The processes leading to the assembly of the Rodinia supercontinent through Grenvillian collisional orogeny are relatively well known.In contrast,accretionary orogenic processes occurring at the supercontinent periphe...The processes leading to the assembly of the Rodinia supercontinent through Grenvillian collisional orogeny are relatively well known.In contrast,accretionary orogenic processes occurring at the supercontinent periphery following Rodinia assembly are poorly understood.To fill this gap,we have identified metamorphic rocks in the Mongolia collage of the Central Asian Orogenic Belt,where numerous data testify for Meso-to Neoproterozoic magmatic reworking.The tectono-metamorphic evolution of the periSiberian tract of the Central Asian Orogenic Belt is mainly characterized by the late Proterozoic–early Cambrian(Baikalian)cycle.However,we document here a Tonian age metamorphism at the northern part of the Precambrian Baidrag block,previously considered as a typical example of the Baikalian metamorphic belt.This study incorporates zircon and in-situ monazite geochronology linked to P-T modelling of Grt-Sil-Ky migmatite gneiss and Grt-St micaschist.Grt-Sil-Ky gneiss records initial burial to the sillimanite stability field at 720℃ and 6.0 kbar followed by further burial to the kyanite stability field at 750℃ and 9 kbar and decompression to 650℃ and 8 kbar.The Grt-St schist records initial burial to the staurolite stability field at 620℃ and 6 kbar,followed by further burial to 590℃ and 8.5 kbar.The monazite data yield a continuum of ^(207)Pb-corrected ^(238)U/^(206)Pb dates of ca.926–768 Ma in the Grt-Sil-Ky gneiss,and ca.937–754 Ma in the Grt-St schist.Based on monazite textural positon,internal zoning,and REE patterns,the time of prograde burial to 6.0 kbar under a thermal gradient of 27–32℃/km is estimated at ca.890–853 Ma.It is not clear whether such high-grade conditions prevailed until a phase of further burial under a geothermal gradient of 18–22℃/km dated at ca.835–815 Ma.The late monazite recrystallization at ca.790 Ma is related to decompression.Additionally,monazite with dates of ca.568–515 Ma occur as whole grains or as rims with sharp boundaries on Tonian monazite in Grt-St schi展开更多
Mid-Devonian high-pressure(HP)and high-temperature(HT)metamorphism represents an enigmatic early phase in the evolution of the Variscan Orogeny.Within the Bohemian Massif this metamorphism is recorded mostly in alloch...Mid-Devonian high-pressure(HP)and high-temperature(HT)metamorphism represents an enigmatic early phase in the evolution of the Variscan Orogeny.Within the Bohemian Massif this metamorphism is recorded mostly in allochthonous complexes with uncertain relationship to the major tectonic units.In this regard,the MariánskéLázně Complex(MLC)is unique in its position at the base of its original upper plate(Teplá-Barrandian Zone).The MLC is composed of diverse,but predominantly mafic,magmatic-metamorphic rocks with late Ediacaran to mid-Devonian protolith ages.Mid-Devonian HP eclogite-facies metamorphism was swiftly followed by a HT granulite-facies overprint contemporaneous with the emplacement of magmatic rocks with apparent supra-subduction affinity.New Hf in zircon isotopic measurements combined with a review of whole-rock isotopic and geochemical data reveals that the magmatic protoliths of the MLC,as well as in the upper plate Teplá-Barrandian Zone,developed above a relatively unaltered Neoproterozoic lithospheric mantle.They remained coupled with this lithospheric mantle throughout a geological timeframe that encompasses separate Ediacaran and Cambrian age arc magmatism,protracted early Paleozoic rifting,and the earliest phases of the Variscan Orogeny.These results are presented in the context of reconstructing the original architecture of the Variscan terranes up to and including the mid-Devonian HP-HT event.展开更多
基金supported by the Czech Science Foundation,Czechia(grant number 19-27682X to K.S.)。
文摘The processes leading to the assembly of the Rodinia supercontinent through Grenvillian collisional orogeny are relatively well known.In contrast,accretionary orogenic processes occurring at the supercontinent periphery following Rodinia assembly are poorly understood.To fill this gap,we have identified metamorphic rocks in the Mongolia collage of the Central Asian Orogenic Belt,where numerous data testify for Meso-to Neoproterozoic magmatic reworking.The tectono-metamorphic evolution of the periSiberian tract of the Central Asian Orogenic Belt is mainly characterized by the late Proterozoic–early Cambrian(Baikalian)cycle.However,we document here a Tonian age metamorphism at the northern part of the Precambrian Baidrag block,previously considered as a typical example of the Baikalian metamorphic belt.This study incorporates zircon and in-situ monazite geochronology linked to P-T modelling of Grt-Sil-Ky migmatite gneiss and Grt-St micaschist.Grt-Sil-Ky gneiss records initial burial to the sillimanite stability field at 720℃ and 6.0 kbar followed by further burial to the kyanite stability field at 750℃ and 9 kbar and decompression to 650℃ and 8 kbar.The Grt-St schist records initial burial to the staurolite stability field at 620℃ and 6 kbar,followed by further burial to 590℃ and 8.5 kbar.The monazite data yield a continuum of ^(207)Pb-corrected ^(238)U/^(206)Pb dates of ca.926–768 Ma in the Grt-Sil-Ky gneiss,and ca.937–754 Ma in the Grt-St schist.Based on monazite textural positon,internal zoning,and REE patterns,the time of prograde burial to 6.0 kbar under a thermal gradient of 27–32℃/km is estimated at ca.890–853 Ma.It is not clear whether such high-grade conditions prevailed until a phase of further burial under a geothermal gradient of 18–22℃/km dated at ca.835–815 Ma.The late monazite recrystallization at ca.790 Ma is related to decompression.Additionally,monazite with dates of ca.568–515 Ma occur as whole grains or as rims with sharp boundaries on Tonian monazite in Grt-St schi
基金funded by the Grant Agency of the Czech Republic(GACR)project 19-25035S to P.Štípskáand the International Partnership Program of CAS 773(132744KYSB20190039)to Y.JiangInstitutional supports of the Research Project no.310760(Strategic Research Plan of the Czech Geological Survey-DKRVO/CGS 2018-2022)Centre for Geosphere Dynamics(UNCE/SCI/006)of Faculty of Sciences,Charles University
文摘Mid-Devonian high-pressure(HP)and high-temperature(HT)metamorphism represents an enigmatic early phase in the evolution of the Variscan Orogeny.Within the Bohemian Massif this metamorphism is recorded mostly in allochthonous complexes with uncertain relationship to the major tectonic units.In this regard,the MariánskéLázně Complex(MLC)is unique in its position at the base of its original upper plate(Teplá-Barrandian Zone).The MLC is composed of diverse,but predominantly mafic,magmatic-metamorphic rocks with late Ediacaran to mid-Devonian protolith ages.Mid-Devonian HP eclogite-facies metamorphism was swiftly followed by a HT granulite-facies overprint contemporaneous with the emplacement of magmatic rocks with apparent supra-subduction affinity.New Hf in zircon isotopic measurements combined with a review of whole-rock isotopic and geochemical data reveals that the magmatic protoliths of the MLC,as well as in the upper plate Teplá-Barrandian Zone,developed above a relatively unaltered Neoproterozoic lithospheric mantle.They remained coupled with this lithospheric mantle throughout a geological timeframe that encompasses separate Ediacaran and Cambrian age arc magmatism,protracted early Paleozoic rifting,and the earliest phases of the Variscan Orogeny.These results are presented in the context of reconstructing the original architecture of the Variscan terranes up to and including the mid-Devonian HP-HT event.
