COLLISION AND INTRAPLATE GRANITOID MAGMATISM OF DZHIDA AND UDA-VITIM ZONES OF CALEDONIDES IN THE WESTERN TRANSBAIKALIA

Vetlujskih T.A., Elbaev A.L.

Institute of Geology SB RAS, Ulan-Ude, Russia, vetluga-work@mail.ru

On the Western Transbaikalia territory are widely spread magmatic formations of various ages and compositions. Granitoids located in the Uda-Vitim and Dzida zones of caledonides of the Central Asian folded belt are investigated by us.

The most interesting rocks in Uda-Vitim zone of caledonides is granitoids which connected with formation of Eravna island arc. (Gordienko et. al. 2004, 2005) was established that lower cambrian formations occupy territory by the area in 200 square kilometers (60% - volcanic rock, 18% - tuffite, 15% - sedimentary rock and 5-7% - different composition). Basis of Eravna island arc complex makes powerful volcanoclastic aprons, acid lavas, andesitic and dacitic lavas. It was supposed that large bodies of gabbro, diorites and plagiogranites produce in the last stage of forming of Eravna island arc complex. Using obtained petrochemical and geochronological characteristics of granitoids of the Kurba river, interfluve Zaza-Holoy and Vitim river we may speak that the granitoids were formed in late Paleozoic. The forming of granitoids was connected with the beginning of formation of Angaro-Vitim batholite and also Selenga-Vitim volcano-tectonic belt (Yarmolyk et. al., 2003; Gordienko et. al., 2006; Tsygankov et. al., 2007). We had been investigated following massifs of granitoids: Atarhan massif located on a right bank Kurba river (U-Pb – 315 Ma, Ar-Ar – 288,7±3,5 Ma), massif Sube is being to the west from Ozernoe ore knot (U-Pb – 284 Ma, Ar-Ar – 271±3,3 Ma), Romanovka massif is opened on the left rim of a valley slope of Vitim river in 15 km above Romanovka village (U-Pb isotope dating (4 tests) from granite and granosienite given age from 293 up to 276 Ma). It is necessary to note that earlier have been certain U-Pb isotope datings from quartz monzonits of southeast part of Romanovka massif which has shown 287,5±2,4 Ma (Tsygankov et. al., 2005). There are data about ordovician-silurian ages of some granitoids massifs of Angaro-Vitim batholite which are referred to the collision type (Gerasimov et. al., 2007; Nenahov et. al., 2007). However till now the question about existence of early Paleozoic granitoids connected with formation of Eravna island arc is discussed.

More than half of area of Dzida zone of caledonides occupies early, average and late Paleozoic granitoids of various genetic types (Petrova, 1972; Distanova, 1975; Gordienko, 1987). In modern structure of a folded frame of the south of Siberian platform the Dzida zone of caledonides is considered as area of development vendian - early paleozoic oceanic, island arc and collisional structurally-material complexes making Dzida island arc system on the active margin of Paleoasian ocean (Gordienko, 1994, 2006, 2007; Kuzmin, et. al., 1995; Almuhomedov, et.al., 1996;). Recent geological structure of Dzida zone was generated as a result of a collision in late carboniferous – permian. There are paleomagnetic data large amplitude shift moving of Dzida zone concerning Siberian platform (Gordienko et. al., 2003).

Dzida zone are distinctly allocated island arc, collisional and intraplate granitoids. Island arc complex of Dzida zone contain following massifs: Modonkul and Sharaazargin. Those massifs are presented by differentiated granitoid association from diorites and tonalite-granodiorite up to granite-trondhjemite. The position of gabbros is very problematical in the massif structure. Earlier those gabbros are concerned to the first phase of Dzida complex. Now it is considered that the main volume gabbro intrusion was generated independently and not connected with granitoid complexes (Distanova, 1975; Gordienko, 1987). Age of gabbro is 506 Ma (U-Pb isotope dating).

In Dzida zone was investigated several massifs referred to the collision type: Darhintuy, Barungol and Huldat massifs. Darhintuy and Barungol massifs are combined by quartz diorites, tonalites and granodiorites. As a result of Ar-Ar dating of biotite from Darhintuy tonalite had been received age 476±2,2 Ma (lower Ordovician). Isotopic datings of this tonalite (U-Pb by zircon) is 489±2 Ma (Reznitskiy et. al., 2005). Huldat massif is combined by diorites, quartz diorites and granodiorites which have an early Ordovician age (U-Pb dating by zircon 490±2 Ma). The granitoid association is considered like calc-alkaline.

In Dzida zone late Paleozoic granitoids (as Daban, Shabartay and other massifs) is connected with interpolate processes. This thesis is executed with supporting of RFFI (project 08-05-00290) and integrating project 7.10.2 DS of E RAS.