Insights into Wasatch fault vertical slip rates using the age of sediments in Timpanogos Cave, Utah

Timpanogos Cave, located near the Wasatch fault, is about 357 m above the American Fork River. Fluvial cave sediments and an interbedded carbonate flowstone yield a paleomagnetic and U–Th depositional age of 350 to 780 ka. Fault vertical slip rates, inferred from calculated river downcutting rates, range between 1.02 and 0.46 mm yr^− 1. These slip rates are in the range of the 0–12 Ma Wasatch Range exhumation rate ( 0.5–0.7 mm yr^− 1), suggesting that the long-term vertical slip rate remained stable through mid-Pleistocene time. However, the late Pleistocene (0–250 ka) decelerated slip rate ( 0.2–0.3 mm yr^− 1) and the accelerated Holocene slip rate ( 1.2 mm yr^− 1) are consistent with episodic fault activity. Assuming that the late Pleistocene vertical slip rate represents an episodic slowing of fault movement and the long-term (0–12 Ma) average vertical slip rate, including the late Pleistocene and Holocene, should be  0.6 mm yr^− 1, there is a net late Pleistocene vertical slip deficit of  50–75 m. The Holocene and late Pleistocene slip rates may be typical for episodes of accelerated and slowed fault movement, respectively. The calculated late Pleistocene slip deficit may mean that the current accelerated Wasatch fault slip rate will extend well into the future.     

Paleomagnetic constraints on the paleogeography and oroclinal bending of the Devonian volcanic arc in Kazakhstan

Numerical modelling, incorporating coupling between surface processes and induced flow in the lower continental crust, is used to address the Quaternary evolution of the Gulf of Corinth region in central Greece. The post-Early Pleistocene marine depocentre beneath this Gulf overlies the northern margin of an older (Early Pleistocene and earlier) lacustrine basin, the Proto Gulf of Corinth Basin or PGCB. In the late Early Pleistocene, relief in this region was minimal but, subsequently, dramatic relief has developed, involving the creation of  900 m of bathymetry within the Gulf and the uplift by many hundreds of metres of the part of the PGCB, south of the modern Gulf, which forms the Gulf's main sediment supply. It is assumed that, as a result of climate change around 0.9 Ma, erosion of this sediment source region and re-deposition of this material within the Gulf began, both processes occurring at spatial average rates of  0.2 mm a^− 1. Modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is  4 × 10¹⁹ Pa s, indicating a Moho temperature of  560 °C. It predicts that the  10 mm a^− 1 of extension across this  70 km wide model region, at an extensional strain rate of  0.15 Ma^− 1, is partitioned with  3 mm a^− 1 across the sediment source,  2 mm a^− 1 across the depocentre, and  5 mm a^− 1 across the ‘hinge zone’ in between, the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the Gulf. This modelling confirms the view, suggested previously, that coupling between this depocentre and sediment source by lower-crustal flow can explain the dramatic development in local relief since the late Early Pleistocene. The effective viscosity of the lower crust in this region is not particularly low; the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity. In detail, the effective viscosity of the lower crust is expected to decrease northward across this model region, due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere; in the south the two are separated by the subducting Hellenic slab. The isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why, since  0.9 Ma, the modern Gulf has developed asymmetrically over the northern part of the PGCB, leaving the rest of the PGCB to act as its sediment source.     

Analysis of crustal deformation in Luzon, Philippines using geodetic observations and earthquake focal mechanisms

We utilize regional GPS velocities from Luzon, Philippines, with focal mechanism data from the Harvard Centroid Moment Tensor (CMT) Catalog, to constrain tectonic deformation in the complex plate boundary zone between the Philippine Sea Plate and Eurasia (the Sundaland block). Processed satellite imagery and digital elevation models are used with existing gravity anomaly, seismicity, and geologic maps to define a suite of six elastic blocks. Geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault-locking parameters for each of the tectonic blocks and faults comprising Luzon. Major tectonic structures that were found to absorb the plate convergence include the Manila Trench (20–100 mm yr^− 1) and East Luzon Trough ( 9–15 mm yr^− 1)/Philippine Trench ( 29–34 mm yr^− 1), which accommodate eastward and westward subduction beneath Luzon, respectively; the left-lateral strike-slip Philippine Fault ( 20–40 mm yr^− 1), and its northward extensions, the Northern Cordillera Fault ( 17–37 mm yr^− 1 transtension), and the Digdig Fault ( 17–27 mm yr^− 1 transpression). The Macolod Corridor, a zone of active volcanism, crustal thinning, extension, and extensive normal and strike-slip faulting in southwestern Luzon, is associated with left-lateral, transtensional slip of  5–10 mm yr^− 1. The Marikina Fault, which separates the Central Luzon block from the Southwestern Luzon block, reveals  10–12 mm yr^− 1 of left-lateral transpression. Our analysis suggests that much of the Philippine Fault and associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. Luzon is best characterized as a tectonically active plate boundary zone, comprising six mobile elastic tectonic blocks between two active subduction zones. The Philippine Fault and associated intra-arc faults accommodate much of the trench-parallel component of relative plate motion.     

Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (60 wt%) and quartz polymorphs (35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10⁻¹⁶ to 10⁻¹⁷ mol s⁻¹ kg tuff⁻¹ with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10⁻¹⁵ to 10⁻¹⁶ mol s⁻¹ kg tuff⁻¹ for percolation fluxes of 15 mm a⁻¹ and 1 mm a⁻¹, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a⁻¹ or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (50 mg L⁻¹) may inhibit feldspar dissolution.     

Anatolian surface wave evaluated at GEOFON Station ISP Isparta, Turkey

We have studied seismic surface waves of 255 shallow regional earthquakes recently recorded at GEOFON station ISP (Isparta, Turkey) and have selected these 52 recordings with high signal-to-noise ratio for further analysis. An attempt was made by the simultaneous use of the Rayleigh and Love surface wave data to interpret the planar crust and uppermost mantle velocity structure beneath the Anatolian plate using a differential least-square inversion technique. The shear-wave velocities near the surface show a gradational change from approximately 2.2 to 3.6 km s^− 1 in the depth range 0–10 km. The mid-crustal depth range indicating a weakly developed low velocity zone has shear-wave velocities around 3.55 km s^− 1. The Moho discontinuity characterizing the crust–mantle velocity transition appears somewhat gradual between the depth range  25–45 km. The surface waves approaching from the northern Anatolia are estimated to travel a crustal thickness of  33 km whilst those from the southwestern Anatolia and part of east Mediterranean Sea indicate a thicker crust at  37 km. The eastern Anatolia events traveled even thicker crust at  41 km. A low sub-Moho velocity is estimated at  4.27 km s^− 1, although consistent with other similar studies in the region. The current velocities are considerably slower than indicated by the Preliminary Reference Earth Model (PREM) in almost all depth ranges.     

Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications

The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr^− 1 in the Little Andaman to 2.80 mm yr^− 1 in South Andaman and 2.45 mm yr^− 1 in the North Andaman. Our radiocarbon dates converge on  600 yr and  1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.     

Linking source and sink: Evaluating the balance between onshore erosion and offshore sediment accumulation since Gondwana break-up, South Africa

The geomorphic origin and evolution of the tectonically unique interior highland of southern Africa, the Kalahari Plateau, and its flanking low-lying coastal planes, remain largely unresolved because of a lack of regional quantitative analyses of its uplift and erosion history. Here we focus on the southern Cape, South Africa and link onshore denudation, based on new apatite fission track thermochronology results, to offshore sediment accumulation, using abundant well data and a seismic reflection profile. We attempt to relate source and sink in order to resolve some first order issues concerning timing of the exhumation and development of the topographic features of southern Africa. The volume of sediment accumulated off South Africa's south coast is calculated using 173 wells and a seismic reflection profile. A total, uncompacted, sediment volume of 268,500 km³ accumulated off South Africa's south coasts since  136 Ma, in the Outeniqua and Southern Outeniqua Basins. Accumulation volumes and rates were highest in the early Cretaceous (48,800 × 10⁴ km³ at  8150 km³/Ma from  136 to 130 Ma, and 57,500 × 10⁴ km³ at 5750 km³/Ma from  130 to 120 Ma) and mid–late Cretaceous (83,700 × 10⁴ km³ at 3200 km³/Ma from  93 to 67 Ma). Volumes and accumulation rates were lowest for the early–mid-Cretaceous (47,400 × 10⁴ km³ at 1750 km³/Ma from  120 to 93 Ma) and the Cenozoic (31,200 × 10⁴ km³ at 450 km³/Ma from  67 to 0 Ma). Although our analysis shows that the accumulated volume of offshore sediments does not match the calculated volume of onshore erosion, as quantified through apatite fission track thermochronology (e.g. Tinker, J.H., de Wit, M.J., Brown, R., 2008. Mesozoic exhumation of the 439 southern Cape, South Africa, quantified using apatite fission track thermochronology. Tectonophysics, doi: 10.1016/j.tecto.2007.10.009), the timing of increased sediment accumulation closely matches the timing of increased onshore denudation. This suggests that the greatest volumes of material were transported from source to sink during two distinct Cretaceous episodes, and that the processes driving onshore denudation decreased by an order of magnitude during the Cenozoic.     

Determination of Cl Production Rates Derived from the Well-Dated Deglaciation Surfaces of Whidbey and Fidalgo Islands, Washington

The ³⁶Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the ³⁶Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms ³⁶Cl (g Ca)⁻¹ yr⁻¹ and are 228±18 atoms ³⁶Cl (g K)⁻¹ yr⁻¹, respectively. The calculated ground-level secondary neutron production rate in air, P_f(0), inferred from thermal neutron absorption by ³⁵Cl is 762±28 neutrons (g air)⁻¹ yr⁻¹ for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is 40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated ³⁶Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated ¹⁴C ages, thereby supporting the validity of our ³⁶Cl production rates integrated over the last 15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators.     

An obliquity-controlled Early Pleistocene river terrace record from Western Turkey?

Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr⁻¹) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.     

Geochemical relation between gas hydrates and water venting in the seismic blanking zone on the northern Cascadia continental margin offshore Vancouver Island, Canada

The isotopic composition (δD and δ¹⁸O) and chloride concentration (Cl⁻) of pore waters from the northern Cascadia continental margin offshore Vancouver Island were measured to characterize the relations between the water flow regime and the distribution, formation and dissociation of gas hydrates. The δD values of pore waters in gas hydrate-bearing sediments are slightly higher ( 1‰) than those of seawater as the result of gas hydrate dissociation during core recovery and handling. Within the seismic blanking zone, the δD values were slightly lower (− 1‰) than values measured from sites outside the blanking area (0‰). We attribute these differences to 1) distillation of D-rich water during hydrate formation in the center of the blanking zone and 2) limited migration of pore water between inside and outside of the blanking zone due to different fluid fluxes. In contrast, the δ¹⁸O values and Cl⁻ concentrations do not show significant spatial variation due to decreased isotopic fractionation of oxygen and small fraction of chloride relative to hydrogen isotope during gas hydrate formation. The δD value of pore water, therefore, appears to be a sensitive indicator of gas hydrate occurrence. We estimate that gas hydrate occupied at least 2.0 to 6.3% of sediment pore space using δD distribution in this area.     

Examination of diatom-based changes from a climatically sensitive prairie lake (Saskatchewan, Canada) at different temporal perspectives

Paleoclimatic records from the climatically sensitive Canadian prairies are relatively rare due to the scarcity of study sites with continuous Holocene stratigraphic sequences. Oro Lake, a meromictic lake in the dry grasslands of Saskatchewan (Canada), contains a continuous Holocene diatom record spanning the last 10,000 years. Here we present analyses at three different time scales and resolution: (1) 1–3 yr resolution of the past 80 years, (2) century-scale analysis of the Holocene, and (3) decadal-scale analysis of the past 7000 years. Recent changes in the diatom assemblages and their respective salinity inferences were significantly related to measured effective moisture (precipitation minus evaporation, P−ET). The droughts of the 1930s, and a wet period during the 1950s are clearly evident in the diatom record, suggesting the Oro Lake record contains a sensitive archive of past climatic conditions. Century-scale analysis of the diatom record during the Holocene is consistent with a cool and moist climate in the early Holocene (prior to ca 9700 cal yr BP, 8600 ¹⁴C yr BP). An abrupt increase in diatom-inferred salinity at 9600 cal yr BP (8500 ¹⁴C yr BP) indicates the onset of an arid climate, with continuing arid conditions throughout the mid-Holocene. Decadal-scale analysis of the past 7000 years suggests that the mid-Holocene was more complex, with extended periods of increased variability in precipitation, particularly between ca 5800–3600 cal yr BP (5000–3200 ¹⁴C yr BP) which is characterized by intervals of increased effective moisture. The past 2000 years is characterized by reduced salinities and generally wetter conditions in comparison to the mid-Holocene. The combination of the different scales of analyses in this study provides a detailed account of the dynamic nature of climate from sub-decadal to millennial scale in the Oro Lake region within the Palliser Triangle. Climate model predictions suggest that the Canadian prairie region may see a higher frequency of extreme droughts under projected global warming, potentially similar to the most arid periods seen during the mid-Holocene when many lake basins completely dried out.     

Geochronology of Quaternary glaciations from the tropical Cordillera Huayhuash, Peru

The Cordillera Huayhuash in the central Peruvian Andes (10.3°S, 76.9°W) is an ideal mountain range in which to study regional climate through variations in paleoglacier extents. The range trends nearly north-south with modern glaciers confined to peaks >4800 m a.s.l. Geomorphology and geochronology in the nearby Cordillera Blanca and Junin Plain reveal that the Peruvian Andes preserve a detailed record of tropical glaciation. Here, we use ASTER imagery, aerial photographs, and GPS to map and date glacial features in both the western and eastern drainages of the Cordillera Huayhuash. We have used in situ produced cosmogenic ¹⁰Be concentrations in quartz bearing erratics on moraine crests and ice-polished bedrock surfaces to develop an exposure age chronology for Pleistocene glaciation within the range. We have also collected sediment cores from moraine-dammed lakes and bogs to provide limiting ¹⁴C ages for glacial deposits. In contrast to the ranges to the north and south, most glacial features within the Cordillera Huayhuash are Lateglacial in age, however we have identified features with ages that span 0.2 to 38 ka with moraine sets marking the onset of glacier retreat at 0.3 ka, 9–10 ka, 13–14 ka, 20–22 ka, and >26 ka. The range displays a pronounced east-west variation in maximum down-valley distance from the headwall of moraine crests with considerably longer paleoglaciers in the eastern drainages. Importantly, Lateglacial paleoglaciers reached a terminal elevation of 4000 m a.s.l. on both sides of the Cordillera Huayhuash; suggesting that temperature may have been a dominant factor in controlling the maximum glacier extent. We suggest that valley morphology, specifically valley slope, strongly influences down-valley distance to the maximum glacier extent and potential for moraine preservation. While regionally there is an extensive record of older (>50 ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the apparent lack of old moraines in this locality may be explained by the confined morphology of the Cordillera Huayhuash valleys that has inhibited the preservation of older glacial geomorphic features.     

A late Quaternary paleotemperature record from Hanging Lake, northern Yukon Territory, eastern Beringia

The late Quaternary paleoclimate of eastern Beringia has primarily been studied by drawing qualitative inferences from vegetation shifts. To quantitatively reconstruct summer temperatures, we analyzed lake sediments for fossil chironomids, and additionally we analyzed the sediments for fossil pollen and organic carbon content. A comparison with the δ¹⁸O record from Greenland indicates that the general climatic development of the region throughout the last glaciation–Holocene transition differed from that of the North Atlantic region. Between  17 and 15 ka, mean July air temperature was on average 5°C colder than modern, albeit a period of near-modern temperature at  16.5 ka. Total pollen accumulation rates ranged between  180 and 1200 grains cm^− 2 yr^− 1. At  15 ka, approximately coeval with the Bølling interstadial, temperatures again reached modern values. At  14 ka, nearly 1000 yr after warming began, Betula pollen percentages increased substantially and mark the transition to shrub-dominated pollen contributors. Chironomid-based inferences suggest no evidence of the Younger Dryas stade and only subtle evidence of an early Holocene thermal maximum, as temperatures from  15 ka to the late Holocene were relatively stable. The most recognizable climatic oscillation of the Holocene occurred from  4.5 to 2 ka.     

Paleohydrology of the upper Laurentian Great Lakes from the late glacial to early Holocene

Between 10,500 and 9000 cal yr BP, δ¹⁸O values of benthic ostracodes within glaciolacustrine varves from Lake Superior range from − 18 to − 22‰ PDB. In contrast, coeval ostracode and bivalve records from the Lake Huron and Lake Michigan basins are characterized by extreme δ¹⁸O variations, ranging from values that reflect a source that is primarily glacial ( − 20‰ PDB) to much higher values characteristic of a regional meteoric source ( − 5‰ PDB). Re-evaluated age models for the Huron and Michigan records yield a more consistent δ¹⁸O stratigraphy. The striking feature of these records is a sharp drop in δ¹⁸O values between 9400 and 9000 cal yr BP. In the Huron basin, this low δ¹⁸O excursion was ascribed to the late Stanley lowstand, and in the Lake Michigan basin to Lake Agassiz flooding. Catastrophic flooding from Lake Agassiz is likely, but a second possibility is that the low δ¹⁸O excursion records the switching of overflow from the Lake Superior basin from an undocumented northern outlet back into the Great Lakes basin. Quantifying freshwater fluxes for this system remains difficult because the benthic ostracodes in the glaciolacustrine varves of Lake Superior and Lake Agassiz may not record the average δ¹⁸O value of surface water.     

Holocene climate variability and cultural evolution in the Near East from the Dead Sea sedimentary record

A comprehensive record of lake level changes in the Dead Sea has been reconstructed using multiple, well dated sediment cores recovered from the Dead Sea shore. Interpreting the lake level changes as monitors of precipitation in the Dead Sea drainage area and the regional eastern Mediterranean palaeoclimate, we document the presence of two major wet phases ( 10–8.6 and  5.6–3.5 cal kyr BP) and multiple abrupt arid events during the Holocene. The arid events in the Holocene Dead Sea appear to coincide with major breaks in the Near East cultural evolution (at  8.6, 8.2, 4.2, 3.5 cal kyr BP). Wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions, suggesting a parallelism between climate and Near East cultural development.     

Development of crystallographic preferred orientations by nucleation and growth of new grains in experimentally deformed quartz single crystals

Deformation experiments have been carried out to investigate the effect of dynamic recrystallisation on crystallographic preferred orientation (CPO) development. Cylindrical samples of natural single crystals of quartz were axially deformed together with 1 vol.% of added water and 20 mg of Mn₂O₃ powder in a Griggs solid medium deformation apparatus in different crystallographic orientations with compression direction: (i) parallel to <c>, (ii) at 45° to <c> and 45° to <a> and (iii) parallel to <a>. The experiments were performed at a temperature of 800 °C, a confining pressure of 1.2 GPa, a strain rate of  10^− 6 s^− 1, to bulk finite strains of  14–36%. The deformed samples were analysed in detail using optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Two different microstructural domains were distinguished in the deformed samples: (i) domains with undulatory extinction and deformation lamellae, and (ii) domains with new recrystallised grains. Within the domains of undulatory extinction, crystal-plastic deformation caused gradual rotations of the crystal lattice up to  30° away from the host orientation. New recrystallised grains show a strong CPO with c-axis maxima at  45° to the compression direction. This is the case in all experiments, irrespective of the initial crystallographic orientation. The results show that c-axes are not continuously rotated towards the new maxima. The new grains thus developed through a mechanism different from subgrain rotation recrystallisation. New grains have a subeuhedral shape and numerous microcavities, voids, fluid channels and fluid inclusions at their grain boundaries. No host control is recorded in misorientation axes across their large angle grain boundaries. New grains might have been created by nucleation from solution in the μm-scale voids and microfractures. The CPO most likely developed due to preferred growth of the freshly precipitated grains with orientations suitable for intracrystalline deformation at the imposed experimental conditions.     

Stratigraphic development during the Late Pleistocene and Holocene offshore of the Yellow River delta, Bohai Sea

A 61-m-long sediment core (HB-1) and 690 km of high-resolution seismic profiles from offshore of the Yellow River delta, Bohai Sea, were analyzed to document the stratigraphy and sea-level changes during the Late Pleistocene and Holocene. Accelerator mass spectrometry ¹⁴C dating and analyses of benthic foraminifera, ostracods, the mineral composition, and sedimentary characteristics were performed for core HB-1, and seven depositional units (DU 1–DU 7 in descending order) were identified. The seismic reflection data were interpreted in light of the sedimentological data of the core and correlated with other well-studied cores obtained previously in the Bohai Sea area. Seven seismic units (SU 1 to SU 7 in descending order) were distinguished and interpreted as follows: SU 7 corresponds to marine facies in Marine Isotopic Stage (MIS) 5; SU 6, to terrestrial facies in MIS 4; SU 5 and SU 4, to alternating terrestrial and marine facies (DU 7–DU 5) in MIS 3; SU 3, to terrestrial facies (DU 4) in MIS 2; SU 2, to Holocene marine facies (DU 3 and DU 2); and SU 1, to modern Yellow River delta sediments deposited since 1855 (DU 1).The sedimentary facies from DU 7 to DU 5 reflect sea-level fluctuations during MIS 3, and the boundary between DU 5 and DU 6, which coincides with that between SU 4 and SU 5, is a distinctive, laterally continuous, undulating erosion surface, with up to 20 m of relief. This surface reflects subaerial exposure between transgressions during MIS 3. Estimated sea levels during MIS 3 ranged from −35 ± 5 to −60 ± 5 m or lower, with short-term fluctuations of 20 m. Sedimentary environments in the Bohai Sea area were governed mainly by eustatic sea-level changes and the Bohai Strait topography, which controls the entry of sea water into the Bohai Sea area.The mineral composition of the sediment core suggests that the Yellow River did not discharge into the Bohai Sea, or at least did not influence the study area significantly, during parts of MIS 3 and MIS 2 to the early Holocene (11–8.5 cal kyr BP).     

Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the MORB to SSZ evolution of a marginal basin oceanic crust

The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian and Pelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changes in thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone (SSZ) environment. The  3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro, and gabbro. These peridotites and gabbroic rocks are overlain directly by a  600-m-thick extrusive sequence containing basaltic pillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The  12-km-thick Eastern Mirdita Ophiolite (EMO) includes tectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivine clinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. The plutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites and feeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartz diorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The  1.1-km-thick extrusive sequence comprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flows in the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic and basaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection (TiO₂ = 3.5–0.5%, Zr = 300–50 ppm), while _Nd(T) (+ 8 to + 6.5) varies little. These magmas were derived from partial melting of fertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREE abundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in the evolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO₂ ( 0.5%) and Zr ( 50 ppm) contents but _Nd(T) values (+ 7 to + 6.5) are similar to those of the WMO lavas. These rocks show variable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacites and boninites within the upper 400 meters of EMO lavas show low TiO₂ ( 0.8–0.3%) and _Nd(T) (+ 6.5 to + 3.0). The mantle source of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations in Ba, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative _{Nd (T)} values (− 1.4 and − 4.0, respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. The MORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the _Nd(T) values from + 8.0 to − 4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slab rollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in the evolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin, which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision.     

Structure and geochronology of the southern Xainza-Dinggye rift and its relationship to the south Tibetan detachment system

The Xainza-Dinggye rift is one of several north-south trending rifts in central and southern Tibet created by Cenozoic east-west extension during Indo-Asian convergence. The southern part of the rift cuts through the Tethyan and High Himalayas. In the Tethyan Himalaya, this rift consists of an early domal structure and a late normal fault developed during the progressive deformation. The dome is cored by leucogranitic plutons that intruded during extension. Muscovite ⁴⁰Ar/³⁹Ar ages of the mylonitic leucogranite indicate that extension in the Tethyan Himalaya began at 8 Ma or before. In the High Himalaya, the rift is controlled by a normal fault dipping to the southeast. This fault has a structural constitution similar to a detachment fault. Its lower block is made up of mylonitic High Himalayan gneiss, intruded by early mylonitic leucogranite sills and late less-deformed biotite-bearing leucogranite dikes. Mica ⁴⁰Ar/³⁹Ar ages of these leucogranites and the retrograded metamorphosed gneiss of the lower block range from 13 to 10 Ma. In the study area, the south Tibetan detachment system (STDS) is a ductile shear zone composed of mylonitic leucogranite that is intruded by less-deformed leucogranite and overlain by low grade metamorphic rocks. Mica ⁴⁰Ar/³⁹Ar ages of leucogranites in the shear zone and schist from the detachment hanging wall indicate a protracted deformation history of the STDS from 19 to 13 Ma. The Xainza-Dinggye rift is younger than the STDS because it offsets the STDS; this north-south trending rift belongs to a different tectonic system from the east-west striking STDS, and may be caused by geological process related to India–Asia convergence. This temporal and spatial relationship of the STDS to the rift may indicate an important change in tectonic regime at 13 Ma in the building of the plateau.     

Raised coastal terraces along the Ionian Sea coast of northern Calabria, Italy, suggest space and time variability of tectonic uplift rates

A detailed study of uplifted Middle–Late Pleistocene marine terraces on the eastern side of northern Calabria, southern Italy, provides insights into the temporal and spatial scale variability of vertical displacement rates over a time span of 400 ka. Calabria is located in the frontal orogen of southern Italy above the westerly-plunging Ionian slab, and a combination of lithospheric, crustal, and surface processes concurred to rapid Late Quaternary uplift. Eleven terrace orders and a raised Holocene beach were mapped up to 480 m a.s.l., and were correlated between the coastal slopes of Pollino and Sila mountain ranges across the Sibari Plain, facing the Ionian Sea side of northeastern Calabria. Precise corrections were applied to the measured shoreline angles in order to account for uncertainty in measurement, erosion of marine deposits, recent debris shedding, and bathymetric range of markers. Radiometric (ESR and ¹⁴C) dating of shells provides a crono-stratigraphic scheme, although many samples were found to be resedimented in younger terraces. Terrace T4, whose inner margin stands at elevations of 94–130 m, is assigned to MIS 5.5 (124 ka), based on new ESR dating and previous amino acid racemization estimations. The underlying terraces T3, T2 and T1 are attributed to MIS 5.3 (100 ka), 5.1 (80 ka) and 3 (60 ka), as inferred from their relative position supplemented by ESR and ¹⁴C age determinations. The age of higher terraces is poorly constrained, but conceivably is tracked back to MIS 11 (400 ka). The reconstructed depositional sequence of terraces attributed to MIS 5.5 and 7 reveals two regressive marine cycles separated by an alluvial fanglomerate, which, given the steady uplift regime, points to minor sub-orbital sea-level changes during interstadial highstands. Based on the terrace chronology, uplift in the last 400 ka occurred at an average rate of 1 mm/a, but was characterized by the alternation of more rapid (up to 3.5 mm/a) and slower (down to 0.5 mm/a) periods of displacement. Spatial variability in uplift rates is recorded by the deformation profile of terraces parallel to the coast, which document the growth of local fold structures.