GPS-derived velocity field of the Iznik-Mekece segment of the North Anatolian Fault Zone

Space-based tectonic studies on the western part of the North Anatolian Fault Zone (NAFZ) have been conducted over two decades. After the August 17, 1999, Izmit earthquake (M_w = 7.4), this region attracted greater scientific interest, and the collected data became more valuable. The Geodesy Department of the Kandilli Observatory and Earthquake Research Institute (KOERI) at Bogazici University established three micro-geodetic networks to the east of Akyazi, east of Iznik, and west of Lake Sapanca in the eastern part of the Marmara region; GPS data have been continually collected at these locations since 1994. The NAFZ branches out in the western part of the Marmara region and extends up to the Aegean Sea. Segments of the fault passing through the Marmara Sea are considered active, and this has increased concern regarding imminent earthquakes. Conventional geodetic measurements made between 1990 and 1994 are not sufficient for monitoring small movements. However, GPS has played a very important role in detecting such deformations in the area after 1994. The Iznik network, with 10 points, is bilaterally located on the Iznik-Mekece fault. Six years of GPS data for 2004–2010 collected for the monitoring of crustal deformation showed that the Iznik-Mekece fault segment moves westward at about 22 ± 1 mm/yr with respect to the Eurasia fixed reference frame. The GPS observations show that there is no strain accumulation in the area.     

Kinematics of the eastern part of the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 km × 200 km with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16–24 mm/year, which are consistent with the regional tectonics. The principal strain rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacik Fault (OF).     

Velocity field and tectonic strain in Southern Spain and surrounding areas derived from GPS episodic measurements

The goal of this paper is to study the velocity field and deformation parameters in Southern Spain and surrounding areas (Ibero-Maghrebian region) using GPS episodic measurements. Results are compared to those previously published as well as deformation parameters derived from seismic data. For this purpose, a geodetic GPS network of 12 stations was observed during eight field campaigns from 1998 to 2005 by the San Fernando Naval Observatory (ROA), Spain. Relative GPS velocities in the Gulf of Cadiz with respect to the stable part of Eurasia are ～4.1 mm/yr in a NW–SE to NNW–SSE direction. In the Betics, Alboran Sea and North of Morocco, velocities are ～4.4 mm/yr in a NW–SE direction, and they are ～2.3 mm/yr in a N–S direction in the eastern part of the Iberian Peninsula. These results are in agreement with the anticlockwise rotation of the African plate. GPS strain tensors are determined from the velocity model, to obtain a more realistic crustal deformation model. The Gulf of Cadiz is subjected to uniform horizontal compression in a NNW–SSE direction, with a rotation to N–S in the Alboran Sea and Northern Morocco. An extensional regime in a NW–SE direction, which rotates to W–E, is present in the Internal Betics area. In the Betic, Alboran Sea and North of Morocco regions we compare seismic deformation rates from shallow earthquakes with the determined GPS deformation rates. The comparison indicates a seismic coupling of 27%, while the remaining 73% might be generated in aseismic processes. Deformations measured in the Ibero-Maghrebian region with GPS could be interpreted in terms of either elastic loading or ductile deformation.     

Intra-plate deformation in west-central Europe

The central part of Europe north of the alpine orogenic belt is generally seen as a relatively stable area of the western tip of the Eurasian plate. Indeed, up to now, no geodetically significant motions have been detected although an active rift system running roughly in SSE–NNW direction along the Rhine valley could have some effect on the stability of this region. Presently, the increasing accuracy of geodetic point motions should allow the study of small motions at levels down to nearly 0.1 mm/yr. We start our investigation with a closer look at the ‘true’ accuracy and significance of GPS derived point velocities of permanent stations. We compare and discuss the different levels of formal errors obtained by the three analysis centers considered in this study (EPN, JPL and SOPAC) and present additional ways of assessing the accuracy using the redundancy offered by different independent analyses and multiple systems operating at one site. On the average, all results indicate that a one-sigma level of ±0.3 mm/yr can be seen as a conservative estimate for the horizontal accuracy of point motions in central Europe. On the basis of this assumption we find that at present, the actual velocity field as determined by different analysis groups and centers does not show any significant east–west extensional deformation. We do however see a prominent north–south compressional velocity gradient of about 1 mm/yr/1000 km (1 nanostrain/yr) which could be associated with the Alpine thrust in conjunction with a south-directed horizontal component of the Fennoscandian Glacial Isostatic Adjustment.     

High resolution mapping of Earth tide response based on GPS data in Japan

We observe the Earth tidal fields at diurnal and semi-diurnal periods using Kinematic Precise Point Positioning (KPPP) GPS analysis. Our KPPP GPS solutions compare well with super-conducting gravimeter (SG) observations and a theoretical Earth tidal model, that includes both ocean tide loading model and body tides. We make a high resolution map of the observed Earth tidal response fields using the Japanese GEONET GPS network which consists of 1200 sites. We find that: (1) the average phase of GPS data lags 0.11 ± 0.04° from our theoretical Earth tidal model, (2) the average amplitude ratio between GPS and the theoretical Earth tidal model is 1.007 ± 0.003, (3) the amplitude in the Kyushu district is about 1.0–1.5 ± 0.3% larger than in the Hokkaido district, and (4) the amplitude at the Japan Sea side is about 0.5 ± 0.2% larger than that at the Pacific Ocean side. These results suggest that we may be able to place constraints on Earth structure using GPS-derived tidal information.     

Drainage migration and out of sequence thrusting in Bhalukpong,Western Arunachal Himalaya,India

In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between ∼7.5 cm/yr in upper reaches and ∼13.5 cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of ∼1 m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (OOSTs). This is the first such report of OOST in the NE Himalaya. Presence of active OOST is inferred by similar age (∼1 ka) and differing incision rates of the surface of same terrace (T_2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are <1 ka. Average slip rate and horizontal shortening rate on OOST during the Holocene, are calculated as ∼12 mm/yr and 7 mm/yr respectively. Thus any estimation of Holocene shortening in the Siwalik therefore, needs to incorporate slip along the OOSTs given that it accommodates a significant amount of N-S compression of the Himalayan fold-and-thrust belt. The reason for OOST in the WAH Siwalik foreland is discussed in terms of the critical wedge dynamics arising from erosion via tectonics-climate interaction. We estimate a minimum slip rate of Siwalik as ∼27 mm/yr during the Holocene and suggest acceleration in shortening rates east of Bhutan.     

Active tectonics of the Northern Rif (Morocco) from geomorphic and geochronological data

We present results of a geomorphological and morphotectonic analysis of the northeastern part of the Rif. We show that the present day kinematics of the Rif is characterized by active deformation along the Trougout and Nekor faults in the North-East. Digital Elevation Models of offset drainage features (streams, fluvial terraces) allow determining a normal-left-lateral motion along the Trougout fault and a left-lateral strike-slip motion along the Nekor fault. Preliminary ³He cosmogenic dates of tectonic markers yield vertical and horizontal slip rates of ∼0.9 mm/yr and ∼0.5 mm/yr, respectively along the Trougout fault. The present-day localized transtension seen in the north-eastern Rif morphology (Ras Tarf) is coeval with uplifted marine terraces near the Al Hoceima Bay. U/Th dating of shells yield an average uplift rate of ∼0.2 mm/yr during the past 500 ka. These data show that active transtension in the northeastern Rif is also associated with uplift. These new morphotectonic constraints are consistent with the GPS measurements showing southwestward overall motion of most of the Rif belt with respect to stable Africa.     

Global-scale validation of model-based load deformation of the Earth's crust from continental watermass and atmospheric pressure variations using GPS

Temporal mass variations in the continental hydrosphere and in the atmosphere lead to changes in the gravitational potential field that are associated with load-induced deformation of the Earth’s crust. Therefore, models that compute continental water storage and atmospheric pressure can be validated by measured load deformation time series. In this study, water mass variations as computed by the WaterGAP Global Hydrology Model (WGHM) and surface pressure as provided by the reanalysis product of the National Centers for Environmental Prediction describe the hydrological and atmospheric pressure loading, respectively. GPS observations from 14 years at 208 stations world-wide were reprocessed to estimate admittance factors for the associated load deformation time series in order to determine how well the model-based deformation fits to real data. We found that such site-specific scaling factors can be identified separately for water mass and air pressure loading. Regarding water storage variation as computed by WGHM, weighted global mean admittances are 0.74 ± 0.09, 0.66 ± 0.10, 0.90 ± 0.06 for the north, east and vertical component, respectively. For the dominant vertical component, there is a rather good fit to the observed displacements, and, averaged over all sites, WGHM is found to slightly overestimate temporal variations of water storage. For Europe and North America, with a dense GPS network, site-specific admittances show a good spatial coherence. Regarding regional over- or underestimation of WGHM water storage variations, they agree well with GRACE gravity field data. Globally averaged admittance estimates of pre-computed atmospheric loading displacements provided by the Goddard Geodetic VLBI Group were determined to be 0.88 ± 0.04, 0.97 ± 0.08, 1.13 ± 0.01 for the north, east and vertical, respectively. Here, a relatively large discrepancy for the dominant vertical component indicates an underestimation of corresponding loading predictions.     

Crustal deformation before the 2008 Wenchuan MS8.0 earthquake studied using GPS data

We used GPS velocities from approximately 700 stations in western China to study the crustal deformation before the Wenchuan M_S8.0 earthquake. The processing methods included analyses of the strain rate field, inversion of fault locking and the GPS velocity profiles. The GPS strain rate in the E-W direction in the Qinghai-Tibet block shows that extensional deformation was dominant in the western region of the block (west of 92.5° E), while compressive deformation predominated in the eastern region of the block (from 92.5° E to 100° E). On a regional scale, the hypocentral region of the Wenchuan earthquake was located at the edge of an intense compression deformation zone of about 1.9 × 10⁻⁸/a in an east-west direction. The characteristic deformation in the seismogenic fault was compressive with a dextral component. The compression deformation rate was greater in the fault's western region than in its eastern region, and the strain accumulation was very slow on the fault scale. The results of a fault locking inversion show that the locking fraction and slip deficit was greater in the middle-northern section of the seismogenic fault than in the southern section. The GPS velocity profile before the Wenchuan earthquake shows that the compression deformation was smaller than the dextral deformation, which is asymmetrical with respect to the distribution of co-seismic displacement. These deformation characteristics should provide some clues to the Wenchuan earthquake which occurred in the later period of the earthquake cycle.     

Active faulting in the frontal Rif Cordillera (Fes region,Morocco): Constraints from GPS data

The southern Rif cordillera front, between Fes and Meknes, is formed by the Prerif Ridges, which constitute a thrust and fold belt, in contact with the Saïss foreland basin. Geological evidence and regional GPS network data support recent and active tectonics of this Alpine cordillera, with a top-to-the-S-SW motion with respect to stable Africa. A local non-permanent GPS network was installed in 2007 around Fes to constrain the present-day activity of the mountain front. Six GPS sites are located in the Prerif mountain front (jbel Thratt and jbel Zalarh), the Saïss basin and the foreland constituted by the tabular Middle Atlas. Measurements of the GPS network in 2007, 2009 and 2012, over a five year span, seem to indicate that this region is tectonically active and is subjected to significant horizontal motions: (i) a regional displacement toward the SW with respect to stable Africa, showing an average rate of 2 mm/yr; (ii) a southwestward convergent motion between the jbel Thratt with respect to the Saïss basin and the eastern Zalarh ridge, with an average rate of about 4 mm/yr; and (iii) moderate NNE–SSW divergent dextral motion between the Saïss basin and the northern front of the tabular Middle Atlas with an average rate of about 1–2 mm/yr. The regional southwestward motion is related to the activity of the NE–SW sinistral North Middle Atlas-Kert fault zone, which follows the Moroccan Hot Line. Convergence between the Prerif ridges, located at the southern edge of the Rif, and the Saïss basin is accommodated by ENE–WSW striking northward dipping reverse sinistral faults and south vergent folds. In addition, increasing deformation toward the western ridges is in agreement with the stepped mountain front and the development of the arched structures of the Prerif ridges. Normal faults located south of the Saïss basin are responsible for local extension. Whereas the most active deformation occurs in the southern front of the jbel Thratt near Fes, the Saïss foreland basin and the Middle Atlas foreland have only moderate to low tectonic activity, as evidenced by geological and GPS data.     

Sea level rise in the north-western part of the Arabian Gulf

Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10.     

Water mass variation in the Mediterranean and Black Seas

The mass-induced sea level variability and the net mass transport between Mediterranean Sea and Black Sea are derived for the interval between August 2002 and July 2008 from satellite-based observations and from model data. We construct in each basin two time series representing the basin mean mass signal in terms of equivalent water height. The first series is obtained from steric-corrected altimetry while the other is deduced from GRACE data corrected for the contamination by continental hydrology. The series show a good agreement in terms of annual and inter-annual signals, which is in line with earlier works, although different model corrections influence the consistency in terms of seasonal signal and trend.In the Mediterranean Sea, we obtain the best agreement using a steric correction from the regional oceanographic model MFSTEP and a continental hydrological leakage correction derived from the global continental hydrological model WaterGAP2. The inter-annual time series show a correlation of 0.85 and a root mean square (RMS) difference of 15 mm. The two estimates have similar accuracy and their annual amplitude and phase agree within 3 mm and 23 days respectively. The GRACE-derived mass-induced sea level variability yields an annual amplitude of 27 ± 5 mm peaking in December and a trend of 5.3 ± 1.9 mm/yr, which deviates within 3 mm/yr from the altimetry-derived estimate.In the Black Sea, the series are less consistent, with lower accuracy of the GRACE-derived estimate, but still show a promising agreement considering the smaller size of the basin. The best agreement is realized choosing the corrections from WaterGAP2 and from the regional oceanographic model NEMO. The inter-annual time series have a correlation and RMS differences of 0.68 and 55 mm, their annual amplitude and phase agree within 4 mm and 6 days respectively. The GRACE-derived seawater mass signal has an annual amplitude of 32 ± 4 mm peaking in April. On inter-annual time scales, the mass-induced sea level variability is stronger than in the Mediterranean Sea, with an increase from 2003 to 2005 followed by a decrease from 2006 to 2008.Based on mass conservation, the mass-induced sea level variations, river runoff and precipitation minus evaporation are combined to derive the strait flows between the basins and with the Atlantic Ocean. At the Gibraltar strait, the net inflow varies annually with an amplitude of 52 ± 10 × 10⁻³ Sv peaking end of September (1 Sv = 10⁶ m³ s⁻¹). The inflow through the Bosphorus strait displays an annual amplitude of 13 ± 3 ×10⁻³ Sv peaking in the middle of March. Additionally, an increase of the Gibraltar net inflow (3.4 ± 0.8 × 10⁻³ Sv/yr) is detected.     

Tectono-metamorphic evolution of the Briançonnais zone (Modane-Aussois and Southern Vanoise units,Lyon Turin transect,Western Alps)

In the central Western Alps, a combined structural, petrological and ⁴⁰Ar–³⁹Ar geochronological study of the Modane-Aussois and Southern Vanoise units yields important constraints on the timing of deformation and exhumation of the Briançonnais zone. These data help to decipher the respective roles of oceanic subduction, continental subduction and collision in the burial and exhumation of the main units through time. In the Modane-Aussois unit top to the NW thrusting (D1) was followed by top to the east shearing (D2) interpreted by some as normal faulting and by others as backthrusting. Pseudosection calculations imply that D1 deformation occurred at 1.0 ± 0.1 GPa and 350 ± 30 °C. Analysis of chlorite–phengite pairs yield P–T estimates between 0.15 and 0.65 GPa and between 220 and 350 °C for the D2 event. Phengites along the D1 schistosity (sample M80) yields an ⁴⁰Ar–³⁹Ar age of 37.12 ± 0.39 Ma, while D2 phengites yield ages of 35.42 ± 0.38 (sample M173) and 31.60 ± 0.33 Ma (sample M196). It was not possible to test whether these ages are altered by excess argon or not. Our interpretation is that the D1/D2 transition occurred at ∼37 Ma at the beginning of decompression, and that D2 lasted until at least ∼32 Ma. Pseudosection calculation suggests that the Southern Vanoise unit was buried at 1.6 ± 0.2 GPa and 500–540 °C. D1 deformation occurred during exhumation until 0.7–10.5 GPa and 370 ± 30 °C. Published ages suggest that D1 deformation possibly started at ∼50 Ma and lasted until ∼37 Ma. D2 deformations started at P–T conditions close to that recorded in Modane-Aussois unit and lasted until 0.2 ± 0.1 GPa and 280 ± 30 °C at ∼28 Ma. The gap of 0.6 ± 0.3 GPa and 150 ± 130 °C between peak metamorphic conditions in the two units was concealed by thrusting of the South Vanoise unit on top of the Modane-Aussois unit during D1 Deformation. Top to the east deformation (D2) affects both units and is interpreted as backthrusting.Based on these data, we propose a geodynamic reconstruction where the oceanic subduction of the Piedmont unit until ∼50 Ma, is followed by its exhumation at the time of continental subduction of the continental Southern Vanoise unit until ∼45 Ma. The Southern Vanoise is in turn underthrusted by the Modane-Aussois unit until ∼37 Ma (D1). Between 37 and 31 Ma the Modane-Aussois and Southern Vanoise units exhume together during backthrusting to the east (D2). This corresponds to the collision stage and to the activation of the Penninic Thrust. In the ∼50 Ma to ∼31 Ma time period the main thrusts propagated westward as the tectonic context switched from oceanic to continental subduction and finally to collision. During each stage, external units are buried while internal ones are exhumed.     

Constraining the long-term evolution of the slip rate for a major extensional fault system in the central Aegean,Greece, using thermochronology

The brittle/ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary. In this study we examine the slip history of the large-scale Naxos/Paros extensional fault system (NPEFS), Cyclades, Greece, by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime. Based on apatite and zircon fission-track (AFT and ZFT) and (U–Th)/He dating we observe variable slip rates across the brittle/ductile transition on Naxos. ZFT and AFT ages range from 11.8 ± 0.8 to 9.7 ± 0.8 Ma and 11.2 ± 1.6 to 8.2 ± 1.2 Ma and (U–Th)/He zircon and apatite ages are between 10.4 ± 0.4 to 9.2 ± 0.3 Ma and 10.7 ± 1.0 to 8.9 ± 0.6 Ma, respectively. On Paros, ZFT and AFT ages range from 13.1 ± 1.4 Ma to 11.1 ± 1.0 Ma and 12.7 ± 2.8 Ma to 10.5 ± 2.0 Ma while the (U–Th)/He zircon ages are slightly younger between 8.3 ± 0.4 Ma and 9.8 ± 0.3 Ma. All ages consistently decrease northwards in the direction of hanging wall transport. Most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of ∼ 6–8 km Myr^− 1 on the NPEFS across the brittle/ductile transition. Even the intrusion of a large granodiorite body into the narrowing fault zone at ∼ 12 Ma on Naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate. The data also show that the NPEFS accomplished a minimum total offset of ∼ 50 km between ∼ 16 and 8 Ma.     

Spatiotemporal patterns of fault slip rates across the Central Sierra Nevada frontal fault zone

Patterns in fault slip rates through time and space are examined across the transition from the Sierra Nevada to the Eastern California Shear Zone–Walker Lane belt. At each of four sites along the eastern Sierra Nevada frontal fault zone between 38 and 39° N latitude, geomorphic markers, such as glacial moraines and outwash terraces, are displaced by a suite of range-front normal faults. Using geomorphic mapping, surveying, and ¹⁰Be surface exposure dating, mean fault slip rates are defined, and by utilizing markers of different ages (generally, ~ 20 ka and ~ 150 ka), rates through time and interactions among multiple faults are examined over 10⁴–10⁵ year timescales.At each site for which data are available for the last ~ 150 ky, mean slip rates across the Sierra Nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval (~ 20 ky and ~ 150 ky timescales): 0.3 ± 0.1 mm year^? 1 (mode and 95% CI) at both Buckeye Creek in the Bridgeport basin and Sonora Junction; and 0.4 + 0.3/?0.1 mm year^? 1 along the West Fork of the Carson River at Woodfords. Data permit rates that are relatively constant over the time scales examined. In contrast, slip rates are highly variable in space over the last ~ 20 ky. Slip rates decrease by a factor of 3–5 northward over a distance of ~ 20 km between the northern Mono Basin (1.3 + 0.6/?0.3 mm year^? 1 at Lundy Canyon site) to the Bridgeport Basin (0.3 ± 0.1 mm year^? 1). The 3-fold decrease in the slip rate on the Sierra Nevada frontal fault zone northward from Mono Basin is indicative of a change in the character of faulting north of the Mina Deflection as extension is transferred eastward onto normal faults between the Sierra Nevada and Walker Lane belt.A compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the Eastern California Shear Zone-Walker Lane belt. South of the Mina Deflection, extension is accommodated within a diffuse zone of normal and oblique faults, with extension rates increasing northward on the Fish Lake Valley fault. Where faults of the Eastern California Shear Zone terminate northward into the Mina Deflection, extension rates increase northward along the Sierra Nevada frontal fault zone to ~ 0.7 mm year^? 1 in northern Mono Basin. This spatial pattern suggests that extension is transferred from more easterly fault systems, e.g., Fish Lake Valley fault, and localized on the Sierra Nevada frontal fault zone as the Eastern California Shear Zone–Walker Lane belt faulting is transferred through the Mina Deflection.     

40Ar / 39Ar geochronology constraints on late miocene weathering rates in Minas Gerais,Brazil

⁴⁰Ar / ³⁹Ar incremental heating ages for twenty one grains of cryptomelane, collected at 0, 42, 45, and 60 m depths in the Cachoeira Mine weathering profile, Minas Gerais, permit calculating long-term (10 Ma time scale) weathering rate (saprolitization rate) in SE Brazil. Pure well-crystallized cryptomelane grains with high K contents (3–5 wt.%) yield reliable geochronological results. The ⁴⁰Ar / ³⁹Ar plateau ages obtained decrease from the top to the bottom of the profile (12.7 ± 0.1 to 7.6 ± 0.1 Ma at surface; 7.6  ± 0.2 to 6.1 ± 0.2 Ma at 42 m; and 7.1 ± 0.2 to 5.9 ± 0.1 Ma at 45 m; 6.6 ± 0.1 to 5.2 ± 0.1 Ma at 60 m), yielding a weathering front propagation rate of 8.9 ± 1.1 m/m.y. From the geochronological results and the mineral transformations implicit by the current mineralogy in the weathering profiles, it is possible to calculate the saprolitization rate for the Cachoeira Mine lithologies and for adjacent weathering profiles developed on granodiorites and schists. The measured weathering front propagation rate yields a saprolitization rate of 24.9 ± 3.1 t/km²/yr. This average long-term (> 10 Ma) saprolitization rate is consistent with mass balance calculations results for present saprolitization rates in weathering watersheds. These results are also consistent with long-term saprolitization rates estimated by combining cosmogenic isotope denudation rates with mass balance calculations.     

Present day geodynamics in Iceland monitored by a permanent network of continuous GPS stations

Iceland is located on the Mid-Atlantic Ridge and thereby offers a rare opportunity to study crustal movements at a divergent plate boundary. Iceland is not only characterized by the divergence of the Eurasian and North American Plates, as several active volcanoes are located on the island. Moderate size earthquakes occur in the transform zones, causing measurable crustal deformation. In 1999 the installation of a permanent network of continuous GPS stations (ISGPS) was initiated in order to observe deformation due to unrest in the Hengill volcanic system and at the Katla volcano. The ISGPS network has been enlarged over the years and consists today of more than 25 CGPS stations. Most of the stations are located along the plate boundary, where most of the active deformation takes place. Uplift due to post-glacial rebound due to the melting of the largest glacier in Europe, Vatnajökull, is also detected by the ISGPS network. This study presents results from analysis of 9 years of data from the ISGPS network, in the global reference frame PDR05, which has been evaluated by the Potsdam-Dresden-Reprocessing group with reprocessed GPS data only. We thus determine subsidence or land uplift in a global frame. The horizontal station velocities clearly show spreading across the plate boundary of about 20 mm/a. Stations in the vicinity of the glacier Vatnajökull indicate uplift in the range of 12 mm/a, while a station in the central part of Iceland shows uplift rates of about 25 mm/a. Tide gauge readings in Reykjavik and current subsidence rates observed with CGPS agree also quite well.     

Luminescence dating of baked earth and sediments from the Qujialing archaeological site,China

The Qujialing site is a representative Neolithic archaeological site in the middle reaches of the Yangtze River, China. Absence of suitable material for radiocarbon dating in this region makes the timing of the similar sites difficult. Here we applied optically stimulated luminescence (OSL–SAR) and thermoluminescence (TL–SAR) techniques to date the archaeological and natural deposits from the Qujialing site with known age, testing the techniques on samples at archaeological sites in this region. The results showed that the luminescence properties of quartz from sediment and baked earth samples are very similar. The quartz OSL ages obtained for a sediment sample and a baked earth sample from the cultural layer are 5.4 ± 0.3 and 5.1 ± 0.3 ka, respectively. The quartz TL age of the baked earth sample is 5.6 ± 0.5 ka. These dates are consistent with the calibrated radiocarbon ages (4.9 ± 0.1 and 5.1 ± 0.1 ka cal BP (±1σ)) of the two charcoal samples from the cultural layer at a nearby locality, and are also in agreement with the age of Qujialing culture period. The results indicate that the OSL dating techniques can be applied to date similar archaeological sites in the middle reaches of the Yangtze River, China.     

New insights in the geodynamics of the Lipari–Vulcano area (Aeolian Archipelago,southern Italy) from geological,geodetic and seismological data

Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10⁻¹³ s⁻¹, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10⁻¹³ s⁻¹ are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.     

Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone

We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ～1–2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains.