Joint research project

Upper Cretaceous-Paleogene magmatism and thermal waters of Rhodope Massif (Bulgaria): genesis and comparison with Aegean-Anatolian region  

Project leaders
Samuele Agostini, Peter Gochev Marchev
Agreement
BULGARIA - BAS - Bulgarian Academy of Sciences
Call
CNR/BAS 2013-2015
Department
Earth and Environment
Thematic area
Earth system science and environmental technologies
Status of the project
New

Research proposal

Present state of knowledge in the field, significance and objectives of the joint research:
During the last 20 years, different aspects of the geology of the Rhodope Massif have been the subject of considerable attention from the international geological community. In particular, special attention has been paid on its metamorphic history, after finding of micro-diamonds, suggesting deep burial and exhumation of Rhodopean metamorphic rocks. However, less attention has been paid so far on the abundant Upper Cretaceous-Middle Eocene intrusive and Upper Eocene-Oligocene volcanic activities and, in particular, on the characterization of the mantle sources of these magmas, as well as the relationship between the magma sources and tectonic setting of the region. Similar in age igneous activity is recorded in the NW Anatolia and abundant Miocene to Recent volcanism is widely distributed in the southernmost part of the Rhodope Massif and the entire Aegean region. This magmatism was a subject of a long-standing interest of the Italian side of this proposal, which recently developed a new evolution model for the Aegean region (e.g. Agostini et al., 2010 and references therein). Since the Upper Cretaceous-Oligocene magmatism in the Rhodope massif marks the onset of the Late Alpine magmatism in the region, its investigation is of exceptional interest for both Bulgarian and Italian teams, and it can shed a light on the early Alpine geological evolution of the Balkan Peninsula, as well as the subsequent onset of the extensional dynamics of the Aegean region, leading to the opening of the unconventional Aegean back-arc.
The Rhodope Massif along with several other metamorphic terranes in the Aegean region provides an excellent example of Tertiary to present day continental extension resulting in metamorphic core complex and sedimentary basin formation, accompanied by intimately related magmatic activity. Crustal extension in the Rhodope region followed an early phase of Mid-Late Cretaceous crustal thickening and has expressed itself in two distinct structural styles: (1) Early Tertiary onset of ductile extension/exhumation of the metamorphic core complexes, typified as basement domes below presently low-angle detachments, formation of supra-detachment Maastrichtian-Paleocene to Early Eocene sedimentary basins, coeval intrusion of 69-42 Ma granitoids and metamorphism under decreasing pressures; and (2) coeval or subsequent brittle extension through high-angle faulting, marked by a renewed cycle of Late Eocene-Miocene sedimentation and sedimentary basin widening, in turn associated with an acid-intermediate and basic volcanism (39-26 Ma). It is not clear, however, whether extensional structures represent a single continuous extensional regime from Late Cretaceous-Early Tertiary to Miocene, or if they are two timely distinct events. Thus, precise age dating of ductile and brittle extension structures, along with geochemical and isotopic data on magmatic activity are a prerequisite for constraining the relationship between those two magmatic-tectonic phases.
Upper Cretaceous-Paleocene igneous activity in the Rhodope Massif comprises a series of large plutons, being the most important the Rila-West Rhodope (e.g. Peytcheva et al., 2007), Smilian-Yugovo, Barutin-Buynovo-Elatia (e.g. Kamenov et al., 2008), Rozino and Chuchuliga (Marchev et al., 2006), Spanchevo and Dolno Dryanovo (Jahn-Awe et al., 2010). The plutons have calc-alkaline to high-K calc-alkaline affinity and consist of granodiorites, quartz-diorites, monzogranites and granites.
Priabonian-Oligocene intrusive and volcanic rocks are widely distributed along and across the massif from the Pirin Mt to the Eastern Rhodopes. Their petrogenetic affinity spans from calc-alkaline, to high-K calc-alkaline and shoshonitic. The volcanic activity shows a rough southward migration, with a progressive decrease of erupted volumes matched by lowering of the K2O content. Intermediate products, such as andesites, latites and dacites are the most abundant with basalt andesites being subordinate and basalts very rare (Marchev et al., 1998, 2004; Yanev et al., 1998). More evolved varieties, although widely distributed in the Eastern Rhodopes (Yanev, 1998), are most typical for the Central Rhodopes. In this region, the volcanism ends with the emplacement of basaltic dykes (26-28 Ma, Marchev et al., 1998) with intraplate-type affinity, spatially associated with the Eastern Rhodope metamorphic core complexes. The ultramafic/mafic xenoliths entrained in these dykes are also very interesting, because they provide useful information about underplating of hot and wet mafic intrusions beneath the metamorphic core complexes in the Rhodope region (Marchev et al., 2006).
Background of cooperation and envisaged results and benefit:
The project described is a continuation of the scientific collaboration between Geological Institute of Bulgarian Academy of Science and Institute of Geosciences and Earth Resources (IGG) of CNR of Pisa and Florence and the Earth Sciences department of the University of Florence over the past two decades. The quality of the research to date is documented by a large number of publications in the most prestigious international and local journals and conference abstracts. Italian colleagues have a long-standing interest in the study of the young magmatism in the Aegean region. Since the Paleogene magmatism in the Rhodope massif marks the onset of the Late Alpine magmatism, investigation of these rocks is of exceptional interest for both Bulgarian and Italian teams. Precise age dating, along with geochemical and isotopic data will be applied for constraining the relationship between Upper Cretaceous-Paleogene and Oligocene magmatic-tectonic phases and their relationship with the younger Aegean magmatism. High-quality geochemical data and, particularly, C-H-O-He isotopic data, which are lacking for the Rhodope thermal waters, will be useful to investigate the eventual deep source of the fluids (thermal waters).
Structural study will combine remote sensing analysis through analysis of satellite imagery and digital elevation models and classical field work; it will also consider an experimental investigation trough laboratory analogue modelling.
The completion of the project will be possible combining lab facilities in both organizations. Age determinations and detailed mineralogy will be made on the new LA-ICP-MS at the Geological Institute of Sofia and isotopic (Sr-Nd-Pb isotope ratios on selected samples) in the CNR, Pisa. Geochemistry of the waters, structural studies and laboratory analogue modeling will be done in the labs of the University of Florence.
 


 

Research goals

During our previous joint studies a large volume of geochemical and mineralogical data for the potassic rocks in the Eastern Rhodope zones have been collected (e.g. Innocenti et al., 1984; Harkovska et al., 1998; Marchev et al., 1998, 2004, 2006; Yanev et al., 1998). This project will focus on less studied Upper Cretaceous-Paleogene magmatism and Oligocene volcanism in the Central and Western Rhodopes. The new results will be combined with the available analytical database of rocks both from Rhodope area as well as the whole Aegean region (Bulgaria, Macedonia-FYROM, Greece, Thrace and Western Anatolia). Thus, the evolution of the mantle domains, and the subsequent crustal magma modification processes will be reconstructed on the base of the chemical and isotopic features of the magmatic rocks. The final objective is the comprehension the relationships among the Rhodope igneous activity and the magmatism found south and southeast in the Aegean-Anatolian region.
The relations between the mode of continental extension and magmatism will represent a topic of particular interest: extensional tectonics is indeed intimately related to and interacting with upraising magmas, with rheological modifications induced by the presence of crustal melts able to lead to strain localization processes and to the development of core-complex structures within a wide rift. These relations will be investigated through combined field work and laboratory analogue modelling.
An important part of the project is the involvement of complementary studies on thermal waters, ranging between 30 and 100 (maximum 120) °C, which are widely distributed throughout the Rhodope Massif. The objective is obtaining new data on trace-element and isotopic composition of the thermo-mineral waters, to trace the presence of crustal- and mantle-related fluid sources in response to the magmatic activity that has affected the area. By combining the geochemical data, two goals are to be achieved: (1) evaluation of the geothermal potential and its commercial importance accumulated in hosting reservoirs and (2) correlation between the fluid discharges and the present structural setting with the reconnaissance of the deep-seated source affecting the thermo-mineral water and gas discharges.
 
 

Last update: 29/03/2024