CRETACEOUS BATHOLITHS FROM NORTH AMERICA AS PALEOGEODYNAMICAL

ANALOGUES OF THE LATE PALEOZOIC GRANITOIDS FROM THE NORTHERN CAUCASUS

Ruban D.A.*^,**

*Southern Federal University, Rostov-na-Donu, Russia, ruban-d@mail.ru

**Swiss Association of Petroleum Geologists and Engineers, Switzerland

Late Paleozoic granitoids are abundant within the Northern Caucasus, which is a large region to the south of the Russian Platform. It includes the northern part of the Greater Caucasus Terrane and the Ciscaucasian Basin. A typical example of Variscan granitoids from the Greater Caucasus is the Dakh Crystalline Massif exposed in the Belaya River Valley. Its age is not older than Carboniferous (Ruban, 2008). The geophysical exploration of the Ciscaucasus during the past years has also permitted to document the presence of Late Paleozoic granitoid masses within its basement (Lebed'ko, 2007). The recent re-consideration of the Pre-Jurassic tectonic evolution of the whole Caucasus (Ruban et al., 2007; Tawadros et al., 2006) suggests a necessity to re-vitalize a discussion of the models explaining an emplacement of the above-mentioned granitoids. In particular, to search for their paleogeodynamical analogues seems to be sensible.

Numerous batholiths are distributed along the western margin of North America. These include, particularly, the very large masses of the Idaho Batholith and the Sierra Nevada Batholith. Following the nomenclature proposed by Sheth (2007), these batholiths can be defined together as a Large Granite Province. The age of the latter is Cretaceous-Paleogene, although the most of granitoids were formed in the Late Cretaceous (Manduca et al., 1993; Whitney et al., 2004). At least, a part of batholiths from western North America was emplaced along the major shear zone with strike-slip displacements. Its segments were the Salmon River suture zone, the western Nevada shear zone, and the Mojave-Snow Lake fault (Wyld, Wright, 2001). Long-distance lateral displacements occurred along the western margin of North America since the Jurassic (Ruban, 2007). Small terranes were replaced along the continental periphery to form elongated chains and tectonic slices. A direction of their translation changed in the geologic time. A multiple terrane collision and an oroclinal orogeny were among the consequences of such geodynamic setting. The major shear zone and associated faults served well as the natural escapes for arc magmas generated during the Sevier orogeny and other regional deformation events (Wyld, Wright, 2001). A position of some Late Cretaceous batholiths coincides well with the noted shear zone.

It is clear that the major Northern Paleotethyan Shear Zone existed along the southern margin of Laurussia since the Late Devonian. It was similar to those from the Late Mesozoic western margin of North America as argued by Ruban (2007). Interactions between numerous Hunic terranes were superimposed by long-distance dextral displacements (e.g., Arthaud, Matte, 1977). In the Late Paleozoic, the Greater Caucasus was a terrane, which lay somewhere near the Carnic Alps, Bohemia, and Sardinia (Ruban et al., 2007; Tawadros et al., 2006). Its evolution was governed completely by the activity of the Northern Paleotethys Shear Zone. If so, the relevant faults were able to control an emplacement of granitoids by analogy with the batholiths from western North America. As for the Ciscaucasus, its basement was formed as a tectonic collage directly along the shear zone. Thus, the faults related to the latter seem to be the most promising controls of granitoid intrusions. The above-presented decisions are supported by some observations in the European Variscides, where the second-order shear zones, which divided tectonic slices, might control granitoid emplacements. E.g., the batholith-related Klatovy pluton was linked to the large pre-existing Central Bohemian shear zone with vertical displacements (Scheuvens, Zulauf, 2000), its activity having been supported by the terrane contacting within the Variscan belt. Granite intrusions in the External Massifs of the Alps might have been related to the strike-slip deformations (von Raumer et al., 1993).

Considering a similarity of tectonic setting of western North America in the Cretaceous and the Northern Caucasus in the Late Paleozoic (Ruban, 2007), one can hypothesize that their granitoid masses are paleogeodynamical analogues. Such an assumption should further be verified with both structural and petrological techniques. However, the establishing these analogues forms a new basis for broad discussion of the Northern Caucasian granitoids with better knowledge of the North American batholiths.

The author gratefully thanks D. Scheuvens (TU Darmstadt, Germany), K.L. Schmidt (Lewis-Clark State College, USA), J.F. von Raumer (Universitй de Fribourg, Switzerland), and S.J. Wyld (University of Georgia, USA) for their support with literature and helpful explanations.

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