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    Geology and Tectonic Emplacement of Eclogite and Blueschists, Biga Peninsula, Northwest Turkey
    (Tubitak Scientific & Technological Research Council Turkey, 2011) Sengun, Firat; Yiğitbaş, Erdinç; Tunc, Ismail Onur
    The Biga Peninsula in northwestern Anatolia is a tectonic mosaic, comprising different tectonic units, representing the Sakarya Continent and oceanic assemblages of different origin and ages. The Camlica metamorphic association, a member of this orogenic mosaic in the westernmost part of the peninsula, is subdivided into three formations, from bottom to top; the Andiktasi formation, the Dedetepe formation, and the Salihler formation. Eclogite-facies metamorphic rocks occur as tectonic slices within schist-marble intercalations of the Dedetepe formation. These slices, about 2 km long and 500 m wide, include two different rock types; (i) quartz-mica schists, and (ii) metabasite lenses with eclogite/blueschist paragenesis. Foliation in the Dedetepe formation of the Camlica metamorphic association generally dips SW and strikes NW-SE around Dedetepe hill and Camlica village. In contrast, eclogite-facies metabasite slices strike NE-SW with NW-dipping foliation. The eclogite-facies metabasite lenses are typically low-temperature eclogites that may represent tectonic slices of an accretionary complex associated with a subduction zone. Blueschists were produced by retrograde metamorphism from eclogite during late stage shearing. The host rocks record only a single-stage greenschist-facies metamorphism and were juxtaposed with the eclogite-facies metamorphic rocks along ductile-semi-brittle (?) strike-slip faults aft er the eclogite-facies metamorphism and during or aft er the low-grade metamorphism of the Camlica metamorphic unit. Age constraints on the metamorphic units and the age of the common cover units suggest that this juxtaposition by strike-slip tectonics occurred between the late Cretaceous and early Eocene.
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    Örenli metamorphics (Biga Peninsula, NW Anatolia): evidence for Triassic active continental margin of Paleo-Tethys Ocean
    (Tubitak Scientific & Technological Research Council Turkey, 2024) Tunc, Ismail Onur
    The pre-Liassic basement of the Biga Peninsula, located in the westernmost part of the Sakarya Zone, consists of metamorphic assemblages that were considered to represent different continental basements in the north and south, and the suture (ophiolitic/ melange) zone(s) between them. The cetmi melange, defined as between these continental fragments (the Kazdag Massif in the south and the camlica Massif in the north) was evaluated as a subduction accretionary melange of the Intra-Pontide Ocean and it was assumed that a suture passed through this part of the peninsula. This study was carried out on the most widely distributed outcrops of the cetmi melange(?) on the northwest flank of the Kazdag Massif. These units, which are named the orenli metamorphics, are represented by a succession of low-grade metamorphic volcanic-volcaniclastic rocks and alternating metasedimentary rocks and recrystallized limestones. The tectonostratigraphically lowermost levels of the orenli metamorphics are a blocky -chaotic assemblage, whereas the uppermost levels are a regular metavolcanic-metapelite succession, which passes upward into the Late Triassic recrystallized limestones, and is cut by very low-grade metamorphic diabase dykes of 165.81 +/- 1.55 Ma age. Furthermore, metavolcanic rocks of this succession show a calc-alkaline association of Basalt-Andesite-Dacite-Rhyolite (BADR) pattern in the chemical classification diagram, which is the signature volcanic rock suite of convergent margins. In addition, all the metavolcanic rock samples show a significant enrichment in terms of incompatible elements and LIL elements and negative Nb and Ti anomalies on the MORB normalized multielement spider diagram, which indicates that these rocks characterize high -K calc-alkaline volcanism at the active continental margins. Field relationships, zircon U-Pb geochronology, and geochemical data support that these units, outcropping in the study area, represent a Triassic active continental margin, most probably a fore -arc setting, related to the Paleo-Tethyan subduction, but not the subduction melange of the Intra-Pontide Ocean.
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    Pre-Cambrian Metamorphic Rocks of the Sakarya Zone in the Biga Peninsula; Late Ediacaran Gondwanaland Active Continental Margin
    (Tmmob Jeoloji Muhendisleri Odasi, 2020) Yiğitbaş, Erdinç; Tunc, Ismail Onur
    The pre-Jurassic metamorphic rocks of the Biga Peninsula can be evaluated as three main tectonostratigraphic units, which show significant differences from each other in terms of degree of metamorphism, deformation characteristics and tectonic settings. These are: 1) Kazdag Unit, 2) Kalabak Unit, and 3) Karakaya Unit. The Kazdag Unit forms the high-grade metamorphic core rocks of the Kazdag Massif on the visible base of the Biga Peninsula. The Kalabak Unit and the Karakaya Unit are located on this high-grade metamorphic basement as composite tectonic slices and form the lower-grade metamorphic outer envelopes. The Kalabak Unit, which is the main subject of this paper, consists of the Dedetepe Formation, the Sazak Formation, the Torasan Formation, and Devonian camlik metagranodiorite, which cuts all these units. In addition to lithological, stratigraphic and structural similarities of these metamorphic rocks, which are the outer envelope of the metamorphic core in the Kazdag Massif and also outcrop in other metamorphic massifs. of the region such as camhca, Karabiga and Karadag, their U-Pb zircon ages also show that they can be correlated with each other. According to the results obtained from U-Pb zircon dating, the maximum sedimentation ages of the protoliths for the metasedimentary rocks of the Kalabak Unit are in the range of 557-582 Ma. The crystallization age of the protolith for the metabasites, which has primary relationship to these metasedimentary rocks, is 577 Ma. In addition, protolith crystallization age of the eclogites, which are tectonic slices in these metasedimentary rocks, is 565 Ma. In addition to similar protolith ages, the fingerprint of a tectonothermal event at about 300-340 Ma is important in terms of expressing a common geological history for all samples. Formation environment and age of the metavolcanic rocks of the Kalabak Unit represent consistent and significant geotectonic environments. The Dedetepe Formation, which is at the bottom, represents a subduction melange, the Sazak Formation represents an active continental margin and the Torasan Formation represents a coeval sedimentary sequence. These geotectonic environments developed during the late Precambrian-early Paleozoic period while the Proto-Tethys oceanic crust subducted to the south, under the Gondwanaland continent. These oldest rocks of the Sakarya Zone, together with the rocks they were spatially associated with during younger periods, were affected by repetitive deformations which resulted in their present position.
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    U-Pb zircon geochronology of northern metamorphic massifs in the Biga Peninsula (NW Anatolia-Turkey): new data and a new approach to understand the tectonostratigraphy of the region
    (Taylor & Francis Ltd, 2012) Tunc, Ismail Onur; Yiğitbaş, Erdinç; Sengun, Firat; Wazeck, Jana; Hofmann, Mandy; Linnemann, Ulf
    Metamorphic massifs of the Biga Peninsula can be divided into two approximately ENE-WSW-trending belts. It is believed that these two belts represent two different tectonic zones separated by a NE-trending Alpine ophiolitic suture. The Sakarya Zone lies to the S-SE of this Alpine suture, and consists of the Kazdag metamorphic complex which is tectonically overlain by the Permo-Triassic Karakaya Complex. The metamorphic rocks, as an Alpine edifice located N-NW of the suture, have been assigned to the Rhodope and Serbo-Macedonian massifs of Bulgaria and Greece. The northern metamorphic belt is represented by the Karadag Massif in the west, which has been evaluated as a different unit from the others, the Karabiga Massif in the east and the Camlica Massif between them. All three massifs are mapped in detail in light of previous studies and LA-ICP-MS U-Pb zircon dating was applied to stratigraphically compare them. Contrary to previous studies, our data indicate that the basement metamorphic associations in these three areas show similar characteristics concerning their stratigraphical and lithological aspects and also spatial distribution of their outcrops. U-Pb LA-ICP-MS dating of zircons from the three individual metamorphic massifs yielded the following data: maximum sedimentation ages of the protolith of mica schists in the range of 559 +/- 17 to 582 +/- 30 Ma; crystallisation age of the protolith of metavolcanic rocks of 577 +/- 20 Ma; and crystallisation age of the protolith of eclogites at 565 +/- 9 Ma. These ages clearly show that the metamorphic units of the northern massifs are comparable to each other. Also, the U-Pb zircon concordia diagrams from these three metamorphic massifs show remarkably similar patterns. In addition to the similar maximum sedimentation ages for all mica schists with crystallisation ages of the protoliths of the metabasic rocks, there are two major complex tectono-thermal overprints (episodic lead loss events), at c. 330-300 Ma (Variscan?) and c. 100-10 Ma (Alpine and late Alpine?), respectively. Field mapping and analytical data indicate that the basement rocks of the northern massifs in the Biga Peninsula have a correlative Late Ediacaran to Early Cambrian stratigraphic range. In part, Permian strata unconformably overlie basement rocks in the Karadag Massif. Both tectono-thermal events are demonstrated by coeval episodic lead loss of many zircons in all samples from all areas. Finally, the results of this research do not support an Alpine suture between the two metamorphic belts of the Biga Peninsula. Therefore, the geological evolution of the region might require reevaluation.