First-report on Mesozoic eclogite-facies metamorphism preceding Barrovian overprint from the western Rhodope (Chalkidiki, northern Greece)

Abstract

International audienceThe Chalkidiki block in Northern Greece represents the southwesternmost piece of theultrahigh-pressure Rhodope and has played an important role in the evolution of the NorthAegean. The eastern part of the Chalkidiki block is a basement complex (Vertiskos Unit) thatis made largely of Palaeozoic granitoids and clastic sediments metamorphosed during theMesozoic. This basement is traditionally considered as part of the Rhodopean hanging-wall,an assignment mainly supported by the absence of high-pressure mineral indicators and thepresence of a regional medium-pressure/medium-temperature amphibolite-facies Barrovianmetamorphic imprint. Toward the west, the basement is juxtaposed with meta-sedimentary(Circum-Rhodope belt) and arc units (Chortiatis Magmatic Suite) that carry evidence of aMesozoic high-pressure/low-temperature event. In this study, garnet-staurolite-mica schistsfrom the eastern part of the basement were examined by means of micro-textures, mineralchemistry and isochemical phase-diagram sections in the system NCKFMASHMn(Ti)[Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-MnO-(TiO2)]. The schists represent formerMesozoic sedimentary sequences deposited on the Palaeozoic basement. We document thepresence of a relict eclogite-facies mineral assemblage (garnet + chloritoid + phengite +rutile) in an amphibolite-facies matrix composed of garnet + staurolite + phengite ± kyanite.Model results suggest the existence of a high-pressure/medium-temperature metamorphicevent (1.9GPa / 520°C) that preceded regional re-equilibration at medium-pressure/mediumtemperatureconditions (1.2GPa / 620°C). Clearly, the eastern part of the Chalkidiki block(basement complex) retains memory of an as yet unidentified Mesozoic eclogiticmetamorphic event that was largely erased by the later Barrovian overprint. In the light of ourfindings, the basement complex of the Chalkidiki block shares a common tectonometamorphicevolution with both the high-pressure units to the west, and the high-gradeRhodopean gneisses further to the northeast. Our results are consequential for the geodynamic reconstruction of the Rhodope since they require participation of the Chalkidikiblock to the well-established Mesozoic subduction system

Trace Elements in Magnetite from the Pagoni Rachi Porphyry Prospect, NE Greece: Implications for Ore Genesis and Exploration

“…The argon cooling gas flow rate was set to 16 L/min. Before starting an analysis, the system was calibrated to a NIST 612 reference glass measuring 139 27 Al, 29 Si, 43 Ca, 4 5Sc, 49 Ti, 51 V, 53 Cr, 55 Mn, 59 Co, 60 Ni, 63 Cu, 66 Zn, 69 Ga, 85 were quantitatively analyzed using the NIST 612 glass as an external standard while stoichiometric Fe (97% wt.% FeO) was the internal standard, since total concentration of minor elements is <3 wt.% (cf. Milani et al [60]).…”

The two-stage Aegean extension, from localized to distributed, a result of slab rollback acceleration

“…In summary, the exhumation of core complexes (high-temperature metamorphism) and blueschists (high-pressure metamorphism) results from significantly different mechanisms of development, primarily controlled by temperature-dependent rheology of the crustal units. Therefore, their location in the Aegean, as well as their relative timing of development, has an important mechanical significance: • The SRCC started to develop in Middle-Late Eocene in North Aegean when the CBU started to exhume in central Aegean, • The CCCC developed in central Aegean in lower Miocene almost synchronous with the onset of HP-LT PQN exhumation in Peloponnese and Crete.• The sense of shear and detachment dip in core complexes and sense of shear in highpressure rocks, is top to SW in North Aegean (SRCC), to NE in central Aegean (CBU The high-pressure to ultrahigh-pressure metamorphic units of the Southwest Rhodope(Kydonakis et al 2015b) and the North Rhodope(Mposkos and Kostopoulos 2001, Liati 2005) developed during the Cretaceous, and were exhumed before Eocene, prior to the onset of back-arc extension in the Aegean(Kydonakis et al 2014, Kydonakis et al 2015band 2015c) controlled by the Hellenic slab rollback. Therefore, they are outside the scope of the present paper.Stage 2: Neogene basins, segmentation of metamorphic units and dextral transtensional faultingThe Neogene basins(Fig.…”

Mineralogical Study of the Advanced Argillic Alteration Zone at the Konos Hill Mo–Cu–Re–Au Porphyry Prospect, NE Greece

“…The Hellenides are part of the Alpine orogenic system and form the link between the Dinarides (e.g., Albania) to the NW and the Pontides in the east (e.g., Turkey). They comprise a SW-vergent succession of tectonic units, which were integrated in three continental blocks (Rhdopes, Pelagonia, External Hellenides/Adria) and two oceanic domains, the Vardar and Pindos, respectively [36,37].…”

“…The North Rhodope domain consists of (a) a lower high-grade unit of basement rocks, including the metamorphic core complexes of Arda, Biala Reka-Kechros, and Kesebir-Kardamos; (b) an intermediate unit comprising high-grade basement rocks; and (c) an upper unit consisting of lowgrade metamorphic sequences of the Circum-Rhodope belt and ophiolitic rocks [42]. The Southern Rhodope Core Complex comprises Paleozoic orthogneisses (possibly equivalent to those of the metamorphic core complexes of the North Rhodope domain [37]) and a thick succession of Triassic marbles, with intercalations of amphibolitic and metapelitic rocks. Locally, anatectic conditions were achieved, as evidenced by migmatites on Thasos island and within the Kerdyllion unit.…”

“…[42]. The Southern Rhodope Core Complex comprises Paleozoic orthogneisses (possibly equivalent to those of the metamorphic core complexes of the North Rhodope domain [37]) and a thick succession of Triassic marbles, with intercalations of amphibolitic and metapelitic rocks. Locally, anatectic conditions were achieved, as evidenced by migmatites on Thasos island and within the Kerdyllion unit.…”