Semih Gürsu

Geology and Geochemistry of the Pre-early Cambrian Rocks in the Sandikli Area: Implications for the Pan-African Evolution of NW Gondwanaland

Abstract The pre-Early Cambrian Sandikli Basement Complex in western Central Anatolia comprises a low-grade meta-sedimentary succession (Guvercinoluk Formation) and meta-rhyolites intruded by meta-quartz porphyry rocks (Kestel Cayi Porphyroid Suite). The Guvercinoluk Formation consists of alternation of meta-siltstones and meta-sandstones with olistostromal conglomerates, rare black chert and cherty meta-dolomite lenses. The Kestel Cayi Porphyroid Suite is a deformed, highly sheared dome-shaped rhyolitic body with quartz porphyry rocks. Quartz porphyry dykes intrude both the volcanic carapace and the meta-sedimentary rocks of the Guvercinoluk Formation. Both the meta-quartz porphyry rocks and meta-rhyolites are typically mylonitic with relict igneous textures. Geochemical data indicate that the felsic rocks of the Kestel Cayi Porphyroid Suite are subalkaline and display characteristic features of post-collisional, I-type granitoids. The basement complex is unconformably overlain by variegated conglomerates, mudstones and arkosic sandstones with andesitic lavas, followed by siliciclastic rocks and carbonates that yielded Early Middle Cambrian fossils. Based on the geochemical characteristics of the felsic rocks of Kestel Cayi Porphyroid Suite and the depositional features of the associated sediments it is suggested that the Sandikli Basement Complex is related to a post-collisional extension event in NW Gondwanaland. Similar occurrences elsewhere have been related to a transition from continental plate convergence to continental plate divergence along the Pan-African Belt.

Petrogenesis and geodynamic evolution of the Late Neoproterozoic post-collisional felsic magmatism in NE Afyon area, western central Turkey

Abstract In western Turkey, Late Neoproterozoic basement rocks are represented by variably deformed metasedimentary and meta-igneous rocks within different tectonostratigraphical units that make up the Alpine Tauride–Anatolide Platform. In the Kütahya–Bolkar Dagı unit to the NE of Afyon this basement mainly includes garnet-bearing mica schists intruded by metamorphic granitic rocks with relict porphyritic textures. The youngest zircon ages obtained from the granitic rocks by the single zircon evaporation method are 542±5.0 Ma on average, which correlate with the Late Pan-African–Cadomian granitic magmatism. The granitic rocks are rhyodacitic or dacitic and peraluminous in composition, and display geochemical characteristics of I-type (tonalite–trondhjemite–granodiorite (TTG) source) felsic intrusive rocks. Trace and rare earth element patterns with distinct depletion in Rb, K, Nb, Sr, P and Ti relative to the other trace elements correlate very well with a Proterozoic TTG source. The petrogenetic modelling also implies that they were developed by partial melting of a TTG source by 20% fractional melting plus 20% Rayleigh fractional crystallization. The emplacement temperatures estimated by using zircon (790–820 °C), apatite and monazite saturation thermometry are about 827–1035 °C; these are in accordance with I-type rather than S-type granite melts. A geochemical comparison of the NE Afyon granitic rocks with the coeval quartz-porphyries in the Sandikli area of the Geyik Dag tectonic unit suggests that the latter may represent the more evolved felsic part of the Cadomian magmatism. Hence, both basement complexes are parts of the same Gondwanan terrane and represent the eastern continuation of the North African–Southern European terrane assemblage.

Petrogenetic and Tectonic Significance of Rift-Related Pre-Early Cambrian Mafic Dikes, Central Taurides, Turkey

Widespread swarms of tholeiitic dikes of pre-Early Cambrian age intrude Cadomian post-collisional Late Neoproterozoic granitoid rocks of the Sandikli Basement Complex in the Central Taurides, and the succession is disconformably overlain by Early Cambrian rift-controlled clastic and mafic rocks of the Gögebakan Formation. The studied dikes show distinct negative anomalies for Nb, Zr, Hf, and Ti, and enrichment of Th and LREE. These data indicate a MORB signature with subduction-modified mantle chemistry. The dikes are less intensely enriched in LREE with rather unfractionated spider diagrams ([Nb/Yb]N = 1.10-4.28) than N-MORB, and lack conclusive chemical evidence of crustal contamination. All analyzed rocks possess slightly negative Eu anomalies (Eu/Eu* = 0.77-1.02). The dikes show sharp negative Nb and Ta anomalies relative to LREE and low Ti/Y, Zr/Y, and Nb/U ratios, suggesting that they were derived through incorporating subduction-released fluids at the source during the partial melting of a spinel lherzolitic source. Petrogenetic modeling suggests that the dikes were produced by low-degree partial melting (<5%) of spinel lherzolite subsequent to subduction enrichment during magma ascent. The mafic dikes apparently erupted in a marginal basin formed during an initial stage of pre-Early Cambrian rifting of peri-Gondwanan continental margin. Emplacement was controlled by an extensional regime that followed after calc-alkaline granitoidic intrusion of the Cadomian orogeny.

Comments on “Deformation of the Lower Cambrian Sequence in the Sandikli Region (Afyon), central Turkey” by T. Güngör

Güngör [1] has recently presented his data and interpretations on the geology and deformational history of a series of slightly metamorphic rocks in the Sandıklı region (Afyon), Western Anatolia. We have been working since 1995 on the geological, petrological, and deformational features of the same rock-units in the same area [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14] and will comment on several issues including very critical field observations, geological mapping and petrographic/microtectonic features. The comments of ours are more than local disagreements in the fieldwork. They are of crucial importance, as they directly concern the regional geological interpretations regarding the presence of a Cadomian (or Pan-African sensu Şengör et al. [15]) tectonothermal event in the Taurides. This event is a critical feature of the Peri-Gondwanan terranes but does not occur in Baltica and Siberia and hence important for the correlation of the Late Neoproterozoic terranes.

Laser Ablation Inductively Coupled Plasma Mass Spectrometry U-Pb Dating of Detrital and Magmatic Zircons of Glacial Diamictites and Pebbles in Late Ordovician Sediments of the Taurides and Southeast Anatolian Autochthon Belt, Turkey: Indications for Their Arabian-Nubian Provenance

Late Ordovician (Hirnantian) glacio-marine deposits in the Central and Eastern Taurides and Southeast Anatolian Autochthon Belt (SAAB) in Turkey are mainly composed of diamictites, subrounded granitic pebbles, and rounded/subrounded lonestone pebbles. The granitic pebbles are dated as 576.5 ± 3.3, 576.7 ± 5.7, 598.4 ± 7.5, 717.5 ± 8.0, 789.5 ± 3.7, and 964.6 ± 4.6 Ma. The geochemical signatures and dated granitic pebbles in the Central and Eastern Taurides are interpreted to have been derived from the Late Neoproterozoic granitoids/metagranitic rocks of the Arabian-Nubian Shield (ANS; the Sinai Peninsula and the Eastern Desert of Egypt). The youngest 206Pb/238U ages in the diamictites (499.1 ± 4.2 Ma in the SAAB, 530.5 ± 5.3 Ma in the Eastern Taurides, and 562.5 ± 5.4 Ma in the Central Taurides) and in the lonestones (528.2 ± 4.5 Ma in the Central Taurides, 530.8 ± 5.2 Ma in the Eastern Taurides) indicate that detrital zircons were directly transported mainly from the northern margin of Gondwana and/or Arabia during the Late Ordovician, not from peri-Gondwanan parts of the European margin. Kernel/probability density diagrams of zircon ages from the lonestone pebbles in the Eastern and Central Taurides are interpreted as evidence for their derivation from Late/Middle Cambrian siliciclastic rocks in the Israeli part of the Sinai Peninsula. The provenance of detrital zircon populations in the diamictites in the Central and Eastern Taurides is directly correlated with magmatic activity of the Elat (Taba)–Feiran island arc, the Sa’al island arc, and the postcollisional magmatic suites in the Sinai Peninsula (Egypt). However, the corresponding successions in the SAAB have more abundant Late Cryogenian age components, suggesting the Ha’il/Afif/Ad Dawadimi/Ar-Rayn terranes of the eastern Arabian Shield as their provenance. These distinctive age patterns indicate that glacio-marine successions in the SAAB had different paleogeographic positions than their equivalent units in the Central and Eastern Taurides during deposition of the Late Ordovician glacio-marine units.