Attenuation of possible peak ground acceleration (PGA) from potential sources of earthquakes in and around the city of Antakya

Deprem riski analizleri ve uzun süreli deprem tahminlerinde bulunabilmek için yapılan çalışmalar, özellikle tektonik yönden oldukça aktif olan ülkemiz için çok daha büyük bir önem taşımaktadır. Bu tür çalışmalarda öncelikle çalışma alanı içindeki deprem kaynaklarının belirlenmesi ve daha sonra bu kaynaklar üzerindeki depremselliğe ait istatistiksel çalışmaların yapılması gerekmektedir. Deprem episantrlarının dünya üzerindeki dağılımına bakıldığında, bunların genelde aktif faylar ile büyük bir uyum içerisinde olduğu gözlenmektedir. Yakın zamanda yapılan istatistik çalışmalar sonucunda, aktif fayların uzunluklarıyla, bu fayların hareketi sonucunda oluşabilecek depremlerin maksimum magnitüd değerleri arasında belirgin bir ilişki olduğu ortaya çıkarılmış ve bunun için gerekli bağıntılar geliştirilmiştir. Bu çalışmada da, öncelikle çalışma alanı olarak seçilen Antakya ve civarında deprem kaynağı olabilecek aktif faylar ve bunların uzunlukları saptanarak, oluşturabilecekleri depremlere ilişkin maksimum magnitüd değerleri belirlenmiştir. Daha sonra, çalışma alanı içerisinde oluşturulan bir ağın her bir düğüm noktası için, fayların bu noktalara olan uzaklığı ve yaratabileceği maksimum magnitüd değerleri de göz önüne alınmak sureliyle, Campbell (1981) tarafından geliştirilen azalım ilişkisi kullanılarak, oluşabilecek maksimum yer ivmesi azalımı değerleri belirlenmiştir. Son olarak elde edilen değerlerin konturlanması ile çalışma alanının eş şiddet maksimum yer ivmesi azalımı haritası hazırlanmıştır.Seismic risk analysis and long-term earthquake prediction studies are crucial for a country, such as Turkey. In these studies, it is necessary first to determine the potential sources of earthquakes, and second to perform, statistical analyses on these earthquake sources. In general, the earthquake epicenters throughout the world are associated with active faults. Recent statistical studies confirmed a relationship between the lengths of these active faults and possible maximum magnitudes of earthquakes caused by the movement of these faults, and necessary formulas for this relationship have been developed. In this study around the city of Antakya, first, the active faults as potential sources of earthquakes, their lengths and the maximum magnitudes they can create, were determined. Then, for each point in a grid laid on the study area, peak ground acceleration (PGA) values, with respect to the distances of the faults to the points in the grid and the maximum magnitudes the faults can create, were calculated using Campbell (1981)

The Eldivan ophiolite and volcanic rocks in the İzmir–Ankara–Erzincan suture zone, Northern Turkey: Geochronology, whole-rock geochemical and Nd–Sr–Pb isotope characteristics

Gabbros and dolerite dikes of the Eldivan ophiolite and basaltic volcanic rocks of the ophiolitic mélange in the central part of the İzmir–Ankara–Erzincan (IAE) suture zone were investigated for their 40Ar/39Ar age and whole-rock-major-trace element and Sr–Nd–Pb isotope compositions. Based on geological and geochemical characteristics basaltic volcanic rocks in the ophiolitic mélange are subdivided into two groups (Groups I and II) with ocean island basalts or enriched mid-ocean ridge basalt characteristics, respectively. Gabbros and dolerite dikes of the Eldivan ophiolite (Groups III and IV) have instead geochemical compositions indicative of a subduction-related environment. The volcanic rocks of Group I have 87Sr/86Sr(i) between 0.7037 and 0.7044, ƐNd(i)–DM of −4.5 to −5.6, and 206Pb/204Pb(i) ranging between 18.35 and 18.75. Group II volcanic rocks have higher 87Sr/86Sr(i) values (0.7049–0.7055), ƐNd(i)–DM ranging between −5.4 and −6.0, and 206Pb/204Pb(i) between 18.14 and 18.62. The Nd isotopic signatures and 207Pb/204Pb(i) values of the volcanic rocks of both groups point to a different source with respect to those of the Eldivan ophiolite. The low 206Pb/204Pb(i) values relative to the ophiolitic rocks seem to exclude a significant contribution from a HIMU reservoir, whereas the 207Pb/204Pb(i) values slightly above the NHRL might indicate some contribution from an EM2-type reservoir. Gabbros (Group III) of the Eldivan ophiolite and dolerite dikes (Group IV) cross-cutting the ultramafic part of the ophiolite show 87Sr/86Sr(i) between 0.7038 and 0.7053, ƐNd(i)–DM from −2 to −3.6 and 206Pb/204Pb(i) between 18.10 and 18.80. The gabbros yield ca. 150 Ma 40Ar/39Ar amphibole-plateau ages, which, together with the geochemical data, indicate that they were produced above subducted oceanic lithosphere in the IAE ocean domain in Late Jurassic times. Therefore, the Eldivan ophiolite in the IAE suture zone constitutes a link between the Hellenide–Dinaride ophiolite belts to the west and the Armenian–Iranian ophiolites to the east

Low-sulfidation type Au-Ag mineralization at Bergama, Izmir, Turkey

Bergama, the center of Bergarna County, is located in western Turkey and includes the villages of Ovacik, Narlica and Saganci. The Ovacik epitherinal gold-silver deposit is located in the Western Anatolian Volcanic and Extensional Province, adjacent to the ENE-trending Bergama graben, some 100 kin north of the city of Izmir. Gold of economic grades at the Ovacik deposit (reserves 4.19 Mt at 7.6 g/t) occurs in epithermal quartz veins which display low-temperature epithermal textures, including crustiform banding, quartz pseudomorphs after bladed calcite, and multiphase hydrothermal breccias. Alteration minerals at both Ovacik and Narlica are dominated by smectite, mixed-layer illite/smectite, chalcedonic quartz and adularia, whereas major kaolinite and minor inixed-layer smectite/illite (> 13.4 angstrom) occur at Saganci. The total sulfide content at Ovacik is low (< 2%) and is dominated by pyrite with traces of electrum, chalcopyrite, arsenopyrite, acanthite, tetrahedrite, pyrargyrite, stibmte, galena, chalcocite, bomite, covellite and sphalerite, occurring mainly within breccia clasts. Pyrite and mareasite appear to be the most common opaque minerals at Narlica and form dark sulfide-rich bands along with traces of electrum, native silver and chalcopyrite; pyrite is the only sulfide identified at Saganci. Ar-40/Ar-39 dating of adularia from gold-bearing quartz veins indicates an age of mineralization of about 18.2 +/- 0.2 Ma. Fluid inclusion studies at Ovacik reveal that main-stage quartz contains predominantly liquid-rich inclusions with homogenization temperatures (T-h) ranging from 150 to 305 degrees C, with the majority of T-h, varying between 165 to 205 degrees C: ice-melting temperatures (T-h) ranging from - 0.4 to - 1.2 degrees C (salinity < 2 wt.% NaCl equiv.) are dominant. Higher T-h, (220 to 248 degrees C) at the Narlica deposit may be attributed to the deeper level of exposure

Andean-type active margin formation in the eastern Taurides: Geochemical and geochronogical evidence from the Baskil granitoid (Elazig, SE Turkey)

WOS: 000268847200012The Southeast Anatolian Orogen resulted from collision of the Afro-Arabian and the Eurasian plates following the Cretaceous to Miocene closure of the southern Neotethyan oceanic basin. In this orogenic belt, there are number of tectonomagmatic/stratigraphic units in the Kahramanmaras-Malatya-Elazig region that are important to understand the geological evolution of southeast Anatolia during the Late Cretaceous. These are (a) metamorphic massifs (i.e. Malatya-Keban platform), (b) ophiolites (i.e. Goksun, Ispendere, Komurhan), (c) ophiolite-related metamorphics (i.e. Berit metaophiolite) and (d) granitoids (i.e. Goksun, Dogansehir and Baskil). The Baskil granitoid crops out to the northwest of Elazig and is a large magmatic body (170 km(2)) that intruded all of the above-mentioned units during Late Cretaceous time. The Baskil granitoid comprises both mafic and felsic plutonic/sub-plutonic rock associations. The felsic plutonic phase includes granite, granodiorite, tonalite and quartz monzonite whereas the felsic sub-plutonic phase is characterized by aplite, granophyre, granite porphyry and granodiorite porphyry. The granite and granodiorite contain mafic microgranular enclaves (MME). The mafic plutonic phase comprises gabbro, diorite, quartz diorite. whereas the mafic sub-plutonic phase is represented by diabase, microdiorite, quartz microdiorite, diorite porphyry, quartz diorite porphyry and dykes of orbicular gabbro dyke. Geochemically, the Baskil granitoid rocks have I-type, metaluminous-peraluminous calc-alkaline characteristics. The REE-and ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, together with biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The Ar-40/Ar-39 geochronology of the granitoid rocks yielded biotite ages of 81.9 +/- 0.7 Ma and 81.5 +/- 0.8 Ma (95% confidence level). Coexisting hornblende. and hornblende from additional samples, yielded ages ranging from 84.0 +/- 0.7 Ma to 81.5 +/- 1.1 Ma. The ophiolites are believed to have formed in a suprasubduction zone tectonic setting, whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or later-stage thrusting (similar to 90 Ma). These units were then thrust beneath the Malatya-Keban platform during the progressive closure of the southern Neotethys. This was followed by intrusion of the granitoids (85-82 Ma) along the Tauride active continental margin of the southern Neotethys. (C) 2008 Elsevier B.V. All rights reserved