POLYMETAMORPHIC EVOLUTION OF THE PAN-AFRICAN BASEMENT AND PALAEOZOIC–EARLY TERTIARY COVER SERIES OF THE MENDERES MASSIF

Autor: CANDAN, Osman, OBERHÄNSLI, Roland, DORA, O. Özcan, ÇETİNKAPLAN, Mete, KORALAY, Ersin, RIMMELÉ, Gaëtan, CHEN, Fukun, AKAL, Cüneyt
Jazyk: angličtina
Rok vydání: 2009
Předmět:
Zdroj: Volume: 142, Issue: 142 121-163
Bulletin of the Mineral Research and Exploration
ISSN: 0026-4563
Popis: The Menderes Massif exposing in the Western Anatolia substantially presents a complex tectonostratigraphyas a result of Late Alpine compressional tectonism. The lithostratigraphical succession of this crystallinecomplex can be divided into two units: 1- The Pan-African basement (core series) and 2-Palaeozoic - EarlyTertiary metasedimentary rocks (cover series). The Pan-African basement of the Menderes Massif is made up ofa Late Neoproterozoic metaclastic sequence consisting of paragneisses and conformably overlying micaschists.This high-grade metaclastic sequence is extensively migmatized and intruded by the syn- to post-Pan-Africangabbros and granitoids. The primary contact relationship between the core and cover series is a regional unconformityin character. The Palaeozoic (?Upper Devonian - Permian) cover units, which are cut by the intrusion ofTriassic leucocratic metagranites are consisted of phyllites, quartzites and marbles. The Mesozoic cover units arecharacterized by Triassic to Upper Cretaceous platform-type thick marbles at lower levels of the sequence. UpperCampanian - Upper Maastrichtian pelagic carbonates and the overlying Middle Paleocene - Eocene flysch-typeblocky unit constitute the uppermost units of cover series. Relic mineral assemblages observed in the PanAfricanbasement reveal a complex polyphase metamorphic evolution of this basement under granulite, eclogiteand amphibolite-facies conditions. The high temperature metamorphism developing under granulite facies ischaracterized by the presence of hypersthene type pyroxene. Pelitic granulites, orthopyroxene gneisses, orthopyroxeneparagneisses and metagabbroic / metanoritic rocks form typical granulite-facies relics observed in themassif. Geothermobarometric estimations characterize an average temperature of 730 °C and pressure of 6 kbarfor the granulite-facies metamorphism. By means of SHRIMP II method, clustering ages of 583±5.7 Ma weredated from the outer parts zircons in pelitic granulites which have no zoning but have overgrown under granulitefacies. High grade metamorphism relics in the Pan-African basement are characterized by eclogite and eclogiticmetagabbros. Fully recrystallized, fine grained massif eclogites, with non bearing relic texture belonging toprotolith are composed of 'omphacite (jd40-52) + garnet + clinozoisite + amphibole + quartz + rutile'. However; relictexture and minerals are extensively observed in metagabbros derived from eclogitic gabbros. The pressuretemperature(P-T) conditions of the Pan-African high-pressure metamorphism were estimated as 644°C with aminimum pressure of about 15 kbar, which corresponds to a burial depth of about 50 km. 206Pb/ 238U zircon agesobtained from eclogitic metagabbros by TIMS yield 529.9±22 Ma, reveal the high-pressure metamorphism asPan-African in age. The Barrowian type medium pressure metamorphism reaching up migmatization stage inwhich anatectic granites developed caused extensive retrogradations. Geothermobarometric estimates fromgarnet amphibolites, retrograded from eclogites indicate that this metamorphism developed under P/T conditionsof 7 kbar in pressure and 628°C in temperature. The crystallization ages of these anatectic granites range from551 to 540 Ma. They were generated by migmatization of paragneisses and reveal that this medium-pressureevent is related to the last stage of polyphase Pan-African metamorphism. All metamorphic ages obtained fromthe Pan-African basement are compatible with the latest stages of assemblage of Gondwana super continent. Itis considered that protoliths of paragneisses and schists of the Pan-African basement were deposited on apassive continental margin of a basin occurring between East and West Gondwana during the Late Proterozoictime (Mozambique Ocean). The Pan-African basement of the Menderes Massif was deeply buried and metamorphosedunder granulite, eclogite and amphibolite-facies conditions as a result of the closure of this basin andcollision of East and West Gondwana during Late Neoproterozoic time. Both core and cover series of theMenderes Massif were affected by an Alpine aged old regional metamorphism. In the Palaeozoic sequence of cover series, this metamorphism is characterized by a Barrowian type medium-pressure metamorphism. Thismetamorphism developed under greenschist to lower amphibolite-facies (6 kbar in pressure / 430-550 °C in temperature)and described by the occurrences of garnet, staurolite and kyanite (disthene) in phyllites. MesozoicEarlyTertiary cover series at the southern part of Çine submassif contain data associated with Alpine aged HP/LTmetamorphism. Carpholite-kyanite assemblage within Triassic quartz metaconglomerates shows a metamorphismunder a pressure of 10-12 kbar and temperature of 440 °C corresponding to a minimum depth of 30 km.So far, there has not been detected any data for an Alpine HP / LT metamorphism, neither in the Pan-Africanbasement nor in the Palaeozoic sequence of the Menderes Massif. Based on the fossil content obtained fromyoungest unit of the cover series and from the oldest non metamorphic sedimentary cover on the massif, theAlpine metamorphism can biostratigraphically be constrained into Eocene and Oligocene time interval. Fewisotopic data (37±1 Ma, Late Eocene Rb/Sr biotite age; 36±2 Ma, Middle Eocene Ar/Ar muscovite age; 43-37 Ma,Eocene Ar/Ar muscovite age) related to Alpine metamorphism are compatible with the related time interval. TheAlpine metamorphisms of tectonical zones belonging to Anatolides is substantially associated with the closure ofthe northern branch of Neothethys Ocean and with the collision in Paleogene. In such a tectonic model, thesegment of the Anatolide-Tauride platform corresponding to the Menderes Massif was subjected to intenseinternal imbrication during the subduction process of the northern branch of Neotethys and the following periodin which the continental collision occurred. The tectonical slices being formed were buried at different depths andmetamorphosed under varying conditions related with burial depths under the load of Afyon zone at north inEocene-Oligocene times, and of Lycian nappes passing south and of ophiolites.
Databáze: OpenAIRE
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