Kaan Sayit

Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Dağ Unit, the Saka Unit, the Daday Unit and the Arkot Dağ Mèlange) have been studied in detail along two selected transects. The Domuz Dağ Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Dağ Mèlange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis corroborates the available data collected from the Aylı Dağ Ophiolite Unit cropping out in the westernmost studied transect. This finding can provide new insights for the reconstruction of the geodynamic history of the Intra-Pontide domain.

The Intra-Pontide suture zone in the Tosya-Kastamonu area, Northern Turkey

ABSTRACT We present the first detailed geological map of the tectonic units documented in the easternmost branch of the Intra-Pontide suture (IPS) zone in the Tosya-Kastamonu area (Northern Turkey). The Main Map is at 1:50,000 scale and covers an area of about 350 km2. It derived from 1:25,000 scale classic field mapping and represents a detailed overview of the complexities documented in the IPS zone, a tectonic nappe stack originating from the closure of the Intra-Pontide Oceanic basin and the subsequent collision between the Istanbul-Zonguldak terrane and the Sakarya composite terrane. The map shows the orientations of superposed foliations, fold axes and mineral lineations on the basis of geometric cross-cutting relationships documented within the five tectonic units of the IPS zone and provides information on its present-day architecture resulting from activity of the North Anatolian Fault.

Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basinC. FRASSI AND OTHERSBurial and exhumation in Central Pontides

In northern Turkey, the Intra-Pontide suture zone represents one of the first-order tectonic structures located between the Istanbul–Zonguldak and the Sakarya continental terranes. It consists of an E–W-trending assemblage of deformed and variably metamorphosed tectonic units, including sedimentary rocks and ophiolites derived from a Neo-Tethyan oceanic basin, known as the Intra-Pontide oceanic basin. One of these units is represented by the Daday Unit that consists of a block-in-matrix assemblage derived from supra-subduction oceanic crust and related deep-sea sedimentary cover of Middle Jurassic age. This setting was acquired during Late Jurassic time by tectonic underplating at a depth of 35–42 km associated with blueschist-facies metamorphism (D1 phase). The following D2, D3 and D4 phases produced the exhumation of the Daday Unit up to shallower structural levels in a time span running from the Albian to late Paleocene. The high geothermal gradient detected during the D2 phase indicates that the Daday Unit was exhumed during a continent–arc collisional setting. The tectonic structures of the Intra-Pontide suture zone, resulting from the previously described tectonic history, are unconformably sealed by the upper Paleocene – Eocene deposits. This tectonic setting was intensely reworked by the activity of the North Anatolian Fault Zone, producing the present-day geometrical relationships of the Intra-Pontide suture zone of the Central Pontides.

Middle Carnian Arc-Type Basalts from the Lycian Nappes, Southwestern Anatolia: Early Late Triassic Subduction in the Northern Branch of Neotethys

The Turunç Unit, which represents one of the tectonic slices within the Lycian Nappes in southwestern Anatolia, preserves the remnants derived from the northern branch of Neotethys. The unit includes basalts intercalated with pelagic limestones of middle Carnian age (early Late Triassic) based on the characteristic radiolarian assemblage of the Tetraporobrachia haeckeli Zone. The Turunç lavas reflect trace element signatures resembling those from subduction zones, displaying selective enrichment of Th and light rare earth elements over high-field strength elements and heavy rare earth elements. Considering the overall geochemical characteristics of the Turunç basalts and given that they are found to be associated with no continent-derived detritus, the Turunç lavas appear to represent fragments of a Late Triassic island arc formed on the Neotethyan oceanic lithosphere. This result is of particular importance, since it reflects the oldest subduction age obtained from the entire Neotethyan realm to date. It may further indicate that the Neotethyan oceanic lithosphere had already been formed by the early Late Triassic, thus suggesting a pre–early Late Triassic oceanization of the northern branch of Neotethys. On the basis of this, we also suggest that the initial rifting leading to the opening of the northern branch of Neotethys should have taken place during the Middle Triassic or earlier.

Geochemical and Geochronological Data from Charnockites and Anorthosites from India's Kodaikanal-Palani Massif, Southern Granulite Terrain, India

The Kodaikanal–Palani Massif is an important component of India’s Southern Granulite Terrain; understanding the tectonic history of its rocks lends considerable insight into its role within South India. The massif is located south of the Palghat Cauvery Shear Zone (PCSZ). Compilations of available geochronologic and geochemical information from charnockites north and south of the PCSZ show these rocks largely differ in age, with northern samples recording Archaean crystallization events, whereas those to the south yielding Cambro-Ordovician and Neoproterozoic ages. The Kodaikanal–Palani charnockitic rocks contain monazite grains that fall within the Cambro-Ordovician timescale. The Oddanchatram anorthosite, located along the northern boundary of the Kodaikanal–Palani Massif, contains zircon grains that record mid-Neoproterozoic to Cambro-Ordovician crystallization ages. This anorthosite differs in texture and composition depending on location, that may be the result of its multi-stage metamorphic and/or intrusion history. Charnockitic rocks north and south of the PCSZ also differ geochemically. For example, north of the PCSZ, these rocks become more calcic with increasing SiO2 contents, whereas those to the south become alkali-calcic. Southern charnockitic rocks tend to have higher K2O/TiO2, Zr/SiO2, Rb/Sr, Ba and Rb contents, but lower Sr/Ba ratios. Using available geochemical data, we find more charnockitic rocks south of the PCSZ record zircon saturation temperatures between 800°C and 900°C than those to the north. Although samples of charnockitic rocks within the Kodaikanal–Palani Massif yield similar monazite ages, the rocks differ in their whole rock geochemistry and zircon and monazite saturation temperatures depending on location. The geochemical data from these rocks suggest that charnockitic rocks within the Kodaikanal–Palani Massif possibly experienced different mechanisms of generation and/or metamorphic histories.

The geodynamic evolution of the Intra-Pontide suture zone, Central Turkey: evidence from the ophiolite bearing Arkot Dağ Mélange

Lucchi, Renata G. ... et. al.-- 87° Congresso della Societa Geologica Italiana e 90° Congresso della Societa Italiana di Mineralogia e Petrologia, The Future of the Italian Geosciences - The Italian Geosciences of the Future, 10-12 September 2014, Milan, Italy.-- 1 pageThe Montellina Spring (370 m a.s.l.) represents an example of groundwater resource in mountain region. It is a significant source of drinking water located in the right side of the Dora Baltea Valley (Northwestern Italy), SW of Quincinetto town. This spring shows a morphological location along a ridge, 400 m from the Renanchio Torrent in the lower sector of the slope. The spring was investigated using various methodologies as geological survey, supported by photo interpretation, structural reconstruction, NaCl and fluorescent tracer tests, discharge measurements. This multidisciplinary approach, necessary due to the complex geological setting, is required for the importance of the Montellina Spring. It is interesting in the hydrogeological context of Western Alps for its high discharge, relatively constant over time (average 150 l/s), and for its location outside a fluvial incision and suspended about 40 m above the Dora Baltea valley floor (Lasagna et al. 2013). According to the geological setting, the hydrogeological reconstruction of the area suggests that the large amount of groundwater in the basin is essentially favoured by a highly fractured bedrock, covered by wide and thick bodies of glacial and gravitational sediments. The emergence of the water along the slope, in the Montellina Spring, is essentially due to a change of permeability between the deep bedrock and the shallow bedrock and/or surficial sediments. The deep bedrock, showing closed fractures and/or fractures filled by glacial deposits, is slightly permeable. The shallow bedrock, strongly loosened as result of gravitational phenomena, and the local gravitational sediments are, on the contrary, highly permeable. The concentration of water at the spring is due to several reasons. a) The spring is immediately downward a detachment niche, dipping towards the spring, that essentially drains the water connected to the change of permeability in the bedrock. b) It is along an important fracture, that carries a part of the losses of the Renanchio Torrent. c) Finally, it is favored by the visible and buried morphology. Although it is located along a ridge, the spring occurs in a small depression between a moraine and a landslide body. It also can be favored by the likely concave trend of buried base of the landslide. At last, tracer tests of the Renanchio Torrent water with fluorescent tracer are performed, with a continuous monitoring in the Montellina Spring. The surveys permit to verify and quantify the spring and torrent hydrogeological relationship, suggesting that only a small fraction of stream losses feeds the spring.