Fig 1 - uploaded by Xiaofeng Gu
Content may be subject to copyright.
Schematic geological map of the Dabie orogen, showing the sample localities and their sample numbers. BZ, Beihuaiyang zone; NDZ, North Dabie complex zone; CDZ, Central Dabie UHP metamorphic zone; SDZ, South Dabie LT eclogite zone; SZ, Susong complex zone; HMZ, Huwan mélange zone; HZ, Hong'an LT eclogite zone; DC, amphibolite-facies Dabie complex; XMF, Xiaotian – Mozitan fault; WSF, Wuhe – Shuihou fault; HMF, Hualiangting – Mituo fault; TSF, Taihu – Shanlong fault; TLF, Tan – Lu fault; SMF, Shangcheng – Macheng fault.
Source publication
Ultrahigh-pressure (UHP) eclogites from the northern Dabie orogen, central China underwent a complex metamorphic evolution during Triassic continental deep subduction and subsequent exhumation. The eclogites were strongly affected by multiple decompression and re-crystallization processes during exhumation, thus making the determination of peak met...
Contexts in source publication
Context 1
... histories, and is subdivided into five major lithotectonic units from north to south ( Xu et al., 2003;Liu et al., 2007a): (1) the Beihuaiyang zone (BZ); (2) the North Dabie complex zone (NDZ); (3) the Central Dabie UHP metamorphic zone (CDZ); (4) the South Dabie low-temperature (LT) eclogite zone (SDZ); and (5) the Susong complex zone (SZ) (Fig. 1). These zones are separated by the Xiaotian-Mozitan fault, Wuhe-Shuihou fault, Hualiangting-Mituo fault and Taihu-Shanlong fault, respectively. The first zone is a low-grade composite unit comprising the Foziling (or Xinyang) Group and the Luzhenguan (or Guishan) complex, whereas the other zones belong to the subducted South China ...
Context 2
... investigated samples were collected from Banchuanshan (samples LT9 and LT10), Luotian (sample 03LT1-1), Jinjiapu (samples 06LT3-2 and 09LT1) and Shiqiaopu (samples 07LT6-1 and 09LT2), respectively (Fig. 1). Details of the petrography and mineral chemistry of the studied samples were given in Liu et al. (2007aLiu et al. ( , 2011a) and are only summarized here. They can be roughly divided into two groups based on zircon typologies: the first eclogite type (Type 1; samples 03LT1-1, 06LT3-2, 07LT6-1, 09LT1 and 09LT2) contains almost ...
Context 3
... . 10 shows the P−T−t path of the NDZ eclogites as constrained by Ti-in-zircon and Zr-in-rutile thermometry (this study), conventional thermometry and SHRIMP U-Pb ages ( Liu et al., 2011a;Gu, 2012). A variety of models for exhumation of UHP metamorphic rocks from mantle depths have been proposed (e.g., Ernst, 1971;Chemenda et al., ...
Context 4
... occurring at different levels of the continental crust ( Liu et al., 2007bLiu et al., , 2011aLiu and Li, 2008). Considering the weighted mean ages of UHP metamorphism (226 Ma) and HP eclogite-facies retrogression (214 Ma), the exhumation from mantle depths (ca. 4.0 GPa) to crustal depths of ca. 2.0 GPa must have been completed within about 12 Ma (Fig. 10). This implies that about 60 km of exhumation should have occurred within about 12 Ma, leading to an average exhumation rate of 0.5 cm/y. A comparatively lower exhumation rate of ~ 0.4 cm/y characterized the following evolution from HP eclogite-facies (214 Ma) to granulite-facies (207 Ma) conditions, corresponding to nearly isothermal ...
Context 5
... rocks formed by the Triassic subduction of the South China Block, simi- A suitable lithology to usefully apply these two novel techniques is the lar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu granulitized eclogites of the Luotian dome in the southwestern part of et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- the North Dabie complex zone (NDZ), central China, which is a portion diamond inclusions in zircon and garnet (Liu et al., 2007b) from the of deeply subducted ma fi c lower continental crust of the South China NDZ banded gneisses suggest that also the gneisses hosting the Block (Liu et al., 2007a). The NDZ eclogites underwent UHP and HP eclogites were involved in the deep subduction of the South China eclogite-facies metamorphism, followed by HP granulite-facies overprint Block, thus implying that the NDZ experienced UHP metamorphism as and later amphibolite-facies retrogression during continental subduction a coherent unit. After the UHP and HP eclogite-facies metamorphism, and exhumation (Liu et al., 2011b). The peak metamorphic assemblages the NDZ eclogites experienced granulite-facies overprinting and later and compositions of such UHP rocks are commonly obliterated or amphibolite-facies retrogression (e.g., Xu et al., 2000; Liu et al., 2001, overprinted by subsequent retrograde metamorphism at UHT (905 − 2005, 2007a). This evidence supports the case for a distinct evolution 917 °C) conditions (Liu et al., 2011b). These metamorphic temperatures in the different units of the Dabie UHP belt. That is, although the three approximated or exceeded the closure temperatures of the Fe – Mg ex- eclogite-bearing units, i.e. the SDZ, CDZ and NDZ, all experienced UHP change thermometer between garnet and clinopyroxene (e.g., Raheim metamorphism, they had different exhumation histories, suggesting and Green, 1974; Baldwin et al., 2007). In this context, it is thus generally that they represent decoupled UHP slices and their precursors most dif fi cult, using conventional geothermometers, to precisely constrain the actual metamorphic temperatures experienced by the eclogites during the various stages of their evolution; nevertheless this information is essential for a robust understanding of the genetic and evolutionary processes of the UHP rocks in the NDZ. Zircon is extremely robust to thermal disturbance and its U – Pb and REE systematics can be preserved despite multiple HT/UHT metamorphic episodes and re-equilibration, thus providing reliable ages and genetic information (Kooijman et al., 2011 and references therein). Although the NDZ eclogites experienced a complex metamorphic evolution and multistage retrograde overprinting, their zircons still preserve multiple metamorphic age-records with REE and mineral inclusion constraints (Liu et al., 2011a). Combining the zircon U – Pb ages and the the peak and post-peak temperatures of polymetamorphic rocks estimated The Dabie temperatures orogen is a and well pressures, known UHP the terrain, whole P located − T − t path in the experi- inter- (e.g., Spear et al., 2006; Zack and Luvizotto, 2006; Baldwin et al., 2007; enced mediate by segment the eclogites of the during Qinling subduction – Dabie – Sulu and orogenic exhumation belt may formed be Miller et al., 2007; Tomkins et al., 2007; Chen and Li, 2008; Liu et al., therefore by the Triassic constrained continental in detail. collision In this between study, we the applied North China Ti-in-zircon Block 2010a; Zhang et al., 2010; Jiao et al., 2011; Meyer et al., 2011; Zheng and and Zr-in-rutile South China thermometers Block (e.g., Xu to et the al., NDZ 1992; eclogites. Li et al., The 1993, results 2000; provide Ames et al., 2011; Kooijman et al., 2012; Ewing et al., 2013). unambiguous et al., 1996). It evidence comprises of several a long-lived fault-bounded HT evolution terranes in with the NDZ. varying In Zircon and rutile are common accessory minerals in metamorphic addition, metamorphic the applicability grades and evolutional of the zircon histories, and rutile and is thermometers subdivided into to rocks. Zircon has been extensively used for U – Pb geochronology, giving UHP fi ve major eclogites lithotectonic is tested. The units implications from north of to our south results (Xu et on al., the 2003; P − T − Liu t useful information about a wide range of tectonic events and related et evolution al., 2007a): of the (1) NDZ the are Beihuaiyang discussed, zone shedding (BZ); new (2) light the North on the Dabie formation com- processes (e.g., Rubatto et al., 1999; Hermann et al., 2001; Möller plex and exhumation zone (NDZ); of (3) the the UHP Central metamorphic Dabie UHP belt metamorphic in the Dabie zone orogen. (CDZ); et al., 2002; Liu et al., 2011a, 2012). Furthermore, the Ti-in-zircon ther- (4) the South Dabie low-temperature (LT) eclogite zone (SDZ); and (5) mometer has the potential to create an invaluable link between U – Pb the Susong complex zone (SZ) (Fig. 1). These zones are separated by the ages and temperatures measured in-situ in zircon (e.g., Baldwin and Xiaotian – Mozitan fault, Wuhe – Shuihou fault, Hualiangting – Mituo fault Brown, 2008): this is particularly true for polyphase metamorphic and Taihu – Shanlong fault, respectively. The fi rst zone is a low-grade rocks, because internal fi ne-scaled growth structures in zircon may be composite unit comprising the Foziling (or Xinyang) Group and the directly correlated with variations in the physicochemical conditions Luzhenguan (or Guishan) complex, whereas the other zones belong to and the duration of each metamorphic event (e.g., Rubatto et al., 1999; the subducted South China Block (Xu et al., 2003, 2005; Liu et al., Corfu et al., 2003; Whitehouse and Platt, 2003). Application of this ther- 2005, 2007a, 2010b, 2011a; Liu and Li, 2008). mometer to two typical UHT granulite localities demonstrated that it is a A variety of UHP metamorphic rocks, including eclogite, gneiss, powerful method to determine the peak temperatures of zircons quartz, jadeitite, schist and impure marble, occur in the CDZ and SDZ (Baldwin et al., 2007). However, there are also studies showing that zir- (e.g., Xu et al., 1992; Okay, 1993; Okay et al., 1993; Li et al., 2004; con re-crystallized after the metamorphic peak and did not preserve Rolfo et al., 2004). The occurrence of diamond and coesite in the meta- UHT, whereas rutile in the same samples did (Ewing et al., 2013). morphic rocks from the CDZ indicates that the UHP metamorphism Zr-in-rutile thermometry, based on the Zr content in rutile occurred at 700 − 850 °C and N 2.8 GPa (e.g., Okay et al., 1989; Wang coexisting with quartz and zircon, is an alternative and complementary et al., 1989; Xu et al., 1992; Okay, 1993; Rolfo et al., 2004), whereas method for estimating temperature of metamorphism, especially useful the peak P − T conditions of the eclogites in the SDZ were estimated for eclogites. Earlier calibrations of the Zr-in-rutile thermometer at 670 °C and 3.3 GPa (Li et al., 2004). In both the CDZ and SDZ units focused on the strong effect of temperature (Zack et al., 2004; Watson the UHP eclogite-facies stage was followed by HP eclogite- and et al., 2006; Ferry and Watson, 2007), without correction for pressure. amphibolite-facies retrograde metamorphism (e.g., Xu et al., 1992; Li The pressure dependence was incorporated into this thermometer et al., 2004; Rolfo et al., 2004). with the calibration of Tomkins et al. (2007). This revised thermometer The NDZ mainly consists of tonalitic and granitic orthogneisses has been demonstrated to be a reliable method for the estimate of the and post-collisional Cretaceous intrusions with subordinate meta- peak temperatures in UHT rocks (e.g., Jiao et al., 2011; Meyer et al., peridotite, garnet pyroxenite, garnet-bearing amphibolite, granulite and 2011; Kooijman et al., 2012). Also, Luvizotto and Zack (2009) obtained eclogite. The oriented mineral exsolutions in garnet and clinopyroxene, Zr-in-rutile temperatures of up to 850 – 930 °C for rutile from granulite- and the occurrence of micro-diamond imply that the NDZ eclogites facies metapelites from Val Strona and Val d'Ossola, though with signif- underwent UHP metamorphism at P N 3.5 GPa (Xu et al., 2003, 2005; icant resetting of Zr-in-rutile temperatures to a spread of lower values. Liu et al., 2005; Malaspina et al., 2006). The Triassic zircon U – Pb ages As a result, combining Ti-in-zircon and Zr-in-rutile thermometry is (Liu et al., 2000, 2007a, 2011a; Wang et al., 2012) and Sm – Nd ages required to constrain peak and post-peak metamorphic temperatures (Liu et al., 2005) of the eclogites from the NDZ suggest that these for eclogites and related high-grade rocks involved in complex processes. rocks formed by the Triassic subduction of the South China Block, simi- A suitable lithology to usefully apply these two novel techniques is the lar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu granulitized eclogites of the Luotian dome in the southwestern part of et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- the North Dabie complex zone (NDZ), central China, which is a portion diamond inclusions in zircon and garnet (Liu et al., 2007b) from the of deeply subducted ma fi c lower continental crust of the South China NDZ banded gneisses suggest that also the gneisses hosting the Block (Liu et al., 2007a). The NDZ eclogites underwent UHP and HP eclogites were involved in the deep subduction of the South China eclogite-facies metamorphism, followed by HP granulite-facies overprint Block, thus implying that the NDZ experienced UHP metamorphism as and later amphibolite-facies retrogression during continental subduction a coherent unit. After the UHP and HP eclogite-facies metamorphism, and exhumation (Liu et al., 2011b). The peak metamorphic assemblages the NDZ eclogites experienced granulite-facies overprinting and later and compositions ...
Context 6
... South China Block (Xu et al., 2003, 2005; Liu et al., 2005, 2007a, 2010b, 2011a; Liu and Li, 2008). A variety of UHP metamorphic rocks, including eclogite, gneiss, quartz, jadeitite, schist and impure marble, occur in the CDZ and SDZ (e.g., Xu et al., 1992; Okay, 1993; Okay et al., 1993; Li et al., 2004; Rolfo et al., 2004). The occurrence of diamond and coesite in the metamorphic rocks from the CDZ indicates that the UHP metamorphism occurred at 700 − 850 °C and N 2.8 GPa (e.g., Okay et al., 1989; Wang et al., 1989; Xu et al., 1992; Okay, 1993; Rolfo et al., 2004), whereas the peak P − T conditions of the eclogites in the SDZ were estimated at 670 °C and 3.3 GPa (Li et al., 2004). In both the CDZ and SDZ units the UHP eclogite-facies stage was followed by HP eclogite- and amphibolite-facies retrograde metamorphism (e.g., Xu et al., 1992; Li et al., 2004; Rolfo et al., 2004). The NDZ mainly consists of tonalitic and granitic orthogneisses and post-collisional Cretaceous intrusions with subordinate meta- peridotite, garnet pyroxenite, garnet-bearing amphibolite, granulite and eclogite. The oriented mineral exsolutions in garnet and clinopyroxene, and the occurrence of micro-diamond imply that the NDZ eclogites underwent UHP metamorphism at P N 3.5 GPa (Xu et al., 2003, 2005; Liu et al., 2005; Malaspina et al., 2006). The Triassic zircon U – Pb ages (Liu et al., 2000, 2007a, 2011a; Wang et al., 2012) and Sm – Nd ages (Liu et al., 2005) of the eclogites from the NDZ suggest that these rocks formed by the Triassic subduction of the South China Block, similar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- diamond inclusions in zircon and garnet (Liu et al., 2007b) from the NDZ banded gneisses suggest that also the gneisses hosting the eclogites were involved in the deep subduction of the South China Block, thus implying that the NDZ experienced UHP metamorphism as a coherent unit. After the UHP and HP eclogite-facies metamorphism, the NDZ eclogites experienced granulite-facies overprinting and later amphibolite-facies retrogression (e.g., Xu et al., 2000; Liu et al., 2001, 2005, 2007a). This evidence supports the case for a distinct evolution in the different units of the Dabie UHP belt. That is, although the three eclogite-bearing units, i.e. the SDZ, CDZ and NDZ, all experienced UHP metamorphism, they had different exhumation histories, suggesting that they represent decoupled UHP slices and their precursors most probably represent different levels of crustal rocks (see Liu and Li, 2008 for a review). The Luotian dome in the southwestern segment of the NDZ is a deeply eroded area with both felsic and ma fi c granulite lenses (Chen et al., 1998, 2006; Liu et al., 2007a; Wu et al., 2008). Eclogites occur as lenses or blocks in garnet-bearing migmatitic orthogneiss (Liu et al., 2007a). They preserve early granulite-facies mineral relics and have been overprinted by regionally pervasive HP granulite-facies metamorphism, followed by penetrative amphibolite-facies retrogression during exhumation. The eclogite-facies assemblage consists of garnet and relict omphacite, with rutile, quartz, allanite and apatite as common additional constituents. Although the precise time – temperature cooling history is still not well-known in detail, the studies by Liu et al. (2007a, 2011b, 2013) and Gu (2012) showed that the NDZ underwent a complex evolution characterized by a nearly isothermal decompression during the early stages of exhumation and experienced at least two stages of partial melting, i.e. decompression melting at 207 ± 4 Ma and heating melting at ~130 Ma during continental orogeny. At present, fi ve metamorphic stages have been recognized for the eclogites in the Luotian dome area (Liu et al., 2007a; Liu et al., 2011b): (1) granulite-facies stage, suggested by the occurrence of hypersthene, plagioclase and diopside inclusions within garnet (Liu et al., 2007a); (2) UHP eclogite-facies stage at ~ 4.0 GPa, suggested by the occurrence of diamond (Xu et al., 2003, 2005; Liu et al., 2007b) and coesite (Liu et al., 2011b); (3) HP eclogite- facies stage, characterized by the coexistence of garnet, jadeite-poor omphacite and rutile with quartz instead of coesite; (4) granulite- facies retrogression stage, indicated by the presence of hypersthene, plagioclase and diopside symplectite after Na-clinopyroxene; and (5) amphibolite-facies retrograde stage, documented by the widespread growth of amphibole. However, P − T conditions, especially temperatures for different stages have not been well constrained because of multiple decompression and re-crystallization coupled with multiple stages of partial melting processes as mentioned above. The investigated samples were collected from Banchuanshan (samples LT9 and LT10), Luotian (sample 03LT1-1), Jinjiapu (samples 06LT3-2 and 09LT1) and Shiqiaopu (samples 07LT6-1 and 09LT2), respectively (Fig. 1). Details of the petrography and mineral chemistry of the studied samples were given in Liu et al. (2007a, 2011a) and are only summarized here. They can be roughly divided into two groups based on zircon typologies: the fi rst eclogite type (Type 1; samples 03LT1-1, 06LT3-2, 07LT6-1, 09LT1 and 09LT2) contains almost homogeneous Triassic metamorphic zircons with rare or even no Neoproterozoic zircon cores (Liu et al., 2011a; Gu, 2012), whereas the second type (Type 2; samples LT9 and LT10) contains Neoproterozoic igneous and metamorphic zircon cores with rare Triassic metamorphic overgrowth Two Zircons generations were separated of omphacite from the may samples be distinguished by crushing on and the sieving, basis rims (Liu et al., 2007a). of followed their Na by 2 O magnetic contents, and the heavy earlier liquid one being separation Na richer and than hand-picking the later The detailed ages of the samples LT9, LT10, 03LT1-1, 06LT3-2, 07LT6- generation under a binocular (Fig. 4; Table 1). microscope. The Representative later generation zircon often crystals coexists were with 1 and 09LT2 were reported in Liu et al. (2007a, 2011a) and Gu (2012), quartz prepared in zircon for the (Fig. 3b, CL investigations f), suggesting and in-situ a Si-rich U – precursor Pb dating omphacite and trace- respectively (see also Table 2). Based on previous investigations (Liu and element is locally analyses. replaced Together by clinopyroxene with a zircon + U – Pb plagioclase standard + TEM quartz (417 inter- Ma), et al., 2011a; Gu, 2012), by CL images, inclusion assemblages, REE pat- growths crystals were in garnet mounted (Fig. 2d). in epoxy, In samples which 07LT6-1 was then and polished 09LT2 until omphacite all zir- terns and ages, the metamorphic/metamorphosed zircons from samples inclusions con grains were within approximately garnet and cut zircon in half. are The internal particularly zoning abundant, patterns of the Type 1 eclogites contain two mantle domains (inner- and outer- and of the coesite crystals pseudomorphs were observed with by Cathodoluminescence radial fractures were locally (CL) imaging observed at mantles, named as M 1 and M 2 ) with distinct age-records of 230 − within the Beijing garnet SHRIMP (Figs. 2 Center and 3; and Liu the et al., Institute 2011b). of Furthermore, Mineral Resources, low-Na 220 Ma and 220 − 210 Ma, cluster at 226 ± 2 Ma and 214 ± 2 Ma, re- omphacite + quartz and rutile + ilmenite locally occur as coexisting spectively. These two zircon domains grew in distinct stages of the or intergrowth inclusions in zircon (Figs. 3b, d, f, l and 5). This suggests eclogite-facies metamorphic evolution because they show UHP and that mineral inclusions in zircon and garnet from the eclogites have HP eclogite-facies signatures of Ca-rich garnet +omphacite (Jd = 40 been strongly modi fi ed or broken down during decompression and − 50) + coesite + rutile and Mn-rich garnet +omphacite (Jd = 20 − retrogression, also hampering the determination of peak P − T conditions 30) + quartz + rutile, respectively (Liu et al., 2011a; Gu, 2012). Rare by conventional thermobarometry. Thus, in order to better constrain the thin overgrowth rims of 209 − 207 Ma and 200 − 190 Ma, formed at metamorphic temperatures of the UHP and HP stages, the Ti-in-zircon granulite- and amphibolite-facies stages, respectively, are locally ob- thermometry and Zr-in-rutile thermometry on inclusions within zircon served in zircon. and garnet have been applied. The Type 2 eclogite (samples LT9 and LT10) consists of garnet, omphacite and rutile and retrograde quartz, diopside, hypersthene, hornblende, plagioclase and ilmenite. Sample 03LT1-1 is a strongly retrogressed eclogite, mainly consisting of garnet, rutile, hornblende and plagioclase with minor quartz, diopside, hypersthene and ilmenite. Rare coesite in zircon and its pseudomorphs with radial fractures in garnet were observed (Liu et al., 2011b). The other eclogite samples (06LT3-2, 07LT6-1, 09LT1 and 09LT2) are less retrogressed and are composed of garnet, omphacite, diopside and rutile, with minor hypersthene, hornblende, plagioclase, monomineralic quartz or quartz pseudomorphs after coesite and ilmenite. In all the samples, omphacite generally occurs as inclusion in garnet or zircon (Figs. 2a, b and 3). metamorphic zircon cores with rare Triassic metamorphic overgrowth Two Zircons generations were separated of omphacite from the may samples be distinguished by crushing on and the sieving, basis rims (Liu et al., 2007a). of followed their Na by 2 O magnetic contents, and the heavy earlier liquid one being separation Na richer and than hand-picking the later The detailed ages of the samples LT9, LT10, 03LT1-1, 06LT3-2, 07LT6- generation under a binocular (Fig. 4; Table 1). microscope. The Representative later generation zircon often crystals coexists were with 1 and 09LT2 were reported in Liu et al. (2007a, 2011a) and Gu (2012), quartz prepared in zircon for the ...
Context 7
... this thermometer et al., 2004; Rolfo et al., 2004). with the calibration of Tomkins et al. (2007). This revised thermometer The NDZ mainly consists of tonalitic and granitic orthogneisses has been demonstrated to be a reliable method for the estimate of the and post-collisional Cretaceous intrusions with subordinate meta- peak temperatures in UHT rocks (e.g., Jiao et al., 2011; Meyer et al., peridotite, garnet pyroxenite, garnet-bearing amphibolite, granulite and 2011; Kooijman et al., 2012). Also, Luvizotto and Zack (2009) obtained eclogite. The oriented mineral exsolutions in garnet and clinopyroxene, Zr-in-rutile temperatures of up to 850 – 930 °C for rutile from granulite- and the occurrence of micro-diamond imply that the NDZ eclogites facies metapelites from Val Strona and Val d'Ossola, though with signif- underwent UHP metamorphism at P N 3.5 GPa (Xu et al., 2003, 2005; icant resetting of Zr-in-rutile temperatures to a spread of lower values. Liu et al., 2005; Malaspina et al., 2006). The Triassic zircon U – Pb ages As a result, combining Ti-in-zircon and Zr-in-rutile thermometry is (Liu et al., 2000, 2007a, 2011a; Wang et al., 2012) and Sm – Nd ages required to constrain peak and post-peak metamorphic temperatures (Liu et al., 2005) of the eclogites from the NDZ suggest that these for eclogites and related high-grade rocks involved in complex processes. rocks formed by the Triassic subduction of the South China Block, simi- A suitable lithology to usefully apply these two novel techniques is the lar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu granulitized eclogites of the Luotian dome in the southwestern part of et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- the North Dabie complex zone (NDZ), central China, which is a portion diamond inclusions in zircon and garnet (Liu et al., 2007b) from the of deeply subducted ma fi c lower continental crust of the South China NDZ banded gneisses suggest that also the gneisses hosting the Block (Liu et al., 2007a). The NDZ eclogites underwent UHP and HP eclogites were involved in the deep subduction of the South China eclogite-facies metamorphism, followed by HP granulite-facies overprint Block, thus implying that the NDZ experienced UHP metamorphism as and later amphibolite-facies retrogression during continental subduction a coherent unit. After the UHP and HP eclogite-facies metamorphism, and exhumation (Liu et al., 2011b). The peak metamorphic assemblages the NDZ eclogites experienced granulite-facies overprinting and later and compositions of such UHP rocks are commonly obliterated or amphibolite-facies retrogression (e.g., Xu et al., 2000; Liu et al., 2001, overprinted by subsequent retrograde metamorphism at UHT (905 − 2005, 2007a). This evidence supports the case for a distinct evolution 917 °C) conditions (Liu et al., 2011b). These metamorphic temperatures in the different units of the Dabie UHP belt. That is, although the three approximated or exceeded the closure temperatures of the Fe – Mg ex- eclogite-bearing units, i.e. the SDZ, CDZ and NDZ, all experienced UHP change thermometer between garnet and clinopyroxene (e.g., Raheim metamorphism, they had different exhumation histories, suggesting and Green, 1974; Baldwin et al., 2007). In this context, it is thus generally that they represent decoupled UHP slices and their precursors most dif fi cult, using conventional geothermometers, to precisely constrain the actual metamorphic temperatures experienced by the eclogites during the various stages of their evolution; nevertheless this information is essential for a robust understanding of the genetic and evolutionary processes of the UHP rocks in the NDZ. Zircon is extremely robust to thermal disturbance and its U – Pb and REE systematics can be preserved despite multiple HT/UHT metamorphic episodes and re-equilibration, thus providing reliable ages and genetic information (Kooijman et al., 2011 and references therein). Although the NDZ eclogites experienced a complex metamorphic evolution and multistage retrograde overprinting, their zircons still preserve multiple metamorphic age-records with REE and mineral inclusion constraints (Liu et al., 2011a). Combining the zircon U – Pb ages and the The Dabie orogen is a well known UHP terrain, located in the inter- mediate segment of the Qinling – Dabie – Sulu orogenic belt formed by the Triassic continental collision between the North China Block and South China Block (e.g., Xu et al., 1992; Li et al., 1993, 2000; Ames et al., 1996). It comprises several fault-bounded terranes with varying metamorphic grades and evolutional histories, and is subdivided into fi ve major lithotectonic units from north to south (Xu et al., 2003; Liu et al., 2007a): (1) the Beihuaiyang zone (BZ); (2) the North Dabie complex zone (NDZ); (3) the Central Dabie UHP metamorphic zone (CDZ); (4) the South Dabie low-temperature (LT) eclogite zone (SDZ); and (5) the Susong complex zone (SZ) (Fig. 1). These zones are separated by the Xiaotian – Mozitan fault, Wuhe – Shuihou fault, Hualiangting – Mituo fault and Taihu – Shanlong fault, respectively. The fi rst zone is a low-grade composite unit comprising the Foziling (or Xinyang) Group and the Luzhenguan (or Guishan) complex, whereas the other zones belong to the subducted South China Block (Xu et al., 2003, 2005; Liu et al., 2005, 2007a, 2010b, 2011a; Liu and Li, 2008). A variety of UHP metamorphic rocks, including eclogite, gneiss, quartz, jadeitite, schist and impure marble, occur in the CDZ and SDZ (e.g., Xu et al., 1992; Okay, 1993; Okay et al., 1993; Li et al., 2004; Rolfo et al., 2004). The occurrence of diamond and coesite in the metamorphic rocks from the CDZ indicates that the UHP metamorphism occurred at 700 − 850 °C and N 2.8 GPa (e.g., Okay et al., 1989; Wang et al., 1989; Xu et al., 1992; Okay, 1993; Rolfo et al., 2004), whereas the peak P − T conditions of the eclogites in the SDZ were estimated at 670 °C and 3.3 GPa (Li et al., 2004). In both the CDZ and SDZ units the UHP eclogite-facies stage was followed by HP eclogite- and amphibolite-facies retrograde metamorphism (e.g., Xu et al., 1992; Li et al., 2004; Rolfo et al., 2004). The NDZ mainly consists of tonalitic and granitic orthogneisses and post-collisional Cretaceous intrusions with subordinate meta- peridotite, garnet pyroxenite, garnet-bearing amphibolite, granulite and eclogite. The oriented mineral exsolutions in garnet and clinopyroxene, and the occurrence of micro-diamond imply that the NDZ eclogites underwent UHP metamorphism at P N 3.5 GPa (Xu et al., 2003, 2005; Liu et al., 2005; Malaspina et al., 2006). The Triassic zircon U – Pb ages (Liu et al., 2000, 2007a, 2011a; Wang et al., 2012) and Sm – Nd ages (Liu et al., 2005) of the eclogites from the NDZ suggest that these rocks formed by the Triassic subduction of the South China Block, similar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- diamond inclusions in zircon and garnet (Liu et al., 2007b) from the NDZ banded gneisses suggest that also the gneisses hosting the eclogites were involved in the deep subduction of the South China Block, thus implying that the NDZ experienced UHP metamorphism as a coherent unit. After the UHP and HP eclogite-facies metamorphism, the NDZ eclogites experienced granulite-facies overprinting and later amphibolite-facies retrogression (e.g., Xu et al., 2000; Liu et al., 2001, 2005, 2007a). This evidence supports the case for a distinct evolution in the different units of the Dabie UHP belt. That is, although the three eclogite-bearing units, i.e. the SDZ, CDZ and NDZ, all experienced UHP metamorphism, they had different exhumation histories, suggesting that they represent decoupled UHP slices and their precursors most probably represent different levels of crustal rocks (see Liu and Li, 2008 for a review). The Luotian dome in the southwestern segment of the NDZ is a deeply eroded area with both felsic and ma fi c granulite lenses (Chen et al., 1998, 2006; Liu et al., 2007a; Wu et al., 2008). Eclogites occur as lenses or blocks in garnet-bearing migmatitic orthogneiss (Liu et al., 2007a). They preserve early granulite-facies mineral relics and have been overprinted by regionally pervasive HP granulite-facies metamorphism, followed by penetrative amphibolite-facies retrogression during exhumation. The eclogite-facies assemblage consists of garnet and relict omphacite, with rutile, quartz, allanite and apatite as common additional constituents. Although the precise time – temperature cooling history is still not well-known in detail, the studies by Liu et al. (2007a, 2011b, 2013) and Gu (2012) showed that the NDZ underwent a complex evolution characterized by a nearly isothermal decompression during the early stages of exhumation and experienced at least two stages of partial melting, i.e. decompression melting at 207 ± 4 Ma and heating melting at ~130 Ma during continental orogeny. At present, fi ve metamorphic stages have been recognized for the eclogites in the Luotian dome area (Liu et al., 2007a; Liu et al., 2011b): (1) granulite-facies stage, suggested by the occurrence of hypersthene, plagioclase and diopside inclusions within garnet (Liu et al., 2007a); (2) UHP eclogite-facies stage at ~ 4.0 GPa, suggested by the occurrence of diamond (Xu et al., 2003, 2005; Liu et al., 2007b) and coesite (Liu et al., 2011b); (3) HP eclogite- facies stage, characterized by the coexistence of garnet, jadeite-poor omphacite and rutile with quartz instead of coesite; (4) granulite- facies retrogression stage, indicated by the presence of hypersthene, plagioclase and diopside symplectite after Na-clinopyroxene; and (5) amphibolite-facies retrograde stage, documented by the widespread growth of amphibole. However, P − T conditions, especially temperatures for different stages have not been well constrained ...
Context 8
... Temperatures of N 900 °C are, in fact, higher than the closure temperature of most conventional thermometers (Baldwin et al., Peak and post-peak temperature estimates are crucial for better 2007). An accurate estimate of peak temperature for high-grade rocks understanding the genesis and evolution of high-pressure (HP) and is often hampered by the signi fi cant re-equilibration or re- ultrahigh-pressure (UHP) eclogites and related metamorphic rocks in crystallization during retrogression and cooling. This led to the recent subduction zones. However, this task is challenging when investigating development of trace-element thermometers such as those based on high-grade rocks, particularly those formed under extreme metamor- titanium concentration in zircon and zirconium concentration in rutile, phic conditions such as ultrahigh-temperature (UHT) metamorphism which may provide a more precise link between the P − T path and the (Harley, 1998, 2008; Brown, 2007; Kelsey, 2008; Santosh and Kusky, geochronological data (e.g., Watson and Harrison, 2005; Watson et al., 2006; Timms et al., 2011). Since their earlier development, the new Ti-in-zircon and Zr-in-rutile thermometers (Zack et al., 2004; Watson et al., 2006; Baldwin et al., 2007; Ferry and Watson, 2007; Tomkins et al., 2007) have been more and more successfully used to estimate 2010). Temperatures of N 900 °C are, in fact, higher than the closure temperature of most conventional thermometers (Baldwin et al., 2007). An accurate estimate of peak temperature for high-grade rocks is often hampered by the signi fi cant re-equilibration or re- crystallization during retrogression and cooling. This led to the recent development of trace-element thermometers such as those based on titanium concentration in zircon and zirconium concentration in rutile, which may provide a more precise link between the P − T path and the geochronological data (e.g., Watson and Harrison, 2005; Watson et al., 2006; Timms et al., 2011). Since their earlier development, the new Ti-in-zircon and Zr-in-rutile thermometers (Zack et al., 2004; Watson et al., 2006; Baldwin et al., 2007; Ferry and Watson, 2007; Tomkins et al., 2007) have been more and more successfully used to estimate the peak and post-peak temperatures of polymetamorphic rocks estimated The Dabie temperatures orogen is a and well pressures, known UHP the terrain, whole P located − T − t path in the experi- inter- (e.g., Spear et al., 2006; Zack and Luvizotto, 2006; Baldwin et al., 2007; enced mediate by segment the eclogites of the during Qinling subduction – Dabie – Sulu and orogenic exhumation belt may formed be Miller et al., 2007; Tomkins et al., 2007; Chen and Li, 2008; Liu et al., therefore by the Triassic constrained continental in detail. collision In this between study, we the applied North China Ti-in-zircon Block 2010a; Zhang et al., 2010; Jiao et al., 2011; Meyer et al., 2011; Zheng and and Zr-in-rutile South China thermometers Block (e.g., Xu to et the al., NDZ 1992; eclogites. Li et al., The 1993, results 2000; provide Ames et al., 2011; Kooijman et al., 2012; Ewing et al., 2013). unambiguous et al., 1996). It evidence comprises of several a long-lived fault-bounded HT evolution terranes in with the NDZ. varying In Zircon and rutile are common accessory minerals in metamorphic addition, metamorphic the applicability grades and evolutional of the zircon histories, and rutile and is thermometers subdivided into to rocks. Zircon has been extensively used for U – Pb geochronology, giving UHP fi ve major eclogites lithotectonic is tested. The units implications from north of to our south results (Xu et on al., the 2003; P − T − Liu t useful information about a wide range of tectonic events and related et evolution al., 2007a): of the (1) NDZ the are Beihuaiyang discussed, zone shedding (BZ); new (2) light the North on the Dabie formation com- processes (e.g., Rubatto et al., 1999; Hermann et al., 2001; Möller plex and exhumation zone (NDZ); of (3) the the UHP Central metamorphic Dabie UHP belt metamorphic in the Dabie zone orogen. (CDZ); et al., 2002; Liu et al., 2011a, 2012). Furthermore, the Ti-in-zircon ther- (4) the South Dabie low-temperature (LT) eclogite zone (SDZ); and (5) mometer has the potential to create an invaluable link between U – Pb the Susong complex zone (SZ) (Fig. 1). These zones are separated by the ages and temperatures measured in-situ in zircon (e.g., Baldwin and Xiaotian – Mozitan fault, Wuhe – Shuihou fault, Hualiangting – Mituo fault Brown, 2008): this is particularly true for polyphase metamorphic and Taihu – Shanlong fault, respectively. The fi rst zone is a low-grade rocks, because internal fi ne-scaled growth structures in zircon may be composite unit comprising the Foziling (or Xinyang) Group and the directly correlated with variations in the physicochemical conditions Luzhenguan (or Guishan) complex, whereas the other zones belong to and the duration of each metamorphic event (e.g., Rubatto et al., 1999; the subducted South China Block (Xu et al., 2003, 2005; Liu et al., Corfu et al., 2003; Whitehouse and Platt, 2003). Application of this ther- 2005, 2007a, 2010b, 2011a; Liu and Li, 2008). mometer to two typical UHT granulite localities demonstrated that it is a A variety of UHP metamorphic rocks, including eclogite, gneiss, powerful method to determine the peak temperatures of zircons quartz, jadeitite, schist and impure marble, occur in the CDZ and SDZ (Baldwin et al., 2007). However, there are also studies showing that zir- (e.g., Xu et al., 1992; Okay, 1993; Okay et al., 1993; Li et al., 2004; con re-crystallized after the metamorphic peak and did not preserve Rolfo et al., 2004). The occurrence of diamond and coesite in the meta- UHT, whereas rutile in the same samples did (Ewing et al., 2013). morphic rocks from the CDZ indicates that the UHP metamorphism Zr-in-rutile thermometry, based on the Zr content in rutile occurred at 700 − 850 °C and N 2.8 GPa (e.g., Okay et al., 1989; Wang coexisting with quartz and zircon, is an alternative and complementary et al., 1989; Xu et al., 1992; Okay, 1993; Rolfo et al., 2004), whereas method for estimating temperature of metamorphism, especially useful the peak P − T conditions of the eclogites in the SDZ were estimated for eclogites. Earlier calibrations of the Zr-in-rutile thermometer at 670 °C and 3.3 GPa (Li et al., 2004). In both the CDZ and SDZ units focused on the strong effect of temperature (Zack et al., 2004; Watson the UHP eclogite-facies stage was followed by HP eclogite- and et al., 2006; Ferry and Watson, 2007), without correction for pressure. amphibolite-facies retrograde metamorphism (e.g., Xu et al., 1992; Li The pressure dependence was incorporated into this thermometer et al., 2004; Rolfo et al., 2004). with the calibration of Tomkins et al. (2007). This revised thermometer The NDZ mainly consists of tonalitic and granitic orthogneisses has been demonstrated to be a reliable method for the estimate of the and post-collisional Cretaceous intrusions with subordinate meta- peak temperatures in UHT rocks (e.g., Jiao et al., 2011; Meyer et al., peridotite, garnet pyroxenite, garnet-bearing amphibolite, granulite and 2011; Kooijman et al., 2012). Also, Luvizotto and Zack (2009) obtained eclogite. The oriented mineral exsolutions in garnet and clinopyroxene, Zr-in-rutile temperatures of up to 850 – 930 °C for rutile from granulite- and the occurrence of micro-diamond imply that the NDZ eclogites facies metapelites from Val Strona and Val d'Ossola, though with signif- underwent UHP metamorphism at P N 3.5 GPa (Xu et al., 2003, 2005; icant resetting of Zr-in-rutile temperatures to a spread of lower values. Liu et al., 2005; Malaspina et al., 2006). The Triassic zircon U – Pb ages As a result, combining Ti-in-zircon and Zr-in-rutile thermometry is (Liu et al., 2000, 2007a, 2011a; Wang et al., 2012) and Sm – Nd ages required to constrain peak and post-peak metamorphic temperatures (Liu et al., 2005) of the eclogites from the NDZ suggest that these for eclogites and related high-grade rocks involved in complex processes. rocks formed by the Triassic subduction of the South China Block, simi- A suitable lithology to usefully apply these two novel techniques is the lar to those from the CDZ and SDZ. The Triassic metamorphic ages (Liu granulitized eclogites of the Luotian dome in the southwestern part of et al., 2000, 2007b; Xie et al., 2010) and the occurrence of micro- the North Dabie complex zone (NDZ), central China, which is a portion diamond inclusions in zircon and garnet (Liu et al., 2007b) from the of deeply subducted ma fi c lower continental crust of the South China NDZ banded gneisses suggest that also the gneisses hosting the Block (Liu et al., 2007a). The NDZ eclogites underwent UHP and HP eclogites were involved in the deep subduction of the South China eclogite-facies metamorphism, followed by HP granulite-facies overprint Block, thus implying that the NDZ experienced UHP metamorphism as and later amphibolite-facies retrogression during continental subduction a coherent unit. After the UHP and HP eclogite-facies metamorphism, and exhumation (Liu et al., 2011b). The peak metamorphic assemblages the NDZ eclogites experienced granulite-facies overprinting and later and compositions ...
Similar publications
The Andrelândia nappe front is thrusted by Liberdade nappe front, and the entire system is thrusted over Serra da Bandeira Allochton, correlate of Carrancas Group, in the region Santana the Garambéu, southern Minas Gerais State. The lithostratigraphy of Andrelândia nappe, well preserved in Serra dos Cataguases and adjacency, comprehends, from base...
The Xitieshan terrane is one of four metamorphic terranes in the North Qaidam metamorphic belt, which is an early Paleozoic high-pressure to ultrahigh-pressure (HP-UHP) metamorphic belt in NW China. However, conclusive evidence and precise timing of UHP metamorphism in the Xitieshan terrane have not been well documented. In this study, we report an...
Understanding the timing and duration of metamorphism is fundamental to correctly interpreting the geodynamic evolution of orogenic events. Metamorphic constraints are still ambiguous in the Khondalite Belt, North China Craton, so Paleoproterozoic orogenic processes remain unclear. Here, we investigate a suite of high-grade rocks from the Dongpo lo...
Through petrography, mineral compositions and P-T estimate results, an ultrahigh-temperature (UHT) metapelitic granulite has recently been identified from near Kalasu in the east of Altay city, with an assemblage gt-opx-sil-cd-sp-bt-pl-qtz. The orthopyroxene has a high-Al feature, and its Al2O3 content is as high as 8.7 wt%, indicating a UHT metamo...
The formation and evolution of Palaeoarchaean De Kraalen and Witrivier Greenstone Belts (DKGB and WGB) of the Kaapvaal Craton are poorly known. Here we report zircon and rutile in situ U-Pb ages and zircon Hf isotopic data from a variety of supracrustal rocks. The zircon cores from a metamafic amphibole-bearing gneiss from the DKGB give a protolith...
Citations
... The intensity of metamorphism is mainly related to the pressure and temperature conditions prevailing during rock transformation (Bucher, 2005).Zircon is an important accessory mineral, found in a wide range of igneous, sedimentary and metamorphic rocks (Sepidbar et al, 2018;Siégel et al., 2017). Ti-in zircon thermometry and zircon saturation temperatures (TZr) are useful techniques in petrology as a way of constraining magmatic zircon crystallization temperatures in igneous (e.g., Sepidbar et al, 2018) and high-grade metamorphic rocks (e.g., Sepidbar et al, 2018;Liu et al., 2015). The zircon content of the granitoids in the study area is low to moderate concentration (34-132 ppm). ...
... The omphacite-garnet-phengite geothermobarometer (Krogh Ravna and Terry, 2004) yielded 590 − 628 • C and 21-25 kbar for the peak conditions (Davoudian et al., 2008). Zr-in-rutile geothermometry (Liu et al., 2015) also gave an average of 565 • C for the progressive crystallization of rutile in the eclogites (Davoudian et al., 2016). For the retrograde stage, the garnet-plagioclase-amphibole-quartz geobarometer (Dale et al., 2000) and the amphibole-plagioclase geothermometer (Holland and Blundy, 1994) estimated 10.7 kbar and 714 • C, which is consistent with a phase diagram (Davoudian et al., 2008) calculated with THERMOCALC software (Holland and Powell, 1998). ...
High-pressure-low-temperature (HP-LT) rocks such as eclogites and blueschists preserve valuable information about the history and geodynamics of subduction zones. HP-LT rocks exposed in Iran formed during subduction of Paleo-Tethys and Neo-Tethys oceanic lithosphere beneath the Iran microplate and were subsequently exhumed from the Permian to the Early Eocene. The Shanderman and Anarak complexes are associated with Paleo-Tethys, and the Shahrekord, Hajiabad-Esfandaghe, Sistan, Makran, and Sabzevar complexes are related to Neo-Tethys. The assemblage garnet + omphacite + amphibole (Na-, Na-Ca) + white mica + albite ± zoisite formed at the peak metamorphism stage of the eclogites, and amphibole (Na-, Na-Ca) + albite ± white mica ± zoisite ± epidote ± lawsonite formed in blueschists. Retrograde metamorphism replaced peak assemblages with epidote-amphibolite and greenschist facies mineral assemblage (Ca-amphibole + Na-Ca plagioclase + epidote + chlorite). For the various complexes, geothermobarometry calculations and phase diagram modeling show peak P-T conditions of 23 kbar - 600 °C (Shanderman), 14 kbar - 560 °C (Anarak), 25 kbar - 670 °C (Shahrekord), 17 kbar - 530 °C (Hajiabad-Esfandaghe), 24 kbar - 650 °C (Sistan), 15 kbar - 560 °C (Makran), and 17 kbar - 570 °C (Sabzevar). Their retrograde P-T conditions are ~6 kbar - 470 °C, 7 kbar - 500 °C, 6 kbar - 530 °C, 10 kbar - 450 °C, 8 kbar - 500 °C, 7 kbar -500 °C and 6 kbar - 490 °C, respectively. The obtained P-T conditions represent a geothermal gradient of 12-16 °C/km for the Paleo-Tethys HP-LT complexes and 7-11 °C/km for the Neo-Tethys. Field and petrographic studies reveal that subduction metamorphism occurred mostly along clockwise P-T paths, except for the Hajiabad-Esfandaghe, Makarn and a subunit of the Anarak complexes that endured counter-clockwise paths. The differences may show a greater subduction angle of Neo-Tethys oceanic lithosphere than Paleo-Tethys, resulting in a cold geothermal gradient and development of continental back-arc basins during the Mesozoic.
... Considering the estimated closure temperatures for the U-Pb system in the rutile and the size of the grains (around 600 • C for rutile grains > 0.2 mm, Cherniak, 2000;Vry and Baker, 2006; and/or 370 • C to 500 • C, Mezger et al., 1989) (Fig. 5), the TMC amphibolite rocks probably resided at temperatures of ~ 500 • C to 600 • C, which supports the effect of moderate to high-grade metamorphism process in the region. The result of Zr-in-rutile thermometry for the TMC amphibolites also reflects progressive crystallization of the rutile grains at 616 ± 3 to 674 ± 6 C equal to the peak of amphibolite-facies metamorphism ( Fig. 10; Table 1) (e.g., Zack et al., 2004a;Watson et al., 2006;Ferry and Watson, 2007;Tomkins et al., 2007;Liu et al., 2015). The obtained temperatures overlap with the peak of amphibolite-facies metamorphism reported from the mica-schists in the TMC (708 • C and 5.9 kbar; Ahmadi et al., 2015). ...
... Ti concentrations of zircons from six UHP metamorphic terranes: the North Qaidam terrane, NW China (Chen et al., 2019), the Bohemian Massif, Czechia (Bröcker et al., 2010;Walczak et al., 2017;Schmädicke et al., 2018), the Dabie and Sulu orogens, central China (Gao et al., 2010;Zheng et al., 2011;Li et al., 2014Li et al., , 2016Liu et al., 2015Liu et al., , 2019, NE Greenland (Brueckner et al., 2016), and the Kokchetav complex, Kazakhstan (Stepanov et al., 2016), range from ~ 1 to 40 ppm. These zircons are estimated to have formed at pressures between 3.0 and 4.5 GPa (due to the presence of diamond and/or coesite inclusions in zircon and U-Pb ages that match the age of peak metamorphism) and with aSiO 2 and aTiO 2 = 1, since coesite and rutile were present either as inclusions in zircon or in the mineral assemblage (Table S16). ...
... From north to south, the DOB can be divided into the BHYMB, NDMB, MDMB, SDMB, SSC, and DBC [2,7,[27][28][29]. These units are separated by the Xiaotian-Mozitan, Shuihou-Wuhe, Hualiangting, and Taihu-Mamiao faults, respectively. ...
... The Meishan Group comprises sandstone, limestone, and a small quantity of slate and phyllite [8]. The NDMB contains migmatite, granitic gneiss, small amounts of metabasic and ultrabasic rocks, granulite, marble, and diamond-bearing eclogite [2,[27][28][29]37,[39][40][41][42][43]. The MDMB is composed of granitic gneiss, coesite-or diamond-bearing eclogite, epidote-biotite-plagioclase gneiss, marble, and small amounts of schist, jadeitite, and quartzite [27,44,45]. ...
... The SDMB comprises granite gneiss, quartz eclogite, and schist [27,[44][45][46][47]. The SSC consists of schist, granitic gneiss, and meta-basic rocks [8,18,19,27], and the DBC is composed of granitic gneiss and meta-basic rocks [28,29,48]. ...
The Susong metamorphic complex (SSC) in the southern margin of the Dabie orogenic belt (DOB) in central-eastern China is a key metamorphic unit for understanding subduction and exhumation processes in the DOB. However, the formation age and metamorphic grade of the SSC remain uncertain, hampering our understanding of the mechanism of the formation of the DOB. An integrated study of field survey, regional metamorphic petrology, geothermobarometry, and U–Pb dating of zircon was carried out in this study. Our results reveal that the SSC was metamorphosed under epidote amphibolite- to amphibolite-facies conditions with average metamorphic P–T values of 0.98 ± 0.07 GPa and 531 ± 35 °C. The smooth spatial variation in peak P–T conditions and an apparent geothermal gradient of ~17 °C/km indicate that the SSC as a whole fall into Barrovian-type metamorphic environments. Zircon U–Pb dating for garnet–mica schists of sample ZT003, ZT005 and ZT006 yield five (Groups I to V), six (Groups I to VI) and five (Groups I to V) age groups, respectively, concentrating on the Meso-Neoarchean, early-middle Paleoproterozoic, middle Mesoproterozoic, early Neoproterozoic, Palaeozoic and Triassic-lower Jurassic. Therein, a 259–190 Ma (Group V) from zircons with Th/U ratios of
... The key points on analyzing depositional age in multiple stages of magmatic-metamorphic activities are to identify the impacts of late magmatic-metamorphic events that make geodynamic area complex; however, in Archaean terrain where multiple stages of magmatic and metamorphic activities are common, the youngest zircon age cannot be always used specially to constrain the maximum depositional age (Song et al. 2013;Liu et al. 2015). ...
... LREE depletion and HREE enrichment with Eu and Ce anomalies are used to know the magmatic and metamorphic origins of the rocks (Trail et al. 2012). For high-grade metamorphic rocks, magma crystallization temperature is estimated as defined by (Ewing et al. 2013;Liu et al. 2015;Fu et al. 2009). This is calculated using the formula T(°C) = -4800/ (LOG(Ti) + LOG (aSiO2) -LOG(aTiO2)-5.711)-273, ...
The Bidou I polymetallic prospect, located in the Nyong series, belongs to the northwestern edge of the Congo craton and consists of metasedimentary rocks. Combination of geochemistry with U–Pb zircon dating of these metamorphic formations was used to constrain the source and the tectonic setting of their protolith. Samples are highly enriched in SiO2 (54.4–88.06%) and Al2O3 (5.81–19.66%), depleted in CaO with a very high K2O/Na2O ratio > 1, which are characteristics of metasedimentary rocks. The studied samples are garnet gneisses and garnet micaschists having arkoses and greywackes as inferred protoliths, respectively. The felsic/intermediate nature of those protoliths is related to intracrustal differentiation of sedimentary recycling, marked by the accumulation of zircon. The metasediments undergone weak chemical alteration, range from immature to slightly mature and were derived from a moderately altered sedimentary source in an active tectonic setting. The protoliths of the Bidou I metasedimentary rocks are from the upper continental crust and were deposited in an active or passive continental margin. The duality of the tectonic setting highlights the progressive change in the geometry of the basin and the development of a continental island arc. U–Pb zircon dating yields ages of 2065 ± 25 Ma for garnet gneisses and 2405 ± 24 Ma for garnet micaschists. These new ages are consistent with the data presented by previous works at the NW border of the Congo craton in Cameroon.
... These discoveries suggest that the majority of the continental UHP terranes like the Dabie-Sulu Orogen, Bohemian Massif and South Altyn Orogen may have been subducted to depths of over 100-200 km or even to 300 km with the dragging of oceanic crust and exhumed automatically with the facilitation of their positive buoyancy (Ernst et al., 1997;Liu et al., 2007;Afonso and Zlotnik, 2011;Dong et al., 2018a;Chapman et al., 2019). During the exhumation of continental slabs, the UHP parageneses tend to be eliminated by decompression induced partial melting or retrogression to form migmatitic gneisses, amphibolites or (HP-) granulites, which are frequently mistaken for those non-UHP rocks (Liu et al., 2007;Liu and Liou, 2011;Liu et al., 2015;Perraki and Faryad, 2014;Keller and Ague, 2020). With the significant progress in phase equilibrium modelling (White et al., 2014;Green et al., 2016), the metamorphic P-T conditions or paths of exhumed continental rocks from the deep mantle can be retrieved via careful micro-textural observations on mineral assemblages combined with modelling the chemical zonings of refractory minerals like garnet (Jedlicka et al., 2015;Haifler and Kotková, 2016;Dong et al., 2020). ...
The North Qinling Orogen in central China contains a typical continental high- and ultrahigh-pressure (HP-UHP) metamorphic belt, but its metamorphic evolution remains controversial. We report a combined investigation on petrology, geochronology and phase modelling for felsic granulite (samples SN1504 & SN1517) and garnet clinopyroxenite (sample SN1505) from the Songshugou area. Four stages of metamorphic evolution are constrained: (i) A possible prograde from HP amphibolite facies to peak UHP eclogite facies stage (∼3–8 GPa/700–1080 °C) recorded by the chemical zoning of garnet core and mantle in sample SN1504 and also the presence of supersilicic titanite in sample SN1505. (ii) A post-peak decompression evolution is recorded by the formation of coronary garnet and plagioclase around kyanite in sample SN1504 and high-Ti amphibole and plagioclase in sample SN1505, including the evolution from eclogite facies to HP–ultrahigh temperature (UHT) conditions of 1.3–2.2 GPa/900–980 °C for sample SN1504 and 1.0–2.1 GPa/960–1010 °C for SN1505, respectively. (iii) Further decompression is revealed from the growth of corundum + spinel in local domains in sample SN1504, suggesting a low-pressure (LP) condition of ∼0.8 GPa/950 °C. (iv) A subsequent cooling evolution is recorded by thin films of K-feldspar + quartz + biotite in sample SN1504 and low-Ti amphibole in sample SN1505, indicative of melt crystallization towards the solidus with conditions of 830–770 °C/0.55–0.8 GPa and 880–820 °C/0.8–0.9 GPa, respectively. Zircon and monazite U-Pb dating yields three metamorphic ages of c. 521 Ma, c. 503 Ma and c. 500–480 Ma, which are interpreted to represent the prograde HP amphibolite facies stage, the peak eclogite facies stage and the late cooling stage, respectively. The metamorphic P–T–t path suggests a complete history of deep continental subduction to depths of >90–250 km, followed by rapid exhumation to crustal depths for the Qinling micro-continent during the early Proto-Tethys evolution.
... The exhumation revealed by the retrograde eclogite in this study includes two main features: (i) a prominent HP-UHT metamorphism overprint and (ii) rapid exhumation. This type of exhumation process has been deduced for other orogens, such as the Bohemian Massif (Haifler and Kotková, 2016), the Dabie orogen in China (Liu et al., 2015b), and the West Gneiss Region in Norway (Engvik et al., 2018;Butler et al., 2018). A mechanism that can explain the HP-UHT overprint in these (U)HP rocks is rapid exhumation from mantle depth, followed by a temporary stagnation of exhumation at the base of a thickened crust (Haifler and Kotková, 2016;Dong et al., 2018Dong et al., , 2019Dong et al., , 2020Li et al., 2020), which would mean that the high-T condition was inherited from the UHP conditions. ...
... 500-484 Ma, in the eastern segment, subducted slab was heated by the mantle at the plate-mantle interface and became detached from the subducting plate, followed by rapid exhumation to continental crust depth (Zhang et al., 2014a;Dong et al., 2020; this study); and d) at ca. 450 Ma, UHP rocks in the western segment were exhumed to continental depth, accompanied with slab break-off induced widespread contemporaneous magmatism in SAT (Liu et al., 2012(Liu et al., , 2015a. As near-isothermal decompression with (U)HT overprinting has been reported from many other UHP belts (e.g., Dabie, Liu et al., 2015b;Bohemian Massif, Haifler and Kotková, 2016), the identification of differential exhumation processes in SAT, especially the hot and rapid exhumation of the eastern segment, provides valuable insights into the exhumation mechanism of ultra-deep subducted UHP terranes. ...
South Altyn Tagh contains ultrahigh-pressure (UHP) terranes that have been exhumed from ∼300 km mantle depth. Previous zircon U–Pb geochronology has yielded an eclogite-facies age of ca. 500 Ma and a high-pressure (HP) granulite-facies retrograde age of ca. 450 Ma in the Jianggalesayi area in the western segment of South Altyn Tagh. However, in the eastern segment (Yinggelisayi and Danshuiquan localities), an age range of 500–480 Ma has been determined, and it remains uncertain as to whether this age range represents the timing of the peak metamorphic stage or the retrograde overprint. Our study of newly discovered retrograde eclogite in the Danshuiquan locality shows that it underwent three stages of metamorphism, under eclogite-facies, HP granulite-facies and amphibolite-facies P–T conditions of 2.5–4.0 GPa and 870–1050 °C, 2.0–1.4 GPa and 830–940 °C, and 0.7–1.3 GPa and 704–880 °C, respectively. The decompression-dominated P–T path evolved mainly after crossing the solidus, indicating marked retrograde modification under melt-bearing conditions. LA–ICP–MS and SIMS zircon U–Pb dating yielded ca. 500 Ma eclogite-facies and ca. 484 Ma granulite-facies retrograde ages and a later retrograde age of ca. 452 Ma. The clockwise P–T–t path indicates rapid exhumation from eclogite-facies to granulite-facies within around 16 Myr, which is faster than that of the UHP rocks in the western segment. Thus, the HP–UHP rocks in South Altyn Tagh suggest a differential exhumation process for the eastern and western segments. The distinct HP–UHT metamorphism and rapid exhumation of (U)HP rocks in the eastern segment likely resulted from local mantle heating. The continuing P–T evolution of the (U)HP rocks under UHT conditions during exhumation led to a pervasive granulite-facies overprint in the eastern segment of the South Altyn Tagh. The rapid exhumation recorded in the eastern segment provides valuable insights into the exhumation mechanism of ultra-deep subducted UHP terranes.
... The second phase of granitic intrusion is marked by the widespread occurrence of Neoarchean TTG gneisses outcropping continuously in the Wuhe County. Liu et al. (2019) obtained in these lithologies conventional zircon U-Pb ages of 2.7 Ga, which are in accordance with published zircon ages of 2.7 Ga from the TTG gneiss, syenogranite, potassic granite and amphibolite in the Huoqiu complex (Liu et al., 2015;Wang et al., 2014;Xie et al., 2014). The third phase of granitic intrusion is represented by TTG gneisses and potassic granite, and give late-Neoarchean zircon ages of 2.5 Ga, which are in agreement with previously published zircon U-Pb ages of 2.5 Ga from a garnet-bearing mafic gneiss xenolith in the Jiagou Mesozoic intrusion and from marbles at Fengyang Wang et al., 2012). ...
... (Zr))-273; Ferry and Watson, 2007)) obtained in the zircon mantles. Generally, the highest Ti-in-zircon temperature represents the peak metamorphic temperature (Liu et al., 2015). Notably, the highest metamorphic temperatures of 1095 • C for sample 1504MS2 and 1041 • C for sample 1410MS6 are consistent with granulite facies metamorphic conditions (Kunz et al., 2018;Liu et al., 2009b). ...
... This interpretation is also supported by calcite inclusions preserved within these rims (Figs. 6l and S1c), indicating that the gneisses underwent heterogeneous carbonate-bearing hydrous melt/fluid metasomatism, as previously proposed by Liu et al. (2015Liu et al. ( , 2016Liu et al. ( , 2017. Moreover, the occurrence of a great amount of microfractures filled with barite in hematite (Fig. 3e, f) also provides strong evidence for this metamorphic event. ...
The Wuhe complex (WC), exposed at the southeastern margin of the North China Craton (NCC), is an important constituent of the Eastern Block of the NCC. In order to better understand the Precambrian crustal composition and evolution of this region, a comprehensive investigation on zircon geochronology and Hf isotopes, as well as whole-rock geochemistry and Sr-Nd-Pb isotopes was conducted on alkaline ultrapotassic granitic gneisses from the WC at Mashan. These gneisses are considered as meta-igneous rocks based on geochemical and mineralogical criteria (with special reference to zircon cathodoluminescence images). They are characterized by modally abundant alkali feldspar (more than 60%) and quartz (more than 30%) while plagioclase is rare. Mafic minerals are sodic amphiboles such as arfvedsonite and eckermannite, aegirine and rare biotite. Minor constituents are rutile, muscovite, apatite and barite. Major elements geochemistry shows high SiO2 (69.85%–74.51%) and K2O + Na2O (9.67%–12.17%) contents, high K2O/Na2O (7.41–22.53) ratios, and relatively low MgO (0.37%–0.87%) and CaO (0.10%–0.23%) contents. Trace elements geochemistry shows significant depletions of Nb, Y, Ce, Ga, and REE (rare earth elements) relative to anorogenic granites. These features suggest that the magmatic protoliths of the studied gneisses belong to ultrapotassic silica-saturated alkaline series from an extensional background, perhaps in a subduction-related rifting environment. As concerning isotope geochemistry, their ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios are 16.6297–17.1877, 15.4454–15.5066, and 36.6036–38.0304, respectively, and εNd(t) values vary from −1.7 to +9.1. Two samples yielded zircon ²⁰⁷Pb/²⁰⁶Pb ages of 2615 ± 4 Ma and 2617 ± 5 Ma, respectively, representing their precursor ages. The zircon igneous core domains exhibit oscillatory growth zoning with positive εHf (t) values (+2.5 − +6.6). These data, coupled with chondrite-normalized and primitive-mantle-normalized element patterns, suggest that the precursors of the studied granitic gneisses were mainly derived from a subduction-modified ultrapotassic syenitic parental magma, and may be considered as a particular group of A-type granites, involved in an important crustal growth and reworking event at ~2.6 Ga. These rocks experienced a granulite-facies metamorphic stage accompanied by partial melting, as testified by clinopyroxene + rutile + K-feldspar + spinel + quartz + apatite inclusions in zircon metamorphic domains which were dated at ~2.5 Ga. The occurrence of this metamorphic stage is also supported by the lower ΣREE contents, negative Eu anomalies, and high Ti-in-zircon temperatures (>800 °C) of metamorphic zircon mantles dated at ~2.5 Ga. Eventually, the studied rocks suffered a later ~1.85 Ga metamorphic overprinting, possibly related to the Paleoproterozoic collisional orogeny recorded in the region.
... Rutile, in the petrographic study of high-grade metamorphic rocks, plays an important role as a constant component in the paragenesis of metamorphic rocks [51,54,55,57,62,78]. Petrological studies of igneous and metamorphic rocks have documented an increased concentration of trace elements such as Zr, W, Cr, V, Hf, Nb, Ta, and others [54,65,74,79]. ...
... Petrological studies of igneous and metamorphic rocks have documented an increased concentration of trace elements such as Zr, W, Cr, V, Hf, Nb, Ta, and others [54,65,74,79]. These data are used to identify the protoliths of metamorphic rocks and in geothermometry and geobarometry [33,78,80]. The data obtained from PT studies of rutile crystallization conditions in metamorphic and igneous rocks have also been successfully applied to detrital rutile [28,29,33,34,81]. ...
The geochemistry of detrital rutile grains, which are extremely resistant to weathering, was used in a provenance study of the transgressive Albian quartz sands in the southern part of extra-Carpathian Poland. Rutile grains were sampled from eight outcrops and four boreholes located on the Miechów, Szydłowiec, and Puławy Segments. The crystallization temperatures of the rutile grains, calculated using a Zr-in-rutile geothermometer, allowed for the division of the study area into three parts: western, central, and eastern. The western group of samples, located in the Miechów Segment, is characterized by a polymodal distribution of rutile crystallization temperatures (700–800 °C; 550–600 °C, and c. 900 °C) with a significant predominance of high-temperature forms, and with a clear prevalence of metapelitic over metamafic rutile. The eastern group of samples, corresponding to the Lublin Area, is monomodal and their crystallization temperatures peak at 550–600 °C. The contents of metapelitic to metamafic rutile in the study area are comparable. The central group of rutile samples with bimodal distribution (550–600 °C and 850–950 °C) most likely represents a mixing zone, with a visible influence from the western and, to a lesser extent, the eastern group. The most probable source area for the western and the central groups seems to be granulite and high-temperature eclogite facies rocks from the Bohemian Massif. The most probable source area for the eastern group of rutiles seems to be amphibolites and low temperature eclogite facies rocks, probably derived from the southern part of the Baltic Shield.
