International Geologiical Congress - Oslo 2008

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ASI-02 Geology and mineral resources of Northern and Central Eurasia

 

Geodynamic position of ophiolite in Kazarhstan and role exhumation processes in the formation of modern morphology of ophiolite belts

 

Petr Yermolov, Institute of Complex Development of Mineral Resources (Kazakhstan)
Boris Natal'in, Istanbul Technical University (Turkey)
 

 

1 In Kazakhstan, ophiolite appears in the following types of structural settings: narrow linear belts bounded by faults ( Charsky and Tekturmas ), folded nappes ( Itmurundy ), and rootless equidemensional flat-lying or gently dipping bodies which are in places covered by neoautochthon ( Karaulcheku, Talpak and others ).
The alkaline, MORB and calk-alkaline tendency recorded in the basalts of the ophiolite belts in Kazakhstan may suggest the formation of them in marginal seas, island arcs and in intra-plate tectonic setting (a wide ocean) with participation of a seamount chains.
2 . According to conodont ages of cherts associated with ophiolite pillow basalt (O1-2), isotope age of zircon in gabbro-anorthsite of ophiolite layered complex (480 Ma), zircon of UHP quartzite in mélange (460-480 Ma) and Ar-Ar age of white mica and alkali amphibole in diaphthorite eclogite (450 Ma) traces of Ordovician subduction are present on the whole territory of Eastern part of Kazakhstan. At the same time early-middle Ordovician volcanic and granitoid arc complexes (480-450 Ma ) are wide spread on this territory. Some of them contain detrital zircon of the age from 1 to 3 Ga. In general, all these facts testify that in Ordovician crust of Kazakhstan there is a contribution of mantle (ophiolite), the juvenal crust (arc complexes) and partially amalgamated ancient continental crust (shield). Some tens of commercial deposits are related to the mantle (massive pyrite gold bearing copper - base metal) and arc (gold and copper-porphyry) magmatism.
3 Exhumation is the main mechanism responsible for contemporary appearance of the ophiolite belts. The Itmurundy folded belt and numerous others isometric blocks underline with olistostrome are naps and fragments of naps exhumed along the Benioff zone upon a sedimentary accretion wedge. Napping usually has a multistage character and as a result olistoliths of the ophiolith composition as well as jasper and metamorphic rocks may occur in different levels of an olistostrome complex. Linear belts are most often extrusions introduced along regional fault complementary to Benioff zone. They extend for some hundred km in the form of a line or an arc, and at the same time they are baunded by folded complexes.
4 The calculation performed on the base of geological data and isotope dating testify that the processes of exhumation from the peak of UHP metamorphism up to forming of olistostrome complex last in Kazakhstan from 15-18 Ma in the Caledonides up to 100 Ma in the Hercynides.

 

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