TY - JOUR

T1 - Mechanisms of mantle-crust interaction at deep levels of collision orogens (case of the Olkhon region, West Pribaikalie)

AU - Vladimirov, A. G.

AU - Mekhonoshin, A. S.

AU - Khromykh, S. V.

AU - Mikheev, E. I.

AU - Travin, A. V.

AU - Volkova, N. I.

AU - Kolotilina, T. B.

AU - Davydenko, Yu A.

AU - Borodina, E. V.

AU - Khlestov, V. V.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - In the Chernorud granulite zone in the Olkhon region of West Pribaikalie, we studied gabbro-pyroxenites composing tectonic plates (Chernorud, Tonta) and synmetamorphic intrusive bodies (Ulan-Khargana), as well as numerous disintegrated boudins and inclusions embedded in the metamorphic matrix. Based on the results of comparative analysis of the chemical compositions, the gabbro-pyroxenites are classified into a single island-arc tholeiitic series. The COMAGMAT software was used to simulate this series and to estimate the initial composition of the parent magma (magnesian basalt: SiO2=46.0 wt. %, TiO2=0.8 wt. %, AhO3=15.3 wt. %, ΣFeO=9.0 wt. %, MnO=0.15 wt. %, MgO=10.5 wt. %, CaO=17.0 wt. %, Na2O=1.0 wt. %, K2O=0.2 wt. %, P2O5=0.05 wt. %, total = 100.0 %, Mg# = 67.5 %). It is concluded that the granulite metamorphism (P=7.7 to 8.6 kbar, T=770 to 820 °C) was due not only to dipping of the initial sedimentary-volcanic series to a depth of 25-28 km, but also to the presence of a deep chamber of magnesian basalt magma. In our estimations, garnet-pyroxenites (i.e. mafic rocks of the top facies in the above-mentioned chamber) originated at P=8.0-8.3 kbar and T=900-930 °C. Considering petrology, the deep mafic chamber under the layer of granulite facies is evidenced by metamorphic magma mingling, as well as pipe-shaped intrusions characterized by the specific morphology, internal structure and bulk rock compositions. Based on the data on the Ulan-Khargana massif and gabbro-pyroxenite bodies involved in the structure of the marble melange, we propose a petrological model showing two stages of mafic injection - Stage 1: hydraulic fracturing of granulite series and the emergence of tubular structures and bodies, which are similar to kimberlite pipes or channels of different shapes; Stage 2: rising of the fluidized residual alkaline melt through the emerging 'pipes' and fractures armored by hardened zones, which is followed by metamorphic magma mingling under viscous deformation conditions. The mafic magmas intruding to the level of the granulite facies facilitated the deep anatexis and formation of synmetamorphic hypersthene plagiogranites (U-Pb isotope dating: 500-490 Ma) and high-K stress granites. In the Chernorud granulite zone, intense ductile-plastic and brittle-plastic deformations accompanied the processes of metamorphism, intrusion and formation of gabbropyroxenites and the anatexis of the crustal substance. As a result, the intrusive bodies were fragmented, and specific tectonic structures termed 'metamorphic magma-mingling' were formed. All the tectonic and magmatic structures were subsequently 'sealed up' by K-Na synkinematic granites at the regressive stage under conditions of the amphibolite-facies metamorphism (U-Pb and Ar-Ar isotope dating: 470-460 Ma).

AB - In the Chernorud granulite zone in the Olkhon region of West Pribaikalie, we studied gabbro-pyroxenites composing tectonic plates (Chernorud, Tonta) and synmetamorphic intrusive bodies (Ulan-Khargana), as well as numerous disintegrated boudins and inclusions embedded in the metamorphic matrix. Based on the results of comparative analysis of the chemical compositions, the gabbro-pyroxenites are classified into a single island-arc tholeiitic series. The COMAGMAT software was used to simulate this series and to estimate the initial composition of the parent magma (magnesian basalt: SiO2=46.0 wt. %, TiO2=0.8 wt. %, AhO3=15.3 wt. %, ΣFeO=9.0 wt. %, MnO=0.15 wt. %, MgO=10.5 wt. %, CaO=17.0 wt. %, Na2O=1.0 wt. %, K2O=0.2 wt. %, P2O5=0.05 wt. %, total = 100.0 %, Mg# = 67.5 %). It is concluded that the granulite metamorphism (P=7.7 to 8.6 kbar, T=770 to 820 °C) was due not only to dipping of the initial sedimentary-volcanic series to a depth of 25-28 km, but also to the presence of a deep chamber of magnesian basalt magma. In our estimations, garnet-pyroxenites (i.e. mafic rocks of the top facies in the above-mentioned chamber) originated at P=8.0-8.3 kbar and T=900-930 °C. Considering petrology, the deep mafic chamber under the layer of granulite facies is evidenced by metamorphic magma mingling, as well as pipe-shaped intrusions characterized by the specific morphology, internal structure and bulk rock compositions. Based on the data on the Ulan-Khargana massif and gabbro-pyroxenite bodies involved in the structure of the marble melange, we propose a petrological model showing two stages of mafic injection - Stage 1: hydraulic fracturing of granulite series and the emergence of tubular structures and bodies, which are similar to kimberlite pipes or channels of different shapes; Stage 2: rising of the fluidized residual alkaline melt through the emerging 'pipes' and fractures armored by hardened zones, which is followed by metamorphic magma mingling under viscous deformation conditions. The mafic magmas intruding to the level of the granulite facies facilitated the deep anatexis and formation of synmetamorphic hypersthene plagiogranites (U-Pb isotope dating: 500-490 Ma) and high-K stress granites. In the Chernorud granulite zone, intense ductile-plastic and brittle-plastic deformations accompanied the processes of metamorphism, intrusion and formation of gabbropyroxenites and the anatexis of the crustal substance. As a result, the intrusive bodies were fragmented, and specific tectonic structures termed 'metamorphic magma-mingling' were formed. All the tectonic and magmatic structures were subsequently 'sealed up' by K-Na synkinematic granites at the regressive stage under conditions of the amphibolite-facies metamorphism (U-Pb and Ar-Ar isotope dating: 470-460 Ma).

KW - Chernorud granulite zone

KW - Granulite metamorphism

KW - Hypersthene plagiogranite

KW - Mantle-crust interaction

KW - Metamorphic magma-mingling

KW - Olknon region

KW - Stress granite

KW - Synmetamorphic gabbro-pyroxenite

KW - West Pribaikalie

KW - IGNEOUS ROCKS

KW - SYSTEM

KW - EARLY CALEDONIDES

KW - GEODYNAMICS

KW - synmetamorphic gabbro-pyroxenite

KW - TECTONIC POSITION

KW - metamorphic magma-mingling

KW - CONVERGENT BOUNDARIES

KW - mantle-crust interaction

KW - LAKE BAIKAL

KW - GRANITOID MAGMATISM

KW - granulite metamorphism

KW - MODEL

KW - hypersthene plagiogranite

KW - OPTIMIZED STANDARD STATE

KW - stress granite

UR - http://www.scopus.com/inward/record.url?scp=85042314743&partnerID=8YFLogxK

U2 - 10.5800/GT-2017-8-2-0240

DO - 10.5800/GT-2017-8-2-0240

M3 - Article

AN - SCOPUS:85042314743

VL - 8

SP - 223

EP - 268

JO - Geodynamics and Tectonophysics

JF - Geodynamics and Tectonophysics

SN - 2078-502X

IS - 2

ER -