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Mingguo Zhai - One of the best experts on this subject based on the ideXlab platform.
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paleoproterozoic metamorphism of high grade Granulite facies rocks in the north china craton study advances questions and new issues
Precambrian Research, 2017Co-Authors: Ligang Zhou, Jialin Wu, Mingguo Zhai, Haozheng Wang, Lei Zhao, Junsheng Lu, Houxiang ShanAbstract:Abstract High-grade Granulite facies rocks (one of extreme Granulites) refer in particular to a part with high metamorphic temperature (HT) and high metamorphic pressure (HP) within Granulite facies. A part of basement rocks of the North China Craton (NCC) experiences high-grade metamorphisms up to HP-HT Granulite-facies or granuite-eclogite transition facies in Paleoproterozoic, which offers ideal natural laboratories to probe into early Precambrian tectonic evolution of the Earth. The studies of Precambrian high-grade metamorphic rocks have made steady progresses on distributions and occurrences of high-grade Granulite facies rocks, their mineral interactions (including micro-inclusion mineral), metamorphic conditions, metamorphic chronologies, and metamorphic processes and P-T paths in recent decades. The concept of Incipient Plate Tectonics was proposed by Zhai (1997, 2004, 2012, 2014) and Zhai and Santosh (2011). However, some intractable and controversial scientific problems still exist, which are challenging and significant issues to understand early tectonic evolution of continent crust and the Earth. This paper reviews study advances of Paleoproterozoic high-grade Granulite terranes in the NCC and overviews its prospect. Three fundamental characteristics are distinct: 1) Paleoproterozoic high-grade metamorphic rocks seemingly occur in area or broad pan-belt, which widely spread in the northwest NCC, middle NCC, south NCC, eastern NCC and Korean peninsula, in almost all outcrops of Precambrian basements of the NCC (Sino-Korean Craton) except for some coverage districts of Phanerozoic rocks; Three kinds of high-grade rocks have been distinguished, which are HP mafic Granulite, HT pelitic Granulite and ultramafic Granulite. As their country rocks, some tonalite-trondhjemite-granodiorite gneisses (TTGs) could have undergone metamorphism under the same P-T conditions. 2) The HP mafic Granulites and HT pelitic Granulites are commonly spatially-associated with concordant occurrences, showing the both underwent contemporaneous deformation and metamorphism since peak metamorphic stage. The HP mafic Granulites are suggested to be metamorphosed gabboric dykes by previous studies. Detail district geological mappings in some terranes also demonstrate that the gabbroic dykes intruded into sedimentary rocks and had been in position before peak metamorphic stage. In Jiaobei region of northern East Shandong Province, ultramafic Granulites are distributed associated with HP mafic Granulites and/or HT pelitic Granulites. Metamorphism studies demonstrate that all the three Granulite facies rocks record uplift processes and they were uplifted to surface as a whole. 3) All the three types of Granulite facies rocks underwent three major metamorphic stages, which are peak HP-HT Granulite facies, moderate Granulite facies and amphibolites facies. The corresponding metamorphic ages are ∼1980–1900 Ma, ∼1890 ∼ 1820 Ma, and ∼1800 Ma, respectively. Some sedimentary rocks underwent ultra-high temperature (UHT) metamorphism with the indicating mineral assemblages of sappirine + quartz. Eclogite facies minerals were found in a minor amount of HP mafic Granulites, which were presented by pseudomorphed omphacite ± rutile ± quartz preserved as inclusion minerals in garnets, or by some matrix clinopyroxenes broken down to wormy symplektite of albite + Na-poor clinopyroxene. Base on P-T conditions of the metamorphism and the corresponding geochronologic data, it is calculated that the Paleoproterozoic metamorphic terranes in the NCC have obviously high geothermal gradient of about 14–28 °C/km (average 21 °C/km), and abnormally slow uplift rate of about 0.18–0.24 mm/yr, both of which are remarkably different from Phanerozoic continent collisional belts. The concept of incipient plate tectonics is established for Paleoproterozoic metamorphism in the NCC. Being clearly different from tectonic style of Archean high-grade region and greenstone belt, Paleoproterozoic terranes are seemingly more similar to tectonic style of Phanerozoic continent-continent collision. Metamorphic pressures of ∼10–14 Kbar in the HT pelitic Granulites indicate that the supracrustal rocks had sunk into lower crust with depth of 40–50 km and then were uplifted to the surface again. This implies that the NCC had attained a considerable thickness and an extra drive force could be necessary for so great vertical displacement of supracrustal rocks. In consideration of the broad distributions of these high-grade metamorphic rocks, some “quasi-rigid” blocks were proposed to have preliminarily formed in Paleoproterozoic, which could facilitate sinking and uplifting motion of these rocks by subduction-collision-like processes between micro-blocks. In other words, the principle of plate tectonics might have been operated at that time. However, these blocks are limited in rigidity for their disability to sink into depth of boundary between lithosphere and asthenosphere but activation only in crustal scale. In this regard, a process of “hot” subduction-collision is considered, which comprehensively includes various elements, such as smaller continent blocks, high geothermal gradient, tiny density distinction between subducted slab and wall rock (lower crust), which together define a motion limited in crustal scales with lacking in enough strengths of thrust force and buoyancy. The incipient plate tectonics have displayed lateral compressional structure and kinematic interaction between blocks, but it is much smaller in scale relative to Phanerozoic collisional orogeny, although the tectonic style is more or less similar.
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Granulite facies metamorphism and crust melting in the huai an terrane at 1 95 ga north china craton new constraints from geology zircon u pb lu hf isotope and metamorphic conditions of Granulites
Precambrian Research, 2016Co-Authors: Huafeng Zhang, Mingguo Zhai, Haozheng Wang, Lei Zhao, Elson P Oliveira, Zhiyao Ni, Jialin WuAbstract:Abstract Geological implications of ∼1.95 Ga and ∼1.85 Ga metamorphic ages for HP Granulites in the Huai’an terrane are still controversial, which have affected the crustal evolution models for the North China Craton. This study reports two geological sections in which distinct geological relationships of a quartz-dioritic and a tonalitic dike cutting through mafic HP Granulite and Granulite facies meta-sedimentary rocks are described. In these two sections, magmatic dikes, mafic HP Granulites and meta-sedimentary rocks preserve conformable foliation to indicate their similar deformation history. The U–Pb dating and Lu–Hf isotopic analysis of zircons from metamorphic and meta-igneous rocks provide new constraints on the timing and mechanism of thermal events associated with metamorphic and deformation events. Both magmatic dikes were formed around ∼1.95 Ga and overprinted by later metamorphic event during ∼1.85 Ga. The S-type granite, at geological section (GS) 1, revealed its formation age was formed around 1959 ± 34 Ma (n = 3, MSWD = 1.5), and overprinted by later metamorphic event at 1840 ± 8 Ma (n = 10, MSWD = 1.2). Additionally, zircons from the mafic HP Granulite in the GS2 are dominated by metamorphic ages of 1972 ± 22 Ma (n = 6; MSWD = 0.03) with few grains recording an age of 1856 ± 29 Ma (n = 3; MSWD = 0.17). In situ Lu–Hf analyses on zircons from the quartz-dioritic dike, tonalitic dike, mafic HP Granulite and S-type granite, reveal that the magmatic dikes were derived from partial melting of ∼2.0–2.2 Ga meta-basic rocks and the S-type granite was generated by melting of meta-sediments beyond 840 ± 50 °C. It suggested that those meta-sediments were taken into the lower crust in a certain way at Granulite facies conditions ca. 1.95 Ga ago. A clockwise P-T path acquired from mafic HP Granulite revealed peak metamorphic conditions of 880–890 °C and 11–13 kbar. The temperature results recorded in the ∼1.95 Ga zircons of mafic HP Granulite, similar to those of high-pressure mineral assemblage in matrix, suggest that the HP Granulite metamorphism was approximately ∼1.95 Ga ago. According to the results above, this contribution concludes that mafic and meta-sedimentary rocks were metamorphosed together under high-pressure Granulite metamorphic conditions ∼1.95 Ga ago, followed by high-temperature Granulite facies melting event that gave rise to granite and S-type granite at ∼1.95 Ga. The Granulite facies metamorphic rocks and magmatic dikes in the Huangtuyao graphite mine experienced the same evolution history after ∼1.95 Ga. The mafic and pelitic HP Granulites in the Huai’an terrane are interpreted to be collisional products of the Paleoproterozoic cratonization of the NCC.
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discovery of pelitic high pressure Granulite from manjinggou of the huai an complex north china craton metamorphic p t evolution and geological implications
Precambrian Research, 2016Co-Authors: Jialin Wu, Huafeng Zhang, Mingguo Zhai, Wenqiang Yang, Haozheng Wang, Lei Zhao, Wei WangAbstract:Abstract The first report of Paleoproterozoic mafic high-pressure (HP) Granulite terranes in Manjinggou area of the Huai’an Complex, North China Craton (NCC) since 1992 has attracted broad attention from geologists, and accordingly various Early Precambrian continent-continent collision or micro-blocks amalgamation hypotheses were suggested. However, one important issue is still controversial whether the pelitic Granulites and associated mafic H P Granulites underwent similar metamorphic history. Here we report newly recognized pelitic H P Granulites in Manjinggou area of the Huai’an Complex to provide direct evidence that both pelitic and mafic H P Granulites suffered similar metamorphic history. The metamorphic peak mineral assemblage of the pelitic Granulites is characterized by Grt-Ky-Kfs-Bt-Rt-Qz-Liq±Ms, and the subsequent medium-pressure (M P ) Granulite facies retrogression is characterized by Grt-Sil-Kfs-Pl-Bt-Rt-Liq-Qz. Pseudosection approaches were undertaken in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -O (NCKFMASHTO) system to account for textural development, mineral composition and P – T evolution of the pelitic Granulites. The estimated peak and retrograde Granulite facies conditions are 11.5–15 kbar, 810–860 °C and ∼9.5 kbar, ∼850 °C, respectively, comparable with those of associated mafic H P Granulites. Consistently, field geological observations and available geochronological data also indicate their similar deformation and metamorphic history from H P Granulite facies stage (∼1.96–1.90 Ga) to retrograde stages (∼1.88–1.80 Ga). This finding changes previous views that the pelitic rocks and associated mafic Granulites are different slabs with individual metamorphic history. The khondalite series from the Huai’an Complex and adjacent Ji’ning Complex were probably experienced H P Granulite facies metamorphism, but previously derived M P Granulite facies conditions might be attributed to mineral re-equilibrium due to long dwell time under M P Granulite facies. Additionally, these Granulite facies rocks record high apparent geothermal gradients and slow exhumation rates relative to H P –UH P rocks in the Phanerozoic continental collisional orogens. It seems to indicate that the thermal regimes and tectonic mechanisms of Paleoproterozoic probably differ from those of Phanerozoic eons, and these H T –H P Granulite terranes from the NCC were likely formed in a hot and slow cooling orogen.
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zircon u pb ages of paleoproterozoic mafic Granulites from the huai an terrane north china craton ncc implications for timing of cratonization and crustal evolution history
Precambrian Research, 2016Co-Authors: Huafeng Zhang, Mingguo Zhai, Haozheng Wang, M. SantoshAbstract:Abstract The North China Craton (NCC) is considered to have been incorporated into the Columbia supercontinent during late Paleoproterozoic. The Huai’an terrane located in north-central part of the NCC is an important tectonic window to investigate the Paleoproterozoic crustal evolution history of this craton, particularly due to the wide occurrence of high-grade metamorphic rocks including retrograded eclogites and high-pressure Granulites. Available data show two controversial peak metamorphic ages of these rocks as 1.95–1.90 or ∼1.85–1.80 Ga. Thus, determining the precise timing of metamorphism of the high-pressure Granulites is important in reconstructing the collisional history. In this study, we present zircon U–Pb ages, bulk chemistry, and mineral inclusions in zircons and matrix mineral assemblages from the high-pressure Granulites to evaluate the timing of metamorphism. Our results reveal ca. 2.05–2.0 Ga ages from magmatic zircons in these rocks representing the timing of emplacement of mafic magmas. The metamorphic zircons yield two groups of ages at 1.95–1.90 and ∼1.85∼1.80 Ga. Clinopyroxene, plagioclase, titanite, and apatite occur as common mineral inclusions within the ∼1.85–1.80 Ga metamorphic zircons. The chemical compositions of clinopyroxene and plagioclase occurring as inclusions are very similar to those of the rim compositions of those minerals in the matrix, suggesting their formation during retrograde Granulite metamorphism, and are distinctly different from those of the core domains of the minerals in the matrix which represent high-pressure Granulite metamorphism. These results indicate that the metamorphic zircons formed during retrograde Granulite metamorphism dated as ∼1.85–1.80 Ga and the age range of ∼1.95–1.90 Ga corresponds to high-pressure Granulite metamorphism. The dual nature of the geological and geochronological features suggest that the Archean gray gneisses in the Huai’an terrane represent the basement rocks detached from the Khondalite Belt of the NCC after collision. Integrating with published data, a double-side collision with scissor-like suturing model is proposed for the Paleoproterozoic cratonization of the NCC.
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sm nd geochronology and petrography of garnet pyroxene Granulites in the northern sulu region of china and their geotectonic implication
Lithos, 2000Co-Authors: Mingguo Zhai, Bolin Cong, Yonggang Li, Qingchen WangAbstract:Abstract Abundant garnet-bearing Granulite lenses are widely distributed in the northern part of the Sulu region and adjacent areas. They are possibly re-metamorphosed high-pressure metamorphic rocks. On the basis of detailed petrographic study, samples WD01, WD04 and ML06 from Laixi and Wendeng were identified as high-pressure Granulites, and WH1 from Weihai as an original coesite-bearing eclogite. Three high-pressure Granulite samples give mineral-WR isochron ages of 1846±76, 1743±79 and 1752±30 Ma. TDM ages are 3.3, 3.0 and 2.8 Ga. The Sm–Nd mineral-WR isochron ages are interpreted to date as the metamorphic resetting within the medium-pressure Granulite facies, representing an isotopic re-homogeneity during uplifting of the high-pressure Granulites from deep continent crust. It is important that Sm–Nd chronological characteristics are the same as Archaean high-pressure Granulites in the North China craton. However, sample WH1 from Weihai demonstrates abnormal Sm–Nd characteristics. Its whole rock eNd (0) value is +129. TDM age is 1.3 Ga, and constrains the minimum age of re-metamorphosed eclogite protolith formation to the mid-Proterozoic. This result is identical to those reported by Jahn (1994) , showing complicated processes of metamorphism and metasomatism. The data in this paper provide further evidence to define the boundary between the North China craton and UHPM belt in eastern Shandong and to understand the geotectonic nature of the boundary.
Charlotte Moller - One of the best experts on this subject based on the ideXlab platform.
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late sveconorwegian grenville high pressure Granulite facies metamorphism in southwest sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
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Late Sveconorwegian (Grenville) high‐pressure Granulite facies metamorphism in southwest Sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
Xiaolong Huang - One of the best experts on this subject based on the ideXlab platform.
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phanerozoic magma underplating associated with remelting of the lower crust beneath the cathaysia block evidence from zircon upb ages and hfo isotopes of Granulite xenoliths from daoxian south china
Lithos, 2020Co-Authors: Xiaolong Huang, Yang Yu, Xue Wang, Pengli HeAbstract:Abstract Widespread Mesozoic granitoids in the Cathaysia Block of South China are associated with intensive reworking of the lower crust as a result of magma underplating. This inference is based mainly on studies of mafic igneous rocks, whereas there is little evidence from lower-crustal rocks. Lower-crustal xenoliths in Mesozoic basalts in the Daoxian region within the Cathaysia Block might record information on the relationship between magma underplating and remelting of the pre-existing crust beneath the block. The xenoliths are mainly mafic Granulites, with minor felsic Granulites. The mafic Granulites have low SiO2 contents (47.22–49.46 wt%) and high Mg# values (77.8–82.4), suggesting that their protoliths were derived from a mantle source. The felsic Granulite xenoliths have high SiO2 (69.56–70.27 wt%) and low MgO (1.63–2.50 wt%) contents, and zircons in these xenoliths yield negative eHf(t) values (−6.1 to −12.6) and high δ18O values (6.8–7.6‰), consistent with a crustal source. Both mafic and felsic Granulite xenoliths record magmatic (226–218 Ma) and metamorphic (218–193 Ma) events, suggesting a genetic link between mafic and felsic rocks in the lower crust. We propose that the magma underplating was responsible for the origin of the mafic Granulites and partial melting of pre-existing lower crust, as recorded by the felsic xenoliths. The Granulite xenoliths also contain abundant inherited zircons that formed during the Archean–Neoproterozoic (2584–659 Ma), early Paleozoic (peaking at ca. 425 Ma), and late Paleozoic (peaking at ca. 261 Ma). Zircons from the Daoxian Granulite xenoliths have distinct Hf O isotopic compositions that record the multistage evolution of the lower crust beneath the Cathaysia Block. This evolution involved the accretion of juvenile crust during the late Archean (eHf(t) = +4.2 to +4.6) and late Paleozoic (eHf(t) = +1.3 to +5.3; δ18O = 5.8–6.2‰), crustal reworking during the Neoproterozoic (eHf(t) = −7.5 to −11.8; δ18O = 5.1–9.5‰) and early Paleozoic (eHf(t) = −0.5 to −2.2; δ18O = 7.3–7.5‰), and crustal accretion with significant reworking during the early Mesozoic (eHf(t) = −19.2 to +5.9; δ18O = 6.8–7.6‰). The U Pb ages and Hf O isotopic data of zircons from the Daoxian Granulite xenoliths are consistent with the distribution of Phanerozoic igneous rocks in the Cathaysia Block. These data support the inference that Mesozoic magma underplating triggered the remelting of pre-existing crustal materials and produced extensive granitoid magmatism.
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geochronology petrology and geochemistry of the Granulite xenoliths from nushan east china implication for a heterogeneous lower crust beneath the sino korean craton
Geochimica et Cosmochimica Acta, 2004Co-Authors: Xiaolong Huang, Yigang XuAbstract:Abstract The occurrence of both Archean Granulite terrains and Granulite xenoliths in Cenozoic basalts from the Sino-Korean Craton (SKC) provides an ideal opportunity to define composition and evolution of continental lower crust of eastern China. The Granulite xenoliths in Quaternary basanites from Nushan (southeastern SKC) show a basic-intermediate composition that is distinctly different from mafic Granulites from Hannuoba (western SKC). They instead resemble the Archean Granulite terrains in terms of mineral and whole rock compositions. Trace element modeling suggests that the “protoliths” of the Nushan Granulites were likely subjected to fractional crystallization and assimilation of old crustal components. Zircon SHRIMP U-Pb dating shows at least two episodes in the formation of the lower crust at Nushan. The protoliths of the Nushan Granulites were most likely formed at ca. 2.5 Ga and metamorphosed at 1.9 Ga. This late Archean crustal growth was followed by Mesozoic (∼140 Ma) basaltic underplating, which was probably coeval with the widespread thermo-tectonic lithospheric reactivation in eastern China. The Nushan Granulites are therefore interpreted as dominantly derived from the late Archean crystalline basement and subordinately from the mafic layer that was accreted to the basement during late Mesozoic lithospheric thinning. The consistencies between the depth to seismic Moho and the depth to crust-mantle boundary, and between the calculated Vp (mostly Liu et al., 2001) . Such a compositional difference, in conjunction with contrasting age and seismic velocity structure of the lower crust at the two localities, highlights two fundamentally distinct tectonic domains in the SKC. The data presented in this study also yield implication for the origin of the compositional difference between Granulite xenoliths and terrains.
Haozheng Wang - One of the best experts on this subject based on the ideXlab platform.
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paleoproterozoic metamorphism of high grade Granulite facies rocks in the north china craton study advances questions and new issues
Precambrian Research, 2017Co-Authors: Ligang Zhou, Jialin Wu, Mingguo Zhai, Haozheng Wang, Lei Zhao, Junsheng Lu, Houxiang ShanAbstract:Abstract High-grade Granulite facies rocks (one of extreme Granulites) refer in particular to a part with high metamorphic temperature (HT) and high metamorphic pressure (HP) within Granulite facies. A part of basement rocks of the North China Craton (NCC) experiences high-grade metamorphisms up to HP-HT Granulite-facies or granuite-eclogite transition facies in Paleoproterozoic, which offers ideal natural laboratories to probe into early Precambrian tectonic evolution of the Earth. The studies of Precambrian high-grade metamorphic rocks have made steady progresses on distributions and occurrences of high-grade Granulite facies rocks, their mineral interactions (including micro-inclusion mineral), metamorphic conditions, metamorphic chronologies, and metamorphic processes and P-T paths in recent decades. The concept of Incipient Plate Tectonics was proposed by Zhai (1997, 2004, 2012, 2014) and Zhai and Santosh (2011). However, some intractable and controversial scientific problems still exist, which are challenging and significant issues to understand early tectonic evolution of continent crust and the Earth. This paper reviews study advances of Paleoproterozoic high-grade Granulite terranes in the NCC and overviews its prospect. Three fundamental characteristics are distinct: 1) Paleoproterozoic high-grade metamorphic rocks seemingly occur in area or broad pan-belt, which widely spread in the northwest NCC, middle NCC, south NCC, eastern NCC and Korean peninsula, in almost all outcrops of Precambrian basements of the NCC (Sino-Korean Craton) except for some coverage districts of Phanerozoic rocks; Three kinds of high-grade rocks have been distinguished, which are HP mafic Granulite, HT pelitic Granulite and ultramafic Granulite. As their country rocks, some tonalite-trondhjemite-granodiorite gneisses (TTGs) could have undergone metamorphism under the same P-T conditions. 2) The HP mafic Granulites and HT pelitic Granulites are commonly spatially-associated with concordant occurrences, showing the both underwent contemporaneous deformation and metamorphism since peak metamorphic stage. The HP mafic Granulites are suggested to be metamorphosed gabboric dykes by previous studies. Detail district geological mappings in some terranes also demonstrate that the gabbroic dykes intruded into sedimentary rocks and had been in position before peak metamorphic stage. In Jiaobei region of northern East Shandong Province, ultramafic Granulites are distributed associated with HP mafic Granulites and/or HT pelitic Granulites. Metamorphism studies demonstrate that all the three Granulite facies rocks record uplift processes and they were uplifted to surface as a whole. 3) All the three types of Granulite facies rocks underwent three major metamorphic stages, which are peak HP-HT Granulite facies, moderate Granulite facies and amphibolites facies. The corresponding metamorphic ages are ∼1980–1900 Ma, ∼1890 ∼ 1820 Ma, and ∼1800 Ma, respectively. Some sedimentary rocks underwent ultra-high temperature (UHT) metamorphism with the indicating mineral assemblages of sappirine + quartz. Eclogite facies minerals were found in a minor amount of HP mafic Granulites, which were presented by pseudomorphed omphacite ± rutile ± quartz preserved as inclusion minerals in garnets, or by some matrix clinopyroxenes broken down to wormy symplektite of albite + Na-poor clinopyroxene. Base on P-T conditions of the metamorphism and the corresponding geochronologic data, it is calculated that the Paleoproterozoic metamorphic terranes in the NCC have obviously high geothermal gradient of about 14–28 °C/km (average 21 °C/km), and abnormally slow uplift rate of about 0.18–0.24 mm/yr, both of which are remarkably different from Phanerozoic continent collisional belts. The concept of incipient plate tectonics is established for Paleoproterozoic metamorphism in the NCC. Being clearly different from tectonic style of Archean high-grade region and greenstone belt, Paleoproterozoic terranes are seemingly more similar to tectonic style of Phanerozoic continent-continent collision. Metamorphic pressures of ∼10–14 Kbar in the HT pelitic Granulites indicate that the supracrustal rocks had sunk into lower crust with depth of 40–50 km and then were uplifted to the surface again. This implies that the NCC had attained a considerable thickness and an extra drive force could be necessary for so great vertical displacement of supracrustal rocks. In consideration of the broad distributions of these high-grade metamorphic rocks, some “quasi-rigid” blocks were proposed to have preliminarily formed in Paleoproterozoic, which could facilitate sinking and uplifting motion of these rocks by subduction-collision-like processes between micro-blocks. In other words, the principle of plate tectonics might have been operated at that time. However, these blocks are limited in rigidity for their disability to sink into depth of boundary between lithosphere and asthenosphere but activation only in crustal scale. In this regard, a process of “hot” subduction-collision is considered, which comprehensively includes various elements, such as smaller continent blocks, high geothermal gradient, tiny density distinction between subducted slab and wall rock (lower crust), which together define a motion limited in crustal scales with lacking in enough strengths of thrust force and buoyancy. The incipient plate tectonics have displayed lateral compressional structure and kinematic interaction between blocks, but it is much smaller in scale relative to Phanerozoic collisional orogeny, although the tectonic style is more or less similar.
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Granulite facies metamorphism and crust melting in the huai an terrane at 1 95 ga north china craton new constraints from geology zircon u pb lu hf isotope and metamorphic conditions of Granulites
Precambrian Research, 2016Co-Authors: Huafeng Zhang, Mingguo Zhai, Haozheng Wang, Lei Zhao, Elson P Oliveira, Zhiyao Ni, Jialin WuAbstract:Abstract Geological implications of ∼1.95 Ga and ∼1.85 Ga metamorphic ages for HP Granulites in the Huai’an terrane are still controversial, which have affected the crustal evolution models for the North China Craton. This study reports two geological sections in which distinct geological relationships of a quartz-dioritic and a tonalitic dike cutting through mafic HP Granulite and Granulite facies meta-sedimentary rocks are described. In these two sections, magmatic dikes, mafic HP Granulites and meta-sedimentary rocks preserve conformable foliation to indicate their similar deformation history. The U–Pb dating and Lu–Hf isotopic analysis of zircons from metamorphic and meta-igneous rocks provide new constraints on the timing and mechanism of thermal events associated with metamorphic and deformation events. Both magmatic dikes were formed around ∼1.95 Ga and overprinted by later metamorphic event during ∼1.85 Ga. The S-type granite, at geological section (GS) 1, revealed its formation age was formed around 1959 ± 34 Ma (n = 3, MSWD = 1.5), and overprinted by later metamorphic event at 1840 ± 8 Ma (n = 10, MSWD = 1.2). Additionally, zircons from the mafic HP Granulite in the GS2 are dominated by metamorphic ages of 1972 ± 22 Ma (n = 6; MSWD = 0.03) with few grains recording an age of 1856 ± 29 Ma (n = 3; MSWD = 0.17). In situ Lu–Hf analyses on zircons from the quartz-dioritic dike, tonalitic dike, mafic HP Granulite and S-type granite, reveal that the magmatic dikes were derived from partial melting of ∼2.0–2.2 Ga meta-basic rocks and the S-type granite was generated by melting of meta-sediments beyond 840 ± 50 °C. It suggested that those meta-sediments were taken into the lower crust in a certain way at Granulite facies conditions ca. 1.95 Ga ago. A clockwise P-T path acquired from mafic HP Granulite revealed peak metamorphic conditions of 880–890 °C and 11–13 kbar. The temperature results recorded in the ∼1.95 Ga zircons of mafic HP Granulite, similar to those of high-pressure mineral assemblage in matrix, suggest that the HP Granulite metamorphism was approximately ∼1.95 Ga ago. According to the results above, this contribution concludes that mafic and meta-sedimentary rocks were metamorphosed together under high-pressure Granulite metamorphic conditions ∼1.95 Ga ago, followed by high-temperature Granulite facies melting event that gave rise to granite and S-type granite at ∼1.95 Ga. The Granulite facies metamorphic rocks and magmatic dikes in the Huangtuyao graphite mine experienced the same evolution history after ∼1.95 Ga. The mafic and pelitic HP Granulites in the Huai’an terrane are interpreted to be collisional products of the Paleoproterozoic cratonization of the NCC.
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discovery of pelitic high pressure Granulite from manjinggou of the huai an complex north china craton metamorphic p t evolution and geological implications
Precambrian Research, 2016Co-Authors: Jialin Wu, Huafeng Zhang, Mingguo Zhai, Wenqiang Yang, Haozheng Wang, Lei Zhao, Wei WangAbstract:Abstract The first report of Paleoproterozoic mafic high-pressure (HP) Granulite terranes in Manjinggou area of the Huai’an Complex, North China Craton (NCC) since 1992 has attracted broad attention from geologists, and accordingly various Early Precambrian continent-continent collision or micro-blocks amalgamation hypotheses were suggested. However, one important issue is still controversial whether the pelitic Granulites and associated mafic H P Granulites underwent similar metamorphic history. Here we report newly recognized pelitic H P Granulites in Manjinggou area of the Huai’an Complex to provide direct evidence that both pelitic and mafic H P Granulites suffered similar metamorphic history. The metamorphic peak mineral assemblage of the pelitic Granulites is characterized by Grt-Ky-Kfs-Bt-Rt-Qz-Liq±Ms, and the subsequent medium-pressure (M P ) Granulite facies retrogression is characterized by Grt-Sil-Kfs-Pl-Bt-Rt-Liq-Qz. Pseudosection approaches were undertaken in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -O (NCKFMASHTO) system to account for textural development, mineral composition and P – T evolution of the pelitic Granulites. The estimated peak and retrograde Granulite facies conditions are 11.5–15 kbar, 810–860 °C and ∼9.5 kbar, ∼850 °C, respectively, comparable with those of associated mafic H P Granulites. Consistently, field geological observations and available geochronological data also indicate their similar deformation and metamorphic history from H P Granulite facies stage (∼1.96–1.90 Ga) to retrograde stages (∼1.88–1.80 Ga). This finding changes previous views that the pelitic rocks and associated mafic Granulites are different slabs with individual metamorphic history. The khondalite series from the Huai’an Complex and adjacent Ji’ning Complex were probably experienced H P Granulite facies metamorphism, but previously derived M P Granulite facies conditions might be attributed to mineral re-equilibrium due to long dwell time under M P Granulite facies. Additionally, these Granulite facies rocks record high apparent geothermal gradients and slow exhumation rates relative to H P –UH P rocks in the Phanerozoic continental collisional orogens. It seems to indicate that the thermal regimes and tectonic mechanisms of Paleoproterozoic probably differ from those of Phanerozoic eons, and these H T –H P Granulite terranes from the NCC were likely formed in a hot and slow cooling orogen.
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zircon u pb ages of paleoproterozoic mafic Granulites from the huai an terrane north china craton ncc implications for timing of cratonization and crustal evolution history
Precambrian Research, 2016Co-Authors: Huafeng Zhang, Mingguo Zhai, Haozheng Wang, M. SantoshAbstract:Abstract The North China Craton (NCC) is considered to have been incorporated into the Columbia supercontinent during late Paleoproterozoic. The Huai’an terrane located in north-central part of the NCC is an important tectonic window to investigate the Paleoproterozoic crustal evolution history of this craton, particularly due to the wide occurrence of high-grade metamorphic rocks including retrograded eclogites and high-pressure Granulites. Available data show two controversial peak metamorphic ages of these rocks as 1.95–1.90 or ∼1.85–1.80 Ga. Thus, determining the precise timing of metamorphism of the high-pressure Granulites is important in reconstructing the collisional history. In this study, we present zircon U–Pb ages, bulk chemistry, and mineral inclusions in zircons and matrix mineral assemblages from the high-pressure Granulites to evaluate the timing of metamorphism. Our results reveal ca. 2.05–2.0 Ga ages from magmatic zircons in these rocks representing the timing of emplacement of mafic magmas. The metamorphic zircons yield two groups of ages at 1.95–1.90 and ∼1.85∼1.80 Ga. Clinopyroxene, plagioclase, titanite, and apatite occur as common mineral inclusions within the ∼1.85–1.80 Ga metamorphic zircons. The chemical compositions of clinopyroxene and plagioclase occurring as inclusions are very similar to those of the rim compositions of those minerals in the matrix, suggesting their formation during retrograde Granulite metamorphism, and are distinctly different from those of the core domains of the minerals in the matrix which represent high-pressure Granulite metamorphism. These results indicate that the metamorphic zircons formed during retrograde Granulite metamorphism dated as ∼1.85–1.80 Ga and the age range of ∼1.95–1.90 Ga corresponds to high-pressure Granulite metamorphism. The dual nature of the geological and geochronological features suggest that the Archean gray gneisses in the Huai’an terrane represent the basement rocks detached from the Khondalite Belt of the NCC after collision. Integrating with published data, a double-side collision with scissor-like suturing model is proposed for the Paleoproterozoic cratonization of the NCC.
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late sveconorwegian grenville high pressure Granulite facies metamorphism in southwest sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
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Late Sveconorwegian (Grenville) high‐pressure Granulite facies metamorphism in southwest Sweden
Journal of Metamorphic Geology, 1991Co-Authors: Leif Johansson, Anders Lindh, Charlotte MollerAbstract:Mafic Granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with Granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P–T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic Granulites from five localities. The estimated P–T conditions for the peak of metamorphism range from 705°C and 8.1 kbar at Hallandsas in the south, to 770°C and 10.5 kbar at Ullared in the north (medium- to high-P Granulite facies conditions). Sm–Nd geochronology on minerals from the mafic Granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 ± 12 and 916 ± 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.
