From magmatic arc to a post-accretionary setting: Late Palaeozoic granitoid plutons in the northwestern Trans-Altai Zone, Mongolia

Journal of Geosciences

article

Pavel Hanzl¹  Vojtech Janousek¹  Kristyna Hrdlickova¹  David Burianek¹  Ochir Gerel²  Battushig Altanbaatar³  John M. Hora¹  Petr Coupek¹ 

[1] Czech Geological Survey;Geoscience Center, School of Geology and Mining Engineering, Mongolian University of Science and Technology;National Geological Survey of Mongolia

关键词: U–Pb zircon dating;    whole-rock geochemistry;    granite petrogenesis;    Aaj Bogd Pluton;    Trans-Altai Zone;    Central AsianOrogenic Belt;   

DOI  :  10.3190/jgeosci.366

学科分类：自动化工程

来源: Ceska Geologicka Spolecnost / Czech Geological Society

【 摘 要 】

The Trans-Altai Zone in the southern tract of the Central Asian Oceanic Belt is composed of Early Palaeozoic oceaniccrust preserved in Ordovician to Devonian ophiolite fragments and Devonian–Carboniferous igneous arcs. The Edrenand Baaran subzones at the NW tip of the Trans-Altai Zone were intruded by Late Palaeozoic plutons that have beenexamined by the combined geochronological and geochemical study.Mississippian subduction-related plutons intruded Devonian and Carboniferous volcano-sedimentary sequences in twomagmatic pulses. The older, Tournaisian plutons (dated at 352±1 and 347±4 Ma) occur in both subzones; the youngerVisean/Serpukhovian ones (331±1 Ma) are found only at the northern boundary of the Edren Subzone. All Mississippianrocks are high-K calc-alkaline and characterised by a strong enrichment of hydrous fluid mobile lithophile elementsover conservative Nb, Ta and Ti relative to normal mid-ocean ridge basalts. Low 87Sr/86Sri (~ 0.7035–0.7038) and highlypositive εiNd values (+6.6 to +5.2) suggest a relatively juvenile parental magma source with a short mean crustal residence.This corresponds well with the age of scarce inherited zircons, none of which is older than 530 Ma.The Early Permian post-tectonic plutons intruded the shallow crust of the Baaran Subzone (Devonian–Carboniferousflysch and Early Carboniferous volcanic arc). The prominent concentric body of the Aaj Bogd Pluton is composed ofmonzodiorites to monzogabbros (284±1 and 294±3 Ma) in its centre, surrounded by granite with syenite (282±1Ma) in the main mass of the pluton. Whole-rock Sr–Nd isotopic ratios match those of Carboniferous magmatic rocks,while trace-element patterns point to an intra-plate origin influenced by a fertile asthenospheric mantle component. Onthe other hand, the slightly older (290±1 Ma) quartz syenites to alkali feldspar granites in the Baaran Subzone havespurious arc-like geochemistry inherited from their arc-related crustal source(s). Regional distribution of the numerousoval-shaped Early Permian alkaline post-orogenic plutons, some with A2-type granite affinity, follows the major Permianstrike-slip zones spanning from the Dulate Arc in the west to the Khan Bogd Pluton in the east. These late, transcurrentzones apparently played an important role in late-orogenic magma generation, ascent and emplacement.

【 授权许可】

CC BY