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(a) Compositional profile of garnet in the garnet and chloritoidbearing pelitic schist (KG1244). (b) Ternary diagrams showing the chemical compositions of the garnet in the garnet and chloritoid-bearing pelitic schist (KG1244). Arrows indicate compositional zoning from core to rim.
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Garnet-free pelitic schist (KG1251) and garnet and chloritoid-bearing pelitic schist (KG1244) of the Neldy Formation in the Makbal HP-UHP Metamorphic Complex, Kyrgyz Northern Tien-Shan are petrologically and geochronologically described. The pelitic schist (KG1251) consists mainly of phengite, chlorite and quartz, with small amounts of albite, tita...
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Context 1
... 2). The garnet shows a growth zoning with decreasing in spessartine (X Sps 0.12-0.02) and increasing in pyrope (X Pyr 0.04-0.08), and slightly decreasing and subsequently increasing in almandine from core to rim. Grossular shows slightly increasing (X Grs 0.08-0.19) and decreasing (X Grs 0.19-0.16) from core to rim with slight fluctuations ( Fig. 7; Table 2). Schistosityforming white mica consists of resorbed phengite core and overgrowing muscovite rim (Figs. 5c and 5d). The chemical compositions of the white mica vary from core to rim (Si = 6.94-6.10 pfu, X Na = 0.01-0.06, Fe 2+ + Mg = 1.13-0.30 pfu, X Mg 0.64-0.33) (Fig. 6a). The core of a representative white mica grain shows ...
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Citations
... The reasons for this were the great diversity of the rock types combined within the same structures, finds of rare minerals (such as diamond, coesite, high-K clinopyroxene, K-bearing tourmaline, kumdykolite and kokchetavite, which are orthorhombic and hexagonal albite and K-feldspar, respectively, and others) (e.g., Letnikov et al., 1983;Sobolev and Shatsky, 1990;Shatsky et al., 1999;Schertl and Sobolev, 2013). Korsakov et al., 1998;Masago, 2000;Hermann et al., 2001;Korsakov et al., 2002; -627, 694-767, 906-1003and 1952-1981Ma Jagoutz et al., 1989Claoue-Long et al., 1991;Shatsky et al., 1993;Shatsky et al., 1995;Borisova et al., 1995;Zhang et al., 1997;Katayama et al., 2000;Katayama et al., 2001;Reverdatto et al., 2008;Ragozin et al., 2009;Yui et al., 2010;Shatsky et al., 2018;Skuzovatov et al., 2021 528 Shatsky et al., 1993Shatsky et al., , 1998Zhang et al., 1997;Ota et al., 2000;Parkinson et al., 2000;Theunissen et al., 2000;Hacker et al., 2003;Masago et al., 2009;Zhang et al., 2012; Kaneko et al., 2000;Hacker, 2003;Theunissen et al., 2003;Shatsky et al., 1993Shatsky et al., , 2018Dobretsov et al., 2006Shatsky et al., 1993Kaneko et al., 2000Kaneko et al., , 2002Glorie et al., 2015 Katayama et al., 2001;Kaneko et al., 2002;Terabayashi et al., 2002;Buslov et al., 2010 482 ± 17Ma; 509 ± 7 and 498 ± 7 Ma Basalts N-MORB (?)/ intraplate basalts (?) Zircon cores ~820 and ~700 Ma Tagiri et al., 2010a;Togonbaeva et al., 2010b;Meyer et al., 2013Meyer et al., , 2014Rojas-Agramonte et al., 2014;Klemd et al., 2015;Konopelko et al., 2012Konopelko et al., , 2016Bakirov, 2017;Kasymbekov et al., 2020;Alexeiev et al., 2020 470 Tagiri et al., 1995;Orozbaev et al., 2007Orozbaev et al., , 2010Kroner et al., 2012;Rojas-Agramonte et al., 2013;Klemd et al., 2014Detrital zircons 504-2460 Ma with maxima at ~1100-1300 Ma Zircon rims 460 ± 11 and 486 ± 11 Ma Terrigenous rocks Detrital zircons ~667-834, 868-1051, 1087-1220, 1296-1378 and 2464-2539 Ma and maxima at ~985 and 1151 Ma Kröner et al., 2007;Tretyakov et al., 2011;Alexeiev et al., 2011;Pilitsyna et al., 2018aPilitsyna et al., , 2018bPilitsyna et al., , 2019Pilitsyna and Tretyakov, 2020 Derivatives Bakirov et al., 1996Bakirov et al., , 2003Ivleva, 2003Ivleva, , 2010Rojas-Agramonte et al., 2013;Loury et al., 2015;Alexeiev et al., 2016;Mühlberg et al., 2016 Detrital zircons 510-3000 Ma with maxima at ~1000-1200 Ma The most comprehensive information on the structures, chemical and mineral compositions, P-T-t paths, and settings in which the principal varieties of the diamond-bearing ultrahigh-pressure rocks of the Kokchetav massif were formed is presented in (Schertl and Sobolev, 2013). ...
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The western part of the Central Asian Orogenic Belt, which comprises folded areas in Kazakhstan, Kyrgyzstan, and northwestern China, includes a number of large Precambrian sialic massifs that are framed by deformed and dismembered Paleozoic ophiolites and by island arc and flysch formations. The basements of the massifs are commonly made up of diverse metamorphic complexes, some of which were metamor-phosed under high and ultrahigh pressures in the Early Paleozoic at ~480-530 Ma. These metamorphic formations are the Zerendy Group of the Kokchetav massif in northern Kazakhstan; Akdzhon Group of the Issyk-Kul massif in the northern Tien Shan); Aktyuz, Kemin, and Koyandy complexes of the Chu-Kendyktas and Zheltau massifs in southern Kazakhstan and the northern Tien Shan; and the Kassan Group of the Ishim-Naryn massif in the central Tien Shan. The paper reviews data on the structures, compositions, and metamorphic evolutions of the high-and ultrahigh-, and medium-pressure metamorphic rocks of these mas-sifs. Numerous P-T assessments have been made for the near-peak and/or post-peak retrograde metamor-phism, and some prograde P-T paths have been calculated for the key rock types over the past three decades of the studies. Near-peak and/or post-peak metamorphic ages and some ages of retrograde metamorphism are estimated for most of the high-and ultrahigh-pressure rocks. The paper discusses problems faced by the researcher when building geodynamic models for the high-and ultrahigh-pressure complexes in various mas-sifs of the western part of the Central Asian Orogenic Belt. It is shown that any reliable model shall be underlain by detailed information on the compositions, ages, and formation environments of the protoliths for the ultrahigh-, high-, and medium-pressure rocks and complexes. Moreover, the structures and compositions of Paleozoic complexes surrounding the Precambrian massifs shall also be taken into consideration.
В структуре западной части Центрально-Азиатского орогенного пояса, включающей складчатые сооружения Казахстана, Кыргызстана и северо-западной части Китая, выделяются крупные докембрийские сиалические массивы, которые обрамляются палеозойскими интенсивно дислоцированными офиолитами, островодужными и флишевыми комплексами. В строении фундамента докембрийских массивов принимают участие различные метаморфические комплексы, при этом некоторые из них испытали метаморфизм высоких и сверхвысоких давлений в раннем палеозое (~480-530 млн лет). К таким комплексам относятся зерендинская серия Кокчетавского массива в Северном Казахстане, акджонская серия Иссыккульского массива в Северном Тянь-Шане, актюзский, кеминский и кояндинский комплексы Чуйско-Кендыктасского и Жельтавского массивов в Южном Казахстане, кассанская серия Ишим-Нарынского массива в Срединном Тянь-Шане. Представлен обзор результатов изучения особенностей состава, строения и метаморфической эволюции высоко-и ультравысокобарических образований, а также пород умеренных ступеней, входящих в состав этих комплексов. В ходе иссле-дований, проводившихся в течение последних тридцати лет, были получены многочисленные Р-Т оценки параметров формирования пород на пике метаморфизма, а также на регрессивной и в редких случаях прогрессивной стадиях. Для большей части изученных высоко-и ультравысокобарических пород получены оценки возраста, соответствующие времени проявления пикового или околопикового этапа метаморфизма, а иногда и более поздних этапов диафтореза. Рассмотрены проблемы, возникающие при построении геодинамических моделей формирования (ультра-) высокобарических комплексов различных массивов западной части Центрально-Азиатского пояса. Показано, что для построения обоснованных моделей необходима более детальная информация о составах, возрастах, обстановках формирования протолитов ключевых разностей (ультра-) высокобарических пород и комплексов умеренных давлений, а также образований палеозойских структурно-формационных зон, обрамляющих докембрийские массивы.
The western part of the Central Asian Orogenic Belt, which comprises folded areas in Kazakhstan, Kyrgyzstan, and northwestern China, includes a number of large Precambrian sialic massifs that are framed by deformed and dismembered Paleozoic ophiolites and by island arc and flysch formations. The basements of the massifs are commonly made up of diverse metamorphic complexes, some of which were metamorphosed under high and ultrahigh pressures in the Early Paleozoic at ~480–530 Ma. These metamorphic formations are the Zerendy Group of the Kokchetav massif in northern Kazakhstan; Akdzhon Group of the Issyk–Kul massif in the northern Tien Shan); Aktyuz, Kemin, and Koyandy complexes of the Chu-Kendyktas and Zheltau massifs in southern Kazakhstan and the northern Tien Shan; and the Kassan Group of the Ishim–Naryn massif in the central Tien Shan. The paper reviews data on the structures, compositions, and metamorphic evolutions of the high- and ultrahigh-, and medium-pressure metamorphic rocks of these massifs. Numerous P–T assessments have been made for the near-peak and/or post-peak retrograde metamorphism, and some prograde P–T paths have been calculated for the key rock types over the past three decades of the studies. Near-peak and/or post-peak metamorphic ages and some ages of retrograde metamorphism are estimated for most of the high- and ultrahigh-pressure rocks. The paper discusses problems faced by the researcher when building geodynamic models for the high- and ultrahigh-pressure complexes in various massifs of the western part of the Central Asian Orogenic Belt. It is shown that any reliable model shall be underlain by detailed information on the compositions, ages, and formation environments of the protoliths for the ultrahigh-, high-, and medium-pressure rocks and complexes. Moreover, the structures and compositions of Paleozoic complexes surrounding the Precambrian massifs shall also be taken into consideration.
