Neogene Uplift and Magmatism of Anatolia: Insights from Drainage Analysis and Basaltic Geochemistry

It is generally agreed that mantle dynamics have played a significant role in generating and maintaining the elevated topography of Anatolia during Neogene times. However, there is much debate about the relative importance of subduction zone and asthenospheric processes. Key issues concern onset and cause of regional uplift, thickness of the lithospheric plate, and the presence or absence of temperature and/or compositional anomalies within the convecting mantle. Here, we tackle these interlinked issues by analyzing and modeling two disparate suites of observations. First, a drainage inventory of 1,844 longitudinal river profiles is assembled. This geomorphic database is inverted to calculate the variation of Neogene regional uplift through time and space by minimizing the misfit between observed and calculated river profiles subject to independent calibration. Our results suggest that regional uplift commenced in the east at 20 Ma and propagated westward. Secondly, we have assembled a database of geochemical analyses of basaltic rocks. Two different approaches have been used to quantitatively model this database with a view to determining the depth and degree of asthenospheric melting across Anatolia. Our results suggest that melting occurs at depths as shallow as 60 km in the presence of mantle potential temperatures as high as 1400°C. There is evidence that potential temperatures are higher in the east, consistent with the pattern of sub-plate shear wave velocity anomalies. Our combined results are consistent with isostatic and admittance analyses and suggest that elevated asthenospheric temperatures beneath thinned Anatolian lithosphere have played a first order role in generating and maintaining regional dynamic topography and basaltic magmatism

Geochemical signatures of granitoids associated with skarns in central Anatolia

WOS: 000172227300006Many studies have shown systematic correlations between the composition of plutons worldwide and the metal contents of associated skarns. This is the first report of similar correlations between plutons and the skarns of the Akdagmadeni, Akcakisla, and Keskin districts in Central Anatolia. Herein, die genetic associations of skarn occurrences are investigated using the geochemical compositions of the intrusives. In terms of major- and trace-element data, the granitoids associated with skarns show important differences. Three general groups of plutons, are distinguished, and the distinction among them is based largely on major-element data. In general, the granitoids associated with Pb-Zn skarns in all three districts are classified as subalkaline/calc-alkaline, based on TAS and AFM diagrams, respectively. The Akdagmadeni and Keskin granitoids display S-type characteristics, and those of Akcakisla display I-type characteristics. As a whole, the granitoids in all districts display major-element geochemical characteristics (Harker diagrams) that typify plutons associated with worldwide Zn, W, Mo, and Sn skarns. These data probably indicate that some other elements, like W in the Akdagmadeni district, and Mo + Sn in the Keskin district, could be associated with these skarns. Similarly, the granitoids of Akdagmadeni and Akcakisla have trace-element geochemical signatures (Zr versus Ba and Zr versus Rb/Sr diagrams) that typify plutons associated worldwide with Zn, Cu, Mo, and W skarns. This also helps to underline the possible association of W and Mo skarns in the Akdagmadeni district, and Cu skarns in the Akcakisla district. The average K2O/Na2O ratios of the plutons also serve to differentiate the granitoids associated with different types of skarns. The average K2O/Na2O ratio of the Keskin pluton it; 1.23, close to that of plutons associated with major Mo and Sn skarns. On the other hand, the average K2O/Na2O ratio of Akcakisla granite is very close to 1.0, close to that of plutons associated with major Cu (and W?) as well as Pb and Zn. Therefore, these skarns should be investigated in terms of the potential for those elements. This suggests new exploration possibilities for the Akcakisla, Akdagmadeni, and Keskin districts

Geochemical correlations between effusive and explosive silicic volcanics in the Saraykent region (Yozgat), central Anatolia, Turkey

WOS: 000175737800005Two main volcanic events are distinguished between Saraykent and Akqaki la in the Yozgat province of central Anatolia: (1) early Late Cretaceous-Palaeocene effusive activity, that produced a sequence of intermediate to felsic 'basal lavas'; and (2) marginally later Palaeocene explosive activity that formed a series of covering ignimbrite flows. Due to their close temporal and spatial relation, geochemical comparisons were made between the silicic members of the lavas and ignimbrites, to identify chemical groups and their relative petrogenesis. The basal lavas range from calc-alkaline basaltic andesites to dominant rhyolites. Based on trace element correlations three main geochemical groups were identified: the Akqakisla rhyolites (present as domes); Akcakisla rhyodacites-dacites (lava flows); and Ozan-Saraykent rhyolites (lava flows). Large-ion lithophile elements have been mobile in all the groups, but mainly in the Akqaki la rhyolites. Rare earth element (REE) patterns show marked similarity between the Ozan and Saraykent basal lavas. The Akqaki la dome rhyolites are more fractionated with lower La-N/Yb-N ratios (c. 10), whereas the Akqakisla basal lavas have much higher LaN/YbN ratios (c.30). The chemical coherence and petrographic similarities between the Saraykent and Ozan lavas suggest a single suite related via fractionation. Three geochemical groups were also established for the ignimbrites: Saraykent ignimbrite; Baglica ignimbrite-TokluKizildag crystal tuffs; and Keklikpinar ignimbrite. The ignimbrites, like the basal lavas, display a pronounced depletion in Ba on ORG-normalized plots. Relative to the basal lavas, chondrite-normalized patterns for the ignimbrites are different in displaying negative Eu anomalies that indicate feldspar fractionation. The lack of geochemical overlap or coherence between any of the lava and ignimbrite groups suggests that they represent distinct eruptive events and are not related in ally simple volcanic development and cogenetic sense. Two geochemical features are common to all the volcanic rock groups: (1) the presence of a Nb-Ta anomaly, which is generally accepted as a crustal signature; and (2) the relatively low Y abundances which appear characteristic for the region as a whole. These fundamental features of the local silicic volcanism largely reflect source composition and effects. Copyright (C) 2002 John Wiley Sons, Ltd

Base surge deposits, eruption history, and depositional processes of a wet phreatomagmatic volcano in Central Anatolia (Cora Maar)

2nd International Maar Conference -- SEP 21-25, 2004 -- Lajosmizse, HUNGARYWOS: 000243607900012Cora Maar is a Quaternary volcano located to the 20 km northwest of Mount Erciyes, the largest of the 19 polygenetic volcanic complexes of the Cappadocian Volcanic Province in central Anatolia. Cora Maar is a typical example of a maar-diatreme volcano with a nearly circular crater with a mean diameter of c. 1.2 km, and a well-bedded base surge-dominated maar rim tephra sequence up to 40 m in thickness. Having a diameter/depth ratio (D/d) of 12, Cora is a relatively "mature" maar compared to recent maar craters in the world. Cora crater is excavated within the andesitic lava flows of Quaternary age. The tephra sequence is not indurated, and consists of juvenile clasts up to 70 cm, non-juvenile clasts up to 130 cm, accretionary lapilli up to 1.2 cm in diameter, and ash to lapilli-sized tephra. Base surge layers display well-developed antidune structures indicating the direction of the transport. Both progressive and regressive dune structures are present within the tephra sequence. Wavelength values increase with increasing wave height, and with large wavelength and height values. Cora tephra display similarities to Taal and Laacher See base surge deposits. Impact sags and small channel structures are also common. Lateral and vertical facies changes are observed for the dune bedded and planar bedsets. According to granulometric analyses, Cora Maar tephra samples display a bimodal distribution with a wide range of Md-phi values, characteristic for the surge deposits. Very poorly sorted, bimodal ash deposits generally vary from coarse tail to fine tail grading depending on the grain size distribution while very poorly sorted lapilli and block-rich deposits display a positive skewness due to fine tail grading. (c) 2006 Elsevier B.V. All rights reserved.Int Assoc Volcanol & Chem Earth Interior, IAVCEI, Commiss Volcanogen Sediments, Int Assoc Sedimentol, Int Comm Hungarh, Slovak Republic German

U-Pb and Ar-40-Ar-39 Geochronology and Isotopic Constraints on the Genesis of Copper-Gold-Bearing Iron Oxide Deposits in the Hasancelebi District, Eastern Turkey

The Hasancelebi deposit in eastern Turkey, with proven reserves of 95 million metric tons, is a copper-gold-bearing iron oxide deposit. It is chiefly hosted by rocks that underwent widespread sodic-calcic and potassic styles of alteration. In the Hasancelebi district, pervasive Na-Ca and K-Fe alteration types are overprinted by sericitization and by late alteration that occur in multiple, overprinting systems. The age of hydrothermal alteration and mineralization (ca. between 74-68 Ma) overlaps with the age of alkaline magmatism in the Hasancelebi district. Crystallization and cooling of alkaline magmatism is associated with hydrothermal features that spanned the duration of the district's igneous history. The Ar-40/Ar-39 and U-Pb geochronology of magmatism indicate that the hydrothermal system was synchronous with diabase and syenite and/or microsyenite porphyry intrusions and consisted of several discrete phases of Na-Ca and K-Fe alteration. The oldest alteration (phase 1) formed at ca 74.4 to 74.3 Ma; it is spatially and temporally associated with the emplacement of diabase dikes and contains scapolite and phlogopite. The next younger alteration (phase 2) formed at about 71.3 Ma and is spatially and temporally associated with syenite porphyry and microsyenite porphyry intrusions. It consists of scapolite, garnet, pyroxene, and actinolite that are superimposed on the first alteration phase. The next alteration assemblage (phase 3) formed at about 68.6 Ma and consists of phlogopite 2 and magnetite mineralization. Still later alteration (phase 4) overprints phases 1, 2, and 3 and consists of sericite-quartz, char copyrite, hematite, calcite, fluorite, and barite