Tectonic significance of Late Ordovician granitic magmatism and clastic sedimentation on the northern margin of Gondwana (Tavşanlı Zone, NW Turkey)
01 Jan 2013-Journal of the Geological Society (Geological Society of London)-Vol. 170, Iss: 1, pp 159-173
TL;DR: In this paper, Beyce schists and a small crosscutting metagranite underlie a Mesozoic metamorphosed carbonate platform within the regional Anatolide tectonic belt of northern Turkey.
Abstract: Metasedimentary schists and a small crosscutting metagranite underlie a Mesozoic metamorphosed carbonate platform within the regional Anatolide tectonic belt of northern Turkey. These lithologies are inferred to have formed part of the northern margin of Gondwana during the Palaeozoic. Immobile element geochemistry suggests that the country rock metasediments were derived from upper continental crust and arc-type magmatic rocks. Major and trace element analyses of the metagranite indicate affinities with upper continental crust or a continental margin magmatic arc. Tectonic discrimination of the metagranite is consistent with a rift or post-collisional setting. Niobium depletion relative to Ce on primitive mantle-normalized spidergrams suggests a subduction influence, possibly inherited from Late Precambrian (Cadomian) arc magmatism. Ion microprobe U–Pb dating of zircons from the metagranite yielded a crystallization age of 446 ± 8 Ma (Late Ordovician). An inherited core gave a concordant age of c . 578 Ma, consistent with Cadomian or Pan-African basement. Regional comparisons indicate that the Palaeozoic lithostratigraphy is similar to that of the Taurides (Gondwana) rather than the Pontides (Laurasia). We infer Mid- to Late Ordovician crustal extension along the north Gondwana margin, followed by spreading of Palaeotethys. The entire stratigraphy experienced high-pressure/low-temperature metamorphism during Late Cretaceous closure of the Izmir–Ankara–Erzincan ocean. Supplementary materials: The mineral composition, fabric, coordinates (UTM) and modal composition of the Beyce schist and Sarikaya metagranite samples are available at www.geolsoc.org.uk/SUP18556.
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TL;DR: Gondwana is reviewed from the unification of its several cratons in the Late Neoproterozoic, through its combination with Laurussia in the Carboniferous to form Pangea and up to its progressive fragmentation in the Mesozoic.
460 citations
Cites background from "Tectonic significance of Late Ordov..."
...Near the end of the Ordovician, at about 446 Ma, that activity extended as far east as Turkey, where metagranites are known from the Tavşanh Zone, just north of the Taurides (Özbey et al., 2013)....
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...of the Ordovician, at about 446 Ma, that activity extended as far east as Turkey, where metagranites are known from the Tavşanh Zone, just north of the Taurides (Özbey et al., 2013)....
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...Those terranes include the Taurides of southern Turkey, the Lesser Caucasus Terrane of Georgia, the Sanand, Alborz and Lut terranes of Iran, the Mangyshlak Terrane (which spans the Caspian Sea, and is termed the Kopetdag Terrane by some authors), the Afghan Terrane (which may itself consist of several terranes), the Karakorum Terrane in the northwest of Pakistan, and the Tibetan Lhasa and Qiangtang terranes of the Himalaya, both largely in southern China....
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TL;DR: In this article, a map that correlates tectonic units between Alps and western Turkey accompanied by a text providing access to literature data is presented, explaining the concepts used for defining the mapped Tectonic Units, and first-order paleogeographic inferences.
201 citations
TL;DR: In this article, a long-lived Tethys (Rheic, Palaeotethyan and Neotythyan oceans) was reconstructed for the easternmost Mediterranean and adjacent region.
Abstract: Valid palaeotectonic and palaeogeographical reconstructions of the easternmost Mediterranean and adjacent region involve a long-lived Tethys (Rheic, Palaeotethyan and Neotethyan oceans), northward subduction beneath Eurasia and rifting of continental fragments from Gondwana. Rifted microcontinents bordering Gondwana were separated (from south to north) by the Southern Neotethyan ocean, the Berit ocean (new name), the Inner Tauride ocean and the Izmir–Arkara–Erzincan ocean. Mid-Permian to Mid-Triassic pulsed rifting culminated in Late Triassic–Early Jurassic spreading of the Southern Neotethyan oceans (the main focus here). After Early–Mid-Jurassic passive subsidence, the Late Jurassic–Early Cretaceous was characterized by localized alkaline, within-plate magmatism related to plume activity or renewed rifting. Late Cretaceous ophiolites formed above subduction zones in several oceanic basins. Ophiolites were emplaced southwards onto the Tauride and Arabian platforms during the latest Cretaceous. The Southern Neotethys sutured with the Arabian margin during the Early–Middle Miocene, while oceanic crust remained in the Eastern Mediterranean further west. The leading edge of the North African continental margin, the Eratosthenes Seamount, collided with a subduction trench south of Cyprus during the Late Pliocene–Pleistocene, triggering rapid uplift. Coeval Plio-Quaternary uplift of the Taurides may relate to break-off or delamination of a remnant oceanic slab.
174 citations
TL;DR: In this paper, a review of salient geologic observations and paleomagnetic data from the various continental blocks and terranes of Asia is followed by the presentation of a new, full-plate tectonic model of the region from middle Cambrian to end-Silurian time (500-420 ǫ).
Abstract: Asia is key to a richer understanding of many important lithospheric processes such as crustal growth, continental evolution and orogenesis. But to properly decipher the secrets Asia holds, a first-order tectonic context is needed. This presents a challenge, however, because a great variety of alternative and often contradictory tectonic models of Asia have flourished. This plethora of models has in part arisen from efforts to explain limited observations (in space, time or discipline) without regard for the broader assemblage of established constraints. The way forward, then, is to endeavor to construct paleogeographic models that fully incorporate the diverse constraints available, namely from quantitative paleomagnetic data, the plentiful record of geologic and paleobiologic observations, and the principles of plate tectonics. This paper presents a preliminary attempt at such a synthesis concerning the early Paleozoic tectonic history of Asia. A review of salient geologic observations and paleomagnetic data from the various continental blocks and terranes of Asia is followed by the presentation of a new, full-plate tectonic model of the region from middle Cambrian to end-Silurian time (500–420 Ma). Although this work may serve as a reference point, the model itself can only be considered provisional and ideally it will evolve with time. Accordingly, all the model details are released so that they may be used to test and improve the framework as new discoveries unfold.
91 citations
Cites background from "Tectonic significance of Late Ordov..."
...Although post-Cadomian early Paleozoic magmatism is sparse in the Taurides, Middle and Late Ordovician metagranitoids interpreted to relate to that Mid-to-Late Ordovician rifting have been reported from the northwest of the Taurides, in the Tavşanlı zone (Okay et al., 2008b; Özbey et al., 2013)....
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TL;DR: In this paper, the U-Pb method was used to date metamorphic and igneous rocks exposed in NW-vergent thrust sheets and their autocthonous basement in the NE Pontides.
Abstract: Metamorphic and igneous rocks exposed in NW-vergent thrust sheets and their autocthonous basement in the NE Pontides were dated by the U–Pb method using zircons, supported by geochemical data for granitic rocks. Two meta-sedimentary units (Narlik schist and Karadag paragneiss) yielded detrital zircon populations of 0.50–0.65 and 0.9–1.1 Ga, suggesting an affinity with NE Africa (part of Gondwana). The youngest concordant zircon age is Ediacaran for the schist but Devonian for the paragneiss, bracketing the paragneiss depositional age as Mid-Devonian to Early Carboniferous. Metamorphic rims of zircon cores in the paragneiss gave Carboniferous ages (345–310 Ma). The zircon rim data indicate two Variscan metamorphic events (334 and 314 Ma) separated by a hiatus (320–325 Ma). Granite emplacement took place during early Carboniferous, Early Jurassic and Late Jurassic phases. The crystallization age of the early Carboniferous granites (c. 325 Ma) corresponds to a hiatus in the zircon age data that could reflect subduction slab break-off. The Variscan granitic rocks intruded a Gondwana-derived continental terrane that was loosely accreted to Eurasia during early–late Carboniferous time but remained isolated from Eurasian-derived terrigenous sediment. In contrast, the Jurassic granitic magmatism relates to later back-arc extension along the southern margin of Eurasia. Supplementary material: Full isotope data (8 tables) are available at www.geolsoc.org.uk/
79 citations
Cites background from "Tectonic significance of Late Ordov..."
...Mid-Ordovician (c. 473 Ma) magmatism is known in the Armutlu Peninsula and the Tavşanlı Zone (Okay et al. 2008a, b; Özbey Üçtaş et al. 2010; Özbey et al. 2013), part of the HP/LTmetamorphosed Anatolides (Okay 2002)....
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TL;DR: In this article, trace-element data for mid-ocean ridge basalts and ocean island basalts are used to formulate chemical systematics for oceanic basalts, interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone.
Abstract: Summary Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈ Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (⩽1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (⩽2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type (eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by the recycling of the enriched oceanic lithosphere back into the mantle.
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TL;DR: In this paper, the authors describe the composition of the present upper crust and deal with possible compositions for the total crust and the inferred composition of lower crust, and the question of the uniformity of crustal composition throughout geological time is discussed.
Abstract: This book describes the composition of the present upper crust, and deals with possible compositions for the total crust and the inferred composition of the lower crust. The question of the uniformity of crustal composition throughout geological time is discussed. It describes the Archean crust and models for crustal evolution in Archean and Post-Archean time. The rate of growth of the crust through time is assessed, and the effects of the extraction of the crust on mantle compositions. The question of early pre-geological crusts on the Earth is discussed and comparisons are given with crusts on the Moon, Mercury, Mars, Venus and the Galilean Satellites.
12,457 citations
"Tectonic significance of Late Ordov..." refers background in this paper
...Rare earth elements (REE) can help to determine the provenance of sedimentary rocks (Taylor & McLennan 1985; Guldenpfennig 1998; Silaupa 2002)....
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...In contrast, the elements Ti, Zr, Hf, Nb, Sc, Cr, Ni, V, Co, Th and the REE are considered to be immobile and so can be used as indicators of sediment provenance, magmatic evolution and tectonic setting (Taylor & McLennan 1985; bhatia & Crook, 1986; McLennan 1989; McLennan et al. 1990, 2003)....
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...6d) allows a comparison of the metagranite with possible source tectonic environments (Taylor & McLennan 1985)....
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...arc granites (Pearce et al. 1984) and upper crust generally (Taylor & McLennan 1985)....
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...LREE enrichment typically reflects a dominance of felsic igneous rocks compared with mafic rocks within a source area (Taylor & McLennan 1985)....
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TL;DR: In this article, a data bank containing over 600 high quality trace element analyses of granites from known settings was used to demonstrate using ORG-normalized geochemical patterns and element-SiO2 plots that most of these granite groups exhibit distinctive trace element characteristics.
Abstract: Granites may be subdivided according to their intrusive settings into four main groups—ocean ridge granites (ORG), volcanic arc granites (VAG), within plate granites (WPG) and collision granites (COLG)—and the granites within each group may be further subdivided according to their precise settings and petrological characteristics. Using a data bank containing over 600 high quality trace element analyses of granites from known settings, it can be demonstrated using ORG-normalized geochemical patterns and element-SiO2 plots that most of these granite groups exhibit distinctive trace element characteristics. Discrimination of ORG, VAG, WPG and syn-COLG is most effective in Rb-Y-Nb and Rb-Yb-Ta space, particularly on projections of Y-Nb, Yb-Ta, Rb-(Y + Nb) and Rb—(Yb + Ta). Discrimination boundaries, though drawn empirically, can be shown by geochemical modelling to have a theoretical basis in the different petrogenetic histories of the various granite groups. Post-collision granites present the main problem of tectonic classification, since their characteristics depend on the thickness and composition of the lithosphere involved in the collision event and on the precise timing and location of magmatism. Provided they are coupled with a consideration of geological constraints, however, studies of trace element compositions in granites can clearly help in theelucidation of post-Archaean tectonic settings.
7,144 citations
"Tectonic significance of Late Ordov..." refers background or methods in this paper
...On the Y–Nb diagram three samples lie in the WPG field and five in the combined VAG and syn-collisional granite (Syn-COLG) field (Pearce et al. 1984; Fig....
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...arc granites (Pearce et al. 1984) and upper crust generally (Taylor & McLennan 1985)....
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...On the Y + Nb v. Rb diagram (Pearce et al. 1984; Fig....
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...The chemically immobile major elements, trace elements and REE are commonly used for the classification and tectonic discrimination of granitic rocks (e.g. Pearce et al. 1984)....
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TL;DR: In this article, the abundance and distribution of selected minor and trace elements (Ti, Zr, Y, Nb, Ce, Ga and Sc) in fresh volcanic rocks can be used to classify the differentiation products of subalkaline and alkaline magma series in a similar manner to methods using normative or major-element indices.
4,648 citations