minerals Article Tectonic History of the South Tannuol Fault Zone (Tuva Region of the Northern Central Asian Orogenic Belt, Russia): Constraints from Multi-Method Geochronology Evgeny Vetrov 1,*, Johan De Grave 2, Natalia Vetrova 1, Fedor Zhimulev 1, Simon Nachtergaele 2 , Gerben Van Ranst 2 and Polina Mikhailova 3 1 Sobolev Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, Koptuga ave. 3, 630090 Novosibirsk, Russia; [email protected] (N.V.); [email protected] (F.Z.) 2 Department of Geology, Ghent University, Krijgslaan 281.S8, WE13, 9000 Ghent, Belgium; [email protected] (J.D.G.); [email protected] (S.N.); [email protected] (G.V.R.) 3 Siberian Research Institute of Geology, Geophysics and Mineral Resources, Krasniy ave. 35, 630099 Novosibirsk, Russia; [email protected] * Correspondence: [email protected] or [email protected]; Tel.: +7-913-770-75-10 Received: 12 November 2019; Accepted: 6 January 2020; Published: 9 January 2020 Abstract: In this study, we present zircon U/Pb, plagioclase and K-feldspar 40Ar/39Ar and apatite fission track (AFT) data along the South Tannuol Fault Zone (STFZ). Integrating geochronology and multi-method thermochronology places constraints on the formation and subsequent reactivation of the STFZ. Cambrian (~510 Ma) zircon U/Pb ages obtained for felsic volcanic rocks date the final stage of STFZ basement formation. Ordovician (~460–450 Ma) zircon U/Pb ages were obtained for felsic rocks along the structure, dating their emplacement and marking post-formational local magmatic activity along the STFZ. 40Ar/39Ar stepwise heating plateau-ages (~410–400 Ma, ~365 and ~340 Ma) reveal Early Devonian and Late Devonian–Mississippian intrusion and/or post-magmatic cooling episodes of mafic rocks in the basement. Permian (~290 Ma) zircon U/Pb age of mafic rocks documents for the first time Permian magmatism in the study area creating prerequisites for revising the spread of Permian large igneous provinces of Central Asia. The AFT dating and Thermal history modeling based on the AFT data reveals two intracontinental tectonic reactivation episodes of the STFZ: (1) a period of Cretaceous–Eocene (~100–40 Ma) reactivation and (2) the late Neogene (from ~10 Ma onwards) impulse after a period of tectonic stability during the Eocene–Miocene (~40–10 Ma). Keywords: zircon U/Pb dating; 40Ar/39Ar dating; AFT thermochronology; Tuva Region 1. Introduction The South Tannuol Fault Zone (STFZ) is situated in the Tuva Region (Russian Federation) of the Altay–Sayan Fold Belt (ASFB) in the northwestern (Siberian) part of the Central Asia Orogenic Belt (CAOB) (Figure1). The STFZ is a sub-latitudinal system of normal faults acted in the same mode during its formation and reactivation stages. The shear component is not excluded; however, the normal fault component keeps principal. The STFZ is characterized by steep fall of the fault blocks and the vertical displacement amplitude along the largest fault segments from 300 to 3000 m. It controls the tectonic evolution of the Tannuol Mountain Range, the most prominent topographic feature with an altitude of up to 2400 m in the Tuva–Mongolia border zone (800–1000 m). The Tannuol Range is composed mainly of Paleozoic volcanic rocks of island arc affinity, intruded by various plutons of different ages and compositions (Figure2). The volcanic rocks are deformed into intricate linear folds Minerals 2020, 10, 56; doi:10.3390/min10010056 www.mdpi.com/journal/minerals Minerals 2019, 9, x FOR PEER REVIEW 2 of 22 Minerals 2020, 10, 56 2 of 22 Tannuol Range is composed mainly of Paleozoic volcanic rocks of island arc affinity, intruded by various plutons of different ages and compositions (Figure 2). The volcanic rocks are deformed into with sub-latitudinal strike of the fold axes, conform to the strike of the fault system. Intrusive rocks intricate linear folds with sub-latitudinal strike of the fold axes, conform to the strike of the fault (gabbros and granitoids) often form linear bodies elongated along strike of the STFZ. This indicates the system. Intrusive rocks (gabbros and granitoids) often form linear bodies elongated along strike of STFZ controls the emplacement of the Paleozoic igneous basement rocks of the Tannuol Range and the STFZ. This indicates the STFZ controls the emplacement of the Paleozoic igneous basement rocks controls their deformation during subsequent reactivation phases. of the Tannuol Range and controls their deformation during subsequent reactivation phases. Figure 1. Digital elevation model (SRTM data) of the northern part of the Central Asian Orogenic Belt (CAOB).(CAOB). OurOur studystudy areaarea ofof thethe SouthSouth TannuolTannuol FaultFault ZoneZone (STFZ)(STFZ) is is indicated indicated byby thethe black black box. box. The PaleozoicPaleozoic igneous igneous basement basement rocks rocks exposed exposed along along the STFZ the provideSTFZ provide insights intoinsights the formation into the andformation subsequent and subsequent reactivation reactivation episodes of episodes the STFZ. of Itthe is hypothesizedSTFZ. It is hypothesized that in the studiedthat in the part studied of the CAOBpart of (e.g.,the CAOB Kuznetsk (e.g., Alatau, Kuznetsk West Alatau, Sayan, GornyWest Sayan, Altay), theseGorny Paleozoic Altay), these stages Paleozoic are associated stages with are tectonicassociated events with at tectonic the margins events of theat the Paleo margins Asian Oceanof the (PAO) Paleo basinsAsian [1Ocean–4]. In (PAO) addition, basins the Paleozoic[1–4]. In basementaddition, the rocks Paleozoic record evidence basement of rocks subsequent record deformationevidence of andsubsequent exhumation deformation throughout and the exhumation Mesozoic andthroughout Cenozoic. the These Mesozoic same and basement Cenozoic. rocks These also record same Meso-Cenozoicbasement rocks deformation also record andMeso-Cenozoic exhumation events.deformation The present and exhumation mountainous events. morphology The present of the mountainous Tuva Region ismorphology considered toof havethe Tuva formed Region during is reactivationconsidered to of have inherited formed structures, during reactivation such as the STFZ.of inherited structures, such as the STFZ. Despite its its structural structural importance importance to the to thetectonic tectonic evolution evolution of theof Altay–Sayan, the Altay–Sayan, the STFZ the remains STFZ remainspoorly resolved poorly resolvedby modern by geochronological modern geochronological and thermochronological and thermochronological techniques. techniques. Only in the Only last indecade the last modern decade geochronology modern geochronology data have been data obta haveined been for obtainedthe Paleozoic for therocks Paleozoic [5–7]. Previously, rocks [5–7 a]. Previously,general model a general of the Altay–Sayan model of the fold Altay–Sayan belt formation fold belt and formation evolution and was evolution proposed was for the proposed Paleozoic for thehistory Paleozoic and tectonic history events and tectonicalong the events STFZ [1–4]. along Meso-Cenozoic the STFZ [1–4]. de Meso-Cenozoicformation and exhumation deformation events and exhumationin the study area events were in decrypted the study areaonly wereby lithological decrypted and only stratigraphic by lithological dataand of the stratigraphic Jurassic [8–11] data and of theCenozoic Jurassic [12–15] [8–11] sedimentary and Cenozoic basins [12–15 of] sedimentaryTuva and Mongolia. basins of Therefore, Tuva and Mongolia. dating accessory Therefore, and dating rock- accessoryforming minerals and rock-forming from the Paleozoic minerals fromigneous the baseme Paleozoicnt rocks igneous along basement the STFZ rocks using along high-temperature the STFZ using high-temperatureand low-temperature and methods low-temperature is necessary methods to obtain is necessarynew constraints to obtain on tectonic new constraints history of on the tectonic STFZ. historyInterpretation of the STFZ. of these Interpretation data according of these to datatectonic according evolution to tectonic of the evolutionstudy part of of the the study CAOB part allows of the CAOBtesting allowsand clarification testing and of clarification the established of the hypothesis. established hypothesis. Minerals 2020, 10, 56 3 of 22 Minerals 2019, 9, x FOR PEER REVIEW 3 of 22 Figure 2. (a) Simplified geological map of the South Tannuol Fault Zone (STFZ) (based on [5]) with Figure 2. (a) Simplified geological map of the South Tannuol Fault Zone (STFZ) (based on [5]) with sample positions indicated; (b) digital relief model (SRTM data, Mercator projection—WGS84) of the sample positions indicated; (b) digital relief model (SRTM data, Mercator projection—WGS84) of STFZ with indication of main structural features, basins and mountain ranges. Sample sites are the STFZ with indication of main structural features, basins and mountain ranges. Sample sites are indicated, see Table 1 for details. indicated, see Table 1 for details. The aim of this study is to reconstruct the chronology of formation, reactivation and deformation The aim of this study is to reconstruct the chronology of formation, reactivation and deformation of the area within the STFZ. Zircon U/Pb, plagioclase 40Ar/39Ar and K-feldspar 40Ar/39Ar dating of of the area within the STFZ. Zircon U/Pb, plagioclase 40Ar/39Ar and K-feldspar 40Ar/39Ar dating of igneous rocks along the STFZ allows identifying formation and activation stages and apatite fission igneoustrack thermochronology rocks along the