Evolution And Relationships Between Volcanism And Tectonics In The Central-Eastern Part Of The Oligocene Borovitsa Caldera (Eastern Rhodopes, Bulgaria)

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Journal Article: Evolution And Relationships Between Volcanism And Tectonics In The Central-Eastern Part Of The Oligocene Borovitsa Caldera (Eastern Rhodopes, Bulgaria)

Abstract
The nested Borovitsa caldera emplaced during the collision-related Paleogene volcanism in the Eastern Rhodopes. The pre-caldera succession consists in Priabonian to Early Oligocene sediments and lavas (absarokites, shoshonites, latites). The caldera filling corresponds to an acid volcanism Early Oligocene in age. The tectono-magmatic evolution of the caldera can be divided into six main stages. (1) Ignimbritic units (more than 1.5 km thick) with a trachydacitic to trachytic composition deposited. The K-Ar method yields an age of 34-33.5 Ma. The volcanic products are either strongly or not welded in the western and eastern parts of the caldera, respectively. (2) An initial Murga caldera, 7-10 km in diameter, collapsed. This event was accompanied by the intrusion of a circular body consisting of lenses-bearing rocks of trachyrhyodacitic to rhyolitic composition within the border faults. (3) The emission of pyroclastic rocks continued and a large sub-volcanic body (33 Ma) of trachydacitic to trachyrhyolitic composition intruded in the western part of the circular body. (4) The Borovitsa caldera (15 km _ 34 km) collapsed. Rhyolitic and trachydacitic dykes dated at 32.5 Ma intruded along its border faults. (5) High-Si trachyrhyolitic-perlitic domes intruded in the eastern part of the Borovitsa caldera at 30-32 Ma and the Dushka caldera collapsed within the Borovitsa structure. (6) Dykes of various compositions (from shoshonite to rhyolite) and trachydacitic to rhyolitic sub-volcanic stocks finally intruded within the caldera and along its rims at 27.5-29.5 Ma. Observations on radar and optical satellite imagery allowed both a new mapping of the structural pattern in the Borovitsa caldera and the understanding of the relationships between faulting and volcanism in this area. Horse-tail features accommodating the right-lateral throw component at the termination of NW-SE and N-S right-lateral strike-slip faults are superimposed upon the Murga caldera and the eastern part of the Borovitsa caldera respectively. WNW-ESE to NW-SE extension along the horse-tail patterns was responsible for the ascent of pressurized magma through the crust via vertical open fractures leading to volcanic activity and subsequent emplacement of domes and crypto-domes during the fifth magmatic stage. This extension was followed by a compression with various orientations, which may be interpreted as a switch of the tensile stress to a compressive one at the onset of subsidence of the Dushka caldera. The last tectonic event in the area is characterized by a N-S extension that led to the reactivation of part of the previous structures, the formation of NW-SE to E-W normal faults and the emplacement of dykes and stocks during the sixth magmatic stage.

Authors 
Damien Dhont, Yotzo Yanev, Jacques-Marie Bardintzeff and Jean Chorowicz








Published Journal 
Journal of Volcanology and Geothermal Research, 2008





DOI 
Not Provided
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Citation

Damien Dhont,Yotzo Yanev,Jacques-Marie Bardintzeff,Jean Chorowicz. 2008. Evolution And Relationships Between Volcanism And Tectonics In The Central-Eastern Part Of The Oligocene Borovitsa Caldera (Eastern Rhodopes, Bulgaria). Journal of Volcanology and Geothermal Research. (!) .