Petrological and source region characteristics of ophiolitic hornblende gabbros from the Aksaray and Kayseri regions, central Anatolian crystalline complex, Turkey

Many Neo-Tethyan ophiolitic bodies are well exposed as thrust-slices in Central Anatolia and are predominantly represented by massive hornblende gabbros, most of which are cut by Supra Subduction Zone (SSZ) plagiogranites. The allochthonous gabbros are distinct from their autochthonous counterparts, with their mineralogy including both igneous hornblende, relict diopside rimmed by replacement hornblende and their chemical composition corresponding mostly to gabbro rather than diorite.The results of major and trace element analyses of forty-two samples, and REE analyses of nine samples, indicate that the hornblende gabbros are SSZ-type and formed from a wet magma by high-degree partial melting of peridotite possibly coupled with contamination by predominantly neighbouring-slab derived fluids within an intra-oceanic back-arc basin. The mafic magmas then underwent high-level fractional crystallization involving titaniferous magnetite, diopside, tschermakite and possibly olivine. Emplacement was followed by extensive ocean–floor metamorphism, which has induced crystallization (or recrystallization) of chlorite, biotite, amphiboles and mobilisation of most of the major elements such as alkali and alkali earth elements, and some LREE.     

Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey

Plagiogranites associated with the Sarikaraman ophiolite of the Central Anatolian Crystalline Complex, Turkey, closely resemble other plagiogranites from supra-subduction zone-type ophiolites of Neotethys. The ophiolite is remarkable in displaying a higher proportion of the plagiogranite suite (ca. 10% by volume) than is usually associated with such bodies. The Sarikaraman plagiogranites are represented by intrusive sheets and netvein trondhjemites largely developed at the top of the upper gabbros and as multiphase dykes within the sheeted dyke complex. The plagiogranite dykes are considered to feed extrusive silicified rhyolites associated with the basaltic lavas in the volcanic section of the ophiolite. Field relations suggest that the trondhjemites were probably generated from the roof section of a dynamic and evolving gabbroic magma chamber. Both the deep-seated trondhjemites and the volcanic rhyolites constitute the Sarikaraman plagiogranite suite. Geochemically there is complete overlap between the intrusive trondhjemites and extrusive rhyolites, which are characterised by (MORB-normalized) low HFS element contents with small negative Nb---Ta anomalies and variably enhanced LIL element abundances. Unlike other plagiogranites, however, the Sarikaraman suite is not characterized by consistently low K₂O contents; a feature that reflects the variable mobilization of the LIL elements under lower greenschist facies conditions. The REE are uniformly enriched relative to the basic components of the complex, but have similar normalized patterns exhibiting mild light REE depletion. In terms of their origin, the initial or most primitive plagiogranite melts could have been generated by either fractional crystallization (70–85% of clinopyroxene-feldspar ± amphibole) or partial melting (5–15% batch melting) of a gabbroic ‘source material’, although only the first process can produce most of the range of the plagiogranite compositions. As a group the plagiogranites exhibit some degree of internal variation which can be generated by further fractionation largely dominated by feldspar with minor apatite and amphibole.     

Evaluation of water quality parameters for the Mamasin dam in Aksaray City in the central Anatolian part of Turkey by means of artificial neural networks

Sustaining the human ecological benefits of surface water requires carefully planned strategies for reducing the cumulative risks posed by diverse human activities. The municipality of Aksaray city plays a key role in developing solutions to surface water management and protection in the central Anatolian part of Turkey. The responsibility to provide drinking water and sewage works, regulate the use of private land and protect public health provides the mandate and authority to take action. The present approach discusses the main sources of contamination and the result of direct wastewater discharges into the Melendiz and Karasu rivers, which recharge the Mamasın dam sites by the use of artificial neural network (ANN) modeling techniques. The present study illustrates the ability to predict and/or approve the output values of previously measured water quality parameters of the recharge and discharge areas at the Mamasin dam site by means of ANN techniques. Using the ANN model is appreciated in such environmental research. Here, the ANN is used for estimating if the field parameters are agreeable to the results of this model or not. The present study simulates a situation in the past by means of ANN. But in case any field measurements of some relative parameters at the outlet point “discharge area” have been missed, it could be possible to predict the approximate output values from the detailed periodical water quality parameters. Because of the high variance and the inherent non-linear relationship of the water quality parameters in time series, it is difficult to produce a reliable model with conventional modeling approaches. In this paper, the ANN modeling technique is used to establish a model for evaluating the change in electrical conductivity (EC) and dissolved oxygen (DO) values in recharge (input) and discharge (output) areas of the dam water under pollution risks. A general ANN modeling scheme is also recommended for the water parameters. The modeling process includes four main stages: (1) source data analysis, (2) system priming, (3) system fine-tuning and (4) model evaluation. Results of the ANN modeling scheme indicate that the output values are agreeable to the water quality parameters, which were measured at the field in the static water mass of the Mamasın dam lake. Water contamination at the dam site is caused by the continuous increase of nutrient contents and decrease of the O₂ level in water causing an anaerobic condition. It may stimulate algae growth flow in such water bodies, consequently reducing water quality.     

Influences of wastewater discharges on the water quality of Mamasın dam watershed in Aksaray, Central Anatolian part of Turkey

Sustaining the human ecological benefits of surface water requires carefully planned strategies for reducing the cumulative risks posed by diverse human activities. Municipal governments in Aksaray City play a key role in developing solutions to surface water management and protection problems. The responsibility to provide drinking water and sewage works, regulate the use of private land, and protect public health provides the mandate and authority to take action. A large part of Aksaray City uses Mamasın dam water as its primary source for drinking water. Several point sources of contamination may result from direct wastewater discharges from Melendiz and Karasu rivers, which recharge the Mamasın dam watershed. Relevant studies were carried out for monitoring the eutrophication process, which usually occurs in the static water mass of the Mamasın dam lake. This process may be caused by the continual increase in nutrients and decrease of O₂ levels, causing anaerobic conditions. Stimulated algae growth in these water bodies consequently reduces water quality. Hydrochemical parameters were evaluated to estimate the types of pollution sources, the level of pollution, and its environmental impacts on the Mamasın dam drinking water reservoir.     

滇西吉义独蛇绿混杂岩的岩石地球化学特征、成因和构造环境探讨

滇西吉义独蛇绿混杂岩位于金沙江缝合带的南端,岩石组合出露较齐全,包括堆晶橄榄岩、堆晶辉石岩、堆晶辉长岩以及玄武岩等,它们呈构造岩片的形式产出并与外来岩块组成蛇绿混杂岩.堆晶橄榄岩和辉石岩具低Al_2O_3,低TiO_2,而高Mg~#值(Mg~#=0.88～0.92),富集Cr和Ni,稀土总量偏低(∑REE=14.82×10~(-6)～27.75×10~(-6)),倒U型的稀土元素分布特征.堆晶辉长岩和玄武岩的Mg~#值较低,分别为0.70～0.79和0.51～0.66,具拉斑系列的演化趋势.玄武岩可以细分为2组:第一组玄武岩以平坦型稀土配分模式,低Mg~#(Mg~#=0.44～0.46),低稀土总量(∑REE=52.29×10~(-6)～60.26×10~(-6))为特征;第二组玄武岩则为LREE弱富集型的稀土配分模式,其Mg~#较高(Mg~#=0.54～0.68),稀土总量也较高(∑REE=62.13×10~(-6)～101.87×10~(-6)).在原始地幔标准化的微量元素配分图解中,两组玄武岩均相对富集大离子亲石元素而亏损Nb、Ta和Ti,与岛弧岩浆岩类似,明显不同于N-MORB.岩石的Sr-Nd同位素组成较为均一和稳定,堆晶橄榄岩和辉石岩的(~(87)Sr/~(86)Sr)_i=0.7051～0.7056,5_(Nd)(t)=2.8～4.1,玄武岩的(~(87)Sr/~(86)Sr)_i=0.7050～0.7056,ε_(Nd)(t)=5.1～5.8,且显示出原始地幔的同位素组成特征,暗示这些岩石为同源岩浆分异演化而成的岩浆产物.岩浆演化的主要方式为分离结晶作用,受地壳混染不明显.岩浆结晶形成岩石的顺序为:堆晶橄榄岩→堆晶辉石岩→堆晶辉长岩→玄武岩2组→玄武岩1组.岩石地球化学特征表明,吉义独蛇绿岩的形成与俯冲作用有关,且形成于金沙江洋内俯冲的消减环境.     

Petrological characteristics of the Damiao anorthosite complex in Hebei Province,China

The Damiao anorthosite complex occurs in the high-grade metamorphic Precambrian rocks in the axial part of the Nei Mongol (Inner Mongolia) Anticline. It is a monoclinal, layered intrusion, with distinguishable layers of anorthosite, monzonite and quartz-monzonite from bottom to top. Gradation evidence can be noticed between these layers. Accumulation structure is obvious in anorthositic rocks. In the anorthositic rocks feldspars, mainly antiperthite and plagioclase, are hosted with An 44–49, while in the acid rock facies, perthite and plagioclase are present. The complex investigated can be assigned to andesine-type rocks. Both the Damiao anorthosites and the Miyun rapakivi granites are calc-alkaline in terms of petrochemical characteristics, and the latter exhibits a very close petrochemical similarity, i.e., high in Al and K, with the acid members in the upper layers of the complex at Damiao. In view of the close temporal-spatial relationship and the resemblance of rock structure, it is thought that the two suites are resulted from a single parent magma under approximate tectonic environments, and that gravitative fractionation may have played an important role in their evolution. Calculations show that the parent magma responsible for the suites bears obvious resemblance to quartz diorite and quartz monzonite in composition, which is in agreement with the experiments by T. H. Green. The Damiao anorthosite complex is characterized by deep source and shallow emplacement as evidenced by high-pressure and high-temperature experiments, geothermometry and petrochemical features as well as the occurrence of both pigeonite and primary “Al-pyroxene”.     

The geochemistry and petrogenesis of dolerites and gabbros from the Tertiary central volcanic complex of Slieve Gullion,North East Ireland

Basaltic magmas emplaced into the root zone of the Slieve Gullion volcano have crystallised to rocks varying in texture from dolerite to gabbro. A mineralogical variation from olivine bearing to quartz bearing varieties has been recorded and with the presence of coexisting Ca-rich and Ca-poor pyroxenes, a tholeiitic assemblage is indicated.Geochemical data confirm this prognosis and a continuous spread of compositions from basalt to tholeiitic andesite are interpreted in terms of fractional crystallisation. Modelling of the fractional crystallisation processes indicate an approach to cotectic conditions with fractionation at low pressures involving olivine, plagioclase, clinopyroxene and Ti-magnetite. Primitive magma compositions, indicated by low values of D.I. and 100 Mg/Mg + Fe²⁺ (atomic)>61, show low concentrations of the large ion lithophile elements such as Rb, Ba, Zr, Y, and K. The relatively high CaO content (>11 %) of these rocks invite comparison with high-calcium low-alkali tholeiitic liquids recognised in extrusive and intrusive magmas elsewhere in the North Atlantic Tertiary volcanic province and with magmas currently erupted at active spreading ridges.In north west Britain the field and stratigraphic distribution of these high-calcium low-alkali magmas suggests that they occupy a distinct chronological niche towards the top of the Palaeocene-Eocene volcanic succession succeeding eruption of mildly alkali and transitional basalts. As such, the refractory (high CaO, MgO, etc.) and large ion lithophile depleted geochemistry can be explained either by differential partial melting in the upper mantle source region or melting of a depleted and refractory mantle source which has already contributed to basalt genesis.     

藏北羌塘中部早古生代蛇绿岩堆晶岩中斜长花岗岩的地球化学特征

桃形湖蛇绿岩是龙木错－双湖缝合带近期的重要发现。这一发现回答了龙木错－双湖缝合带中不存在完整蛇绿岩剖面的质疑,是该缝合带存在的重要证据,也是古特提斯洋早期裂解时间确定的主要依据之一。其中斜长花岗岩的岩石地球化学特征反映出洋脊花岗岩的属性,包括Al2O3含量较高,准铝质至过铝质（12.56％～16.19％）,富Na2O,贫K2O（Na2O／K2O＞3）,主量元素、微量元素和稀土元素含量较低等,但是其稀土元素配分曲线、微量元素蛛网图又与标准大洋斜长花岗岩有所区别,表现为轻重稀土元素分异很明显,具强烈的Eu正异常（Eu／Eu?鄢=1.92～9.19,均值为5.18）,初步推测原因是岩浆迅速上升过程中Ca分离不完全和样品中石榴子石分布不均匀。结合斜长花岗岩的野外产状及以往的研究成果,初步结论是：桃形湖蛇绿岩中的斜长花岗岩形成于近洋脊或准洋脊环境,岩浆源自地幔,与桃形湖蛇绿岩中的变质橄榄岩、堆晶辉长岩、基性熔岩的岩浆同源,是基性—超基性岩浆分异的残余,应属桃形湖蛇绿岩中的浅色岩组分,是蛇绿岩的端元岩石。     

藏北羌塘中部早古生代蛇绿岩堆晶岩中斜长花岗岩的地球化学特征

桃形湖蛇绿岩是龙木错－双湖缝合带近期的重要发现。这一发现回答了龙木错－双湖缝合带中不存在完整蛇绿岩剖面的质疑,是该缝合带存在的重要证据,也是古特提斯洋早期裂解时间确定的主要依据之一。其中斜长花岗岩的岩石地球化学特征反映出洋脊花岗岩的属性,包括Al2O3含量较高,准铝质至过铝质（12.56％～16.19％）,富Na2O,贫K2O（Na2O／K2O＞3）,主量元素、微量元素和稀土元素含量较低等,但是其稀土元素配分曲线、微量元素蛛网图又与标准大洋斜长花岗岩有所区别,表现为轻重稀土元素分异很明显,具强烈的Eu正异常（Eu／Eu?鄢=1.92～9.19,均值为5.18）,初步推测原因是岩浆迅速上升过程中Ca分离不完全和样品中石榴子石分布不均匀。结合斜长花岗岩的野外产状及以往的研究成果,初步结论是：桃形湖蛇绿岩中的斜长花岗岩形成于近洋脊或准洋脊环境,岩浆源自地幔,与桃形湖蛇绿岩中的变质橄榄岩、堆晶辉长岩、基性熔岩的岩浆同源,是基性—超基性岩浆分异的残余,应属桃形湖蛇绿岩中的浅色岩组分,是蛇绿岩的端元岩石。     

Geochemistry of post-collisional mafic lavas from the North Anatolian Fault zone, Northwestern Turkey

Extensive magmatic activity developed at the northwestern part of the Anatolian block and produced basaltic lavas that are situated along and between the two segments of the North Anatolian Fault zone. This region is a composite tectonic unit formed by collision of continental fragments after consumption of Neotethyan ocean floor during the late Cretaceous. Northwestern Anatolian basalts and evolved lavas exhibit both tholeiitic and calc-alkaline characteristics. Mafic lavas are moderately enriched in LILE (except depleted part of Yuvacık and İznik samples) and depleted in HFSE (but not Zr, Hf) relative to primitive mantle values, suggesting derivation from a MORB-like mantle source that is unexpected in this subduction environment. Sr and Nd isotopes are close to the mantle array and vary beyond analytical error (⁸⁷Sr/⁸⁶Sr 0.70404–0.70546, ¹⁴³Nd/¹⁴⁴Nd 0.51270–0.51289). These geochemical features may result from two possible processes: (1) melting of a MORB-like mantle source that was modified by subduction-released fluids and melts or (2) modification of mafic liquids derived from a dominantly MORB-like source by crustal or lithospheric mantle material. Geochemical characteristics of the lavas (e.g., Ba/Rb, Rb/Sr, Ba/Zr, ⁸⁷Sr/⁸⁶Sr, Sr/P) vary systematically along the fault zone from east to west, consistent with a decrease in the degree of melting from east to west or a change in the nature of the source composition itself. Thus, the difference in incompatible elements and Sr–Nd isotopic ratios seems to result from small-scale mantle heterogeneity in a post-collisional tectonic environment.     

Geochemical characteristics of ophiolitic rocks from the southern margin of the Sivas basin and their implications for the Inner Tauride Ocean,Central-Eastern Turkey

Number of dismembered ophiolite bodies crop out between Sivas and Malatya on the top of the Eastern Tauride platform in the central-eastern Turkey. One of which at the southern margin of the Sivas basin in the Tecer Mountain area comprises melange and the lower part of an oceanic lithospheric section on top of the Tauride platform. The mantle tectonites are characterized by variably serpentinized harzburgites and dunites, and are intruded by numerous isolated dykes. The gabbroic cumulates consist of olivine gabbro, gabbro and gabbronorite. The major and trace element geochemistry of the mafic cumulate rocks suggests that the primary magma was compositionally similar to those observed in modern island-arc tholeiitic sequences. The isolated dykes are exclusively basaltic in composition and display geochemically two distinct subgroups: Group I is represented by high TiO₂ (.87–1.47 wt.%) and other incompatible elements, whereas Group II is characterized by low TiO₂ (.36–.66 wt.%) and other incompatible elements. The Group I isolated diabase dykes have flat to slightly LREE-depleted profiles (La/Yb_N = .32–.79), whereas the Group II isolated diabase dykes are more depleted in general and have a LREE-depleted character (La/Yb_N = .19–.49). This suggests that the isolated dykes were derived from an island arc tholeiitic magma (Nb/Y = .02–.05) with different degrees of partial melting (Group II > Group I) and relatively high oxygen fugacity in intra-oceanic subduction zone. The ophiolitic rocks in the study area may well be compared with the Divri?i ophiolite to the southeast. All the evidence suggests that the isolated dykes in the Tecer Mountain area differ from the alkaline isolated dykes cutting the Divri?i ophiolite. Since the late stage dykes (~76 Ma) in the Divri?i area are alkaline, the tholeiitic isolated dykes in the present study should have been emplaced prior to the alkaline dykes during Late Cretaceous SSZ-spreading (~90 Ma) within the Inner Tauride Ocean.     

燕山中段常州沟组砂岩岩石学、地球化学特征及地质意义

中元古代常州沟组是华北克拉通北缘燕山地区变质结晶基底上的第一套沉积盖层,不整合覆盖于新太古代各类片麻岩之上。为了解常州沟组时期的古环境、古气候及其物质来源、构造环境和盆地性质,在野外地质调查的基础上,对常州沟组砂岩进行了粒度分析和地球化学分析测试。岩石组合、沉积构造和粒度分析结果指示区内常州沟组沉积环境演化由下至上依次为冲积扇、辫状河和碎屑潮坪。常州沟组砂岩地球化学特征具有高SiO₂、Al₂O₃和K₂O,低TiO₂、Fe₂O₃、FeO、MgO含量的特点,成熟度较高,化学蚀变指数(CIA)介于52.00～73.23之间,化学风化作用指数(CIW)范围为93.04～98.68。由于岩石遭受钾交代作用影响,结合A-CN-K图解、Th/U-Th图解和古气候判别图综合分析,认为源区可能经历了较强的风化作用,古气候温暖、潮湿。Cr/Zr、Th/Sc、Ba/Sr、Rb/Sr值和La/Th-Hf图解指示常州沟组源区属性主要为上地壳环境,原岩成分以长英...     

Early to Middle Carboniferous hornblende 40Ar/39Ar ages of amphibolites and gabbros from the Bergsträsser Odenwald

Summary Pre- to Early Variscan metamorphic rocks and intrusive calc-alkaline rocks are constituting the Odenwald accretionary complex. The predominant regional metamorphic formation of the amphibolite is postdated by the intrusion of the Frankenstein gabbro complex in the NW Odenwald at about 362 Ma. Thus indications of older metamorphic events might be preserved in the amphibolites. However, for the central and southern Odenwald zircon data revealed a thermal peak of regional metamorphism at about 336 Ma. Nine amphibole separates from two gabbroic intrusives and from seven amphibolites were dated by the K-Ar method, mainly using the ⁴⁰Ar/³⁹Ar technique. The two gabbro amphibole separates yielded ages of 335 and 329 Ma; i.e. they are about 30 Ma younger than the Frankenstein gabbro. The total argon ages of the amphibolite hornblendes are at about 359 Ma in the north and about 330 to 320 Ma in the south (early and late stages of the Early Carboniferous). The ages of the three metamorphic amphiboles from the north are in the age range of the Frankenstein gabbro intrusion, however, the four from the south slightly postdate the regional metamorphic climax. Two of the older amphibole separates of the north and two of the younger ones from the south yielded plateau ages slightly older than the total argon ages (about 358 Ma and 329 Ma, respectively). The southernmost amphibolite with a total argon age of 320 Ma shows an irregular spectrum with a maximum age step for 40% of its argon corresponding to an age of 344 Ma. It possibly has partly preserved an older argon component during the younger phase of regional metamorphism. Together with published data the results show that hornblende of amphibolites from the Odenwald offer the chance to unravel the metamorphic veil of the Mid-Carboniferous regional metamorphism.

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Zusammenfassung Früh- bis mittel-karbonische ⁴⁰ Ar/ ³⁹ Ar-Alter an Amphibolit- und Gabbro-Hornblenden des Bergstr?sser Odenwaldes Der Odenwald, als ehemaliger akkretion?rer Komplex, besteht aus pr?- bis frühvariskischen metamorphen, sowie kalk-alkalischen Intrusivgesteinen. Die Bildung der regionalmetamorphen Gesteine erfolgte vor der Intrusion des Frankenstein-Gabbro-Komplexes im NW-Odenwald um 362 Ma. Ihre Amphibol-führenden Vertreter bieten die Chance, mittels Hornblende-Datierungen nach zeitlichen Anzeichen dieser Metamorphose zu suchen. Im zentralen und südlichen Odenwald sprechen andererseits Zirkon-Daten für einen Peak der Regionalmetamorphose um ca. 336 Ma. Aus sieben Amphiboliten und zwei Gabbros der drei strukturellen Einheiten des Bergstr?sser Odenwaldes wurden neun Hornblende-Pr?parate unter strenger Beachtung m?glicher Kontaminationen und Umbildungen hergestellt und nach der K-Ar-Methode datiert, wobei sowohl konventionelle als auch ⁴⁰Ar/³⁹Ar-Technik eingesetzt wurde. Die Gabbro-Hornblenden ergaben mit 335 und 329 Ma um ca. 30 Ma jüngere Werte als die Alter des Frankenstein-Gabbros. Die Totalargon-Alter der Hornblenden aus den Amphiboliten im Norden und Süden unterscheiden sich deutlich und geh?ren mit ca. 359 Ma bzw. 330 Ma dem frühen und sp?ten Unterkarbon an. Die Alter der drei untersuchten metamorphen Hornblenden aus dem Norden fallen in den Altersbereich der Frankenstein-Intrusion. Die Alter der drei ungest?rten Hornblenden aus dem Süden sind etwas jünger als der Zeitraum der sp?ten Regionalmetamorphose. Zwei Hornblenden aus dem Norden und zwei aus dem Süden zeigen Plateau-Alter, die geringfügig über den Totalargon-Altern liegen (ca. 358 und 329 Ma). Die südlichste Probe mit einem Total-Argonalter von 320 Ma hat ein irregul?res Spektrum mit einem Altersmaximum (für ca. 40% des Argons) bei 344 Ma. M?glicherweise rührt es von einer Hornblendekomponente her, welche durch die sp?tere Regionalmetamorphose nicht verjüngt worden ist. Zusammen mit wenigen Literaturdaten best?tigen die gewonnenen Hornblende-Daten aus dem Norden, da? Hornblenden aus Amphiboliten potentiell geeignet sind, Ereignisse vor der mittelkarbonen Metamorphose- und Intrusionsphase isotopisch zu datieren.

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Received August 5, 1999; revised version accepted August 7, 2000     

New field and seismic data about the intraplate strike-slip deformation in Van region,East Anatolian plateau,E. Turkey

The study area is the Van earthquake region. It is located in the western section of the East Anatolian–Iranian plateau outside and to the east of the Karlıova triple junction. Based on the tectonic periods, the rock units exposed in the study area are classified into two common categories. These are the Pre-Late Pliocene paleotectonic units and the Plio-Quaternary neotectonic units. The Paleotectonic units are composed of the Yüksekova Complex of Campanian–Maastrichtian age and the Kırkgeçit Formation of Oligo-Miocene age. The paleotectonic units are intensely deformed (folded, thrust to reverse faulted and converted into an imbricate stack). The neotectonic units are composed of fluvio-lacustrine sedimentary facies with volcanic interclations. It is full of soft-sedimentary structures such as deltaic structure, slump fold, sand dikes to sills and normal to reverse types of growth faults which imply to a sedimentation accompanied by both a volcanic activity and active tectonics. Originally the Paleotectonic units are overlain with an angular unconformity by the nearly flat-lying neotectonic units. This angular unconformity and the big difference in the deformational patterns of both categories of rock units indicate an inversion in tectonic regime in Late Pliocene. The new tectonic regime is the strike-slip faulting-dominated neotectonic regime. It is governed by an approximately N–S-directed compression, and composed of NW- to NE-trending strike-slip faults, N–S trending oblique-slip normal faults to fissures and the E–W trending thrust to reverse faults. Most of thrust to reverse faults are inherited from the Pre-Late Pliocene paleotectonic regime. Some of them have reactivated and led to the occurrence of large and devastative earthquakes. The last devastative seismic event is the 23 October 2011 Tabanlı (Van) earthquake of Mw = 7.2 that caused 644 deaths and moderate to heavy damage of ¼ of structures (28,532) in Van earthquake region. The source of the Tabanlı earthquake is the Everek erosional reverse fault. In addition the Tabanlı earthquake is the largest seismic event occurred till now in Turkey. It was followed by a series (over 6000) of small-sized aftershocks and severeal moderate-sized indepentent earthquakes of reverse, normal and strike-slip faulting origin. Both the field and new seismic data strongly reveal that the prominent tectonic regime in the East Anatolian plateau is the strike-slip neotectonic regime, not the tensional tectonic regime as has been reported in some previous works. The strike-slip faulting and related deformation are confined into the upper shallowing part (up to 40 km) of the crust, whilst the extensional deformations are the subcrustal processes and being taking place in a squashy zone at the depths of approximately 40–60 km.     

吉林中部敖花村角闪辉长岩锆石U-Pb定年、Hf同位素和岩石地球化学特征

古太平洋板块的俯冲在欧亚大陆东缘的区域构造演化中发挥了重要作用,但其发生的时间尚不清楚。本文报道了吉林中部新发现的敖花村角闪辉长岩的锆石U-Pb年龄、Hf同位素组成和岩石地球化学数据。锆石U-Pb定年显示,角闪辉长岩形成于早侏罗世(180.3±2.3 Ma),锆石εHf(t)值高且均一(9.6～11.3)。岩石地球化学分析显示样品低Si和Al,高Fe、Mg和Ca,富集轻稀土和大离子亲石元素(如Rb、Ba、U、K和Sr),亏损重稀土和高场强元素(如Nb、Ta和Ti),具有弱Eu负异常(δEu=0.67～0.98)。岩石起源于板片流体交代的亏损岩石圈地幔,形成过程中分离结晶、地壳混染和堆晶作用不明显。结合东北地区东段早中生代火成岩组合及时空分布,认为古太平洋板块向欧亚大陆下的俯冲开始于早侏罗世,敖花村角闪辉长岩形成于与古太平洋俯冲密切相关的弧后环境。     

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

The course of the active North Anatolian Fault system from Lake Abant to Lake Sapanca was traced by its high micro-earthquake activity. If approaching from the east this section includes a broad south to north overstep (fault offset) of the main fault. Local seismicity has been recorded in this area by a semi-permanent network of 8 stations since 1985 within the frame of the Turkish–German Joint Project for Earthquake Research. The effect of the overstep and its complex fracture kinematics are reflected by the seismicity distribution, the variations of composite fault-plane solutions, and by the spatial coda-Q distribution. Areas of different stress orientation can be distinguished and assigned to different groups of faults. The stresses and the tectonic pattern only in part correspond to a simple model of an extensional overstep and its correlative pull-apart basin. Other types of deformation involved are characterized by normal faulting on faults parallel to the general course of the main strike-slip fault and by synthetic strike-slip faults oriented similar to Riedel shears. Shear deformation by this fault group widely distributed in an area north and east of the main fault line may play an important role in the evolution of the overstep. The development of a pull-apart basin is inhibited along the eastern half of the overstep and compatibility of both strands of the main fault (Bolu–Lake Abant and Lake Sapanca– Izmit–Marmara Sea) seems to be achieved with the aid of the fault systems mentioned. The extension of the missing part of the pull-apart basin seems to be displaced to positions remote from the Lake Abant–Lake Sapanca main fault line, i.e. to the Akyaz?–Düzce basin tract. Highest Q-values (lowest attenuation of seismic waves) were found in the zone of highest seismicity north and west of the overstep which is the zone of strongest horizontal tension. If high coda-Q is an indicator for strong scattering of seismic waves it might be related to extensional opening of fractures.     

New evidence and solution to the Maden complex controversy of the Southeast Anatolian orogenic belt (Turkey)

The volcanosedimentary units of Late Mesozoic-Tertiary age that outcrop in the Southeast Anatolian orogenic belt are commonly referred to as the Maden complex. There is a long-lasting controversy over its definition, age, stratigraphic and structural position, and the origin, and thus, the orogenic evolution. To solve this problem, large strips across the Southeast Anatolian orogenic belt have been studied extensively, and different rock groups which were regarded previously as the Maden unit have been differentiated. Their major characteristics and differences have been identified. The Maden unit sensu stricto is here redefined as a volcanosedimentary succession of Middle Eocene age representing a short-lived back-arc basin which reached the stage of an embryonic ocean. Presently, the Maden group occurs mainly within the lower nappe stack of the nappe zone of the Southeast Anatolian orogen. It rests stratigraphically on an amalgamated nappe package consisting of the different metamorphic tectonic units and, in turn, is overlain tectonically by the upper nappe units.