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Extensional Regime (extensional + regime)
Selected AbstractsEvidence for two episodes of volcanism in the Bigadiç borate basin and tectonic implications for western TurkeyGEOLOGICAL JOURNAL, Issue 5 2005Fuat Erkül Abstract Western Turkey has been dominated by N,S extension since the Early Miocene. The timing and cause of this N,S extension and related basin formation have been the subject of much debate, but new data from the Bigadiç borate basin provide insights that may solve this controversy. The basin is located in the Bornova Flysch Zone, which is thought to have formed as a major NE-trending transform zone during Late Cretaceous-Palaeocene collisional Tethyan orogenesis and later reactivated as a transfer zone of weakness, and which separates two orogenic domains having different structural evolutions. Volcanism in the Bigadiç area is characterized by two rock units that are separated by an angular unconformity. These are: (1) the Kocaiskan volcanites that gives K/Ar ages of 23,Ma, and (2) the Bigadiç volcano-sedimentary succession that yields ages of 20.6 to 17.8,Ma. Both units are unconformably overlain by Upper Miocene-Pliocene continental deposits. The Kocaiskan volcanites are related to the first episode of volcanic activity and comprise thick volcanogenic sedimentary rocks derived from subaerial andesitic intrusions, domes, lava flows and pyroclastic rocks. The second episode of volcanic activity, represented by basaltic to rhyolitic lavas and pyroclastic rocks, accompanied lacustrine,evaporitic sedimentation. Dacitic to rhyolitic volcanic rocks, called the S,nd,rg, volcanites, comprise NE-trending intrusions producing lava flows, ignimbrites, ash-fall deposits and associated volcanogenic sedimentary rocks. Other NE-trending olivine basaltic (Gölcük basalt) and trachyandesitic (Kay,rlar volcanites) intrusions and lava flows were synchronously emplaced into the lacustrine sediments. The intrusions typically display peperitic rocks along their contacts with the sedimentary rocks. It is important to note that the Gölcük basalt described here is the first recorded Early Miocene alkali basalt in western Turkey. The oldest volcanic episode occurred in the NE-trending zone when the region was still experiencing N,S compression. The angular unconformity between the two volcanic episodes marks an abrupt transition from N,S collision-related convergence to N,S extension related to retreat of the Aegean subduction zone to the south along an extensional detachment. Thrust faults with top-to-the-north sense of shear and a series of anticlines and synclines with subvertical NE-striking axial planes observed in the Bigadiç volcano-sedimentary succession suggest that NW,SE compression was reactivated following sedimentation. Geochemical data from the Bigadiç area also support the validity of the extensional regime, which was characterized by a bimodal volcanism related to extrusion of coeval alkaline and calc-alkaline volcanic rocks during the second volcanic episode. The formation of alkaline volcanic rocks dated as 19.7,±,0.4,Ma can be related directly to the onset of the N,S extensional regime in western Turkey. Copyright © 2005 John Wiley & Sons, Ltd. [source] Insights into biaxial extensional tectonics: an examplefrom the Sand,kl, Graben, West Anatolia, TurkeyGEOLOGICAL JOURNAL, Issue 1 2003Mustafa Cihan Abstract West Anatolia, together with the Aegean Sea and the easternmost part of Europe, is one of the best examples of continental extensional tectonics. It is a complex area bounded by the Aegean,Cyprus Arc to the south and the North Anatolian Fault Zone (NAFZ) to the north. Within this complex and enigmatic framework, the Sand,kl, Graben (10,km wide, 30,km long) has formed at the eastern continuation of the Western Anatolian extensional province at the north-northwestward edge of the Isparta Angle. Recent studies have suggested that the horst,graben structures in West Anatolia formed in two distinct extensional phases. According to this model the first phase of extension commenced in the Early,Middle Miocene and the last, which is accepted as the onset of neotectonic regime, in Early Pliocene. However, it is controversial whether two-phase extension was separated by a short period of erosion or compression during Late Miocene,Early Pliocene. Both field observations and kinematic analysis imply that the Sand,kl, Graben has existed since the Late Pliocene, with biaxial extension on its margins which does not necessarily indicate rotation of regional stress distribution in time. Although the graben formed later in the neotectonic period, the commencement of extension in the area could be Early Pliocene (c. 5,Ma) following a severe but short time of erosion at the end of Late Miocene. The onset of the extensional regime might be due to the initiation of westward motion of Anatolian Platelet along the NAFZ that could be triggered by the higher rate of subduction at the east Aegean,Cyprus Arc in the south of the Aegean Sea. Copyright © 2003 John Wiley & Sons, Ltd. [source] Palaeomagnetic evidence for the Gondwanian origin of the Taurides and rotation of the Isparta Angle, southern TurkeyGEOLOGICAL JOURNAL, Issue 4 2002John D. A. Piper Abstract The Taurides, the southernmost of the three major tectonic domains that constitute present-day Turkey, were emplaced following consumption of the Tethyan Ocean in Late Mesozoic to mid-Tertiary times. They are generally assigned an origin at the northern perimeter of Gondwana. To refine palaeogeographic control we have investigated the palaeomagnetism of a range of Jurassic rocks. Forty-nine samples of Upper Jurassic limestones preserve a dual polarity remanence (D/I=303/,9°, ,95=6°) interpreted as a primary magnetization acquired close to the equator and rotated during emplacement of the Taurides. Result from mid-Jurassic dolerites confirm a low palaeolatitude for the Tauride Platform during Jurassic times at the Afro,Arabian sector of Gondwana. Approximately 4000,km of Tethyan closure subsequently occurred between Late Jurassic and Eocene times. Although related Upper Jurassic limestones and Liassic redbeds preserve a sporadic record of similar remanence, the dominant signature in these latter rocks is an overprint of probable mid-Miocene age, probably acquired during a single polarity chron and imparted by migration of a fluid front during nappe loading. This is now rotated consistently anticlockwise by c. 30° and conforms to results of previous studies recording bulk Neogene rotation of the Isparta region following Lycian nappe emplacement. The regional distribution of this overprint implies that the Isparta Angle (IA) has been subject to only small additional closure (<10°) since Late Miocene time. A smaller amount (c. 6°) of clockwise rotation within the IA since Early Pliocene times is associated with an ongoing extensional regime and reflects an expanding curvature of the Tauride arc produced by southwestward extrusion of the Anatolian collage as a result of continuing northward motion of Afro,Arabia. Copyright © 2002 John Wiley & Sons, Ltd. [source] Tectonic and environmental evolution of Quaternary intramontane basins in Southern Apennines (Italy): insights from palaeomagnetic and rock magnetic investigationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010M. Porreca SUMMARY Southern Apennines is characterized by active extensional tectonics with NE,SW stretching direction. The seismicity of the region is very well understood and continuously monitored. In contrast, the onset of extensional tectonics is chronologically poorly constrained. The aim of this study is that to give important constraints on the development of extensional regime and the onset of the continental deposition during Quaternary in Southern Apennines. We report the results of palaeomagnetic and rock magnetic analyses from four Quaternary small intramontane basins in the Picentini Mountains (Southern Apennines). The sedimentary sequences are located at different altitudes, from 600 to 1200 m a.s.l., and were deposited in fluvial-lacustrine environments. We sampled 29 sites in clays and lacustrine limestones from Tizzano, Piano del Gaudo and Acerno basins and in red palaeosoils and matrix-supported conglomerates from the Iumaiano basins. In the clay and limestones samples magnetite, titano-magnetite, hematite and iron-sulphide have been recognized as the main magnetic carriers, whereas magnetite and hematite characterize the Iumaiano conglomerates and red soils. Palaeomagnetic results have been integrated with published radiometric data in order to constrain the age of each sedimentary basins. Sites from the Iumaiano basin, which represents the substrate of the Tizzano and Piano del Gaudo basins, show a reverse polarity and therefore have been attributed to the lower Matuyama chron. In contrast, palaeomagnetic data from Tizzano basin show a transition from reversed to normal polarity along the exposed section, which has been interpreted as the Matuyama/Brunhes transition. Sites from Acerno and Piano del Gaudo basins show a normal polarity, which, according to radiometric and pollen data, have been correlated to the Brunhes epoch. On the base of such results we discuss the tectono-stratigraphic evolution of the basins and the role of extensional tectonics in this portion of the Southern Apennine during the Quaternary. [source] Analyses of the stress field in southeastern France from earthquake focal mechanismsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Emmanuel Baroux Summary Owing to the apparent deformation field heterogeneity, the stress regimes around the Provence block, from the fronts of the Massif Central and Alpine range up to the Ligurian Sea, have not been well defined. To improve the understanding of the SE France stress field, we determine new earthquake focal mechanisms and compute the present-day stress states by inversion of the 89 available focal mechanisms around the Provence domain, including 17 new ones calculated in the current study. This study provides evidence of six distinct deformation domains around the Provence block, with different tectonic regimes. On a regional scale, we identify three zones characterized by significantly different stress regimes: a western one affected by an extensional stress (normal faulting) regime; a southeastern one characterized by a compressional stress (reverse to strike-slip faulting) regime with NNW- to WNW-trending ,1; and a northeastern one, namely the Digne nappe front, marked by a NE-trending compression. Note that the Digne nappe back domain is controlled by an extensional regime that is deforming the western Alpine core. This extensional regime could be a response to buoyancy forces related to the Alpine high topography. The stress regimes in the southeast of the Argentera Massif and around the Durance fault are consistent with a coherent NNW-trending ,1, implying a left-lateral component of the active reverse oblique slip of the Moyenne Durance Fault. In the Rhone Valley, an E-trending extension characterizes the tectonic regime, implying a normal component of the present-day N,^mes fault displacement. This study provides evidence for short-scale variation of the stress states, which arises from abrupt changes in the boundary force influences on upper crustal fragments (blocks). These spatial stress changes around the Provence block result from the coeval influence of forces applied at both its extremities, namely in the northeast the Alpine front push, and in the southeast the northward African plate drift. In addition to these boundary forces, the mantle plume under the Massif Central influences the western block boundary. [source] The tectonic regime along the Andes: Present-day and Mesozoic regimesGEOLOGICAL JOURNAL, Issue 1 2010Victor A. Ramos Abstract The analyses of the main parameters controlling the present Chile-type and Marianas-type tectonic settings developed along the eastern Pacific region show four different tectonic regimes: (1) a nearly neutral regime in the Oregon subduction zone; (2) major extensional regimes as the Nicaragua subduction zone developed in continental crust; (3) a Marianas setting in the Sandwich subduction zone with ocean floored back-arc basin with a unique west-dipping subduction zone and (4) the classic and dominant Chile-type under compression. The magmatic, structural and sedimentary behaviours of these four settings are discussed to understand the past tectonic regimes in the Mesozoic Andes based on their present geological and tectonic characteristics. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate relative to the hotspot frame and the consequent trench roll-back velocity are the first order parameters that control the deformation. Locally, the influences of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, have secondary roles. Ridge collisions of seismic and seismic oceanic ridges as well as fracture zone collisions have also a local outcome, and may produce an increase in coupling that reinforces compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than the absolute motion relative to the Pacific hotspot frame, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland. Copyright © 2009 John Wiley & Sons, Ltd. [source] Transition from arc- to post-collision extensional setting revealed by K,Ar dating and petrology: an example from the granitoids of the Eastern Pontide Igneous Terrane, Arakl,-Trabzon, NE TurkeyGEOLOGICAL JOURNAL, Issue 4 2005Sabah Yilmaz- Abstract The Eastern Pontide Igneous Terrane (EPIT) includes several Cretaceous to Neogene intrusive rocks, ranging in composition from low-K tholeiitic gabbros through calc-alkaline and high-K calc-alkaline metaluminous granitoids or peraluminous leucogranites to alkaline syenites. Such high diversity in age and composition is also accompanied by a broad spectrum in terms of geodynamics,i.e. from arc through syn-collisional thickening to post-collisional extensional regimes. Shallow-seated porphyritic acidic to intermediate rocks are from oldest to youngest, on the basis of field relations, the Gündo,du altered microgranite, the Bo,al, K-feldspar-megacrystic monzogranite and the Uzuntarla porphyritic granodiorite. These rocks, exposed in the southern part of the Arakl, region, east of Trabzon, Turkey, were studied in terms of their mineralogy and petrography, whole-rock geochemistry and hornblende K,Ar dating. The mineralogical and geochemical data reveal an apparent diversity in incompatible-element enrichment and depletion, for the Bo,al, unit and Uzuntarla unit, respectively. The Bo,al, and Uzuntarla units yield hornblende K,Ar ages ranging from 75.7,±,1.55 to 61.4,±,1.47,Ma and from 42.4,±,0.87 to 41.2,±,0.89,Ma, respectively. The diversity in both mineralogy,geochemistry and hornblende K,Ar ages suggests that the Bo,al, and Uzuntarla units are parts of the Cretaceous arc and Eocene post-collision extensional-related igneous activity, respectively, in the EPIT of northern Turkey. Copyright © 2005 John Wiley & Sons, Ltd. [source] Jurassic depositional records and sandstone provenances in Hefei Basin, central China: Implication for Dabie orogenesisISLAND ARC, Issue 2 2004Zhong Li Abstract Detrital composition and major element geochemistry of Jurassic sandstones in the south Hefei Basin, central China, show their provenance to be the Dabie Mountains, whose tectonic attributes are closely related to continent,island arc complexes. It was found that a provenance change, from recycled orogen signatures and mixed orogenic sandstones to arc orogen, occurs from the lower Middle Jurassic to the Upper Jurassic (the Zhougongshan Formation). Dissected magmatic arc sources were gradually exposed in the Dabie Mountains due to intensive exhumation during the Late Jurassic, particularly after the Fenghuangtai depositional phase. Furthermore, it can be infered that the magmatic arc was initially present in both the Early Paleozoic and the Triassic, according to isotopic dating studies in previously published reports. ,13C,,18O tracing between existing marbles of different strata in the Dabie block and marble gravels of the Fenghuangtai Formation in the Hefei Basin indicate that partial lithostratigraphic units for the Jurassic provenances have entirely disappeared from the Dabie block; therefore, it is impossible to reconstruct integral orogenic processes from studies on the remaining Dabie block alone. These findings, together with basin-fill sequences, also suggest that the Hefei Basin was mainly subjected to compressive mechanical regimes rather than extensional regimes in the Jurassic, which resulted in reverse-grading clastic depositional sequences, and is probably related to the northward intracontinental deep subduction of the Yangtze Plate. Regional exhumation properties and a tectonic model of the Late Mesozoic Dabie orogenesis are discussed in this paper. [source] | ||||||||||