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Communication Dans Un Congrès Année : 2024

Correlation between the Trans-Altai Zone and Mongolian Altai: Evidence from detrital zircon U-Pb and Hf isotopic data

Résumé

The Trans-Altai Zone (TAZ) represents a narrow linear segment of the Silurian–Devonian oceanic realm in southern Mongolia (Helo et al., 2006 ; Rippington et al., 2013 ). It records the mid to late Paleozoic geodynamic evolution of the Paleo-Pacific Ocean. In general, the TAZ is composed of several terranes interpreted as island arcs, back-arc basins/forearcs and accretionary wedges (Badarch et al., 2002 ; Lamb & Badarch, 1997 ). Here, we present new structural, whole-rock geochemical and zircon U-Pb ages and Hf isotopic data from the Carboniferous rocks of the TAZ to decipher the tectonic-sedimentary evolution of this tectonic zone. The sedimentary rocks studied were collected from key units of the TAZ called the Khuvinkhar and Zoolon subzones. The Khuvinkhar subzone marks the northernmost extremity of the TAZ separated from the northerly Mongolian Altai by the Trans-Altai Fault (Kozakov, 2002 ; Lamb & Badarch, 1997 ). The Zoolon subzone represents the southernmost part of the TAZ limited by the Gobi-Tianshan Fault (Cunningham et al., 1996 ) in the south. The rocks of the Khuvinkhar subzone preserve a low-grade (D 2 ) cleavage (potentially of Permian–Triassic age) that affected the bedding of Devonian–Carboniferous strata. Ontheotherhand, therocksintheZoolonsubzonerecordedtheearlierdeformationevent(D 1 )as- sociatedwithgreenschist-toamphibolite-faciesmetamorphismthatwasreworkedbyS 2 verticalcleavage. However, the age of the D 1 deformation remains unconstrained. The sediments studied from both sub- zones are poorly sorted greywackes which indicates proximal sources (CIA = 45–55). The sediments from both subzones show subduction-influenced geochemical characteristics such as low HFSE (Ta, Nb, Ti) con- tents. In detail, the greywackes in the Zoolon subzone reveal the oceanic arc-derived sources, whereas those in the Khuvinkhar subzone are characterized by active continental margin tectonic affinity. New results of U-Pb isotopic dating of detrital zircons collected from TAZ sediments suggest Mississippian– Permian depositional ages (ca. 297–348 Ma). The depositional ages of the sediments in the Khuvinkhar subzone (ca. 297–325 Ma) are younger than those in the Zoolon subzone (ca. 322–348 Ma). Interest- ingly, the Cambrian–Ordovician and Silurian–Devonian age populations in all dated samples may imply a direct correlation between the TAZ and Mongolian Altai. However, the youngest detrital zircon age popu- lations indicate a source from the proximal Carboniferous volcanic arc (Nguyen et al., 2018 ). In addition, a litharenite collected from the northernmost part of the Khuvinkhar subzone yields an Ordovician depo- sitional age (ca. 475 Ma) similar to the sediments typical of the Gobi-Altai Zone in the Mongolian Altai to the north (Gibson et al., 2013 ; Kröner et al., 2010 ). This Ordovician litharenite is unconformably overlain by Carboniferous sequences of the TAZ. Therefore, the boundary between the TAZ and Mongolian Altai can be interpreted as having a stratigraphic and not tectonic significance. The greywackes and tuffaceous sandstoneintheZoolonsubzoneshowmainlypositiveinitialepsilonHfvalues(+15.2to-1.7; T DM.2stg =0.4– 1.1 Ga) that support a juvenile source. However, several zircons with CHUR-like initial Hf values indicate a contribution of a crustal source. Comparison with East Junggar sedimentary sequences allows the stud- 25 ied greywacke-type sediments of the Khuvinkhar and Zoolon subzones to be attributed to Carboniferous Dulateback-arcsequences (Jiang etal., 2024 ; Sukhbaataretal., 2024 ). It canbeconcludedthatboth Khu- vinkharandZoolonCarboniferoussequencesrepresentacontinuationoftheEastJunggarDulateback-arc system sourced in a nearby Carboniferous arc.

Domaines

Géochimie
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Dates et versions

insu-04600662 , version 1 (04-06-2024)

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  • HAL Id : insu-04600662 , version 1

Citer

Turbold Sukhbaatar, Ondrej Lexa, Karel Schulmann, Igor Soejono, Vojtěch Janoušek, et al.. Correlation between the Trans-Altai Zone and Mongolian Altai: Evidence from detrital zircon U-Pb and Hf isotopic data. CAOB 2024 International Geological Conference, May 2024, Ulaanbaatar, Mongolia. pp.25-26. ⟨insu-04600662⟩
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