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Arc volcanism across Iran is dominated by a Paleogene pulse, despite protracted and presumably continuous subduction along the northern margin of the Neotethyan ocean for most of Mesozoic and Cenozoic time. New U‐Pb and 40Ar/39Ar data from volcanic arcs in central and northern Iran constrain the duration of the pulse to ∼17 Myr, roughly 10% of the total duration of arc magmatism. Late Paleocene‐Eocene volcanic rocks erupted during this flare‐up have major and trace element characteristics that are typical of continental arc magmatism, whereas the chemical composition of limited Oligocene basalts in the Urumieh‐Dokhtar belt and the Alborz Mountains which were erupted after the flare‐up ended are more consistent with derivation from the asthenosphere. Together with the recent recognition of Eocene metamorphic core complexes in central and east central Iran, stratigraphic evidence of Eocene subsidence, and descriptions of Paleogene normal faulting, these geochemical and geochronological data suggest that the late Paleocene‐Eocene magmatic flare‐up was extension related. We propose a tectonic model that attributes the flare‐up to decompression melting of lithospheric mantle hydrated by slab‐derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. We suggest that Paleogene magmatism and extension was driven by an episode of slab retreat or slab rollback following a Cretaceous period of flat slab subduction, analogous to the Laramide and post‐Laramide evolution of the western United States. Key Points Iranian arc volcanism is dominated by a Paleogene flare‐up The volcanic flare‐up overlaps in time with a phase of extensional tectonism The extensional flare‐up is ascribed to Neotethyan slab rollback

The Doruneh Fault System is one of the major transcurrent faults in central Asia, extending ~900 km from western Afghanistan into West-Central Iran. The left-lateral Doruneh Fault System is also a key structure in the Arabia–Eurasia collisional zone, bounding the northern margin of the independent Central Iranian Microplate. The Doruneh Fault System exhibits a curved geometry, and is divided here into three segments: Eastern, Central and Western. We present the results of geological, structural and geomorphic studies into the nature of recent activity along the Doruneh Fault System segments. A surprising observation is that small, relatively young drainage systems often show recent systematic left-lateral displacement across the fault, whereas large rivers indicate a former more complex right-lateral history. Furthermore, the existence of right-lateral offsets of pre-Pliocene rocks and S-C fabrics confirm this earlier phase of right-lateral movement on the fault. We suggest that the early right-lateral kinematics resulted from an earlier NW–SE-directed regional shortening, associated with the anticlockwise rotation of the Central Iranian Microplate. The shortening is characterized by the NE–SW-striking en échelon folds within the fault slivers, the right-lateral Taknar imbricate fan and the superimposed folding exposed north of Kashmar. Thus, assuming an initiation age of Eocene (55.8 Ma) for the fault, we estimate a former right-lateral slip rate of about 5.2–5.5 mm yr−1, which accompanied the 35° anticlockwise rotation of the Central Iranian Microplate. According to our study, the youngest units exhibiting right-lateral displacement are Middle Miocene in age, suggesting a post-Middle Miocene timing for the onset of slip-sense inversion.

Mantle convection helps create continental plateaux. Seismic imaging of the mantle beneath the Canadian Cordillera—an ancient plateau—suggests the plateau formed when upwelling mantle caused a block of lithosphere to detach. Continental plateaux, such as the Tibetan Plateau in Asia and the Altiplano–Puna Plateau in South America, are thought to form partly because upwelling, hot asthenospheric mantle replaces some of the denser, lower lithosphere 1 , 2 , 3 , 4 , making the region more buoyant. The spatial and temporal scales of this process are debated, with proposed mechanisms ranging from delamination of fragments to that of the entire lithosphere 1 , 2 , 3 , 4 . The Canadian Cordillera is an exhumed ancient plateau that abuts the North American Craton 5 . The region experienced rapid uplift during the mid-to-late Eocene, followed by voluminous magmatism 6 , a transition from a compressional to extensional tectonic regime 7 and removal of mafic lower crust 8 . Here we use Rayleigh-wave tomographic and thermochronological data to show that these features can be explained by delamination of the entire lithosphere beneath the Canadian Cordillera. We show that the transition from the North American Craton to the plateau is marked by an abrupt reduction in lithospheric thickness by more than 150 km and that asthenosphere directly underlies the crust beneath the plateau region. We identify a 250-km-wide seismic anomaly about 150–250 km beneath the plateau that we interpret as a block of intact, delaminated lithosphere. We suggest that mantle material upwelling along the sharp craton edge 9 triggered large-scale delamination of the lithosphere about 55 million years ago, and caused the plateau to uplift.

Background, aim, and scope The rapid growth of the world's population over the past few decades has led to a concentration of people, buildings, and infrastructure in urban areas. The tendency of urban areas to develop in sedimentary valleys has increased their vulnerability to earthquakes due to the presence of soft soil and sediment. Several earthquakes have clearly demonstrated that local soil and sediment conditions can have a significant influence on earthquake-induced ground motion and damage pattern, respectively. Many studies confirm the relationship between site effect and ground motion (Borcherdt in Bull Seismol Soc Am 60:29-61, 1970; Bouckovalas et al. in Geotech Geolog Eng (Historical Archive) 14(2):111-128, 1996; Fäh et al. in Seismology 1:87-10, 1997; Atakan et al. in Nat Hazards 15(2-3):139-164, 1997; Christaras et al. in Geodynamics 26(2-4):393-411, 1998; Raptakis et al. in Bull Earthquake Eng 2(3):285-301, 2004a; Raptakis et al. in Soil Dyn Earthq Eng 25:871-887, 2005; Marka et al. in Pure Appl Geophys 158:2349-2367, 2001; Marka et al. in Soil Dyn Earthq Eng 25(4):303-315, 2005; Importa et al. in Seismology 9(2):191-210, 2005; Tyagunov et al. in Nat Hazards 38:199-214, 2006; Lombardo et al. in Nat Hazards 38:339-354, 2006; Rayhani et al. in Geotech Geol Eng 21(1):91-100, 2008). In order to classify the suitability of the soil and subsurface sediment units for urban planning and compare their mechanical behavior with the non-uniform damage observed in the 2003 earthquake, we performed some geotechnical and geophysical analyses of soil and sediment samples collected from different locations in Bam City. Methodology Geophysical and geotechnical properties, such as grain size distribution, sorting, plasticity, Poison's ratio, shear strength, compression index, permeability, and P and S wave velocities in soil and subsurface sediments, were measured. Maps (in GIS environment) and cross-sections were prepared for the study area. Results According to our observations, a great number of buildings were damaged in areas of the city where silty and clayey soils dominate, presenting very low permeability, low wave velocity together with high plasticity, and compressibility. In the study area, we recognized eight sediment types. Shear wave propagation velocities allowed for the identification of four seismic layers referred to as the surface layer, second layer, and third layer and seismic bedrock. We found that the damages observed in the Bam area were related to the physical and mechanical properties of the soil and subsurface sediment units. We also found that the soil thickness that was estimated by geophysical surveying shows a direct relationship with damage rate observations. Furthermore, we observed that landslide and qanat collapses have occurred in some areas where sand and silty sand soils and subsurface sediments dominate. Discussion The distribution of the damage shows a microzonation that is very serious in some points in the city along the main fault, especially where it is located on thick, fine, medium, and loose soil and sediments. In general, there is a discernable west to east increase in the damage across the city. The average level of destruction for the entire city was ~75%, while the eastern part of the city locally reached 100% destruction level. The major factors that influenced the damage and destruction in the Bam region were the distance of a given site from the seismic source, the quality of foundation soil and subsurface sediment, and the type of building. The Bam earthquake occurred on a single fault network comprising the Bam and Arg-e-Bam faults (Funning et al. in J Geophys Res 100(B09406):1-23, 2005). The sediments and soil of the area (unconsolidated silty sand and sandy gravel) belong to braided fluvial and alluvial facies. Most of the buildings near the epicenter area were old and constructed of mud bricks using mud cement. Recommendations and perspectives A combined sedimentological, geological, neotectonic, geotechnical, paleoseismological, and geophysical investigation in urban areas (especially in alluvial valleys) will give the detailed knowledge of the subsurface structure required for the accurate and precise seismic hazard assessments needed for effective earthquake protection planning. This paper shows that for the Bam situation, sedimentological data are required to provide an interpretive context for the geophysical data.

Paleozoic and Mesozoic tectonic reconstructions of the Arctic regions have been a subject of debate in recent years. The Permian emergence of a landmass north of the Sverdrup Basin in the Canadian Arctic led to the shedding of northerly derived detritus, an event that followed volcanism and basin inversion pulses that began in the late Pennsylvanian. However, the mechanisms for these events and the Paleozoic to Mesozoic paleogeography of this region remain controversial. New detrital zircon U-Pb geochronology results from Permian to Lower Triassic strata from northern Axel Heiberg and Ellesmere islands constrain the magmatic events within this northern landmass and its implications for the tectonic regime of the Sverdrup Basin and adjacent domains. Permian to lowermost Triassic strata along the northern margin of the Sverdrup Basin contain zircons derived from Silurian to Devonian rocks (420-350 Ma), Timanian-aged basement (700-500 Ma), and a Permian syndepositional source (300-250 Ma). Coeval strata in the southern margin are dominated by zircons formed during the Taconic, Scandian, and post-Scandian phases of the Appalachian and Caledonian orogenies, respectively (480-400 Ma). The detrital zircon signatures of the analyzed strata on the northern margin of the Sverdrup Basin record continuous magmatism within the northern landmass from latest Carboniferous (ca. 300 Ma) to at least earliest Triassic (ca. 250 Ma) time. These results are indicative of ongoing subduction and development of a magmatic arc off the northern margin of Laurentia, with the Sverdrup Basin potentially located in the backarc region of a proto-Pacific convergent margin involving parts of Arctic Alaska, Chukotka, and the Chukchi Shelf. The hypothesized onset of subduction in latest Carboniferous time and closure of this backarc basin in the latest Permian to earliest Triassic provides an explanation for the shift in stress regimes in the Sverdrup Basin that led to basin inversion and volcanism episodes. Therefore, the data presented here supports a backarc to retroarc setting for the Sverdrup Basin and the possibility of a convergent margin regime for the northern edge of Laurentia during the late Paleozoic to Triassic, contrasting with the generally accepted rift and passive margin settings.

The Satah Mountain and Baldface Mountain volcanic fields (SMVF, BMVF) comprise more than three dozen small volcanic centers and erosional remnants thereof. These fields are located in the Chilcotin Highland of west-central British Columbia, Canada, and are spatially associated with the Anahim Volcanic Belt (AVB), a linear feature of alkaline to peralkaline plutonic and volcanic centers of Miocene to Holocene ages. The AVB has been postulated to be the track of a hot spot passing beneath the westward moving Cordilleran lithosphere. We test the AVB hot spot model by applying whole-rock 40 Ar/ 39 Ar geochronology ( n  = 24) and geochemistry. Whole-rock chemical compositions of volcanic rock samples ( n  = 59) from these two fields suggest a strong geochemical affinity with the nearby Itcha Range shield volcano; however, SMVF and BMVF centers are mostly small in volume (<1 km 3 ) and differ in composition from one another, even where they are in close spatial proximity. Trace element and REE patterns of mafic AVB lavas are similar to ocean island basalts (OIB), suggesting a mantle source for these lavas. The age ranges for the SMVF ( n  = 11; ~2.21 to ~1.43 Ma) and BMVF ( n  = 7; ~3.91 to ~0.91 Ma) are largely coeval with the Itcha Range. The distribution of volcanoes in these two volcanic fields is potentially consistent with the postulated AVB hot spot track. Eruption rates in the SMVF were high enough to build an elongated ridge that deviates from the E-W trend of the AVB by almost 90°. This deviation might reflect the mechanisms and processes facilitating magma generation and ascent through the lithosphere in this tectonically complex region and may also indicate interaction of the potential hot spot with (pre)existing fracture systems in vicinity of the Itcha Range.

The rapid growth of the world's population over the past few decades has led to a concentration of people, buildings, and infrastructure in urban areas. The tendency of urban areas to develop in sedimentary valleys has increased their vulnerability to earthquakes due to the presence of soft soil and sediment. Several earthquakes have clearly demonstrated that local soil and sediment conditions can have a significant influence on earthquake- induced ground motion and damage pattern, respectively. Many studies confirm the relationship between site effect and ground motion (Borcherdt in Bull Seismol Soc Am 60:29-61, 197 Bouckovalas et al. in Geotech Geolog Eng (Historical Archive) 14(2):111-128, 199 Faeh et al. in Seismology 1:87-10, 199 Atakan et al. in Nat Hazards 15(2-3):139-164, 199 Christaras et al. in Geodynamics 26(2-4):393-411, 199 Raptakis et al. in Bull Earthquake Eng 2(3):285-301, 2004a; Raptakis et al. in Soil Dyn Earthq Eng 25:871-887, 200 Marka et al. in Pure Appl Geophys 158:2349-2367, 200 Marka et al. in Soil Dyn Earthq Eng 25(4):303-315, 200 Importa et al. in Seismology 9(2):191-210, 200 Tyagunov et al. in Nat Hazards 38:199-214, 200 Lombardo et al. in Nat Hazards 38:339-354, 200 Rayhani et al. in Geotech Geol Eng 21(1):91-100, 2008). In order to classify the suitability of the soil and subsurface sediment units for urban planning and compare their mechanical behavior with the non-uniform damage observed in the 2003 earthquake, we performed some geotechnical and geophysical analyses of soil and sediment samples collected from different locations in Bam City. Methodology Geophysical and geotechnical properties, such as grain size distribution, sorting, plasticity, Poison's ratio, shear strength, compression index, permeability, and P and S wave velocities in soil and subsurface sediments, were measured. Maps (in GIS environment) and cross-sections were prepared for the study area. Results According to our observations, a great number of buildings were damaged in areas of the city where silty and clayey soils dominate, presenting very low permeability, low wave velocity together with high plasticity, and compressibility. In the study area, we recognized eight sediment types. Shear wave propagation velocities allowed for the identification of four seismic layers referred to as the surface layer, second layer, and third layer and seismic bedrock. We found that the damages observed in the Bam area were related to the physical and mechanical properties of the soil and subsurface sediment units. We also found that the soil thickness that was estimated by geophysical surveying shows a direct relationship with damage rate observations. Furthermore, we observed that landslide and qanat collapses have occurred in some areas where sand and silty sand soils and subsurface sediments dominate. Discussion The distribution of the damage shows a microzonation that is very serious in some points in the city along the main fault, especially where it is located on thick, fine, medium, and loose soil and sediments. In general, there is a discernable west to east increase in the damage across the city. The average level of destruction for the entire city was similar to 75%, while the eastern part of the city locally reached 100% destruction level. The major factors that influenced the damage and destruction in the Bam region were the distance of a given site from the seismic source, the quality of foundation soil and subsurface sediment, and the type of building. The Bam earthquake occurred on a single fault network comprising the Bam and Arg-e-Bam faults (Funning et al. in J Geophys Res 100(B09406):1-23, 2005). The sediments and soil of the area (unconsolidated silty sand and sandy gravel) belong to braided fluvial and alluvial facies. Most of the buildings near the epicenter area were old and constructed of mud bricks using mud cement. Recommendations and perspectives A combined sedimentological, geological, neotectonic, geotechnical, paleoseismological, and geophysical investigation in urban areas (especially in alluvial valleys) will give the detailed knowledge of the subsurface structure required for the accurate and precise seismic hazard assessments needed for effective earthquake protection planning. This paper shows that for the Bam situation, sedimentological data are required to provide an interpretive context for the geophysical data.

An application of the artificial neural network (ANN) approach for predicting mean grain size using electric resistivity data from Bam city is presented. A feed forward back propagation network was developed employing 45 sets of input data. The input variables in the ANN model are the electrical resistivity, water table as a Boolean value and depth; the output is the mean grain size. To demonstrate the authenticity of this approach, the network predictions are compared with those from interpolation methods and the same data. This comparison shows that the ANN approach performs better results. The predicted and observed mean grain size values were compared and show high correlation coefficients. The ANN approach maps show a high degree of correlation with well data based grain size maps and can therefore be used conservatively to better understand the influence of input parameters on sedimentological predictions.

The Arabia-Eurasia collision is the youngest impact site in the Alpine-Himalayan collisional belt and is an analogue for understanding the early stages of collisional systems where early features were overprinted or removed by subsequent deformation and erosion. However, the spatial and temporal distribution of collision-related deformation and the pre-collisional lithospheric structure of the Arabia-Eurasia system is poorly understood. We focus on the thermal, sedimentological and structural evolution of the west-central Alborz Mountains which form the northern edge of the Turkish-Iranian plateau and extend along the southern margin of the south Caspian Sea. The Alborz are important because they include the highest topography in the central Arabia-Eurasia collisional zone (peak heights between 4000 and 6000 m) but lie >500 km north of the suture between Arabia and Eurasia and stand adjacent to the super-deep south Caspian basin which contains >20 km of post-Jurassic sediment. Furthermore, the Alborz are isostatically unsupported. 40Ar/39Ar and U-Th/He thermochronological data constrain the onset of collision-related deformation in the west-central Alborz to 11.7 ± 3.5 Ma. Sedimentological data from intermontane basins supports this, indicating syntectonic sedimentation in the range during Middle to Late Miocene time. Structural data and geologic mapping indicate that the range probably developed by sinistral transpression and that 59 ± 6 km of shortening has accumulated by a combination of thrusting, folding, and conjugate strike-slip faulting since 11.7 ± 3.5 Ma. This is in good agreement with the 5 ± 2 km/yr GPS shortening rates across the central Alborz, which, assuming a constant shortening rate of ∼5 km/yr, predicts ∼60 km of net shortening across the Alborz since ∼12 Ma. A mechanical model of the central Iran-Alborz-south Caspian system indicates that the Alborz may be supported by upward flexure of the crust due to the horizontal crompressional forces imposed by the collision. This model also predicts downward flexure of the lithosphere to the north and south of the Alborz, which is consistent with the presence of the south Caspian basin and the central Iranian basin. The data, observations and interpretations presented in this thesis are consistent with the view that the collision between Arabia and Eurasia occurred between ∼15 and 10 Ma and that deformation was occurring across the present collision zone immediately after the onset of collision.

Abstract In both Britain and the USA, the majority of the shares in quoted companies are owned by institutional shareholders such as pension funds and insurance companies. But, in most cases these major shareholders are ''passive'', that is they prefer not to become involved in the management of the companies in which they invest - unless there is a crisis.