Petrology of Garnet Amphibolites from the Hualong Group: Implications for Metamorphic Evolution of the Qilian Orogen, NW China

Abstract

The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a systematic study of petrography, mineral chemistry and phase equilibria of garnet amphibolites from the Hualong Group, which represents the Precambrian basement in the southern accretionary belt of the Qilian Orogen. The garnet amphibolites mainly consist of amphibole, plagioclase, garnet and quartz, with minor pyroxene, biotite and ilmenite. A peak stage of upper amphibolite facies to low-temperature granulite facies metamorphism and retrograde metamorphism in the amphibolite facies affected the samples. Garnet has a homogeneous composition of Alm_66–71Grs_14–17Prp_9–12Sps_3–5, amphibole is ferro-hornblende, biotite belongs to the ferro-biotite species and pyroxene is dominated by orthopyroxene with few clinopyroxene. Pseudosection modeling of the garnet amphibolite samples indicates clockwise P-T paths. The samples witness peak metamorphism at conditions of ~4.9–6.3 kbar and ~755–820 ºC in the upper amphibolite facies to lowtemperature granulite facies, and retrograde cooling and decompression at conditions of ~2.5–3.1 kbar and ~525–545 ºC. It is inferred that peak metamorphism with high temperature and low pressure occurred at ca. 450 Ma during northward subduction of the South Qilian oceanic crust beneath the central Qilian Block. When continental collision occurred between the central Qilian and the Qaidam blocks, the Hualong Block was accreted onto the South Qilian accretionary complex and experienced amphibolite facies retrograde metamorphism at ca. 440 Ma.

Keywords

Qilian Orogen / Hualong Group / garnet amphibolite / petrology / metamorphic P-T path / Perple_X

References

[1] BGMR-GP Bureau of GeologyMineral Resources of Gansu Province Regional Geology of Qinghai Province, 1989.

[2] BGMR-QP Bureau of GeologyMineral Resources of Qinghai Province Regional Geology of Qinghai Province, 1991.

[3] Chen N.-S., Gong S. L., Xia X. P., . Zircon Hf Isotope of Yingfeng Rapakivi Granites from the Quanji Massif and ~2.7 Ga Crustal Growth. Journal of Earth Science, 2013, 24(1): 29-41.

[4] Chung S. L., Liu D. Y., Ji J. Q., . Adakites from Continental Collision Zones: Melting of Thickened Lower Crust beneath Southern Tibet. Geology, 2003, 1021.

[5] Connolly J. A. D. Computation of Phase Equilibria by Linear Programming: A Tool for Geodynamic Modeling and Its Application to Subduction Zone Decarbonation. Earth and Planetary Science Letters, 2005, 236(1/2): 524-541.

[6] Cui J. W., Zheng Y. Y., Sun X., . Origin of Granodiorite and Mafic Microgranular Enclave in Saizhisi, Qinghai Province: Zircon U-Pb Geochronological, Geochemical and Sr-Nd-Hf Isotopic Constraints. Earth Science—Journal of China University of Geosciences, 2016, 41: 1156-1170.

[7] Dale J., Powell R., White R. W., . A Thermodynamic Model for Ca-Na Clinoamphiboles in Na₂O-CaO-FeO-MgO-Al₂O₃-SiO₂-H₂O-O for Petrological Calculations. Journal of Metamorphic Geology, 2005, 23(8): 771-791.

[8] Dale J., Holland T. J. B., Powell R. Hornblende-Garnet-Plagioclase Thermobarometry: A Natural Assemblage Calibration of the Thermodynamics of Hornblende. Contributions to Mineralogy and Petrology, 2000, 140(3): 353-362.

[9] Fan G. M., Lei D. N. Precise Timing and Significance of Caledonian Structural Deformation Chronology in Southeast Qilian. Earth Science—Journal of China University of Geosciences, 2007, 32: 39-44.

[10] Feng Y. M., He S. P. Research for Geology and Geochemistry of Several Ophiolites in the North Qilian Mountains, China. Acta Petrologica Sinica, 1995, 11: 125-146.

[11] Feng Y. M., He S. P. Geotectonics and Orogeny of the Qilian Mountains, 1996.

[12] Foster M. D. Interpretation of the Composition of Trioctahedral Micas. United States Geological Survey Professional Paper 354-B, 1960, 11-49.

[13] Fu C. L., Yan Z., Guo X. Q., . Assembly and Dispersal History of Continental Blocks within the Altun-Qilian-North Qaidam Mountain Belt, NW China. International Geology Review, 2018, 43: 1-24.

[14] Fu C. L., Yan Z., Wang Z. Q., . Lajishankou Ophiolite Complex: Implications for Paleozoic Multiple Accretionary and Collisional Events in the South Qilian Belt. Tectonics, 2018, 37(5): 1321-1346.

[15] Fu C. L., Yan Z., Wang Z. Q., . Texture and Composition of the Lajishankou Accretionary Wedge of the South Qilian Belt, NW China. Acta Petrologica Sinica, 2018, 34(7): 2049-2064.

[16] Fu C. L., Yan Z. The Composition, Age and Tectonic Setting of Lajishan Ophiolitic Mélange. Acta Geoscientica Sinica, 2017, 38: 29-32.

[17] Fu C. L., Yan Z., Guo X. Q., . Geochemistry and SHRIMP Zircon U-Pb Age of Diabases in the Lajishankou Ophiolitic Mélange, South Qilian Terrane. Acta Petrologica Sinica, 2014, 30: 1659-1706.

[18] Gehrels G. E., Kapp P., DeCelles P., . Detrital Zircon Geochronology of Pre-Tertiary Strata in the Tibetan-Himalayan Orogen, 2011.

[19] Gehrels G. E., Yin A., Wang X. F. Magmatic History of the Northeastern Tibetan Plateau, 2003.

[20] Guo J. J., Zhao F. Q., Li H. K., . New Chronological Evidence of the Age of Huangyuan Group in the Eastern Segment of Mid-Qilian Massif and Its Geological Significance. Regional Geology of China, 2000, 19: 26-31.

[21] He S. P., Li R. S., Wang C., . The Further Age Constraint of Hualong Rock Group in the Eastern Segment of South Qilian Mountains. Acta Petrologica et Mineralogica, 2011, 30: 34-44.

[22] He S. P., Li R. S., Wang C., . Geochronology of Gneissic Plagioclase-Amphibolite from Beidahe Group-Complex in Western Segment of Qilian Mountains, China. Geological Bulletin of China, 2010, 29: 1275-1280.

[23] He S. P., Wang H. L., Chen J. L., . LA-ICP-MS U-Pb Zircon Geochronology of Basic Dikes within Maxianshan Rock Group in the Central Qilian Mountains and Its Tectonic Implications. Earth Sciences—Journal of China University of Geosciences, 2008, 33: 35-45.

[24] Holland T. J. B., Powell R. Activity-Composition Relations for Phases in Petrological Calculations: An Asymmetric Multicomponent Formulation. Contributions to Mineralogy and Petrology, 2003, 145(4): 492-501.

[25] Holland T. J. B., Powell R. An Internally Consistent Thermodynamic Data Set for Phases of Petrological Interest. Journal of Metamorphic Geology, 1998, 16(3): 309-343.

[26] Holland T. J. B., Powell R. Thermodynamics of Order-Disorder in Minerals; II, Symmetric Formalism Applied to Solid Solutions. American Mineralogist, 1996, 81(11/12): 1425-1437.

[27] Holland T. J. B., Powell R. A Compensated-Redlich-Kwong (CORK) Equation for Volumes and Fugacities of CO₂ and H₂O in the Range 1 bar to 50 kbar and 100–1 600 ºC. Contributions to Mineralogy and Petrology, 1991, 109(2): 265-273.

[28] Hou Q. Y., Zhang H. F., Zhang B. R., . Characteristics and Tectonic Affinity of Lajishan Paleo-Mantle in Qilian Orogenic Belt: A Geochemical Study of Basalts. Earth Science—Journal of China University of Geosciences, 2005, 30: 61-70.

[29] Huang H., Niu Y. L., Nowell G., . The Nature and History of the Qilian Block in the Context of the Development of the Greater Tibetan Plateau. Gondwana Research, 2015, 28(1): 209-224.

[30] Leake B. E. Nomenclature of Amphiboles. Mineralogical Magazine, 1978, 42(324): 533-563.

[31] Li C. Y., Liu Y. W., Zhu B. C., . Structrual Evolutions of Qinling and Qilian, 1978, 174-189.

[32] Qiu J. X., Zeng G. C., Wang S. Y., . Early Paleozoic Volcanic Rocks in Lajishan Mountains. Northwest Geoscience, 1995, 16: 69-83.

[33] Smith J. V. Feldspar Minerals, 1974

[34] Song S. G., Niu Y. L., Su L., . Continental Orogenesis from Ocean Subduction, Continent Collision/subduction, to Orogen Collapse, and Orogen Recycling: The Example of the North Qaidam UHPM Belt, NW China. Earth-Science Reviews, 2014, 129: 59-84.

[35] Song S. G., Niu Y. L., Su L., . Tectonics of the North Qilian Orogen, NW China. Gondwana Research, 2013, 23(4): 1378-1401.

[36] Song S. G., Niu Y. L., Zhang L. F., . Time Constraints on Orogenesis from Oceanic Subduction to Continental Subduction, Collision, and Exhumation: An Example from North Qilian and North Qaidam HP-UHP Belts. Acta Petrologica Sinica, 2009, 25: 2067-2077.

[37] Song S. G., Yang L. M., Zhang Y. Q., . Qi-Qin Accretionary Belt in Central China Orogen: Accretion by Trench Jam of Oceanic Plateau and Formation of Intra-Oceanic Arc in the Early Paleozoic Qin-Qi-Kun Ocean. Science Bulletin, 2017, 62(15): 1035-1038.

[38] Song S. G., Zhang L. F., Niu Y. L., . Eclogite and Carpholite-Bearing Metasedimentary Rocks in the North Qilian Suture Zone, NW China: Implications for Early Palaeozoic Cold Oceanic Subduction and Water Transport into Mantle. Journal of Metamorphic Geology, 2007, 25(5): 547-563.

[39] Song S. G., Zhang L. F., Niu Y. L., . Evolution from Oceanic Subduction to Continental Collision: A Case Study from the Northern Tibetan Plateau Based on Geochemical and Geochronological Data. Journal of Petrology, 2006, 47(3): 435-455.

[40] Song S. G., Zhang L. F., Niu Y. L., . Zircon U-Pb SHRIMP Ages of Eclogites from the North Qilian Mountains in NW China and Their Tectonic Implication. Chinese Science Bulletin, 2004, 49(8): 848-852.

[41] Tajčmanová L., Connolly J. A. D., Cesare B. A Thermodynamic Model for Titanium and Ferric Iron Solution in Biotite. Journal of Metamorphic Geology, 2009, 27(2): 153-165.

[42] Tung K. A., Yang H. J., Yang H. Y., . SHRIMP U-Pb Geochronology of the Zircons from the Precambrian Basement of the Qilian Block and Its Geological Significances. Chinese Science Bulletin, 2007, 52(19): 2687-2701.

[43] Tung K. A., Yang H. Y., Liu D. Y., . The Amphibolite-Facies Metamorphosed Mafic Rocks from the Maxianshan Area, Qilian Block, NW China: A Record of Early Neoproterozoic Arc Magmatism. Journal of Asian Earth Sciences, 2012, 46: 177-189.

[44] Tung K. A., Yang H. Y., Yang H. J., . Magma Sources and Petrogenesis of the Early–Middle Paleozoic Backarc Granitoids from the Central Part of the Qilian Block, NW China. Gondwana Research, 2016, 38: 197-219.

[45] Wan Y. S., Zhang J. X., Yang J. S., . Geochemistry of High-Grade Metamorphic Rocks of the North Qaidam Mountains and Their Geological Significance. Journal of Asian Earth Sciences, 2006, 28(2/3): 174-184.

[46] Wan Y. S., Xu Z. Q., Yang J. S., . The Precambrian High-Grade Basement of the Qilian Terrane and Neighboring Areas: Its Age and Compositions. Acta Geoscientia Sinica, 2003, 24: 319-324.

[47] Wan Y. S., Yang J. S., Xu Z. Q., . Geochemical Characteristics of Rocks from the Maxianshan Complex and Xinglongshan Group in the Eastern Segment of Qilian Orogenic Belt. Journal of the Geological Society of China, 2000, 43: 52-68.

[48] Wang C., Li R. S., Smithies R. H., . Early Paleozoic Felsic Magmatic Evolution of the Western Central Qilian Belt, Northwestern China, and Constraints on Convergent Margin Processes. Gondwana Research, 2017, 41: 301-324.

[49] Wang T., Wang Z. Q., Yan Z., . Geochronological and Geochemical Evidence of Amphibolite from the Hualong Group, Northwest China: Implication for the Early Paleozoic Accretionary Tectonics of the Central Qilian Belt. Lithos, 2016, 248–251: 12-21.

[50] Wu C. L., Xu X. Y., Gao Q. M., . Early Palaezoic Granitoid Magmatism and Tectonic Evolution in North Qilian, NW China. Acta Petrologica Sinica, 2010, 26: 1027-1044.

[51] Wu C. L., Wooden J. L., Yang J. S., . Granitic Magmatism in the North Qaidam Early Paleozoic Ultrahigh-Pressure Metamorphic Belt, Northwest China. International Geology Review, 2006, 48(3): 223-240.

[52] Xia L. Q., Li X. M., Yu J. Y., . Mid–Late Neoproterozoic to Early Paleozoic Volcanism and Tectonic Evolution of the Qilianshan, NW China. GeoResJ, 2016, 9–12: 1-41.

[53] Xia L. Q., Xia Z. C., Ren Y. X., . Marine Volcanic Rocks from Qilian and Qinling Mountains, 1991.

[54] Xiao W. J., Windley B. F., Yong Y., . Early Paleozoic to Devonian Multiple-Accretionary Model for the Qilian Shan, NW China. Journal of Asian Earth Sciences, 2009, 35(3/4): 323-333.

[55] Xu W. C., Zhang H. F., Liu X. M. U-Pb Zircon Dating Constraints on Formation Time of Qilian High-Grade Metamorphic Rock and Its Tectonic Implications. Chinese Science Bulletin, 2007, 52(4): 531-538.

[56] Xu X., Song S. G., Allen M. B., . An 850–820 Ma LIP Dismembered during Breakup of the Rodinia Supercontinent and Destroyed by Early Paleozoic Continental Subduction in the Northern Tibetan Plateau, NW China. Precambrian Research, 2016, 282: 52-73.

[57] Xu Z. Q., Yang J. S., Wu C. L., . Timing and Mechanism of Formation and Exhumation of the Northern Qaidam Ultrahigh-Pressure Metamorphic Belt. Journal of Asian Earth Sciences, 2006, 28(2/3): 160-173.

[58] Xu Z. Q., Xu H. F., Zhang J. X., . The Zoulang Nanshan Caledonian Subduction Complex in the Northern Qilian Mountains and Its Dynamics. Acta Geologica Sinica, 1994, 7: 225-241.

[59] Yan Z., Aitchison J., Fu C. L., . Hualong Complex, South Qilian Terrane: U-Pb and Lu-Hf Constraints on Neoproterozoic Micro-Continental Fragments Accreted to the Northern Proto-Tethyan Margin. Precambrian Research, 2015, 266: 65-85.

[60] Yan Z., Guo X. Q., Fu C. L., . Detrital Heavy Mineral Constraints on the Triassic Tectonic Evolution of the West Qinling Terrane, NW China: Implications for Understanding Subduction of the Paleotethyan Ocean. The Journal of Geology, 2014, 122(5): 591-608.

[61] Yan Z., Li J. L., Wang Z. Q., . Tectonic Settings and Accretionary Orogenesis of the West Qinling Wedge, Northeastern Margin of the Tibet Plateau. Acta Petrologica Sinica, 2012, 26: 1808-1828.

[62] Yang H., Zhang H. F., Luo B. J., . Early Paleozoic Intrusive Rocks from the Eastern Qilian Orogen, NE Tibetan Plateau: Petrogenesis and Tectonic Significance.. Lithos, 2015, 13-31.

[63] Yang J. H., Chung S. L., Wilde S. A., . Petrogenesis of Post-Orogenic Syenites in the Sulu Orogenic Belt, East China: Geochronological, Geochemical and Nd-Sr Isotopic Evidence. Chemical Geology, 2005, 214: 99-125.

[64] Yang J. S., Xu Z. Q., Zhang J. X., . Early Palaeozoic North Qaidam UHP Metamorphic Belt on the North-Eastern Tibetan Plateau and a Paired Subduction Model. Terra Nova, 2002, 14(5): 397-404.

[65] Yin A., Harrison T. M. Geologic Evolution of the Himalayan-Tibetan Orogen. Annual Review of Earth and Planetary Sciences, 2000, 28(1): 211-280.

[66] Yu J. Y., Li X. M., Ma Z. P., . The LA-ICP-MS U-Pb Age and Geological Significance of Hualong Rock Group in South Qilian Mountains. Northwestern Geology, 2012, 45: 79-85.

[67] Zhang J. X., Yu S. Y., Mattinson C. G. Early Paleozoic Polyphase Metamorphism in Northern Tibet, China. Gondwana Research, 2017, 41: 267-289.

[68] Zhang J. X., Mattinson C. G., Meng F. C., . U-Pb Geochronology of Paragneisses and Metabasite in the Xitieshan Area, North Qaidam Mountains, Western China: Constraints on the Exhumation of HP/UHP Metamorphic Rocks. Journal of Asian Earth Sciences, 2009, 35(3/4): 245-258.

[69] Zhang J. X., Meng F. C., Wan Y. S. A Cold Early Palaeozoic Subduction Zone in the North Qilian Mountains, NW China: Petrological and U-Pb Geochronological Constraints. Journal of Metamorphic Geology, 2007, 25(3): 285-304.

[70] Zhang Y. Q., Song S. G., Yang L. M., . Basalts and Picrites from a Plume-Type Ophiolite in the South Qilian Accretionary Belt, Qilian Orogen: Accretion of a Cambrian Oceanic Plateau?. Lithos, 2017, 278–281: 97-110.

[71] Zhang Z. W., Li W. Y., Gao Y. B., . Sulfide Mineralization Associated with Arc Magmatism in the Qilian Block, Western China: Zircon U-Pb Age and Sr-Nd-Os-S Isotope Constraints from the Yulonggou and Yaqu Gabbroic Intrusions. Mineralium Deposita, 2014, 49(2): 279-292.