Geochemical data and zircon ages for rocks in a high-pressure belt of Chu-Yili Mountains, southern Kazakhstan: Implications for the earliest stages of accretion in Kazakhstan and the Tianshan

Abstract The mechanism and age of Palaeozoic accretion in the Central Asian Orogenic Belt remain poorly constrained. One of the most complex belts extends from the Kokchetav area in northern Kazakhstan to the Kyrgyz northern Tianshan. It represents an assemblage of small blocks with Palaeoproterozoic continental crust, intervening slivers containing early Palaeozoic ophiolites and/or deep-marine sediments, and a number of HP and UHP metamorphic complexes. The HP–LT metamorphic rocks provide important clues for reconstructions of the overall structure and evolution of the accretionary collage. This study is aimed to constrain the metamorphic age and tectonic implications of HP garnet pyroxenites and enclosing mica schists in the Anrakhai area of the Chu-Yili Mountains of southern Kazakhstan. The HP belt is located in the central part of the Anrakhai metamorphic block and extends NW–SE between Neoproterozoic gneisses in the SW and undated ophiolites and granodiorites in the NE. Garnet pyroxenites and their retrograded equivalents form tectonic boudins and blocks in garnet–muscovite and muscovite schist of sedimentary origin. Metamorphic zircons from two garnet pyroxenite samples yielded a SHRIMP mean 206Pb/238U age of 489.9 ± 3.1 Ma. This age is interpreted to reflect the time of Early Ordovician peak metamorphism and ongoing subduction in the area as constrained by geological data and suggests that HP metamorphism was related to subduction. Exhumation of the HP rocks occurred between 490 and ∼475 Ma, based on the Early Ordovician age of overlap assemblages. Detrital zircons from a garnet–muscovite schist enclosing the pyroxenites were dated by LA-ICP-MS and range in age from 694 to 2557 Ma. They suggest a maximum late Neoproterozoic age for deposition of the sedimentary protolith and derivation from a continental source including Neoproterozoic to Archaean crustal components. Granodiorites with chemical characteristics of island arc rocks intruded into Proterozoic gneisses in the NE of the HP belt, and magmatic zircons from one sample yielded a SHRIMP 206Pb/238U mean age of 508.3 ± 3 Ma. This signifies the existence of a Cambrian magmatic arc. The early Palaeozoic age of the HP garnet pyroxenites indicates that the Anrakhai block is not part of a extensive Precambrian microcontinent, as previously thought, but represents a package of tectonically interlayered slivers, made up of Precambrian basement and early Palaeozoic rocks. Stacking of these heterogeneous domains may be due to subduction of continental crust, mutual underthrusting of continental and ophiolitic rocks, wedge extrusion of HP rocks, and strike-slip deformation in a subduction and/or collision setting. The Anrakhai collision zone is part of larger accretionary belt which formed by the end of the Early Ordovician and may extend from the Kyrgyz northern Tianshan to the Kokchetav area in northern Kazakhstan.

[1]  R. Coleman,et al.  Ultrahigh Pressure Metamorphism: List of contributors , 1995 .

[2]  F. Corfu,et al.  Atlas of Zircon Textures , 2003 .

[3]  B. Song,et al.  Triassic collision of western Tianshan orogenic belt, China: Evidence from SHRIMP U-Pb dating of zircon from HP/UHP eclogitic rocks , 2007 .

[4]  P. Kinny.  3820 Ma zircons from a tonalitic Armîsoq gneiss in the Godthåb district of Southern West Greenland , 1986 .

[5]  Chuan-Lin Zhang,et al.  Geological and geochronological evidence for the Precambrian evolution of the Tarim Craton and surrounding continental fragments , 2008 .

[6]  P. O'Brien,et al.  Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes , 2000 .

[7]  J. Gill,et al.  Petrology and Geochemistry of Pliocene-Pleistocene Volcanic Rocks from the Izu Arc, Leg 126 , 1992 .

[8]  I. Nikitin,et al.  Paleogeography and Main Features of Volcanicity in the Ordovician of Kazakhstan and North Tien Shan , 1991 .

[9]  M. Bröcker,et al.  New Age Constraints on the Metamorphic Evolution of the High‐Pressure/Low‐Temperature Belt in the Western Tianshan Mountains, NW China , 2005, The Journal of Geology.

[10]  A. Didenko,et al.  The Vendian-Early Paleozoic history of the continental margin of eastern Paleogondwana, Paleoasian Ocean, and Central Asian Foldbelt , 2003 .

[11]  R. Stern.  The GSC Sensitive High Resolution Ion Microprobe (SHRIMP): analytical techniques of zircon U-Th-Pb age determinations and performance evaluation , 1997 .

[12]  R. Coleman,et al.  Ultrahigh Pressure Metamorphism: Overview of the geology and tectonics of UHPM , 1995 .

[13]  A. Sobolev,et al.  Zircon response to diamond-pressure metamorphism in the Kokchetav massif, USSR , 1991 .

[14]  R. Klemd,et al.  Formation of HP–LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: geochemical and age constraints , 2003 .

[15]  Wang,et al.  P–T path of high‐pressure/low‐temperature rocks and tectonic implications in the western Tianshan Mountains, NW China , 1999 .

[16]  E. B. Sal’nikova,et al.  Age of Palaeozoic granites and metamorphism in the Tuvino-Mongolian Massif of the Central Asian Mobile Belt: loss of a Precambrian microcontinent , 2001 .

[17]  A. Tindle,et al.  Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks , 1984 .

[18]  A. Avdeyev.  OPHIOLITE ZONES AND THE GEOLOGIC HISTORY OF KAZAKHSTAN FROM THE MOBILIST STANDPOINT , 1984 .

[19]  I. Katayama,et al.  Geology of the Kokchetav UHP‐HP metamorphic belt, Northern Kazakhstan , 2000 .

[20]  W. McDonough,et al.  Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes , 1989, Geological Society, London, Special Publications.

[21]  V. Shatsky,et al.  Geochemistry and age of ultrahigh pressure metamorphic rocks from the Kokchetav massif (Northern Kazakhstan) , 1999 .

[22]  R. Hatcher.  4-D framework of continental crust , 2007 .

[23]  L. Popov,et al.  Evidence for 15 m.y. of continuous deep-sea biogenic siliceous sedimentation in early Paleozoic oceans , 2001 .

[24]  G. Foster,et al.  Common-Pb corrected in situ U–Pb accessory mineral geochronology by LA-MC-ICP-MS , 2003 .

[25]  P. Azimov,et al.  Hercynian granulites of Mongolian and Gobian Altai: Geodynamic setting and formation conditions , 2002 .

[26]  Guochun Zhao,et al.  Spot zircon U-Pb isotope analysis by ICP-MS coupled with a frequency quintupled (213 nm) Nd-YAG laser system , 2004 .

[27]  A. Kennedy,et al.  A double focusing mass spectrometer for geochronology , 1998 .

[28]  L. Medaris.  GARNET PERIDOTITES IN EURASIAN HIGH-PRESSURE AND ULTRAHIGH-PRESSURE TERRANES : A DIVERSITY OF ORIGINS AND THERMAL HISTORIES , 1999 .

[29]  D. Alexeiev,et al.  Palaeomagnetism of Ordovician and Silurian rocks from the Chu-Yili and Kendyktas mountains, south Kazakhstan , 2005 .

[30]  T. Harrison,et al.  The tectonic evolution of Asia , 1996 .

[31]  L. P. Black,et al.  Metamorphic zircon formation by solid‐state recrystallization of protolith igneous zircon , 2000 .

[32]  Dunyi Liu,et al.  Early Paleozoic tectonic evolution of the Chinese South Tianshan Orogen: constraints from SHRIMP zircon U–Pb geochronology and geochemistry of basaltic and dioritic rocks from Xiate, NW China , 2009 .

[33]  A. Sengor.  Paleotectonics of Asia : fragments of a synthesis. , 1996 .

[34]  M. Tagiri,et al.  CHIME monazite ages of garnet-chloritoid-talc schists in the Makbal Complex, Northern Kyrgyz Tien-Shan: First report of the age of the UHP metamorphism , 2009 .

[35]  O. Ishizuka,et al.  Across‐arc geochemical trends in the Izu‐Bonin arc: Constraints on source composition and mantle melting , 2000 .

[36]  B. Taylor,et al.  Rifting and the Volcanic-Tectonic Evolution of the Izu-Bonin-Mariana Arc , 1992 .

[37]  D. Gebauer,et al.  Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) , 1999 .

[38]  O. Vinn,et al.  Brachiopods of the redefined family Tritoechiidae from the Ordovician of Kazakhstan and South Urals , 2001 .

[39]  C. Barnes,et al.  Advances in Ordovician Geology , 1991 .

[40]  B. Windley,et al.  Accretionary growth and crust formation in the Central Asian Orogenic Belt and comparison with the Arabian-Nubian shield , 2007 .

[41]  R. Korsch,et al.  TEMORA 1: a new zircon standard for Phanerozoic U–Pb geochronology , 2003 .

[42]  W. Ernst,et al.  Ultrarapid exhumation of ultrahigh-pressure diamond-bearing metasedimentary rocks of the Kokchetav Massif, Kazakhstan? , 2003 .

[43]  J. Kirschvink,et al.  Zircon U-Pb ages for the Early Cambrian time-scale , 1992, Journal of the Geological Society.

[44]  G. L. Cumming,et al.  Ore lead isotope ratios in a continuously changing earth , 1975 .

[45]  S. Pisarevsky,et al.  The Siberian Craton and its evolution in terms of the Rodinia hypothesis , 2006 .

[46]  E. B. Sal’nikova,et al.  Ophiolite sections of the Dzhalair-Nayman zone, South Kazakhstan: Their structure and age substantiation , 2009 .

[47]  D. Rubatto,et al.  Zircon Behaviour in Deeply Subducted Rocks , 2007 .

[48]  By,et al.  Paleozoic structural and geodynamic evolution of eastern Tianshan (NW China): welding of the Tarim and Junggar plates , 2007 .

[49]  M. Tagiri,et al.  Mineral parageneses and metamorphic P-T paths of ultrahigh-pressure eclogites from Kyrghyzstan Tien-Shan , 1995 .

[50]  N. Dobretsov,et al.  Late Cambrian-Ordovician tectonics and geodynamics of Central Asia , 2007 .

[51]  B. Windley,et al.  Mineral ages and P-T conditions of Late Paleozoic high-pressure eclogite and provenance of mélange sediments from Atbashi in the south Tianshan orogen of Kyrgyzstan , 2010, American Journal of Science.

[52]  K. Degtyarev,et al.  Cambrian arc-continent collision in the Paleozoides of Kazakhstan , 2007 .

[53]  C. Parkinson,et al.  Overview of the geology, petrology and tectonic framework of the high‐pressure–ultrahigh‐pressure metamorphic belt of the Kokchetav Massif, Kazakhstan , 2000 .

[54]  D. Rubatto,et al.  The age of metamorphism of diamondiferous rocks determined with SHRIMP dating of zircon , 2006 .

[55]  Brian F. Windley,et al.  Tectonic models for accretion of the Central Asian Orogenic Belt , 2007, Journal of the Geological Society.

[56]  J. Charvet,et al.  Structural and Geochronological Study of High‐Pressure Metamorphic Rocks in the Kekesu Section (Northwestern China): Implications for the Late Paleozoic Tectonics of the Southern Tianshan , 2010, The Journal of Geology.

[57]  L. Zonenshain,et al.  Geology of the USSR : a plate-tectonic synthesis , 1990 .