450–1050 °C. As mentioned above (see also amphibolite metatexite raft (see Fig. 2 and Supplementary Table 1), Fig. 3C–D), titanite is ubiquitous as an accessory mineral contacting which is supposed to have crystallized in situ from anatectic melt. The amphibole, which allows the application of the thermobarometer. spectra of both the leucosome and the modeled partial melt from Cpx Two compositionally different Amp groups can be distinguished, the show strong enrichment in light REE as well as slight enrichment in Ti-rich and Al-rich Amp-core (main part) and the Ti-poor and Al-poor 232 C. Zhang et al. / Lithos 202–203 (2014) 227–236

Amp-rim (Fig. 4A). When plotted in a P–T diagram (Fig. 4B), the consistent with the presence of Ttn (sometimes enclosing Rut) in the Amp-cores indicate temperatures of ca. 800–850 °C and pressures of liquid‐rutile studied rock (Fig. 3C and D). As shown in Fig. 6 the value of aTiO is in the range of 2–6 kbar, whereas the Amp-rims show lower tempera- 2 in the range 0.2 to 0.3 at temperatures of 850 to 800 °C. It can be noted tures in the range of 650–750 °C and pressures below 2 kbar. that Qtz and Plg are the dominant phases crystallizing in this temperature range, which is consistent with our observations in the metatexite. 6.2. Ti-in-quartz thermobarometry In the investigated sample, the Ti concentrations of the Qtz grains at the contact with Cpx or enclosed in Cpx are similar with those of the Qtz In the last years, Ti concentration in Qtz has been experimentally enclosed in Plg, which are all ranging within 20–80 ppm and culminat- calibrated and can be used as thermobarometer (Huang and Audétat, ing at an average of ~50 ppm (Fig. 7). In contrast, the Qtz enclosed in 2012; Thomas et al., 2010; Wark and Watson, 2006). At constant Amp has a wider range of Ti concentrations with maximum values as temperature and TiO activity, Ti increases with decreasing pressure. 2 high as 140 ppm. Applying the re-calibrated Ti-in-Qtz thermobarometer Hence, decompression-induced Ti variations in Qtz might be of poten- of Huang and Audétat (2012) to all types of Qtz and using a value of tial significance to interpret near-isothermal geological processes such ‐ aliquid rutile estimated at 850 or 800 °C, we obtained pressures varying as magma plumbing systems and crustal doming and can be applied TiO2 to trace decompression paths in this study. Fast exhumation of from zero to 5.5 kbar (Fig. 8). The pressures estimated from the thickened orogenic belts (such as the Dabie orogen) from a great Qtz enclosed in Amp (group iv) yield a low pressure range within depth toward surface usually occurs at near-isothermal conditions ca. 0–2.5 kbar, whereas the values estimated from other Qtz are within (Whitney et al., 2004) and is a geological process which should affect ca. 2–5.5 kbar. These two pressure ranges are in good agreement with the Ti concentration in Qtz. According to the calibrations of Thomas that indicated by Al- and Ti-in-Amp thermobarometry which also indi- et al. (2010) and Huang and Audétat (2012), Ti concentrations should cates two distinctive pressure ranges (Fig. 5B). increase with decreasing pressure, at constant temperature and for a Since Ti concentration in Qtz is expected to increase with decompression, a source for Ti is necessary and can only be provided by the given activity of TiO2. Thus, tracing pressure variations using Ti-in-Qtz host or neighboring minerals. The systematically low Ti concentration requires estimations of temperature and activity of TiO2. We propose that the temperature range of 800–850 °C which of the Qtz enclosed in Cpx and Plg compared to that of the Amp- corresponds to the major group of Amp (Fig. 4B) is the dominant condi- enclosed Qtz (Fig. 6) can be explained by the insufficient Ti supply tion for equilibrating Ti distribution in both crystallization-type and from Plg or Cpx during exhumation. In contrast, Amp which contains fi residue-type Qtz. As indicated by amphibole thermobarometry up to ~2 wt.% TiO2 (Supplementary Table 4) can offer suf cient Ti via (Fig. 4B), the amphibolitic metatexite has likely undergone a rapid diffusion for its incorporation into Qtz. This interpretation is verified shallow cooling after being exhumed from ~6 kbar to less than 2 kbar. by the concentration profiles measured in contacting Qtz and Amp. As Considering that the diffusivity of Ti in Qtz becomes exponentially shown in Fig. 9A, the measured Ti concentrations across a subhedral lower with decreasing temperature (Cherniak et al., 2007), the Ti con- Qtz grain enclosed in Amp show gradual increase in Ti from core to centration of Qtz formed at higher temperature during partial melting rim. Furthermore, the Ti concentration across the host Amp decreases and exhumation is not expected to be modified significantly during gradually from the inner part to the Qtz-Amp boundary (Fig. 9B), the low-pressure cooling process. liquid‐rutile The activity of TiO2 inthemeltrelativetorutilesaturation(a ) TiO2 is an essential parameter for applying Ti-in-Qtz thermobarometry. This 15 parameter was estimated with the program rhyolite-MELTS (Gualda Group (i) : et al., 2012) by simulating a crystallization route, using a starting melt 10 crystallized Qtz surrounded by Cpx composition which was assumed to be identical to a high-SiO2 melt derived from an experimental partial melting of a Qtz-bearing metabasalt Count 5 at 6.9 kbar (Beard and Lofgren, 1991). The experimental melt containing 0 0.16 wt.% TiO2 is nearly saturated with respect to Ttn (but not Rut) at ca. 0 20 40 60 80 100 120 140 850 °C according to the experiments of Price et al. (1999), which is 10 Group (ii) : 50 1.0 residual Qtz enclosed in Cpx liquid-rutile 5 quartz a 0.9 magnetite TiO2 Count 40 clinopyroxene 0.8 plagioclase 0 orthopyroxene 0.7 020406080 100 120 140 30 amphibole 0.6 50 Group (iii) : titanite 40 muscovite 0.5 residual Qtz enclosed in Plg 20 30

liquid-rutile 0.4 TiO2 a 20 Count 0.3 10 10 0

Phase proportion (wt%) 0.2 0 20 40 60 80 100 120 140 0 0.1 15 Group (iv): 0.0 residual Qtz enclosed in Amp 900 850 800 750 700 650 600 10 Temperature (°C)

Count 5

liquid‐rutile Fig. 6. Variation of phase proportions and a during crystallization of a high-SiO2 TiO2 0 melt, calculated using rhyolite-MELTS (Gualda et al., 2012). The starting composition for 0 20 40 60 80 100 120 140 crystallization modeling is the partial melt produced by the experiment at 6.9 kbar and 850 °C of Beard and Lofgren (1991) using starting composition 478. The melt composition Ti in quartz (ppm) is: SiO2 75.64 wt.%, TiO2 0.16 wt.%, Al2O3 14.49, FeOtotal 2.10 wt.%, MnO 0.06 wt.%, MgO

0.24 wt.%, CaO 2.70 wt.%, Na2O 2.83 wt.%, K2O 1.76 wt.%; and 5.73 wt.% H2O. Fig. 7. Histograms of Ti concentration in different groups of quartz. C. Zhang et al. / Lithos 202–203 (2014) 227–236 233

Qtz groups i + ii + iii Qtz group iv

8 8 A Temp. = 800°C B Temp. = 850°C 20 7 7 liquid-rutile liquid-rutile 20 aTiO2 = 0.3 aTiO2 = 0.2 6 6

5 5 30 30 4 4

40 3 3 40

Pressure (kbar)

Ti in quartz (ppm) Ti in quartz (ppm) 50 2 2 50 60 60 1 80 1 100 80 100 140 0 0 140 060010 20 30 40 50 70 80 90 10 20 30 40 50 60 70 80 Count Count

‐ ‐ Fig. 8. Histogram of Ti concentration in quartz and estimated pressure. A: Estimation using 800 °C and aliquid rutile of 0.3. B: Estimation using 850 °C and aliquid rutile of 0.2. The Ti-in-quartz TiO2 TiO2 thermobarometer of Huang and Audétat (2012) is used for calculating pressure. It is noted that the estimated pressures for the two different temperatures are consistent with each other. which clearly demonstrates apparent transfer of Ti from Amp to Qtz event (isothermal decompression path at 800 °C), a pressure of ~1 during the exhumation. kbar may have been reached. The concentration profile which can be The concentration profile of Ti in Qtz can also be used to constrain observed at the rim of the Qtz crystal (up to ~140 ppm Ti) must be time scale of decompression in the metatexite. In the example shown the result of incorporation of Ti due to further decompression and in Fig. 9A, the Ti concentration in the Qtz core is ~105 ppm and, assum- cooling. Assuming a constant pressure decrease/temperature decrease ing that this concentration is representative of the high temperature (dP/dT) ratio from 800 to 650 °C at pressures b2 kbar, we performed finite difference modeling for Ti diffusion in Qtz in order to estimate the cooling rate during the last exhumation stage. The modeling method 140 is principally the same as that used by Spear et al. (2012),applyingthe Y’ 0.15 yr°C/ Ti-in-Qtz diffusivity determined by Cherniak et al. (2007). The modeling results for two cooling rates of 0.15 °C/year and 0.5 °C/year are shown Y in Fig. 9A, which can best constrain the measured Ti concentrations in 130 Qtz X’ X’ the Qtz grain. The estimated cooling rate is surprisingly fast. However, this modeling on the basis one grain needs to be interpreted with X caution and should be confirmed by additional data. 120 7. Petrological and tectonic implications Amp 20 mµ The post-collisional exhumation history of the Dabie orogen after Ti in quartz (ppm) A continental subduction has been investigated widely by multiple ap- 110 0.5yr°C/ proaches, as discussed previously in the introduction. Thermodynamic and geochronological studies on UHP-HP rocks revealed fast exhuma- X tion and cooling from 700–800 °C to below 400 °C from ~230 Ma to Distance (µm) ~180 Ma [see views of Li et al. (2005), Wang et al. (2008) and Wu and 100 0 10 20 30 Zheng (2013)], and these exhumation P–T paths can hardly be related 1.9 to the core complex basement of the Dabie orogen because they were not in the same structural unit. In general, the UHP-HP rocks 1.8 B were exhumated as xenoliths or over-thrusting units above the core 1.7 complex (Li et al., 2005; Suo et al., 2004). The low-temperature Y’ thermochronological approaches yielded estimates of the exhumation 1.6 rate for the orogenic basement about 0.05–0.07 km per million years in Amp (wt%)

2 1.5 Y in the last 100 Ma, and about 0.1–0.5 km per million years within – TiO 1.4 Distance (µm) 140 100 Ma combining the estimation on pluton emplacement depths (Ratschbacher et al., 2000; Reiners et al., 2003). However, the syn- 0 10 20 30 exhumation petrological evolution and potential exhumation-induced anatexis in the core complex are still vague. As indicated by the thermo- Fig. 9. A: Ti concentration profile (□,X-X′) across a Qtz grain enclosed in Amp (see inserted BSE image). Also shown are two modeled diffusion-induced concentration dynamic studies on granulites (Chen et al., 2006), a high temperature of patterns assuming different cooling rates (0.15 °C/year and 0.5 °C/year) within the 850–900 °C could be reached during the last exhumation stage at pres- shallow cooling stage (800–650 °C, b2 kbar). The modeling is performed using finite sures below 6 kbar, and consequently dehydration melting would take difference solution for semi-infinite plate and the Ti-in-quartz diffusivity determined by place which might have resulted in the widespread formation of grey Cherniak et al. (2007). The initial Ti concentration is set to be 106 ppm, while the right- diatexites in the core complex (Faure et al., 1999; Wu et al., 2007). boundary Ti concentration is set to be solubility (after Huang and Audétat, 2012)atchang- Based on the petrological evidence of anatexis and mineral ing temperature and pressure along the cooling path. B: TiO2 content profile (■, Y-Y′) across amphibole, showing a decrease in Ti toward the Amp–Qtz boundary. thermobarometry data presented above, we propose a clockwise P–T– 234 C. Zhang et al. / Lithos 202–203 (2014) 227–236

8 than the cooling rates below 300 °C estimated from thermochronology a 1 near-isothermal b (~10 °C/Ma, Reiners et al., 2003). Although the uncertainty of our pre- exhumation liminary modeling using Ti-in Qtz is hard to constrain, we believe that 2 shallow cooling 6 20 it implies qualitatively that the post-anatexis exhumation and cooling are both extremely fast due to large scale anatexis and concomitant vis- dehydration cosity decrease in the core complex (Brown et al., 2011; Rosenberg and partial melting 1 Handy, 2005), and such rapid exhumation processes have been also 4 P-T path of Huangtuling observed in migmatite core complex for many other orogenic belts granulite (e.g., Brown and Dallmeyer, 1996; Ganguly et al., 2000; Harris et al.,

10 Depth (km) 2004).

Pressure (kbar) 2 8. Conclusions Solidus Reaction 2 a. Amp + Plg = Cpx + Melt b. Amp + Plg + Qtz = Cpx + Melt (1) Petrography and mineral compositions indicate low-degree par- 0 0 tial melting in the amphibolite metatexite from the core complex 700 800 900 1000 of the northern Dabie orogen, and the reaction can be described Temperature (°C) as Amp + Plg + Qtz = Cpx + H2O-bearing Melt. (2) The pressure and temperature estimates from Al- and Ti- in am- Fig. 10. P–T path for interpreting the relationship between anatexis and exhumation of the core complex in the northern Dabie. As indicated by Al- and Ti-in amphibole phibole thermobarometry and Ti-in-quartz thermobarometry thermobarometry and Ti-in-quartz thermobarometry, two stages of exhumation are pro- are principally consistent to each other, showing an early stage posed: (1) near-isothermal exhumation and (2) shallow cooling. The dehydration solidus of near-isothermal exhumation from 6 to 2 kbar, which was of quartz-free protolith (solid line a) is after Vielzeuf and Schmidt (2001) and Zhang et al. then followed by shallow cooling at pressures b2kbar. (2013), and that of quartz-bearing protolith (dashed line b) is proposed in this study. Also (3) Ti-in-quartz thermobarometer is a powerful tool in revealing shown for comparison is the P–T path of the Huangtuling granulite (Chen et al., 2006)in the core complex of the northern Dabie. decompression processes, provided that temperature and ‐ aliquid rutile could be fairly estimated. TiO2 t path which crossed the dehydration melting solidus of Qtz-bearing Supplementary data to this article can be found online at http://dx. amphibolitic protoliths (Fig. 10). The position of this solidus drawn in doi.org/10.1016/j.lithos.2014.05.024. Fig. 10 is modified from that for a Qtz-free amphibolite proposed by Vielzeuf and Schmidt (2001) and experimentally confirmed by Zhang Acknowledgments et al. (2013). The new solidus is explained by the presence of Qtz which should lead to a decrease of the melting temperature by ~50 °C The reference quartz was offered by Andreas Audetat (Bayerisches (Fig. 10). However, the exact position of the dehydration melting soli- Geoinstitut) for which we appreciate very much. We also thank Torsten dusisdifficult to constrain because it should be also dependent on the Bolte for helps concerning quartz analysis. We thank two anonymous compositions of coexisting Amp and Plg (see discussion in Zhang reviewers for their insightful and helpful comments. This work was sup- et al., 2013). Thus, a near-isothermal decompression is suggested to be ported partly by the German Research Council (DFG) (KO 1723/17-1) responsible for triggering low-degree partial melting at Qtz-present and the National Nature Science Foundation of China (NSFC) locations of the amphibolite protolith. For other more fertile protoliths (40334037 & 41272079). (felsic gneiss, metapelite, etc), anatexis should have undergone in a large temperature range and with a high melting degrees, which is References supported by the widespread grey diatexite and granitoids intrusives throughout the migmatite dome of the Dabie orogen. Audétat, A., Garbe-Schönberg, D., Kronz, A., Pettke, T., Rusk, B., Donovan, J., Lowers, H., 2014w. Characterization of a natural quartz crystal as reference material for microan- According to the P–T path constrained from Amp and Qtz, we alytical determination of Ti, Al, Li, Fe, Mn, Ga and Ge. Geostandards and Geoanalytical propose a two-stage exhumation path for the migmatite dome of the Research. Dabie orogen (Fig. 10). The early-stage exhumation is characterized by Beard, J., Lofgren, G., 1991. Dehydration melting and water-saturated melting of basaltic ≥ – and andesitic greenstones and amphibolites at 1, 3, and 6.9 kb. Journal of Petrology near-isothermal decompression from 6 kbar to ~2 1.5 kbar at tem- 32, 365–401. peratures of 850–800 °C, which induced dehydration partial melting Bédard, J.H., 2006. A catalytic delamination-driven model for coupled genesis of Archaean at Qtz-present locations. This early-stage high-temperature (N800 °C) crust and sub-continental lithospheric mantle. Geochimica et Cosmochimica Acta 70, 1188–1214. near-isothermal exhumation is suggested to have occurred within a Brown, M., Dallmeyer, R.D., 1996. Rapid Variscan exhumation and the role of magma in short period, because crustal extension is promoted by orogenic core complex formation: southern Brittany metamorphic belt, France. Journal of anatexis (Jamieson et al., 2011). After exhumation, the core complex Metamorphic Geology 14, 361–379. b Brown, M., Schulmann, K., White, R., 2011. Granulites, partial melting and the rheology of then suffered a late cooling stage at shallow depths ( 2kbar). the lower crust. Journal of Metamorphic Geology 29, 1–6. As shown in Fig. 10 for comparison, mineral assemblages and ther- Chen, N., Sun, M., You, Z., Malpas, J., 1998. Well-preserved garnet growth zoning in modynamic modeling of the Huangtuling granulite from the northern granulite from the Dabie Mountains, central China. Journal of Metamorphic Geology – 16, 213–222. Dabie core complex also reveal a clockwise P T path roughly parallel Chen, Y., Ye, K., Liu, J.-B., Sun, M., 2006. Multistage metamorphism of the Huangtuling gran- to that estimated from the amphibolite metatexite, particularly consid- ulite, Northern Dabie Orogen, eastern China: implications for the tectonometamorphic ering that the granulite and amphibolite metatexite reached their peak evolution of subducted lower continental crust. Journal of Metamorphic Geology 24, – temperature at a similar depth of about 5 kbar. However, there are 633 654. Chen, Y.-X., Zheng, Y.-F., Hu, Z., 2013. Synexhumation anatexis of ultrahigh-pressure differences in the estimates of peak temperature and shallow cooling metamorphic rocks: petrological evidence from granitic gneiss in the Sulu orogen. pressure, and our interpretation is that the granulite might be closer Lithos 156–159, 69–96. to the dome center than the amphibolite metatexite during the doming Cherniak, D.J., Watson, E.B., Wark, D.A., 2007. Ti diffusion in quartz. Chemical Geology 236, 65–74. process. In that case, the former would record a higher peak tempera- Cong, B., Zhai, M., Carswell, D.A., Wilson, R.N., Wang, Q., Zhao, Z., Windley, B.F., 1995. ture and the latter would suffer faster exhumation due to stronger Petrogenesis of ultrahigh-pressure rocks and their country rocks at Shuanghe in Dabieshan, central China. European Journal of Mineralogy 7, 119–138. shearing outwards the dome center. 40 39 – Eide, E.A., McWilliams, M.O., Liou, J.G., 1994. Ar/ Ar geochronology and exhumation The cooling rate within 800 650 °C estimated from Ti diffusion in of high-pressure to ultrahigh-pressure metamorphic rocks in east-central China. Qtz is surprisingly fast (0.15–0.5 °C/yr, Fig. 9A), which is much faster Geology 22, 601–604. C. Zhang et al. / Lithos 202–203 (2014) 227–236 235

England, P., Molnar, P., 1990. Surface uplift, uplift of rocks, and exhumation of rocks. Reiners, P.W., Zhou, Z., Ehlers, T.A., Xu, C., Brandon, M.T., Donelick, R.A., Nicolescu, S., 2003. Geology 18, 1173–1177. Post-orogenic evolution of the Dabie Shan, eastern China, from (U–Th)/He and England, P., Thompson, A., 1984. Pressure–temperature–time paths of regional metamor- fission-track thermochronology. American Journal of Science 303, 489–518. phism I. Heat transfer during the evolution of regions of thickened continental crust. Rey, P., Vanderhaeghe, O., Teyssier, C., 2001. Gravitational collapse of the continental Journal of Petrology 25, 894. crust: definition, regimes and modes. Tectonophysics 342, 435–449. Ernst, W.G., Liu, J., 1998. Experimental phase-equilibrium study of Al- and Ti-contents Rosenberg, C.L., Handy, M.R., 2005. Experimental deformation of partially melted granite of calcic amphibole in MORB—a semiquantitative thermobarometer. American revisited: implications for the continental crust. Journal of Metamorphic Geology 23, Mineralogist 83, 952–969. 19–28. Faure, M., Lin, W., Shu, L., Sun, Y., Scharer, U., 1999. Tectonics of the Dabieshan Rushmer, T., 1991. Partial melting of two amphibolites: contrasting experimental results (eastern China) and possible exhumation mechanism of ultra high-pressure rocks. under fluid-absent conditions. Contributions to Mineralogy and Petrology 107, Terra Nova 11, 251–258. 41–59. Ganguly, J., Dasgupta, S., Cheng, W., Neogi, S., 2000. Exhumation history of a section of Sawyer, E.W., 1999. Criteria for the recognition of partial melting. Physics and Chemistry the Sikkim Himalayas, India: records in the metamorphic mineral equilibria and of the Earth Part a—Solid Earth and Geodesy 24, 269–279. compositional zoning of garnet. Earth and Planetary Science Letters 183, 471–486. Schulmann, K., Lexa, O., Štípská, P., Racek, M., Tajčmanová, L., Konopásek, J., EDEL, J.B., Griffin, W., Powell, W., Pearson, N., O'Reilly, S., 2008. GLITTER: data reduction software Peschler, A., Lehmann, J., 2008. Vertical extrusion and horizontal channel flow of for laser ablation ICP-MS. Laser Ablation-ICP-MS in the Earth Sciences. Mineralogical orogenic lower crust: key exhumation mechanisms in large hot orogens? Journal of Association of Canada Short Course Series 40, 204–207. Metamorphic Geology 26, 273–297. Grimmer, J., Ratschbacher, L., McWilliams, M., Franz, L., Gaitzsch, I., Tichomirowa, M., Solar, G.S., Brown, M., 2001. Deformation partitioning during transpression in response to Hacker,B.,Zhang,Y.,2003.When did the ultrahigh-pressure rocks reach the sur- Early Devonian oblique convergence, northern Appalachian orogen, USA. Journal of face? A 207Pb/206Pb zircon, 40Ar/39Ar white mica, Si-in-white mica, single-grain Structural Geology 23, 1043–1065. provenance study of Dabie Shan synorogenic foreland sediments. Chemical Spear, F., Ashley, K., Webb, L., Thomas, J., 2012. Ti diffusion in quartz inclusions: implica- Geology 197, 87–110. tions for metamorphic time scales. Contributions to Mineralogy and Petrology 164, Gualda, G.A.R., Ghiorso, M.S., Lemons, R.V., Carley, T.L., 2012. Rhyolite-MELTS: a modified 977–986. calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: Journal of Petrology 53, 875–890. implications for mantle compositions and processes. In: Saunders, A.D., Norry, M.J. Hacker, B., Ratschbacher, L., Webb, L., Shuwen, D., 1995. What brought them up? (Eds.), Magmatism in the Ocean Basins. Geological Society of London, pp. 313–345. Exhumation of the Dabie Shan ultrahigh-pressure rocks. Geology 23, 743–746. Suo, S., Zhong, Z., Zhou, H., You, Z., 2004. Tectonic evolution of Dabie-Sulu UHP and HP Hacker, B., Ratschbacher, L., Webb, L., McWilliams, M., Ireland, T., Calvert, A., Dong, S., metamorphic belts, East-Central China. Earth Science Frontiers 11, 71–82. Wenk, H., Chateigner, D., 2000. Exhumation of ultrahigh-pressure continental crust Thomas, J.B., Watson, B.E., Spear, F.S., Shemella, P.T., Nayak, S.K., Lanzirotti, A., 2010. in east central China: Late Triassic–Early Jurassic tectonic unroofing. Journal of TitaniQ under pressure: the effect of pressure and temperature on the solubility of Geophysical Research 105, 13339. Ti in quartz. Contributions to Mineralogy and Petrology 160, 743–759. Harris, N., Massey, J., 1994. Decompression and anatexis of Himalayan metapelites. Thompson, A., Ridley, J., Mason, R., 1987. Pressure–temperature–time (P–T–t) histories of Tectonics 13, 1537–1546. orogenic belts. Philosophical Transactions for the Royal Society of London. Series A. Harris, N.B.W., Caddick, M., Kosler, J., Goswami, S., Vance, D., Tindle, A.G., 2004. The Mathematical and Physical Sciences 321, 27–45. pressure–temperature–time path of migmatites from the Sikkim Himalaya. Journal Van Achterbergh, E., Ryan, C., Jackson, S., Griffin, W., 2001. Data reduction software for of Metamorphic Geology 22, 249–264. LA-ICP-MS. In: Sylvester, P. (Ed.), Laser-Ablation-ICPMS in the Earth Sciences. Miner- He, Y., Li, S., Hoefs, J., Huang, F., Liu, S.-A., Hou, Z., 2011. Post-collisional granitoids from the alogical Association of Canada, pp. 239–243. Dabie orogen: new evidence for partial melting of a thickened continental crust. Vielzeuf, D., Schmidt, M.W., 2001. Melting relations in hydrous systems revisited: applica- Geochimica et Cosmochimica Acta 75, 3815–3838. tion to metapelites, metagreywackes and metabasalts. Contributions to Mineralogy Holness, M.B., Cesare, B., Sawyer, E.W., 2011. Melted rocks under the microscope: and Petrology 141, 251–267. microstructures and their interpretation. Elements 7, 247–252. Wang, X., Neubauer, F., Genser, J., Yang, W., 1998. The Dabie UHP unit, central China: a Huang, R., Audétat, A., 2012. The titanium-in-quartz (TitaniQ) thermobarometer: a critical Cretaceous extensional allochthon superposed on a Triassic orogen. Terra Nova 10, examination and re-calibration. Geochimica et Cosmochimica Acta 84, 75–89. 260–267. Huang, F., Li, S.G., Dong, F., Li, Q.L., Chen, F.K., Wang, Y., Yang, W., 2007. Recycling of deeply Wang, Q., Wyman, D.A., Xu, J.F., Jian, P., Zhao, Z.H., Li, C.F., Xu, W., Ma, J.L., He, B., 2007. subducted continental crust in the Dabie Mountains, central China. Lithos 96, Early Cretaceous adakitic granites in the Northern Dabie Complex, central China: im- 151–169. plications for partial melting and delamination of thickened lower crust. Geochimica Jahn, B.M., Wu, F.Y., Lo, C.H., Tsai, C.H., 1999. Crust-mantle interaction induced by deep et Cosmochimica Acta 71, 2609–2636. subduction of the continental crust: geochemical and Sr–Nd isotopic evidence from Wang, Q., Shi, Y., Lin, W., Guo, J., 2008. Exhumation of the Dabie UHP Terrane, China. post-collisional mafic-ultramafic intrusions of the northern Dabie complex, central International Geology Review 50, 15–31. China. Chemical Geology 157, 119–146. Wang, Y., Xiang, B., Zhu, G., Jiang, D., 2011. Structural and geochronological evidence for Jamieson, R.A., Unsworth, M.J., Harris, N.B.W., Rosenberg, C.L., Schulmann, K., 2011. Early Cretaceous orogen-parallel extension of the ductile lithosphere in the northern Crustal melting and the flow of mountains. Elements 7, 253–260. Dabie orogenic belt, East China. Journal of Structural Geology 33, 362–380. Li, Z., Li, X., 2007. Formation of the 1300-km-wide intracontinental orogen and Wang, S.-J., Li, S.-G., Chen, L.-J., He, Y.-S., An, S.-C., Shen, J., 2013. Geochronology and postorogenic magmatic province in Mesozoic South China: a flat-slab subduction geochemistry of leucosomes in the North Dabie Terrane, East China: implication for model. Geology 35, 179. post-UHPM crustal melting during exhumation. Contributions to Mineralogy and Li, S., Jagoutz, E., Chen, Y., Li, Q., 2000. Sm–Nd and Rb–Sr isotopic chronology and cooling Petrology 165, 1009–1029. history of ultrahigh pressure metamorphic rocks and their country rocks at Shuanghe Wark, D., Watson, E., 2006. TitaniQ: a titanium-in-quartz geothermometer. Contributions in the Dabie Mountains, Central China. Geochimica et Cosmochimica Acta 64, to Mineralogy and Petrology 152, 743–754. 1077–1093. Wei, C., Shan, Z., Zhang, L., Wang, S., Chang, Z., 1998. Determination and geological Li, S., Li, Q., Hou, Z., Yang, W., Wang, Y., 2005. Cooling history and exhumation mechanism significance of the eclogites from the northern Dabie Mountains, central China. of the ultrahigh-pressure metamorphic rocks in the Dabie mountains, central China. Chinese Science Bulletin 43, 253–256. Acta Petrologica Sinica 21, 1117–1124. White, R.W., Pomroy, N.E., Powell, R., 2005. An in situ metatexite–diatexite transition in Liu, Q., Wu, Y., 2013. Dehydration melting of UHP eclogite and paragneiss in the Dabie upper amphibolite facies rocks from Broken Hill, Australia. Journal of Metamorphic orogen: evidence from laboratory experiment to natural observation. Chinese Science Geology 23, 579–602. Bulletin 58, 4390–4396. Whitney, D.L., Teyssier, C., Fayon, A.K., 2004. Isothermal decompression, partial melting Liu, S., Zhang, G., Ritts, B.D., Zhang, H., Gao, M., Qian, C., 2010. Tracing exhumation of the and exhumation of deep continental crust. Geological Society, London, Special Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record Publications 227, 313–326. in the Hefei Basin, China. Geological Society of America Bulletin 122, 198–218. Wu, Y.-B., Zheng, Y.-F., 2013. Tectonic evolution of a composite collision orogen: an over- Ma, C., Li, Z., Ehlers, C., Yang, K., Wang, R., 1998. A post-collisional magmatic plumbing view on the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt in central China. system: Mesozoic granitoid plutons from the Dabieshan high-pressure and Gondwana Research 23, 1402–1428. ultrahigh-pressure metamorphic zone, east-central China. Lithos 45, 431–456. Wu, F., Lin, J., Wilde, S., Zhang, X., Yang, J., 2005. Nature and significance of the Early Ma, C.Q., Yang, K.G., Ming, H.L., Lin, G.C., 2004. The timing of tectonic transition from Cretaceous giant igneous event in eastern China. Earth and Planetary Science Letters compression to extension in Dabieshan: evidence from Mesozoic granites. Science 233, 103–119. in China Series D: Earth Sciences 47, 453–462. Wu, Y.B., Zheng, Y.F., Zhang, S.B., Zhao, Z.F., Wu, F.Y., Liu, X.M., 2007. Zircon U–Pb ages Nash, W., 1992. Analysis of oxygen with the electron microprobe; applications to and Hf isotope compositions of migmatite from the North Dabie terrane in China: hydrated glass and minerals. American Mineralogist 77, 453–457. constraints on partial melting. Journal of Metamorphic Geology 25, 991–1009. Pouchou, J.L., Pichoir, F., 1991. Quantitative analysis of homogeneous or stratified Xie, G., Mao, J., Zhao, H., 2011. Zircon U–Pb geochronological and Hf isotopic constraints microvolumes applying the model “PAP”. In: Heinrich, Newbury (Ed.), Electron on petrogenesis of Late Mesozoic intrusions in the southeast Hubei Province, Probe Quantitation. Plenum Press, New York, pp. 31–75. Middle–Lower Yangtze River belt (MLYRB), East China. Lithos 125, 693–710. Price, J.D., Hogan, J.P., Gilbert, M.C., London, D., Morgan, G.B., 1999. Experimental study of Xu, H., Ma, C., Ye, K., 2007. Early cretaceous granitoids and their implications for the titanite-fluorite equilibria in the A-type Mount Scott Granite: implications for collapse of the Dabie orogen, eastern China: SHRIMP zircon U–Pb dating and geo- assessing F contents of felsic magma. Geology 27, 951–954. chemistry. Chemical Geology 240, 238–259. Ratschbacher, L., Hacker, B., Webb, L., McWilliams, M., Ireland, T., Dong, S., Calvert, A., Xu, H., Ye, K., Song, Y., Chen, Y., Zhang, J., Liu, Q., Guo, S., 2013. Prograde metamorphism, Chateigner, D., Wenk, H., 2000. Exhumation of the ultrahigh-pressure continental decompressional partial melting and subsequent melt fractional crystallization in the crust in east central China: Cretaceous and Cenozoic unroofing and the Tan-Lu Weihai migmatitic gneisses, Sulu UHP terrane, eastern China. Chemical Geology 341, fault. Journal of Geophysical Research 105, 13303–13308. 16–37. 236 C. Zhang et al. / Lithos 202–203 (2014) 227–236

You, Z., Han, Y., Yang, W., Zhang, Z., Wei, B., Liu, R., 1996. The high-pressure and ultra China, based on distribution, geochronology, and geochemistry of Late Mesozoic high-pressure metamorphic belt in the East Qinling and Dabie Mountains, China. volcanic rocks. International Journal of Earth Sciences 100, 1665–1684. China University of Geosciences Press, Wuhan. Zhang, C., Holtz, F., Koepke, J., Wolff, P.E., Ma, C., Bédard, J.H., 2013. Constraints from exper- Zhang, R.Y., Liou, J.G., Tsai, C.H., 1996. Petrogenesis of a high-temperature metamorphic imental melting of amphibolite on the depth of formation of garnet-rich restites, and terrane; a new tectonic interpretation for the North Dabieshan, central China. Journal implications for models of Early Archean crustal growth. Precambrian Research 231, of Metamorphic Geology 14, 319–333. 206–217. Zhang, J., Wei, C., Lou, Y., Su, X., 2009. Phase equilibria of hornblende-bearing eclogite in Zhao, Z.F., Zheng, Y.F., Wei, C.S., Wu, Y.B., Chen, F.K., Jahn, B.M., 2005. Zircon U–Pb age, el- the Western Dabie Mountain, Central China. Acta Geologica Sinica 83, 57–69. ement and C–O isotope geochemistry of post-collisional mafic–ultramaficrocksfrom Zhang, C., Ma, C., Holtz, F., 2010. Origin of high-Mg adakitic magmatic enclaves from the the Dabie orogen in east-central China. Lithos 83, 1–28. Meichuan pluton, southern Dabie orogen (central China): implications for delamina- Zhao, Z.-F., Zheng, Y.-F., Zhang, J., Dai, L.-Q., Li, Q., Liu, X., 2012. Syn-exhumation tion of the lower continental crust and melt-mantle interaction. Lithos 119, 467–484. magmatism during continental collision: evidence from alkaline intrusives of Triassic Zhang, C., Ma, C.-Q., Liao, Q.-A., Zhang, J.-Y., She, Z.-B., 2011. Implications of subduction age in the Sulu orogen. Chemical Geology 328, 70–88. and subduction zone migration of the Paleo-Pacific Plate beneath eastern North