SOME PECULIARITIES OF GLOBAL MANIFESTING THE EARLY PALEOZOIC GRANITOID MAGMATISM ON EXAMPLE OF CENTRAL ASIAN, BRITISH – SCANDINAVIAN AND

EAST AUSTRALIAN CALEDONIDES

Distanova A.N.

Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia, distanova@uiggm.nsc.ru

The peculiarities of Early Paleozoic granitoid magmatism that manifested in accretional – collisional and collisional strike-slip fault zones of the main Caledonian granitoid provinces in the world have been analyzed.

This generalization is a result of author's investigations of granitoid magmatism in the Altai-Sayan and West Transbaikalian (Central-Asian orogenic belt) fold areas, as well as summarizing the published data on granitoid magmatism of North Kazakhstan region, North-Scotland and Norway regions of the British-Scandinavian belt of caledonides.

The comparative study of Caledonian granitoid formations in different regions of the world indicates their relation to the time-span of total Paleoocean closing and connection with oblique transpressional collision of orogen, microcontinents and craton margins.

Summarized data make it possible to affirm a global nature of Caledonian granitoid magmatism manifestation mainly during the Ordovician.

Initial global Vendian – Early Cambrian rifting and spreading processes were changed by tension, collision and orogenesis in the Central Asian orogenic belt, British-Scandinavian province and other Caledonian fold belts in the Middle Cambrian. They were accompanied by metamorphism and global granitoid magmatism. Initial tension deformations connected with collisional and shift movements, accompanied by granitoid magmatism appeared in the Late Cambrian – Early Ordovician (Australia, North Scotland and Norway, Central Asian mobile belt).

The global processes of Late Ordovician granitoid formation occurred later in Ordovician time in connection with Taconian tectogenesis. The examples of Taconian orogenesis (O₂²-O₃) and subsequent Late Ordovician granitoid magmatism are known for Australia, North Scotland, North Kazakhstan.The following stage of orogenesis and qranitoid magmatism covered O_{3 -} S₁ time-span (Lachlan part of Tasmanian belt in Australia). The period of main Caledonian orogenesis in Scottish, East Australian and North Kazakhstanian caledonides was Late Silurian – Early Devonian (S₂ -D₁).

Within the limits of the Altai-Sayan fold area, as a part of the Central-Asian mobile belt, Caledonian granitoid areals were formed for a long time from Late Cambrian to Silurian. They originated in connection with successive accrecionary-collisional and collisional-shift movements which took place up to conclusive collision of island arcs, microcontinents and North-Asian Craton margin. Granitoid batholiths have varied composition and occur in different local geodynamic environments (Distanova, Teleshev, 2005). Separate granitoid areals were formed in intraplate situation under influence of the North-Asian mantle superplume (Yarmoluk et. al., 2000).

Specific peculiarities manifested in Zerendinsk batholith of Kokchetav microcontinent (Northern Kazakhstan), that formed in three stages. Petrogeochemical peculiarities and specific composition of accessory minerals of the latest stage evidence to great influence of mantle fluidization (Letnikov, 2005). Almost all above instances of Early Paleozoic granitoid areals evidence analogous relationships between granitoids and regular preceding basic mantle magmatism. Thus, mantle-related differentiated basic intrusions of Scotland, that contain syenite components, have preceded the Ordovician collisional-type granites. Repeated peculiarities of relationships between Caledonian granitoids and mantle-related basic rocks were observed for Norway, Scotland and other regions (Hutton, 1988).

“Appinites” inclusions in granites, which are analogous, by mineral composition, to lamprophyres, indicate the influence of mantle processes,, and the latest cross-cutting lamprophyre dykes for the Silurian – Devonian (S₂-D₁) granitoids of collisional-shift settings in Scotland. In Australia (Lachlan Caledonian belt), relics of remelted basic rocks are traced in granitoids by residual pyroxene inclusions within rock-forming hornblende and biotite.

The previous basic intrusions also occur in the Altai-Sayan region (Kuznetsk Alatau, Cambrian Sayan, Tuva) and West–Transbaikalia (Dzhida zone). Coincidence of Ordovician granitoids and basic mantle magmatism, as evidence of conjunction in time and space of collisional granitoids and plume-related basic magmatism, was pointed out by N.L. Dobretsov (2003). Association of basic mantle precursors and Ordovician granitoids in Altai-Sayan fold area with mantle plume, that initiated powerful granite generation, was also shown by A.E. Izokh, G.V. Polyakov end others (Izokh et. al., (2007).

In Kokchetav area of Early Paleozoic granitotids occurring in intraplate situation, three times granite formation (O, S, D) has been established, but previous mantle-related basites are absent. However, extensive mantle-related fluidization within interblock zones was noted (Letnikov, 2005).

In some cases, vice versa relations between basic and granitoid magmatism took place. In Norwegian Ordovician – Silurian Bindal batholith basic magmatism appears as postcollisional event, that caused secondary diatexis of granitoids-hosted Precambrian rocks (Barnes et. al., 2002).

Global manifestation of Early Paleozoic granitoid magmatism related to mantle plume processes allows to establish the Planetary Ordovician-Silurian epoch of large igneous provinces of batholith type granitoid formation.

References

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Letnikov F.A. Geochemistry of polychronous granitoid complexes of Zerendinsk massif (North Kazakhstan). Geochimia, № 7 , 2005, P.691-711 (in Russian).

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