Analytical data for Sr, Rb, Cs, Ba, Pb, rare earth elements, Y, Th, U, Zr, Hf, Sn, Nb, Mo, Ni, Co, V, Cr, Sc, Cu and major elements are reported for eocene volcanic rocks cropping out in the Kastamonu area, Pontic chain of Northern Turkey. SiO2% versus K2O% relationship shows that the analyzed samples belong to two major groups: the basaltic andesitic and the andesitic ones. High-K basaltic andesites and low-K andesites occur too. Although emplaced on continental type basement (the North Anatolian Crystalline Swell), the Pontic eocene volcanics show elemental abundances closely comparable with typical island arc calc-alkaline suites, e.g. low SiO2% range, low to moderate K2O% and large cations (Cs, Rb, Sr, Ba, Pb) contents and REE patterns with fractionated light and almost flat heavy REE patterns. ΣREE and highly charged cations (Th, U, Hf, Sn, Zr) are slightly higher than typical calc-alkaline values. Ferromagnesian elements show variable values. Within the basaltic andesite group the increase of K%, large cations, ΣREE, La/Yb ratio and high valency cations and the decrease of ferromagnesian element abundances with increasing SiO2% content indicate that the rock types making up this group developed by crystalliquid fractionation of olivine and clinopyroxene from a basic parent magma. Trace element concentration suggest that the andesite group was not derived by crystal-liquid fractionation processes from the basaltic andesites, but could represent a distinct group of rocks derived from a different parent magma.

Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey

http://www.zetaware.com/public/McKenzie_1978.pdf

Some remarks on the development of sedimentary basins

1) Three indices of global climate have been monitored in the record of the past 450,000 years in Southern Hemisphere ocean-floor sediments. 2) Over the frequency range 10(-4) to 10(-5) cycle per year, climatic variance of these records is concentrated in three discrete spectral peaks at periods of 23,000, 42,000, and approximately 100,000 years. These peaks correspond to the dominant periods of the earth's solar orbit, and contain respectively about 10, 25, and 50 percent of the climatic variance. 3) The 42,000-year climatic component has the same period as variations in the obliquity of the earth's axis and retains a constant phase relationship with it. 4) The 23,000-year portion of the variance displays the same periods (about 23,000 and 19,000 years) as the quasi-periodic precession index. 5) The dominant, 100,000-year climatic [See table in the PDF file] component has an average period close to, and is in phase with, orbital eccentricity. Unlike the correlations between climate and the higher-frequency orbital variations (which can be explained on the assumption that the climate system responds linearly to orbital forcing), an explanation of the correlation between climate and eccentricity probably requires an assumption of nonlinearity. 6) It is concluded that changes in the earth's orbital geometry are the fundamental cause of the succession of Quaternary ice ages. 7) A model of future climate based on the observed orbital-climate relationships, but ignoring anthropogenic effects, predicts that the long-term trend over the next sevem thousand years is toward extensive Northern Hemisphere glaciation.

http://science.sciencemag.org/content/sci/194/4270/1121.full.pdf

Variations in the Earth's Orbit: Pacemaker of the Ice Ages

The chemical composition of subducting sediment and its consequences for the crust and mantle

Tethyan evolution of Turkey: A plate tectonic approach

Previously proposed models for the evolution of the Tyrrhenian basin-Apenninic arc system do not seem to satisfactorily explain the dynamic relationship between extension in the Tyrrhenian and compression in the Apennines. The most important regional plate kinematic constraints that any model has to satisfy in this case are: (1) the timing of extension in the Tyrrhenian and compression in the Apennines, (2) the amount of shortening in the Apennines, (3) the amount of extension in the Tyrrhenian, and (4) Africa-Europe relative motion. The estimated contemporaneous (post-middle Miocene) amounts of extension in the Tyrrhenian and of shortening in the Apennines appear to be very similar. The extension in the Tyrrhenian Sea is mostly accomplished in an E-W direction, and cannot be straightforwardly related to the calculated N-S Africa-Europe convergence. A model of outward arc migration fits all these constraints. In a subducting system, the subduction zone is expected to migrate outward due to the sinking of the underthrusting plate into the mantle. The formation of a back-arc or internal basin, i.e. of a basin internal to the surrounding belt of compression, (in this case the Tyrrhenian Sea) is then expected to take place if the motion of the overriding plate does not compensate for the retreat of the subduction zone. The sediment cover will be stripped from the underthrusting plate by the outward migrating arc of the overriding plate, and will accumulate to form an accretionary wedge. This accretionary body will grow outward in time, and will eventually become an orogenic belt, (in this case the present Apennines) when the migrating arc collides with the stable continental foreland on the subducting plate. An arc migration model satisfactorily accounts for the basic features of the Tyrrhenian-Apennine system and for its evolution from 17 Ma to the present, and appears to be analogous to the tectonic evolution of other back-arc settings both inside and outside the Mediterranean region. An interesting implication of the proposed accretionary origin of the Apennines is that the problematic “Argille Scagliose” (scaly clays) melange units might have been emplaced as overpressured mud diapirs, as observed in other accretionary prisms, and not by gravity slides from the internal zones.

Extension in the Tyrrhenian Sea and Shortening in the Apennines as Result of Arc Migration Driven by Sinking of the Lithosphere

It is contended that the Late Triassic to present-day gross evolution of the Alpine system in the Mediterranean region has been the result of activity along an evolving network of accreting, transform, and subducting plate boundaries between the large stable cratons of Europe and Africa. A refined assembly of the outlines of the continents around the North and central Atlantic, before the initial dispersion of Gondwanaland in Early Jurassic times, is presented. By considering geologic facies, structural fabric, and paleomagnetic criteria, the smaller continental fragments now found within the Alpine system are restored to their proposed initial positions relative to each other in the reconstruction offered. The motion of the major plate of Africa relative to Europe, commencing with the initial continental fragmentation, is documented by analysis of the sea-floor spreading history of the Atlantic Ocean, with the assumption that plate accretion there has occurred between torsionally rigid lithospheric plates. By the computerized fitting of well-defined and well-dated key pairs of symmetric magnetic anomaly lineations back together by a series of finite rotations, the relative position of North America to both Europe and Africa has been determined for the following times: 180 m.y. (Toarcian Stage, Early Jurassic); 148 m.y. (Kimmeridgian Stage, Late Jurassic); 80 m.y. (Santonian Stage, Late Cretaceous); 63 m.y. (Danian Stage, Paleocene); 53 m.y. (Ypresian Stage, Eocene); and 9 m.y. (Tortonian Stage, Miocene). From these positions, a series of rotation poles presumed to describe the stepwise motion of Africa relative to Europe were computed. The motions of the smaller intervening microplates have been inferred from the style of tectonic deformation on their borders, and these motions have been constrained to satisfy both changes in paleo-latitude with time and progressive rotations relative to the large macroplates that can be deduced from paleomagnetic measurements. The evolution of Tethys does not involve a single simple plate boundary between Europe and Africa, as has been envisioned previously, but, instead, a constantly evolving mosaic of subsiding continental margins, migrating mid-oceanic ridges, transform faults, trenches, island arcs, and marginal seas (back-arc basins). The periods of passive-continental margin development are recognized by a transgressive facies of platform carbonate rocks and thick prisms of continental-rise type sedimentation; accreting ridges by ultramafic rocks, gabbro, pillow basalt, deep-sea pelagic ooze, and abyssal red clay of the ophiolite suite; trenches by a migrating series of progressively younger linear flysch troughs whose immature mineral composition reflects nearby andesitic and metamorphic source terrains; the arcs themselves by calc-alkaline volcanism and the intrusion of silicic to intermediate plutons; the polarities of these arcs by the direction of overthrust nappe sheets and gradients in the ratio of potash to silica in the extrusives; their orientation by paired belts of high T and P and high P-T metamorphics; and finally the spreading back-arc basins by outpourings of basaltic magmas and evidence of flipping Benioff planes. A compilation of eight phases or chapters in Atlantic spreading history are outlined, which are based on the recognition of discrete differences and (or) relative motion between the continents bordering the Atlantic. All of these changes are reflected in the Tethys by reorganizations of the intervening plate boundaries and, we believe, are most explicitly recorded in the deformational history of the subducting zones. A montage of geometrically assembled plate-boundary interpretations are pictorially displayed as time-lapse frames of the evolving Alpine system. The montage begins with the Late Triassic (pre-Atlantic) setting of the Tethys 1 Ocean and extends to the present through nine phases of Tethyan history. Each phase is recognized on the basis of the age of intrusion and extrusion of basic lavas in ophiolite complexes, which mark the creation of new oceanic areas by both axial accretion in rift valleys of mid-oceanic ridges between rigid plates or by a more uncertain type of spreading in basins behind active island arcs. All the schemes presented are best estimates of the gross geometrical arrangements at discrete time intervals and should be treated as merely educated guesses. Despite the fact that we only have rigorous constraints for the relative positions of the nondeformed forelands of Europe and Africa, our models nevertheless imply that the motions of the larger plates will, by and large, dictate the general behavior of the smaller microplates through the particular styles of deformation set up along the adjoining plate boundaries. The Tethys 1 Ocean, located between Africa and Europe in Triassic times, has been almost entirely swallowed up in subduction zones of the Major Caucasus Mountains along its former northern margin and in similar zones of the Pontides and Minor Caucasus along its southern margin. The only remnants of Tethys 1 are the areas of oceanic crust in the Black and South Caspian Seas. There is considerable evidence to suggest that the Tethys 1 Ocean had an actively spreading ridge. Some tens of millions of years prior to the opening of the central North Atlantic, a branch of this ridge system entered into the Vardar Zone of eastern Greece and broke off fragments of northeast North Africa to initiate the development of the present-day Ionian and Levantine Basins of the eastern Mediterranean. Additional fragments (the Moroccan and Oranaise Meseta) were ruptured from northwest Africa following its separation from North America. The intervening Jurassic Atlas, seaway developed along an accreting plate boundary extending from the eastern Tethys to the crest of the embryonic Mid-Atlantic Ridge where it formed a migrating triple junction whose trace, we believe, follows the trend of the New England seamount chain. The western Mediterranean basins of the Alboran, Balearic, and Tyrrhenian Seas are very much younger, being initially opened in the early Miocene as a string of back-arc marginal seas behind the developing Apennine, Tel Atlas, and Rif suture zone that today marks the sites of subduction of Jurassic and Lower Cretaceous oceanic crust. The contemporary Alpine system displays a spectrum of stages in the building of mountain belts. Embryonic nappes within the Mediterranean Ridge in proximity to melange zones of the inner wall of the Hellenic Trench are, perhaps, signs of the initial deformation of sedimentary passengers on oceanic crust arriving at a subduction zone. Total closure of an ocean followed by the partial consumption of a passive continental margin leads to events such as the tectonic emplacement of crystalline basement nappes of the European “chaine calcaire” onto northwest Africa. Arc-continent collisions of this type which have then been succeeded by total destruction of marginal back-arc basins are recognizable in the Hellenides and Pontides. There are, as well, collisions that have not involved the disappearance of large oceanic areas; these are most apparent in the particular tectonic style of the Pyrenees and High Atlas Mountains.

Plate Tectonics and the Evolution of the Alpine System

[1] Seafloor bathymetric data acquired with modern swath echo sounders provide coverage for only a small fraction of the global seabed yet are of high value for studies of the dynamic processes of seafloor volcanism, tectonics, mass wasting, and sediment transport that create and shape the undersea landscape. A new method for compilation of global seafloor bathymetry that preserves the native resolution of swath sonars is presented. The Global Multi-Resolution Topography synthesis consists of a hierarchy of tiles with digital elevations and shaded relief imagery spanning nine magnification doublings from pole to pole (http://www.marine-geo.org/portals/gmrt). The compilation is updated and accessible as surveys are contributed, edited, and added to the tiles. Access to the bathymetry tiles is via Web services and with WMS-enabled client applications such as GeoMapApp®, Virtual Ocean, NASA World Wind®, and Google Earth®.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008GC002332

Global Multi-Resolution Topography synthesis

This article presents evidence that the Mediterranean Sea was a desiccated deep basin some 6 million years ago.

William B. F. Ryan

Papers

Extension in the Tyrrhenian Sea and Shortening in the Apennines as Result of Arc Migration Driven by Sinking of the Lithosphere

Plate Tectonics and the Evolution of the Alpine System

Global Multi-Resolution Topography synthesis

Late Miocene Desiccation of the Mediterranean

An abrupt drowning of the Black Sea shelf