Geodinamica Acta 19/5 (2006) 265-280
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i`>V> VÌ> Geodinamica Acta 19/5 (2006) 265-280 40Ar/39Ar ���chr���l��y c���tr���t� �� th� M�ddl� T�rt��ry ����ÊÊÊÊÊm��t extensional exhumation, and its relation to ore-forming and magmaticÊÊÊÊÊ processes in the Eastern Rhodope (Bulgaria) Nikolay Bonev a* , Peter Marchev �, Brad Singer c a Department of Geology and Paleontology, Faculty of Geology and Geography, Sofia University “St. Kliment Ohridski”, 15 Tzar Osvoboditel Bd., 1504 Sofia, Bulgaria b Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev St.,Bl.24., 1113 Sofia, Bulgaria c Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton St., Madison, WI 53706, USA Received: 22/12/03, accepted: 07/12/04 Abstract The interaction of distinct geologic processes involved during late orogenic extensional exhumation history of the metamorphic units in the E��t�r� Rh�d�p� �� r���d �y ��w ��d r�v��w��� 40Ar/39Ar ���chr���l���c�l ��d �tr�ct�r�l d�t�� M���r�l� w�th d�ff�r��t cl���r� t�mp�- r�t�r�� fr�m m�t�m�rph�c r�c�� ��v��t���t�d �� th�� �t�dy �r� c�m����d w�th th��� fr�m m��m�t�c ��d �r��f�rm��� hydr�th�rm�l r�c�� �� tw� l�t� �t��� m�t�m�rph�c d�m�� – th� K�����r�K�rd�m�� ��d th� B��l� r����K�hr�� d�m��� Th� 38�37 M� m��c�v�t� ��d ���t�t� c��l��� ages bel�w 350°�300°C ch�r�ct�r�z� basement m�t�m�rph�c r�cks th�t typifid c�r� �f th� Kesebir�K�rd�mos d�m�, constraining their �xh�m�t��� �t �h�ll�w cr��t�l l�v�l� �� th� f��tw�ll �f d�t�chm��t� Th��� ���� �r� ��t�rpr�t�d �� r�fl�ct��� l��t �t��� �f d�ct�l� �ct�v�ty �� �h��r z��� ��l�w d�t�chm��t, wh�ch c��t����d t� �p�r�t� ��d�r l�w�t�mp�r�t�r� c��d�t���� w�th�� th� ��m��d�ct�l� t� �r�ttl� �ld� Th�y �r� close t� and �v�rl�p w�th �xisting cooling ages in south�r� B�lgaria and north�r� Greec�, ind�c�ting supp�rt�v�ly th�t th� basement r�cks regionally cool�d between 42�36 M� bel�w t�mp�r�t�res 350°�300°C� Th� �p�tial distribution �f ages �h�w� � southw�rd �r�dual increase up structural section, suggesting an asymmetrical mode of extension, cooling and exhumation from south to the north at latitude �f th� K�����r�K�rd�m�� d�m�� Th� �l��htly y�����r 36�5�35 M� cry�t�ll�z�t��� ���� �f �d�l�r�� �� �lt�r�d r�c�� fr�m th� �r� d�p���t� �� th� �mm�d��t� h�������w�ll �f d�t�chm��t� �r� �ttr���t�d t� �r�ttl� d�f�rm�t��� �� h��h����l� ��rm�l f��lt�, wh�ch f�rth�r c��tr���t�d t� �pp�r cr��t�l �xt������, ��d th�� c���tr������ th� t�m� wh�� �lt�r�t��� t��� pl�c� ��d d�f�rm�t��� c��t����d �t �r�ttl� cr��t�l l�v�l�� S�l�c�c dy��� y��ld�d ���� ��tw��� 32�33 M�, typ�c�lly c���c�d��� w�th th� m��� ph��� �f P�l������� m��m�t�c �ct�v�ty, wh�ch �t�rt�d �� E��t�r� Rh�d�p� r����� �� L�t� E�c��� (Pr��������) t�m��� Th� 40Ar/39Ar pl�t��� ���� fr�m th� ���v� d��t��ct r�c� typ�� �p�� t�m� ��t�rv�l l��t��� approximately ca. 6 Ma. Consequently, our geochronologic results consistently indicate that extensional tectonics and related exhumation and d�ming, �p�th�rm�l miner�l�z�tions and v�lcanic �ct�v�ty �r� closely �p�c�d in t�me. These new 40Ar/39Ar age result� f�rth�r contribut� t� t�mp�r�l c���tr���t� �� th� t�m��� �f t�ct���c, r�l�t�v� t� �r��f�rm��� ��d m��m�t�c �v��t�, ������t��� �� �dd�t��� th�t �ll ���v� m��t����d processes interfered during the late orogenic extensional collapse in the Eastern Rhodope region. © 2006 Lavoisier SAS. All rights reserved Keywords: 40Ar/39Ar geochronology, extensional tectonics, magmatism, ore deposits, Rhodope, Bulgaria * Corresponding author. Tel: +3592 9308 431 - Fax: +3592 944 64 87 E-mail address: ������������������� © 2006 Lavoisier SAS. All rights reserved 266 Nikolay Bonev et al. / Geodinamica Acta 19/5 (2006) 265-280 1. Introduction pr�v�d� � wind�w f�r th� th�rm�chronologic�l �v�l�tion Recent advance in the study of structural and metamorphic �� th� E��t�r� Rh�d�p� r�����, ��th �� S��th B�l��r�� ��d evolution of metamorphic terrains and dating their exhu- Northern Greece. mation history in the north Aegean domain of the Eastern M�d�t�rranean region, has �h�w� distinct t�ctonom�t�m�rph�c �pisodes �f thrust �m�r�c�tion and subsequent crust�l thinning 2. Geological framework through �xtension d�ring distinct t�mes [1–8]� Preserv�tion �f pr��Alp��� ���� [7, 9, 10], ��d c��t������ Alp��� ���chr�- 2.1. General setting ��l���c r�c�rd fr�m �t l���t l�t� E�rly Cr�t�c���� w�th ���� �r�dually d�creasing w�ll int� th� E�cene t� Miocene [10–13] The Rhodope metamorphic province, outcropping mainly demonstrate a protracted cooling history of the accretionary �� ���th�r� B�l��r�� ��d ��rth�r� Gr��c�, �� r���rd�d t� �� �rogenic w�dge �long th� conv�rgent E�rasian pl�t� m�rgin, th� most int�rnal zone in this sect�r �f th� Alpine-H�m�l�yan possibly in � pr�d�minant �xtensional env�ronment d�ring orogenic system in the Eastern Mediterranean region (Fig. 1). the late orogenic evolution. This tectonic setting includes It r���lt� fr�m th� t�ct���c h��t�ry r�l�t�d t� th� Cr�t�c����� an early �tage �f �yn-t� post�th�ckening �xtension as w�ll R�cent subd�ction and conv�rgent setting �long th� �ct�v� as l�t� post-orogenic Aegean back-arc �xtension. A l�rge E�rasian pl�t� m�rgin [18, 19]� Th� M�d�Cr�t�ceous c��v�r- ��m��r �f ���v� ���chr���l���c �t�d��� �� th� Gr��� p�rt genc� between Afr�c� and E�rasia was responsibl� f�r th� of the Rhodope metamorphic province have shed light on �r�wing Rh�d�p� Massif as � crust�l-sc�l� m�t�m�rph�c the temporal evolution of tectonic and metamorphic events w�dge pair�d w�th th� V�rd�r �listostr�m�c trench [20]� Syn- d�ring th� Alpine �rogeny [10–12]� H�w�v�r, th� t�ming metamorphic thrusting and crustal thickening in the convergent of extensional exhumation of the Rhodope metamorphic region inv�lv�d both coev�l and subsequent �xtension [2]� pr�vinc� in B�l��ria r�mains gener�lly less w�ll c���trained Generally, the Rhodope metamorphic province consists of d�� t� th� l�c� �f ��fc���t ��d pr�c��� ��� d�t�rm���t����� high-gr�d� m�t�m�rph�c basement (mainly �mphibol�t� f�cies) Generally, the tectonic and magmatic processes are tightly ��tr�d�d �y L�t� Cr�t�c���� t� M�d�T�rt��ry pl�t���c r�c�� inv�lv�d d�ring th� �xtensional c�ll�pse �f �rogens [5, 14–16]� [21–23]� V�l�minous f�lsic and basic, Eo-Oligocene v�lcanic� Th�r�f�r�, r����� c��l��� h��t�ry �f m�t�m�rph�c t�rr���� [16, 24, 25] ��d L�t� Cr�t�c����/E�rly T�rt��ry t� Pl��c��� ��d �t� c����ct��� w�th m���r�l�z�t��� ��d m��m�t�c �v��t� ��d�m��t� [26, 27] c�v�r th� cry�t�ll��� ����m��t� d�r��� cr��t�l �xt������ �� �mp�rt��t t� ��tt�r ��d�r�t��d��� �f t�mp�r�l �v�l�tion �f �xh�m�tion pr�cess w�thin th� Alpine 2.2. Regional geology of the Eastern Rhodope region orogen in the northernmost Aegean domain. We focus our attention on the eastern Rhodope area in The eastern Rhodope region in Bulgaria and Greece B�l��r��, wh�r� cr��t�l �xt������ ��d ����c��t�d pr�c����� (Fig. 1) �xposes t�ctonom�t�m�rph�c c�mpl�xes, wh�ch �f magm�tism and miner�l�z�tion �r� best p�rtr�y�d� Tw� �r� ch�r�ct�r�z�d �y d�ff�r��t m�t�m�rph�c P�T h��t�ry ��d key �reas �r� consid�r�d in this �t�dy, incl�ding th� Kesebir� geochronologic ages [28], sep�r�t�d �y t�ctonic cont�ct� K�rd�mos and th� Bial� reka-K�chros d�mes w�th �r� d�posit� �f pr�d�minant �xtensional �rigin [29]� I� B�lgaria, th�y l�c�t�d w�thin �r �long their bord�rs. I� this p�p�r w� present �r� r�pr����t�d �y �������m��m�t�t� c�mpl�x �� l�w�rm��t new 40Ar/39Ar geochronologic d�t� fr�m th� basement gneiss.