Mineral reconnaissance of the southern part of the Wadi Qaraqir quadrangle, Saudi Arabia

USGS Publications Warehouse

Johnson, Robert Francis; Trent, Virgil A.

1972-01-01

Introduction At the end of a field trip to the Wadi as Surr quadrangle (Johnson and Trent, 1967) a few days were spent in the southern part of the adjoinning Wadi Qaraqir quadrangle in order to extend our mineral reconnaissance as far east as the Arabian Plateau. The area examine is shown by the distribution of sample localities on the accompanying map. No mineral deposits of economic interest were seen. The terrain is one of broad plains and low hills that extend westward from the base of a prominent erosional scarp which forms the western edge of the Arabian Plateau. Streams cutting headward into the low-dipping massive sandstone of the Plateau have carved deep canyongs with vertical walls, and outliers of the sandstone are preserved as buttes and erosional forms of varied shapes. There are no permanent settlements in the mapped areas. The one road leads up a tributary of Wadi Qaraqir to some date gardens at the base of the sandstone cliffs. A well-travelled caravan route crosses the passes at Al Khuraytah to reach the Plateau H. St. John Philby strongly recommended that a road be constructed through these passes to provide direct access from Tabuk to the Red Sea coast. Burton (1878) was probably the first European to visit the area. He was searching for mineral deposits and he also located some Nabatcan ruins. Philby in company with R. G. Bogue, U. S. Geological Survey, explored the scarp in the Wadi Qaraqir valley and drove northwestward to Al Khuraytah pass. The geology of the Wadi Qaraqir quadrangle shown on the geologic map of the Northwestern Hijaz (Brown and others, 1963) was compiled from Bogue's work. Our work consisted of making traverses around the hilly area and up accessible wadis. We examined the rocks along the traverse routes and visited target areas that had been selected by examination of aerial photographs. Samples of wadi sediment were collected from fault zones, granite contacts, and areas that showed some evidence of hydrothermal alteration

Water exploration using Magnetotelluric and gravity data analysis; Wadi Nisah, Riyadh, Saudi Arabia

NASA Astrophysics Data System (ADS)

Aboud, Essam; Saud, Ramzi; Asch, Theodore; Aldamegh, Khaled; Mogren, Saad

2014-12-01

Saudi Arabia is a desert country with no permanent rivers or lakes and very little rainfall. Ground water aquifers are the major source of water in Saudi Arabia. In the Riyadh region, several Wadies including Wadi Nisah store about 14 × 106 m3 of water, which is extracted for local irrigation purposes. In such areas, the water wells are as shallow as 200-300 m in depth. The importance of Wadi Nisah is because the subsurface water aquifers that are present there could support the region for many years as a water resource. Accordingly, in this study, we performed a Magnetotelluric survey using a portable broadband sounding system (MT24/LF) to evaluate the ground water aquifer at great depths. We collected 10 broadband Magnetotelluric sounding stations (1 station/day) with an interval of about 2-3 km reaching a profile length of about 25-30 km along Wadi Nisah. Additionally, we used available gravity data to image the subsurface structure containing the aquifer. MT results indicated a low resistivity layer, associated with alluvium deposits, which was defined at a depth of about 1-2 km and extended horizontally about 15 km. Gravity data analysis was used to model this resistivity layer indicating a basement surface at 3-4 km depth.

The effects of kinds of lumus and the storage period on the quality of patin wadi based on the results of nutrient tests

NASA Astrophysics Data System (ADS)

Dewi, Indah Sari; Hastuti, Utami Sri; Lestari, Umi; Suwono, Hadi

2017-05-01

Wadi is the processed product of fish, due to local knowledge of the Dayak community, made of fresh fish with salt and lumus. The efforts to increase the quality of wadi as a kind of food were based on local knowledge, and are still ongoing. It is one of the ways to conserve wadi existence in the middle of the modern culture. It is important to add a variety of spices in suitable amounts as the innovation in producing wadi. People process wadi by using lumus made of rice and corn. Lumus gives a special taste and aroma t o wadi, furthermore, the effects of kinds of lumus and their concentrates, and the storage period on the nutrients of wadi are not known yet. This research used patin fish (Pangasius sp), white rice (Oryza sativa), white sticky rice (Oryza sativa var.glutinous), and corn (Zea mays) as the kinds of lumus. Each kind of lumus is mixed with fresh patin fish in different concentrations: 15%, 25% and 35%. The results of nutrient tests include measures of protein, carbohydrate, and fat, and show that patin which has been processed into wadi has more nutrients than fresh patin. The storage period and the varying concentrates of lumus effect the level of nutrients in patin wadi.

Geological and geochemical studies in the Wadi Bidah District, Kingdom of Saudi Arabia

USGS Publications Warehouse

Smith, C.W.; Waters, B.C.; Naqvi, M.; Worl, R.G.; Helaby, A.M.; Flanigan, V.J.; Sadek, H.S.; Samater, R.M.

1983-01-01

Geological and geochemical followup studies of airborne electromagnetic anomalies in the Wadi Bidah district, southwestern Saudi Arabia, did not reveal metals of economic grade. Investigation of an anomaly enclosing the Rabathan ancient mine disclosed tightly folded and sheared Proterozoic tuffaceous rocks interlayered mostly with chert, dolomite, carbonaceous rocks, and volcanic wacke including cherty iron-manganese formations slightly anomalous in copper and zinc. Three drill holes placed to test anomalies within these formations yielded negative results. Studies of a long, narrow anomaly north of the Rabathan area indicated a similar geological environment. This northern area also contains limited zones that are highly anomalous in copper and zinc and extensive zones that are slightly anomalous in those metals. Drilling was not undertaken in this area. The Bilajimah airborne electromagnetic anomaly west of Wadi Bidah coincides with a broad synclinorium of layered felsic turfs and gossans. Geochemical studies indicated slightly anomalous copper, zinc, and silver values in gossans within the anomaly area. Two drill holes intersected carbonaceous rock that contained approximately 15 percent pyrrhotite and traces of sphalerite and chalcopyrite. Two geophysically anomalous areas west of Wadi Bidah surround ancient mines at Mahawiyah and Khayal al Masna'ah. Results of geochemical sampling at these workings were positive. An airborne electromagnetic anomaly located in the Assifar area in the southwestern corner of the Wadi Bidah district is underlain principally by metasedimentary rocks that include large linear zones of cherty iron-manganese formation and a few gossans .containing secondary base metal minerals. Detailed mapping and sampling of the Mulhal ancient mine, located west of Wadi Bidah, revealed two types of polymetallic gossans : (1) stratiform deposits interlayered with ignimbrites and mafic volcanic rocks and (2) barite-bearing gossanous material in shear

An Extension of Analysis of Solar-Heated Thermal Wadis to Support Extended-Duration Lunar Exploration

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Gokoglu, S. A.; Sacksteder, K. R.; Wegeng, R. S.; Suzuki, N. H.

2010-01-01

The realization of the renewed exploration of the Moon presents many technical challenges; among them is the survival of lunar surface assets during periods of darkness when the lunar environment is very cold. Thermal wadis are engineered sources of stored solar energy using modified lunar regolith as a thermal storage mass that can supply energy to protect lightweight robotic rovers or other assets during the lunar night. This paper describes an extension of an earlier analysis of performance of thermal wadis based on the known solar illumination of the Moon and estimates of producible thermal properties of modified lunar regolith. The current analysis has been performed for the lunar equatorial region and validates the formerly used 1-D model by comparison of predictions to those obtained from 2-D and 3-D computations. It includes the effects of a thin dust layer covering the surface of the wadi, and incorporating either water as a phase-change material or aluminum stakes as a high thermal conductivity material into the regolith. The calculations indicate that thermal wadis can provide the desired thermal energy and temperature control for the survival of rovers or other equipment during periods of darkness.

When was irrigation first used in Bat (Wadi Sharsah, northwestern Oman)?

NASA Astrophysics Data System (ADS)

Fouache, E.; Desruelles, S.; Eddargach, W.; Cammas, C.; Wattez, J.; Martin, C.; Tengberg, M.; Cable, C.; Thornton, C.

2012-04-01

The extensive archaeological site of Bat, registered as a World Heritage Site by UNESCO in 1989, is situated within the Wadi Sharsah and around the modern village and palm grove of Bat, approximately 24 km from the modern city of Ibri in northwestern Oman. The archaeological remains from the Bronze Age excavated by the Bat Archaeological Project are located in two main areas. The northern area consists of a chain of low limestone hills cut by wadi tributaries leading to the main Wadi Sharsah. It is characterised by an exceptionally high density of graves from two successive Bronze Age periods: Hafit (ca. 3100-2700 BCE) and Umm an-Nar (ca. 2700-2000 BCE). South of the Bat cemetery, in the flat part of the valley, there are several large circular structures (known historically as "towers") and remains from both Hafit and Umm an-Nar periods, as well as later periods. Geomorphological mapping of the floodplain, associated with archaeological survey, have identified walls suggesting that during the Umm an-Nar period there was a system of irrigation which controlled flood water. Sedimentological, malacological, C14 dating and micromorphological studies of a 10 m long and 2.5 m high section located 143 m northeast of the Tower 1146 on the left bank of a small tributary of the Wadi Sharsah provide strong arguments for the presence of an irrigation system that began before the Hafit period. Botanical macro-remains collected during the excavation of early Bronze Age structures at Bat further indicate the presence of date palm gardens since the early 3rd millennium BCE allowing the cultivation of several crop species, in particular cereals. Most generally, the global palaeoenvironmental reconstruction from our data supports a model of a general trend of aridification from Bronze to Iron Ages. Key words : Bronze Age, Holocene, Geomorphology, Micromorphology, Irrigation, Oman

Fate and transport of heavy metals and radioelements in groundwater aquifers of Al-Qunfudhah and Wadi Haliy quadrangles, southwest of Saudi Arabia

NASA Astrophysics Data System (ADS)

Bajabaa, S. A.; Abd El-Naby, H.; Dawood, Y.

2009-12-01

The fate and transport of heavy metals and radioelements in groundwater aquifers in five wadis located in the Al Qunfudhah and Wadi Haliy quadrangles were investigated. These wadis are an important source of water to the Red Sea coastal plain. Copper, zinc and other base-metals mineralization occur at eastern parts of these quadrangles that dominates the water catchments area of these wadis. Water, rock and soil samples were collected from all wadis and they were analyzed for major, trace elements, heavy metals and stable isotopes. The chemical and isotopic results showed active water/rock interaction. The preliminary investigation of the data analyses showed some samples with high heavy metals and uranium contents. Generally, the uranium and heavy metal contents are higher in samples collected from the upstream area of each wadi where the crystalline rocks are exposed and direct contact with the runoff. The uranium contents were as high as 120 ppb in some water samples. These elevated values are mainly due to two factors water rock interaction and concentration through evaporation. It was also observed to have elevated heavy metal contents near mining activates, which suggests that these mining activates are playing an important role in mobilizing the heavy elements and in turn affecting the water quality in these wadis.

Geophysical investigations in the Bi'r Idimah-Wadi Wassat area, Saudi Arabia, Part One

USGS Publications Warehouse

Allen, R.V.; Davis, W.E.

1969-01-01

The area is near latitude 18°20'N., longitude 44°20'E, about 20 Km south of Bi'r Idirah (Fig. 1). Most of the area lies in a wadi bounded by low hills that reach elevations near 1250 meters and rise as ranch as 50 meters above the wadi floor. The gossan is exposed in the wadi and near the crests of a few hills in the southern part of the surveyed area. It is underlain by andesite porphyry and greenstone intruded by granitic rocks, and appears to have been displaced laterally by faulting in the central part of the area. An inclined test hole north of the offset cut massive pyrite between depths 98 and 141 feet, 250 and 260 feet, and between depths 299 and 351 feet. This test and the character of the gossan suggest that the mineralized zone continues southward for a considerable distance.

Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: New constraints on the tectonic evolution during ophiolite formation from high-precision U-Pb zircon geochronology

NASA Astrophysics Data System (ADS)

Rioux, Matthew; Garber, Joshua; Bauer, Ann; Bowring, Samuel; Searle, Michael; Kelemen, Peter; Hacker, Bradley

2016-10-01

The Semail (Oman-United Arab Emirates) and other Tethyan-type ophiolites are underlain by a sole consisting of greenschist- to granulite-facies metamorphic rocks. As preserved remnants of the underthrust plate, sole exposures can be used to better understand the formation and obduction of ophiolites. Early models envisioned that the metamorphic sole of the Semail ophiolite formed as a result of thrusting of the hot ophiolite lithosphere over adjacent oceanic crust during initial emplacement; however, calculated pressures from granulite-facies mineral assemblages in the sole suggest the metamorphic rocks formed at >35 km depth, and are too high to be explained by the currently preserved thickness of ophiolite crust and mantle (up to 15-20 km). We have used high-precision U-Pb zircon dating to study the formation and evolution of the metamorphic sole at two well-studied localities. Our previous research and new results show that the ophiolite crust formed from 96.12-95.50 Ma. Our new dates from the Sumeini and Wadi Tayin sole localities indicate peak metamorphism at 96.16 and 94.82 Ma (±0.022 to 0.035 Ma), respectively. The dates from the Sumeini sole locality show for the first time that the metamorphic rocks formed either prior to or during formation of the ophiolite crust, and were later juxtaposed with the base of the ophiolite. These data, combined with existing geochemical constraints, are best explained by formation of the ophiolite in a supra-subduction zone setting, with metamorphism of the sole rocks occurring in a subducted slab. The 1.3 Ma difference between the Wadi Tayin and Sumeini dates indicates that, in contrast to current models, the highest-grade rocks at different sole localities underwent metamorphism, and may have returned up the subduction channel, at different times.

Assessment of future variability in extreme precipitation and the potential effects on the wadi flow regime.

PubMed

Gunawardhana, Luminda Niroshana; Al-Rawas, Ghazi A; Kazama, So; Al-Najar, Khalid A

2015-10-01

The objective of this study is to investigate how the magnitude and occurrence of extreme precipitation events are affected by climate change and to predict the subsequent impacts on the wadi flow regime in the Al-Khod catchment area, Muscat, Oman. The tank model, a lumped-parameter rainfall-runoff model, was used to simulate the wadi flow. Precipitation extremes and their potential future changes were predicted using six-member ensembles of general circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Yearly maxima of the daily precipitation and wadi flow for varying return periods were compared for observed and projected data by fitting the generalized extreme value (GEV) distribution function. Flow duration curves (FDC) were developed and compared for the observed and projected wadi flows. The results indicate that extreme precipitation events consistently increase by the middle of the twenty-first century for all return periods (49-52%), but changes may become more profound by the end of the twenty-first century (81-101%). Consequently, the relative change in extreme wadi flow is greater than twofolds for all of the return periods in the late twenty-first century compared to the relative changes that occur in the mid-century period. Precipitation analysis further suggests that greater than 50% of the precipitation may be associated with extreme events in the future. The FDC analysis reveals that changes in low-to-moderate flows (Q60-Q90) may not be statistically significant, whereas increases in high flows (Q5) are statistically robust (20 and 25% for the mid- and late-century periods, respectively).

Phase 3 geophysical studies in the Wadi Bidah District, Kingdom of Saudi Arabia

USGS Publications Warehouse

Flanigan, V.J.; Sadek, Hamdy; Smith, C.W.

1982-01-01

Detailed geophysical measurements have been made in the Rabathan area, Wadi Bidah district, Kingdom of Saudi Arabia, at the site of diamond drill holes RAB-1, -2, and -3; these measurements suggest that the causative source for the anomalous EM (electromagnetic) and SP (self-potential) responses is probably highly conductive zones of Precambrian siliceous-carbonaceous rocks. Although many of the zones are no more than a few meters wide, they commonly contain 50 to 80 percent carbonaceous material and locally abundant pyrite. In places, several thin layers of highly concentrated carbonaceous material interlayered with chert form a multiple conductive zone that is seen in the geophysical data as complex anomaly patterns. In the geologic environment of Wadi Bidah, massive sulfide-bearing zones cannot be distinguished from siliceous-carbonaceous zones on the basis of the EM-SP responses. In North America in similar environments, complex resistivity methods used in experimental research have successfully discriminated between sulfide and carbonaceous conductors. Tests of such methods in the Wadi Bidah district are recommended. Geologic, geochemical, and geophysical data at the Jabal Mohr prospect suggest the possibility of mineralized rocks at depth over a possible strike length of 400 m.

Quaternary alluvial deposits of Wadi Gaza in the middle of the Gaza Strip (Palestine): Facies, granulometric characteristics, and their paleoflow direction

NASA Astrophysics Data System (ADS)

Ubeid, Khalid Fathi

2016-06-01

The Quaternary rocks of the Gaza Strip mainly consist of clastic sedimentary rocks. In Wadi Gaza, the outcropping rocks consist of brownish fine-grained deposits, sandstones, and conglomerates. The deposits have been studied from a genetic point of view, and six facies have been described: (i) graded clast-supported conglomerates, (ii) cross-bedded clast-supported conglomerates, (iii) sandy matrix conglomerates, (iv) cross-laminated medium-grained sandstones, (v) graded coarse-grained sandstones, and (vi) massive sandstones. The field work observations and granulometric analysis show that the sphericity of the grains increase toward the west, where its value ranges from ∼0.64 in the east to ∼0.70 in the west. In addition, the grain forms tend to be disc shape in the east, whereas they tend to be disc-to spheroid shape in the west, and they become well rounded to well sorted toward the west. Moreover, the features, geometry, and spatial relationship among these facies suggest that the Wadi Gaza was meandering wadi fed from Beir Sheva and the Northern Negev in the southeast of Gaza Strip through Wadi Al Shallala and Wadi Sheneq and from Hebron mountains in the West Bank at the east through Wadi Al Shari'a alluvials. Within the Gaza Strip, paleocurrent data ranges from 210° to 310°, indicating a mean a paleoflow direction to the W (276°) and a median value about 275°. The sedimentary rocks in the Wadi Gaza are considered to be deposited in two periods of climate conditions: the coarse-grained rocks were deposited during the period of wet condition before 12.4 ka age, whereas the eolinite fine-grained rocks were deposited during semiarid climate conditions which are younger in age than 12.4 ka.

Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt

NASA Technical Reports Server (NTRS)

Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.; Basta, N. Z.; Melek, Y. S.

1984-01-01

During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea.

Spatial thermal radiometry contribution to the Massif armoricain and the Massif central (France) litho-structural study

NASA Technical Reports Server (NTRS)

Scanvic, J. Y. (Principal Investigator)

1980-01-01

The author has identified the following significant results. Although the limited number of images received did not permit construction of a thermal inertia map, important geological details were obtained in the areas of lithology and tectonics. Interpretation of day, night, and seasonal imagery resulted in differentiating broad calcareous and dolomitic units in the Causse Plateau. In the Massif amoricain, some granite massifs were delineated which were not observed by LANDSAT. Neotectonic faults were also revealed.

Wadi el-Sheikh: A new archaeological investigation of ancient Egyptian chert mines

PubMed Central

2017-01-01

This article provides an overview of the first results from archaeological investigations at Wadi el-Sheikh in Egypt by the University of Vienna Middle Egypt Project. Chert was an important raw material used to produce tools, implements and jewelry in ancient times. Wadi el-Sheikh was exploited over thousands of years as it was probably the most important source of chert in Pharaonic civilization. The results of our new investigations that involved surveys and test excavations indicate the presence of large scale mining activities in the first half of the 3rd Millennium B.C.E. which allow for detailed insights into the amount of raw material extracted, the mining methods used and the lithic products manufactured in this area. These aspects are contextualized on the background of ancient Egyptian state-organized resource acquisition strategies and economy. PMID:28152079

Determining heterogeneous deformation for granitic rocks in the northern thrust in Wadi Mubarak belt, Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Kassem, Osama M. K.

2011-05-01

Finite-strain was studied in the mylonitic granitic and metasedimentary rocks in the northern thrust in Wadi Mubarak belt to show a relationship to nappe contacts between the old granitic and metavolcano-sedimentary rocks and to shed light on the heterogeneous deformation for the northern thrust in Wadi Mubarak belt. We used the Rf/ϕ and Fry methods on feldspar porphyroclasts, quartz and mafic grains from 7 old granitic and 7 metasedimentary samples in the northern thrust in Wadi Mubarak belt. The finite-strain data shows that old granitic rocks were moderate to highly deformed and axial ratios in the XZ section range from 3.05 to 7.10 for granitic and metasedimentary rocks. The long axes (X) of the finite-strain ellipsoids trend W/WNW and E/ENE in the northern thrust in Wadi Mubarak belt. Furthermore, the short axes (Z) are subvertical associated with a subhorizontal foliation. The value of strain magnitudes mainly constants towards the tectonic contacts between the mylonitic granite and metavolcano-sedimentary rocks. The data indicate oblate strain symmetry (flattening strain) in the mylonitic granite rocks. It is suggested that the accumulation of finite strain was formed before or/and during nappe contacts. The penetrative subhorizontal foliation is subparallel to the tectonic contacts with the overlying nappes and foliation was formed during nappe thrusting.

Ordovician magmatism in the Lévézou massif (French Massif Central): tectonic and geodynamic implications

NASA Astrophysics Data System (ADS)

Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Van Den Driessche, Jean

2017-03-01

New U-Pb dating on zircon yielded ca. 470 Ma ages for the granitoids from the Lévézou massif in the southern French Massif Central. These new ages do not support the previous interpretation of these granitoids as syn-tectonic intrusions emplaced during the Late Devonian-Early Carboniferous thrusting. The geochemical and isotopic nature of this magmatism is linked to a major magmatic Ordovician event recorded throughout the European Variscan belt and related to extreme thinning of continental margins during a rifting event or a back-arc extension. The comparable isotopic signatures of these granitoids on each side of the eclogite-bearing leptyno-amphibolitic complex in the Lévézou massif, together with the fact that they were emplaced at the same time, strongly suggest that these granitoids were originally part of a single unit, tectonically duplicated by either isoclinal folding or thrusting during the Variscan tectonics.

Hydrogeochemistry and groundwater quality assessment along Wadi Al Showat, Khamis Mushiet District, Southwest Saudi Arabia

NASA Astrophysics Data System (ADS)

Alhumidan, S. M.; Alfaifi, H. J.; Ibrahim, E. K. E.; Abdel Rahman, K.

2015-12-01

In the present study, the hydrochemistry and geologic characteristics of the shallow groundwater aquifer along Wadi Al Showat, Khamis Mushiet District, Southwest Saudi Arabia was evaluated and assessed. Along this wadi the fractured/weathered basement rocks house significant quantity of groundwater that usually used by local people for agricultural and domestic purposes. Assessing and evaluation of the quality of the groundwater in such shallow aquifers is very important; especially the groundwater is generally occurred within the fractured basement rocks at shallow depths, thus exposing the groundwater to surface or near-surface contaminants is expected. For this purpose hydrochemical and biological analysis was conducted for 25 water samples collected from the available shallow dug wells along the studied wadi. The study reveals that the groundwater quality changed due to the agriculture and urbanization practices along the wadi. The effect of domestic waste water and septic tanks was obvious. In addition, the field investigation indicates that the basement rocks in the area is dissected by two main sets of fractures that oriented in the west-northwest and east-west directions. In some places, the basement rocks is intruded by coarse-grained, quartz-rich quartzite grained monzogranite, and pegmatite veins that have a coarse-grained weathering product, therefore, they tend to develop and preserve open joint systems between the granitic blocks. These fracturing system are important from the hydrogeological point of view, as they facilitate the storage, water flow movement through them and also facilitate the vertical infiltration of the surface pollutants. These results led to a better understanding of the groundwater characteristics that is important in groundwater management in the study area.

Tethyan Anhydrite Preserved in the Lower Ocean Crust of the Samail Ophiolite? Evidence from Oman Drilling Project Holes GT1A and 2A

NASA Astrophysics Data System (ADS)

Teagle, D. A. H.; Harris, M.; Crispini, L.; Deans, J. R.; Cooper, M. J.; Kelemen, P. B.; Alt, J.; Banerjee, N.; Shanks, W. C., III

2017-12-01

Anhydrite is important in mid-ocean ridge hydrothermal systems because of the high concentrations of calcium and sulfate in modern seawater and anhydrite's retrograde solubility. Because anhydrite hosts many powerful tracers of fluid-rock interactions (87Sr/86Sr, δ18O, δ34S, trace elements, fluid inclusions) it is useful for tracing the chemical evolution of hydrothermal recharge fluids and estimating time-integrated fluid fluxes. Anhydrite can form from heated seawater (>100°C), through water-rock reaction, or by mixing of seawater and hydrothermal fluids. Although abundant in active hydrothermal mounds, and predicted to form from downwelling, warming fluids during convection, anhydrite is rare in drill core from seafloor lavas, sheeted dikes and upper gabbros, with only minor amounts in ODP Holes 504B and 1256D. Because anhydrite can dissolve during weathering, its occurrence in ophiolites is unexpected. Instead, gypsum is present in Macquarie Island lavas and Miocene gypsum fills cavities within the Cretaceous Troodos ore deposits. Thus, the occurrence of numerous anhydrite veins in cores from the gabbroic lower crust of the Samail ophiolite in Oman was unanticipated. To our knowledge, anhydrite in Oman gabbros has not been previously reported. Oman Drilling Project Holes GT1A and GT2A were drilled into the Wadi Gideah section of the Wadi Tayin massif. Both recovered 400 m of continuous core from sections of layered gabbros (GT1) and the foliated-layered gabbro transition (GT2). Anhydrite is present throughout both holes, some in vein networks but more commonly as isolated 1-110 mm veins (>60 mm ave). Anhydrite is mostly the sole vein filling but can occur with greenschist minerals such as epidote, quartz, chlorite and prehnite. Anhydrite commonly exhibits prismatic and bladed textures but can also be capriciously microcrystalline. Though definitive cross cutting relationships are elusive, anhydrite veins cut across some greenschist veins. Anhydrite is

Hydrogeochemical evolution of inland lakes’ water: A study of major element geochemistry in the Wadi El Raiyan depression, Egypt

PubMed Central

Mohamed, Essam A.; El-Kammar, Ahmed M.; Yehia, Mohamed M.; Abu Salem, Hend S.

2015-01-01

Wadi El Raiyan is a great depression located southwest of Cairo in the Western Desert of Egypt. Lake Qarun, located north of the study area, is a closed basin with a high evaporation rate. The source of water in the lake is agricultural and municipal drainage from the El Faiyum province. In 1973, Wadi El Raiyan was connected with the agricultural wastewater drainage system of the Faiyum province and received water that exceeded the capacity of Lake Qarun. Two hydrogeological regimes have been established in the area: (i) higher cultivated land and (ii) lower Wadi El Raiyan depression lakes. The agricultural drainage water of the cultivated land has been collected in one main drain (El Wadi Drain) and directed toward the Wadi El Raiyan depression, forming two lakes at different elevations (upper and lower). In the summer of 2012, the major chemical components were studied using data from 36 stations distributed over both hydrogeological regimes in addition to one water sample collected from Bahr Youssef, the main source of freshwater for the Faiyum province. Chemical analyses were made collaboratively. The major ion geochemical evolution of the drainage water recharging the El Raiyan depression was examined. Geochemically, the Bahr Youssef sample is considered the starting point in the geochemical evolution of the studied surface water. In the cultivated area, major-ion chemistry is generally influenced by chemical weathering of rocks and minerals that are associated with anthropogenic inputs, as well as diffuse urban and/or agricultural drainage. In the depression lakes, the water chemistry generally exhibits an evaporation-dependent evolutionary trend that is further modified by cation exchange and precipitation of carbonate minerals. PMID:26644942

Massification to Marketization of Higher Education: Private University Education in Bangladesh

ERIC Educational Resources Information Center

Ahmed, Jashim Uddin

2016-01-01

Massification of higher education is a contemporary phenomenon, and Bangladesh is an excellent example of massification in the sector. With increased alertness worldwide among nations, policy-makers and development bodies, massification of higher education is a requirement of time. Increasing number of youth also contribute to the phenomenon…

Kondyor Massif, Russia

NASA Technical Reports Server (NTRS)

2008-01-01

This is neither an impact crater nor a volcano. It is a perfect circular intrusion, about 10 km in diameter with a topographic ridge up to 600 m high. The Kondyor Massif is located in Eastern Siberia, Russia, north of the city of Khabarovsk. It is a rare form of igneous intrusion called alkaline-ultrabasic massif and it is full of rare minerals. The river flowing out of it forms placer mineral deposits. Last year 4 tons of platinum were mined there. A remarkable and very unusual mineralogical feature of the deposit is the presence of coarse crystals of Pt-Fe alloy, coated with gold. This 3-D perspective view was created by draping a simulated natural color ASTER composite over an ASTER-derived digital elevation model.

The image was acquired on June 10, 2006, and is located at 57.6 degrees north latitude, 134.6 degrees east longitude.

The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

Desert Wadis and Smoke from Kuwait Oil Fires, Saudi Arabia

NASA Technical Reports Server (NTRS)

1991-01-01

Smoke from the Kuwait Oil Fires obscures the view of the desert wadis, Saudi Arabia (29.5N, 42.5E). During the brief Gulf war between Iraq and the Allied forces, many of the oil wells in Kuwait were destroyed and set afire. For several months, those fires burned out of control, spewing smoke and ash for hundreds of miles in many directions depending on the altitude, time of year and the prevailing winds.

Local Seismicity of the Rainbow Massif on the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Horning, G.; Sohn, R. A.; Canales, J. P.; Dunn, R. A.

2018-02-01

The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid-Atlantic Ridge (36°N), is notable for hosting high-temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013-2014. High rates ( 300 per day) of low-magnitude (average ML 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low-magnitude deformation at relatively shallow (< 3 km) depths beneath the massif, sandwiched in between the seafloor and seismic reflectors interpreted to be magmatic sills driving hydrothermal convection. Most of the seismicity is located in regions where seismic refraction data indicate serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.

The tectonics of anorthosite massifs

NASA Technical Reports Server (NTRS)

Seyfert, C. K.

1981-01-01

Anorthosite massifs developed approximately 1.4 to 1.5 billion years ago along an arch which developed parallel to a zone of continental separation as a block which included North America, Europe, and probably Asia separated from a block which included parts of South America, Africa, India, and Australia. Anorthosite massifs also developed at the same time along a belt which runs through the continents which comprise Gondwanaland (South America), Africa, India, Australia, and Antarctica. This was a zone of continental separation which subsequently became a zone of continental collision about 1.2 billion years ago. The northern anorthosite belt also parallels an orogenic belt which was active between 1.8 and 1.7 billion years ago. Heat generated during this mountain building period helped in the formation of the anorthosites.

Finite Strain Analysis of the Wadi Fatima Shear Zone in Western Arabia, Saudi Arabia

NASA Astrophysics Data System (ADS)

Kassem, O. M. K.; Hamimi, Z.

2018-03-01

Neoproterozoic rocks, Oligocene to Neogene sediments and Tertiary Red Sea rift-related volcanics (Harrat) are three dominant major groups exposed in the Jeddah tectonic terrane in Western Arabia. The basement complex comprises amphibolites, schists, and older and younger granites unconformably overlain by a post-amalgamation volcanosedimentary sequence (Fatima Group) exhibiting post-accretionary thrusting and thrust-related structures. The older granites and/or the amphibolites and schists display mylonitization and shearing in some outcrops, and the observed kinematic indicators indicate dextral monoclinic symmetry along the impressive Wadi Fatima Shear Zone. Finite strain analysis of the mylonitized lithologies is used to interpret the deformation history of the Wadi Fatima Shear Zone. The measured finite strain data demonstrate that the amphibolites, schists, and older granites are mildly to moderately deformed, where XZ (axial ratios in XZ direction) vary from 2.76 to 4.22 and from 2.04 to 3.90 for the Rf/φ and Fry method respectively. The shortening axes ( Z) have subvertical attitude and are associated with subhorizontal foliation. The data show oblate strain ellipsoids in the different rocks in the studied area and indication bulk flattening strain. We assume that the different rock types have similar deformation behavior. In the deformed granite, the strain data are identical in magnitude with those obtained in the Fatima Group volcanosedimentary sequence. Finite strain accumulated without any significant volume change contemporaneously with syn-accretionary transpressive structures. It is concluded that a simple-shear deformation with constant-volume plane strain exists, where displacement is strictly parallel to the shear plane. Furthermore, the contacts between various lithological units in the Wadi Fatima Shear Zone were formed under brittle to semi-ductile deformation conditions.

Safe drinking water and clean air: an experimental study evaluating the concept of combining household water treatment and indoor air improvement using the Water Disinfection Stove (WADIS).

PubMed

Christen, Andri; Navarro, Carlos Morante; Mäusezahl, Daniel

2009-09-01

Indoor air pollution and unsafe water remain two of the most important environmental risk factors for the global burden of infectious diseases. Improved stoves and household water treatment (HWT) methods represent two of the most effective interventions to fight respiratory and diarrhoeal illnesses at household level. Since new improved stoves are highly accepted and HWT methods have their drawbacks regarding sustained use, combining the two interventions in one technical solution could result in notable positive convenience and health benefits. A WAter DIsinfection Stove (WADIS) based on a Lorena-stove design with a simple flow-through boiling water-treatment system was developed and tested by a pilot experimental study in rural Bolivia. The results of a post-implementation evaluation of two WADIS and 27 Lorena-stoves indicate high social acceptance rather due to convenience gains of the stove than to perceived health improvements. The high efficacy of the WADIS-water treatment system, with a reduction of microbiological contamination load in the treated water from 87600 thermotolerant coliform colony forming units per 100mL (CFU/100mL) to zero is indicative. The WADIS concept unifies two interventions addressing two important global burdens of disease. WADIS' simple design, relying on locally available materials and low manufacturing costs (approx. 6 US) indicates potential for spontaneous diffusion and scaling up.

Tracer Tests History in the Alburni Massif (Southern Italy)

NASA Astrophysics Data System (ADS)

Parise, Mario; Santo, Antonio

2017-12-01

The Alburni Massif (Campania, southern Italy) is among the most important Italian karst areas, due to high number of caves (about 300), with several karst systems reaching depth of 500 m, and development of some kilometres. This remarkable karst is mainly related to three geological factors: presence of highly karstifiable and low-fractured Cretaceous and Tertiary limestones; peculiar morphological and structural conformation, with four main faults bounding the massif, forming a wide highplain with a variety of infiltration sites; presence of blind valleys and small catchments on flysch deposits, feeding the many swallets at the contact with the limestone rocks. The Alburni Massif represents an important hydrogeological structure, with a potential of about 10 mc/sec. Three basal spring systems are the main outcomes (Castelcivita, Tanagro and Pertosa) while other minor systems are located at higher elevation, as the Auso spring. The Castelcivita and Pertosa caves, located on the Alburni SW and NE foothills, respectively, are of particular importance also for the local economy, since Castelcivita became a show cave in 1930, followed two years later by Pertosa. Since 1950 many cavers have explored the Alburni Massif, due to the high potential of overall karstification, estimated in about 1 300m, and to the presence on its southern slope of the spectacular Auso spring. In this paper, the tracer tests carried out in the Massif are summarized, with the aim to update the available hydrogeological data, with particular regard to the most recent explorations and tests, carried out during the last 5 years, which brought significant new data to the overall knowledge of this remarkable karst area.

Preliminary geologic map of the Wadi As Sirhan Quadrangle, sheet 30C, Kingdom of Saudi Arabia

USGS Publications Warehouse

Meissner, C.R.; Griffin, M.B.; Riddler, G.P.; Van Eck, Marcel; Aspinall, N.C.; Farasani, A.M.; Dini, S.M.

1990-01-01

Several deep drill holes in the Wadi as Sirhan depression have penetrated thick sequences of marine rocks that are potential sources of oil and gas. Geological and geophysical conditions are favorable for the accumulation of hydrocarbons, and additional exploration is recommended.

Zirconology of lherzolites in the Nurali Massif

NASA Astrophysics Data System (ADS)

Krasnobaev, A. A.; Rusin, A. I.; Anfilogov, V. N.; Valizer, P. M.; Busharina, S. V.; Medvedeva, E. V.

2017-06-01

The age trend (SHRIMP U/Pb) of the evolution of zircon is obtained for the first time in lherzolites of the Nurali Massif. Zircons are subdivided into groups by the crystallomorphological and geochemical features. These specific features in zircon development are confirmed by the age dates. Precambrian dates (no younger than 1190 Ma) correspond to mantle sources of the lherzolite block. The Early Silurian (445-448 and 439-440 Ma) wass the time of lherzolite magmatism of 10-15 Ma in duration. The Middle Devonian (382.9 ± 8.7 Ma) corresponded to postmagmatic processes related to the effect of gabbro-diorite intrusions crowning in the Nurali Massif.

Occurrence of 222Rn in irrigation water from Wadi Al-Rummah Qassim province, Saudi Arabia

NASA Astrophysics Data System (ADS)

El-Taher, Atef; Alashrah, Saleh

2015-08-01

Naturally accruing radioactive materials in the environment have received attention since they may be present in high level and pose risk to human health. The present work deals with measuring of 222Rn in irrigation water samples from Wadi Al-Rummah, Qassim province, in central of Saudi Arabia. 222Rn concentrations were measured by RAD7. It was found that the concentration of 222Rn ranged from 2.1 ± 1.2 to 7.2 ± 1.5 BqL-1. These values are below 11.1 BqL-1 the maximum contamination level recommended from the U.S. Environmental Protection Agency. The calculated annual effective dose (AED) ranging from 7.5 to 26.1 µSv/y. It was evident that the total annual effective dose resulting from radon in irrigation groundwater in Wadi Al-Rummah in Qassim area were significantly lower than the recommended limit 1 mSv/y for the public.

Geology and mineral deposits of the Wadi an Nuqumi quadrangle, Kingdom of Saudi Arabia

USGS Publications Warehouse

Hummel, C.L.

1972-01-01

The rocks, structures, and mineral deposits of the Wadi an Nuqumi quadrangle were formed during three periods of deformation, two of Precambrian age and one of Tertiary and Recent age. The older Precambrian Halaban cycle produced the thick eugeosynclinal suite of interlayered metasedimentary and metavolcanic rocks comprising the Halaban Formation, the numerous synorogenic granitic masses which intrude the layered rocks, and the northward-trending tectonic, plutonic, and metamorphic features of all these rocks which constitute the basic grain of the area. The older Halaban features are everywhere strongly transected, but only slightly deformed and offset, by many eastward-northeastward-, and northwestward-striking fractures and strike-slip faults. Silicic dikes are emplaced in these fractures, and several kinds of barren and metalliferous veins are closely associated with them. All these features are here thought to have formed during a period of deformation of late Precambrian age which produced the Najd Wrench Fault Zone; therefore, these features are named for it. Sporadic remnants of once far more extensive basaltic lava fields and the north-northwestward-striking vertical fractures which occur in them and contain volcanic vents from which they were extruded are the youngest rocks and structures in the Wadi an Nuqumi area. They are thought to have formed during the period of tectonic and volcanic activity which also produced the Red Sea graben. The principal mineral deposits of the Wadi an Nuqumi area are silicified-carbonate breccia veins which occur in structures of the Najd Wrench Fault deformation and metalliferous quartz veins which are closely associated with them. Only the latter possesses any economic potential, the most promising being the gold and silver-bearing quartz-base metal veins of the Al Numrahniyah and Muthaheel ancient mines.

Diversity of mire massif types in the boreal zone of European Russia

NASA Astrophysics Data System (ADS)

Kuznetsov, O. L.

2018-03-01

In Russia, mire massif type is the principal structural unit for descriptions of the diversity of regional mire ecosystems of various ranks, vegetation mapping, and decision-making on the use of mires. The classification of mire massifs is based on various criteria and indicators. The botanical-geographical classification of mire massifs of the boreal zone of European Russia is four-tiered, and includes 22 types gathered in groups, subgroups and three classes. For most of the types their characteristic associations and diagnostic species are stated.

Lunar Prospecting Using Thermal Wadis and Compact Rovers. Part A; Infrastructure for Surviving the Lunar Night

NASA Technical Reports Server (NTRS)

Sacksteder, Kurt R.; Wegeng, Robert S.; Suzuki, Nantel H.

2012-01-01

Recent missions have confirmed the existence of water and other volatiles on the Moon, both in permanently-shadowed craters and elsewhere. Non-volatile lunar resources may represent significant additional value as infrastructure or manufacturing feedstock. Characterization of lunar resources in terms of abundance concentrations, distribution, and recoverability is limited to in-situ Apollo samples and the expanding remote-sensing database. This paper introduces an approach to lunar resource prospecting supported by a simple lunar surface infrastructure based on the Thermal Wadi concept of thermal energy storage and using compact rovers equipped with appropriate prospecting sensors and demonstration resource extraction capabilities. Thermal Wadis are engineered sources of heat and power based on the storage and retrieval of solar-thermal energy in modified lunar regolith. Because Thermal Wadis keep compact prospecting rovers warm during periods of lunar darkness, the rovers are able to survive months to years on the lunar surface rather than just weeks without being required to carry the burdensome capability to do so. The resulting lower-cost, long-lived rovers represent a potential paradigm breakthrough in extra-terrestrial prospecting productivity and will enable the production of detailed resource maps. Integrating resource processing and other technology demonstrations that are based on the content of the resource maps will inform engineering economic studies that can define the true resource potential of the Moon. Once this resource potential is understood quantitatively, humans might return to the Moon with an economically sound objective including where to go, what to do upon arrival, and what to bring along.

Flash Floods Simulation Using a Physical based hydrological Model at the Eastern Nile Basin: Case studies; Wadi Assiut, Egypt and Wadi Gumara, Lake Tana, Ethiopia.

NASA Astrophysics Data System (ADS)

Saber, M.; Sefelnasr, A.; Yilmaz, K. K.

2015-12-01

Flash flood is a natural hydrological phenomenon which affects many regions of the world. The behavior and effect of this phenomenon is different from one region to the other regions depending on several issues such as climatology and hydrological and topographical conditions at the target regions. Wadi assiut, Egypt as arid environment, and Gumara catchment, Lake Tana, Ethiopia, as humid conditions have been selected for application. The main target of this work is to simulate flash floods at both catchments considering the difference between them on the flash flood behaviors based on the variability of both of them. In order to simulate the flash floods, remote sensing data and a physical-based distributed hydrological model, Hydro-BEAM-WaS (Hydrological River Basin Environmental Assessment Model incorporating Wadi System) have been integrated used in this work. Based on the simulation results of flash floods in these regions, it was found that the time to reach the maximum peak is very short and consequently the warning time is very short as well. It was found that the flash floods starts from zero flow in arid environment, but on the contrary in humid arid, it starts from Base flow which is changeable based on the simulated events. Distribution maps of flash floods showing the vulnerable regions of these selected areas have been developed. Consequently, some mitigation strategies relying on this study have been introduced. The proposed methodology can be applied effectively for flash flood forecasting at different climate regions, however the paucity of observational data.

Geochemistry of carbonatites of the Tomtor massif

USGS Publications Warehouse

Kravchenko, S.M.; Czamanske, G.; Fedorenko, V.A.

2003-01-01

Carbonatites compose sheet bodies in a 300-m sequence of volcanic lamproites, as well as separate large bodies at depths of >250-300 m. An analysis of new high-precision data on concentrations of major, rare, and rare earth elements in carbonatites shows that these rocks were formed during crystallization differentiation of a carbonatite magma, which resulted in enrichment of the later melt fractions in rare elements and was followed by autometasomatic and allometasomatic hydrothermal processes. Some independent data indicate that the main factor of ore accumulation in the weathered rock zone (also known as the "lower ore horizon" comprising metasomatized volcanics with interbedded carbonatites) was hydrothermal addition of Nb and REEs. The giant size of the Tomtor carbonatite-nepheline syenite massif caused advanced magma differentiation, extensive postmagmatic metasomatism and recrystallization of host rocks, and strong enrichment of carbonatites in incompatible rare and rare earth elements (except for Ta, Zr, Ti, K, and Rb) compared to the rocks of many other carbonatite massifs. We suggest that a wide range of iron contents in carbonatites-2 can be related to extensive magnetite fractionation at the magmatic stage in different parts of the huge massif. Copyright ?? 2003 by MAIK "Nauka/Interperiodica" (Russia).

Thermal Wadis in Support of Lunar Exploration: Concept Development and Utilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyas, Josef; Wegeng, Robert S.; Burgess, Jeremy M.

2009-10-12

Thermal wadis, engineered sources of heat, can be used to extend the life of lunar rovers by keeping them warm during the extreme cold of the lunar night. Thermal wadis can be manufactured by sintering or melting lunar regolith into a solid mass with more than two orders of magnitude higher thermal diffusivities compared to native regolith dust. Small simulant samples were sintered and melted in the electrical furnaces at different temperatures, different heating and cooling rates, various soaking times, under air, or in an argon atmosphere. The samples were analyzed with scanning electron microscopy and energy dispersive spectroscopy, X-raymore » diffraction, a laser-flash thermal diffusivity system, and the millimeter-wave system. The melting temperature of JSC-1AF simulant was ~50°C lower in an Ar atmosphere compared to an air atmosphere. The flow of Ar during sintering and melting resulted in a small mass loss of 0.04 to 0.1 wt% because of the volatization of alkali compounds. In contrast, the samples that were heat-treated under an air atmosphere gained from 0.012 to 0.31 wt% of the total weight. A significantly higher number of cavities were formed inside the samples melted under an argon atmosphere, possibly because of the evolution of oxygen bubbles from iron redox reactions. The calculated emissivity of JSCf-1AF simulant did not change much with temperature, varying between 0.8 and 0.95 at temperatures from 100 to 1200°C. The thermal diffusivities of raw regolith that was compressed under a pressure of 9 metric tons ranged from 0.0013 to 00011 in the 27 to 390°C temperature range. The thermal diffusivities of sintered and melted JSC-1AF simulant varied from 0.0028 to 0.0072 cm2/s with the maximum thermal diffusivities observed in the samples that were heated up 5°C/min from RT to 1150°C under Ar or air. These thermal diffusivities are high enough for the rovers to survive the extreme cold of the Moon at the rim of the Shackleton Crater and allow

Occurrence of {sup 222}Rn in irrigation water from Wadi Al-Rummah Qassim province, Saudi Arabia

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Taher, Atef; Alashrah, Saleh

Naturally accruing radioactive materials in the environment have received attention since they may be present in high level and pose risk to human health. The present work deals with measuring of {sup 222}Rn in irrigation water samples from Wadi Al-Rummah, Qassim province, in central of Saudi Arabia. {sup 222}Rn concentrations were measured by RAD7. It was found that the concentration of {sup 222}Rn ranged from 2.1 ± 1.2 to 7.2 ± 1.5 BqL{sup −1}. These values are below 11.1 BqL{sup −1} the maximum contamination level recommended from the U.S. Environmental Protection Agency. The calculated annual effective dose (AED) ranging frommore » 7.5 to 26.1 µSv/y. It was evident that the total annual effective dose resulting from radon in irrigation groundwater in Wadi Al-Rummah in Qassim area were significantly lower than the recommended limit 1 mSv/y for the public.« less

Social Class Barriers of the Massification of Higher Education in Taiwan

ERIC Educational Resources Information Center

Ru-Jer, Wang

2012-01-01

In recent years, the rapid growth of higher education in Taiwan has led to an essential shift from education for the elite to the massification of higher education. Although this massification is making higher education more accessible, one of the main concerns is whether opportunities for higher education are the same among all social classes in…

3D geometry and kinematic evolution of the Wadi Mayh sheath fold, Oman, using detailed mapping from high-resolution photography

NASA Astrophysics Data System (ADS)

Cornish, Sam; Searle, Mike

2017-08-01

The Wadi Mayh sheath fold in north-eastern Oman is one of the largest and best-exposed sheath folds known, and presents a unique opportunity to better understand this somewhat enigmatic style of deformation. We undertook high-resolution photographic surveying along Wadi Mayh to document the sheath fold in 61 georeferenced panoramic photomerges. Here we present ten such images that provide a structural interpretation of the sheath fold and surrounding structure. We resolve this structure in a simplified three-dimensional model and in two orthogonal cross sections, and propose a kinematic evolution to explain the geometry. The Wadi Mayh sheath fold is the most prominent example within what we suggest is a composite sequence of sheath folds, which is itself enclosed within a SSW-closing recumbent syncline at the base of the major Saih Hatat nappe. Sheath folding is accommodated within Permian Saiq Formation limestones showing carpholite assemblages (6-8 kbar; 275-375 °C). A major discontinuity separates this sequence from enveloping older rock units. The sequence formed during progressive top-to-north, ductile shearing as the overlying nappe migrated northwards with respect to the underthrusting Hulw unit. This process occurred during SSW-directed exhumation of partially subducted continental crust in NE Oman, approximately 15 Ma after obduction of the Oman ophiolite initiated.

North Massif lithologies and chemical compositions viewed from 2-4 mm particles of soil sample 76503

NASA Technical Reports Server (NTRS)

Bishop, Kaylynn M.; Jolliff, Bradley L.; Korotev, Randy L.; Haskin, Larry A.

1992-01-01

We identify the lithologic and compositional components of soil 76503 based on INAA of 243 2-4-mm particles and 72 thin sections from these and associated 1-2-mm particles (76502). We present a statistical distribution of the major compositional types as the first step of a detailed comparative study of the North and South Massifs. The soil sample was collected well away from any boulder and is more representative of typical North Massif material than any single large rock or boulder sample. So far, our examination of the 76503 particles has provided a better definition of precursor igneous lithologies and their petrogenetic relationships. It has enabled us to refine the nature of mixing components for the North Massif less than 1-mm fines. It has confirmed the differences in lithologies and their proportions between materials of the North and South Massifs; e.g., the North Massif is distinguished by the absence of a 72275-type KREEP component, the abundance of a highly magnesian igneous component, and the absence of certain types of melt compositions found in the South Massif samples.

Reactivation of the Pleistocene trans-Arabian Wadi ad Dawasir fluvial system (Saudi Arabia) during the Holocene humid phase

NASA Astrophysics Data System (ADS)

Matter, Albert; Mahjoub, Ayman; Neubert, Eike; Preusser, Frank; Schwalb, Antje; Szidat, Sönke; Wulf, Gerwin

2016-10-01

The Wadi ad Dawasir fluvial system in central Saudi Arabia is investigated using remote sensing and sedimentology, in combination with bio-proxy analyses (molluscs and ostracods). Age control is provided by radiocarbon as well as luminescence dating, using both quartz and feldspar grains. It is shown that the fluvial system was active from the Asir Mountains across the partially sand-covered interior of the Arabian Peninsula to the Arabian Gulf during the Holocene humid period. Sedimentology and faunal analysis reveal the presence of perennial streams and a permanent freshwater lake in the distal reach of the Dawasir system that are synchronous with fluvial accumulation in the headwaters of its major tributary, Wadi Tathlith. The increased runoff during the Holocene led to a re-activation of streams that largely followed pre-existing Late Pleistocene courses and eroded into older sediments. The absence of Holocene lakes in most of the Rub' al-Khali implies that trans-Arabian rivers were mainly fed by precipitation in the Asir Mountains. Monsoonal rainfall was apparently stronger there as well as in the northern, south-eastern and southern part of the Arabian Peninsula (southern Yemen and Oman), but it apparently did not directly affect the interior during the Holocene. The palaeoenvironmental reconstruction shows a narrow trans-Arabian green freshwater corridor as the result of phases of sustained flow lasting up to several centuries. The permanent availability of water and subsistence for wildlife provided a favourable environment for human occupation as documented by Neolithic stone tools that are found all along Wadi ad Dawasir.

Petrotectonics of lawsonite eclogite exhumation: Insights from the Sivrihisar massif, Turkey

NASA Astrophysics Data System (ADS)

Davis, Peter B.

2011-02-01

The Sivrihisar massif of the Tavşanlı Zone of Turkey is 1 of less than 10 known lawsonite eclogite localities worldwide. Rocks of the Sivrihisar massif consist of eclogite and blueschist in contact with metasedimentary host rocks and record decreasing maximum pressure conditions across three WNW-ESE striking belts from 16-24 kbar in the northern Halilbaǧı belt to 14-16 kbar in the Karacaören belt and 8-10 kbar in the Kertek belt. Where present, sodic-amphibole, phengite, chlorite, and quartz define a pervasive S0/S1 foliation; garnet, omphacite, and lawsonite define stretching lineations and kinematic indicators. D1 and D2 structures are similar in the Halilbaǧı and Karacaören belts but differ to those in the Kertek belt. D3 structures are uniform across the massif including fibrous calcite that occurs parallel to F3 fold axes. Shear sense indicators from field observations and asymmetric type-I cross girdle of quartz c axes obtained from electron backscatter diffraction (EBSD) show top to the south thrusting throughout much of the massif. D1 and D2 structures are interpreted to have formed during exhumation by extrusion along a ˜5°C/km gradient. The Halilbaǧı and Karacaören belts were juxtaposed possibly as deep as 45 km within the subduction channel and exhumed by the arrival of the Anatolide microcontinent at approximately 70 Ma. Homogeneity of F3 axes and calcite fibers across the massif suggests that assembly occurred at blueschist conditions before exhumation through the aragonite-calcite transition (˜350°C) above 8 kbar.

New results to discuss possibility of irrigation in Bat (Wadi Sharsah, northwestern Oman) before Hafit period (ca. 3100-2700 BCE)

NASA Astrophysics Data System (ADS)

Fouache, Eric; Desruelles, Stéphane; Eddargach, Wassel; Cammas, Cecilia; Wattez, Julia; Martin, Chloé; Tengberg, Margareta; Beuzen-Waller, Tara; Cable, Charlotte; Thornton, Christopher

2014-05-01

Registered as a World Heritage Site by UNESCO in 1989, the extensive archaeological site of Bat is situated within the Wadi Sharsah and around the modern village and palm grove of Bat, 24 km from the modern city of Ibri in northwestern Oman. The archaeological remains from the Bronze Age excavated by the Bat Archaeological Project are located in two mains areas. The northern area consists of a chain of low limestone hills cut by wadi tributaries leading to the main Wadi Sharsah. It is characterised by an exceptionnally high density of graves from two successive Bronze Age periods : Hafit (ca. 3100-2700 BCE) and Umm an-Nar (ca. 2700-2000 BCE). South of the Bat cemetery, in the flat part of the valley, there are several large circular structures (known historically as « towers ») and remains from both Hafit and Umm an-Nar periods, as well as later periods. Geomorphological mapping of the floodplain, associated with archaeological survey, have identified walls suggesting that during the Umm an-Nar period there was a system of irrigation which controlled flood water. Sedimentological, malacological, C14 dating and micromorphological studies of a 10 m long and 2.5 m high section located 143 m northeast of the Tower 1146 on the left bank of a small tributary of the Wadi Sharsah provide strong argument for the presence of an irrigation system that began before the Hafit period. New C14 datings confirm this hypothesis. Botanical macro-remains collected during the excavation of early Bronze Age structures at Bat further indicate the presence of date palm gardens since the 3rd millenium BCE allowing the cultivation of several crop species, in particular cereals. Most generally the global palaeoenvironmental reconstruction from our data supports a model of a general trend of aridification from Bronze Age to iron Age. Key words : Bronze Age, Holocene, Geomoephology, Micromorphology, Irrigation, Oman.

Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

NASA Astrophysics Data System (ADS)

Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

2013-05-01

The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

The mineral resource potential of the Wadi Habawnah and Najran quadrangles, sheets 17/44A and 17/44C, Kingdom of Saudi Arabia

USGS Publications Warehouse

Fenton, Michael D.

1983-01-01

The metallic resource potential of the Wadi Habawnah and Najran quadrangles in the southern Precambrian Arabian Shield has been determined primarily by reconnaissance rock geochemistry, limited wadi-sediment and colluvium geochemistry, and gossanous and ferruginous outcrop geochemistry. These surveys were guided by geological information acquired during previous reconnaissance mapping. Locally anomalous areas in alkalic and calc-alkalic granitic terrane are possible sources of niobium-zirconiumthorium-fluorite, tin-tungsten, and copper-molybdenum, although the potential of these areas does not appear to be outstanding. The reconnaissance geochemistry of the layered volcanic terrane and the geochemistry of gossanous and ferruginous outcrops indicate that the potential for stratiform base metal sulfide deposits is low.

Anthropogenic Influence On Groundwater Quality In Jericho and And Adjoining Wadis (Lower Jordan Valley, Palestine)

NASA Astrophysics Data System (ADS)

Geyer, S.; Khayat, S.; Roediger, T.; Siebert, C.

2008-12-01

The Lower Jordan Valley is part of the Jordan-Dead Sea Rift. The graben is filled by sedmiments of limnological and marine origin. Towards the Dead Sea, the occurance of gipseous and salty sediments on the valley floor increase. The southern part of the Lower Jordan Valley, where the city of Jericho is situated, is an arid area (<150 mm precipitation/year), with less amount of exploitable fresh groundwater or surface water. Jericho was founded on an alluvial fan, closely to the western mountain range in front of mouth of Wadi Qilt. The fan serves as reservoir for infiltrating water from wadi runoff and groundwater from the crataceous aquifers of the western shoulder. The fan is surrounded by unsuitable aquifers of the graben, which are filled with saline water. The aim of this study, which takes place inside the multilateral SMART-project, is to understand the vulnerability of the Jericho groundwater aquifers in connection with lowering the groundwater table by overexploitation and the intensively use of pesticides Jericho and its vicinity are of most importance for the Palestinians. However, beside the about 25,000 residents, the tourism industry and the vital agriculture depend on sufficient and expoitable fresh water resources. Because the demand of water is increasing, overexpoitaion takes place. Due to over extraction of groundwater a huge depression cone is evolving during the dry season which is filled up again according to the groundwater recharge in the rainy season. Concomitantly, depression cone in the fresh water aquifers leads to an infiltration of the surrounding saltwater. The amount of saltwater which infiltrates into the freshwater resource was calculated by different stable isotope methods (d2H, d18O) and hydrochemical analyses of wellwater. The agriculture is main consumer of groundwater - over 60% of the pumped water is used for inefficient irrigation. Additionally, an intensive use of pesticides in concentrated liquid and gaseous forms for

Long lasting paleolandscapes stability of the French Massif Central during the Mesozoic

NASA Astrophysics Data System (ADS)

Ricordel-Prognon, C.; Thiry, M.; Theveniaut, H.; Lagroix, F.

2009-04-01

Regional geodynamical evolution is mainly constrained by the sedimentary record in the basins. Usually, little is known about geodynamics of the peripheral areas and even less on the evolution of the basement areas. Continental unconformities are essential to estimate erosion rates of basement and to model the crustal dynamics that control subsidence of surrounding sedimentary basins but also uplift and erosion on their edges. Dating such unconformities has always been the stumbling block while it is a prerequisite to constrain geodynamical models. Paleomagnetism has been proven as a suitable tool to date ferrugineous paleoweathering features. The method has been applied to paleoweathering occurrences resting on the Massif Central crystalline basement as well as to paleoweathering features affecting the crystalline basement itself. The remanence measurements were obtained at the Paleomagnetic Laboratory of the Institut Physique du Globe de Paris and data analyses were carried out using PaleoMac 5 software (Cogné, 2003). Relative dating of the paleoweathering profiles have been acquired by comparing the recorded paleomagnetic poles from the analysed samples to the apparent polar wandering path of the Eurasian plate (Edel et Duringer, 1997 ; Besse and Courtillot, 2003). Thick red kaolinitic formations rest locally on the Massif Central basement. They are generally bounded by the Tertiary grabens and buried by the Oligocene formations. Thus these azoic red formations have classically been ascribed to the "Siderolithic" formations of Eocene-Oligocene age. They show many pedogenic features (termites burrows, illuviation and hydromorphic features and nodules) and strong relationships with paleolandscape organisation (leaned against fault scarps, infilling paleovalleys, etc.). Macro and micromorphological arrangements show that these formations are in situ paleosols. Paleomagnetic ages range from 160 Ma (Late Jurassic) in the centre of the Massif Central to 140 Ma (Early

Estimates of Ground-Water Recharge in Wadis of Arid, Mountainous Areas Using the Chloride Mass-Balance Approach

NASA Astrophysics Data System (ADS)

Wood, W. W.; Wood, W. W.

2001-05-01

Evaluation of ground-water supply in arid areas requires estimation of annual recharge. Traditional physical-based hydrologic estimates of ground-water recharge result in large uncertainties when applied in arid, mountainous environments because of infrequent, intense rainfall events, destruction of water-measuring structures associated with those events, and consequent short periods of hydrologic records. To avoid these problems and reduce the uncertainty of recharge estimates, a chloride mass-balance (CMB) approach was used to provide a time-integrated estimate. Seven basins exhibiting dry-stream beds (wadis) in the Asir and Hijaz Mountains, western Saudi Arabia, were selected to evaluate the method. Precipitation among the basins ranged from less than 70 mm/y to nearly 320 mm/y. Rain collected from 35 locations in these basins averaged 2.0 mg/L chloride. Ground water from 140 locations in the wadi alluvium averaged 200 mg/L chloride. This chloride concentration ratio of precipitation to ground water suggests that on average, approximately 1 percent of the rainfall is recharged, while the remainder is lost to evaporation. Ground-water recharge from precipitation in individual basins ranged from less than 1 to nearly 4 percent and was directly proportional to total precipitation. Independent calculations of recharge using Darcy's Law were consistent with these findings and are within the range typically found in other arid areas of the world. Development of ground water has lowered the water level beneath the wadis and provided more storage thus minimizing chloride loss from the basin by river discharge. Any loss of chloride from the basin results in an overestimate of the recharge flux by the chloride-mass balance approach. In well-constrained systems recharge in arid, mountainous areas where the mass of chloride entering and leaving the basin is known or can be reasonably estimated, the CMB approach provides a rapid, inexpensive method for estimating time

UC Irvine CHRS Real-time Global Satellite Precipitation Monitoring System (G-WADI PERSIANN-CCS GeoServer) for Hydrometeorological Applications

NASA Astrophysics Data System (ADS)

Sorooshian, S.; Hsu, K. L.; Gao, X.; Imam, B.; Nguyen, P.; Braithwaite, D.; Logan, W. S.; Mishra, A.

2015-12-01

The G-WADI Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) GeoServer has been successfully developed by the Center for Hydrometeorology and Remote Sensing (CHRS) at the University of California Irvine in collaboration with the UNESCO's International Hydrological Programme (IHP) and a number of its international centers. The system employs state-of-the-art technologies in remote sensing and artificial intelligence to estimate precipitation globally from satellite imagery in real-time and high spatiotemporal resolution (4km, hourly). It offers graphical tools and data service to help the user in emergency planning and management for natural disasters related to hydrological processes. The G-WADI PERSIANN-CCS GeoServer has been upgraded with new user-friendly functionalities. The precipitation data generated by the GeoServer is disseminated to the user community through support provided by ICIWaRM (The International Center for Integrated Water Resources Management), UNESCO and UC Irvine. Recently a number of new applications for mobile devices have been developed by our students. The RainMapper has been available on App Store and Google Play for the real-time PERSIANN-CCS observations. A global crowd sourced rainfall reporting system named iRain has also been developed to engage the public globally to provide qualitative information about real-time precipitation in their location which will be useful in improving the quality of the PERSIANN-CCS data. A number of recent examples of the application and use of the G-WADI PERSIANN-CCS GeoServer information will also be presented.

Quantifying surface water runoff from Wadi Arogut towards the Dead Sea

NASA Astrophysics Data System (ADS)

Geyer, Stefan; Khayat, Saed; Marei, Amer

2015-04-01

The surrounded area of the Dead Sea, especially the west side suffers from many hydrological problems. While the Dead Sea level drop considered a major problem that affect the quality of the surrounded freshwater resources, a lot of the surface water flood from the adjacent Wadi are lost through direct run off without any exploitation. Therefore, it is necessary to maintain a type of balance between surface water exploitation through the Wadi and at the same time allow a sufficient amount of flow to the Dead Sea to ensure its sustainability. In this study, we choose one of the larger tributaries in the western side of the Dead Sea basin. The stream was modelled for runoff response to different rainfall amount and climate conditions (dry, normal, and wet seasons) which were chosen from the rainy seasons in the previous 30 years. Finally, the amount of surface water contribution from each of the three seasons of the Dead Sea was quantified. The outcome of the model shows the results from the normal rainy season, which is frequently reoccurs and common in the region. The model data show that such events normally contribute with about 18-22 MCM annually to the Dead Sea. The problem is with the recurrence of dry season such as 2005/2006, by which the amount of the surface water decrease and consequently has adverse effect on the Dead Sea. However, the presence of less frequent thunder storm season such as that one in 1991/1992 has also a positive effect on the Dead Sea level. In the rainy season 1991/1992 there was a higher amount of rainfall over the study area that reaches around 155 MCM. Despite the presence of this high amount most of the recharge lost to the ground as groundwater recharge. The high amount of rain increases the amount of inundated surface water out of the Wadi banks and covers more surfaces all over the study area, which in role promote more water loss to the ground. That is why the total loss (rather than surface runoff) was much higher (77

Modulations of MLT turbulence by waves observed during the WADIS sounding rocket project.

NASA Astrophysics Data System (ADS)

Strelnikov, Boris; Latteck, Ralph; Strelnikova, Irina; Lübken, Franz-Josef; Baumgarten, Gerd; Rapp, Markus

2017-04-01

The WADIS project (WAve propagation and DISsipation in the middle atmosphere) aimed at studying waves, their dissipation, and effects on trace constituents. Among other things, it addressed the question of the variability of MLT turbulence, both in time and space. A unique feature of the WADIS project was multi-point turbulence sounding applying different measurement techniques including rocket-borne ionization gauges, VHF MAARSY radar, and VHF EISCAT radar in Tromsø. The project comprised two sounding rocket campaigns conducted at the Andøya Space Center (69 °N, 16 °E). One sounding rocket was launched in summer 2013 and one in winter 2015. The joint in-situ and ground-based observations showed horizontal variability of the turbulence field in the MLT at scales from a few to 100 km. We found that the turbulence dissipation rate varied in space in a wave-like manner both horizontally and in the vertical direction. This wave-like modulation reveals the same vertical wavelengths as those seen in gravity waves. We also found that vertical mean value of radar turbulence observations reveals wave-like modulation in time domain. This time variability results in up to two orders of magnitude change of the energy dissipation values with periods of 24 h. It also shows 12 h and shorter ( hours) modulations resulting in one decade variation. In this paper we present recent measurement results of turbulence-mean flow interaction and discuss possible reasons of the observed modulations.

Research of dynamical Characteristics of slow deformation Waves as Massif Responses on Explosions

NASA Astrophysics Data System (ADS)

Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

2013-04-01

The research of massif state with use of approaches of open system theory [1-3] was developed for investigation the criterions of dissipation regimes for real rock massifs, which are under heavy man-caused influence. For realization of that research we used the data of seismic catalogue of Tashtagol mine. As a result of the analyze of that data we defined character morphology of phase trajectories of massif response, which was locally in time in a stable state: on the phase plane with coordinates released by the massif during the dynamic event energy E and lg(dE/dt) there is a local area as a ball of twisted trajectories and some not great bursts from that ball, which are not greater than 105 joules. In some time intervals that burst can be larger, than 105 joules, achieving 106 joules and yet 109 joules. [3]. Evidently there are two reciprocal depend processes: the energy accumulation in the attracted phase trajectories area and resonance fault of the accumulated energy. But after the fault the system returns again to the same attracted phase trajectories area. For analyzing of the thin structure of the chaotic area we decided to add the method of processing of the seismic monitoring data by new parameters. We shall consider each point of explosion as a source of seismic or deformation waves. Using the kinematic approach of seismic information processing we shall each point of the massif response use as a time point of the first arrival of the deformation wave for calculation of the wave velocity, because additionally we know the coordinates of the fixed response and the coordinates of explosion. The use of additional parameter-velocity of slow deformation wave propagation allowed us with use method of phase diagrams identify their hierarchic structure, which allow us to use that information for modeling and interpretation the propagation seismic and deformation waves in hierarchic structures. It is researched with use of that suggested processing method the thin

Structural and kinematic evolution of a Miocene to Recent sinistral restraining bend: the Montejunto massif, Portugal

NASA Astrophysics Data System (ADS)

Curtis, Michael L.

1999-01-01

The Montejunto massif lies in the apex of a large-scale restraining bend at the southern termination of a sinistral transpressive fault system, in the Lusitanian basin of Portugal. Cenozoic deformation within the Montejunto massif initiated with southerly directed thrusting along the southern boundary of the massif, in association with the development of the E-W oriented Montejunto anticline, probably during the Langhian. Deformation switched to the northern boundary of the massif, in association with a change to NW-directed thrusting and continued development of the Montejunto anticline. The youngest set of structures within the massif is related to the sinistral reactivation of the Arieiro fault system, and steeply inclined bedding. This late phase of deformation represents the accommodation of a component of sinistral displacement across the restraining bend along mechanical anisotropies formed during this progressive Cenozoic deformation event. Variation in the kinematic style of the Main Arieiro fault is related to the angle ( α) between the fault plane and the displacement vector. Where α≈20°, abrupt pene-contemporaneous switches in displacement direction are recorded along the fault, whereas strike-slip kinematics predominate where α<20°. The timing of deformation events in the Montejunto massif is uncertain. However, correlation with the established Cenozoic Africa/Europe plate convergence directions may provide potential temporal constraints.

Discussion on Ubeid, K.A., 2016. Quaternary alluvial deposits of Wadi Gaza in the middle of the Gaza Strip (Palestine): Facies, granulometric characteristics, and their paleoflow direction. JAES 118: 274-283

NASA Astrophysics Data System (ADS)

Roskin, Joel

2017-10-01

The location of the Gaza Strip at the southeastern corner of the Mediterranean Sea along a transition zone between Mediterranean and arid climate zones at the meeting point between fluvial, coastal, and aeolian sediments makes the Strip an important region for Quaternary, hydrogeologic, geomorphic, and palaeoclimatic studies (Aish, 2004). Wadi Gaza, the only water course that fully crosses the Gaza Strip into the southeastern Mediterranean Sea is an important water source for the proliferating and dense population of the Gaza Strip (Zaineldeen and Aish, 2012), is an indispensable part of natural life in Gaza and has an interesting history and rich vegetation (Abd Rabou et al., 2016). As such, the hydrogeologic conditions of Wadi Gaza need to be fully resolved. This includes the study of the wadi's palaeohydrology and the current anthropogenic impact upon flow and deposition along the watercourse.

Crustal structure of the northern Menderes Massif, western Turkey, imaged by joint gravity and magnetic inversion

NASA Astrophysics Data System (ADS)

Gessner, Klaus; Gallardo, Luis A.; Wedin, Francis; Sener, Kerim

2016-10-01

In western Anatolia, the Anatolide domain of the Tethyan orogen is exposed in one of the Earth's largest metamorphic core complexes, the Menderes Massif. The Menderes Massif experienced a two-stage exhumation: tectonic denudation in the footwall of a north-directed Miocene extensional detachment, followed by fragmentation by E-W and NW-SE-trending graben systems. Along the northern boundary of the core complex, the tectonic units of the Vardar-Izmir-Ankara suture zone overly the stage one footwall of the core complex, the northern Menderes Massif. In this study, we explore the structure of the upper crust in the northern Menderes Massif with cross-gradient joint inversion of gravity and aeromagnetic data along a series of 10-km-deep profiles. Our inversions, which are based on gravity and aeromagnetic measurements and require no geological and petrophysical constraints, reveal the salient features of the Earth's upper crust. We image the northern Menderes Massif as a relatively homogenous domain of low magnetization and medium to high density, with local anomalies related to the effect of interspersed igneous bodies and shallow basins. In contrast, both the northern and western boundaries of the northern Menderes Massif stand out as domains where dense mafic, metasedimentary and ultramafic domains with a weak magnetic signature alternate with low-density igneous complexes with high magnetization. With our technique, we are able to delineate Miocene basins and igneous complexes, and map the boundary between intermediate to mafic-dominated subduction-accretion units of the suture zone and the underlying felsic crust of the Menderes Massif. We demonstrate that joint gravity and magnetic inversion are not only capable of imaging local and regional changes in crustal composition, but can also be used to map discontinuities of geodynamic significance such as the Vardar-Izmir-Ankara suture and the West Anatolia Transfer Zone.

Evidence for polymetamorphic garnet growth in the Çine (southern Menderes) Massif, Western Turkey

NASA Astrophysics Data System (ADS)

Baker, C. B.; Catlos, E. J.; Sorensen, S. S.; Çemen, I.; Hancer, M.

2008-07-01

Garnet-based thermobarometry is often used to develop models for the evolution of the Menderes Massif, a key Aegean metamorphic core complex. Here we present X-ray element maps and high-contrast backscattered electron (BSE) and cathodoluminescence (CL) images from a garnet-bearing rock from the Çine (southern Menderes) Massif. The images document a polymetamorphic history as plagioclase and garnet grains show distinct cores and rims. The sample contains matrix monazite in reaction with allanite. The garnet in the sample is likely not in equilibrium with its matrix minerals. This is evidenced by BSE images that document compositional variability in both core and rim zoning and tracks of bright streaks extending from rim to core. We propose that some garnet that is now present in the Menderes Massif formed due to collision during Cambro-Ordovician and may have recrystallized during subsequent collisional and extensional events. These processes led to non-equilibrium compositions and can result in spurious pressure-temperature (P-T) calculations. To establish the feasibility of the P-T estimates of rocks from the Çine Massif for input into tectonic models for the region, more than one sample from single outcrops should be analyzed. Rocks within the Çine Massif have been suggested to display inverted metamorphism, an increase in T towards structurally higher levels. Based on the garnet documented here, we propose that the inverted metamorphism may be a consequence of apparent P-T rather than a real phenomenon.

Ground-followup studies of the 1977 airborne electromagnetic survey in the Assifar and Mulhal areas, Wadi Bidah district, Kingdom of Saudi Arabia

USGS Publications Warehouse

Flanigan, Vincent J.; Sadek, Hamdy

1983-01-01

A brief review of the AEM ground-followup studies in the Wadi Bidah district suggests that most, if not all, of the AEM conductors are carbonaceous rocks. Secondary causes of conductivity are intense faulting and shearing.

Reconnaissance geochemical survey of Al Jurdhawiyah and Wadi al Jarir quadrangles, sheets 25/42 D and 25/42 C, Kingdom of Saudia Arabia

USGS Publications Warehouse

Samater, Rashid M.

1983-01-01

A reconnaissance wadi-sediment geochemical survey was conducted in the Al Jurdhawiyah (sheet 28/42 D) and Wadi al Jarir (sheet 2G/42 C) quadrangles in order to identify anomalies potentially related to mineralized rock. Sieved bulk-sediment fractions and pan concentrates were created from the original samples collected from wadis in the two quadrangles. A semiquantitative 30-element spectrographic analysis was completed on both the sieved bulk-sediment fraction and the pan concentrate of each sample. The results were statistically analyzed in an attempt to identify anomalous regions. Anomaly threshold values were calculated for most elements; the threshold value of an element in a data set is defined as the geometric mean value plus two standard deviations. The Bald al Jimalah West tin-tungsten deposit (MODS 02661) in the southern part of the Al Jurdhawiyah quadrangle was identified by one pan-concentrate sample containing anomalous concentrations of tin and tungsten. Samples near the Bald al Jimalah East ancient lead-zinc-silver mines (MODS 00960) contain strongly anomalous concentrations of tin and lead and to a lesser extent of tungsten and copper. Both of these regions and other regions containing anomalous concentrations of certain elements are recommended for additional studies. A comparison of results obtained from sieved bulk-sediment fractions and pan concentrates indicates that the latter is the better medium for these geochemical investigations.

Higher Education, Changing Labour Market and Social Mobility in the Era of Massification in China

ERIC Educational Resources Information Center

Mok, Ka Ho; Wu, Alfred M.

2016-01-01

This article attempts to investigate the relationship between the massification of higher education, labour market and social mobility in contemporary China. Though only a short period of time has elapsed from elite to mass education, China's higher education has been characterised as a wide, pervasive massification process. Similar to other East…

The Apollo 17 samples: The Massifs and landslide

NASA Technical Reports Server (NTRS)

Ryder, Graham

1992-01-01

More than 50 kg of rock and regolith samples, a little less than half the total Apollo 17 sample mass, was collected from the highland stations at Taurus-Littrow. Twice as much material was collected from the North Massif as from the South Massif and its landslide (the apparent disproportionate collecting at the mare sites is mainly a reflection of the large size of a few individual basalt samples). Descriptions of the collection, documentation, and nature of the samples are given. A comprehensive catalog is currently being produced. Many of the samples have been intensely studied over the last 20 years and some of the rocks have become very familiar and depicted in popular works, particularly the dunite clast (72415), the troctolite sample (76535), and the station 6 boulder samples. Most of the boulder samples have been studied in Consortium mode, and many of the rake samples have received a basic petrological/geochemical characterization.

New radiocarbon dates on the cereals from Wadi Kubbaniya

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wendorf, F.; Schild, R.; Close, A.E.

1984-01-01

In 1978, three carbonized grains of barley and a carbonized grain of einkorn wheat were found in a buried hearth at a Late Paleolithic site at Wadi Kubbaniya in Egypt. In 1981, two large clusters of barley seeds, which were identified as six-row barley and thus domestic, were found at a nearby site of comparable age. Numerous grinding stones, presumed to have been used for processing the cereals, were found in these and other sites, often deeply buried, and 30 radiocarbon dates placed the occupations between 18,500 and 17,000 radiocarbon years ago. These finds led us to suggest an earlymore » origin of food production, with implications for the initial development of complex societies. Several barley seeds were analyzed by electron spin resonance spectroscopy to determine the maximal temperature to which they had been subjected before burial. Six barley seeds and three small pieces of wood charcoal were dated directly by using a tandem accelerator mass spectrometer.« less

Structure, age, and ore potential of the Burpala rare-metal alkaline massif, northern Baikal region

NASA Astrophysics Data System (ADS)

Vladykin, N. V.; Sotnikova, I. A.; Kotov, A. B.; Yarmolyuk, V. V.; Sal'nikova, E. B.; Yakovleva, S. Z.

2014-07-01

The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.

Mineralogy and geochemistry of the Tartai massif, East Siberian metallogenic province

NASA Astrophysics Data System (ADS)

Podlipsky, M. Yu.; Mekhonoshin, A. S.; Tolstykh, N. D.; Vishnevskiy, A. V.; Polyakov, G. V.

2015-05-01

The Tartai ultramafic-mafic massif is located in the central part of the East Siberian metallogenic (PGE-Cu-Ni) province (728-712 Ma), which constitutes part of the southern margin of the Siberian craton. This dunite-peridotite-pyroxenite-gabbro massif is the host to low-sulfide PGE-Cu-Ni mineralization. The massif was formed by fractional crystallization of picritic magmas and is composed of wehrlite, dunite, plagiowehrlite, and olivine melanogabbro. The composition of olivine varies from Fo89.9 in dunite to Fo83 in melanocratic olivine gabbro; clinopyroxene is esentially augite. Chrome-spinels crystallized at a low degree of oxidation and have a high iron content. Disseminated sulfide mineralization (pentlandite and heazlewoodite) with high PGE concentrations was identified in wehrlites. Pentlandite is enriched in Fe and Co and depleted in S. These features and the association pentlandite with heazlewoodite suggest that the sulfide mineralization was formed over a wide temperature range (600-400°C) at low sulfur activity (log fS2 from -16 to -9). PGM are represented by Ir-bearing sperrylite, Pd-Cu-Sb panning compounds of variable compositions, Pt-Fe-Cu and Pt-Cu alloys. The evolutionary trend of the ore system was from essentially Ni compositions at the early magmatic stage during formation of disseminated mineralization toward Cu-rich composition at the post-magmatic stage. The PGM assemblage from heavy concentrate haloes differs from bedrock-hosted mineralization in its wider variety of mineral species and the presence of refractory platinoids. Sperrylite from heavy concentrate haloes of the Tartai massif serves as a reliable prospecting guide for bedrock-hosted sulfide Cu-Ni deposits.

Strain analysis and microstructural evolution characteristic of neoproterozoic rocks associations of Wadi El Falek, centre Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Kassem, Osama M. K.; Rahim, Said H. Abd El; Nashar, El Said R. El

2012-09-01

The estimation of finite strain in rocks is fundamental to a meaningful understanding of deformational processes and products on all scales from microscopic fabric development to regional structural analyses. The Rf/φ and Fry methods on feldspar porphyroclasts and mafic grains from 5 granite, 1 metavolcanic, 3 metasedimentary and 1 granodiorite samples were used in Wadi El Falek region. Finite-strain data shows that a high to moderate range of deformation of the granitic to metavolcano-sedimentary samples and axial ratios in the XZ section range from 1.60 to 4.10 for the Rf/φ method and from 2.80 to 4.90 for the Fry method. Furthermore, the short axes are subvertical associated with a subhorizontal foliation. We conclude that finite strain in the deformed granite rocks is of the same order of magnitude as that from metavolcano-sedimentary rocks. Furthermore, contacts formed during intrusion of plutons with some faults in the Wadi El Falek area under brittle to semi-ductile deformation conditions. In this case, finite strain accumulated during superimposed deformation on the already assembled nappe structure. It indicates that the nappe contacts formed during the accumulation of finite strain.

The peculiarities of structurizing enclosing rock massif while developing a coal seam

NASA Astrophysics Data System (ADS)

Kozyreva, E. N.; Shinkevich, M. V.

2017-09-01

Different concepts of the development of geo-mechanical processes during longwall mining of a seam which are fundamentally different from the conventional ones are introduced in the article. Fundamental principles of the model for structurizing enclosing rock mass while longwall mining along the strike are described. The model was developed on the bases of non-linear geomechanical laws. According to the model, rock mass in the area of mining operation is organized as rock geomechanical layers with shifting arches. And the formation period of shifting arches in disintegrated rock mass is divisible by the length of the stope. Undulate characteristic of a massif as a peculiarity of man-made structurization of a massif is defined. It is shown that structuring the broken massif causes the formation of block-structured system and it can be detected while monitoring the ground pressure in powered support props. The results of the research allow decreasing the negative influence of a ground pressure and can be applied to specify parameters for controlling the roof, defining geometrical dimensions of a mining section and positioning of holing chute (face entry).

A-type granites from the Guéra Massif, Central Chad: Petrology, geochemistry, geochronology, and petrogenesis.

NASA Astrophysics Data System (ADS)

Pham, Ngoc Ha T.; Shellnutt, J. Gregory; Yeh, Meng-Wan; Lee, Tung-Yi

2017-04-01

The poorly studied Saharan Metacraton of North-Central Africa is located between the Arabian-Nubian Shield in the east, the Tuareg Shield in the west and the Central African Orogenic Belt in the south. The Saharan Metacraton is composed of Neoproterozoic juvenile crust and the relics of pre-Neoproterozoic components reactivated during the Pan-African Orogeny. The Republic of Chad, constrained within the Saharan Metacraton, comprises a Phanerozoic cover overlying Precambrian basement outcroppings in four distinct massifs: the Mayo Kebbi, Tibesti, Ouaddaï, and the Guéra. The Guéra massif is the least studied of the four massifs but it likely preserves structures that were formed during the collision between Congo Craton and Saharan Metacraton. The Guéra Massif is composed of mostly granitic rocks. The granitoids have petrologic features that are consistent with A-type granite, such as micrographic intergrowth of sodic and potassic feldspar, the presence of sodic- and iron-rich amphibole, and iron-rich biotite. Compositionally, the granitic rocks of the Guéra Massif have high silica (SiO2 ≥ 68.9 wt.%) content and are metaluminous to marginally peraluminous. The rocks are classified as ferroan calc-alkalic to alkali-calcic with moderately high to very high Fe* ratios. The first zircon U/Pb geochronology of the silicic rocks from the Guéra Massif yielded three main age groups: 590 Ma, 570 Ma, 560 Ma, while a single gabbro yielded an intermediate age ( 580 Ma). A weakly foliated biotite granite yielded two populations, in which the emplacement age is interpreted to be 590 ± 10 Ma, whereas the younger age (550 ± 11 Ma) is considered to be a deformation age. Furthermore, inherited Meso- to Paleoproterozoic zircons are found in this sample. The geochemical and geochronology data indicate that there is a temporal evolution in the composition of rocks with the old, high Mg# granitoids shifting to young, low Mg# granitoids. This reveals that the A-type granites in

Quaternary glaciation of the Lato Massif, Zanskar Range of the NW Himalaya

NASA Astrophysics Data System (ADS)

Orr, Elizabeth N.; Owen, Lewis A.; Saha, Sourav; Caffee, Marc W.; Murari, Madhav K.

2018-03-01

The glacial chronostratigraphy and history of the Lato Massif of Zanskar northern India is defined for the first time using geomorphic mapping and 10Be surface exposure dating. Three local glacial stages, the Lato, Shiyul and Kyambu, are dated to 244-49, 25-15 and 3.4-0.2 ka, respectively. The Lato glacial stage was the most extensive period of glaciation, characterized by expanded ice caps with glaciers advancing to ∼16 km from their present position. Large till deposits are associated with this glacial stage, which represent a time of heightened glacial erosion and localized incision, and increased rates of sediment transfer and deposition. The glacial style transitioned to entrenched valley glaciation during the Shiyul glacial stage. Hummocky moraine complexes reflecting fluctuating glacier margins characterize this glaciation. Glaciers have been confined to the cirques and headwalls of the massif during and since the Kyambu glacial stage. Equilibrium-line altitude (ELA) reconstructions help define the shifts in glaciation over time, with ELA depressions changing from 470 ± 140, 270 ± 80 to 100 ± 30 m for the Lato, Shiyul and Kyambu glacial stages, respectively. The change of glacial style during the latter part of the Quaternary is similar to other regions of the Transhimalaya and Tibet suggesting that this pattern of glaciation may reflect regional climatic forcing. The evolution of the Lato Massif from an isolated alpine plateau to a steeply incised massif over the last several glacial-interglacial cycles may have also influenced the shifts from ice cap to valley glaciation.

Towards Responsible Massification: Some Pointers for Supporting Lecturers

ERIC Educational Resources Information Center

Albertyn, Ruth M; Machika, Pauline; Troskie-de Bruin, Christel

2016-01-01

Teaching large classes poses many challenges to lecturers where massification is a reality in higher education. There are implications for both teaching and effective learning in this context. The need for accountability to learners in education provision served as motivation for a study of large classes in the largest faculty of one university…

Crustal thinning recorded by the shape of the Namurian-Westphalian leucogranite in the Variscan belt of the northwest Massif Central, France

NASA Astrophysics Data System (ADS)

Faure, Michel; Pons, José

1991-07-01

In the western part of the Variscan belt of the French Massif Central, the Guéret massif is an extensional allochthon emplaced to the southeast during Namurian-Westphalian time. The internal structure of the coeval leucogranites surrounding the western edge of the Guéret massif consists of the Plateau d'Aigurande, Brame-St. Sylvestre, and St. Goussaud massifs. These plutons are asymmetric diapirs rooted in the Marche, Bussière-Madeleine, and Arrènes faults, respectively. The plutons indicate diverging extravasation from the Guéret massif. Whatever their shapes, the plutons have a northwest-trending stretching lineation that is also marked in the granite host rocks by retrograde metamorphic minerals. The same extension direction is also inferred from Namurian-Westphalian leucogranites and dikes intruding the Guéret massif. Extension-related granitoids present typical structural patterns such as asymmetric shapes, extravasation from the collapsing area, and persistence of a stretching lineation parallel to the regional extension direction. These features may be used to diagnose crustal thinning.

Monitoring of soil and air-rock temperatures in the Western Massif of the Picos de Europa (Spain)

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesús; Vieira, Gonçalo; García, Cristina

2013-04-01

In this paper we study the ground thermal regime and air-rock interface in the Western Massif of the Picos de Europa (Cantabrian Range, Spain). This calcareous massif is highly affected by karstification processes. Quaternary glaciers, fluvio-torrential processes and present-day periglacial processes also contribute to explain the landforms present in this massif. Up to 9 dataloggers were installed during 6 years in different sites in terms of altitude, orientation, slope and geomorpolohical setting recording temperatures every two hours. The number of freeze-thaw cycles in the soil(between 0 and 16) was controlled by the depth of the snow cover. The temperatures in the interface rock-air showed between 30-60 cycles, reaching 119 and 130 during the year 2007-2008. Extreme minimum temperatures in the soil oscillate between 0.3 and -6.3, while in the rocky walls the loggers recorded temperatures between -7.3 and -14.3°C. Monitoring of soil temperatures around the ice patch - the only one in the massif today - resulted in slightly negative mean annual temperatures. These conditions may reveal the existence of sporadic permafrost on debris that cover the ice patch. Both the buried ice and the permafrost are in disequilibrium with the current environmental conditions of the massif.

Geomorphological and sedimentological evidences in the Western Massif of Picos de Europa since the Last Glaciation

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesus; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Conceição Freitas, Maria; García-Hernández, Cristina; Nieuwendam, Alexandre; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

2015-04-01

The Western Massif of Picos de Europa includes some of the highest peaks of the Cantabrian Mountains. However, the environmental evolution in this massif since the Last Glaciation is still poorly understood. This research provides a new geochronological approach to the sequence of environmental events occurred here since the maximum expansion of glaciers during the last Pleistocene glaciation. The distribution of the glacial landforms suggests four main stages regarding the environmental evolution in the massif: maximum glacial advance, phase of second maximum glacial expansion, Late Glacial and Little Ice Age. A 5.4-m long sedimentological section retrieved from the kame terrace of Belbín, in a mid-height area of the massif, complements the geomorphological interpretation and provides a continuous paleoenvironmental sequence from this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, a new glacial expansion occurred around 18.7-22.5 ka cal BP. The melting of the glaciers after this phase generated a shallow lake in the Belbín depression. Lake sediments do not reveal the occurrence of a cold stage during the Late Glacial, whilst, at higher locations, moraine complexes were formed suggesting a glacier readvance. The terrestrification of this lake started at 8 ka cal BP, when Belbín changed to a peaty environment. At 5 ka cal BP human occupation started at the high lands of the massif according to the existence of charcoal particles in the section. The presence of moraines in the highest northern cirques evidences the last phase with formation of small glaciers in the Western Massif of Picos de Europa, corresponding to the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers.

Massification without Equalisation: The Politics of Higher Education, Graduate Employment and Social Mobility in Hong Kong

ERIC Educational Resources Information Center

Lee, Siu-yau

2016-01-01

This article explains why the massification of higher education in Hong Kong has, contrary to the predictions of received wisdom, failed to enhance the upward social mobility of the youth in the city. Building upon recent literature in political science, it argues that massification can take different forms, which in turn determine the effects of…

Subcontinental rift initiation and ocean-continent transitional setting of the Dinarides and Vardar zone: Evidence from the Krivaja-Konjuh Massif, Bosnia and Herzegovina

NASA Astrophysics Data System (ADS)

Faul, Ulrich H.; Garapić, Gordana; Lugović, Boško

2014-08-01

The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to the Albanian and Greek ophiolites. Detailed sampling of the Krivaja-Konjuh massif, one of the largest massifs in the Dinaride belt, reveals fertile compositions and an extensive record of deformation at spinel peridotite facies conditions. High Na2O clinopyroxene and spinel-orthopyroxene symplectites after garnet indicate a relatively high pressure, subcontinental origin of the southern and western part of Krivaja, similar to orogenic massifs such as Lherz, Ronda and the Eastern Central Alpine peridotites. Clinopyroxene and spinel compositions from Konjuh show similarities with fertile abyssal peridotite. In the central parts of the massif the spinel lherzolites contain locally abundant patches of plagioclase, indicating impregnation by melt. The migrating melt was orthopyroxene undersaturated, locally converting the peridotites to massive olivine-rich troctolites. Massive gabbros and more evolved gabbro veins cross-cutting peridotites indicate continued melt production at depth. Overall we infer that the massif represents the onset of rifting and early stages of formation of a new ocean basin. In the south of Krivaja very localized chromitite occurrences indicate that much more depleted melts with supra-subduction affinity traversed the massif that have no genetic relationship with the peridotites. This indicates that volcanics with supra-subduction affinity at the margins of the Krivaja-Konjuh massif record separate processes during closure of the ocean basin. Comparison with published compositional data from other Balkan massifs shows that the range of compositions within the Krivaja-Konjuh massif is similar to the compositional range of the western massifs of the Dinarides. The compositions of the Balkan massifs show a west to east gradient, ranging from subcontinental on the western side of the Dinarides to depleted mid-ocean ridge/arc compositions in the Vardar

Defining conditions of garnet growth across the central and southern Menderes Massif, western Turkey

NASA Astrophysics Data System (ADS)

Etzel, T. M.; Catlos, E. J.; Kelly, E. D.; Cemen, I.; Ozerdem, C.; Atakturk, K. R.

2017-12-01

Here we apply thermodynamic modeling using Theriak-Domino to garnet-bearing rocks from the central and southern portions of the Menderes Massif to gain insight into the dynamics of western Turkey as the region experienced a transition from collisional to extensional tectonics. To this end, we report new pressure-temperature (P-T) paths from garnet-bearing rocks collected along the Alasehir detachment fault, a prominent exhumation structure in the central portion of the Menderes Massif in western Turkey, constituting the southern margin of the Alasehir Graben. These paths are compared to those from the Selimiye shear zone in the Southern (Cine) Massif. Two Alasehir garnets collected from the same outcrop record two P-T paths: 1) a prograde path beginning at 565oC and 6.4 kbar increasing to 592 oC and 7.5 kbar; and 2) near isobaric growth initiating at 531oC and 7.1 kbar and terminating at 571oC and 7.3 kbar. High-resolution P-T paths could not be modeled for the majority of Alasehir samples due to diffusional modification of garnet. However, conditions were estimated by garnet isopleth thermobarometry at the point of highest spessartine content for each crystal. Calculated P-T values for this subset of samples range between 566-651oC and 6.2-6.8 kbar. Despite this broad range, these P-T conditions are consistent with what is observed in the modeled paths. Th-Pb ages of matrix monazite range from 35.8±3.0 to 20.6±2.4 Ma, suggesting metamorphism in the central Menderes Massif occurred over a 15 m.y. period. Selimiye shear zone rocks show distinct N-shaped P-T paths, suggesting garnets in the central and southern portion of the Menderes Massif record distinctly different tectonic histories.

Critical Reflection on the Massification of Higher Education in Korea: Consequences for Graduate Employment and Policy Issues

ERIC Educational Resources Information Center

Yeom, Min-ho

2016-01-01

The paper critically reviews the results of Korean massification in higher education (HE) and focuses on the consequences related to graduate employment. By analysing statistical data and reviewing related articles, this study explores the process of the massification of HE, investigates major factors influencing the expansion, and analyses and…

Mastritherium (Artiodactyla, Anthracotheriidae) from Wadi Sabya, southwestern Saudi Arabia; an earliest Miocene age for continental rift-valley volcanic deposits of the Red Sea margin

USGS Publications Warehouse

Madden, Gary T.; Schmidt, Dwight Lyman; Whitmore, Frank C.

1983-01-01

A lower jaw fragment with its last molar (M/3) from the Baid formation in Wadi Sabya, southwestern Saudi Arabia, represents the first recorded occurrence in the Arabian Peninsula of an anthracotheriid artiodactyl (hippo-like, even-toed ungulate). This fossil is identified as a primitive species of Masritherium, a North and East African genus restricted, previously to the later early Miocene. This identification indicates that the age of the Baid formation, long problematical, is early Miocene and, moreover, shows that the age of the fossil site is earliest Miocene (from 25 to 21Ma). The Wadi Sabya anthracothere is the first species of fossil mammal recorded from western Saudi Arabia, and more important, it indicates an early Miocene age for the volcanic deposits of a continental rift-valley that preceded the initial sea-floor spreading of the Red Sea.

A Library Response to the Massification of Higher Education: The Case of the University of Zambia Library

ERIC Educational Resources Information Center

Kanyengo, Christine Wamunyima

2009-01-01

This paper looks at the challenges that libraries in Africa face in responding to massification of higher education by discussing the University of Zambia library's response in library and information resources provision. As a result of massification of higher education, libraries have been forced not only to employ new and different strategies to…

Miocene mass-transport sediments, Troodos Massif, Cyprus

USGS Publications Warehouse

Lord, A.R.; Harrison, R.W.; BouDagher-Fadel, M.; Stone, B.D.; Varol, O.

2009-01-01

Sediment mass-transport layers of submarine origin on the northern and southern flanks of the Troodos ophiolitic massif are dated biostratigraphically as early Miocene and late Miocene, respectively and therefore represent different seismogenic events in the uplift and erosional history of the Troodos terrane. Analysis of such events has potential for documenting Miocene seismic and uplift events regionally in the context of changing stress field directions and plate vectors through time. ?? 2009 The Geologists' Association.

A Comparative Analysis on Models of Higher Education Massification

ERIC Educational Resources Information Center

Pan, Maoyuan; Luo, Dan

2008-01-01

Four financial models of massification of higher education are discussed in this essay. They are American model, Western European model, Southeast Asian and Latin American model and the transition countries model. The comparison of the four models comes to the conclusion that taking advantage of nongovernmental funding is fundamental to dealing…

Understanding the Tectonic Deformation of Turkish Blocks since Mesozoic; A Paleomagnetic study on the Nigde-Kirsehir Massif and the Taurides

NASA Astrophysics Data System (ADS)

Mualla, Cinku; Mumtaz, Hisarli; Ulker, Beyza; Kaya, Nurcan; Oksum, Erdinc; Yilmaz, Yucel; Orbay, Naci

2015-04-01

It is reported that the Nigde-Kirsehir massif which constitutes the main fragment of Anatolia is rifted from the Taurides-Anatolides in Mesozoic and that the Intra-Tauride ocean exist between these blocks. Another group of researchers believed that the Intra Tauride ocean did not exist. They assumed that the Nigde-Kirsehir massif existed as a promotory of the Taurides. In this sense, both the Nigde-Kirsehir massif and the Taurides experienced several deformation phases due to the consumption of the oceanic strand (s) and the amalgamation of the Anatolian blocks after collision in the end of the paleotectonic time, whereas in the neotectonic time the traces of the westwards excursion of Anatolia was effective. Previous paleomagnetic studies showed that the Nigde-Kirsehir massif rotated 90° anticlockwise during Jurassic to Eocene time and other studies showed that the collision between the Nigde-Kirsehir massif and the Pontides resulted by deformation which was accomodated by regional faults. In the south of the Nigde-Kirsehir massif, it was proposed that all the rocks in Carboniferous to Eosen were remagnetized due to nap emplacement in Eocene. Because of several alternative interpretations about the tectonic deformation of the Nigde-Kirsehir massif in relation between the Taurides and the Pontides, we report new paleomagnetic results from Late Jurassic to Miocene rocks in the Nigde-Kirsehir massif and its surrounding. A total of 138 different sites were sampled from Jurassic to Miocene rocks in the south of the Nigde-Kirsehir massif around Ki ri kkale, Tuzgölü, Uluki şla and Kayseri, whereas in the Central Taurides Late Jurassic- Lower Cretaceous platform type carbonates and ophiolitic rocks from Mersin and Pozanti were collected. Paleomagnetic results evaluated together with previous paleomagnetic data indicate that all the studied rocks carry a magnetization before folding according to positive incremental fold tests. It has been shown that in the SE/E (SE

Man-induced transformation of mountain meadow soils of Aragats mountain massif (Armenia)

NASA Astrophysics Data System (ADS)

Avetisyan, M. H.

2018-01-01

The article considers issues of degradation of mountain meadow soils of the Aragats mountain massif of the Republic of Armenia and provides the averaged research results obtained for 2013 and 2014. The present research was initiated in the frames of long-term complex investigations of agroecosystems of Armenia’s mountain massifs and covered sod soils of high mountain meadow pasturelands and meadow steppe grasslands lying on southern slope of Mt. Aragats. With a purpose of studying the peculiarities of migration and transformation of flows of major nutrients namely carbon, nitrogen, phosphorus in study mountain meadow and meadow steppe belts of the Aragats massif we investigated water migration of chemical elements and regularities of their leaching depending on different belts. Field measurement data have indicated that organic carbon and humus in a heavily grazed plot are almost twice as low as on a control site. Lysimetric data analysis has demonstrated that heavy grazing and illegal deforestation have brought to an increase in intrasoil water acidity. The results generated from this research support a conclusion that a man’s intervention has brought to disturbance of structure and nutrient and water regimes of soils and loss of significant amounts of soil nutrients throughout the studied region.

Geological mapping of the Rainbow Massif, Mid-Atlantic Ridge, 36°14'N

NASA Astrophysics Data System (ADS)

Ildefonse, B.; Fouquet, Y.; Hoisé, E.; Dyment, J.; Gente, P.; Thibaud, R.; Bissessur, D.; Yatheesh, V.; Momardream 2008 Scientific Party*, T.

2008-12-01

The Rainbow hydrothermal field at 36°14'N on the Mid-Atlantic Ridge is one of the few known sites hosted in ultramafic basement. The Rainbow Massif is located along the non-transform offset between the AMAR and South AMAR second-order ridge segments, and presents the characteristic dome morphology of oceanic core complexes, although no corrugated surface has been observed so far. One of the objectives of Cruises MOMAR DREAM (July 2007, R/V Pourquoi Pas ?; Aug-Sept 2008, R/V Atalante) was to study the petrological and structural context of the hydrothermal system at the scale of the Rainbow Massif. Our geological sampling complements previous ones achieved during Cruises FLORES (1997) and IRIS (2001), and consisted in dredge hauls, and submersible dives by manned submersible Nautile and ROV Victor. The tectonics of the Rainbow Massif is dominated by a N-S trending fault pattern on the western flank of the massif, and a series of SW-NW ridges on its northeastern side. The active hydrothermal site is located in the area were these two systems crosscut. The most abundant recovered rock type is peridotite (harzburgite and dunite) that presents a variety of serpentinization styles and intensity, and a variety of deformation styles (commonly undeformed, sometimes displaying ductile or brittle foliations). Serpentinites are frequently oxidized. Some peridotite samples have melt impregnation textures. Massive chromitite was recovered in one dredge haul. Variously evolved gabbroic rocks were collected as discrete samples or as centimeter to decimeter-thick dikes in peridotites. Basalts and fresh basaltic glass were also sampled in talus and sediments on the southwestern and northeastern flanks of the massif. Our sampling is consistent with the lithological variability encountered in oceanic core complexes along the Mid-Atlantic Ridge and Southwest Indian Ridge. The stockwork of the hydrothermal system has been sampled on the western side of the present-day hydrothermal

Gold in Accessory Zircon (the Kozhim Massif, Subpolar Urals)

NASA Astrophysics Data System (ADS)

Denisova, Yuliya; Pystin, Aleksandr

2017-12-01

The crystals of zircon due to their resistance to external impact of various processes can reveal information about the environment of their formation and the inclusions observed of them. Zircon contains different mineral inclusions: biotite, plagioclase, quartz, apatite, etc. However, there is no information about gold inclusions in the zircons from granites of the Sudpolar Urals. The study results of the inclusions of gold in accessory zircon of the Kozhim granitic massif are presented in this paper. The studied mineral is a dark-brown translucent short-prismatic crystal containing the inclusion of gold and the allocations of quartz. According to studies, the inclusion of gold formed during the growth of zircon and it is the gold covered with a thin film of oxide gold. It was confirmed that the crystallization of the studied zircon occurred at a temperature of 800°C and above on the stage of formation of granites of Kozhim massif. The assumption is made about the additional temperature in the course of which was caused by decreasing of temperature up to 700° C and below during postmagmatic stage.

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Xu, Ting; Xu, Wen-Liang; Wang, Feng; Ge, Wen-Chun; Sorokin, A. A.

2018-02-01

This paper presents new geochronological and geochemical data for early Paleozoic intrusive rocks from the Khanka Massif in the Russian Far East, with the aim of elucidating the Paleozoic evolution and tectonic attributes of the Khanka Massif. New U-Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages: 502, 492, 462-445, and 430 Ma. The 502 Ma pyroxene diorites contain 58.28-59.64 wt% SiO2, 2.84-3.69 wt% MgO, and relatively high Cr and Ni contents. Negative εHf(t) values (- 1.8 to - 0.4), along with other geochemical data, indicate that the primary magma was derived from partial melting of mafic lower crust with the addition of mantle material. The 492 Ma syenogranites have high SiO2 and K2O contents, and show positive Eu anomalies, indicating the primary magma was generated by partial melting of lower crust at relatively low pressure. The 445 Ma Na-rich trondhjemites display high Sr/Y ratios and positive εHf(t) values (+ 1.8 to + 3.9), indicating the primary magma was generated by partial melting of thickened hydrous mafic crust. The 430 Ma granitoids have high SiO2 and K2O contents, zircon εHf(t) values of - 5.4 to + 5.8, and two-stage model ages of 1757-1045 Ma, suggesting the primary magma was produced by partial melting of heterogeneous Proterozoic lower crustal material. The geochemistry of these early Paleozoic intrusive assemblages indicates their formation in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif. The εHf(t) values show an increasingly negative trend with increasing latitude, revealing a lateral heterogeneity of the lower crust beneath the Khanka Massif. Regional comparisons of the magmatic events indicate that the Khanka Massif in the Russian Far East has a tectonic affinity to the Songnen-Zhangguangcai Range Massif rather than the adjacent Jiamusi Massif.

Lithologic Distribution and Geologic History of the Apollo 17 Site: The Record in Soils and Small Rock Particles from the Highland Massifs

NASA Technical Reports Server (NTRS)

Jolliff, Bradley L.; Rockow, Kaylynn M.; Korotev, Randy L.; Haskin, Larry A.

1996-01-01

Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm-4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm-4 mm fragments provide a bridge between compositions of less than 1 mm fines and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm-4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% Incompatible-Trace-Element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm - 4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31 % agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass- weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their

Zircon (U-Th)/He evidence for pre-Eocene orogenic exhumation of eastern North Pyrenean massifs, France

NASA Astrophysics Data System (ADS)

Ternois, Sébastien; Vacherat, Arnaud; Pik, Raphaël; Ford, Mary; Tibari, Bouchaïb

2017-04-01

Orogens and their associated foreland basins are considered as part of a single dynamic system evolving from an early, non equilibrated, growth stage to a late, mature, steady-state stage. Most of our understanding in foreland basins, in particular early convergence-stage deposition, comes from the subducting plate, so that the classic paradigm for foreland basins is the pro-wedge. Models that clearly depict the relationship between erosion of the orogenic wedge and sedimentation into its associated foreland basin only focus on the late post-orogenic phase. Relatively little is known and understood about the very long phase of initiation of orogenesis. In the doubly wedged Pyrenean orogen, where we know and understand relatively little about how the early retro-wedge developed, the record of the onset of orogenic denudation from massifs is quite limited, not only in time but also in space. As part of the OROGEN project funded by TOTAL and the BRGM, this study presents first single-grain zircon (U-Th)/He data from two Palaeozoic massifs of the external Northern Pyrenean Zone, the Agly and Salvezines massifs. It aims at constraining the exhumation history of eastern Pyrenean massifs and understanding what is their significance for early orogenic wedge growth. The Pyrenean orogeny was generated from end Santonian (84 Ma) to Oligocene-Miocene due to convergence of the Iberian and European plates. Aquitaine foreland basin history (Ariège region) indicates that convergence took place in two phases, Campanian to Maastrichian and Eocene, separated by a quiet Paleocene phase. Yet, only Eocene cooling events are recorded by low-temperature thermochronometers in the central Pyrenean massifs (Arize and Trois-Seigneurs). Nine bedrock samples were collected along a WNW-ESE traverse (Salvezines and Saint-Arnac granites, Belesta-Caramany gneisses) and analysed for ZHe dating. Zircon (U-Th)/He data for the Agly and Salvezines massifs, together with forward modelling of data for

Geodynamic movements and deformations of the Sudetic structural unit of the Bohemian Massif

NASA Astrophysics Data System (ADS)

Schenk, V.; Jechumtálová, Z.; Schenková, Z.; Kottnauer, P.

2003-04-01

The African plate pushes to European orogenic Alpine structures that transfer the compression further to Variscan structural units, including the Bohemian Massif. Central parts of the Bohemian Massif are relatively deep-seated and, therefore, some of marginal parts of the Massif and its border geological structures should be affected intensively and moved distinctly with respect to the central parts. The geodynamical GPS network EAST SUDETEN is located just over the area mentioned above, i.e. it covers both kinetically quasi-effected and quasi-non-effected structural blocks. GPS data observed already for six annual campaigns (1997-2002) were processed and movement vectors of individual network sites were assessed. Applied data processing did not allow errors in the horizontal direction 2 mm and in the vertical direction 5-6 mm to be exceeded. Since time series of coordinate changes for several network sites gave rather pronounce movement trends, preliminary deformations among individual structural blocks were evaluated and compared to other geological, geophysical and geodetic materials. The investigation has been supported by the Grant Agency of the Czech Republic, projects 205/97/0679 and 205/01/0480, and by the research programme of the Ministry of Education, Youth and Sport of the Czech Republic, project LN00A005 "Dynamics of the Earth".

Subsurface Implications of Spatially Variable Seafloor Character on the Atlantis Massif

NASA Astrophysics Data System (ADS)

Greene, J. A.; Tominaga, M.; Blackman, D. K.

2014-12-01

We documented and mapped the characteristics of the seafloor on the Atlantis Massif, an ocean core complex located at 30°N on the Mid-Atlantic Ridge. Our goal is to investigate the implications of these surficial features, particularly whether their spatial variations might reflect subsurface lithology and geological processes. We utilized data collected during the MARVEL 2000 cruise AT3-60, specifically Alvin videos and rock samples, Argo II digital still photos, and TOBI/DSL-120 side-scan sonar mosaic. The Alvin dives studied occurred over the Central Dome and Eastern Block, which is interpreted as the hanging wall to the detachment that unroofed the dome. We also studied two Argo II dives located over the Central Dome, one over the Eastern Block, and one over the Western Shoulder of the southern dome. The TOBI/DSL-120 side-scan sonar followed a widespread, looped track providing near total coverage of the massif. We classified the character of the seafloor based on imagery, the acoustic reflectivity, and the basic composition of rock samples. To aid in our classification, we merged Argo II still images to produce photo-mosaics displaying tens of meters long transects. We then classified the seafloor as unconsolidated sediment, lithified sediment (a carbonate crust or cap), exposed bedrock, or rubble. To obtain a broader understanding of the Atlantis Massif, we analyzed the distribution of these classes of seafloor. Over the Central Dome and Western Shoulder, we found most seafloor classes present in notable amounts, with many individual areas dominated by a particular type.

A Gradient in Cooling Rate Beneath the Moho at the Oman Ophiolite: Fresh Insights into Cooling Processes at Mid-Ocean Ridges from REE-Based Thermometry

NASA Astrophysics Data System (ADS)

Dygert, N. J.; Kelemen, P. B.; Liang, Y.

2015-12-01

The Wadi Tayin massif in the southern Oman ophiolite has a more than 10 km thick mantle section and is believed to have formed in a mid-ocean ridge like environment with an intermediate to fast spreading rate. Previously, [1] used major element geothermometers to investigate spatial variations in temperatures recorded in mantle peridotites and observed that samples near the paleo-Moho have higher closure temperatures than samples at the base of the mantle section. Motivated by these observations, we measured major and trace elements in orthopyroxene and clinopyroxene in peridotites from depths of ~1-8km beneath the Moho to determine closure temperatures of REE in the samples using the REE-in-two-pyroxene thermometer [2]. Clinopyroxene are depleted in LREE and have REE concentrations that vary depending on distance from the Moho. Samples nearer the Moho have lower REE concentrations than those deeper in the section (e.g., chondrite normalized Yb ranges from ~1.5 at the Moho to 4 at 8km depth), consistent with near fractional melting along a mantle adiabat. Orthopyroxene are highly depleted in LREE but measurements of middle to heavy REE have good reproducibility. We find that REE-in-two-pyroxene temperatures decrease with increasing distance from the Moho, ranging from 1325±10°C near the Moho to 1063±24°C near the base of the mantle section. Using methods from [3], we calculate cooling rates of >1000°C/Myr near the Moho, dropping to rates of <10°C/Myr at the bottom of the section. The faster cooling rate is inconsistent with conductive cooling models. Fast cooling of the mantle lithosphere could be facilitated by infiltration of seawater to or beneath the petrologic Moho. This can explain why abyssal peridotites from ultra-slow spreading centers (which lack a crustal section) have cooling rates comparable to those of Oman peridotites [3]. [1] Hanghøj et al. (2010), JPet 51(1-2), 201-227. [2] Liang et al. (2013), GCA 102, 246-260. [3] Dygert & Liang (2015

Effect of Hydrochemistry on Mineral Precipitation and Textural Diversity in Serpentinization-driven Alkaline Environments; Insights from Thermal Springs in the Oman Ophiolite.

NASA Astrophysics Data System (ADS)

Bach, W.; Giampouras, M.; Garcia-Ruiz, J. M.; Garrido, C. J.; Los, C.; Fussmann, D.; Monien, P.

2017-12-01

Interactions between meteoric water and ultramafic rocks within Oman ophiolite give rise to the formation of thermal spring waters of variable composition and temperature. Discharge of two different types of water forms complex hydrological networks of streams and ponds, in which the waters mix, undergo evaporation, and take up atmospheric CO2. We conducted a pond-by-pond sampling of waters and precipitates in two spring sites within the Wadi Tayin massif, Nasif and Khafifah, and examined how hydrochemistry and associated mineral saturation states affect the variations in mineral phases and textures. Three distinctive types of waters were identified in the system: a) Mg-type (7.9 < pH < 9.5); Mg-HCO3-rich waters, b) Ca-type (pH > 11.6); Ca-OH-rich waters, and c) Mix-type (9.6 < pH < 11.5); waters arising upon mixing of Mg-type and Ca-type. PHREEQC was used to evaluate the role of mixing in aqueous speciation and the evolution of the saturation index value of different mineral phases. Mineral and textural characterization by X-ray diffraction, Raman spectroscopy and scanning electron microscopy were combined with these hydrogeochemical constraints to determine the factors controlling mineralogical and textural diversity in the system. In Ca-type waters, uptake of CO2 during the exposure of the fluids to the atmosphere is the predominant precipitation mechanism of CaCO3. High Mg:Ca ratios and high supersaturation rate of CaCO3 favor the growth of aragonite over calcite in mixed fluids. Changes in morphology and texture of aragonite crystals and crystal aggregates indicate the variations in the values of supersaturation and supersaturation rate of CaCO3 in the different water types. Brucite precipitation is common and driven by fluid mixing, while interaction with air-derived CO2 causes its alteration to hydromagnesite. The proximity of gabbroic lithologies appears to affect the presence of Al-bearing layered double hydroxides (LDHs). Furthermore, transformation of

Experimental and Modeling Studies of Massif Anorthosites

NASA Technical Reports Server (NTRS)

Longhi, John

1999-01-01

This termination report covers the latter part of a single research effort spanning several grant cycles. During this time there was a single title, "Experimental and Modeling Studies of Massif Anorthosites", but there were several contract numbers as the mode and location of NASA contract administration changed. Initially, the project was funded as an increment to the PI's other grant, "Early Differentiation of the Moon: Experimental and Modeling Studies", but subsequently it became an independent grant. Table 1 contains a brief summary of the dates and contract numbers.

New data for paleoprotherozoic PGE-bearing anorthosite of Kandalaksha massif (Baltic shield): U-Pb and Sm-Nd ages

NASA Astrophysics Data System (ADS)

Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

2015-04-01

The aims of this researches were to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) on Kandalaksha anorthosite massif due to study of polimetamorphic history. In marginal zone firstly have been obtained the presence of sulphide mineralization with PGE (Chashchin, Petrov , 2013). Kandalaksha massif is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate polymetamorphism. Two fractions of single grains from anorthosite of the massif gave precise U-Pb age, which is equal to 2450± 3 Ma. Leucocratic gabbro-norite were dated by U-Pb method, with age up to 2230 ± 10 Ma. This age reflects the time of granulite metamorphism according to data of (Mitrofanov, Nirovich, 2003). Two fractions of rutile have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile is 400-450 ° C (Mezger et.al., 1989), thus cooling processes of massif rocks to these temperatures was about 1.7 Ga. These data reflect one of the stages of metamorphic alteration of the massif. Three stages of metamorphism are distinguished by Sm-Nd method. Isotope Sm-Nd dating on Cpx-WR line gives the age of 2311 Ma which suggested of high pressure granulite metamorphism. Moreover Cpx-Pl line reflect the age 1908 Ma of low pressure granulite metamorphism. Also two-points (Grt-Rt) Sm-Nd isochrone yield the age 1687 Ma of the last metamorphic alterations in Kandalaksha anorthosite massif. Model Sm-Nd age of the leucocratic gabbro-norite is 2796 Ma with positive ɛNd (+0.32). It means that the source of gabbro-norite was mantle reservoir. All investigations are devoted to memory of academician PAS F. MItrofanov which was a leader of scientific school for

N-S crustal shear system in the Bundelkhand massif: A unique crustal evolution signature in the northern Indian peninsula

NASA Astrophysics Data System (ADS)

Singh, S. P.; Bhattacharya, A. R.

2017-12-01

The Bundelkhand massif, located in the northern part of the Indian shield, is a poly-deformed and poly-metamorphic terrain. This paper reports a new shear system developed throughout the massif in the form of N-S trending quartz veins that are sometimes quartzo-feldspathic and rarely granitic in composition. The veins are vertical and commonly occur in conjugate sets. This tectono-magmatic event appears to represent the youngest shear system of the massif as it cross-cuts all the earlier shear systems (E-W, NE-SE and NW-SE). Emplacement of this N-S vein system may have taken place due to extensional processes that developed some cracks along which siliceous magma was vertically emplaced. The complete absence of signature of the N-S event from the surrounding sedimentary cover of Vindhyan Supergroup, Bijawar and Gwalior Groups suggests that this shear system is pre-tectonic to the nearly E-W trending passive basins developed at the margins of the Bundelkhand craton. Further, several workers have considered the Bundelkhand massif as a part of the Aravalli craton. However, due to the absence of N-S, as well as the other (i.e., E-W, NW-SE and NW-SE), tectonic fabrics of the Bundelkhand massif in other cratons of the Peninsular India, and vice versa, makes the Bundelkhand block a separate and unique craton of its own and is not part of the Aravalli craton.

MODERN BEAMS FOR ANCIENT MUMMIES COMPUTERIZED TOMOGRAPHY OF THE HOLOCENE MUMMIFIED REMAINS FROM WADI TAKARKORI (ACACUS, SOUTH-WESTERN LIBYA; MIDDLE PASTORAL).

PubMed

Di Vincenzo, Fabio; Carbone, Iacopo; Ottini, Laura; Profico, Antonio; Ricci, Francesca; Tafuri, Mary Anne; Fornaciari, Gino; Manzi, Giorgio

2015-01-01

The Middle Pastoral human remains from Wadi Takarkori in the Libyan Acacus mountains (Fezzan) are exceptionally preserved partial mummies ranging between 6100 and 5000 uncal years BP; this small sample represents the most ancient of its kind ever found. In this report, we present a survey of the skeletal anatomy of these mummifed corpses, based on high resolution CT-scan data, including a preliminary phenetic interpretation of their cranial morphology.

Biodiversity impact of the aeolian periglacial geomorphologic evolution of the Fontainebleau Massif (France)

NASA Astrophysics Data System (ADS)

Thiry, M.; Liron, M. N.

2009-04-01

Landscape features The geomorphology of the Fontainebleau Massif is noteworthy for its spectacular narrow ridges, up to 10 km long and 0.5 km wide, armored by tightly cemented sandstone lenses and which overhang sandy depressions of about 50m. Denudation of the sandstone pans lead to a highly contrasted landscape, with sandstone ridges ("platières") towering sandy depressions ("vallées") and limestone plateaus ("monts"). This forms the geological frame of the spectacular sceneries of the Fontainebleau Massif (Thiry & Liron, 2007). Nevertheless, there is little know about the erosive processes that have built-up these landscapes. Periglacial processes, and among them aeolian ones, appear significant in the development of the Fontainebleau Massif physiography. The periglacial aeolian geomorphology Dunes and dune fields are known since long and cover about 15% to 25% of the Fontainebleau Massif. The aeolian dunes developed as well on the higher parts of the landscape, as well as in the lower parts of the landscape. The dunes are especially well developed in the whole eastern part of the massif, whereas the western part of the massif is almost devoid of dunes. Nevertheless, detailed mapping shows that dunes can locally be found in the western district, they are of limited extension, restricted to the east facing backslope of outliers. Loamy-sand covers the limestone plateaus of the "monts". The loam cover is of variable thickness: schematically thicker in the central part of the plateaus, where it my reach 3 m; elsewhere it may thin down to 0,20-0,30 m, especially at the plateau edges. Blowout hollows are "negative" morphologies from where the sand has been withdrawed. Often these blowouts are decametric sized and well-delimited structures. Others, more complex structures, are made up of several elongated hectometric hollows relaying each other from and which outline deflation corridor more than 1 km long. A characteristic feature of these blowout hollows is the

The Triassic reworking of the Yunkai massif (South China): EMP monazite and U-Pb zircon geochronologic evidence

NASA Astrophysics Data System (ADS)

Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Sano, Yuji; Zhou, Han-Wen; Xiang, Hua; Takahata, Naoto

2017-01-01

Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244-236 Ma and 236-233 Ma, respectively. They also yield ages of 233-230 Ma for core domain gneissic granites and 232-229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, 245 Ma and 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0-0.9 Ga) and Early Paleozoic (444-431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP).

Massification and the Large Lecture Theatre: From Panic to Excitement

ERIC Educational Resources Information Center

Arvanitakis, James

2014-01-01

In this article I examine the role of the contemporary university in light of the mass increase in class sizes that has occurred on an international scale. While we may look nostalgically back to a time when lectures numbered a few hundred students and tutorials had as few as ten, massification at undergraduate level is an inescapable fact of…

Massification and Diversity of Higher Education Systems: Interplay of Complex Dimensions

ERIC Educational Resources Information Center

Guri-Rosenblit, Sarah; Sebkova, Helena; Teichler, Ulrich

2007-01-01

This paper provides a synthetic overview of the complex dimensions that shape the interrelations between the massification of higher education systems and their structure and composition. Many higher education systems worldwide expanded extensively in the last decades, and have undergone wide and deep structural changes. Most notably, the…

Jurassic hot spring deposits of the Deseado Massif (Patagonia, Argentina): Characteristics and controls on regional distribution

NASA Astrophysics Data System (ADS)

Guido, Diego M.; Campbell, Kathleen A.

2011-06-01

The Deseado Massif, Santa Cruz Province, Argentinean Patagonia, hosts numerous Middle to Late Jurassic age geothermal and epithermal features represented by siliceous and calcareous chemical precipitates from hot springs (sinters and travertines, respectively), hydrothermal breccias, quartz veins, and widespread hydrothermal silicification. They indicate pauses in explosive volcanic activity, marking the final stages in the evolution of an extensive Jurassic (ca. 178-151 Ma) volcanic complex set in a diffuse extensional back-arc setting heralding the opening of the Atlantic Ocean. Published paleo-hot spring sites for the Deseado Massif, plus additional sites identified during our recent field studies, reveal a total of 23 locations, five of which were studied in detail to determine their geologic and facies associations. They show structural, lithologic, textural and biotic similarities with Miocene to Recent hot spring systems from the Taupo and Coromandel volcanic zones, New Zealand, as well as with modern examples from Yellowstone National Park, U.S.A. These comparisons aid in the definition of facies assemblages for Deseado Massif deposits - proximal, middle apron and distal siliceous sinter and travertine terraces and mounds, with preservation of many types of stromatolitic fabrics - that likely were controlled by formation temperature, pH, hydrodynamics and fluid compositions. Locally the mapped hot spring deposits largely occur in association with reworked volcaniclastic lacustrine and/or fluvial sediments, silicic to intermediate lava domes, and hydrothermal mineralization, all of which are related to local and regional structural lineaments. Moreover, the numerous geothermal and significant epithermal (those with published minable resources) deposits of the Deseado Massif geological province mostly occur in four regional NNW and WNW hydrothermal-structural belts (Northwestern, Northern, Central, and Southern), defined here by alignment of five or more hot

Iron sulfide deposits at Wadi Wassat, Kingdom of Saudi Arabia

USGS Publications Warehouse

Roberts, R.J.; Rossman, D.L.; Bagdady, A.Y.; Conway, C.M.; Helaby, A.M.

1981-01-01

Massive and disseminated iron sulfide deposits in Wadi Wassat form lenticular, stratabound deposits in cherty Precambrian sedimentary rocks interlayered with Precambrian calcareous sedimentary rocks, pyroclastic rocks, and andesitic flow rocks. These rocks have been cut by a wide variety of plutonic and dike rocks including gabbro, diorite, granodiorite, diabase, rhyolite, and granite. The zone containing the sulfide lenses is nearly 16 km long and is cut off by granitic rocks at both the northern and southern ends. The lenses are as much as 200 m thick; one can be traced along strike for more than 4 km. The lenses consist mostly of iron sulfides. Pyrite is the principal sulfide mineral; near intrusive bodies the pyrite has been partially converted to pyrrhotite and locally mobilized into fractures. The sulfides have been oxidized to a depth of about 25 m. Preliminary calculations indicate that about 107,500,000 tons of sulfides, averaging 40 percent iron and 35 percent sulfur, are available to a depth of i00 m. Small amounts of nickel, cobalt, zinc, and copper are also present, but at metal prices prevailing in early 1981, these do not constitute significant resources.

Possible petrogenetic associations among igneous components in North Massif soils: Evidence in 2-4 mm soil particles from 76503

NASA Technical Reports Server (NTRS)

Jolliff, Bradley L.; Bishop, Kaylynn M.; Haskin, Larry A.

1992-01-01

Studies of Apollo 17 highland igneous rocks and clasts in breccias from the North and South Massifs have described magnesian troctolite, norite, anorthositic gabbro, dunite, spinel cataclasites, and granulitic lithologies that may have noritic anothosite or anorthositic norite/gabbro as igneous precursors, and have speculated on possible petrogenetic relationships among these rock types. Mineral compositions and relative proportions of plagioclase and plagioclase-olivine particles in samples 76503 indicate that the precursor lithology of those particles were troctolitic anorthosite, not troctolite. Mineral and chemical compositions of more pyroxene-rich, magnesian breccias and granulites in 76503 indicate that their precursor lithology was anorthositic norite/gabbro. The combination of mineral compositions and whole-rock trace-element compositional trends supports a genetic relationship among these two groups as would result from differentiation of a single pluton. Although highland igneous lithologies in Apollo 17 materials have been described previously, the proportions of different igneous lithologies present in the massifs, their frequency of association, and how they are related are not well known. We consider the proportions of, and associations among, the igneous lithologies found in a North Massif soil, which may represent those of the North Massif or a major part of it.

Crystal structure of modular sodium-rich and low-iron eudialyte from Lovozero alkaline massif

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rozenberg, K. A.; Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru; Aksenov, S. M.

2016-09-15

The structure of the sodium-rich representative of the eudialyte group found by A.P. Khomyakov at the Lovozero massif (Kola Peninsula) is studied by X-ray diffraction. The trigonal cell parameters are: a = 14.2032(1) and c = 60.612(1) Å, V = 10589.13 Å3, space group R3m. The structure is refined to the final R = 5.0% in the anisotropic approximation of atomic displacement parameters using 3742|F| > 3σ(F). The idealized formula (Z = 3) is Na{sub 37}Ca{sub 10}Mn{sub 2}FeZr{sub 6}Si{sub 50}(Ti, Nb){sub 2}O{sub 144}(OH){sub 5}Cl{sub 3} · H{sub 2}O. Like other 24-layer minerals of the eudialyte group, this mineral has amore » modular structure. Its structure contains two modules, namely, “alluaivite” (with an admixture of “eudialyte”) and “kentbrooksite,” called according to the main structural fragments of alluaivite, eudialyte, and kentbrooksite. The mineral found at the Lovozero alkaline massif shows some chemical and symmetry-structural distinctions from the close-in-composition labyrinthite modular mineral from the Khibiny massif. The difference between the minerals stems from different geochemical conditions of mineral formation in the two regions.« less

HT-LP thermometamorphism modelling : Agly massif, French Pyrenees.

NASA Astrophysics Data System (ADS)

Tournaire Guille, Baptiste; Pascal, Marie-Lola; Lejeune, Anne-Marie; Annen, Catherine

2017-04-01

Owing to the strongly anomalous thermal gradients implied, HT-LP metamorphism is a worldwide type of processes in which magma emplacement and solidification at relatively high levels in the crust must be considered as a potentially major heat source. Thermal modelling (e.g. Annen et al. 2005) is an appropriate tool for constraining the part played by such processes in practical cases of thermometamorphism. We study the Agly massif, an exhumed part of middle crust from the Variscan belt in the French Pyrenees. This massif is a classical example of HT-LP metamorphism (Vielzeuf 1996), composed of a metasedimentary cover, mainly micaschists aged from upper Cambrian to Devonian, unconformably overlying an older basement of para- and orthogneisses. The Variscan metamorphic facies extend from greenschists, in the upper part of the cover, to granulites in the basement (Fonteilles 1976). The apparent geotherm of about 110°/km in the metasedimentary cover (amphibolite and greenschist facies) has given way to contrasting interpretations. Magmatic activity partly synchronous with and probably related to the Variscan thermometamorphism is observed at the outcropping level as at least 4 magmatic bodies of mantle origin (Touil 1994), of Stephanian age, including granodiorites and subordinate diorites and gabbros. Recent U/Pb datations on zircons (Tournaire-Guille et al., in prep) also reveal the presence of lower Cambrian magmatism in the gneisses, therefore confirming their interpretation as a pre-Variscan basement. The location (depth), volume (thickness), temperature (composition) and timing of magma emplacement are the parameters controlling the thermal effect to be modelled with a Matlab® code (Annen et al. 2005). In order to constrain these parameters, we have updated the lithostratigraphy and the PT conditions of the Variscan metamorphism in the Agly area. Mineralogic and petrologic data exploited in thermobarometric analyses compared with thermodynamic PerpleX modelling

Mapping of the Ronda peridotite massif (Spain) from AVIRIS spectro-imaging survey: A first attempt

NASA Technical Reports Server (NTRS)

Pinet, P. C.; Chabrillat, S.; Ceuleneer, G.

1993-01-01

In both AVIRIS and ISM data, through the use of mixing models, geological boundaries of the Ronda massif are identified with respect to the surrounding rocks. We can also yield first-order vegetation maps. ISM and AVIRIS instruments give consistent results. On the basis of endmember fraction images, it is then possible to discard areas highly vegetated or not belonging to the peridotite massif. Within the remaining part of the mosaic, spectro-mixing analysis reveals spectral variations in the peridotite massif between the well-exposed areas. Spatially organized units are depicted, related to differences in the relative depth of the absorption band at 1 micron, and it may be due to a different pyroxene content. At this stage, it is worth noting that, although mineralogical variations observed in the rocks are at a sub-pixel scale for the airborne analysis, we see an emerging spatial pattern in the distribution of spectral variations across the massif which might be prevailingly related to mineralogy. Although it is known from fieldwork that the Ronda peridotite massif exhibits mineralogical variations at local scale in the content of pyroxene, and at regional scale in different mineral facies, ranging from garnet-, to spinel- to plagioclase-lherzolites, no attempt has been done yet to produce a synoptic map relating the two scales of analysis. The present work is a first attempt to reach this objective, though a lot more work is still required. In particular, for the purpose of mineralogical interpretation, it is critical to relate the airborne observation to field work and laboratory spectra of Ronda rocks already obtained, with the use of image endmembers and associated reference endmembers. Also, the pretty rough linear mixing model used here is taken as a 'black-box' process which does not necessarily apply correctly to the physical situation at the sub-pixel level. One may think of using the ground-truth observations bearing on the sub-pixel statistical

Transpressional regime in southern Arabian Shield: Insights from Wadi Yiba Area, Saudi Arabia

NASA Astrophysics Data System (ADS)

Hamimi, Zakaria; El-Shafei, Mohamed; Kattu, Ghazi; Matsah, Mohammed

2013-10-01

Detailed field-structural mapping of Neoproterozoic basement rocks exposed in the Wadi Yiba area, southern Arabian Shield, Saudi Arabia illustrates an important episode of late Neoproterozoic transpression in the southern part of the Arabian-Nubian Shield (ANS). This area is dominated by five main basement lithologies: gneisses, metavolcanics, Ablah Group (meta-clastic and marble units) and syn- and post-tectonic granitoids. These rocks were affected by three phases of deformation (D1-D3). D1 formed tight to isoclinal and intrafolial folds (F1), penetrative foliation (S1), and mineral lineation (L1), which resulted from early E-W (to ENE-WSW) shortening. D2 deformation overprinted D1 structures and was dominated by transpression and top-to-the-W (-WSW) thrusting as shortening progressed. Stretching lineation trajectories, S-C foliations, asymmetric shear fabrics and related mylonitic foliation, and flat-ramp and duplex geometries further indicate the inferred transport direction. The N- to NNW-orientation of both “in-sequence piggy-back thrusts” and axial planes of minor and major F2 thrust-related overturned folds also indicates the same D2 compressional stress trajectories. The Wadi Yiba Shear Zone (WYSZ) formed during D2 deformation. It is one of several N-S trending brittle-ductile Late Neoproterozoic shear zones in the southern part of the ANS. Shear sense indicators reveal that shearing during D2 regional-scale transpression was dextral and is consistent with the mega-scale sigmoidal patterns recognized on Landsat images. The shearing led to the formation of the WYSZ and consequent F2 shear zone-related folds, as well as other unmappable shear zones in the deformed rocks. Emplacement of the syn-tectonic granitoids is likely to have occurred during D2 transpression and occupied space created during thrust propagation. D1 and D2 structures are locally overprinted by mesoscopic- to macroscopic-scale D3 structures (F3 folds, and L3 crenulation lineations and

Petrology of Ortsog-Uul peridotite-gabbro massif in Western Mongolia

NASA Astrophysics Data System (ADS)

Shapovalova, M.; Tolstykh, N.; Shelepaev, R.; Cherdantseva, M.

2017-12-01

The Ortsog-Uul mafic-ultramafic massif of Western Mongolia is located in a tectonic block with overturned bedding. The massif hosts two intrusions: a rhythmically-layered peridotite-gabbro association (Intrusion 1) and massive Bt-bearing amphibole-olivine gabbro (Intrusion 2). Intrusions 1 and 2 have different petrology features. Early Intrusion 1 (278±2.5Ma) is characterized by lower concentrations of alkalis, titanium and phosphorus than late Intrusion 2 (272±2Ma). The chondrite-normalized REE and primitive mantle-normalized rare elements patterns of Ortsog-Uul intrusions have similar curves of elements distribution. However, Intrusion 2 is characterized higher contents of REE and rare elements. High concentrations of incompatible elements are indicative of strong fractionation process. It has been suggested that Intrusions 1 and 2 derived from compositionally different parental melts. Model calculations (COMAGMAT-3.57) show that parental melts of two intrusions were close to high-Mg picrobasaltic magmas. The concentration of MgO in melt is 16.21 (Intrusion 1) and 16.17 (Intrusion 2). Isotopic data of Ortsog-Uul magmatic rocks exhibit different values of εNd (positive and negative) for Intrusion 1 and 2, respectively.

Thematic mapping of likely target areas for the occurence of cassiterite in the Serra do Mocambo (GO) granitic massifs using LANDSAT 2 digital imaging

NASA Technical Reports Server (NTRS)

Almeidofilho, R. (Principal Investigator)

1984-01-01

The applicability of LANDSAT/MSS images, enhanced by computer derived techniques, as essential tools in mineral research was investigated and the Serra do Mocambo granitic massif was used as illustration. Given the peculiar factors founded in this area, orbital imagery permitted the delineation of potential target areas of mineralization occurrences, associated to albitized/greisenized types. Follow up prospection for primary tin deposits in this granitic massif should be restricted to the delineated areas which are less than 5% of the total superficial area of the massif.

Massification of University Education in Nigeria: Private Participation and Cost Challenges

ERIC Educational Resources Information Center

Ahunanya, S.; Chineze, U.; Nnennaya, I.

2013-01-01

This study investigated the massification of university education in Nigeria as a result of the reforms in the education subsector that led to private participation in the provision of university education from 1999. The question of the study hinges on the percentage of access and if the increased number of universities has led to increased…

Isotope-Geochemical Evidence for the Nature of Protolite Eclogite of the Kokchetav Massif (Kazakhstan)

NASA Astrophysics Data System (ADS)

Shatsky, V. S.; Skuzovatov, S. Yu.; Ragozin, A. L.; Dril, S. I.

2018-03-01

In the present paper, the results of our isotope-geochemical studies on eclogites of the ultrahighpressure metamorphic complex of the Kokchetav massif are reported. The fact that the distribution of nonmobile elements in most of the samples was close to that of E-type MORB basalts is shown by using geochemical multielement diagrams normalized to N-MORB. Six samples were found to have a negative anomaly over niobium that may have resulted from contamination with crustal material. For eclogites of the Kokchetav massif, the 147Sm/144Nd ratio was found to range widely from 0.143 to 0.367. The ɛNd-values calculated for the age of the highly barometric stage of metamorphism (530 million years) varied from-10.3 to +8.1. Eclogites show a dispersion of model ages from 1.95 billion years to 670 million years. On the graphs in the ɛNd( T)-87Sr/86Sr and ɛNd( T)- T coordinates, eclogites were shown to form trends that can be interpreted as a result of contamination of the eclogite protolith by the host rocks. Based on the data obtained, it is proposed that the basalts of rift zones that may have geochemical characteristics of N-MORB basalts and at the same time may be contaminated by the continental crust may have served as proxies for eclogite protoliths of the Kokchetav massif.

The Galicia-Ossa-Morena Zone: Proposal for a new zone of the Iberian Massif. Variscan implications

NASA Astrophysics Data System (ADS)

Arenas, Ricardo; Díez Fernández, Rubén; Rubio Pascual, Francisco J.; Sánchez Martínez, Sonia; Martín Parra, Luis Miguel; Matas, Jerónimo; González del Tánago, José; Jiménez-Díaz, Alberto; Fuenlabrada, Jose M.; Andonaegui, Pilar; Garcia-Casco, Antonio

2016-06-01

Correlation of a group of allochthonous terranes (referred to as basal, ophiolitic and upper units) exposed in the NW and SW of the Iberian Massif, is used to propose a new geotectonic zone in the southern branch of the Variscan Orogen: the Galicia-Ossa-Morena Zone. Recent advances in SW Iberia identify most of the former Ossa-Morena Zone as another allochthonous complex of the Iberian Massif, the Ossa-Morena Complex, equivalent to the Cabo Ortegal, Órdenes, Malpica-Tui, Bragança and Morais complexes described in NW Iberia. The new geotectonic zone and its counterparts along the rest of the Variscan Orogen constitute an Internal Variscan Zone with ophiolites and units affected by high-P metamorphism. The Galicia-Ossa-Morena Zone includes a Variscan suture and pieces of continental crust bearing the imprint of Ediacaran-Cambrian events related to the activity of peri-Gondwanan magmatic arcs (Cadomian orogenesis). In the Iberian Massif, the general structure of this geotectonic zone represents a duplication of the Gondwanan platform, the outboard sections being juxtaposed on top of domains located closer to the mainland before amalgamation. This interpretation offers an explanation that overcomes some issues regarding the differences between the stratigraphic and paleontological record of the central and southern sections of the Iberian Massif. Also, equivalent structural relationships between other major geotectonic domains of the rest of the Variscan Orogen are consistent with our interpretation and allow suspecting similar configurations along strike of the orogen. A number of issues may be put forward in this respect that potentially open new lines of thinking about the architecture of the Variscan Orogen.

Isotope Sm-Nd age of the paleoproterozoic PGE-bearing Monchetundra massif trachytoid gabbronorites (Fennoscandian shield)

NASA Astrophysics Data System (ADS)

Kunakkuzin, Evgeniy; Bayanova, Tamara; Serov, Pavel; Borisenko, Elena

2015-04-01

Monchetundra massif is located in the central part of the Kola Peninsula (Russia) and it is the south-eastern part of the Main Ridge Intrusion. Monchetundra massif together with well-known layered mafic-ultramafic PGE-bearing intrusions in the Fennoscandian shield such as the Fedorovo-Pansky complex, the mt. Generalskaya, the Monchepluton is of interest as a target for the PGE prospecting (Mitrofanov et al. 2006; Nerovich et al., 2009; Grokhovskaya et al., 2003). According to some previously researchers (Nazimova, Rayan, 2008, Nerovich et al., 2009, Layered intrusions…p.1, 2004) rocks of the Monchetundra massif is subdivided into two to five syngenetic zones. Hence the last isotope-geochronological and isotope-geochemical data revealed that the massif includes at least four groups of mafic rocks distinguished by formation ages (Bayanova et al., 2010). The aim of this work is to present Sm-Nd dating results of trachytoid gabbronorites, which are the second mafic rocks group in the Monchetundra massif. The Sm-Nd investigations for these rocks were carried out for the first time. The second group of mafic rocks comprises of medium-grained and coarse-grained mesocratic gabbronorites of trachytoid texture, with they characterized by well-preserved primary magmatic minerals and gabbro-ophitic texture. The U-Pb ages on single zircon-baddeleyite for these rocks recently obtained (2505 ± 6 Ma, 2501 ± 8 Ma, 2504.4±2.7 Ma and 2507.5±7.7 Ma (Layered intrusions…p.1., 2004, Borisenko et al., 2013)). Two samples of trachytoid gabbronorites were selected to study these rocks by Sm-Nd isotopic method. Mineral isochrons plotted from plagioclase, ortho- and clinopyroxene and whole-rock minerals gave ages of 2496±27 (MSWD = 0.9; ɛNd = -1.6±0.5) and 2492±55 Ma (MSWD = 0.5; ɛNd = -1.7±0.5). The new Sm-Nd ages obtained are close to the U-Pb data on zircons and baddeleyites for this rocks group and consider as oridin of second mafic rocks group. All investigations are

Two-stage fluid flow and element transfers in shear zones during collision burial-exhumation cycle: Insights from the Mont Blanc Crystalline Massif (Western Alps)

NASA Astrophysics Data System (ADS)

Rolland, Y.; Rossi, M.

2016-11-01

The Mont-Blanc Massif was intensely deformed during the Alpine orogenesis: in a first stage of prograde underthrusting at c. 30 Ma and in a second stage of uplift and exhumation at 22-11 Ma. Mid-crustal shear zones of 1 mm-50 m size, neighbouring episyenites (quartz-dissolved altered granite) and alpine veins, have localised intense fluid flow, which produced substantial changes in mineralogy and whole-rock geochemistry. Four main metamorphic zones are oriented parallel to the strike of the massif: (i) epidote, (ii) chlorite, (iii) actinolite-muscovite ± biotite and (iv) muscovite ± biotite. In addition, phlogopite-bearing shear zones occur in the chlorite zone, and calcite-bearing shear zones are locally found in the muscovite zone. The initial chemical composition of the granitic protolith is relatively constant at massif scale, which allows investigating compositional changes related to shear zone activity, and subsequent volume change and elements mobility. The variations of whole-rock composition and mineral chemistry in shear zones reflect variations in fluid/rock ratios and fluid's chemistry, which have produced specific mineral reactions. Estimated time-integrated fluid fluxes are of the order of 106 m3/m2. The mineral assemblages that crystallised upon these fluid-P-T conditions are responsible for specific major and trace element enrichments. The XFe (Fe/Fe + Mg) pattern of shear zone phyllosilicates and the δ13C pattern of vein calcite both show a bell-type pattern across the massif with high values on the massif rims and low values in the centre of the massif. These low XFe and δ13C values are explained by down temperature up-flow of a Fe-Mg-CO2-rich and silica-depleted fluid during stage 1, while the massif was underthrusting. These produced phlogopite, chlorite and actinolite precipitation and quartz hydrolysis, resulting in strong volume losses. In contrast, during stage 2 (uplift), substantial volume gains occurred on the massif rims due to the

The Massification of Higher Education in the UK: Aspects of Service Quality

ERIC Educational Resources Information Center

Giannakis, Mihalis; Bullivant, Nicola

2016-01-01

This article explores several aspects of service quality for the provision of higher education. Alongside the trend of the massification of higher education over the past two decades, higher education institutions are required to review quality across a range of outputs, besides teaching and learning. The study was undertaken within the…

New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

USGS Publications Warehouse

Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

2007-01-01

The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

New species from the Galoka and Kalabenono massifs: two unknown and severely threatened mountainous areas in NW Madagascar

PubMed Central

Callmander, Martin W.; Rakotovao, Charles; Razafitsalama, Jeremi; Phillipson, Peter B.; Buerki, Sven; Hong-Wa, Cynthia; Rakotoarivelo, Nivo; Andriambololonera, Sylvie; Koopman, Margaret M.; Johnson, David M.; Deroin, Thierry; Ravoahangy, Andriamandranto; Solo, Serge; Labat, Jean-Noël; Lowry, Porter P.

2011-01-01

The Galoka mountain chain, comprising principally the Galoka and Kalabenono massifs, situated at the northern edge of the Sambirano Region in NW Madagascar is an area that was virtually unknown botanically. It was visited three times between 2005 and 2007 as part of a floristic inventory. Both massifs contain the last remaining primary forests in the Galoka chain, which extends parallel to the coastline from South of Ambilobe to North of Ambanja. Several new species have been discovered amongst the collections, eight of which are described here. PMID:21857767

Preliminary results of spectral induced polarization measurements, Wadi Bidah District, Kingdom of Saudi Arabia

USGS Publications Warehouse

Smith, Bruce D.; Tippens, C.L.; Flanigan, V.J.; Sadek, Hamdy

1983-01-01

Laboratory spectral induced polarization (SIP) measurements on 29 carbonaceous schist samples from the Wadi Bidah district show that most are associated with very long polarization decays or, equivalently, large time constants. In contrast, measurements on two massive sulfide samples indicate shorter polarization decays or smaller time constants. This difference in time constants for the polarization process results in two differences in the phase spectra in the frequency range of from 0.06 to 1Hz. First, phase values of carbonaceous rocks generally decrease as a function of increasing frequency. Second, phase values of massive sulfide-bearing rocks increase as a function of increasing frequency. These results from laboratory measurements agree well with those from other reported SIP measurements on graphites and massive sulfides from the Canadian Shield. Four SIP lines, measured by using a 50-m dipole-dipole array, were surveyed at the Rabathan 4 prospect to test how well the results of laboratory sample measurements can be applied to larger scale field measurements. Along one line, located entirely over carbonaceous schists, the phase values decreased as a function of increasing frequency. Along a second line, located over both massive sulfides and carbonaceous schists as defined by drilling, the phase values measured over carbonaceous schists decreased as a function of increasing frequency, whereas those measured over massive sulfides increased. In addition, parts of two lines were surveyed down the axes of the massive sulfide and carbonaceous units. The phase values along these lines showed similar differences between the carbonaceous schists and massive sulfides. To date, the SIP survey and the SIP laboratory measurements have produced the only geophysical data that indicate an electrical difference between the massive sulfide-bearing rocks and the surrounding carbonaceous rocks in the Wadi Bidah district. However, additional sample and field measurements in

Œdème vulvaire massif pendant la grossesse: à propos d'un cas

PubMed Central

El Hassani, Moulay Elmehdi; Kassidi, Farid; Benabdejlil, Youssef; Kouach, Jaouad; Moussaoui, Driss Rahali; Dehayni, Mohammed

2014-01-01

L’œdème vulvaire massif est rare pendant la grossesse, mais requiert une attention particulière car il peut se greffer de complications maternelles et fœtales. Il peut être associé à plusieurs pathologies spécifiques ou non spécifiques à la grossesse dont le diagnostic fait appel obligatoirement à un interrogatoire et un examen clinique minutieux, puis à un bilan biologique standard. Le traitement doit être étiologique chaque fois que possible à coté du traitement symptomatique. Cette situation peut nécessiter un accouchement par césarienne. En dehors du risque potentiel de nécrose tissulaire et du risque exceptionnel de décès maternel associé à l’œdème vulvaire massif du post-partum l’évolution est favorable sous traitement bien conduit. PMID:25922627

Constraining the deformation and exhumation history of the Ronda Massif, Southern Spain

NASA Astrophysics Data System (ADS)

Myall, Jack; Donaldson, Colin

2016-04-01

The Ronda peridotite, southern Spain is comprised of four peridotite units hosted within metasedimentary units of the Betic Cordillera, Western Alps. These four areas of differing mineral facies are termed: the Garnet Mylonite , the Foliated Spinel Peridotite, the Granular Spinel Peridotite and the Foliated Plagioclase Peridotite. Whilst two of these units show a strong NE-SW foliation, the granular unit has no foliation and the Plagioclase facies shows a NW-SE foliation. The massif is separated from the metasedimentary host through a mylonite shear zone to the NW and thrust faults to the SE. The Garnets contain rims of Kelyphite which when combined with the rims of Spinel on the Plagioclase crystals illustrate the complicated exhumation of this massif. The Kelyphite shows the breakdown of garnet back to spinel and pyroxene showing the deeper high pressure high temperature mineral is under shallowing conditions whereas in contrast to this the low pressure low temperature plagioclase crystals have spinel rims showing that they have been moved into deeper conditions. The P-T-t pathway of the massif suggests slow exhumation to allow for partial recrystallisation of not only the garnets and plagioclases but of a 100m band of peridotite between the Foliated Spinel Peridotite and the Granular Spinel Peridotite facies. The tectonic model for the Ronda Peridotite that best describes the field data and subsequent lab work of this study is Mantle Core complex and slab roll back models. These models support mantle uprising during an extensional event that whereby slab roll back of the subducting lithosphere provides uplift into a void and emplacement into the crust. Further extension and final exhumation causes rotation of a mantle wedge into its present day position.

Lithologic distribution and geologic history of the Apollo 17 site: The record in soils and small rock particles from the highland massifs

NASA Astrophysics Data System (ADS)

Jolliff, Bradley L.; Rockow, Kaylynn M.; Korotev, Randy L.; Haskin, Larry A.

1996-01-01

Through analysis by instrumental neutron activation (INAA) of 789 individual lithic fragments from the 2 mm-4 mm grain-size fractions of five Apollo 17 soil samples (72443, 72503, 73243, 76283, and 76503) and petrographic examination of a subset, we have determined the diversity and proportions of rock types recorded within soils from the highland massifs. The distribution of rock types at the site, as recorded by lithic fragments in the soils, is an alternative to the distribution inferred from the limited number of large rock samples. The compositions and proportions of 2 mm-4 mm fragments provide a bridge between compositions of <1 mm fines, and types and proportions of rocks observed in large collected breccias and their clasts. The 2 mm-4 mm fraction of soil from South Massif, represented by an unbiased set of lithic fragments from station-2 samples 72443 and 72503, consists of 71% noritic impact-melt breccia, 7% incompatible-trace-element-(ITE)-poor highland rock types (mainly granulitic breccias), 19% agglutinates and regolith breccias, 1% high-Ti mare basalt, and 2% others (very-low-Ti (VLT) basalt, monzogabbro breccia, and metal). In contrast, the 2 mm-4 mm fraction of a soil from the North Massif, represented by an unbiased set of lithic fragments from station-6 sample 76503, has a greater proportion of ITE-poor highland rock types and mare-basalt fragments: it consists of 29% ITE-poor highland rock types (mainly granulitic breccias and troctolitic anorthosite), 25% impact-melt breccia, 13% high-Ti mare basalt, 31% agglutinates and regolith breccias, 1% orange glass and related breccia, and 1% others. Based on a comparison of mass-weighted mean compositions of the lithic fragments with compositions of soil fines from all Apollo 17 highland stations, differences between the station-2 and station-6 samples are representative of differences between available samples from the two massifs. From the distribution of different rock types and their compositions

The French Atlantic littoral and the Massif Armoricain, part 3

NASA Technical Reports Server (NTRS)

Verger, F. (Principal Investigator); Scanvic, J. Y.; Monget, J. M.

1977-01-01

The author has identified the following significant results: (1) An original map of lineaments of the Armorican Massif and the Vendean platform was prepared. (2) Validity of spatial information through comparison with maps of various kinds, such as geological, geophysical, morphological, etc., was verified. (3) It was confirmed that LANDSAT images, in many cases, reflect data on deep phenomena which were only accessible geophysically and by means of borings. Tectonic domains were outlined, and known lineaments were extended.

Soil erodibility mapping using the RUSLE model to prioritize erosion control in the Wadi Sahouat basin, North-West of Algeria.

PubMed

Toubal, Abderrezak Kamel; Achite, Mohammed; Ouillon, Sylvain; Dehni, Abdelatif

2018-03-12

Soil losses must be quantified over watersheds in order to set up protection measures against erosion. The main objective of this paper is to quantify and to map soil losses in the Wadi Sahouat basin (2140 km 2 ) in the north-west of Algeria, using the Revised Universal Soil Loss Equation (RUSLE) model assisted by a Geographic Information System (GIS) and remote sensing. The Model Builder of the GIS allowed the automation of the different operations for establishing thematic layers of the model parameters: the erosivity factor (R), the erodibility factor (K), the topographic factor (LS), the crop management factor (C), and the conservation support practice factor (P). The average annual soil loss rate in the Wadi Sahouat basin ranges from 0 to 255 t ha -1  year -1 , maximum values being observed over steep slopes of more than 25% and between 600 and 1000 m elevations. 3.4% of the basin is classified as highly susceptible to erosion, 4.9% with a medium risk, and 91.6% at a low risk. Google Earth reveals a clear conformity with the degree of zones to erosion sensitivity. Based on the soil loss map, 32 sub-basins were classified into three categories by priority of intervention: high, moderate, and low. This priority is available to sustain a management plan against sediment filling of the Ouizert dam at the basin outlet. The method enhancing the RUSLE model and confrontation with Google Earth can be easily adapted to other watersheds.

The Chineysky layered massif (Siberia, Russia) and Upper Zone of the Bushveld Complex: resemblance and difference features

NASA Astrophysics Data System (ADS)

Gongalskiy, B.; Krivolutskaya, N.

2009-04-01

Layered intrusions represent a small part of a large group of continental basic-ultrabasic complexes. They attract geologists' attention due to their unusual magmatic structures and associated PGE, Cr and V deposits. The outstanding example of this phenomenon is the Bushveld Complex in South Africa. The largest layered intrusion in Russia is the Chineysky massif (Transbaikalia, Siberia). It is characterized by excellent layering and accompanying titanomagnetite and sulfide mineralization. It hosts Russia's largest deposits of Fe-Ti-V ores which are also among the world's largest [1]. Origin of such huge metal concentrations in the crust is unsettled problem. Therefore the ore conditions' determination from different intrusions is very actually. We compared the structure, rock and parental magmas compositions for two plutons mentioned above. The Chineysky massif consists of gabbronorites and anorthozites and the petrography of the rocks resembles that of the Upper Zone of the Bushveld [3]. Vanadium ores from these two intrusions are very similar: they are represented by massive and disseminated varieties. However, the small size of Chineysky massiv gives an opportunity to observe the number of petrological processes in a frame of one area, as opposed to Bushveld, where this is impossible. The separateness of the bodies and the scarcity of geochemical data on their rocks precluded the development of a comprehensive model for the evolution of magmatism in this part of the Kodar- Udokan trough. So one of the tasks of our research was to study the spatial and genetic relations between the ultrabasite-basite intrusive bodies and their possible grouping within a single magmatic system, with the Chineysky massif being its part. The second tasks was to determine the phase characteristics of the parental magma of the massif . An important aspect of this study was the examination of the inner structure of the Chineysky massiv. The main features of the structure are following

Massification and Diversification as Complementary Strategies for Economic Growth in Developed and Developing Countries

ERIC Educational Resources Information Center

Tyndorf, Darryl; Glass, Chris R.

2016-01-01

Numerous microeconomic studies demonstrate the significant individual returns to tertiary education; however, little empirical evidence exists regarding the effects of higher education massification and diversification agendas on long-term macroeconomic growth. The researchers used the Uzawa-Lucas endogenous growth model to tertiary education…

Spatial distribution of quartz recrystallization microstructures across the Aar massif (Swiss Central Alps)

NASA Astrophysics Data System (ADS)

Peters, M.; Herwegh, M.

2012-04-01

In the Aar massif, main foliation and major deformation structures were developed during NW-SE compression associated with the Alpine orogeny (Steck 1968). To be precise, shearing at the brittle to ductile transition may have initiated at different stages between 22-20 Ma and 14-12 Ma, followed by purely brittle deformation at around 10 Ma (Rolland et al. 2009). In light of the onset of dynamic recrystallization in quartz, Bambauer et al. (2009) defined a quartz recrystallization isograd in the northern part of the Aar massif. To the south, the grain size of recrystallized grains increases due to an increase of metamorphic temperatures from N to S. The aim of the current project is to carry out quantitative analysis on changes of the dynamic and static recrystallization behavior of quartz. Across the Aar massif, two general types of microstructures have to be discriminated: (i) weakly to moderately deformed host rocks and (ii) intensely deformed mylonites to ultramylonites out of high strain shear zones. In (i), volume fraction and size of recrystallized quartz grains increase towards the S showing grain size changes from around 5 µm up to ca. 200 µm. Southern microstructures are characterized by complete recrystallization. In terms of recrystallization processes, a transition from bulging recrystallization in the N to subgrain rotation recrystallization in the S occurs. Such a change in dynamic recrystallization processes combined with a grain size increase points towards reduced differential stresses with increasing temperature. This temperature gradient is also corroborated by a switch in the active glide systems in quartz from basal to rhomb dominated glide. In contrast to the granitic host rocks, the mylonites and ultramylonites (ii) show smaller recrystallized grain sizes due to enhanced strain rates. However, they also reveal a general increase of recrystallized grain sizes from N to S. In the S, microstructures from (i) and (ii) show equidimensional

The Nahuel Niyeu basin: A Cambrian forearc basin in the eastern North Patagonian Massif

NASA Astrophysics Data System (ADS)

Greco, Gerson A.; González, Santiago N.; Sato, Ana M.; González, Pablo D.; Basei, Miguel A. S.; Llambías, Eduardo J.; Varela, Ricardo

2017-11-01

Early Paleozoic basement of the eastern North Patagonian Massif includes low- and high grade metamorphic units, which consist mainly of alternating paraderived metamorphic rocks (mostly derived from siliciclastic protoliths) with minor intercalations of orthoderived metamorphic rocks. In this contribution we provide a better understanding of the tectonic setting in which the protoliths of these units were formed, which adds to an earlier suggested idea. With this purpose, we studied the metasedimentary rocks of the low-grade Nahuel Niyeu Formation from the Aguada Cecilio area combining mapping and petrographic analysis with U-Pb geochronology and characterization of detrital zircon grains. The results and interpretations of this unit, together with published geological, geochronological and geochemical information, allow us to interpret the sedimentary and igneous protoliths of all metamorphic units from the massif as formed in a forearc basin at ∼520-510 Ma (Nahuel Niyeu basin). It probably was elongated in the ∼NW-SE direction, and would have received detritus from a proximal source area situated toward its northeastern side (present coordinates). The basin might be related to an extensional tectonic regime. Most likely source rocks were: (1) 520-510 Ma, acidic volcanic rocks (an active magmatic arc), (2) ∼555->520 Ma, acidic plutonic and volcanic rocks (earlier stages of the same arc), and (3) latest Ediacaran-Terreneuvian, paraderived metamorphic rocks (country rocks of the arc). We evaluate the Nahuel Niyeu basin considering the eastern North Patagonian Massif as an autochthonous part of South America, adding to the discussion of the origin of Patagonia.

Research the dynamical characteristics of slow deformation waves as a rock massif response to explosions during its outworking

NASA Astrophysics Data System (ADS)

Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

2015-04-01

As a result of long-term natural geomechanics and geophysical observation data on mines of complex ore rocks, generalization of the non-linear reaction of rock massif to heavy dynamic influences have been established. In addition, pendulum type waves have been observed and the sources of them have been located inside geoblocks of different hierarchic levels (Oparin et al., 2010). At the same time, these waves propagate with wide low (compared with seismic waves) velocity values (Kurlenja et al., 1993; Oparin et al., 2006). Research into the massif state with the use of the dynamic systems theory approach (Naimark et al., 2009; Chulichkov, 2003; Hachay et al., 2010) has been developed to ascertain the criteria of dissipative regimes changing for real rock massifs, which are under heavy man-caused influence. To realize such research we used the data from the seismic record of the Tashtagol mine for the two-year period from June 2006 up to June 2008. We used the space-time coordinates for all dynamic massif event responses, which occurred during that period inside the mine space and for the explosions - values fixed by seismic station energy (Hachay et al., 2010). The phase diagrams of the massif state for the northern and southern parts of the mine space were plotted in coordinates Ev(t) and d(Ev(t))/dt, t - time - in parts of 24 hours, Ev - the dissipated massive seismic energy - in joules. Hachay et al., (2010) analysed the morphology of seismic response phase trajectories on the explosion influences during different serial intervals in the southern part of the mine. In that period, according to data for different explosions in the mine, the majority of the total energy had been injected into the southern part of the mine. Moreover, at the end of 2007, just in the southern part, the strongest rock burst during the whole history of the working mine happened. We developed a new processing method of seismological information in real, which we can use directly in the

Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

NASA Astrophysics Data System (ADS)

Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.

2014-12-01

In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.

Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Ferrando, Simona; Compagnoni, Roberto; Lombardo, Bruno

2010-04-01

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded H P granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.

Géométrie et cinématique des chevauchements varisques du Nord-Est du Massif armoricain (France)Geometry and kinematics of Variscan thrusts in the northeastern Armorican Massif (France)

NASA Astrophysics Data System (ADS)

Butaeye, Damien; Laville, Edgard; Le Gall, Jean

2001-02-01

Variscan structures of the northeastern Armorican massif consist of folds induced by south-verging thrust faults. This thin-skinned process is controlled by a major décollement that would be expected at the base of the Brioverian flysch. So, the northeastern Armorican domain can be integrated to the tectonic model admitted at the Variscan Orogenesis scale.

Supergene oxidation of epithermal gold-silver mineralization in the Deseado massif, Patagonia, Argentina: response to subduction of the Chile Ridge

NASA Astrophysics Data System (ADS)

Sillitoe, Richard H.

2018-06-01

Radiometric ages for supergene alunite and jarosite effectively date the oxidation of former concentrations of pyrite and any associated sulfide minerals. These K-bearing sulfate minerals, formed under low-pH conditions, are uncommon supergene products in low-sulfidation epithermal deposits because of the general paucity of pyrite for acid generation. For this reason, the age of supergene oxidation—locally to depths of 200 m or more—in the epithermal Au-Ag deposits of the Deseado massif, located in the extra-Andean foreland of Patagonia, southern Argentina, has remained unknown. Although, theoretically, the oxidation could have taken place anytime between the Late Jurassic, when the Au-Ag mineralization formed, and Pleistocene, K-Ar ages for alunite and jarosite from two widely separated and unusually pyritic, Ag-bearing hydrothermal breccias (Lejano and Libanesa) show it to have been mid-Miocene, 13.8 ± 1.8 Ma. This is the time when the Deseado massif underwent appreciable regional-scale tectonic uplift and valley incision, following 140 myr during which the region was topographically subdued and the site of either fluvio-lacustrine or shallow-marine sedimentation. The uplift, combined with increasing aridity due to the orographic rain shadow caused by growth of the Patagonian Andes to the west and enhanced by global cooling, would have depressed regional groundwater tables, thereby promoting the supergene sulfide oxidation. The mid-Miocene uplift appears to have been triggered by development of a slab tear and slab window beneath the Deseado massif during early stages of subduction of the Chile oceanic-ridge spreading center at the Pacific margin. Supergene sulfide oxidation in both the Deseado massif and Atacama Desert of northern Chile was the result of Cenozoic uplift during progressive aridification, although the causes of these phenomena were radically different. However, when the supergene oxidation was taking place in the Deseado massif, up to 30 myr

Long-term simulations of thermal and hydraulic characteristics in a mountain massif: The Mont Blanc case study, French and Italian Alps

NASA Astrophysics Data System (ADS)

Maréchal, J. C.; Perrochet, P.; Tacher, L.

1999-08-01

The use of hydrothermal simulation models to improve the prediction of water inflows in underground works during drilling is tested in the Mont Blanc tunnel, French and Italian Alps. The negative thermal anomaly that was observed during the drilling of this tunnel in 1960 is reproduced by long-term, transient hydrothermal simulations. Sensitivity analysis shows the great inertia of thermal phenomena at the massif scale. At the time of tunnel drilling, the massif had not reached thermal equilibrium. Therefore, a set of simulation scenarios, beginning at the end of the last glacial period, was designed to explain the anomaly encountered in the tunnel in 1960. The continuous cooling of alpine massifs due to infiltration of waters from the surface has occurred for 12,000 years and is expected to continue for about 100,000 years. Comparisons of water-discharge rates simulated in the tunnel with those observed indicate that this hydrothermal method is a useful tool for predicting water inflows in underground works.

A magnetotelluric study from over Dharwar cratonic nucleus into Billigiri Rangan charnockitic massif, India

NASA Astrophysics Data System (ADS)

Pratap, A.; Kusham; Pradeep Naick, B.; Naganjaneyulu, K.

2018-07-01

The electrical resistivity structure of the crust beneath the Dharwar craton in southern India was investigated by magnetotelluric method. In the present study, a northwest-southeast oriented 220 km long profile of 18 stations with a station spacing of ∼10-15 km is used. The profile extends from Dharwar cratonic nucleus in the north to Billigiri Rangan charnockitic massifs in the south. Time series data are processed to get the apparent resistivity and phase. The dominant geoelectric strike direction (75°) was calculated in a period range of 0.01-1000 s. The data are rotated to 75° strike direction. Two-dimensional inversion is carried out by using the non-linear conjugate gradient scheme for both apparent resistivity and phase. Our inversion results show a conductor in the northern side of the profile and two distinct prominent conductors in southern part of the profile. The mid-lower crust in southern part of the profile shows less resistive (<300 ohm-m) nature in the depth range of 20-50 km and is related with the Chitradurga shear zone and Billigiri Rangan charnockite massif. These zones were interpreted as CO2 flushed terranes. Regional-scale carbonation occurred in Late Archaean is associated with Chitradurga shear zone and in Late Proterozoic is associated with Salem-Attur shear zone. The CO2 rich fluids derived during that time might have exhausted in dehydration reactions. Later events such as the Indian plate passing over several hotspots and the metasomatized fluids associated with the Cretaceous-Tertiary magmatism in the region is the reason for observed low resistivity near Billigiri Rangan massif and surrounding regions in the south.

Instrument-Aided Assessment of the Effect of Natural and Technogenic Factors on the Geomechanical State of a Massif Enclosing an HPP Turbine Room

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abramov, N. N., E-mail: Abramov@goi.kolasc.net.ru; Epimakhov, Yu. A.

2016-05-15

A package of geophysical criteria has been developed using seismic spatiotemporal tomography (SST) of a rock massif to perform an instrument-aided assessment of the effect of natural and technogenic factors on the geomechanical state of a rock massif enclosing an underground turbine room at an HPP. Results are presented for a detailed assessment for the underground turbine room at the Verkhnyaya Tuloma HPP on the Kola peninsula.

Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif

NASA Astrophysics Data System (ADS)

Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Anczkiewicz, Robert; Van Den Driessche, Jean

2018-05-01

Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15-20 kbar, 560-630 °C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 ± 13 Ma.

Metagenomic identification of active methanogens and methanotrophs in serpentinite springs of the Voltri Massif, Italy.

PubMed

Brazelton, William J; Thornton, Christopher N; Hyer, Alex; Twing, Katrina I; Longino, August A; Lang, Susan Q; Lilley, Marvin D; Früh-Green, Gretchen L; Schrenk, Matthew O

2017-01-01

The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12). Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif.

Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

2014-05-01

This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz

Uplift history of the Sila Massif, southern Italy, deciphered from cosmogenic 10Be erosion rates and river longitudinal profile analysis

USGS Publications Warehouse

Olivetti, Valerio; Cyr, Andrew J.; Molin, Paola; Faccenna, Claudio; Granger, Darryl E.

2012-01-01

The Sila Massif in the Calabrian Arc (southern Italy) is a key site to study the response of a landscape to rock uplift. Here an uplift rate of ∼1 mm/yr has imparted a deep imprint on the Sila landscape recorded by a high-standing low-relief surface on top of the massif, deeply incised fluvial valleys along its flanks, and flights of marine terraces in the coastal belt. In this framework, we combined river longitudinal profile analysis with hillslope erosion rates calculated by 10Be content in modern fluvial sediments to reconstruct the long-term uplift history of the massif. Cosmogenic data show a large variation in erosion rates, marking two main domains. The samples collected in the high-standing low-relief surface atop Sila provide low erosion rates (from 0.09 ± 0.01 to 0.13 ± 0.01 mm/yr). Conversely, high values of erosion rate (up to 0.92 ± 0.08 mm/yr) characterize the incised fluvial valleys on the massif flanks. The analyzed river profiles exhibit a wide range of shapes diverging from the commonly accepted equilibrium concave-up form. Generally, the studied river profiles show two or, more frequently, three concave-up segments bounded by knickpoints and characterized by different values of concavity and steepness indices. The wide variation in cosmogenic erosion rates and the non-equilibrated river profiles indicate that the Sila landscape is in a transient state of disequilibrium in response to a strong and unsteady uplift not yet counterbalanced by erosion.

Specifics of geological composition, geochemistry and geochronology of rocks from the Kresty alkaline-ultrabasic massif (Maimecha-Kotui province, Polar Siberia)

NASA Astrophysics Data System (ADS)

Sazonov, A. M.; Zvyagina, E. A.; Gertner, I. F.; Krasnova, T. S.; Lipenkov, G. P.

2017-12-01

In this work, we demonstrate new data that allows us to accurate geochronological ranges of formation of the Kresty alkaline-ultrabasic massif, which is considered to be a satellite of the Gulinian giant pluton. We also interpreted geological, geochemical and isotope-geochemical data obtained earlier for major varieties of this volcanic-plutonic association taking into account new geochronological results, as well as considered new aspects/information on matter source of alkaline-ultrabasic massifs from this province. One of the main aspects is interaction of Siberian super plume matter with hosting substrate of Siberian craton continental crust.

Utilization of digital LANDSAT imagery for the study of granitoid bodies in Rondonia: Case example of the Pedra Branca massif

NASA Technical Reports Server (NTRS)

Parada, N. D. J. (Principal Investigator); Almeidafilho, R.; Payolla, B. L.; Depinho, O. G.; Bettencourt, J. S.

1984-01-01

Analysis of digital multispectral MSS-LANDSAT images enhanced through computer techniques and enlarged to a video scale of 1:100.000, show the main geological and structura features of the Pedra Branca granitic massif in Rondonia. These are not observed in aerial photographs or adar images. Field work shows that LANDSAT photogeological units correspond to different facies of granitic rocks in the Pedra Branca massif. Even under the particular characteristics of Amazonia (Tropical Forest, deep weathering, and Quaternary sedimentary covers), an adequate utilization of orbital remote sensing images can be important tools for the orientation of field works.

Metagenomic identification of active methanogens and methanotrophs in serpentinite springs of the Voltri Massif, Italy

PubMed Central

Thornton, Christopher N.; Hyer, Alex; Twing, Katrina I.; Longino, August A.; Lang, Susan Q.; Lilley, Marvin D.; Früh-Green, Gretchen L.; Schrenk, Matthew O.

2017-01-01

The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12). Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif. PMID:28149702

New Paleomagnetic Data from the Wadi Abyad Crustal Section and their Implications for the Rotation History of the Oman Ophiolite

NASA Astrophysics Data System (ADS)

Meyer, M.; Morris, A.; Anderson, M.; MacLeod, C. J.

2014-12-01

The Oman ophiolite is an important natural laboratory for understanding the construction of oceanic crust at fast spreading axes and its subsequent tectonic evolution. Previous paleomagnetic research in lavas of the northern ophiolitic blocks (Perrin et al., 2000, Mar. Geophys. Res.) has demonstrated substantial clockwise intraoceanic tectonic rotations. Paleomagnetic data from lower crustal sequences in the southern blocks, however, have been more equivocal due to complications arising from remagnetization, and have been used to infer that clockwise rotations seen in the north are internal to the ophiolite rather than regionally significant (Weiler, 2000, Mar. Geophys. Res.). Here we demonstrate the importance and advantages of sampling crustal transects in the ophiolite in order to understand the nature and variability in magnetization directions. By systematically sampling the lower crustal sequence exposed in Wadi Abyad (Rustaq block) we resolve for the first time in a single section a pattern of remagnetized lowermost gabbros and retention of earlier magnetizations by uppermost gabbros and the overlying dyke-rooting zone. Results are supported by a positive fold test that shows that remagnetization of lower gabbros occurred prior to the Campanian structural disruption of the Moho. NW-directed remagnetized remanences in the lower units are consistent with those used by Weiler (2000, Mar. Geophys. Res.) to infer lack of significant rotation of the southern blocks and to argue, therefore, that rotation of the northern blocks was internal to the ophiolite. In contrast, E/ENE-directed remanences in the uppermost levels of Wadi Abyad imply a large, clockwise rotation of the Rustaq block, of a sense and magnitude consistent with intraoceanic rotations inferred from extrusive sections in the northern blocks. We conclude that without the control provided by systematic crustal sampling, the potential for different remanence directions being acquired at different times

New paleomagnetic data from the Wadi Abyad crustal section and their implications for the rotation history of the Oman ophiolite

NASA Astrophysics Data System (ADS)

Meyer, Matthew; Morris, Antony; Anderson, Mark; MacLeod, Chris

2015-04-01

The Oman ophiolite is an important natural laboratory for understanding the construction of oceanic crust at fast spreading axes and its subsequent tectonic evolution. Previous paleomagnetic research in lavas of the northern ophiolitic blocks (Perrin et al., 2000) has demonstrated substantial clockwise intraoceanic tectonic rotations. Paleomagnetic data from lower crustal sequences in the southern blocks, however, have been more equivocal due to complications arising from remagnetization, and have been used to infer that clockwise rotations seen in the north are internal to the ophiolite rather than regionally significant (Weiler, 2000). Here we demonstrate the importance and advantages of sampling crustal transects in the ophiolite in order to understand the nature and variability in magnetization directions. By systematically sampling the lower crustal sequence exposed in Wadi Abyad (Rustaq block) we resolve for the first time in a single section a pattern of remagnetized lowermost gabbros and retention of earlier magnetizations by uppermost gabbros and the overlying dyke-rooting zone. Results are supported by a positive fold test that shows that remagnetization of lower gabbros occurred prior to the Campanian structural disruption of the Moho. NW-directed remagnetized remanences in the lower units are consistent with those used by Weiler (2000) to infer lack of significant rotation of the southern blocks and to argue, therefore, that rotation of the northern blocks was internal to the ophiolite. In contrast, E/ENE-directed remanences in the uppermost levels of Wadi Abyad imply large, clockwise rotation of the Rustaq block, of a sense and magnitude consistent with intraoceanic rotations inferred from extrusive sections in the northern blocks. We conclude that without the control provided by systematic crustal sampling, the potential for different remanence directions being acquired at different times may lead to erroneous tectonic interpretation.

Automated data collection based on RoboDiff at the ESRF beamline MASSIF-1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nurizzo, Didier, E-mail: Didier.nurizzo@esrf.fr; Guichard, Nicolas; McSweeney, Sean

2016-07-27

The European Synchrotron Radiation Facility has a long standing history in the automation of experiments in Macromolecular Crystallography. MASSIF-1 (Massively Automated Sample Screening and evaluation Integrated Facility), a beamline constructed as part of the ESRF Upgrade Phase I program, has been open to the external user community since July 2014 and offers a unique completely automated data collection service to both academic and industrial structural biologists.

Catalog of Apollo 17 rocks. Volume 1: Stations 2 and 3 (South Massif)

NASA Technical Reports Server (NTRS)

Ryder, Graham

1993-01-01

The Catalog of Apollo 17 Rocks is a set of volumes that characterize each of 334 individually numbered rock samples (79 larger than 100 g) in the Apollo 17 collection, showing what each sample is and what is known about it. Unconsolidated regolith samples are not included. The catalog is intended to be used by both researchers requiring sample allocations and a broad audience interested in Apollo 17 rocks. The volumes are arranged geographically, with separate volumes for the South Massif and Light Mantle, the North Massif, and two volumes for the mare plains. Within each volume, the samples are arranged in numerical order, closely corresponding with the sample collection stations. The present volume, for the South Massif and Light Mantle, describes the 55 individual rock fragments collected at Stations two, two-A, three, and LRV-five. Some were chipped from boulders, others collected as individual rocks, some by raking, and a few by picking from the soil in the processing laboratory. Information on sample collection, petrography, chemistry, stable and radiogenic isotopes, rock surface characteristics, physical properties, and curatorial processing is summarized and referenced as far as it is known up to early 1992. The intention has been to be comprehensive: to include all published studies of any kind that provide information on the sample, as well as some unpublished information. References which are primarily bulk interpretations of existing data or mere lists of samples are not generally included. Foreign language journals were not scrutinized, but little data appears to have been published only in such journals. We have attempted to be consistent in format across all of the volumes, and have used a common reference list that appears in all volumes. Where possible, ages based on Sr and Ar isotopes have been recalculated using the 'new' decay constants recommended by Steiger and Jager; however, in many of the reproduced diagrams the ages correspond with the

Hydration of the Atlantis Massif: Halogen, Noble Gas and In-Situ δ18O Constraints

NASA Astrophysics Data System (ADS)

Williams, M. J.; Kendrick, M. A.; Rubatto, D.

2017-12-01

A combination of halogen (Cl, Br, I), noble gases (He, Ne, Ar, Kr and Xe) and in situ oxygen isotope analysis have been utilized to investigate the fluid-mobile element record of hydration and alteration processes at the Atlantis Massif (30°N on the Mid-Atlantic Ridge). The sample suite investigated includes serpentinite, talc-amphibole ± chlorite schist and hydrated gabbro recovered by seafloor drilling undertaken at sites on a transect across the Atlantis Massif during IODP Expedition 357. Serpentine mesh and veins analysed in-situ by SHRIMP SI exhibit δ18O from 6‰ down to ≈0‰, suggesting serpentinization temperatures of 150 to >280°C and water/rock ratios >5. Differences of 1.5-2.5‰ are observed between adjacent generations of serpentine, but the δ18O range is similar at each investigated drilling site. Halogen and noble gas abundances in serpentinites, talc-amphibole schist and hydrated gabbro have been measured by noble gas mass spectrometry of both irradiated and non-irradiated samples. Serpentinites contain low abundances of halogens and noble gases (e.g. 70-430 ppm Cl, 4.7-12.2 x 10-14 mol/g 36Ar) relative to other seafloor serpentinites. The samples have systematically different Br/Cl and I/Cl ratios related to their mineralogy. Serpentinites retain mantle-like Br/Cl with a wide variation in I/Cl that stretches toward seawater values. Talc-amphibole schists exhibit depletion of Br and I relative to Cl with increasing Cl abundances, suggesting tremolite exerts strong control on halogen abundance ratios. Serpentinites show no evidence of interaction with halogen-rich sedimentary pore fluids. Iodine abundances are variable across serpentinites, and are decoupled from Br and Cl; iodine enrichment (up to 530 ppb) is observed within relatively oxidised and clay-bearing samples. Serpentinized harzburgites exhibit distinct depletion of Kr and Xe relative to atmospheric 36Ar in seawater. Oxygen isotope compositions and low abundances of both halogens

Kinematics of Post-Collisional Extensional Tectonics and Exhumation of the Menderes Massif in the Western Anatolia Extended Terrane, Turkey

NASA Astrophysics Data System (ADS)

Cemen, I.; Catlos, E. J.; Diniz, E.; Gogus, O.; Ozerdem, C.; Baker, C.; Kohn, M. J.; Goncuoglu, C.; Hancer, M.

2006-12-01

The Western Anatolia Extended Terrane in Turkey is one of the best-developed examples of post-collisional extended terranes and contains one of the largest metamorphic core complexes in the world, the Menderes massif. It has experienced a series of continental collisions from the Late Cretaceous to the Eocene as the Neotethys Ocean closed and the Izmir-Ankara-Erzincan suture zone was formed. Based our field work and monazite ages, we suggest that the north-directed postcollisional Cenozoic extension in the region is the product of three consecutive, uninterrupted stages, triggered by three different mechanisms. The first stage was initiated about 30 Ma ago, in the Oligocene by the Orogenic Collapse the thermally weakened continental crust along the north-dipping Southwest Anatolian shear zone. The shear zone was formed as an extensional simple-shear zone with listric geometry at depth and exhibits predominantly normal- slip along its southwestern end. But, it becomes a high-angle oblique-slip shear zone along its northeastern termination. Evidence for the presence of the shear zone includes (1) the dominant top to the north-northeast shear sense indicators throughout the Menderes massif, such as stretching lineations trending N10E to N30E; and (2) a series of Oligocene extensional basins located adjacent to the shear zone that contain only carbonate and ophiolitic rock fragments, but no high grade metamorphic rock fragments. During this stage, erosion and extensional unroofing brought high-grade metamorphic rocks of the central Menderes massif to the surface by the early Miocene. The second stage of the extension was triggered by subduction roll-back and associated back-arc extension in the early Miocene and produced the north-dipping Alasehir and the south-dipping Buyuk Menderes detachments of the central Menderes massif and the north-dipping Simav detachment of the northern Menderes massif. The detachments control the Miocene sedimentation in the Alasehir, Buyuk

Paleoenvironmental analysis and paleobiogeography of the Langhian-Serravallian succession in Wadi Trakee, westcentral Sinai (Egypt): An implication for Mediterranean and Paratethys faunal exchange

NASA Astrophysics Data System (ADS)

Ied, I. M.; Nagwa Ibrahim, A.; Abd-Elaziz, M. A.

2018-01-01

This paper aims to determine the probable paleoenvironments (ecozones) of Miocene sediments at Wadi Trakee, westcentral Sinai, Egypt. To achieve this work, both benthonic and planktonic foraminiferal assemblages were identified. Six paleoecologic zones (ecozones) are distinguished from Wadi Trakee Miocene succession in west-central Sinai; open marine environments were predominated during the deposition of these sediments; occasionally lagoonal. Great oscillation in sea level represented by lagoons and open marine conditions were prevailed in the earliest Langhian that came after the latest Burdigalian sea regression this was followed by great sea transgression phase and open marine environments during the latest Langhian. Serravallian Sea came after sea regression and a short hiatus preserved at the end of Langhian and ended by lagoons environments in the latest Serravallian. Seventy-one species of the identified benthic foraminifera indicate the Langhian, whereas forty-eight species recorded from the Serravallian. Due to the great similarity between the identified fauna with the previously recorded from the Paratethys countries, it can be suggested that high rate of faunal exchanges occurred and sea connections between the Mediterranean and Paratethys were occurred during these ages. Two unconformity surfaces are detected, the first lies within the Langhian while the second lies at the end of the Serravallian. Thirty-two planktonic foraminiferal species are also recorded from the Langhian - Serravallian succession that helped us to subdivide the studied succession into two planktonic zones; these zones correlated with the international schemes for biozones in the subtropical areas and the Mediterranean regions.

Assessment of groundwater potentiality using geophysical techniques in Wadi Allaqi basin, Eastern Desert, Egypt - Case study

NASA Astrophysics Data System (ADS)

Helaly, Ahmad Sobhy

2017-12-01

Electrical resistivity surveying has been carried out for the determination of the thickness and resistivity of layered media in Wadi Allaqi, Eastern Desert, Egypt. That is widely used geophysical tool for the purpose of assessing the groundwater potential and siting the best locations for boreholes in the unconfined Nubian Sandstone aquifers within the study area. This has been done using thirteen 1D Vertical Electrical Sounding (VES) surveys. 1D-VES surveys provide only layered model structures for the subsurface and do not provide comprehensive information for interpreting the structure and extent of subsurface hydro-geological features. The integration of two-dimensional (2D) geophysical techniques for groundwater prospecting has been done to provide a more detailed identification for the subsurface hydro-geological features from which potential sites for successful borehole locations are recognized. In addition, five magnetic profiles were measured for basement depth determination, expected geological structures and thickness of sedimentary succession that could include some basins suitable for groundwater accumulation as groundwater aquifers.

Clockwise rotation of the Santa Marta massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and Cesar-Ranchería basins

NASA Astrophysics Data System (ADS)

Montes, Camilo; Guzman, Georgina; Bayona, German; Cardona, Agustin; Valencia, Victor; Jaramillo, Carlos

2010-10-01

A moderate amount of vertical-axis clockwise rotation of the Santa Marta massif (30°) explains as much as 115 km of extension (stretching of 1.75) along its trailing edge (Plato-San Jorge basin) and up to 56 km of simultaneous shortening with an angular shear of 0.57 along its leading edge (Perijá range). Extensional deformation is recorded in the 260 km-wide, fan-shaped Plato-San Jorge basin by a 2-8 km thick, shallowing-upward and almost entirely fine-grained, upper Eocene and younger sedimentary sequence. The simultaneous initiation of shortening in the Cesar-Ranchería basin is documented by Mesozoic strata placed on to lower Eocene syntectonic strata (Tabaco Formation and equivalents) along the northwest-verging, shallow dipping (9-12° to the southeast) and discrete Cerrejón thrust. First-order subsidence analysis in the Plato-San Jorge basin is consistent with crustal stretching values between 1.5 and 2, also predicted by the rigid-body rotation of the Santa Marta massif. The model predicts about 100 km of right-lateral displacement along the Oca fault and 45 km of left-lateral displacement along the Santa Marta-Bucaramanga fault. Clockwise rotation of a rigid Santa Marta massif, and simultaneous Paleogene opening of the Plato-San Jorge basin and emplacement of the Cerrejón thrust sheet would have resulted in the fragmentation of the Cordillera Central-Santa Marta massif province. New U/Pb ages (241 ± 3 Ma) on granitoid rocks from industry boreholes in the Plato-San Jorge basin confirm the presence of fragments of a now segmented, Late Permian to Early Triassic age, two-mica, granitic province that once spanned the Santa Marta massif to the northernmost Cordillera Central.

Geochronology and geochemistry of Mesozoic intrusive rocks in the Xing'an Massif of NE China: Implications for the evolution and spatial extent of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Tang, Jie; Pei, Fu-Ping; Wang, Feng; Sun, Chen-Yang

2018-04-01

This study presents new zircon U-Pb-Hf and whole-rock geochemical data for intrusive rocks in the Xing'an Massif of NE China, with the aim of furthering our understanding of the evolution and spatial influence of the Mongol-Okhotsk tectonic regime. Zircon U-Pb dating indicates that five stages of Mesozoic magmatism are recorded in the Xing'an Massif, namely during the Middle Triassic ( 237 Ma), the Late Triassic ( 225 Ma), the Early Jurassic ( 178 Ma), the Middle Jurassic ( 168 Ma), and the late Early Cretaceous ( 130 Ma). The Middle Triassic-Early Jurassic intrusive rocks in the Xing'an Massif are dominantly granodiorites, monzogranites, and syenogranites that formed from magma generated by partial melting of newly accreted continental crust. Geochemistry of the Middle Triassic-Early Jurassic granitoid suites of the Xing'an Massif indicates their formation at an active continental margin setting, related to the southwards subduction of the Mongol-Okhotsk oceanic plate. The Middle Jurassic monzogranites in the Xing'an Massif are geochemically similar to adakites and have εHf(t) values (+3.8 to +5.8) and Hf two-stage model ages (TDM2; 979-850 Ma) that are indicative of derivation from magma generated by partial melting of thickened juvenile lower crust. The Middle Jurassic monzogranites formed in a compressional setting related to the closure of the Mongol-Okhotsk Ocean. The late Early Cretaceous intrusive rocks in the Xing'an Massif are dominated by A-type granitoids that are associated with bimodal volcanic rocks, suggesting their formation in an extensional environment related to either (i) delamination of a previously thickened region of the crust, associated with the Mongol-Okhotsk tectonic regime; (ii) the subduction of the Paleo-Pacific Plate; or (iii) the combined influence of these two tectonic regimes.

Compositional variations and tectonic settings of podiform chromitites and associated ultramafic rocks of the Neoproterozoic ophiolite at Wadi Al Hwanet, northwestern Saudi Arabia

NASA Astrophysics Data System (ADS)

Ahmed, Ahmed Hassan; Harbi, Hesham M.; Habtoor, Abdelmonem M.

2012-08-01

Wadi Al Hwanet area in NW of Saudi Arabia is part of the Jebel Ess ophiolite constituting the northeastern part of the ˜700 Ma Yanbu-Sol Hamed-Onib-Allaqi-Heiani suture of the northern Arabian-Nubian Shield. The mantle section of Wadi Al Hwanet ophiolite consists mainly of voluminous harzburgites overlain by thick, massive transition-zone dunites, and small-scale chromitite pods. The harzburgites and massive dunites are exceptionally fresh; primary magmatic textures and silicate minerals are still preserved. Two modes of podiform chromitites exist; small lensoidal pods (group I), and relatively large dike-like pods (group II). Geochemically, the former chromitite type contains chromian spinels with high Cr# (0.79-0.81) and displays a PGE-poor character, with steep negatively-sloped PGE distribution patterns, whereas the latter chromitite type contains chromian spinels with relatively lower Cr# (0.61-0.71) and is PGE-rich (up to 1000 ppb), with positively-sloped PGE distribution patterns. The group II chromitites have much higher sulfide content than the group I suite. Parental melt compositions, in equilibrium with podiform chromitites, vary in Al2O3, FeO*/MgO and TiO2 contents from group I to group II chromitites, although both of them are in the range of the boninitic melts. The differences in the chromitites chemistry are most probably due to variable degrees of partial melting of the involved melts. Two stages of a magmatic activity were inferred for the chromitites genesis. The group I chromitites, of high Cr# of chromian spinels and PGE-poor negatively-sloped patterns, were precipitated in the first stage from a boninitic melt produced by a high degree of partial melting at a supra-subduction zone setting. The second chromitite-forming stage involves a relatively low degree of partial melting under high activities of sulfur and oxygen to produce the group II chromitites with enrichment in sulfides and PGE contents, possibly in a supra-subduction zone setting

Thermochronology and tectonics of the Mérida Andes and the Santander Massif, NW South America

NASA Astrophysics Data System (ADS)

van der Lelij, Roelant; Spikings, Richard; Mora, Andrés

2016-04-01

New apatite U-Pb and multiphase 40Ar/39Ar data constrain the high to medium temperature ( 500 °C- 300 °C) thermal histories of igneous and metamorphic rocks exposed in the Mérida Andes of Venezuela, and new apatite and zircon fission track data constrain the 500 °C- 60 °C thermal histories of pre-Jurassic igneous and metamorphic rocks of the adjacent Santander Massif of Colombia. Computed thermal history envelopes using apatite U-Pb dates and grain size information from an Early Palaeozoic granodiorite in the Mérida Andes suggest that it cooled from > 500 °C to < 350 °C between 266 Ma and 225 Ma. Late Permian to Triassic cooling is also recorded in Early Palaeozoic granitoids and metasedimentary rocks in the Mérida Andes by numerous new muscovite and biotite 40Ar/39Ar plateau dates spanning 257.1 ± 1.0 Ma to 205.1 ± 0.8 Ma. This episode of cooling is not recognised in the Santander Massif, where 40Ar/39Ar data suggest that some Early Palaeozoic rocks cooled below 320 °C in the Early Palaeozoic. However, most data from pre-Jurassic rocks reveal a regional heat pulse at 200 Ma during the intrusion of numerous shallow granitoids, resulting in temperatures in excess of 520 °C, obscuring late Palaeozoic histories. The generally accepted timing of amalgamation of Pangaea along the Ouachita-Marathon suture pre-dates Late Permian to Triassic cooling recorded in basement rocks of the Mérida Andes by > 30 Ma, and its effect on rocks preserved in north-western South America is unknown. We interpret late Permian to Triassic cooling in the Mérida Andes to be driven by exhumation. Previous studies have suggested that a short phase of shortening and anatexis is recorded at 253 Ma in the Maya Block, which may have been adjacent to the basement rocks of the Mérida Andes in the Late Permian. The coeval onset of exhumation in the Mérida Andes may be a result of increased coupling in the magmatic arc, which was located along the western margin of Pangaea. Triassic

New fission-track age constraints on the exhumation of the central Santander Massif: Implications for the tectonic evolution of the Northern Andes, Colombia

NASA Astrophysics Data System (ADS)

Amaya, Sergio; Zuluaga, Carlos Augusto; Bernet, Matthias

2017-06-01

The Late Cretaceous to late Neogene exhumation history of the central Santander Massif in the Northern Andes of Colombia is controlled by the geodynamic interactions between the Caribbean, South American and Nazca plates, as well as the Neogene collision and accretion of the Panama arc. Slab-breakoff of the Caribbean plate, with the tip of the slab tear presently being located beneath Bucaramanga, and the east-west oriented Caldas tear are the main structures relating seismic activity and Late Miocene to Pleistocene magmatic/hydrothermal activity and associated gold mineralization in the central Santander Massif. Here we present new apatite (AFT) and zircon fission-track (ZFT) data from 18 samples collected along two profiles in the California-Vetas block (including the Rio Charta), to the south of the Rio Charta fault, and from Bucaramanga to Picacho on the western flank of the central Santander Massif. The fission-track data are used for time-temperature history modelling and for estimating long-term average exhumation rates. The California-Vetas block in the central Santander Massif to the north of the Rio Charta fault cooled rapidly at a rate of about 24 °C/Myr between 10 and 5 Ma. Fast cooling was not related to post-magmatic cooling or hydrothermal activity, but rather to exhumation, with rates based on apatite fission-track cooling ages on the order of 0.3-0.4 km/Myr. However, long-term average exhumation rates since the Late Cretaceous, based on zircon fission-track data, were only on the order of 0.1-0.2 km/Myr. Our data indicate that next to the Rio Charta fault also the Surata fault contributed to the exhumation of the California-Vetas block. The western flank of the central Santander Massif, shows a more complete thermal history along the Bucaramanga-Picacho profile, with the exposure of an exhumed zircon fission-track partial annealing zone. Thermal history modelling of zircon fission-track data of this profile shows that after burial and heating from

Generalization and formalization of the US EPA procedure for design of treated wastewater aquifer recharge basins: II. Retrofit of Souhil Wadi (Nabeul, Tunisia) pilot plant.

PubMed

Kallali, Hamadi; Yoshida, Mitsuo; Tarhouni, Jamila; Jedidi, Naceur

2013-01-01

The 'Cap Bon' peninsula in Tunisia suffers from intensive tourist activities, high demographic increase and industrial development. As groundwater had been for a long time the main water source, aquifers had been subject to a severe depletion and seawater intrusion. Despite the measures taken prohibiting new drillings and water carrying by the construction of a waterway linking the region to the north-west region of Tunisia, the problem of water shortage persists. Artificial recharge of groundwater with treated wastewater has been decided as a technique to replenish the region aquifers. A pilot plant was constructed in the early 1980s in Souhil Wadi (Nabeul) area. Many experiments have been carried out on this plant and have led to controversial opinions about its performance and its impact on groundwater contamination. This contribution concerns the application of the procedure that we developed from the generalization and the formalization of the United States Environmental Protection Agency (US EPA) methodology for the design of treated wastewater aquifer recharge basins. This upgrading procedure implemented in a spreadsheet, has been used to retrofit the Souhil Wadi facility in order to improve its performance. This method highlighted the importance of the safety factor to estimate wastewater infiltration rate from clean water permeability measurements. It has, also, demonstrated the discordance between the initial design parameters of Souhil Wadi facility and their current status as they have changed with time and the infiltration capacity of the basins has been affected by clogging. Indeed, it has been demonstrated that with the current state of clogging of the basins, the design infiltration rate limited by the most restrictive layer (6.1 cm/hr) corresponds to 22% of the surface infiltration rate reached after a drying period of 10 d, which means that we need more basins to absorb the daily loading rate. The design method leads to the construct ion of five

Reforming Higher Education in Hong Kong towards Post-Massification: The First Decade and Challenges Ahead

ERIC Educational Resources Information Center

Wan, Calvin

2011-01-01

The process of reforming Hong Kong's higher education sector commenced in 2001, and the system moved into the post-massification era. Within five years, the post-secondary participation rate for the 17-20 age cohort had increased to 66 per cent. This target was achieved much earlier than the Government had planned. More educational opportunities…

Structural investigations in the Massif-Central, France

NASA Technical Reports Server (NTRS)

Scanvic, J. Y.

1974-01-01

This survey covered the French Massif-Central (where crystalline and volcanic rocks outcrop) and its surrounding sedimentaries, Bassin de Paris, Bassin d'Aquitaine and Rhodanian valley. One objective was the mapping of fracturing and the surveying of its relationship with known ore deposits. During this survey it was found that ERTS imagery outlines lithology in some sedimentary basins. On the other hand, in a basement area, under temperature climate conditions, lithology is rarely expressed. These observations can be related to the fact that band 5 gives excellent results above sedimentary basins in France and generally band 7 is the most useful in a basement area. Several examples show clearly the value of ERTS imagery for mapping linear features and circular structures. All the main fractures are identified with the exception of new ones found both in sedimentaries and basement areas. Other interesting findings concern sun elevation which, stereoscopic effect not being possible, simulates relief in a better way under certain conditions.

The Atlantis Bank Gabbro Massif, SW Indian Ridge: the Largest Know Exposure of the Lower Crust in the Oceans

NASA Astrophysics Data System (ADS)

Dick, H. J.; Kvassnes, A. J.; Kinoshita, H.; MacLeod, C. J.; Robinson, P. T.

2017-12-01

Until the discovery of oceanic core complexes little was known and much inferred about the lower ocean crust at slow-spreading ridges. Their study shows the ocean crust isn't simply a uniform layer-cake of pillow lavas, sheeted dikes and gabbros, but is highly variable in thickness, composition and architecture, and even absent over large regions. The 660 km2 Atlantis Bank Gabbro Massif in the rift-mountains of the SW Indian Ridge flanking the Atlantis II Transform is the magmatic end member for ocean core complexes, and best approximates `average' slow-spread crust. Thus it has been a focus for drilling since its discovery in 1986, leading to the current attempt to drill to Moho there (Project SloMo). There are 3 ODP and IODP drill holes on its crest: 1508-m deep Hole 735B, 158-m deep Hole 1105A, and 809.4-m deep Hole U1473. These provide a 200 Kyr view of lower crustal accretion at a slow-spread ocean ridge. Here we extend this view to 2.7 Myr. Mapping and sampling shows the gabbro massif extends nearly the length of a single 2nd order magmatic ridge segment. With numerous inliers of the dike-gabbro transition at numerous locations, and a crust-mantle boundary, traced for 30-km along the transform wall, it would appear to represent a full section of the lower crust. As Moho is at 5.5 ± 1 km mbsf near Hole 735B, and 4.5 km beneath the transform, it is likely a serpentinization front. The crust-mantle boundary was crossed by dives at 4 locations. In each case gabbros at the base of the crust crystallized from melt that had previously fractionated 50% or more from a likely parent. Thus the gabbro massif must be laterally zoned, and the parental mantle melts had to have been emplaced at the center of the paleo-ridge segment, before intruding laterally to the distal end of the complex. Gabbros on a lithospheric flow line down the center of the massif closely resemble those from the drill holes. This shows that while lateral variations in crustal composition and

Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

NASA Astrophysics Data System (ADS)

Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

2016-09-01

Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

Assessment of groundwater potential of the crystalline basement of Wadi-Fira (Eastern Chad) using a multi-criteria correlation analysis and Remote Sensing data

NASA Astrophysics Data System (ADS)

Brahim Mahamat, Hamza; Coz Mathieu, Le; Abderamane, Hamit; Razack, Moumtaz

2017-04-01

Access to water in the Wadi-Fira aquifer system is a crucial problem in Eastern Chad because of (i) the complexity of the hydrogeological context (fractured basement), (ii) large extent of the study area (50,000 km2); And (iii) hard-to-access field data (only 34 water points were available to determine physicochemical and hydrodynamic parameters) often associated with high uncertainty. This groundwater resource is paramount in this arid environment, to meet the water needs of an increasingly growing population (refugees from Darfur) with a predominant pastoral activity. In order to optimally exploit the available data, correlative analyzes are carried out by integrating the spatial dimension of the data with GIS tools. A three-step strategy is thus implemented, based on: (i) point field data with physicochemical and hydrodynamic parameters; (ii) maps interpolated from point data, to increase the number of ''comparable'' parameters for each site; and (iii) interpolated maps coupled to maps from Remote Sensing results describing the area's structural geomorphology (slopes, hydrographic network, faults). The first results show marked correlations between physico-chemical and hydrodynamical parameters. According to the correlation matrix, the static level correlates significantly with the dominant cations (Ca2+ ; R = 0.52) and anions (HCO3- ; R = 0.53). Correlations are lower between electrical conductivity and transmissivity, and electrical conductivity and measured static level. A negative correlation is observed between Fluorine and transmissivity (r = -0.65), and the altered horizon (r = -0.5). The most significant discharges are obtained in fissured horizons. The correlative analysis allowsto differentiate mapped sectors according to the productivity and chemical quality regarding groundwater resource. Keywords: Hydrodynamics, Hydrochemistry, Remote Sensing, SRTM, Basement aquifer, Alteration, Lineaments, Wadi-Fira, Tchad.

Rockfall hazard assessment by means of the magnitude-frequency curves in the Montserrat Massif (central Catalonia, Spain): first insights

NASA Astrophysics Data System (ADS)

Janeras, Marc; Domènech, Guillem; Pons, Judit; Prat, Elisabet; Buxó, Pere

2016-04-01

Montserrat Massif is located about 50 km North-West of Barcelona (Catalonia, North-Eastern Spain). The rock massif is constituted by an intercalation of conglomerate and fine layers of siltstones due to the Montserrat fan-delta sedimentation within the Eocene age. The current relief is consequence of the several depositional episodes and the later tectonic uplift, leading to stepped slopes up to 250 m high, and a total height difference close to 1000 m. Montserrat Mountain has been a pilgrimage place since the settlement of the monastery, around the year 1025, and a spot of touristic interest, mostly within the last 150 years, when the first rack railway was inaugurated to reach the sanctuary. The amount of 2.4 M visitors in 2014 reveals the potential risk derived from rockfalls. To assess and mitigate this risk, a plan funded by the Catalan government is currently under development. Three rockfall mechanisms and magnitude ranges have been identified (Janeras et al. 2011): 1) physicochemical weathering causing the detachment of pebbles and aggregates (0.0001 - 0.1 m3); 2) thermic-induced tensions responsible for the generation of slabs and plates (0.1 - 10 m3); and 3) intersection of structural joints within the rock mass resulting in blocks of 10 - 10,000 m3. In order to quantify the rockfall hazard, a magnitude-frequency analysis has been performed starting from an event-based inventory gathered from field surveillance and historical research. A methodology has been applied to take the maximum profit of only 30 registers with information on volume and date. The massif has been split into several domains with sampling homogeneity. For each one, there have been defined several periods of time during which, all the rockfall events of a given volume have been recorded. Thus, the magnitude-frequency relationship, for each domain, has been calculated. Results show that the curves are well fitted by a power law with exponents ranging from -0.59 to -0.68 for magnitudes

Crystal structure of hydrogen-bearing vuonnemite from the Lovozero alkaline massif

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru; Aksenov, S. M.; Verin, I. A.

2011-05-15

Hydrogen-bearing vuonnemite from the Shkatulka hyperagpaitic pegmatite (the Lovozero alkaline massif, Kola Peninsula) was studied by single-crystal X-ray diffraction. The triclinic unit-cell parameters are as follows: a = 5.4712(1) Angstrom-Sign , b = 7.1626(1) Angstrom-Sign , c = 14.3702(3) Angstrom-Sign , {alpha} = 92.623(2) Degree-Sign , {beta} = 95.135(1) Degree-Sign , {gamma} = 90.440(1) Degree-Sign , sp. gr. P1, R = 3.4%. The Na{sup +} cations and H{sub 2}O molecules are ordered in sites between the packets. The water molecules are hydrogen bonded to the PO{sub 4} tetrahedra.

Palaeomagnetic constraints on the evolution of the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N)

NASA Astrophysics Data System (ADS)

Morris, A.; Pressling, N.; Gee, J. S.

2012-04-01

Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. They represent a fundamental component of the seafloor spreading system at slow and ultraslow axes. One of the most extensively studied oceanic core complexes is Atlantis Massif, located at 30°N at the intersection of the Atlantis Transform Fault and the Mid Atlantic Ridge (MAR). The central dome of the massif exposes the corrugated detachment fault surface and was drilled during IODP Expedition 304/305 (Hole U1309D). This sampled a 1.4 km faulted and complexly layered footwall section dominated by gabbroic lithologies with minor ultramafic rocks. Palaeomagnetic analyses demonstrate that the gabbroic sequences at Atlantis Massif carry highly stable remanent magnetizations that provide valuable information on the evolution of the section. Thermal demagnetization experiments recover high unblocking temperature components of reversed polarity (R1) throughout the gabbroic sequences. Correlation of structures observed on oriented borehole (FMS) images and those recorded on unoriented core pieces allows reorientation of R1 remanences. The mean remanence direction in true geographic coordinates constrains the tectonic rotation experienced by the Atlantis Massif footwall, indicating a 46°±6° counterclockwise around a MAR-parallel horizontal axis trending 011°±6°. The detachment fault therefore initiated at a steep dip of >50° and then rotated flexurally to its present day low angle geometry (consistent with a 'rolling-hinge' model for detachment evolution). In a number of intervals, the gabbros exhibit a complex remanence structure with the presence of additional intermediate temperature normal (N1) and lower temperature reversed (R2) polarity components, suggesting an extended period of remanence acquisition during different polarity intervals. Sharp break-points between different polarity components suggest

Palaeomagnetic constraints on the evolution of the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N)

NASA Astrophysics Data System (ADS)

Morris, A.; Pressling, N.; Gee, J. S.

2011-12-01

Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. They represent a fundamental component of the seafloor spreading system at slow and ultraslow axes. One of the most extensively studied oceanic core complexes is Atlantis Massif, located at 30°N at the intersection of the Atlantis Transform Fault and the Mid Atlantic Ridge (MAR). The central dome of the massif exposes the corrugated detachment fault surface and was drilled during IODP Expedition 304/305 (Hole U1309D). This sampled a 1.4 km faulted and complexly layered footwall section dominated by gabbroic lithologies with minor ultramafic rocks. Palaeomagnetic analyses demonstrate that the gabbroic sequences at Atlantis Massif carry highly stable remanent magnetizations that provide valuable information on the evolution of the section. Thermal demagnetization experiments recover high unblocking temperature components of reversed polarity (R1) throughout the gabbroic sequences. Correlation of structures observed on oriented borehole (FMS) images and those recorded on unoriented core pieces allows reorientation of R1 remanences. The mean remanence direction in true geographic coordinates constrains the tectonic rotation experienced by the Atlantis Massif footwall, indicating a 46°±6° counterclockwise around a MAR-parallel horizontal axis trending 011°±6°. The detachment fault therefore initiated at a steep dip of >50° and then rotated flexurally to its present day low angle geometry (consistent with a 'rolling-hinge' model for detachment evolution). In a number of intervals, the gabbros exhibit a complex remanence structure with the presence of additional intermediate temperature normal (N1) and lower temperature reversed (R2) polarity components, suggesting an extended period of remanence acquisition during different polarity intervals. Sharp break-points between different polarity components suggest

Geological and geochemical reconnaissance in the central Santander Massif, Departments of Santander and Norte de Santander, Colombia

USGS Publications Warehouse

Evans, James George

1976-01-01

The central Santander Massif is composed of Precambrian Bucaramanga Gneiss and pre-Devonian Silgara Formation intruded by Mesozoic quartz diorite, quartz monzonite, and alaskite and Cretaceous or younger porphyry. Triassic (Bocas Formation), Jurassic (Jordan and Giron Formations).and Cretaceous (Tambor, Rosa Blanca, Paja, Tablazo, Simiti, La Luna, and Umir Formations) sedimentary rocks overlie the metamorphic rocks and are younger than most of the intrusions. A geological and geochemical reconnaissance of part of the central Santander Massif included the Vetas and California gold districts. At Vetas the gold is generally in brecciated aphanitic quartz and phyllonite. Dark-gray material in the ore may be graphite. The ore veins follow steep west-northwest- and north-northeast-striking fracture zones. No new gold deposits were found. Additional geochemical studies should concentrate on western Loma Pozo del Rey and on improvement of the gold extraction process. At California the gold is in pyritiferous quartz veins and quartz breccia. Ore containing black sooty material (graphite?) is highly radioactive. Some of the mineralization is post-Lower Cretaceous. Soil samples indicate that gold deposits lie under the thick blanket of soil on the ridges above the zone of mining. Three principal gold targets are outlined by gold and associated minerals in pan concentrates. The close relation of gold and copper anomalies suggests that copper may be useful as a pathfinder for gold elsewhere in the region. Based on occurrences of gold or high concentrations of pyrite or chalcopyrite in pan concentrates and on analytical data, eight potential gold targets are outlined in the central massif. Reconnaissance of the surrounding region is warranted.

Evidence for early irrigation at Bat (Wadi Sharsah, northwestern Oman) before the advent of farming villages

NASA Astrophysics Data System (ADS)

Desruelles, Stéphane; Fouache, Eric; Eddargach, Wassel; Cammas, Cecilia; Wattez, Julia; Beuzen-Waller, Tara; Martin, Chloé; Tengberg, Margareta; Cable, Charlotte; Thornton, Christopher; Murray, Andrew

2016-10-01

Decades of archaeological research in southeastern Arabia (Oman and the UAE) have provided a good understanding of the evolution of human societies in this arid region, with the transition from mobile pastoralism to settled agricultural villages occurring at the start of the Hafit period (ca. 3100-2700 BCE). The delayed adoption of farming, ceramics, mudbrick architecture, metallurgy, and other technologies until the start of the 3rd millennium BCE has been a particularly salient feature of this region relative to its neighbours in Mesopotamia, southern Iran, and northwestern South Asia. However, recent geoarchaeological research at the World Heritage Site of Bat, situated within the Wadi Sharsah valley in northwest Oman, has provided evidence of irrigation practices that have been dated to the early-mid 4th millennium BCE. While direct evidence of farming from this early period remains elusive, the presence of irrigated fields at this time raises new questions about the supposedly mobile pastoralist groups of the Arabian Neolithic and the beginning of farming practices in the region.

Palaeomagnetism in the Sines massif (SW Iberia) revisited: evidences for Late Cretaceous hydrothermal alteration and associated partial remagnetization

NASA Astrophysics Data System (ADS)

Ribeiro, P.; Silva, P. F.; Moita, P.; Kratinová, Z.; Marques, F. O.; Henry, B.

2013-10-01

This study revisits the palaeomagnetism of the Sines massif (˜76 Ma) in the southwestern Iberian Margin (Portugal). The palaeomagnetic analysis was complemented by a comprehensive study of the magnetic mineralogy by means of rock magnetic measurements and petrographic observations. The overall dispersion of palaeomagnetic directions (declination ranging between ˜N0° and ˜N50°) and their migration observed during stepwise demagnetizations have revealed the superposition of remanence components. We interpret this complex palaeomagnetic behaviour as related to the regional hydrothermalism associated with the last stages of Late Cretaceous magmatic activity. This environment favoured mineralogical alteration and a partial chemical remagnetization, giving in most samples a composite magnetization, which has been erroneously interpreted as the primary one in a previous study, then leading to a questionable model for Cretaceous Iberia rotation. Nonetheless, for some samples a single component has been isolated. Interesting rock magnetic properties and microscopic observations point to a well-preserved magnetic mineralogy for these samples, with magnetite clearly of primary origin. The associated ChRM mean direction (D/I = 3.9°/46.5°, α95 = 1.7°, N = 31 samples) then represents the true primary magnetization of the Sines massif. This new palaeomagnetic direction and the corresponding palaeomagnetic pole (long = 332.0°, lat = -79.5°, A95 = 1.7°) agrees with those from the other palaeomagnetic works for the same period and region (e.g. the Sintra and Monchique massifs), yielding a lack of significant rotation of Iberia relative to stable Europe since the uppermost Late Cretaceous (Campanian-Maastrichtian).

Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: An integrated geodynamic and petrological modelling approach

NASA Astrophysics Data System (ADS)

Palin, Richard M.; Reuber, Georg S.; White, Richard W.; Kaus, Boris J. P.; Weller, Owen M.

2017-06-01

The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India-Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure-temperature-time (P-T-t) path has been derived from thermomechanical simulations tailored for Eocene subduction in the northwestern Himalaya. Phase equilibrium modelling performed along this P-T path has described the petrological evolution of felsic and mafic components of the massif crust, and shows that differences in their fluid contents would have controlled the degree of metamorphic phase transformation in each during subduction. Our model predicts that peak P-T conditions of ∼2.6-2.8 GPa and ∼600-620 ∘C, representative of 90-100 km depth (assuming lithostatic pressure), could have been reached just ∼3 Myr after the onset of subduction of continental crust. This P-T path and subduction duration correlate well with constraints reported for similar UHP eclogite in the Kaghan Valley, Pakistan Himalaya, suggesting that the northwest Himalaya contains dismembered remnants of what may have been a ∼400-km-long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. A maximum overpressure of ∼0.5 GPa was calculated in our simulations for a homogeneous crust, although small-scale mechanical heterogeneities may produce overpressures that are larger in magnitude. Nonetheless, the extremely high pressures for peak metamorphism reported by some workers (up to 4.8 GPa) are unreliable owing to conventional thermobarometry

Successive post-Variscan stress fields in the French Massif Central and its borders (Western European plate): comparison with geodynamic data

NASA Astrophysics Data System (ADS)

Blés, J. L.; Bonijoly, D.; Castaing, C.; Gros, Y.

1989-11-01

Structural analysis and particularly microtectonic methods have made it possible to define the different stages of brittle deformation of the Massif Central basement and the surrounding sedimentary cover from the end of the Hercynian orogeny to the end of the Tertiary. During the Stephanian a compressional tectonic regime prevailed: regional faults appeared or were react vated reactivation as a result of initial N-S compression, becoming NW then E-W. These regional strike-slip faults caused local extension which led to the formation of small coal-bearing basins. This compressional regime, which marked the end of the formation of Pangea. was followed by a series of extension episodes: Permian-Triassic extension oscillating around N-S. E-W to NW-SE extension in the Early and Middle Jurassic and finally N-S to NE-SW extension in the Late Jurassic to Cretaceous. The normal faults formed during these episodes strongly influenced the distribution of emerging continents and sedimentary basins. From the Campanian (75 Ma) to the Present, the convergence of Africa and Eurasia involved the distribut on of stresses in the West European plate. Several tectonic episodes are distinguished in the Massif Central. During the Eocene approximately N-S compression predominated. General E-W extension in the Late Eocene-Oligocene resulted in grabens with general northerly strike, mainly in the centre of the Massif Central and on its east and southeast borders. Lastly, compression, varying from NW-SE to E-W, in the north and south of the Massif Central, prevailed during the Alpine orogenic phase at the end of the Miocene. These successive stages of brittle deformation are interpreted in the context of the evolution of the West European plate and its displacement in relation to the African plate. The correspondences between the major geodynamic periods and the distribution of stresses over the West European continent are noted as well as the problems which remair to be resolved.

Two-phase southward subduction of the Mongol-Okhotsk oceanic plate constrained by Permian-Jurassic granitoids in the Erguna and Xing'an massifs (NE China)

NASA Astrophysics Data System (ADS)

Liu, Huichuan; Li, Yinglei; He, Hongyun; Huangfu, Pengpeng; Liu, Yongzheng

2018-04-01

Geodynamics of the Mongol-Okhotsk oceanic plate southward subduction are still pending problems. This paper presents new zircon LA-ICP-MS U-Pb age and whole-rock geochemical data for the middle Permian to Middle Jurassic granitoids in the western Erguna and central Xing'an massifs. 267-264 Ma, 241 Ma and 173 Ma I-type granites, and 216 Ma A-type granites were identified in the Erguna and Xing'an massifs (NE China). The I-type granites were produced by partial melting of the lower mafic crust. The 216 Ma A-type granites were derived from partial melting of crustal materials with tonalitic to granodioritic compositions. The 267-264 Ma and 241 Ma I-type granites were generated in an Andean-type arc setting, wheras the 216 Ma A-type and 173 Ma granites were formed in supra subduction extensional setting. We summarized previous age data of the middle Permian to Middle Jurassic magmtaic rocks in the Erguna and Xing'an Massifs and identified two isolated phases of magmatic activity including the ca. 267-225 Ma and ca. 215-165 Ma periods, with a significant magmatic gap at ca. 225-215 Ma. These middle Permian to Middle Jurassic magmatic rocks are closely related to the southward subduction of the Mongol-Okhotsk ocean. A two-stage tectonic evolutionary model was proposed to account for these geological observations in the Erguna and Xing'an massifs, involving Permian to Middle Triassic continuous southward subduction of the Mongol-Okhotsk oceanic plate and Late Triassic to Jurassic slab-rollback and supra subduction extension.

Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians

NASA Astrophysics Data System (ADS)

Bąk, Krzysztof; Bąk, Marta

2013-06-01

Bąk, K. and Bąk M. 2013. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians. Acta Geologica Polonica, 63 (2), 223-237. Warszawa. The foraminiferal and radiolarian biostratigraphy of selected sections of the Zabijak Formation, the youngest sediments of the Tatra massif (Central Western Carpathians), have been studied. Benthic foraminifers, mainly agglutinated species, occur abundantly and continuously throughout the studied succession, while planktic foraminifers are generally sparse. Five planktic and two benthic foraminiferal zones have been recognized. The marly part of the Zabijak Formation comprises the Pseudothalmanninella ticinensis (Upper Albian) through the Rotalipora cushmani (Upper Cenomanian) planktic foraminiferal zones, and the Haplophragmoides nonioninoides and Bulbobaculites problematicus benthic foraminiferal zones. The radiolarians were recognized exclusively in the Lower Cenomanian part of the formation.

A MASSIF Effort To Determine The Mass-Luminosity Relation for Stars of Various Ages, Metallicities, and Evolution States

NASA Technical Reports Server (NTRS)

Henry, Todd J.; Beedict, G. Fritz; Gies, Douglas R.; Golimowski, David A.; Ianna, Philip A.; Mason, Brian; McArthur, Barbara; Nelan, Edmund; Torres, Guillermo

2004-01-01

The MASSIF (Masses and Stellar Systems with Interferometry) Team will use SIM to investigate the mass content of the Galaxy - from huge stars to barely glimmering brown dwarfs, and from hot white dwarfs to exotic black holes. We will target various samples of the Galactic population to determine and relate the fundamental characteristics of mass, luminosity, age, composition, and multiplicity - attributes that together yield an extensive understanding of the stars. Our samples will include distant clusters that span a factor of 5000 in age, and commonplace stars and substellar objects that lurk near the Sun. The principal goals of the MASSIF Key Project are to (1) define the mass-luminosity relation for main sequence stars in five fundamental clusters so that effects of age and metallicity can be mapped (Trapezium, TW Hydrae, Pleiades, Hyades, and M67), and (2) determine accurate masses for representative examples of nearly every type of star, stellar descendant or brown dwarf in the Galaxy.

The Oldest Granites of Russia: Paleoarchean (3343 Ma) Subalkali Granites of the Okhotsk Massif

NASA Astrophysics Data System (ADS)

Kuzmin, V. K.; Bogomolov, E. S.; Glebovitskii, V. A.; Rodionov, N. V.

2018-02-01

The Paleoarchean age (3.34 Ga) of subalkali granite magmatism first established for the Kukhtui uplift of the Okhotsk Massif suggests a formation time of the mature continental K-rich crust in this region as early as the Paleoarchean. According to the geological structural, mineralogical-geochemical, geochronological, and isotopic-geochemical data, the Kukhtui uplift can be considered as the most ancient Paleoarchean province in Russia: the ancient consolidation core of the sialic protocrust of the Okhotsk-Omolon Craton.

Has Massification of Higher Education Led to More Equity? Clues to a Reflection on Portuguese Education Arena

ERIC Educational Resources Information Center

Dias, Diana

2015-01-01

Massification is an undeniable phenomenon in the higher education arena. However, there have been questions raised regarding the extent to which a mass system really corresponds to an effective democratisation not only of access, but also of success. With regards to access, this article intends, through a brief analysis of the expansion of higher…

Multi-decadal evolution of ice/snow covers in the Mont-Blanc massif (France)

NASA Astrophysics Data System (ADS)

Guillet, Grégoire; Ravanel, Ludovic

2017-04-01

Dynamics and evolution of the major glaciers of the Mont-Blanc massif have been vastly studied since the XXth century. Ice/snow covers on steep rock faces as part of the cryosphere however remain poorly studied with only qualitative descriptions existing. The study of ice/snow covers is primordial to further understand permafrost degradation throughout the Mont-Blanc massif and to improve safety and prevention for mountain sports practitioners. This study focuses on quantifying the evolution of ice/snow covers surface during the past century using a specially developed monoplotting tool using Bayesian statistics and Markov Chain Monte Carlo algorithms. Combining digital elevation models and photographs covering a time-span of 110 years, we calculated the ice/snow cover surface for 3 study sites — North faces of the Tour Ronde (3792 m a.s.l.) and the Grandes Jorasses (4208 m a.s.l.) and Triangle du Tacul (3970 m a.s.l.) — and deduced the evolution of their area throughout the XXth century. First results are showing several increase/decrease periods. The first decrease in ice/snow cover surface occurs between the 1940's and the 1950's. It is followed by an increase up to the 1980's. Since then, ice/snow covers show a general decrease in surface which is faster since the 2010's. Furthermore, the gain/loss during the increase/decrease periods varies with the considered ice/snow cover, making it an interesting cryospheric entity of its own.

A new species of Pristimantis (Anura, Craugastoridae) from the Cajas Massif, southern Ecuador.

PubMed

Sánchez-Nivicela, Juan C; Celi-Piedra, Elvis; Posse-Sarmiento, Valentina; Urgiles, Verónica L; Yánez-Muñoz, Mario; Cisneros-Heredia, Diego F

2018-01-01

A new species of Pristimantis is described from the highland paramos on the eastern slopes of the Cajas Massif, southern Andes of Ecuador, at 3400 m. This new species is characterized by having a distinctive reddish color, cutaneous macroglands in suprascapular region and surfaces of arm and legs, and by lacking dentigerous processes of vomers. The cutaneous macroglands are similar to those exhibited by several species of the Pristimantis orcesi group, and may suggest a close phylogenetic relationship. The new species could be a latitudinal substitution of Pristimantis orcesi in the southern Andes of Ecuador.

Reconnaissance geology of the Wadi Wassat quadrangle, Kingdom of Saudi Arabia

USGS Publications Warehouse

Overstreet, William C.; Rossman, D.L.

1970-01-01

The Wadi Wassat quadrangle covers an area of 2926 sq km in the southwestern part of the Kingdom of Saudi Arabia. The west half of the quadrangle is underlain by crystalline rocks of the Arabian Shield, but in the eastern half of the quadrangle the Precambrian rocks are covered by Permian or older sandstone which is succeeded farther east by aeolian sands of Ar Rub' al Khali. The Shield consists of a sequence of unmetamorphosed to metamorphosed interlayered volcanic and sedimentary rocks intruded by igneous rocks ranging in composition from gabbro to syenite and in age from Precambrian to Cambrian(?). The volcanic rocks range in composition from andesite to rhyolite and in texture from agglomerate to thick, massive flows and lithic tuff. They are interlayered with conglomerate, fine-grained graywacke sandstone, calcareous graywacke, siltstone, tuffaceous laminated shale, pyritiferous sediment, carbonaceous shale, limestone, and dolomite. Most clastic debris is derived from andesite. In places the rocks are polymetamorphosed; elsewhere they are unmetamorphosed. The rocks on which this volcano-sedimentary eugeosynclinal sequence was deposited are not exposed in the area of the quadrangle. Reglonal dynamothermal metamorphism was .the dominant process affecting the volcanic-sedimentary rocks in the western part of the quadrangle. In the eastern part of the Precambrian area the chief metamorphic effect results from contact action along the walls of intrusive plutons. The oldest igneous rock to intrude the volcanic-sedimentary sequence, after the dikes and sills of the sequence itself, is granite gneiss and gneissic granodiorite. The gneiss is sparsely present in the quadrangle, but northwest of the quadrangle it forms an immense batholith which is one of the major geologic features of southwestern Arabia. However, the most common intrusive rocks of the quadrangle are a magnetic differentiation sequence that ranges in composition from gabbro and diorite to granite

Characterization of alluvial dust sources and their temporal development - a multi-sensor approach for the Aïr Massif, Niger

NASA Astrophysics Data System (ADS)

Feuerstein, Stefanie; Schepanski, Kerstin

2017-04-01

One of the world's largest sources of atmospheric dust is the Sahara. It is said that 55% of the total global dust emission can be linked to the desert in northern Africa. Thus, understanding the Saharan dust sources is of great importance to estimate the total global dust load and its variability. Especially one type of dust sources has gained attention in dust research in recent years: The emission of dust from sediments formed by hydrologic processes, so called alluvial dust sources. These sediments were either formed in the past under the influences of a more humid paleoclimate or are deposited recently, e.g. during strong precipitation events when surficial runoff leads to the activation of wadi systems or to the occurrence of flash floods. Especially the latter phenomenon is able to deliver a huge amount of potentially erodible sediments. The research presented here focuses on the characterization of these alluvial dust sources with special attention on their temporal variability in relation to wet and dry phases. A study area covering the Aïr Massif in Niger is analysed over a four years time span from January 2013 to December 2016. The whole cycle from sediment formation to dust emission is illustrated by using data of various satellite sensors that are able to capture the processes taking place at the land surface as well as in the atmosphere: (1) The rainfall distribution for the study area is shown by time series of the TRMM precipitation estimates. A catchment analysis of the area helps to estimate the amount of surficial runoff and to detect areas of potential sediment accumulation. (2) Changes in the sediment structure of the land surface are analysed using atmospherically corrected time series of NASA's Landsat-8 OLI satellite. A land cover classification shows the distribution of alluvial sediments over the area; fresh layers of alluvial deposits are detected. Furthermore, the evolution of the vegetation cover, which inhibits dust emission, is

Time-domain electromagnetic tests in the Wadi Bidah District, Kingdom of Saudi Arabia

USGS Publications Warehouse

Flanigan, Vincent J.; Sadek, Hamdy; Smith, Bruce; Tippens, C.L.

1983-01-01

A time-domain electromagnetic (TDEM) method was tested in two areas of mineralization in Precambrian rocks in the Wadi Bidah district, Kingdom of Saudi Arabia. Transient-decay voltages in profile mode were measured across the Sha'ab at Tare and Rabathan prospects by use of three transmitterreceiver loop configurations. At the Sha'ab at Tare prospect all of the loop configurations indicated the mineralized zone. Analysis of the coincident loop data at Sha'ab at Tare reveals that gossanous and altered rock of i0 ohm-m resistivity extends to a depth of 35 m, where there is an unweathered, dry mineralized zone of about 1 ohm-m resistivity. The model further suggests that the rocks at a depth of 55 m and below the water table are even less resistive (0. 1 ohm-m). The TDEM method successfully discriminated conductors within from those below the weathered zone at the Rabathan prospect. Conductors below the weathered zone are identified by a lack of transient response in the early part of the transient decay curve, followed by an increasing response in the middle to late parts of the transient decay curve. Results of these limited tests suggest the potential value of integrating TDEM with other geophysical tools in the Kingdom. Recommendations are made to expand these tests into a more comprehensive program that will evaluate the TDEM potential in various geologic environments that are host to mineral deposits of diverse origin.

Geotectonic setting of the Suwałki Anorthosite Massif (NE-Poland) - constraints for 3D geological modelling

NASA Astrophysics Data System (ADS)

Wiszniewska, Janina; Petecki, Zdzislaw; Rosowiecka, Olga; Krzemińska, Ewa

2017-04-01

Suwałki Anorthosite Massif (SAM) is located within 200 km long Mesoproterozoic magmatic terrane called Mazury Complex (NE Poland) (Wiszniewska et al. 2002). This is a belt of granitoids and associated mafic and intermediate igneous rocks followed an E-W trending lineament extending from the Baltic Sea through northern Poland and southern Lithuania to western Belarus. Crystalline basement of the Suwałki region is covered by a thick pile (550-1300m) of Phanerozoic sedimentary rocks, which are dipping towards the SW East European Craton`s border. SAM is a complex structure composed primarily of magmatic massif type anorthosites, surrounded by a rim of norite-gabbronorite and diorite rocks. SAM is characterized by magnetic and gravimetric negative anomalies. The gravimetric one is related to anorthosite massif. It is surrounded by a few positive anomalies, which reflect occurrences of denser rocks such as granite, monzodiorite and granodiorite. The large magnetic anomaly is supposed to reflect an effect of an negative inclination of remanent magnetization of anorthosite rocks. This hypothesis was confirmed by magnetic modelling along DSS POLONAISE'97 profile P4 (Petecki, 2006). Existing measurements however do not show prevailing negative inclinations, even though they prove very high remanent magnetization of anorthosites. A pronounced residual magnetic anomalies of Udryń and Krzemianka are related to Fe-Ti-(V) ore deposits recognized by deep boreholes. Based on potential field data it was suggested that anorthosite bottom reaches 2,5-4,5 km depth. Thus it is evident that the geological architecture of SAM and its surrounding area is not fully recognized. The problem is supposed to be resolved using modern methods of geophysical transformations and 3D modelling using GeoModeller software. The final result of the research will be to recognize spatial structure of the SAM and its surrounding. Petrological, mineralogical, geochronological (U-Pb SHRIMP method on

Episodic exhumation and relief growth in the Mont Blanc massif, Western Alps from numerical modelling of thermochronology data

NASA Astrophysics Data System (ADS)

Glotzbach, C.; van der Beek, P. A.; Spiegel, C.

2011-04-01

The Pliocene-Quaternary exhumational and topographic evolution of the European Alps and its potential climatic and tectonic controls remain a subject of controversy. Here, we apply inverse numerical thermal-kinematic modelling to a spatially dense thermochronological dataset (apatite fission-track and (U-Th)/He) of both tunnel and surface samples across the Mont Blanc massif in the Western Alps, complemented by new zircon fission-track data, in order to better quantify its Neogene exhumation and relief history. Age-elevation relationships and modelling results show that an episodic exhumation scenario best fits the data. Initiation of exhumation in the Mont Blanc massif at 22 ± 2 Ma with a rate of 0.8 ± 0.15 km/Myr is probably related to NW-directed thrusting during nappe emplacement. Exhumation rates decrease at 6 ± 2 Ma to values of 0.15 ± 0.65 km/Myr, which we interpret to be the result of a general decrease in convergence rates and/or extensive exposure of less erodible crystalline basement rocks from below more easily erodible Mesozoic sediments. Finally, local exhumation rates increase up to 2.0 ± 0.6 km/Myr at 1.7 ± 0.8 Ma. Modelling shows that this recent increase in local exhumation can be explained by valley incision and the associated increase in relief at 0.9 ± 0.8 Ma, leading to erosional unloading, isostatic rebound and additional rock uplift and exhumation. Given the lack of tectonic activity as evidenced by constant thermochronological ages along the tunnel transect, we suggest that the final increase in exhumation and relief in the Mont Blanc massif is the result of climate change, with the initiation of mid-Pleistocene glaciations leading to rapid valley incision and related local exhumation.

Tectonic evolution of part of the Southern Metamorphic Belt of the Armorican Massif including the Ile de Groix

NASA Astrophysics Data System (ADS)

Richards, Lawrence Edward

The Southern Metamorphic Belt (SMB) of the Armorican Massifextends 400km along the south coast of Brittany and into Vendee. It is separated from the Central Armorican Domain by a major, late-Hercynian shear belt, known as the South Armorican Shear Zone. In the area studied, belts of metasedimentary and metavolcanic schist of uncertain age are separated by belts of granitic gneiss; areas of migmatite and Hercynian granite plutons cross-cut these belts. Three distinctive lithologic assemblages have been identified in the schist belts, characteristic of different depositional environments: the Le Pouldu Group, Kerleven and Gouesnach formations probably originated as abyssal black shales deposited on oceanic crust; the St. Laurent Formation and Melgven Schists probably formed as distal greywacke deposits on a deep continental shelf; the Nerly and Beg-Meil formations probably formed in a proximal marine or fluviatile environment. These disparate assemblages were tectonically juxtaposed by overthrusting (obduction) before an amphibolite facies metamorphism and deformation during the Cadomian Orogeny. The Moelan Gneiss, a Lower Ordovician alkali-granite intrusion, postdates M1/D1 and probably formed in a rifting environment at the onset of ocean-floor spreading along an axis south of the present Armorican Massif. The famous blueschists of the Ile de Groix probably formed in a subduction zone on the south side of the ocean and were obducted onto the passive southern margin of the Armorican Massif following closure of the ocean and continental collision. A second phase of regional deformation, producing a cataclastic foliation in the Moelan Gneiss, probably resulted from the collision. Large-scale overthrusting of the southern continent onto the Armorican Massif took place, causing metamorphism with partial melting at depth generating migmatites. A third phase of pervasive deformation may correlate with oroclinal bending of the Ibero-Armorican Arc during the Hercynian

Perceptions of social and environmental changes in a Mediterranean forest during the last 100 years: the Gavarres Massif.

PubMed

Rodríguez-Carreras, Roser; Ubeda, Xavier; Outeiro, Luís; Asperó, Francesc

2014-06-01

During the last century the landscape of the mid-Mediterranean mountains has undergone major transformations. The precipitous decline in the economic viability of forest products has engendered ever-thickening forests and agricultural lands have reverted to forest land cover. The related exodus of existing inhabitants since 1960 has led to new styles of occupancy: residential and touristic land uses have emerged while the primary and secondary sectors have largely disappeared. The object of the present study is to review how these transformations have developed in a specific area of north-eastern of Catalonia, known as the Gavarres Massif. The study applies a qualitative approach, based on interviews with stakeholders including active members of the local community and others who utilize or visit the area, all of whom are representatives of different social groups with a wide range of interests and points of view with regard to the massif. The information collected from the perspectives and opinions of the participants is coupled with objective data about the area. The result of this investigation is a rich variety of perceptions on landscape and social transformation and its current functional dynamics. Analyzing the information obtained allows us to understand the fact that the disappearance of the rural world is directly related to the collapse of an entire economic system that relied on the environment. In this study, two divergent points of view arise, one which supports recovering past landscapes and another which favours managing changes, conserving the existing landscape. Proposals for the current and future territorial management of Les Gavarres are presented. The diversity of opinions which emerges with regard to managing necessary changes in the massif emphasizes the importance of increased social dialogue. Copyright © 2013 Elsevier Ltd. All rights reserved.

A re-analysis of 533 rockfalls occurred since 2003 in the Mont Blanc massif for the study of their relationship with permafrost

NASA Astrophysics Data System (ADS)

Ravanel, Ludovic; Magnin, Florence; Deline, Philip

2015-04-01

Rockfall is one of the main natural hazards in high mountain regions and its frequency is growing, especially since two decades. Collapses at high elevation are with an increasing certainty assumed to be a consequence of the climate change through the warming permafrost. In the Mont Blanc massif, data on present rockfalls (occurrence time when possible, accurate location, topographical and geological settings, volume, weather and snow conditions) were acquired for 2003 and for the period 2007-2014 thanks to a satellite image of the massif and a network of observers in the central part of the massif, respectively. The study of the 533 so-documented rockfalls shows a strong correlation at the year scale between air temperature and rockfall. Along with this data acquisition, a statistical model of the Mean Annual Rock Surface Temperature (MARST) for the 1961-1990 period has been implemented on a 4-m-resolution DEM of the Mont Blanc massif. The model runs with Potential Incoming Solar radiation (PISR) calculated with GIS tools and air temperature parameters computed from Chamonix Météo France records. We cross here the data on rockfalls with the permafrost distribution model to show that: (i) rockfall occurs mainly over modeled negative MARST (context of permafrost); (ii) simulated warm permafrost areas (> -2°C) are the most affected by instabilities; (iii) as the 1961-1990 period is supposed to be representative of the conditions at depth that are not affected by the climate warming during the two last decades, the latest results are mainly valuable for rockfalls related to pluri-decadal signal; and (iv) the higher (close to 0°C) the MARST, the deeper the detachment (possibly related to the deepening of the permafrost active layer). These results and field observations confirm that warming permafrost corresponds to the main required configuration for rockfall triggering at high elevation. In addition, we show that rockfalls for which ice observed in their scar

Genesis and significance of the silico-aluminous nodules in the Ordovician of the Montagne Noire and the Massif Armoricain (France)

NASA Astrophysics Data System (ADS)

Becq-Giraudon, Jean-François; Bouillé, Suzanne; Chauvel, Jean-Jacques

1992-04-01

Siliceous nodules of the Arenigian of the Montagne Noire (southern France) and the Massif Armoricain (western France) are made up of quartz, illite and chlorite with secondary apatite and, less frequently, dolomite. Diffractometrical and geochemical data indicate that the chlorite is a chamosite (trioctahedral 2:1 chlorite), whose development may be accompanied by that of apatite and diminution of illite. Three types of nodules are defined: Type 1, siliceous nodules, with more than 85% of SiO 2, very frequent in the Montagne Noire; Type II, nodules made of a micaceous siltstone with chlorite matrix, abundant in the Massif Armoricain but present also in the Montagne Noire; Type III, chloritic nodules with a finely globular structure, especially developed in the Massif armoricain but observed in the Montagne Noire as well. The nodules are always poorer in illite than their host sediments and often show traces of the initial sediments. Their formation occurs after the deposition and prior to the development of foliation. The frequent presence of undistorted fossil remains suggests an early formation linked to the physico-chemical modifications occurring in an unconsolidated sediment around a decaying organism. The post-depositional mineralogical evolution should have started with an illite/dolomite assemblage and end up with a chamosite-dominant one, under cold climatic conditions. The simultaneous presence of the three types of nodules in the same formation, or even in the same beds, shows that this mineralogical differentiation is not strictly related to the diagenetic and metamorphic transformation of this material.

The Dilemma and Solutions for the Conflicts between Equality and Excellence in the Massification of Higher Education in Taiwan

ERIC Educational Resources Information Center

Hsiou-Huai, Wang

2012-01-01

Equality and excellence are two core values underlying many educational endeavors; however, they are often in conflict and controversy. This article intends to examine the dilemma created by such controversies in the context of massification of higher education in Taiwan and attempt to provide solutions from both the theoretical and policy…

Late Cenozoic cooling history of the central Menderes Massif and the contribution of erosion to rock exhumation during active continental extension

NASA Astrophysics Data System (ADS)

Nilius, Nils-Peter; Wölfler, Andreas; Heineke, Caroline; Glotzbach, Christoph; Hetzel, Ralf; Hampel, Andrea; Akal, Cüneyt; Dunkl, István

2017-04-01

The Menderes Massif constitutes the western part of the Anatolide belt in western Turkey and experienced a prolonged history of post-orogenic extension. A large amount of the extension was accommodated by the two oppositely dipping Gediz and Büyük Menderes detachment faults, which led to the exhumation of the central Menderes Massif (Gessner et al., 2013). Previous studies proposed a synchronous, bivergent exhumation of the central Menderes Massif since the Miocene (Gessner et al., 2001), although only the evolution of the north-dipping Gediz detachment is well constrained (Buscher et al., 2013). Detailed structural and thermochronological investigations from the south-dipping Büyük Menderes detachment have still been missing. Here we present results from different thermochronometers, which constrain the cooling and exhumation history of footwall and hanging wall rocks of the Büyük Menderes detachment. Our new zircon and apatite (U-Th)/He and fission track ages of footwall rocks from the Büyük Menderes detachment document two phases of increased cooling and exhumation (Wölfler et al., in revision). The first episode of increased footwall exhumation ( 0.9 km/Myr) occurred during the middle Miocene, followed by a second phase during latest Miocene and Pliocene ( 1.0 km/Myr). Apatite fission track ages yield a slip rate for the Pliocene movement along the Büyük Menderes detachment of 3.0 (+1.1/-0.6) km/Myr. Thermochronological data of hanging wall units reflect a slow phase of exhumation ( 0.2 km/Myr) in the late Oligocene and an increased exhumation rate of 1.0 km/Myr during the early to middle Miocene, when hanging wall units cooled below 80 °C. In comparison with the Gediz detachment, our thermochronological data from the Büyük Menderes detachment confirms the concurrent activity of both detachments during the late Miocene and Pliocene. With respect to the relative importance of normal faulting and erosion to rock exhumation, a comparison with 10Be

A new species of Pristimantis (Anura, Craugastoridae) from the Cajas Massif, southern Ecuador

PubMed Central

Sánchez-Nivicela, Juan C.; Celi-Piedra, Elvis; Posse-Sarmiento, Valentina; Urgiles, Verónica L.; Yánez-Muñoz, Mario; Cisneros-Heredia, Diego F.

2018-01-01

Abstract A new species of Pristimantis is described from the highland paramos on the eastern slopes of the Cajas Massif, southern Andes of Ecuador, at 3400 m. This new species is characterized by having a distinctive reddish color, cutaneous macroglands in suprascapular region and surfaces of arm and legs, and by lacking dentigerous processes of vomers. The cutaneous macroglands are similar to those exhibited by several species of the Pristimantis orcesi group, and may suggest a close phylogenetic relationship. The new species could be a latitudinal substitution of Pristimantis orcesi in the southern Andes of Ecuador. PMID:29713233

Development of a Comprehensive Plan for Scientific Research, Exploration, and Design: Creation of an Undergroung Radioactive Waste Isloation Facility at the Nizhnekansky Rock Massif

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jardine, L J

2005-06-15

ISTC Partner Project No.2377, ''Development of a General Research and Survey Plan to Create an Underground RW Isolation Facility in Nizhnekansky Massif'', funded a group of key Russian experts in geologic disposal, primarily at Federal State Unitary Enterprise All-Russian Design and Research Institute of Engineering Production (VNIPIPT) and Mining Chemical Combine Krasnoyarsk-26 (MCC K-26) (Reference 1). The activities under the ISTC Partner Project were targeted to the creation of an underground research laboratory which was to justify the acceptability of the geologic conditions for ultimate isolation of high-level waste in Russia. In parallel to this project work was also undermore » way with Minatom's financial support to characterize alternative sections of the Nizhnekansky granitoid rock massif near the MCC K-26 site to justify the possibility of creating an underground facility for long-term or ultimate isolation of radioactive waste (RW) and spent nuclear fuel (SNF). (Reference 2) The result was a synergistic, integrated set of activities several years that advanced the geologic repository site characterization and development of a proposed underground research laboratory better than could have been expected with only the limited funds from ISTC Partner Project No.2377 funded by the U.S. DOE-RW. There were four objectives of this ISTC Partner Project 2377 geologic disposal work: (1) Generalize and analyze all research work done previously at the Nizhnekansky granitoid massif by various organizations; (2) Prepare and issue a declaration of intent (DOI) for proceeding with an underground research laboratory in a granite massif near the MCC K-26 site. (The DOI is similar to a Record of Decision in U.S. terminology). (3) Proceeding from the data obtained as a result of scientific research and exploration and design activities, prepare a justification of investment (JOI) for an underground research laboratory in as much detail as the available site

Cenozoic volcanism in the Bohemian Massif in the context of P- and S-velocity high-resolution teleseismic tomography of the upper mantle

NASA Astrophysics Data System (ADS)

Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk.; Kissling, Eduard; Achauer, Ulrich; Babuška, Vladislav

2016-08-01

New high-resolution tomographic models of P- and S-wave isotropic-velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel-time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30-50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity-perturbations of the P- and S-wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low-velocity anomaly, which would validate the "baby-plume" concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low-velocity perturbations beneath the Eger Rift, observed in about 200km-broad zone, agree with shear-velocity models from full-waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.

The timberline as result of the interactions among forest, abiotic environment and human activity in the Babia Gora massif, Western Carpathians

NASA Astrophysics Data System (ADS)

Lajczak, Adam

2016-04-01

The timberline is one of the clearest and most easily discernible boundaries in nature (Troll 1973). Among the existing conceptual models clarifying the complex nature of the relationship between the timberline and the environment and human impact, the fullest seems to be the one presented by K. Holtmeier (2009). The quoted author comprehensively characterizes the timberline, taking into account its course, appearance and ecological characteristics. The aim of the work is to quantitatively assess the factors influencing the course of timberline and its changes over the last ca. 400 years in the Babia Góra massif (1725 m a.s.l.), the highest flysch ridge in the Western Carpathians, which is formed as an asymmetric ridge of kuesta type. Forests mainly in the upper montane zone have preserved their natural character in many areas. Old spruce tree growths are a particular advantage of the Babia Góra Mt., being there on the predominant section of the altitude zone of the timberline. In the rest of this zone, spruce forests have been under a direct or indirect influence of changes resulting from grazing with its 400-year history and forestry taking place about 100 years ago. The 60 m difference between the average altitude of the timberline on the northern (1335 m a.s.l.) and the southern slope (1395 m a.s.l.) on the Babia Góra Mt. can be explained with climatic conditions of these areas. The average gradient of the slope within the timberline ecotone on the southern slope of the massif is by 100 smaller, and the amount of solar energy delivered during the growing season is 40% higher (960 kWh/m2) than on the northern slope. The higher position of the timberline on the windward southern slope is favored by the dominant winds from S-W sector, thinner snow cover and earlier melting due to the lower precipitation on the slope and also due to the winnowing of snow onto the steep northern slope of the ridge. On the southern slope of the ridge there are no larger snow

Water erosion and soil protection technology in the agro-industrial farms around the Wadi El Ouaar, Taroudant sedimentary fan, Morocco

NASA Astrophysics Data System (ADS)

Ghafrani, Hassan; Hssaine, Ali Ait

2013-04-01

Soil erosion is a phenomenon of global order. Similarly, it affects the soils around the Mediterranean, by removing considerable amounts of arable land and reducing their fertility. Thus, it reduces their agricultural productivity. In the Maghrebian countries, the erosion continues to degrade soils despite the techniques adopted by farmers and state efforts initiated since the 1940s in the field of erosion control. The negative impacts of this phenomenon increase by the combination of natural (climate, topography, lithology and soils) and anthropogenic factors (forest clearance, overgrazing, inappropriate and artificial development). The sedimentary fan of Taroudant (in the south of the High Atlas) is in a morphological imbalance. Therefore, the recent morphological activity leads to a threat of the agricultural development. The resulting forms are leading to a large wadi. Around the Wadi El Ouaar, there are currently situated both types of oppositional farms, traditional and modern ones. Indeed, traditional agriculture is still practiced by the majority of the inhabitants of the 11 population groups (douars) installed in this area. Modern agriculture is installed there since 1960, but since the 1990s, the number of farms is exploding. Clearing for farming purposes and pastoralism, combined with climatic conditions and soil formation mainly of silt have accelerated the phenomenon of gullies formed by erosion in this area. Thus, in the occasion of each precipitation event, gully growth is triggered enormously. In addition, farmers and residents are feared to lose their land. In this context, farmers are fighting hard against the gullies to protect their property. A survey of farmers conducted in the region of Taroudant shows that gully growth requires them to spend a high portion of their profits to constantly fight against the erosion. Despite the diversity of the used resources (concrete, gabion, vegetation, etc.) to prevent the arable land from soil erosion

Using Telepresence to Connect and Engage Classes and the Public in the Exploration of Tamu Massif, the World's Largest Single Volcano

NASA Astrophysics Data System (ADS)

Nanez-James, S. E.; Sager, W.

2016-02-01

Research published in 2013 showed that TAMU Massif, the largest mountain in the Shatsky Rise oceanic plateau, located approximately 1500 kilometers east of Japan, is the "World's Largest Single Volcano." This claim garnered widespread public interest and wonder concerning how something so big could remain so mysterious in the 21st century. This disconnect highlights the fact that oceans are still widely unexplored, especially the middle of the deep ocean. Because there is so much interest in TAMU Massif, a diverse outreach team lead by chief scientist Dr. William Sager from the University of Houston in partnership with the Texas State Aquarium and the Schmidt Ocean Institute (SOI) conducted a multifaceted ship-to-shore outreach project that included secondary school students, formal and informal educators, university students and professors, the aquarium and museum audience, and the general public. The objective was to work in conjunction with SOI and various other partners, including the Texas Regional Collaborative, the Aquarium of the Pacific, and the Houston Museum of Natural Science, to promote science and ocean literacy while inspiring future scientists - especially those from underserved and underrepresented groups - through ocean connections. Participants were connected through live ship-to-shore distance learning broadcasts of ongoing marine research and discovery of TAMU Massif aboard the R/V Falkor, allowing audiences to participate in real-time research and apply real world science to curriculum in the classrooms. These ship-to-shore presentations connected to existing curriculums and standards, lessons, and career interests of the students and educators with special teacher events and professional development workshops conducted from aboard the R/V Falkor.

Major and trace element investigation of the Pine Mountain massif--The southernmost exposure of Grenville age crust in North America

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salpas, P.A.; Daniell, N.

1992-01-01

The Pine Mountain massif is a 1.1 Ga basement massif exposed in Alabama and Georgia. The Whatley Mill Gneiss (WMG) constitutes a major exposure of rock in the Pine Mountain massif of eastern Alabama. Based on appearance in outcrop, the WMG can be divided into three distinct lithologies. The first is a massive augen gneiss (AG) consisting of K-spar augen in a finer grained matrix of biotite, K-spar, plagioclase, and quartz. The second lithology is a fine-grained gneiss (FG) composed predominantly of quartz with minor muscovite. The FG occurs sporadically as band of mylonite within the AG. The third lithologymore » is generally accepted to be the protolith of the AG. It is a relatively unfoliated and undeformed rock (UN) of sparse occurrence whose mineralogy is similar to that of the AG but also contains hornblende and rounded mafic inclusions of biotite gneiss. AG and FG samples were collected along a traverse through over 220 meters of stratigraphic thickness of the WMG and were analyzed for major element compositions by XRF and for trace element compositions by INAA. Relative to the AG samples, the FG samples are enriched in SiO[sub 2] and depleted in FeO and ferromagnesian trace elements such as Sc. REE concentrations are generally higher in the AG than in the FG but the sizes of the ranges in concentrations among both groups of rocks are similar. REE systematics indicate that the silica-rich fluid introduced into the AG during shearing appears to have made negligible contributions to the absolute and relative whole-rock REE concentrations but, instead, simply diluted the REE in the parent AG. Based upon the limited sampling of UN so far, deformation to produce the foliated AG, including augen formation, appears to have occurred isochemically.« less

Strain partitioning in the Belledonne and Pelvoux massifs. Some clues to understand the Variscan tectono-thermal evolution.

NASA Astrophysics Data System (ADS)

Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jeremie; Blein, Olivier

2016-04-01

This contribution presents new structural, petrological, geochemical and geochronological data obtained in the Variscan basement of the Alpine Belledonne and Pelvoux External Crystalline massifs. The Belledonne-Pelvoux area is a stack of four litho-tectonic units. The uppermost unit is the early Ordovician Chamrousse ophiolite. It overthrusts a volcanic-sedimentary unit (VSU) made of an alternation of volcanoclastic rocks, plagiogranites and metapelites. The VSU crops out in the eastern Belledonne and western Pelvoux massifs. It is unconformably overlain by a Visean sandstone-conglomerate series with felsic lava (keratophyres). The lowermost litho-tectonic unit is made of felsic and mafic migmatites and granitoids that form the major part of the Pelvoux massif. The western boundary of this tectonic pile is the "synclinal median" strike-slip fault, on the western side of which crops out the Belledonne micaschist unit made of Cambro-ordovician turbiditic series. The structural analysis revealed four main tectono-thermal events: Dx, D1, D2, and D3. Dx is only recorded in relictual metamorphic assemblage in Ky-Grt-Ab bearing micaschist from the VSU holding an obduction metamorphic gradient (3kbar, 370°C up to 7kbar, 430°C). The age of the Dx event remains unknown. The D1 event, characterized by westward low-angle dipping foliation (S1) and a NE-SW striking stretching lineation (L1), is responsible for the crustal thickening resulting of the Eastward emplacement of the Chamrousse ophiolite upon the VSU. D1 is coeval with a barrovian metamorphism with P-T conditions of 6kbar, 600°C recorded in metapelites, and partial melting developed at the base of the VSU. Monazite LA-ICP-MS U-Pb dating revealed that D1 crustal thickening occurred at 337±7 Ma. D2 is a sinistral transpressional deformation responsible for the folding of S1 and L1, and the development of a NE-SW trending pervasive sub-vertical foliation S2. In the lower structural domain, i.e. the partially molten

Mass-balance modelling of Ak-Shyirak massif Glaciers, Inner Tian Shan

NASA Astrophysics Data System (ADS)

Rets, Ekaterina; Barandun, Martina; Belozerov, Egor; Petrakov, Dmitry; Shpuntova, Alena

2017-04-01

Tian Shan is a water tower of Central Asia. Rapid and accelerating glacier downwasting is typical for this region. Study sites - Sary-Tor glacier and Glacier No.354 are located in Ak-Shyirak massif, Naryn headwaters. Sary-Tor was chosen as representative for Ak-Shyirak (Ushnurtsev, 1991; Oledeneniye TianShanya, 1995) for direct mass-balance measurements in 1985-1991. Glacier No.354 was an object of direct mass-balance measurements for 2011-2016. An energy-balance distributed A-Melt model (Rets et al, 2010) was used to reconstruct mass-balance for the glaciers for 2003-2015. Verification of modelingresults showed a good reproduction of direct melting measurements data on ablation stakes and mass loss according to geodetic method. Modeling results for Glacier No. 354 were compared to different modeling approach: distributed accumulation and temperature-index melt (Kronenberg et al, 2016)

Water-Rock Interactions in the Peridotite Aquifer of the Oman-UAE Ophiolite: Strontium Isotopic Ratio and Geochemical Evolution of Groundwater

NASA Astrophysics Data System (ADS)

Bompard, Nicolas; Matter, Juerg; Teagle, Damon

2016-04-01

The peridotite aquifer in Wadi Tayin, Sultanate of Oman, is a perfect example of natural carbonation of ultramafic rocks. In situ mineral carbonation is considered the most safest and permanent option of CO2 Capture and Sequestration (CCS). However, the process itself is yet to be characterised and a better understanding of the mechanisms involved in natural mineral carbonation is needed before geo-engineering it. We used the 87Sr/86Sr system to follow the water-rock interactions along the groundwater flowpath in the peridotite aquifer and to determine the sources of divalent cations (Mg2+, Ca2+) required for mineral carbonation. The Sr-isotope data of groundwater show that the aquifer rocks are the main source for divalent cations (Mg2+, Ca2+ and Sr2+) and secondary carbonates are their main sink. The groundwater 87Sr/86Sr ratio evolves with its pH: from 87Sr/86Sr = 0.7087 (n=3) to 0.7082 (n=8) between pH 7 and 8, and from 0.7086 (n=6) at pH 9 to 0.07075 (n=9) at pH 11. This evolution seems to support a two-step model for the water-rock interactions in the peridotite aquifer. From pH 7 to 8, secondary Ca-carbonate precipitation buffers the pH rise resulting from peridotite serpentinisation. From pH 9 to 11, peridotite serpentinisation drives the pH to alkaline condition. The change from a Mg-rich to a Ca-rich groundwater at pH 9 seems to confirm the two-step model.

Use of Digital Elevation Models to understand map landforms and history of the magmatism Khibiny Massif (Kola Peninsula, Russia)

NASA Astrophysics Data System (ADS)

Chesalova, Elena; Asavin, Alex

2016-04-01

This work presents an improved geomorphological methodology that uses 3D model of relief, remotely-sensed data, geological, geophysical maps and tools of Geographical Information Systems. On the basis of maps of 1: 50,000 and 1: 200,000 the Digital Elevation model (DEM) of Khibiny massif was developed. We used software ARC / INFO v10.2 ESRI. A DEM was used for analyzing landform by extracting the slope gradient, curvature, valley pro?les, slope, aspect and so on. The results were gradually re?ned from the interpretation of satellite imagery and geological map Geomorphological analysis will allow us to determine spatial regularities in inner massive construction. We try to found areas where gas emissions (CH4/H2) enrich, according to morphometry, geology, tectonic and other environments. The main regional blocks were de?ned by different morphological evidences: impression zone, similar to subsidence caldera; uplift zone, domed area (located in the highest part of massif and zone of intersection of main faults) and others. It says that there are the few stages in the development of the Khibiny massif. There is no common concept of the consequence of intrudes magmatic phases now. And we hope that our geomorphical analysis take a new evidences about this problems. Locations of the blocks' borders (tectonic zones) were recognized by lineament analysis of valleys and tectonic faults presented in relief. Erosion system is represented by valleys of 4 ranks. It inherits the zone of tectonic disturbances 3 groups of faults were recognized: 1) Global lineament system cross whole peninsula - existing before Khibiny massif intrusion; 2) Faults associated with the formation of the intrusive phases sequence and magma differentiation and with later collision history during magma cooling; 3) Crack system related to neotectonic process. We believed that if different magmatic phases intrude in similar tectonic environment, the common spatial system of faults will be formed. Really we

Restoration of degraded arid farmland at Project Wadi Attir: Impact of conservation on biological productivity and soil organic matter

NASA Astrophysics Data System (ADS)

Mor-Mussery, Amir; Helman, David; Ben Eli, Michael; Leu, Stefan

2017-04-01

The Israeli Negev Desert, as most Mediterranean drylands, is profoundly degraded. We have been documenting degradation and successful rehabilitation approaches in recent research, aiming at maximizing environmental and economic benefits while restoring healthy dryland soils and perennial vegetation to act as carbon sinks. These methods have been implemented for rehabilitation of Project Wadi Attir's. 50 hectares of heavily degraded farmland suffering from intensive soil erosion (expressed in dense gullies net and massive overland flow). Project Wadi Attir is a groundbreaking initiative of the Bedouin community in the Negev, for establishing a model sustainable agricultural operation. The project was initiated by the US-based Sustainability Laboratory and the Hura Municipal Council. The project is designed to demonstrate implementation of holistic sustainability principles developed by The Lab. The project's ecosystem restoration component involves site development, erosion control, soil conservation and improvement, planting of native and agroforestry trees, together with conservation and protection of biodiversity hotspots and avoiding grazing have, within three years, revealed the high biodiversity and productivity potential of this arid/semi-arid landscape. A number of shrublands and loess plots were subject to strict conservation, avoiding tilling and grazing. Soil fertility, productivity and biodiversity of these conserved plots inside the farm boundaries was compared to similar unprotected plots outside the farm fences by sampling in the field and by using satellite imaging. Our findings indicate a gradual improvement of SOM content specifically in the conserved shrubland area. Water infiltration, herbaceous biomass productivity and ants' activity of the protected plots also significantly increased within 3 years compared to the unprotected control areas. Starting from similar soil organic matter content in 2013 (3.3%) in the rocky slopes, in 2016 1% higher

Granulite-facies rocks in the Whatley Mill gneiss, Pine Mountain basement massif, Eastern Alabama

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daniell, N.; Salpas, P.A.

1993-03-01

The Pine Mountain basement massif is a granulite terrane exposed in a tectonic window through the Inner Piedmont of western Georgia and eastern Alabama. Investigations of the westernmost extent of the massif, the Whatley Mill Gneiss, have revealed four distinct lithologies: (1) an augen gneiss, the type lithology; (2) mylonite that develops in the shear zones cutting the unit; (3) a phaneritic rock showing weak to no foliation; (4) enclaves of biotite gneiss within the weakly-foliated rock. Additionally, the weakly-foliated rock comprises two distinct phases which are in sharp contact along curved and undulating boundaries: phase 1 is a coarser-grainedmore » rock; phase 2 is a finer-grained rock of the same mineralogy as phase 1 except it contains rare hypersthene. This first recorded observation of hypersthene unequivocally confirms the granulite-facies origin of the unit. Major and trace element compositions of the phase 1 rock are identical to those of the augen gneiss. The phase 2 rock, has a distinct composition with higher SiO[sub 2] and lower incompatible trace elements than the phase 1 rock. The enclaves display a range in major elements but higher incompatible elements than the other lithologies. Geochemical and petrologic relationships leads one to interpret: (1) the weakly-foliated rock retains many of its primary igneous features including its two phases and enclaves; (2) the two phases of the weakly-foliated rock arose as a result of injection of one magma (phase 2) into a cooler, crystal mush solidifying from another magma (phase 1); (3) the enclaves represent either autoliths of xenoliths; (4) the augen gneiss arose by isochemical deformation of the phase 1 rock.« less

Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

NASA Astrophysics Data System (ADS)

Javier Álvaro, J.; Colmenar, Jorge; Monceret, Eric; Pouclet, André; Vizcaïno, Daniel

2016-06-01

Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing. The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances.

Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history?

NASA Astrophysics Data System (ADS)

Jedlicka, Radim; Faryad, Shah Wali

2017-08-01

High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite

Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdağ Massif, NW Turkey

NASA Astrophysics Data System (ADS)

Şengün, Fırat; Zack, Thomas

2016-08-01

In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdağ Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdağ Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdağ Massif are dominated by subchondritic Nb/Ta (11-19) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe-Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 °C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdağ metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the İzmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdağ metamorphic sequence resulting from southerly directed compression during the collision.

From ocean depths to mountain tops: uplift of the Troodos Massif (Cyprus) constrained by (U-Th)/He thermochronology and geomorphic analysis

NASA Astrophysics Data System (ADS)

Morag, N.; Haviv, I.; Katzir, Y.

2013-12-01

The Troodos Massif of Cyprus, rising to nearly 2000 meters above sea level, encompasses one of the world's classic ophiolites. Following its formation at a seafloor spreading center in Late Cretaceous times, this slice of the NeoTethyan oceanic lithosphere was uplifted and eventually exposed on mountain tops during the Neogene. The final uplift and exhumation of the Troodos was previously assigned to Pleistocene age by observations in the circum-Troodos sedimentary strata. However, quantitative thermochronological and geomorphological data from the Massif itself were not available. Here we use apatite (U-Th)/He low-temperature thermochronology complemented by zircon (U-Th)/He and apatite fission track data, and combined with geomorphic analysis to constrain the exhumation and uplift history of the Troodos ophiolite. Apatite (U-Th)/He ages vary with depth from ~ 22 Ma at the top of the Gabbro sequence to ~ 6 Ma at the bottom of the sequence. The deepest sample from a Gabbro pegmatitic dyke intruding the ultramafic sequence yielded an age of ~ 3 Ma. Thermal modeling of apatite (U-Th)/He and fission track data delineates Plio - Pleistocene initiation of rapid uplift and exhumation of the Troodos ophiolite. The estimated cumulative exhumation since its initiation is 2-3 km. No evidence was found for significant uplift of the central Troodos area prior to that time. The geomorphic analysis delineates a bull's-eye zone at the center of the Troodos Massif, where local relief and channel steepness index are highest. The boundaries of this zone roughly correspond with the Mt. Olympus mantle outcrop and suggest recent, differential uplift of this zone relative to its surroundings. The most likely mechanism, which could drive such a focused bull's-eye uplift pattern is hydration of ultramafic rocks (serpentinization) leading to a decrease in rock density and subsequent diapiric uplift of the serpentinized lithospheric mantle.

Les dykes basiques du massif ancien de l'Ourika (Atlas de Marrakech, Maroc): géochimie et significationThe basic dykes of the Ourika old massif (High Atlas of Marrakech): Geochemistry and significance

NASA Astrophysics Data System (ADS)

Barakat, Ahmed; Marignac, Christian; Bouabdelli, Mohamed

The Precambrian massif of Ourika is crosscut by two systems of basic dykes, striking N40°E and N90-120°E. Using incompatible trace elements, the two systems form two distinct chemical groups, displaying a continental tholeiitic affinity. The composition variations between the two defined groups can be due to heterogeneities of mantle sources and to contamination, during the magma ascent, by the continental crust. The emplacement of these basic dykes, before the late-PIII formations, can be related to the Neoproterozoic distension generalised to the Anti-Atlas chain. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 827-833.

In situ U-Pb and Lu-Hf isotopic studies of zircons from the Sancheong-Hadong AMCG suite, Yeongnam Massif, Korea: Implications for the petrogenesis of ∼1.86 Ga massif-type anorthosite

NASA Astrophysics Data System (ADS)

Lee, Yuyoung; Cho, Moonsup; Yi, Keewook

2017-05-01

Isotopic and geochemical characteristics of Proterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite have long been used for tracing the mantle-crustal source and magmatic evolution. We analyzed Lu-Hf isotopic compositions of zircon from the Sancheong-Hadong AMCG complex, Yeongnam Massif, Korea, in order to understand tectonomagmatic evolution of the Paleoproterozoic AMCG suite occurring at the southeastern margin of the North China Craton (NCC). The anorthositic rocks in this complex, associated with charnockitic and granitic gneisses, were recrystallized to eradicate magmatic features. In situ SHRIMP (sensitive high-resolution ion microprobe) U-Pb analyses of zircon from a leuconorite and an oxide-bearing gabbroic dyke yielded weighted mean 207Pb/206Pb ages of 1870 ± 2 Ma and 1861 ± 6 Ma, respectively. Charnockitic, granitic, and porphyroblastic gneisses yielded weighted mean 207Pb/206Pb zircon ages of 1861 ± 6 Ma, 1872 ± 6 Ma, and 1873 ± 4 Ma, respectively. These crystallization ages, together with our previous geochronological data for anorthosites (1862 ± 2 Ma), are indicative of episodic AMCG magmatism over an ∼10 Ma interval. Initial εHf(t) values of zircon analyzed from five anorthositic rocks and four felsic gneisses range from +2.1 to -6.1 and -0.3 to -5.4, respectively. Zircon Hf isotopic data in combination with available whole rock Sr-Nd isotopic data suggest that anorthositic parental magma was most likely derived from a mantle source and variably affected by crustal contamination. This crustal component is also reflected in charnockitic-granitic magmas produced primarily by the melting of lower crust. Taken together, the AMCG magmatism at 1.87-1.86 Ga in the Yeongnam Massif is most likely a late orogenic product of Paleoproterozoic NCC amalgamation tectonically linked to assembly of the Columbia supercontinent.

Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

NASA Astrophysics Data System (ADS)

Amelin, Yuri V.; Ritsk, Eugeni Yu.; Neymark, Leonid A.

1997-04-01

Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/ 144Nd- 143Nd/ 144Nd and 238U/ 204Pb- 206Pb/ 204Pb mineral isochrons, corresponding to ages of 640 ± 58 Ma (95% confidence level) and 620 ± 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ± 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites withɛ Nd = +6.6 to +7.1 andɛ Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit:ɛ Nd = +4.6 to +6.1 andɛ Sr = -8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/ 204Pb= 16.994 ± 0.023 and 207Pb/ 204Pb= 15.363 ± 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with

Effects of interaction between ultramafic tectonite and mafic magma on Nd-Pb-Sr isotopic systems in the Neoproterozoic Chaya Massif, Baikal-Muya ophiolite belt

USGS Publications Warehouse

Amelin, Y.V.; Ritsk, E. Yu; Neymark, L.A.

1997-01-01

Sm-Nd, Rb-Sr and U-Pb isotopic systems have been studied in minerals and whole rocks of harzburgites and mafic cumulates from the Chaya Massif, Baikal-Muya ophiolite belt, eastern Siberia, in order to determine the relationship between mantle ultramafic and crustal mafic sections. Geological relations in the Chaya Massif indicate that the mafic magmas were emplaced into, and interacted with older solid peridotite. Hand picked, acid-leached, primary rock-forming and accessory minerals (olivine, orthopyroxene, clinopyroxene and plagioclase) from the two harzburgite samples show coherent behavior and yield 147Sm/144Nd- 143Nd/144Nd and 238U/204Pb-206Pb/204Pb mineral isochrons, corresponding to ages of 640 ?? 58 Ma (95% confidence level) and 620 ?? 71 Ma, respectively. These values are indistinguishable from the crystallization age of the Chaya mafic units of 627 ?? 25 Ma (a weighted average of internal isochron Sm-Nd ages of four mafic cumulates). The Rb-Sr and Sm-Nd isotopic systems in the harzburgite whole-rock samples were disturbed by hydrothermal alteration. These alteration-related isotopic shifts mimic the trend of variations in primary isotopic compositions in the mafic sequence, thus emphasizing that isotopic data for ultramafic rocks should be interpreted with great caution. On the basis of initial Sr and Nd values, ultramafic and mafic rocks of the Chaya Massif can be divided into two groups: (1) harzburgites and the lower mafic unit gabbronorites with ??Nd = +6.6 to +7.1 and ??Sr = -11 to -16; and (2) websterite of the lower unit and gabbronorites of the upper mafic unit: ??Nd = + 4.6 to + 6.1 and ??Sr = - 8 to -9. Initial Pb isotopic ratios are identical in all rocks studied, with mean values of 206Pb/204Pb = 16.994 ?? 0.023 and 207Pb/204Pb = 15.363 ?? 0.015. The similarity of ages and initial isotopic ratios within the first group indicates that the isotopic systems in the pre-existing depleted peridotite were reset by extensive interaction with basaltic

Estimate of size distribution of charged MSPs measured in situ in winter during the WADIS-2 sounding rocket campaign

NASA Astrophysics Data System (ADS)

Asmus, Heiner; Staszak, Tristan; Strelnikov, Boris; Lübken, Franz-Josef; Friedrich, Martin; Rapp, Markus

2017-08-01

We present results of in situ measurements of mesosphere-lower thermosphere dusty-plasma densities including electrons, positive ions and charged aerosols conducted during the WADIS-2 sounding rocket campaign. The neutral air density was also measured, allowing for robust derivation of turbulence energy dissipation rates. A unique feature of these measurements is that they were done in a true common volume and with high spatial resolution. This allows for a reliable derivation of mean sizes and a size distribution function for the charged meteor smoke particles (MSPs). The mean particle radius derived from Schmidt numbers obtained from electron density fluctuations was ˜ 0.56 nm. We assumed a lognormal size distribution of the charged meteor smoke particles and derived the distribution width of 1.66 based on in situ-measured densities of different plasma constituents. We found that layers of enhanced meteor smoke particles' density measured by the particle detector coincide with enhanced Schmidt numbers obtained from the electron and neutral density fluctuations. Thus, we found that large particles with sizes > 1 nm were stratified in layers of ˜ 1 km thickness and lying some kilometers apart from each other.

Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

NASA Astrophysics Data System (ADS)

Bonin, Bernard; Tatu, Mihai

2016-08-01

The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

Geochemistry and evolution of MORB-type eclogites from the Münchberg Massif, southern Germany

NASA Astrophysics Data System (ADS)

Stosch, H.-G.; Lugmair, G. W.

1990-08-01

In the Münchberg Massif in the Variscan foldbelt of southern Germany two varieties of eclogite are known which are intercalated with amphibolite-facies meta-igneous and meta-sedimentary rocks: a dark kyanite-free and a lighter colored kyanite-bearing type. Kyanite-free eclogites, which are discussed here, have a major and trace element composition which suggests derivation from ocean-floor basalts with melt to cumulate compositions. Internal Sm sbnd Nd isochrons (clinopyroxene-amphibole-garnet) and one Rb sbnd Sr isochron (clinopyroxene-amphibole-mica) yield eclogitization ages in the range of 380 to 395 Ma. Thus, the age of eclogitization is only marginally higher ( < 15 Ma) than the age of amphibolite-facies metamorphism in the Münchberg Massif as derived from K sbnd Ar ages of amphiboles and micas from metasediments and meta-igneous rocks. A seven point whole-rock Sm sbnd Nd isochron for one eclogite body results in an age of 480 ± 23Ma with an initial ɛ Nd of 8.7 ± 0.6 and is likely to record the age of igneous formation of the eclogite protoliths. Sr isotopic compositions back-calculated to that time are anomalously high and variable if compared to Nd isotopes. This can be explained by alteration with an aqueous or fluid phase with high 87Sr 86Sr , most likely seawater, either during igneous formation in an oceanic rift environment or subduction-related eclogitization. In addition, some eclogites show a marked enrichment of incompatible, immobile elements and plot far below the whole-rock Sm sbnd Nd isochron. These features are ascribed to the presence of an evolved crustal component, probably acquired during extrusion of the basaltic protoliths by mixing with country-rock gneisses.

Geological structure and ore mineralization of the South Sopchinsky and Gabbro-10 massifs and the Moroshkovoe Lake target, Monchegorsk area, Kola Peninsula, Russia

NASA Astrophysics Data System (ADS)

Pripachkin, Pavel V.; Rundkvist, Tatyana V.; Miroshnikova, Yana A.; Chernyavsky, Alexey V.; Borisenko, Elena S.

2016-12-01

The South Sopchinsky massif (SSM), Gabbro-10 (G-10) massif, and Moroshkovoe Lake (ML) target Monchegorsk area, Kola Peninsula, are located at the junction of the Monchepluton and Monchetundra layered intrusions. The intrusions were studied in detail as they are targets for platinum-group element (PGE) mineralization. The rocks in these targets comprise medium- to coarse-grained mesocratic to leucocratic gabbronorites, medium-grained mesocratic to melanocratic norites and pyroxenites, and various veins mainly comprising norite, plagioclase-amphibole-magnetite rocks, and quartz-magnetite rocks. The veins contain Ni-Cu-PGE mineralization associated with magnetite and chromite. In all targets, the contacts between gabbronorite and norite-pyroxenite are undulating, and the presence of magmatic (intrusive) breccias suggests that these rocks formed through mingling of two distinct magmatic pulses. In places, the gabbronorites clearly crosscut the modal layering of the norites and pyroxenites. Trace element data indicate that the gabbronorites have similar compositions to rocks of the upper part of the Monchetundra intrusion, whereas the norites and pyroxenites resemble rocks from the lower to intermediate stratigraphic levels of the Monchepluton, such as in the Nude-Poaz and Sopcha massifs. Sulfide mineralization in the studied targets principally consists of secondary bornite, millerite, and chalcopyrite. In contrast, the primary sulfide assemblage within the layered sequence of the adjacent Monchepluton is characterized by pentlandite, chalcopyrite, and pyrrhotite. Therefore, the mineralization in the studied targets is interpreted to be of a contact style. We argue that the studied area represents the contact zone between gabbronorites of the Monchetundra intrusion and norites and pyroxenites of the Monchepluton. In addition, the rocks were overprinted by postmagmatic veining and remobilization of contact style sulfide and PGE mineralization.

Mineral compositions of plutonic rocks from the Lewis Hills massif, Bay of Islands ophiolite

NASA Technical Reports Server (NTRS)

Smith, Susan E.; Elthon, Don

1988-01-01

Mineral compositions of residual and cumulate rocks from the Lewis Hills massif of the Bay of Islands ophiolite complex are reported and interpreted in the context of magnetic processes involved in the geochemical evolution of spatially associated diabase dikes. The mineral compositions reflect greater degrees of partial melting than most abyssal peridotites do and appear to represent the most depleted end of abyssal peridotite compositions. Subsolidus equilibration between Cr-Al spinal and olivine generally has occurred at temperatures of 700 to 900 C. The spinel variations agree with the overall fractionation of basaltic magmas producing spinels with progressively lower Cr numbers. The compositions of clinopyroxenes suggest that the fractionation of two different magma series produced the various cumulate rocks.

An integrated geophysical study wajid formation of water-bearing aquifers: Case study at Wadi Aldwasir area-Saudi Arabia

NASA Astrophysics Data System (ADS)

Alasmari, Abdulsalam; Suliman, Asim

2015-04-01

Wadi Aldwasir area is very important province in Saudi Arabia. It contains the main water aquifer that attains a proven groundwater reserve (Wajid aquifer). This study aims to investigate the subsurface features of this aquifer (thickness, depth to basement, overlying section and the structural elements) using an integrated gravity survey (2D profiles) and aeromagnetic interpretation (RTP, low pass and high-pass maps). Gravity data are measured in the field using CG-5 AutoGrav, while magnetic data are taken from a survey made by Saudi Geological Survey. The interpretation of aeromagnetic data revealed structural elements trending towards N-S, NNE-SSW, WNW and NNW-SSE directions. Positive magnetic anomalies are found indicating the presence of anticlinal blocks and strike-slip fault patterns. These structural elements are associated with the prevailing Najd fault and the transform fault systems. Gravity data showed that the depth to basement vary from 600 m to 1150 m, giving rise to a considerable range for aquifer thickness of 250 m to 700 m. Local basins of good thicknesses are indicated. Finally, a basement relief map is conducted based on an integrated interpretation of the magnetic and gravity outputs. It shows an increase of depth from south to north (good aquifer thickness).

Hydrologic analysis of the challenges facing water resources and sustainable development of Wadi Feiran basin, southern Sinai, Egypt

NASA Astrophysics Data System (ADS)

Ahmed, Ayman A.; Diab, Maghawri S.

2018-04-01

Wadi Feiran basin is one of the most promising areas in southern Sinai (Egypt) for establishing new communities and for growth in agriculture, tourism, and industry. The present challenges against development include water runoff hazards (flash flooding), the increasing water demand, and water scarcity and contamination. These challenges could be mitigated by efficient use of runoff and rainwater through appropriate management, thereby promoting sustainable development. Strategies include the mitigation of runoff hazards and promoting the natural and artificial recharge of aquifers. This study uses a watershed modeling system, geographic information system, and classification scheme to predict the effects of various mitigation options on the basin's water resources. Rainwater-harvesting techniques could save more than 77% of the basin's runoff (by volume), which could be used for storage and aquifer recharge. A guide map is provided that shows possible locations for the proposed mitigation options in the study basin. Appropriate measures should be undertaken urgently: mitigation of groundwater contamination (including effective sewage effluent management); regular monitoring of the municipal, industrial and agricultural processes that release contaminants; rationalization and regulation of the application of agro-chemicals to farmland; and regular monitoring of contaminants in groundwater. Stringent regulations should be implemented to prevent wastewater disposal to the aquifers in the study area.

Detrital zircon age distribution from Devonian and Carboniferous sandstone in the Southern Variscan Fold-and-Thrust belt (Montagne Noire, French Massif Central), and their bearings on the Variscan belt evolution

NASA Astrophysics Data System (ADS)

Lin, Wei; Faure, Michel; Li, Xian-hua; Chu, Yang; Ji, Wenbin; Xue, Zhenhua

2016-05-01

In the Southern French Massif Central, the Late Paleozoic sedimentary sequences of the Montagne Noire area provide clues to decipher the successive tectonic events that occurred during the evolution of the Variscan belt. Previous sedimentological studies already demonstrated that the siliciclastic deposits were supplied from the northern part of the Massif Central. In this study, detrital zircon provenance analysis has been investigated in Early Devonian (Lochkovian) conglomerate and sandstone, and in Carboniferous (Visean to Early Serpukhovian) sandstone from the recumbent folds and the foreland basin of the Variscan Southern Massif Central in Montagne Noire. The zircon grains from all of the samples yielded U-Pb age spectra ranging from Neoarchean to Late Paleozoic with several age population peaks at 2700 Ma, 2000 Ma, 980 Ma, 750 Ma, 620 Ma, 590 Ma, 560 Ma, 480 Ma, 450 Ma, and 350 Ma. The dominant age populations concentrate on the Neoproterozoic and Paleozoic. The dominant concordant detrital zircon age populations in the Lochkovian samples, the 480-445 Ma with a statistical peak around 450 Ma, are interpreted as reflecting the rifting event that separated several continental stripes, such as Armorica, Mid-German Crystalline Rise, and Avalonia from the northern part of Gondwana. However, Ediacaran and Cambrian secondary peaks are also observed. The detrital zircons with ages at 352 - 340 Ma, with a statistical peak around 350 Ma, came from the Early Carboniferous volcanic and plutonic rocks similar to those exposed in the NE part of the French Massif Central. Moreover, some Precambrian grains recorded a more complex itinerary and may have experienced a multi-recycling history: the Archean and Proterozoic grains have been firstly deposited in Cambrian or Ordovician terrigenous rocks, and secondly re-sedimented in Devonian and/or Carboniferous formations. Another possibility is that ancient grains would be inherited grains, scavenged from an underlying but not

Dating of the youngest volcanoes of Ardeche (Massif Central, France) using 40Ar/39Ar and unspiked K/Ar

NASA Astrophysics Data System (ADS)

Nomade, Sebastien; Sasco, Romain; Guillou, Herve; Scao, Vincent; Kissel, Catherine; Genty, Dominique

2014-05-01

Since the first description in 1778 of the relationship between prismatic basaltic flow and volcano in the high valleys of the Ardèche (Faujas Saint-Font, 1778), "L'Ardèche", a small region at the south-west of Massif Central, became worldwide famous among volcanologists. This volcanism is found dispersed over an area of more than 20 km2 and is made of strombolian cones and prismatic flows filling NS to NW-SE valleys. This volcanism has then been considered as one of the most recent one in the entire Massif Central (40 ka to 170 ka, TL ages, Guérin et al., 2007). Unfortunately and despite several attempts over the last 25 years this volcanism has never been dated using radio-isotopic methods. The two main reasons usually advocated to explain this lack of success were the young age of the volcanism itself and the large amounts of mantle and lower crust xenoliths in the lavas (Guérin et al., 2007). In this contribution, we will present combined 40Ar/39Ar ages and unspiked K/Ar results obtained on five lava flows. The obtained ages range from 26 ± 5.5 ka to 55 ± 6.0 ka (1s, full propagated uncertainty relative to ACS-2 at 1.194Ma, Nomade et al., 2005). The ages from three of the investigated lava flows coming from distinct cones, are clustered between 26 ± 5.5 ka and 34 ± 4 ka. These cones are found stretched along a NW-SE tectonic accident. These first radio-isotopic constraints prove that the volcanic activity occurred during the last glacial period and is as young as "la chaîne de Puys" located in the northern part of the Massif Central. Incidentally, the volcanic activity is contemporaneous with the first Aurignacian occupation and related art found in the Chauvet cave (37-29 ka, Valladas et al., 2005) localized only 35 km SE. Based on both the spatial and chronological coincidences reported above we suggest that the Aurignacian population(s) that lived in this area have witnessed one or several of these eruptions.

Lower crust exhumation and ongoing continental convergence in the Variscan Maures-Tanneron Massif, France, geological synthesis and numerical models

NASA Astrophysics Data System (ADS)

Gerbault, Muriel; Schneider, Julie; Corsini, Michel; Reverso-Peila, Alexandre

2015-04-01

The Maures-Tanneron Massif together with Corsica and Sardinia compose the present day southeastern part of the Variscan belt. Pressure-temperature-time patterns were compiled to adress how rocks once forming a thick orogenic crust were exhumed, from burial conditions of ca. 10 kb and ca. 800°C. A continuous evolution from subduction to collision, from ca. 420 Ma to 290 Ma has recently been proposed by Schneider et al., 2014, ending with orthogonal Permean rifting. Here we complement this study by exploring the thermo-mechanical conditions prevailing during the massive exhumation of this orogenic crust. Based on field observations and petrological analysis indicative of the acceleration of partial melting during ongoing convergence, our numerical models test a scenario in which pre-thickened units located at 40-60 km depth, would have molten due to internal heating and burrial, and were progressively exhumed by gravitationally-driven instabilities to the surface, within ~15-25 Myrs. Assuming temperature dependent elasto-visco-plastic behavior, we have tested rheological layering including mafic or felsic units, far-field convergence and surface processes, as well as temperature-dependent melting conditions and density and viscosity evolution. In order to reproduce asymmetrical exhumation over the given time-scales and over an extent area of more than 50 km synchroneous with the development of compressional folds in the upper crust, a best fit was obtained for an applied far-field convergence of 0.5 cm/yr, equivalent to present day Alpine convergence rates, and a bulk crustal viscosity of at least 102° Pa.s. Crustal heat source had to contribute significantly, whereas a too shallow mantle heat source triggers exceedingly warm and fast exhumation. We propose that the evolution from transpressional to tensile conditions perpendicular to the orogenic axis (north-south Permean rifting versus East-West vergence of the orogenic structures), occurred progressively as

Setting new constrains on the age of crustal-scale extensional shear zone (Vivero fault): implications for the evolution of Variscan orogeny in the Iberian massif

NASA Astrophysics Data System (ADS)

Lopez-Sanchez, Marco A.; Marcos, Alberto; Martínez, Francisco J.; Iriondo, Alexander; Llana-Fúnez, Sergio

2015-06-01

The Vivero fault is crustal-scale extensional shear zone parallel to the Variscan orogen in the Iberian massif belt with an associated dip-slip movement toward the hinterland. To constrain the timing of the extension accommodated by this structure, we performed zircon U-Pb LA-ICP-MS geochronology in several deformed plutons: some of them emplaced syntectonically. The different crystallization ages obtained indicate that the fault was active at least between 303 ± 2 and 287 ± 3 Ma, implying a minimum tectonic activity of 16 ± 5 Ma along the fault. The onset of the faulting is established to have occurred later than 314 ± 2 Ma. The geochronological data confirm that the Vivero fault postdates the main Variscan deformation events in the NW of the Iberian massif and that the extension direction of the Late Carboniferous-Early Permian crustal-scale extensional shear zones along the Ibero-Armorican Arc was consistently perpendicular to the general arcuate trend of the belt in SW Europe.

Deforestation Along the Maya Mountain Massif Belize-Guatemala Border

NASA Astrophysics Data System (ADS)

Chicas, S. D.; Omine, K.; Arevalo, B.; Ford, J. B.; Sugimura, K.

2016-06-01

In recent years trans-boundary incursions from Petén, Guatemala into Belize's Maya Mountain Massif (MMM) have increased. The incursions are rapidly degrading cultural and natural resources in Belize's protected areas. Given the local, regional and global importance of the MMM and the scarcity of deforestation data, our research team conducted a time series analysis 81 km by 12 km along the Belize-Guatemalan border adjacent to the protected areas of the MMM. Analysis drew on Landsat imagery from 1991 to 2014 to determine historic deforestation rates. The results indicate that the highest deforestation rates in the study area were -1.04% and -6.78% loss of forested area per year in 2012-2014 and 1995-1999 respectively. From 1991 to 2014, forested area decreased from 96.9 % to 85.72 % in Belize and 83.15 % to 31.52 % in Guatemala. During the study period, it was clear that deforestation rates fluctuated in Belize's MMM from one time-period to the next. This seems linked to either a decline in deforestation rates in Guatemala, the vertical expansion of deforestation in Guatemalan forested areas and monitoring. The results of this study urge action to reduce incursions and secure protected areas and remaining forest along the Belize-Guatemalan border.

The promotion of geotourism in protected areas: a proposal of itinerary through the Matese Massif (Campania and Molise regions, Italy).

NASA Astrophysics Data System (ADS)

Rosskopf, Carmen Maria; Filocamo, Francesca; Amato, Vincenzo; Cesarano, Massimo

2016-04-01

The Matese Massif is a ca. 1000 km2 wide and NW-SE elongated carbonate relief, located in the inner sector of the Southern Apennine chain. It has a tabular setting with steep structural slopes bordering the central high mountain sector including its major peaks and is crossed from approximately west to east by the border between Campania and Molise regions. The Matese Mountains represent a key area for the comprehension of the geological and tectonic evolution of the Southern Apennines since Mesozoic times. Its long-term geomorphological evolution has been controlled by Quaternary tectonics and climate variations that have allowed the temporary or permanent establishment of various environments and morphodynamics. Deposits and landforms originated by glacial, periglacial, karst and fluvial processes, along with a rich assemblage of tectonic-structural features and landforms of complex origin have given origin to a geological heritage of exceptional value. The geosites actually censured within the Campanian sector of Matese are reported in the Geosites Map of Campania, available at the website of Campania Region and partly included in the Italian Geosites Inventory of ISPRA. The geosites of the Molise sector have been recently assessed within the geosite inventory carried out by Molise University. They are reported in the Geosites Map of Molise, available at the website of Molise Region, and partly included in the ISPRA's National Inventory of Geosites. The Matese area is largely included in protected areas: the Campania portion falls within the Matese Regional Park, established in 2002, while most of the Molise sector falls in the extensive ZPS/SIC IT72222287. To better protect and exploit the unique natural and geological heritage of the Matese Massif, numerous initiatives aimed at the establishment of the National Park of Matese have continued for several years and very recent attempts to promote the Matese Geopark have been made, but unfortunately without any

Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China

NASA Astrophysics Data System (ADS)

Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan

2017-04-01

Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

Conservation planning as an adaptive strategy for climate change and groundwater depletion in Wadi El Natrun, Egypt

NASA Astrophysics Data System (ADS)

Switzman, Harris; Salem, Boshra; Gad, Mohamed; Adeel, Zafar; Coulibaly, Paulin

2018-05-01

In drylands, groundwater is often the sole source of freshwater for industrial, domestic and agricultural uses, while concurrently supporting ecosystems. Many dryland aquifers are becoming depleted due to over-pumping and a lack of natural recharge, resulting in loss of storage and future water supplies, water-level declines that reduce access to freshwater, water quality problems, and, in extreme cases, geologic hazards. Conservation is often proposed as a strategy for managing groundwater to reduce or reverse the depletion, although there is a need to better understand its potential effectiveness and benefits at the local scale. This study assesses the impact of water-conservation planning strategies on groundwater resources in the Wadi El Natrun (WEN) area of northern Egypt. WEN has been subjected to groundwater depletion and quality degradation since the 1990s, attributed to agricultural and industrial groundwater usage. Initiatives have been proposed to increase the sustainability of the groundwater resource in the study area, but they have yet to be evaluated. Simultaneously, there are also proposals to increase the extent of arable land and thus demand for freshwater. In this study, three water management scenarios are developed and assessed to the 2060s for their impact on groundwater resources using a hydrogeologic model. Results demonstrate that demand management implemented through an optimized irrigation and crop rotation strategy has the greatest potential to significantly reduce risk of groundwater depletion compared to the other two scenarios—"business as usual" and "30% water-use reduction"—that were evaluated.

Mentoring Temporal and Spatial Variations in Rainfall across Wadi Ar-Rumah, Saudi Arabia

NASA Astrophysics Data System (ADS)

Alharbi, T.; Ahmed, M.

2015-12-01

Across the Kingdom of Saudi Arabia (KSA), the fresh water resources are limited only to those found in aquifer systems. Those aquifers were believed to be recharged during the previous wet climatic period but still receiving modest local recharge in interleaving dry periods such as those prevailing at present. Quantifying temporal and spatial variabilities in rainfall patterns, magnitudes, durations, and frequencies is of prime importance when it comes to sustainable management of such aquifer systems. In this study, an integrated approach, using remote sensing and field data, was used to assess the past, the current, and the projected spatial and temporal variations in rainfall over one of the major watersheds in KSA, Wadi Ar-Rumah. This watershed was selected given its larger areal extent and population intensity. Rainfall data were extracted from (1) the Climate Prediction Centers (CPC) Merged Analysis of Precipitation (CMAP; spatial coverage: global; spatial resolution: 2.5° × 2.5°; temporal coverage: January 1979 to April 2015; temporal resolution: monthly), and (2) the Tropical Rainfall Measuring Mission (TRMM; spatial coverage: 50°N to 50°S; spatial resolution: 0.25° × 0.25°; temporal coverage: January 1998 to March 2015; temporal resolution: 3 hours) and calibrated against rainfall measurements extracted from rain gauges. Trends in rainfall patterns were examined over four main investigation periods: period I (01/1979 to 12/1985), period II (01/1986 to 12/1992), period III (01/1993 to 12/2002), and period IV (01/2003 to 12/2014). Our findings indicate: (1) a significant increase (+14.19 mm/yr) in rainfall rates were observed during period I, (2) a significant decrease in rainfall rates were observed during periods II (-5.80 mm/yr), III (-9.38 mm/yr), and IV (-2.46 mm/yr), and (3) the observed variations in rainfall rates are largely related to the temporal variations in the northerlies (also called northwesterlies) and the monsoonal wind regimes.

Phase equilibria of HP mica schists from the Kamieniec Metamorphic Belt (Sudetes, NE Bohemian Massif)

NASA Astrophysics Data System (ADS)

Szczepanski, Jacek; Golen, Marcin; Anczkiewicz, Robert

2017-04-01

The Kamieniec Metamorphic Belt (KMB), situated in the north-eastern part of the Bohemian Massif, represents the easternmost part of the Variscan Belt of Europe and is interpreted as a fragment of Central Sudetic accretionary wedge containg vestiges of the Saxothuringian crust (Mazur et al., 2015). The KMB comprises a volcano-sedimentary succession dominated by mica schists with intercalations of quartzo-feldspatic schists and subordinate marbles, amphibolites and eclogites. These rocks bear an imprint of Variscan tectonometamorphic reworking. PT conditions of these events were previously estimated at ca. 550 - 590 oC and 7.5 up to 12 kbars (Nowak, 1998; Józefiak, 2000) for mica schists and at 15 kbar and 575 oC for eclogites (Achramowicz et al., 1997). The metamorphic evolution of micaschists comprise the early HP/LT assemblage M1 with Cld+Phe and also earlier reported pseudomorphs after lawsonite (Nowak, 1998) followed by MP/MT mineral assemblage M2 comprising Grt+Pl+Bt+Ms+Qtz±St. Minerals of the M1 and M2 metamorphic events were overprinted by the LP/MT assemblage M3 containing Pl+Chl+Bt+Ms+Qtz±And. Thermodynamic modelling suggests that mineral assemblages record peak-pressure conditions of 20-25 kbar at 520 oC (M1) followed by nearly isothermal decompression to 6-7 kbar, and subsequent metamorphism with record of temperature progression from 500 to 600 oC at 10 kbar (M2) and final retrogression to 3 kbar and 550 oC (M3). The calculated PT conditions indicate a surprisingly low geothermal gradient during the M1 event of 5.5-7.1 oC/km. However, similar eclogitic mica schists with recognised geothermal gradient of ca. 8 oC/km were documented elsewhere from the Saxothuringian domain (Konopásek, 2001). Presented data provides the first report on mica schists from the KMB metamorphosed under eclogite-facies conditions at such low geothermal gradient. Acknowledgements: The study was supported from NCN research grant UMO-2015/17/B/ST10/02212. References Achramowicz

Impact of soil and groundwater corrosion on the Hierakonpolis Temple Town archaeological site, Wadi Abu Sufian, Idfu, Egypt.

PubMed

El-Shishtawy, A M; Atwia, M G; El-Gohary, A; Parizek, R R

2013-06-01

Hierakonpolis, Greek for City of the Hawk, nearly 25 km NW of Idfu (Egypt), is an important and extensive archaeological discovery covering a large area. Its richness in archaeological artifacts makes it a valuable site. It has a valid claim to be the first nation state, as indicated by the Palette of Narmer discovered in its main mound. Geological and hydrogeological investigations at the Hierakonpolis Temple Town site documented nearly a 4.0-m water table rise from as early as 1892 to the present. In addition to the rising water levels, the increase of both subsoil water salinity and humidity threatens and damages fragile carvings and paintings within tombs in Kingdom Hill, the foundation stability of the site, and the known and still to be discovered artifact that recent pottery finds dates at least 4,000 BCE. Representative rock and soil samples obtained from drilled cores in the study area were chosen for conducting detailed grain size and X-ray analysis, light and heavy mineral occurrences, distribution of moisture and total organic matter, and scanning electron microscopy investigations. Mineralogical analysis of clays indicated that the soil samples are composed of smectite/illite mixed layers with varying proportions of smectite to illite. Kaolinite is the second dominant clay constituent, besides occasional chlorite. Swelling of the clay portion of the soil, due to the presence of capillary groundwater, in contact with buried mudbrick walls expands and causes severe damage to important exposed and buried mudbrick structures, including the massive ancient "fort" believed to date from the Second Dynasty (from 2,890 to 2,686 BC). The "fort" is 1.0 km south of the Temple Town mounds near to confluence of Wadi Abu Sufian. Groundwater samples from the shallow aquifer close by the intersection of Wadi Abu Sufian and the Nile flood plain were analyzed for chemical composition and stable isotope ratios. The groundwater in the upper zone (subsoil water) within fine

Link between surface temperature and documented rockfalls in the Mont Blanc massif rockwalls

NASA Astrophysics Data System (ADS)

Magnin, Florence; Deline, Philip; Ravanel, Ludovic

2014-05-01

Recent studies show that rockfall activity has increased along the three past decades in high mountain areas, and permafrost degradation is regarded as the main triggering factor. 433 rockfalls affecting the steep rockwalls of the Mont Blanc massif have been inventoried and documented (time and precise location, topographical and geological settings, volume, conditions, etc.) from 2007 to 2011. With the aim of better understanding geomorphic processes, we address questions about the thermal state of the unstable rockwalls within this study area. A statistical model of the Mean Annual Rock Surface Temperature (MARST) for the 1961-1990 period has been implemented on a 4-m-resolution DEM of the Mont Blanc massif. The model runs with Potential Incoming Solar radiation (PISR) calculated with GIS tools and air temperature parameters computed from Chamonix Météo France's records. 87 rockfalls are located at the geographical margins of the DEM, where the PISR calculation doesn't take account of the surrounding hillshading and biased MARST simulation. Thus, only 346 rockfalls were kept and linked to a MARST value after data sorting. Preliminary results show that rockfalls occurred over a modelled MARST range of -6°C to 5°C. MARSTs ranging from -2.5°C to 2.5°C encompass about 60% of the rockfalls. The mean MARST value for the 346 rockfalls is of -0.9°C. Simulated warm permafrost areas (> -2°C) are therefore appearing as the most affected by instabilities. These first observations reinforce the hypothesis that permafrost degradation is likely the dominant triggering factor of these rockfalls. The 1961-1990 period is supposed to be representative of the conditions at depth that are not affected by the recent climate warming. This means that the here presented results are mainly valuable for rockfalls related to pluri-decadal signal. But they also suggest that MARST model is an interesting tool to explore the link between rockwall instability and permafrost state

Geochemistry and tectonostratigraphy of the basal allochthonous units of SW Iberia (Évora Massif, Portugal): Keys to the reconstruction of pre-Pangean paleogeography in southern Europe

NASA Astrophysics Data System (ADS)

Fernández, Rubén Díez; Fuenlabrada, José Manuel; Chichorro, Martim; Pereira, M. Francisco; Sánchez-Martínez, Sonia; Silva, José B.; Arenas, Ricardo

2017-01-01

The basal allochthonous units of NW and SW Iberia are members of an intra-Gondwana suture zone that spreads across the Iberian Massif and was formed during the collision of Gondwana and Laurussia in the late Paleozoic. This suture zone is made of allochthonous terranes and is currently preserved as a tectonically dismembered ensemble. A multi-proxy analysis is applied to the basal allochthonous units of Iberia to test their affinity and potential usage for tracing a suture zone. A comparison of the lithostratigraphy, tectonometamorphic evolution, geochronology, and geochemical characteristics of the Ediacaran series of these units reveals striking affinities. They derive from rather similar immature sedimentary successions, deposited along the same continental margin, and in relation to a Cadomian magmatic arc. Sm-Nd systematics indicates that the isotopic sources are among the oldest of the Iberian Massif (ca. 2.15-1.5 Ga), suggesting a very strong contribution from the West African Craton. These Ediacaran series were affected by high-P and low- to medium-T metamorphism (blueschist to eclogite facies) during the Late Devonian (ca. 370 Ma). They occur below allochthonous ophiolitic sequences, and on top of autochthonous or parautochthonous domains lacking of high-P and low- to medium-T Devonian metamorphism, i.e., tectonically sandwiched between lithosphere-scale thrusts. The combination of all these characteristics makes these particular Ediacaran series different from the rest of the terranes of the Iberian Massif. Such singularity could be useful for tracing more occurrences of the same suture zone along the Variscan orogen, particularly in cases where its preservation and recognition may be cryptic. It also contributes to improve the paleogeographic reconstruction of the margin of Gondwana during the Ediacaran.

Late Mesoproterozoic to Early Paleozoic history of metamorphic basement from the southeastern Chiapas Massif Complex, Mexico, and implications for the evolution of NW Gondwana

NASA Astrophysics Data System (ADS)

Weber, Bodo; González-Guzmán, Reneé; Manjarrez-Juárez, Román; Cisneros de León, Alejandro; Martens, Uwe; Solari, Luigi; Hecht, Lutz; Valencia, Victor

2018-02-01

In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined "El Triunfo Complex" located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at 650 °C and 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian ( 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from 457 to 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of

The cooling history and the depth of detachment faulting at the Atlantis Massif oceanic core complex

NASA Astrophysics Data System (ADS)

Schoolmeesters, Nicole; Cheadle, Michael J.; John, Barbara E.; Reiners, Peter W.; Gee, Jeffrey; Grimes, Craig B.

2012-10-01

Oceanic core complexes (OCCs) are domal exposures of oceanic crust and mantle interpreted to be denuded to the seafloor by large slip oceanic detachment faults. We combine previously reported U-Pb zircon crystallization ages with (U-Th)/He zircon thermochronometry and multicomponent magnetic remanence data to determine the cooling history of the footwall to the Atlantis Massif OCC (30°N, MAR) and help establish cooling rates, as well as depths of detachment faulting and gabbro emplacement. We present nine new (U-Th)/He zircon ages for samples from IODP Hole U1309D ranging from 40 to 1415 m below seafloor. These data paired with U-Pb zircon ages and magnetic remanence data constrain cooling rates of gabbroic rocks from the upper 800 m of the central dome at Atlantis Massif as 2895 (+1276/-1162) °C Myr-1 (from ˜780°C to ˜250°C); the lower 600 m of the borehole cooled more slowly at mean rates of ˜500 (+125/-102) °C Myr-1(from ˜780°C to present-day temperatures). Rocks from the uppermost part of the hole also reveal a brief period of slow cooling at rates of ˜300°C Myr-1, possibly due to hydrothermal circulation to ˜4 km depth through the detachment fault zone. Assuming a fault slip rate of 20 mm/yr (from U-Pb zircon ages of surface samples) and a rolling hinge model for the sub-surface fault geometry, we predict that the 780°C isotherm lies at ˜7 km below the axial valley floor, likely corresponding both to the depth at which the semi-brittle detachment fault roots and the probable upper limit of significant gabbro emplacement.

Late Carboniferous remagnetisation of Palaeozoic rocks in the NE Rhenish Massif, Germany

NASA Astrophysics Data System (ADS)

Zwing, A.; Bachtadse, V.; Soffel, H. C.

During stepwise thermal and alternating field demagnetisation experiments on Devonian and Lower Carboniferous carbonate and clastic rocks from the north-eastern part of the Rhenish Massif, Germany, three components of magnetisation (A, B, C) are identified. Component A is a recent viscous overprint that parallels the local present day geomagnetic field. Component B is mainly observed from 260 up to 550 °C during thermal demagnetisation and is carried by magnetite. In two localities, where red siltstones and red carbonate rocks were sampled, component B is stable up to 670 °C, indicating the presence of hematite. Three clusters of in situ B directions can be identified, which are controlled by the tectonic position of the sampling areas. These are from NW to SE: the Remscheid anticline (RA), the Lüdenscheid syncline (LS) and the Attendorn and Wittgenstein synclines (AS/WS). Standard and inclination-only fold tests, using parametric resampling, yield optimal statistical parameters at increasing amounts of untilting ranging from 0% in the South up to 57% in the North of the NE Rhenish Massif. Despite the variations in optimal untilting, the resulting site mean directions of component B do not differ significantly in inclination. These results are interpreted to reflect the acquisition of magnetisation during progressive northward migration of the deformation front in Late Carboniferous times. The resulting palaeolatitudes (RA: 1°S +2°-3°; LS: 2°S +3°-2°; AS/WS: 1°S +3°-4°) are in good agreement with the predicted position of the sampling area in the Late Carboniferous, as derived from a published Apparent Polar Wander Path for Baltica and Laurentia. The unblocking temperature spectra and the synfolding nature of B yield strong evidence that chemical processes, possibly driven by fluid migration during orogenesis, caused this remagnetisation. A third component C was observed in zones of tight folding with steeply dipping to overturned bedding planes and is

The influence of melt infiltration on the Li and Mg isotopic composition of the Horoman Peridotite Massif

NASA Astrophysics Data System (ADS)

Lai, Yi-Jen; Pogge von Strandmann, Philip A. E.; Dohmen, Ralf; Takazawa, Eiichi; Elliott, Tim

2015-09-01

We have analysed the Li and Mg isotope ratios of a suite of samples from the Horoman Peridotite Massif. Our results show that most Li and all Mg isotopic compositions of the Horoman peridotites are constant over 100 metres of continuous outcrop, yielding values for pristine mantle of δ7Li = 3.8 ± 1.4‰ (2SD, n = 9), δ25Mg = -0.12 ± 0.02‰ and δ26Mg = -0.23 ± 0.04‰ (2SD, n = 17), in keeping with values for undisturbed mantle xenoliths. However, there are also some anomalously low δ7Li values (-0.2‰ to 1.6‰), which coincide with locations that show enrichment of incompatible elements, indicative of the prior passage of small degree melts. We suggest Li diffused from infiltrating melts with high [Li] into the low [Li] minerals and kinetically fractionated 7Li/6Li as a result. Continued diffusion after the melt flow had ceased would have resulted in the disappearance of this isotopically light signature in less than 15 Ma. In order to preserve this feature, the melt infiltration must have been a late stage event and the massif must have subsequently cooled over a maximum of ∼0.3 Ma from peak temperature (950 °C, assuming the melts were hydrous) to Li closure temperature (700 °C), likely during emplacement. The constant δ26Mg values of Horoman peridotites suggest that chemical potential gradients caused by melt infiltration were insufficient to drive associated δ26Mg fractionation greater than our external precision of 0.03‰.

Petrology and geochemistry of primary magmas trapped in melt inclusions in scoria of Beaunit Maar (Chaîne des Puys, Massif Central, France)

NASA Astrophysics Data System (ADS)

Jannot, S.; Schiano, P.; Boivin, P.; Clocchiatti, R.; Chazot, G.

2003-04-01

The Massif Central area, characterized by a typical intraplate alkaline serie, is the largest magmatic province of the West-European Rift system. Although it has been the subject of several studies, the nature of Massif Central sources is still a matter of debate and many hypotheses are proposed, including deep-rooted continental hotspot, metasomatised spinel lherzolites and an asthenospheric flow linked to the lithospheric root of the Alpine chain. The Chaîne des Puys is the last magmatic province of the French Massif Central and is composed of hundred young well-preserved volcanoes. The present work aims to supply information on the nature and the origin of the source chemistry of alkaline serie from the Chaîne des Puys, by characterizing the trace and major element composition of minute melts preserved as quenched glass inclusions inside olivines phenocrysts in scoria from the Beaunit Maar. Heating stage experiments performed at ambient pressure on partially crystallised primary melt inclusions suggest CO_2 oversaturation of the trapped melt, and an entrapment temperature around 1200^oC±10^oC. Daughter minerals analyses point to a Ti-and Ca-rich basaltic paragenesis, in good agreement with that of erupted basalts from the Chaîne des Puys. Major element compositions show that melts trapped in inclusions evolve by limited fractional crystallization. Inclusions trapped in the more primitive olivine phenocrysts (Fo85) have alkali-basalt compositions that fall on the primitive end of the compositional trend define by the lavas of the Chaîne des Puys. Their major element chemistry rules out the hypothesis of a mantle source in the spinel stability field and requires a garnet-bearing mantle source. Analyzed for trace-element composition by LA-ICP-MS, they display homogeneous, enriched patterns, similar to those characterizing oceanic island and continental basalts. They have high concentration of LILE and LREE/HREE ratios. Such trace-element feature are typical of

A continuous structural characterisation of Atlantis Massif using an integrated analysis of oriented downhole imagery and logging data

NASA Astrophysics Data System (ADS)

Pressling, Nicola; Morris, Antony; John, Barbara; MacLeod, Christopher

2010-05-01

Continuous wireline logging data are invaluable when less than 100% of drilled core material is recovered. The data provide information on missing units, record the true depth of features and uniquely constrain spatial orientation. Only by fully integrating continuous, oriented logging data and discrete, finer-scale core data can we develop a complete structural interpretation for drill holes that is not limited by sampling bias. Integrated Ocean Drilling Program (IODP) Expedition 304/305 sampled the Atlantis Massif oceanic core complex at the intersection between the Mid-Atlantic Ridge and the Atlantis Transform fault at 30°N. Hole U1309D penetrated 1415.5m into the central dome of the massif, which exposes the corrugated detachment fault surface denuding the lower crust and upper mantle. The recovered section is dominated by gabbro compositions that are complexly faulted and layered on a variety of scales, reflecting the complicated interplay between magmatic and tectonic processes controlling the formation, evolution and deformation of oceanic crust at slow-spreading ridges. The average core recovery at Atlantis Massif was 74%. Therefore, to augment and constrain structural interpretations based on limited core material, we used the Formation MicroScanner (FMS) wireline logging tool that measures microresistivity contrasts in the immediate vicinity of the borehole wall formation. The data are presented as an unwrapped image of the borehole cylinder, and inclined planar structural features that intersect the borehole, such as faults or veins, are shown as darker (more conductive) sinusoidal traces. The true dip and azimuth of these features can be calculated directly due to the inclusion of an accelerometer and magnetometer on the toolstring, which record the position and spatial orientation (with respect to magnetic north) of the tool within the borehole, respectively. 4324 distinct structural features have been identified in the FMS images between 97 and 1415

Application of GIS technologies to monitor secondary radioactive contamination in the Delegen mountain massif

NASA Astrophysics Data System (ADS)

Alipbeki, O.; Kabzhanova, G.; Kurmanova, G.; Alipbekova, Ch.

2016-06-01

The territory of the Degelen mountain massif is located within territory of the former Semipalatinsk nuclear test site and it is an area of ecological disaster. Currently there is a process of secondary radioactive contamination that is caused by geodynamic processes activated at the Degelen array, violation of underground hydrological cycles and as a consequence, water seepage into the tunnels. One of the methods of monitoring of geodynamic processes is the modern technology of geographic information systems (GIS), methods of satellite radar interferometry and high accuracy satellite navigation system in conjunction with radioecological methods. This paper discusses on the creation of a GIS-project for the Degelen array, facilitated by quality geospatial analysis of the situation and simulation of the phenomena, in order to maximize an objective assessment of the radiation situation in this protected area.

Reconstruction of the rock fall/avalanche frequency in the Mont Blanc massif since the Last Glacial Maximum. New results using 10Be cosmogenic dating and reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Gallach, Xavi; Ogier, Christophe; Ravanel, Ludovic; Deline, Philip; Carcaillet, Julien

2017-04-01

Rockfalls and rock avalanches are active processes in the Mont Blanc massif, with infrastructure and alpinists at risk. Thanks to a network of observers (hut keepers, mountain guides, alpinists) set up in 2007 present rockfalls are well surveyed and documented. Rockfall frequency over the past 150 years has been studied by comparison of historical photographs, showing that it strongly increased during the three last decades, especially during hot periods like the summer of 2003 and 2015, due to permafrost degradation driven by the climate change. In order to decipher the possible relationship between rockfall occurrence and the warmest periods of the Lateglacial and the Holocene, we start to study the morphodynamics of some selected high-elevated (>3000 m a.s.l.) rockwalls of the massif on a long timescale. Contrary to low altitude, deglaciated sites where study of large rockfall deposits allows to quantify frequency and magnitude of the process, rockfalls that detached from high-elevated rockwalls are no more noticeable as debris were absorbed and evacuated by the glaciers. Therefore, our study focuses on the rockfall scars. Their 10Be dating gives us the rock surface exposure age from present to far beyond the Last Glacial Maximum, interpreted as the rockfall ages. TCN dating of rockfalls has been carried out at the Aiguille du Midi in 2007 (Boehlert et al., 2008), and three other sites in the Mont Blanc massif in 2011 (Gallach et al., submitted). Here we present a new data set of rockfall dating carried out in 2015 that improves the 2007 and 2011 data. Furthermore, a relationship between the colour of the Mont Blanc granite and its exposure age has been shown: fresh rock surface is light grey (e.g. in recent rockfall scars) whereas weathered rock surface is in the range grey to orange/red: the redder a rock surface, the older its age. Here, reflectance spectroscopy is used to quantify the granite surface colour. Böhlert, R., Gruber, S., Egli, M., Maisch, M

Palaeostress perturbations near the El Castillo de las Guardas fault (SW Iberian Massif)

NASA Astrophysics Data System (ADS)

García-Navarro, Encarnación; Fernández, Carlos

2010-05-01

Use of stress inversion methods on faults measured at 33 sites located at the northwestern part of the South Portuguese Zone (Variscan Iberian Massif), and analysis of the basic dyke attitude at this same region, has revealed a prominent perturbation of the stress trajectories around some large, crustal-scale faults, like the El Castillo de las Guardas fault. The results are compared with the predictions of theoretical models of palaeostress deviations near master faults. According to this comparison, the El Castillo de las Guardas fault, an old structure that probably reversed several times its slip sense, can be considered as a sinistral strike-slip fault during the Moscovian. These results also point out the main shortcomings that still hinder a rigorous quantitative use of the theoretical models of stress perturbations around major faults: the spatial variation in the parameters governing the brittle behaviour of the continental crust, and the possibility of oblique slip along outcrop-scale faults in regions subjected to general, non-plane strain.

Geochemistry and mineralogy of Pd in the magnetitite layer within the upper gabbro of the Mesoarchean Nuasahi Massif (Orissa, India)

NASA Astrophysics Data System (ADS)

Prichard, Hazel M.; Mondal, Sisir K.; Mukherjee, Ria; Fisher, Peter C.; Giles, Nicolas

2018-04-01

Palladium concentrations of 1-3 ppm with an average Pt/Pd ratio of 0.15 have been located for the first time in a magnetitite layer in the Nuasahi Massif in Orissa India. This layer occurs at a high stratigraphic level in the complex and is nearly 4-km long and 5-12-m thick. The sections of the Pd-rich zone identified to date extend over a distance of 1 km at the southern end of the layer. Several phases of mineralization are evident. The first, primary assemblage of platinum-group minerals (PGM) contains Pd-sulfides (vysotskite), Pd-Pb alloys (zvyagintsevite), and a Pd-In alloy, a mineral probably new to mineralogy. These PGM are confined to central magnetite grains in the magnetitites. The magnetite grains with exsolved fine laths of ilmenite at centers are referred to as central magnetite grains. These central magnetite grains are commonly surrounded by blebs of ilmenite and magnetite that contain the majority of the PGM. These are dominated by Pd-antimonides, variably altered to Pd-oxides, and other PGM including PtAs2 (sperrylite), RuS2 (laurite), and IrRhAsS (irarsite/hollingwothite). Many of these PGM also occur in the interstitial silicates, with rare occurrences in the central magnetite grains. We propose that the platinum-group elements (PGE) crystallized during a minor sulfide saturation event that occurred as the magnetitites crystallized. This event produced the minor Cu-sulfides in these magnetitites. Later introduction of antimony and arsenic, during the alteration event that produced the blebby ilmenite and magnetite, led to the more primary PGM being succeeded by the main PGM assemblage, dominated by Pd-antimonides. These are associated with secondary Cu minerals and sperrylite. Subsequent oxidation during weathering in the hot wet Indian climate produced the Pd-oxides. The Nuasahi Massif is a sill-like Archean layered ultramafic-mafic intrusion genetically linked to high-Mg siliceous basalt or boninites and is characterized by unusually thick

Structural interpretation of aeromagnetic data for the Wadi El Natrun area, northwestern desert, Egypt

NASA Astrophysics Data System (ADS)

Ibraheem, Ismael M.; Elawadi, Eslam A.; El-Qady, Gad M.

2018-03-01

The Wadi El Natrun area in Egypt is located west of the Nile Delta on both sides of the Cairo-Alexandria desert road, between 30°00‧ and 30°40‧N latitude, and 29°40‧ and 30°40‧E longitude. The name refers to the NW-SE trending depression located in the area and containing lakes that produce natron salt. In spite of the area is promising for oil and gas exploration as well as agricultural projects, Geophysical studies carried out in the area is limited to the regional seismic surveys accomplished by oil companies. This study presents the interpretation of the airborne magnetic data to map the structure architecture and depth to the basement of the study area. This interpretation was facilitated by applying different data enhancement and processing techniques. These techniques included filters (regional-residual separation), derivatives and depth estimation using spectral analysis and Euler deconvolution. The results were refined using 2-D forward modeling along three profiles. Based on the depth estimation techniques, the estimated depth to the basement surface, ranges from 2.25 km to 5.43 km while results of the two-dimensional forward modeling show that the depth of the basement surface ranges from 2.2 km to 4.8 km. The dominant tectonic trends in the study area at deep levels are NW (Suez Trend), NNW, NE, and ENE (Syrian Arc System trend). The older ENE trend, which dominates the northwestern desert is overprinted in the study area by relatively recent NW and NE trends, whereas the tectonic trends at shallow levels are NW, ENE, NNE (Aqaba Trend), and NE. The predominant structure trend for both deep and shallow structures is the NW trend. The results of this study can be used to better understand deep-seated basement structures and to support decisions with regard to the development of agriculture, industrial areas, as well as oil and gas exploration in northern Egypt.

Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

NASA Astrophysics Data System (ADS)

Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

2017-06-01

Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

NASA Astrophysics Data System (ADS)

Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.

2014-03-01

Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

Endolithic microbial communities in carbonate precipitates from serpentinite-hosted hyperalkaline springs of the Voltri Massif (Ligurian Alps, Northern Italy).

PubMed

Quéméneur, Marianne; Palvadeau, Alexandra; Postec, Anne; Monnin, Christophe; Chavagnac, Valérie; Ollivier, Bernard; Erauso, Gaël

2015-09-01

The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmospheric carbon dioxide forms brownish carbonate precipitates covering the bedrock at the springs. Diverse archaeal and bacterial communities were detected in these carbonate precipitates using 454 pyrosequencing analyses of 16S ribosomal RNA (rRNA) genes. Archaeal communities were dominated by members of potential methane-producing and/or methane-oxidizing Methanobacteriales and Methanosarcinales (Euryarchaeota) together with ammonia-oxidizing Nitrososphaerales (Thaumarchaeota) similar to those found in other serpentinization-driven submarine and terrestrial ecosystems. Bacterial communities consisted of members of the Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, Chloroflexi, and Verrucomicrobia phyla, altogether accounting for 92.2% of total retrieved bacterial 16S rRNA gene sequences. Amongst Bacteria, potential chemolithotrophy was mainly associated with Alpha- and Betaproteobacteria classes, including nitrogen-fixing, methane-oxidizing or hydrogen-oxidizing representatives of the genera Azospirillum, Methylosinus, and Hydrogenophaga/'Serpentinomonas', respectively. Besides, potential chemoorganotrophy was attributed mainly to representatives of Actinobacteria and Planctomycetales phyla. The reported 16S rRNA gene data strongly suggested that hydrogen, methane, and nitrogen-based chemolithotrophy can sustain growth of the microbial communities inhabiting the carbonate precipitates in the hyperalkaline springs of the Voltri Massif, similarly to what was previously observed in other serpentinite-hosted ecosystems.

CRE dating on the scarps of large landslides affecting the Belledonne massif ( French Alps)

NASA Astrophysics Data System (ADS)

Lebrouc, V.; Baillet, L.; Schwartz, S.; Jongmans, D.; Gamond, J. F.; Bourles, D.; Le Roux, O.; Carcaillet, J.; Braucher, R.

2012-04-01

The southwestern edge of the Belledonne Massif (French Alps) consists of micaschists unconformably covered with Mesozoic sediments and Quaternary deposits. The morphology corresponds to a glacial plateau (Mont Sec plateau) bordered by steep slopes (around 40°), where moraines and peat bog subsist. The massif is incised by the East-West trending Romanche valley that was shaped by several cycles of quaternary glaciations and deglaciations. Slopes are affected by several active or past large scale rock mass instabilities. Cosmic Ray Exposure (CRE) dating was applied on the head scarps of three large landslides, one of which being the active Séchilienne landslide whose headscarp was already dated by Leroux et al. [2009]. Dating results suggest a concomitant initiation of these instabilities at about 7 ± 2 10Be ka, thousands years after the total downwastage of the valley. A different kinematic behaviour was however observed on two contiguous landslides for which continuous exposure profiles were obtained. On the Séchilienne landslide, 23 samples were collected from internal and lateral scarps, as well as on polished bedrock surfaces, with the aim of dating the internal kinematics of the landslide. Preliminary dating results obtained on polished surfaces and near the top of the scarps show unexpected low 10Be concentrations, suggesting the existence of thin moraine or peat bog deposits masking the bedrock, which have been subsequently eroded. The minimum thickness of these deposits was estimated assuming a constant denudation rate over time. Exposure date profiles show that the studied lateral and internal scarps were initiated at the same period as the Sechilienne headscarp. An increase in the exposure rate was also observed between 2 and 1 ka, in agreement with that evidenced along the headscarp. Forty other samples have been collected in the landslide to corroborate these results. Reference Le Roux, O., S. Schwartz , J.-F. Gamond, D. Jongmans, D. Bourles, R

Trondhjemite-granodiorite intrusive magmatism of the Losevo lithotectonic zone of the Voronezh crystalline massif

NASA Astrophysics Data System (ADS)

Skryabin, V. Yu.; Terentiev, R. A.

2014-10-01

The mineralogical-petrographic, petrochemical, and geochemical characteristics of the trondhjemite-granodiorite intrusions widespread among the volcanoterrigenous rocks of the eastern part of the Voronezh crystalline massif are studied. The rocks are characterized by cotectic quartz-plagioclase differentiation and differentiated (La/Yb = 31) REE pattern and are enriched in LILE with a decrease in the K/Rb and Zr/Hf ratios and an increase in the Th/U ratio by 1.5-2 times relative to subduction trondhjemites and their volcanic analogs from the modern and young island arcs. These data allow us to conclude that generation of the trondhjemite magma is a result of melting of the rocks of the continental crust during collision. The concordant (SHRIMP) age of trondhjemites is 2047 ± 11 Ma, and the age of zircon cores probably entrapped from the host rocks by the trondhjemitic melt is 2172 ± 17 Ma.

Nature of the Paleocene/Eocene (P/E) boundary in Sinai, Egypt

NASA Astrophysics Data System (ADS)

Obaidalla, Nageh A.; Abdel-Maksoud, Nasr A.; Hosny, Atef M.; Mahfouz, Kamel H.

2017-12-01

The P/E boundary is studied at eight stratigraphic sections in Sinai, Egypt, which are nearly distributed in a stratigraphic profile from north to south as follows: Al-Hasanah, Sudr Al-Hitan, Wadi Sudr, Al-Thamad, Abu Qada, Wadi Matulla, Wadi Nukhul and Wadi Feiran. This study includes field, litho- and bio-stratigraphic analyses that enabled to delineate several hiatuses which may be due to the occurrence of tectonic activity that may be related to the echo of the Syrian Arc Orogeny at the P/E boundary. Generally, in Egypt the P/E boundary is marked by the occurrence of distinctive five beds, named by El Dababiya Quarry Member. At Wadi Nukhul, Wadi Matulla and Wadi Feiran sections, El Dababiya Quarry Member is well represented and the P/E boundary is conformable and resembles the GSSP section. Although El Dababiya Quarry Member is represented at Al-Hasanah section, the P/E boundary is marked by the occurrence of a minor hiatus at the end of Paleocene. Moreover, at Al Thamad section, El Dababiya Quarry Member is partially represented. On the other hand, at Sudr Al-Hitan, Wadi Sudr and Abu Qada sections, El Dababiya Quarry Member is completely absent due to a major hiatus.

Geochronology and geochemistry of late Paleozoic-early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng

2017-08-01

We undertook geochemical and geochronological studies on late Paleozoic-early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol-Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral-subhedral, display oscillatory growth zoning, and have Th/U values of 0.14-6.48, indicating a magmatic origin. U-Pb dating of zircon using SIMS and LA-ICP-MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early-Middle Triassic (246-238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe-Nenjiang oceanic plate. Their positive εHf(t) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444-827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf(t) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500-607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna-Xing'an and Songnen-Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol-Okhotsk oceanic plate was subducting beneath the Erguna Massif.

Mineral textures in Serpentine-hosted Alkaline Springs from the Oman ophiolite

NASA Astrophysics Data System (ADS)

Giampouras, Manolis; Garcia-Ruiz, Juan Manuel; Bach, Wolfgang; Garrido, Carlos J.; Los, Karin; Fussmann, Dario; Monien, Monien

2017-04-01

Meteoric water infiltration in ultramafic rocks leads to serpentinization and the formation of subaerial, low temperature, hydrothermal alkaline springs. Here, we present a detailed investigation of the mineral precipitation mechanisms and textural features of mineral precipitates, along as the geochemical and hydrological characterization, of two alkaline spring systems in the Semail ophiolite (Nasif and Khafifah sites, Wadi Tayin massif). The main aim of the study is to provide new insights into mineral and textural variations in active, on-land, alkaline vents of the Oman ophiolite. Discharge of circulating fluids forms small-scale, localized hydrological catchments consisting in unevenly interconnected ponds. Three different types of waters can be distinguished within the pond systems: i) Mg-type; alkaline (7.9 < pH < 9.5), Mg-HCO3-rich waters; ii) Ca-type; hyper-alkaline (pH > 11.6), Ca-OH-rich waters; and iii) Mix-type waters arising from the mixing of Mg-type and Ca-type waters (9.6 < pH < 11.5). Phreeqc geochemical speciation software was used to determine the saturation state and the relationship between the theoretical supersaturation (S) and rate of supersaturation (S˚ ) of solid phases. Simple mixing models using Phreeqc MIX_code revealed good mixing correlation (R2 ≥0.93) between measured and predicted values for K, Na, Cl, Mg and sulphate. Al, Ca, Si, Ba, Sr and TIC showed poorer correlations. Mineral and textural characterization from different types of water and individual ponds were carried out by X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscopy coupled to dispersive energy spectroscopy (FE-SEM-EDS). Aragonite and calcite are the dominant minerals (95 vol.%) of the total mineralogical index in all sites. Mg-type waters host hydrated magnesium carbonates (nesquehonite) and magnesium hydroxycarbonate hydrates (artinite) due to evaporation. Brucite, hydromagnesite and dypingite presence in Mix-type waters

Palaeomagnetic constraints on the evolution of the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N)

NASA Astrophysics Data System (ADS)

Morris, Antony; Pressling, Nicola; Gee, Jeffrey; John, Barbara; MacLeod, Christopher

2010-05-01

Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. They represent a fundamental component of the seafloor spreading system at slow and ultraslow axes. For example, recent analyses suggest that detachment faults may underlie more than 50% of the Mid Atlantic Ridge (MAR) and may take up most of the overall plate divergence at times when magma supply to the ridge system is reduced. The most extensively studied oceanic core complex is Atlantis Massif, located at 30°N on the MAR. This forms an inside-corner bathymetric high at the intersection of the Atlantis Transform Fault and the MAR. The central dome of the massif exposes the corrugated detachment fault surface and was drilled during IODP Expedition 304/305. This sampled a 1.4 km faulted and complexly layered footwall section dominated by gabbroic lithologies with minor ultramafic rocks. The core (Hole U1309D) reflects the interplay between magmatism and deformation prior to, during, and subsequent to a period of footwall displacement and denudation associated with slip on the detachment fault. Palaeomagnetic analyses demonstrate that the gabbroic sequences at Atlantis Massif carry highly stable remanent magnetizations that provide valuable information on the evolution of the section. Thermal demagnetization experiments recover high unblocking temperature components of reversed polarity (R1) throughout the gabbroic sequences. In a number of intervals, however, the gabbros exhibit a complex remanence structure with the presence of intermediate temperature normal (N1) and lower temperature reversed (R2) polarity components, suggesting an extended period of remanence acquisition during different polarity intervals. Sharp break-points between different polarity components suggest that they were acquired by a thermal mechanism. There appears to be no correlation between remanence structure and either the igneous

The mineral resource potential of the Wadi al Jarir and Al Jurdhawiyah quadrangles, sheets 25/42C and 25/42D, Kingdom of Saudi Arabia

USGS Publications Warehouse

Fenton, Michael D.

1983-01-01

Areas with potential for metallic mineral deposits in the Wadi al Jarir and Al Jurdhawiyah quadrangles, northeastern Arabian Shield, have been identified by reconnaissance rock geochemistry, inspection of ancient prospects, and interpretation of previous work. The ancient prospects of Abraq Shawfan, Abraq Shawfan South, Ad Du'ibi, Ad Du'ibi West, and Ad Dirabi are not recommended for further study. The Bald al Jimalah East ancient lead-silver mine should be drilled to investigate its mineral potential at depth and to.determine its apparent relationship to the nearby Baid al Jimalah West tungsten-tin prospect. High precious metal and copper contents confirmed at the Jarrar ancient prospect suggest additional study. Preliminary results of core and percussion drilling at the Bald al Jimalah West tungsten-tin prospect indicate that the mineralized rocks decrease in grade with depth and are not suitable for current economic exploitation. Geochemically anomalous areas in both plutonic and layered volcanic and clastic terrane are possible sites of significant base metal, molybdenum, tin, tungsten, and rare-earth element mineralization.

Structural evolution of the Semail Ophiolite metamorphic sole, Wadi Hawasina and Northern Jebel Nakhl Culmination, Oman

NASA Astrophysics Data System (ADS)

Hurtado, C.; Bailey, C.; Visokay, L.; Scharf, A.

2017-12-01

The Semail ophiolite is the world's largest and best-exposed ophiolite sequence, however the processes associated with both oceanic detachment and later emplacement onto the Arabian continental margin remain enigmatic. This study examines the upper mantle section of the ophiolite, its associated metamorphic sole, and the autochthonous strata beneath the ophiolite at two locations in northern Oman. Our purpose is to understand the structural history of ophiolite emplacement and evaluate the deformation kinematics of faulted and sheared rocks in the metamorphic sole. At Wadi Hawasina, the base of the ophiolite is defined by a 5- to 15-m thick zone of penetratively-serpentinized mylonitic peridotite. Kinematic indicators record top-to-the SW (reverse) sense-of-shear with a triclinic deformation asymmetry. An inverted metamorphic grade is preserved in the 300- to 500-m thick metamorphic sole that is thrust over deep-water sedimentary rocks of the Hawasina Group. The study site near Buwah, in the northern Jebel Nakhl culmination, contains a N-to-S progression of mantle peridotite, metamorphic sole, and underlying Jurassic carbonates. Liswanite crops out in NW-SE trending linear ridges in the peridotite. The metamorphic sole includes well-foliated quartzite, metachert, and amphibolite. Kinematic evidence indicates that the liswanite and a serpentinized mélange experienced top to-the north (normal) sense-of-shear. Two generations of E-W striking, N-dipping normal faults separate the autochthonous sequence from the metamorphic sole, and also cut out significant sections of the metamorphic sole. Fabric analysis reveals that the metamorphic sole experienced flattening strain (K<0.2) that accumulated during pure shear-dominated general shear (Wk<0.4). Normal faulting and extension at the Buwah site indicates that post-ophiolite deformation is significant in the Jebel Akhdar and Jebel Nakhl culminations.

Weathering profiles in granitoid rocks of the Sila Massif uplands, Calabria, southern Italy: New insights into their formation processes and rates

NASA Astrophysics Data System (ADS)

Scarciglia, Fabio; Critelli, Salvatore; Borrelli, Luigi; Coniglio, Sabrina; Muto, Francesco; Perri, Francesco

2016-05-01

In this paper we characterized several weathering profiles developed on granitoid rocks in the Sila Massif upland (Calabria, southern Italy), integrating detailed macro- and micromorphological observations with physico-mechanical field tests and petrographic, mineralogical and geochemical analyses. We focused our attention on the main weathering and pedogenetic processes, trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties, and two common weathering indices, such as the micropetrographic index (Ip) and the chemical index of alteration (CIA). Our results showed that sericite on plagioclase and biotite chloritization, that represent inherited features formed during late-stage hydrothermal alteration of granitoid rocks, may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions, especially in lower weathering grade classes. Moreover, the frequent identification of Fe-Mn oxides and clay coatings of illuvial origin (rather than or in addition to those formed in situ), both at the macro- and microscale, may also explain an overestimation of the weathering degree with respect to field-based classifications. Finally, some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes (cryoclastism and thermoclastism), that lead to rock breakdown even when chemical weathering is not well developed. Hence, our study showed that particular caution is needed for evaluating weathering grades, because traditional field and geochemical-petrographic tools may be biased by inherited hydrothermal alteration, physical weathering and illuvial processes. On the basis of chronological constraints to soil formation obtained from a 42 ka-old volcanic input (mixed to granite parent materials) detected in the soil cover of the Sila Massif upland, a first attempt to estimate

Seismotectonic significance of the 2008–2010 Walloon Brabant seismic swarm in the Brabant Massif, Belgium

USGS Publications Warehouse

Van Noten, Koen; Lecocq, Thomas; Shah, Anjana K.; Camelbeeck, Thierry

2015-01-01

Between 12 July 2008 and 18 January 2010 a seismic swarm occurred close to the town of Court-Saint-Etienne, 20 km SE of Brussels (Belgium). The Belgian network and a temporary seismic network covering the epicentral area established a seismic catalogue in which magnitude varies between ML -0.7 and ML 3.2. Based on waveform cross-correlation of co-located earthquakes, the spatial distribution of the hypocentre locations was improved considerably and shows a dense cluster displaying a 200 m-wide, 1.5-km long, NW-SE oriented fault structure at a depth range between 5 and 7 km, located in the Cambrian basement rocks of the Lower Palaeozoic Anglo-Brabant Massif. Waveform comparison of the largest events of the 2008–2010 swarm with an ML 4.0 event that occurred during swarm activity between 1953 and 1957 in the same region shows similar P- and S-wave arrivals at the Belgian Uccle seismic station. The geometry depicted by the hypocentral distribution is consistent with a nearly vertical, left-lateral strike-slip fault taking place in a current local WNW–ESE oriented local maximum horizontal stress field. To determine a relevant tectonic structure, a systematic matched filtering approach of aeromagnetic data, which can approximately locate isolated anomalies associated with hypocentral depths, has been applied. Matched filtering shows that the 2008–2010 seismic swarm occurred along a limited-sized fault which is situated in slaty, low-magnetic rocks of the Mousty Formation. The fault is bordered at both ends with obliquely oriented magnetic gradients. Whereas the NW end of the fault is structurally controlled, its SE end is controlled by a magnetic gradient representing an early-orogenic detachment fault separating the low-magnetic slaty Mousty Formation from the high-magnetic Tubize Formation. The seismic swarm is therefore interpreted as a sinistral reactivation of an inherited NW–SE oriented isolated fault in a weakened crust within the Cambrian core of

Métamorphisme miocène de granites panafricains dans le massif de l'Edough (Nord-Est de l'Algérie)

NASA Astrophysics Data System (ADS)

Hammor, Dalila; Lancelot, Joël

1998-09-01

The Edough Massif is the easternmost crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595 ± 51 My and 606 ± 55 My for an orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18 ± 5 My U-Pb age that points to a Miocene age of the high-temperature metamorphism.

Raman imaging of fluid inclusions in garnet from UHPM rocks (Kokchetav massif, Northern Kazakhstan).

PubMed

Korsakov, Andrey V; Dieing, Thomas; Golovin, Aleksandr V; Toporski, Jan

2011-10-01

Confocal Raman imaging of fluid inclusions in garnet porphyroblasts from diamond-grade metamorphic calc-silicate rocks from the Kumdy-Kol microdiamond deposit (Kokchetav Massif, Northern Kazakhstan) reveals that these fluid inclusions consist of almost pure water with different step-daughter phases (e.g., calcite, mica and rare quartz). These fluid inclusions are characterized by negative crystal shape of the host-garnet and they exclusively occur within the core of garnet porphyroblasts. These observations are consistent with their primary origin, most likely at ultrahigh-pressure (UHP) metamorphic conditions. The euhedral newly formed garnet, different in color and composition, was found to be associated with these fluid inclusions. It is proposed that newly formed garnet and water fluid inclusions appear by reaction between the hydrous fluid and the garnet-host. These fluid inclusions provide an unequivocal record of almost pure H(2)O fluids, indicating water-saturated conditions within subducted continental crust during prograde stage and/or ultrahigh-P metamorphism. Copyright © 2011 Elsevier B.V. All rights reserved.

Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif

NASA Astrophysics Data System (ADS)

Rastsvetaeva, R. K.; Chukanov, N. V.; Zaitsev, V. A.; Aksenov, S. M.; Viktorova, K. A.

2018-05-01

An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) Å3; sp. gr. R3 m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697 F > 4σ( F). The idealized formula ( Z = 3) was found to be Na12Sr2Ca6Fe 3 2+ Zr3NbSi25O72(OH,O)4Cl(H2O)0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.

The limnology and biology of the Dufek Massif, Transantarctic Mountains 82° South

NASA Astrophysics Data System (ADS)

Hodgson, Dominic A.; Convey, Peter; Verleyen, Elie; Vyverman, Wim; McInnes, Sandra J.; Sands, Chester J.; Fernández-Carazo, Rafael; Wilmotte, Annick; De Wever, Aaike; Peeters, Karolien; Tavernier, Ines; Willems, Anne

2010-08-01

Very little is known about the higher latitude inland biology of continental Antarctica. In this paper we describe the limnology and biology of the Dufek Massif, using a range of observational, microscopic and molecular methods. Here two dry valleys are home to some of the southernmost biota on Earth. Cyanobacteria were the dominant life forms, being found in lakes and ponds, in hypersaline brines, summer melt water, relict pond beds and in exposed terrestrial habitats. Their species diversity was the lowest yet observed in Antarctic lakes. Green algae, cercozoa and bacteria were present, but diatoms were absent except for a single valve; likely windblown. Mosses were absent and only one lichen specimen was found. The Metazoa included three microbivorous tardigrades ( Acutuncus antarcticus, Diphascon sanae and Echiniscus (cf) pseudowendti) and bdelloid rotifer species, but no arthropods or nematodes. These simple faunal and floral communities are missing most of the elements normally present at lower latitudes in the Antarctic which is probably a result of the very harsh environmental conditions in the area.

Opaque mineralogy and resource potential of placer gold in the stream sediments between Duba and Al Wajh, Red Sea coast, northwestern Saudi Arabia

NASA Astrophysics Data System (ADS)

Moufti, Asaad M. B.

2014-11-01

Mineralogical studies revealed that the stream sediments in northwestern Saudi Arabia between Duba and Al Wajh on the Red Sea coast are auriferous and can represent a potential source of easily recoverable placer gold. The detailed ore microscopic study supported by fire assay data of stream sediments at the southern sector of Duba-Al Wajh (Wadi Al Miyah, Wadi Haramil and Wadi Thalbah) in NW Saudi Arabia show economic concentrations of gold in their silt fraction (40-63 μm). However, particles of extremely fine “dusty” gold (⩽40 μm in size) are identified in most stations as independent grains. The maximum gold content in the samples of Wadi Al Miyah is 13.61 wt% which is reported for the light fraction (⩽40 μm). Maximum gold content in the heavy fractions of Wadi Haramil stream sediments amounts 6.90 g/t Au in a relatively coarse fraction (63-125 μm). The size still fulfills the silt fraction, but the coarsening of gold can be correlated with either original size of native gold in the Neoproterozoic mineralized zone or/and distance of transportation. It appears that the most gold-rich fractions of the analyzed samples are those from Wadi Thalbah. They have the highest index figure, which suggests that its placer gold may be economically exploitable. Gold content in the heavy fractions of samples from Wadi Thalbah is high and lies within a wide range (6.27-28.83 g/t), except for a single sample collected at the upstream with 0.77 g/t Au only. Fire assay data of samples from three wadis at the northern sector show that their gold content is clearly lower than in the samples from the southern sector. Only few samples from Wadi South Marwah are promising because they contain reasonable gold content (3.10-3.60 g/t) before heavy liquid separation. The two samples give gold content up to 11.03 g/t in their heavy mineral concentrate. The heavy fractions from both Wadi Al Amud and Wadi Salma are poor in gold where the maximum content of the metal in these

Terraranans of the Lost World: a new species of Pristimantis (Amphibia, Craugastoridae) from Abakapá-tepui in the Chimantá massif, Venezuelan Guayana, and additions to the knowledge of P. muchimuk.

PubMed

Rojas-Runjaic, Fernando J M; Salerno, Patricia E; Señaris, J Celsa; Pauly, Gregory B

2013-01-01

A new frog of the genus Pristimantis is named and described from the summit of Abakapá-tepui in the Chimantd massif, south-eastern Venezuela. The new species is known from two adult specimens and is the second craugastorid species described from this massif. It can be readily distinguished from all congeners inhabiting the highlands of the Guiana Shield by the unique combination of the following characters: dorsal skin shagreen and ventral skin coarsely areolate, tympanum small and ill-defined, vocal slits absent in males, finger I shorter than II, thumbs with two whitish and non-spinous nuptial pads in adult males, fingers and toes with broad lateral fringes, basal webbing between all toes, throat and chest nacreous white in life. Also, based on five specimens of Pristimantis muchimuk recently collected from Churi-tepui, we provide new information on this little known species, including an amended diagnosis, notes on morphology, color variation, advertisement calls, and natural history.

Linking microcracks and mineral zoning of detachment-exhumed granites to their tectonomagmatic history: Evidence from the Salihli and Turgutlu plutons in western Turkey (Menderes Massif)

NASA Astrophysics Data System (ADS)

Catlos, Elizabeth J.; Baker, Courteney B.; Sorensen, Sorena S.; Jacob, Lauren; Çemen, Ibrahim

2011-05-01

The Menderes Massif (western Turkey) is a metamorphic core complex that displays linked syntectonic plutonism and detachment faulting. Fabrics in S-type peraluminous granites (Salihli and Turgutlu) in the detachment (Alaşehir) footwall change from isotropic to protomylonitic to mylonitic towards the structure. Samples from the isotropic and protomylonitic zones were imaged in transmitted light, cathodoluminescence (CL), backscattered (BSE), and secondary electrons (SE), and show that these rocks contain abundant microcracks, and that plagioclase grains have zoning consistent with magma mixing. The granites contain fluid inclusion planes (FIPs), myrmekite replacing plagioclase, and the removal of blue luminescence in K-feldspar along microcracks and grain boundaries. Calcite and hydrous minerals commonly fill microcracks. The samples record features that formed due to (1) magma crystallization and ductile deformation (FIPs, mineral zoning), (2) changes in P and/or T (impingement and stress-induced microcracks in protomylonitic rocks), and (3) differences in intrinsic mineral properties (radial, cleavage, blunted, and deflected microcracks). Overprinted microcracks indicate exhumation during pulses. The Middle Miocene ages of these granites reported elsewhere are similar to those from large-scale extensional structures in Greece's Cycladic Massif. The Menderes and Cycladic core complexes may have developed simultaneously due to the widespread intrusion of subduction-related granitoids.

Zircon-pyrochlore ores of Proterozoic Gremyakha-Vyrmes polyphase massif, Kola Peninsula: source and evolution

NASA Astrophysics Data System (ADS)

Sorokhtina, Natalia; Belyatsky, Boris; Antonov, Anton; Kononkova, Natalia; Lepekhina, Elena; Kogarko, Lia

2017-04-01

The alkaline-ultrabasic Gremyakha-Vyrmes massif occurs within the Central Kola terrane in the northern part of the Fennoscandian Shield and consists of diverse rock complexes: basic-ultrabasic rocks, foidolites, alkaline metasomatic rocks and carbonatites, alkaline granites and granosyenites. Nb-Zr ore deposit is confined to alkaline metasomatic rocks developed over foidolites. The metasomatites are represented by albitites and aegirinites occur as submeridionally orientated zones extending up to 6-8 km and several hundred meters thickness. They are mainly composed of albite and aegirine, but amphibole, annite, microcline, fluorapatite, titanite, ilmenite, pyrochlore group minerals, zircon are present [Sorokhtina et al., 2016]. Carbonatites are developed sporadically and accessory zircon but not the pyrochlore is observed only in contact zones with albitites and aegerinites. In metasomatites, zircon and pyrochlore are main rare metal minerals, which are formed at the latest stages of crystallization. Ca-dominant fluorcalcio- and hydroxycalciopyrochlores are the most abundant, whereas U-dominant pyrochlore, oxyuranobetafite, zero-valent-dominant (Ba, Sr-dominant) pyrochlore, hydro- or kenopyrochlore are rare. The pyrochlore-group minerals form heterogeneous metacrystals containing inclusions of host rock minerals, calcite, ilmenite, zircon, sulfides, and graphite. While pyrochlore is replaced by Si-rich "pyrochlore" (SiO2 is up to 18 wt.%.), cation-deficient hydrated pyrochlore, Fe-Si-Nb, U-Si-Nb, and Al-Si-Nb phases along fracture zones and margins. The early generation zircon is represented by large heterogeneous metacrystals filled with inclusions of various host rock minerals, calcite, ilmenite, thorite, thorianite and sulfides, while the late zircons are empty of inclusions. Zircons are nearly stoichiometric in composition; but intermediate zones are enriched in Pb, Y and Th, and overgrowths are enriched Hf only. According to CL and ion-microprobe analysis

High frequency measurement of P- and S-wave velocities on crystalline rock massif surface - methodology of measurement

NASA Astrophysics Data System (ADS)

Vilhelm, Jan; Slavík, Lubomír

2014-05-01

For the purpose of non-destructive monitoring of rock properties in the underground excavation it is possible to perform repeated high-accuracy P- and S-wave velocity measurements. This contribution deals with preliminary results gained during the preparation of micro-seismic long-term monitoring system. The field velocity measurements were made by pulse-transmission technique directly on the rock outcrop (granite) in Bedrichov gallery (northern Bohemia). The gallery at the experimental site was excavated using TBM (Tunnel Boring Machine) and it is used for drinking water supply, which is conveyed in a pipe. The stable measuring system and its automatic operation lead to the use of piezoceramic transducers both as a seismic source and as a receiver. The length of measuring base at gallery wall was from 0.5 to 3 meters. Different transducer coupling possibilities were tested namely with regard of repeatability of velocity determination. The arrangement of measuring system on the surface of the rock massif causes better sensitivity of S-transducers for P-wave measurement compared with the P-transducers. Similarly P-transducers were found more suitable for S-wave velocity determination then P-transducers. The frequency dependent attenuation of fresh rock massif results in limited frequency content of registered seismic signals. It was found that at the distance between the seismic source and receiver from 0.5 m the frequency components above 40 kHz are significantly attenuated. Therefore for the excitation of seismic wave 100 kHz transducers are most suitable. The limited frequency range should be also taken into account for the shape of electric impulse used for exciting of piezoceramic transducer. The spike pulse generates broad-band seismic signal, short in the time domain. However its energy after low-pass filtration in the rock is significantly lower than the energy of seismic signal generated by square wave pulse. Acknowledgments: This work was partially

Natronolimnobius aegyptiacus sp. nov., an extremely halophilic alkalithermophilic archaeon isolated from the athalassohaline Wadi An Natrun, Egypt.

PubMed

Zhao, Baisuo; Hu, Qingping; Guo, Xiaomeng; Liao, Ziya; Sarmiento, Felipe; Mesbah, Noha M; Yan, Yanchun; Li, Jun; Wiegel, Juergen

2018-02-01

An obligately aerobic extremely halophilic alkalithermophilic archaeon, strain JW/NM-HA 15 T , was isolated from the sediments of Wadi An Natrun in Egypt. Phylogenetic analysis based on 16S rRNA and rpoB' gene sequences indicated that it belongs to the family Natrialbaceae of the order Natrialbales. The closest relatives were Natronolimnobius baerhuensis IHC-005 T and Natronolimnobius innermongolicus N-1311 T (95.3 and 94.5 % 16S rRNA gene sequence similarity, respectively). Genome relatedness between strain JW/NM-HA 15 T and its neighbours was evaluated using average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity with the values of 75.7-85.0, 18.1-20.0, and 70.2-71.0%, respectively. Cells were obligately aerobic, rod-shaped, non-motile, Gram-stain-negative and chemo-organotrophic. The strain grew in the presence of 2.57 M to saturating Na + (optimum 3.25-4.60 M Na + ), at pH 55 °C 7.5-10.5 (optimum pH 55 °C 9.0-9.5), and at 30-56 °C (optimum 52 °C). The major polar lipids consisted of phosphatidylglycerol, methylated phosphatidylglycerolphosphate and two phospholipids. The complete genome size of strain JW/NM-HA 15 T is approximately 3.93 Mb, with a DNA G+C content of 64.1 mol%. On the basis of phylogenetic features, genomic relatedness, phenotypic and chemotaxonomic data, strain JW/NM-HA 15 T was thus considered to represent a novel species within the genus Natronolimnobius, for which the name Natronolimnobius aegyptiacus sp. nov. is proposed. The type strain is JW/NM-HA 15 T (=ATCC BAA-2088 T =DSM 23470 T ).

Incidence of mass movement processes after an historical episode of heavy snowfall in the Asturian Massif (Northern Spain)

NASA Astrophysics Data System (ADS)

Garcia-Hernandez, Cristina; Ruiz-Fernández, Jesús; Gallinar, David

2015-04-01

This research examines a mass movement event caused in the context of the Great Blizzard of 1888, one of the most severe recorded blizzards in the history of Europe, whose implications go far beyond. In the Asturian Massif the episode consisted in four linked and consecutive snowstorms that took place between the 14th of February 1888 and the 8th of April 1888, creating snow covers with a depth ranging between 5 and 7 m, snow avalanches and flooding, causing dozens of deaths and large material damage. The Asturian Massif belongs to the Atlantic-climate area and is composed mainly by sedimentary and metamorphic paleozoic rocks. Many sectors of the Massif are between 1.000 and 2.000 m a.s.l., and its topography is characterized by a great height difference and steep slopes. Because of the lack of deep soils suitable for farming, the main traditional activity has been livestock keeping, and goods traffic. We have devised a method that enables the reconstruction of this event on the basis of nivo-meteorogical conditions, geographical location and socio-economic impact. The mass movement episode has been studied through the issues of 6 newspapers published in Asturias between the 20th of January and 30th of May 1888, the ancient meteorological station data of the University of Oviedo, and field work. A logical database structure has been designed with the aim to store and cross the information for statistical analysis. Thirty six mass movement worthy of consideration were documented, 28 of them causing material damage (six homes destroyed and at least 22 interruptions with the traffic flow on roads, highways and railways). Ten high- and mid-elevation mountain municipalities were affected by mass movement. We must consider that only the most important events, or those that happened in crowded places, have been considered by the newspapers, so the total number of mass movements should be considered as a minimum figure. We have got to identify and classify 27 of them; 16

Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central

NASA Astrophysics Data System (ADS)

Harvey, J.; Gannoun, A.; Burton, K. W.; Schiano, P.; Rogers, N. W.; Alard, O.

2010-01-01

Spinel lherzolite xenoliths from Mont Briançon, French Massif Central, retain evidence for multiple episodes of melt depletion and melt/fluid infiltration (metasomatism). Evidence for primary melt depletion is still preserved in the co-variation of bulk-rock major elements (MgO 38.7-46.1 wt.%; CaO 0.9-3.6 wt.%), and many samples yield unradiogenic bulk-rock Os isotope ratios ( 187Os/ 188Os = 0.11541-0.12626). However, many individual xenoliths contain interstitial glasses and melt inclusions that are not in equilibrium with the major primary minerals. Incompatible trace element mass balance calculations demonstrate that metasomatic components comprise a significant proportion of the bulk-rock budget for these elements in some rocks, ranging to as much as 25% of Nd and 40% of Sr Critically, for Re-Os geochronology, melt/fluid infiltration is accompanied by the mobilisation of sulfide. Consequently, bulk-rock isotope measurements, whether using lithophile (e.g. Rb-Sr, Sm-Nd) or siderophile (Re-Os) based isotope systems, may only yield a perturbed and/or homogenised average of these multiple events. Osmium mass balance calculations demonstrate that bulk-rock Os in peridotite is dominated by contributions from two populations of sulfide grain: (i) interstitial, metasomatic sulfide with low [Os] and radiogenic 187Os/ 188Os, and (ii) primary sulfides with high [Os] and unradiogenic 187Os/ 188Os, which have been preserved within host silicate grains and shielded from interaction with transient melts and fluid. The latter can account for >97% of bulk-rock Os and preserve geochronological information of the melt from which they originally precipitated as an immiscible liquid. The Re-depletion model ages of individual primary sulfide grains preserve evidence for melt depletion beneath the Massif Central from at least 1.8 Gyr ago despite the more recent metasomatic event(s).

Platinum potential of mafic-ultramafic massifs in the western part of the Dambuka ore district (Upper Amur Region, Russia)

NASA Astrophysics Data System (ADS)

Melnikov, A. V.; Stepanov, V. A.; Moiseenko, V. G.

2016-02-01

New data on the Pt potential of mafic-ultramafic massifs of the Khani-Maya, Uldegit, and Dzhalta complexes in the western part of the Dambuka ore district are discussed. The Khani-Maya Complex is represented by metamorphosed gabbro, gabbronorites, gabbro anorthosites, subordinate pyroxenites, hornblendites, and peridotites. The Uldegit Complex is composed of pyroxenites, hornblendites, gabbro, gabbronorites, norites, troctolites, peridotites, dunites, actinolite-tremolites, serpentinites, anthophyllites, and tremolite-plagioclase rocks. The Dzhalta Complex is formed of peridotites, gabbro, eclogitized gabbro, hornblendites, cortlandites, and pyroxenites. All these complexes differ from each other by the concentrations of Ni, Cu, Co, Au, and platinoids depending on the composition of the constituting rocks and the presence of sulfide minerals.

Crustal melting during subduction at mantle depth: anatomy of near-UHP nanogranites (Orlica-Śnieżnik Dome, Bohemian Massif)

NASA Astrophysics Data System (ADS)

Ferrero, Silvio; Ziemann, Martin; Walczak, Katarzyna; Wunder, Bernd; O'Brien, Patrick J.; Hecht, Lutz

2015-04-01

Small volumes (≤ 50µm) of hydrous melt were trapped as primary inclusions in peritectic garnets during partial melting of metagranitoids from the Orlica-Śnieżnik Dome (Bohemian Massif) at mantle depth [1]. Detailed microstructural/microchemical investigation confirmed the occurrence of a granitic assemblage (biotite+feldspars+quartz) in every investigated inclusion, i.e they are nanogranites [2]. MicroRaman mapping of unexposed inclusions showed the occurrence of residual, H2O-rich glass in interstitial position. Despite the oddity of this finding within a classic regional HP/HT terrain, an incomplete crystallization of the melt inclusions (MI) is consistent with the (relatively) rapid exhumation of the Orlica-Śnieżnik Dome proposed by some authors [e.g. 3]. Moreover glassy and partially crystallized MI have been already reported in lower-P (<1 GPa) migmatites [4]. MicroRaman investigation also showed the possible presence of kumdykolite, a high-temperature polymorph of albite reported in UHP rocks from the Kokchetav Massif as well as the Bohemian massif ([5] and references therein). Experimental re-homogenization of nanogranites was achieved using a piston cylinder apparatus at 2.7 GPa and 875°C under dry conditions, in order to investigate melt composition and H2O content with in situ techniques. The trapped melt is granitic, hydrous (6 wt% H2O) and metaluminous (ASI=1.03), and it is similar to those produced experimentally from crustal lithologies at mantle conditions. Re-homogenization conditions are consistent with the results of geothermobarometric calculations on the host rock, suggesting that no H2O loss occurred during exhumation - this would have caused a shift of the inclusion melting T toward higher values. Coupled with the absence of H2O-loss microstructural evidence, e.g. decrepitation cracks and/or vesciculation [4] in re-homogenized nanogranites, this evidence suggests that the nanogranites still preserves the original H2O content of the

Chemical and isotopic constraints on the origin of Wadi El-Tarfa ground waters, Eastern Desert, Egypt.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sultan, M.; Sturchio, N. C.; Abdel Hady, Y.

2000-10-01

We evaluated the use of the renewable ground water resources of the Eastern Desert to develop sustainable agriculture in Upper Egypt, an alternative that could alleviate some of Egypt's dependence on water from the Nile River. Ground water from shallow aquifers in the Eastern Desert of Egypt, near the intersection of Wadi El-Tarfa and the Nile River, was analyzed for chemical compositions, stable isotope ratios, and tritium activities. The ground water has a range in total dissolved solids of 300 to 5000 mg/L. Values of {delta}D and {delta}{sup 18}O range from -10 to +34 %o and -2 to +5.2 %o,more » respectively, and defines a line having a slope of 5.7 that intersects the meteoric water line at about {delta}D = -15% on a plot of 8D versus {delta}{sup 18}O. These findings indicate that the water might have been derived by a combination of evaporation of and salt addition to regional precipitation. Only one sample could have been derived directly by evaporation and transpiration of modern Nile River water. Salinization of the ground water could have occurred through dissolution of marine aerosol dry fallout, carbonate minerals, gypsum, and other trace evaporitic minerals at and near the ground surface. Tritium activities ranged from 0.04 to 12.9 TU (tritium unite), indicating that all but one of the samples were derived at least partly from precipitation that occurred within the last 45 years. These data indicate that Nubian Aquifer paleowater is not a significant component of the shallow aquifers of this portion of the Eastern Desert. The most likely source of this ground water is sporadic flash flood events yielding locally voluminous recharge that accumulates in coarse sediments and fractured rock beneath alluvial channels. The magnitude of this renewable ground water resource and its potential for supporting sustainable agriculture require further investigation.« less

Biostratigraphy and paleoecology of the Burdigalian-Serravallian sediments in Wadi Sudr (Gulf of Suez, Egypt): comparison with the Central Paratethys evolution

NASA Astrophysics Data System (ADS)

Ied, Ibrahim M.; Holcová, Katarína; Abd-Elshafy, Ezzat

2011-06-01

Two main Miocene facies were recorded in the Gulf of Suez area: a deep marine and a coastal facies. The analysed sections in the Wadi Sudr area belong to the marine facies. The Lower Miocene (Burdigalian) is represented by coastal, shallow marine sediments, rich in coral, algae, gastropods and large pectinids followed by Langhian open marine sediments and Serravallian lagoonal carbonates. The open marine sediments contain well preserved planktonic and benthic foraminifers and abundant ostracods. The parts of the sections containing foraminifers have been correlated with three planktonic foraminiferal zones (Praeorbulina glomerosa Zone, Orbulina Zone and Globorotalia praemenardii-Globorotalia peripheroronda Zone). Two benthic ecozones were defined (Heterolepa dutemplei-Laevidentalina elegans Zone and Bolivina compressa-Elphidium spp. Zone). Two cycles of sea-level changes can be distinguished and correlated with global sea-level cycles Bur5/Lan1 and Ser1. The first (Langhian) cycle culminated in open marine sublittoral to upper bathyal well aerated sediments. The second (Serravallian) cycle was shallower, littoral suboxic sediments were overlaid by euryhaline carbonates. The studied foraminifera-bearing sediments can be correlated with the lower and Middle Badenian of the Central Paratethys. Though the area of the Gulf of Suez and the Central Paratethys were situated in different climatic zones, and influenced by different tectonic events, the main paleoenvironmental events (sea-level changes, oxygen decrease, salinity changes) are comparable. This correspondence shows that the decisive factors triggering these events were global climatic events.

Provenance and sequence architecture of the Middle-Late Eocene Gehannam and Birket Qarun formations at Wadi Al Hitan, Fayum Province, Egypt

NASA Astrophysics Data System (ADS)

Anan, Tarek; El Shahat, Adam

2014-12-01

The Middle-Upper Eocene Gehannam and Birket Qarun formations at Wadi Al Hitan (Valley of Whales) in Fayum Province of Egypt are dominated by marine siliciclastic sediments. Sedimentation took place in synclinal basins that were inherited from the Late Cretaceous tectonism. The siliciclastic sediments accumulated in low energy open shallow marine shelf. Most of the siliciclastics are heavily bioturbated by Thalassinoides. The abundance of unstable and moderately stable heavy minerals suggests that the Middle-Upper Eocene clastics were largely derived from the weathered regolith of the exhumed basement rocks of the Red Sea mountains. The ultrastable heavies were mainly recycled from positive landmass that bound the Eocene basins. Two sequence boundaries were observed in the studied succession. The first boundary lies within a rhizolith bearing-sandstone unit that occurs at the boundary between the Gehannam and Birket Qarun formations. The second sequence boundary occurs within the upper part of the Birket Qarun Formation, in a shale horizon bioturbated by Thalassinoides. Three 3rd order depositional sequences were recognized. These sequences may be formed due to tectonic activity that started in the Late Cretaceous and may be rejuvenated again during the Eocene time. Also emergence activities that were active during the Eocene led to the formation of the picked sequences by changing relative sea level. The recorded systems tracts are transgressive systems tract (TST), highstand systems tract (HST), and falling-stage systems tract (FSST).

The rockfall observatory in the Reintal, Wetterstein Massif, German Alps

NASA Astrophysics Data System (ADS)

Schöpa, Anne; Turowski, Jens M.; Hovius, Niels

2017-04-01

The Reintal is an Alpine valley in the Wetterstein Massif close to the Zugspitze, Germany's highest mountain. Due to the variety of active geomorphic processes, including rockfalls off the steep limestone cliffs, debris flows, and snow avalanches, and the river Partnach, the Reintal has been the field area of many geomorphological and hydrological research campaigns over the last few decades. In 2014, the Geomorphology Section of the GFZ Potsdam started to install a monitoring network to detect and classify rockfalls in the Reintal. The network includes six seismic stations, optical and infrared cameras, and two weather stations measuring air and rock temperature, air pressure and relative humidity, precipitation, wind speed and direction, and solar radiation. The continuous observations of the network are supplemented by repeated field campaigns including terrestrial laser scans of a prominent rockfall niche at the Hochwanner mountain. The about 1,500 m high north face of the Hochwanner experienced the detachment of a 2.8 Mio m3 rockfall about 500 years ago that created the so-called Steingerümpel (German for rock debris deposit) and dammed the river Partnach. The cliff still shows high rockfall activity, and an 80,000 m3 block can be expected to fall in the near future. In this contribution, the layout of the observatory and details of the seismic network centered around the Hochwanner north face are described. Furthermore, the network data of a severe thunderstorm event in June 2016, that triggered many rockfalls and debris flows in the Reintal, is presented.

Lower Brioverian formations (Upper Proterozoic) of the Armorican Massif (France): geodynamic evolution of source areas revealed by sandstone petrography and geochemistry

NASA Astrophysics Data System (ADS)

Dabard, Marie Pierre

1990-11-01

Formations with interbedded cherts constitute an important part of the Lower Brioverian succession (Upper Proterozoic age) in the Armorican Massif (northwest France). These formations are composed of shale-sandstone alternations with interbedded siliceous carbonaceous members. Petrographic and geochemical study of the detrital facies shows that these rocks are compositionally immature. The wackes are rich in lithic fragments (volcanic fragments: 3-20% modal; sedimentary and metamorphic fragments: 0-7% modal) and in feldspar (5-16%). From the geochemical point of view, they are relatively enriched in Fe 2+MgO (about 5.5%) and in alkalis with {Na 2O }/{K 2O } ratios greater than 1. The CaO contents are low (about 0.3%). Slightly negative Eu anomalies are observed ( {Eu}/{Eu ∗} = 0.8 ). Their chemical compositions are in agreement with a dominantly acidic source area with deposition in a continental active margin setting. Compared with other Upper Proterozoic deposits of the Armorican Massif, the interbedded-chert formations appear rather similar to other deposits in North Brittany which accumulated in an intra-arc or back-arc basin environment. The formations with interbedded cherts are interpreted as having been deposited during an early stage of magmatic arc activity (around 640-630 Ma ago) in an immature marginal basin. The clastic supply to these formations is derived in part from early volcanic products (acidic to intermediate) which are linked to subduction beneath the North Armorican Domain. Another component is inherited from the reworking of 2000 Ma old basement relics. The opening of the back-arc domain, with associated basaltic volcanism, would bring about a progressive displacement of the interbedded-chert depositional basin towards the continental margin.

First findings of monocrystalline aragonite inclusions in garnet from diamond-grade UHPM rocks (Kokchetav Massif, Northern Kazakhstan).

PubMed

Korsakov, Andrey V; Vandenabeele, Peter; Perraki, Maria; Moens, Luc

2011-10-01

The presence of aragonite inclusions in garnet from diamond-grade metamorphic rocks from the Kokchetav Massif, Northern Kazakhstan was identified for the first time by means of Raman analyses and mapping. Aragonite appears within the inclusions up to 50 μm in size as a single crystal. These inclusions have rounded shape. The grain boundary between the host-garnet is smooth. No cracks occur around the aragonite inclusions. No significant shift in the main aragonite Raman band was measured. These observations indicate that residual pressure within the inclusion is minor. These findings imply either non-UHPM origin of the host garnet or significant plastic deformation of host minerals during retrograde stage. These features should be taken into account for recovery peak metamorphic conditions and modeling of exhumation processes of UHPM complexes. Copyright © 2010 Elsevier B.V. All rights reserved.

The Alleret Maar lacustrine sequence (French Massif Central): a 150 ka long early-middle Pleistocene continental paleoenvironmental record.

NASA Astrophysics Data System (ADS)

Nomade, S.; Pastre, J.; Guillou, H.; Gauthier, A.; Scaillet, S.

2008-12-01

Lacustrine maar sequences of the French Massif Central are of great interest for paleoclimatic and paleoenvironmental reconstructions of mid-latitudes Quaternary continental environments. In particular, the western Velay region yields exceptional sequences spanning the last 450 ka (Reille et al., J. Quat. Sci. 2000). However, older sequences remain largely unknown despite the presence of interbedded alkaline tephras allowing precise absolute radiochronological control of many lacustrine squences. The Alleret maar is a 1500 m wide phreatomagmatic crater that provides a long lacustrine sequence (41 m). The upper part of this sequence (AL2 core, 14.6 m) was studied between 2005 and 2006 (Pastre et al., C. R. Acad Sci, 2007). A 39Ar/40Ar date (557 ± 5ka) obtained from an interbedded tephra layer located at 7m as well as the associated pollen data attribute the beginning of this sequence to the MIS 15. Thanks to the AL3 core recovered in 2005 (40.6 m, CNRS Meudon) several new tephra layers were discovered in the bottom part of this lacustrine sequence. Three new 39Ar/40Ar ages (single crystal analyses) from trachytic tephra layers were obtained at the LSCE Argon Laboratory (France). These layers are located at -30.2, -36.2 and -39.2m. Ages obtained relative to the ACR-2 flux standard (1,201Ma, Kuiper et al., Science, 2008) range from 692 ± 6 ka (MSWD: 2.3, n=18) for the youngest (-30.2m) to 726 ± 9Ka Ka (MSWD: 2.2, n=12) for the lowest tephra located at -39.2m. These new dates indicate a relatively homogeneous deposition rate of 3.5cm/ka and that the last 10 meters cover the MIS 17-MIS18 period. According to these current radiochronological data the complete lacustrine sequence last more than 150ka. Ongoing sedimentary and pollen studies will allow to extend the paleoenvironmental and paleoclimatic records of the French Massif Central towards the beginning of the early middle Pleistocene.

New bulk and in situ isotopic and elemental geochemistry of shallow drill core from Atlantis Massif: insights into the sources and paths of fluids and clasts

NASA Astrophysics Data System (ADS)

Bilenker, L.; Weis, D.; Scoates, J. S.

2017-12-01

We present stable Fe and radiogenic isotope and complementary trace element data for samples from Atlantis Massif. This oceanic core complex is located at 30°N where the Atlantis Transform Fault intersects the Mid-Atlantic Ridge (MAR) and is associated with the Lost City Hydrothermal Field (LCHF). It is a unique place to investigate the abiotic and biotic geochemical processes that play a role in the alteration of both crustal and mantle seafloor rocks. The samples analyzed represent a shallow (<15 m) survey of five drill sites (IODP Expedition 357) within Atlantis Massif, varying in distance from the LCHF and MAR. Analyses were performed on a sample set spanning a wide range in degree of alteration and lithology. Bulk measurements involved dissolving whole rock powders, whereas in situ analyses were performed on digested microdrilled samples or by laser ablation. Bulk rock Fe isotope values (n = 34) are correlated with loss-on-ignition (LOI) by sample lithology and location relative to LCHF. Using LOI as a proxy for degree of alteration, this observation indicates that the Fe isotope systematics of seafloor crustal and mantle rocks preserve indicators of fluid flow and source. The Hf and Nd isotope compositions for various lithologies form all analyzed sites are homogeneous, indicating minimal alteration of these isotopic systems. Bulk Sr values provide insight into elemental exchange between seawater and the surface of Atlantis Massif and bulk Pb isotopes allow for fingerprinting of the source of basalt breccias through comparison with published Pb isotope values of MAR basalts. The new results cluster around the Pb, Hf, Nd isotopic composition of mid-ocean ridge basalt from 30.68°N and do not match samples north or south of that location. In situ Fe isotope data within three altered samples reflect varying degrees of hydrothermal and seawater interaction, where the Fe isotope ratios within each sample are likely correlated with extent of exchange or redox

Garnet from diamondiferous metamorphic rocks of Kokchetav massif, Kazakhstan as a peak pressure recorder

NASA Astrophysics Data System (ADS)

Sobolev, N. V.; Palyanov, Y. N.; Shatsky, V. S.; Sokol, A. G.; Tomilenko, A. A.

2003-12-01

Garnet is a key mineral coexisting with diamond both in kimberlite (as xenocrysts, in diamondiferous garnet peridotites and eclogites, as inclusions in diamond) and in UHP metamorphic rocks of Kokchetav massif (diamondiferous gneisses, garnet-pyroxene rocks, dolomitic marbles and diamond facies eclogites). In UHPM rocks garnets are of particular importance as inclusions in zircons protected from retrograde metamorphism. Diamond formation conditions in eclogitic (E-type) upper mantle environment are estimated based upon Grt-Cpx thermometry and coesite barometry (e.g. Sobolev et al., PNAS, 2000, 97:11875) at P=5.5-6.0 GPa and T=1000-1300° C. These data are supported by diamond synthesis in carbonate-silicate fluid (e.g. Palyanov et al., Nature, 1999, 400: 417). E-type garnet may dissolve up to 0.3 wt.% Na2O (Sobolev, Lavrentyev, Contr. Min. Petr., 1971, 31:1) depending on pressure and Na2O contents in coexisting pyroxene and melts (fluids). Majorite component (pyroxene solid solution) was reported in rare garnets from diamonds (e.g. Moore, Gurney, Nature, 1985, 318:553) and UHP conditions were experimentally confirmed for such garnets (Irifune, Phys. Eart. Pl. Int., 1987, 45:324; Gasparik, Phys. Chem. Min., 2002, 29:170; Luth, Am. Miner., 1997, 82:1198). Garnets from Kokchetav diamondiferous metamorphic rocks demonstrate considerably lower Na2O solubility (up to 0.2 wt.% in rare samples) and absence of majorite component. However, coexisting pyroxenes may contain up to 50 mol.% jadeite. Several UHP experiments performed with Kokchetav eclogites and dolomitic marbles using a split-sphere apparatus resulted in detection of up to 0.3-0.4 wt.% Na2O in newly formed eclogitic garnets at P=5.7 and 7.0 GPa, T=1400 and 1700° C respectively. Majorite component was also determined in newly formed garnets reaching about 5% with Si (pfu)=3.05-3.06. Similar garnets without Na2O were also obtained in UHP experiments with diamondiferous dolomitic marbles (e.g. Palyanov et al

Review of metamorphic and kinematic data from Internal Crystalline Massifs (Western Alps): PTt paths and exhumation history

NASA Astrophysics Data System (ADS)

Gasco, Ivano; Gattiglio, Marco; Borghi, Alessandro

2013-01-01

Detailed geological mapping combined with micro-structural and petrological investigation allowed to clarify the tectono-metamorphic relationships between continental and oceanic units transition in the Penninic domain of the Western Alps. The three study areas (Gressoney, Orco and Susa sections) take into consideration the same structural level across the axial metamorphic belt of the Western Italian Alps, i.e., a geological section across the Internal Crystalline Massifs vs Piedmont Zone boundary. The units outcropping in these areas can be grouped into two Tectonic Elements according to their tectono-metamorphic evolution. The Lower Tectonic Element (LTE) consists of the Internal Crystalline Massifs and the Lower Piedmont Zone (Zermatt-Saas like units), both showing well preserved eclogite facies relics. Instead, the Upper Tectonic Element (UTE) consists of the Upper Piedmont Zone (Combin like units) lacking evidence of eclogite facies relics. In the Lower Tectonic Element two main Alpine tectono-metamorphic stages were identified: M1/D1 developed under eclogite facies conditions and M2/D2 is related to the development of the regional foliation under greenschist to epidote-albite amphibolite facies conditions. In the Upper Tectonic Element the metamorphic stage M1/D1 developed under bluschist to greenschist facies conditions and M2/D2 stage under greenschist facies conditions. These two Tectonic Elements are separated by a tectonic contact of regional importance generally developed along the boundary between the Lower and the Upper Piedmont zone under greenschist facies conditions. PT data compared to geochronology indicate that the first exhumation of ICM can be explained by buoyancy forces acting along the subduction channel that occurred during the tectonic coupling between the continental and oceanic eclogite units. These buoyancy forces vanished at the base of the crust where the density difference between the subducted crustal units and the surroundings

Multistage evolution of UHT granulites from the southernmost part of the Gföhl Nappe, Bohemian Massif, Lower Austria

NASA Astrophysics Data System (ADS)

Schantl, Philip; Hauzenberger, Christoph; Linner, Manfred

2016-04-01

A detailed petrological investigation has been undertaken in leucocratic kyanite-garnet bearing and mesocratic orthopyroxene bearing granulites from the Dunkelsteiner Wald, Pöchlarn-Wieselburg and Zöbing granulite bodies from the Moldanubian Zone in the Bohemian Massif (Austria). A combination of textural observations, conventional geothermobarometry, phase equilibrium modelling as well as major and trace element analyses in garnet enables us to confirm a multistage Variscan metamorphic history. Chemically homogenous garnet cores with near constant grossular-rich plateaus are considered to reflect garnet growth during an early HP/UHP metamorphic evolution. Crystallographically oriented rutile exsolutions restricted to those grossular-rich garnet cores point to a subsequent isothermal decompression of the HP/UHP rocks. Overgrowing garnet rims show a pronounced zonation and are interpreted as the result of dehydration melting reactions during an isobaric heating phase which could have taken place near the base of an overthickened continental crust, where the previously deeply subducted rocks were exhumed to. For this HP granulite facies event maximum PT conditions of ~1050 °C and 1.6 GPa have been estimated from leucocratic granulites comprising the peak mineral assemblage quartz, ternary feldspar, garnet, kyanite and rutile. The pronounced zoning of garnet rims indicates that the HP granulite facies event must have been short lived since diffusion in this temperature region is usually sufficient fast to homogenize a zoning pattern in garnet. A retrogressive metamorphic stage is documented in these rocks by the replacement of kyanite to sillimanite and the growth of biotite. This retrograde event took place within the granulite facies but at significantly lower pressures and temperatures with ~0.8 GPa and ~760 °C. This final stage of re-equilibration is thought to be linked with a second exhumation phase into middle crustal levels accompanied by intensive

Serpentinite Carbonation in the Pollino Massif (southern Italy) for CO2 Sequestration

NASA Astrophysics Data System (ADS)

Carmela Dichicco, Maria; Mongelli, Giovanni; Paternoster, Michele; Rizzo, Giovanna

2015-04-01

Anthropogenic gas emissions are projected to change future climates with potentially nontrivial impacts (Keller et al., 2008 and references therein) and the impacts of the increased CO2 concentration are, among others, the greenhouse effect, the acidification of the surface of the ocean and the fertilization of ecosystems (e.g. Huijgen and Comans, 2003). Geologic Sequestration into subsurface rock formations for long-term storage is part of a process frequently referred to as "carbon capture and storage" or CCS. A major strategy for the in situ geological sequestration of CO2 involves the reaction of CO2 with Mg-silicates, especially in the form of serpentinites, which are rocks: i) relatively abundant and widely distributed in the Earth's crust, and ii) thermodynamically convenient for the formation of Mg-carbonates (e.g., Brown et al., 2011). In nature, carbonate minerals can form during serpentinization or during hydrothermal carbonation and weathering of serpentinites whereas industrial mineral carbonation processes are commonly represented by the reaction of olivine or serpentine with CO2 to form magnesite + quartz ± H2O (Power et al., 2013). Mineral carbonation occurs naturally in the subsurface as a result of fluid-rock interactions within serpentinite, which occur during serpentinization and carbonate alteration. In situ carbonation aims to promote these reactions by injecting CO2 into porous, subsurface geological formations, such as serpentinite-hosted aquifers. In the northern sector of the Pollino Massif (southern Italy) extensively occur serpentinites (Sansone et. al., 2012) and serpentinite-hosted aquifers (Margiotta et al., 2012); both serpentinites and serpentinite-hosted aquifers are the subject of a comprehensive project devoted to their possible use for in situ geological sequestration of CO2. The serpentinites derived from a lherzolitic and subordinately harzburgitic mantle, and are within tectonic slices in association with metadolerite dykes

Thermal conditions of rock slopes below unstable infrastructure in Alpine permafrost area: the cases of the Cosmiques hut and the Grands Montets cable-car station (Mont Blanc massif)

NASA Astrophysics Data System (ADS)

Duvillard, Pierre-Allain; Magnin, Florence; Mörtl, Christian; Ravanel, Ludovic; Deline, Philip

2017-04-01

Thermal state of steep permafrost-affected rock faces is crucial to assess the safety and reliability of mountain infrastructure as current permafrost degradation affects the rock slope stability. In the Mont-Blanc massif, 23 infrastructures are built on such a rock face with 13 of them that are characterized by a high risk of destabilization (Duvillard et al., 2015), including the upper station of the Grands Montets cable car (3325 m a.s.l.) as well as the Cosmiques hut (3613 m a.s.l.) on which we will focus. These two buildings have already been affected by different geomorphological processes. A rockfall event (600 m3) occurred for example on the SE face on the Arête inférieure des Cosmiques on the 21st of August 1998 (Ravanel et al., 2013) and the Grands Montets case shows a slow subsidence of the stairway over the last decade. In order to better assess the role of the permafrost in these processes and to gain insight on possible future geomorphic activity, we characterized the current permafrost conditions and simulated its changes up to the end of the 21st century using two complementary approaches: (i) the result of ERT (Electrical Resistivity Tomography) surveys carried out in October 2016 on the northern and southern faces right below the Cosmiques hut (at the level of the foundations) and at the Aiguilles des Grands Montets; (ii) the modeling of mean annual rock surface temperature for 2016 and at the end of the 21st century (Magnin et al., in rev.). Duvillard P.-A., Ravanel L., Deline P. (2015). Risk assessment of infrastructure destabilisation due to global warming in the high French Alps. Journal of Alpine Research, 103 (2). Magnin F., Josnin J.-Y., Ravanel L., Pergaud J., Pohl B., Deline P. (in rev.). Modelling rock wall permafrost degradation in the Mont Blanc massif from the LIA to the end of the 21st century. The Cryosphere Discuss., doi:10.5194/tc-2016-132. Ravanel L., Deline P., Lambiel C. and Vincent C. (2013). Instability of a high alpine

Experimental and Numerical Research of Stress-Strain State of Homogeneous Soil Massif at Interaction with Single Barrette

NASA Astrophysics Data System (ADS)

Ter-Martirosyan, Z. G.; Ter-Martirosyan, A. Z.; Sidorov, V. V.

2017-11-01

Deep foundations are used for the design of high-rise buildings due to a large pressure transfer on the soil base. The foundations of buildings sometimes use barrettes which are able to perceive significant vertical and horizontal loads due to improved lateral surface. Barrettes have increased load bearing capacity as compared with large diameter piles. In modern practice the interaction between barrettes and soil is investigated by analytical and numerical methods and has no sufficient experimental confirmation. The review of experimental methods for the research of the intense stress-strain state of the uniform soil massif at interaction with elements of a deep foundation is provided in this article. Experimental research are planned with the use of laboratory stand for the purpose of qualitative data obtaining on the interaction barrettes with an assessment of a settlement model adequacy and also at the research of the intense stress-strain state by numerical methods.

A preliminary spatial-temporal study of some soil characteristics in the calcareous massif of Sicó, Portugal.

PubMed

Torres, Maria Odete; Neves, Maria Manuela

2016-04-18

The mountainous massif of Sicó, in the centre of Portugal, is an extensive area composed of calcareous Jurassic formations. Hillside calcareous soils, with high pH, present chemical restrictions to support plant growth and are subjected to important erosion processes leading to their degradation if not protected by vegetation. In a first year of study some soil physicochemical characteristics have been measured in some geo-referenced locations of a larger design experiment and an exploratory spatial analysis has been performed. The objective of this study was to present some suggestions in order to give sustainable phosphorus fertiliser recommendations aiming to establish pastures in these soils and thus support traditional livestock activity. Ten years apart, those soil characteristics have been measured again in the same locations and comparisions have been made. The objective was to understand the variability of the soil properties under study in order to better adequate the fertiliser soil management regarding the area restoration.

Palaeomagnetism and geochemistry of Early Palaeozoic rocks of the Barrandian (Teplé-Barrandian Unit, Bohemian Massif): palaeotectonic implications

NASA Astrophysics Data System (ADS)

Patočka, F.; Pruner, P.; Štorch, P.

The Barrandian area (the Teplá-Barrandian unit, Bohemian Massif) provided palaeomagnetic results on Early Palaeozoic rocks and chemical data on siliciclastic sediments of both Middle Cambrian and Early Ordovician to Middle Devonian sedimentary sequences; an outcoming interpretation defined source areas of clastic material and palaeotectonic settings of the siliciclastic rock deposition. The siliciclastic rocks of the earliest Palaeozoic sedimentation cycle, deposited in the Cambrian Příbram-Jince Basin of the Barrandian, were derived from an early Cadomian volcanic island arc developed on Neoproterozoic oceanic lithosphere and accreted to a Cadomian active margin of northwestern Gondwana. Inversion of relief terminated the Cambrian sedimentation, and a successory Prague Basin subsided nearby since Tremadocian. Source area of the Ordovician and Early Silurian shallow-marine siliciclastic sediments corresponded to progressively dissected crust of continental arc/active continental margin type of Cadomian age. Since Late Ordovician onwards both synsedimentary within-plate basic volcanics and older sediments had been contributing in recognizable proportions to the siliciclastic rocks. The siliciclastic sedimentation was replaced by deposition of carbonate rocks throughout late Early Silurian to Early Devonian period of withdrawal of the Cadomian clastic material source. Above the carbonates an early Givetian flysch-like siliciclastic suite completed sedimentation in the Barrandian. In times between Middle Cambrian and Early/Middle Devonian boundary interval an extensional tectonic setting prevailed in the Teplá-Barrandian unit. The extensional regime was related to Early Palaeozoic large-scale fragmentation of the Cadomian belt of northwestern Gondwana and origin of Armorican microcontinent assemblage. The Teplá-Barrandian unit was also engaged in a peri-equatorially oriented drift of Armorican microcontinent assemblage throughout the Early Palaeozoic: respective

Magmatism and crustal extension: Constraining activation of the ductile shearing along the Gediz detachment, Menderes Massif (western Turkey)

NASA Astrophysics Data System (ADS)

Rossetti, Federico; Asti, Riccardo; Faccenna, Claudio; Gerdes, Axel; Lucci, Federico; Theye, Thomas

2017-06-01

The Menderes Massif of western Turkey is a key area to study feedback relationships between magma generation/emplacement and activation of extensional detachment tectonics. Here, we present new textural analysis and in situ U-(Th)-Pb titanite dating from selected samples collected in the transition from the undeformed to the mylonitized zones of the Salihli granodiorite at the footwall of the Neogene, ductile-to-brittle, top-to-the-NNE Gediz-Alaşheir (GDF) detachment fault. Ductile shearing was accompanied by the fluid-mediated sub-solidus transformation of the granodiorite to orthogneiss, which occurred at shallower crustal levels and temperatures compatible with the upper greenschist-to-amphibolite facies metamorphic conditions (530-580 °C and P < 2 GPa). The syn-tectonic metamorphic overgrowth of REE-poor titanite on pristine REE-rich igneous titanite offers the possibility to constrain the timing of magma crystallisation and solid-state shearing at the footwall of the Gediz detachment. The common Pb corrected 206Pb/238U (206Pb*/238U) ages and the REE re-distribution in titanite that spatially correlates with the Th/U zoning suggests that titanite predominantly preserve open-system ages during fluid-assisted syn-tectonic re-crystallisation in the transition from magma crystallization and emplacement (at 16-17 Ma) to the syn-tectonic, solid-state shearing (at 14-15 Ma). A minimum time lapse of ca. 1-2 Ma is then inferred between the crustal emplacement of the Salihli granodiorite and nucleation of the ductile extensional shearing along the Gediz detachment. The reconstruction of the cooling history of the Salihli granodiorite documents a punctuated evolution dominated by two episodes of rapid cooling, between 14 Ma and 12 Ma ( 100 °C/Ma) and between 3 and 2 Ma ( 105 °C/Ma). We relate the first episode to nucleation and development of post-emplacement of ductile shearing along the GDF and the second to brittle high-angle faulting, respectively. Our dataset

Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France)

NASA Astrophysics Data System (ADS)

Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jérémie; Li, Xian-Hua; Lin, Wei; Blein, Olivier; Bruguier, Olivier; Poujol, Marc

2018-02-01

A structural and petrochronological study was carried out in the southern part of the Belledonne crystalline massif. A first tectonometamorphic event, Dx, corresponds to the eastward thrusting of the Chamrousse ophiolitic complex characterized by a low-temperature-moderate-pressure metamorphism reaching 0.535 ± 0.045 GPa and 427.5 ± 17.5 °C. A subsequent D1 deformation is defined by a penetrative S1 foliation that mostly dips toward the west and displays an E-W- to NE-SW-trending mineral and stretching lineation L1. D1 is associated with a top-to-the east shearing and is responsible for the crustal thickening accommodated by the eastward nappe stacking and the emplacement of the Chamrousse ophiolitic complex upon the Rioupéroux-Livet unit. This event is characterized by an amphibolite facies metamorphism (0.58 GPa ± 0.06; 608 ± 14 °C) that attains partial melting at the base of the nappe pile (0.78 ± 0.07 GPa; 680.5 ± 11.5 °C). LA-ICP-MS U-Pb dating of monazite grains from the mica schists of the Rioupéroux-Livet unit constrain the age of D1 to 337 ± 7 Ma. The D2 tectono-metamorphic event is characterized by NE-SW trending, upright to NE-verging synfolial folding. Folding associated with D2 is pervasively developed in all lithotectonic units with the development of a steeply-dipping S2 foliation. In particular, D2 involves the uppermost weakly metamorphosed Taillefer unit. LA-ICP-MS U-Pb dating performed on detrital zircon grains shows that the Taillefer conglomerates was deposited during the Visean. A zircon SIMS U-Pb age of 352 ± 1 Ma from a plagioglase-rich leucocratic sill of the Rioupéroux-Livet unit is interpreted as the age of magmatic emplacement. Our results suggest that the D2 event took place between 330 Ma and 310 Ma. We propose a new interpretation of the tectonometamorphic evolution of the southern part of the Belledonne massif, focusing on the Middle Carboniferous stages of the Variscan orogeny.

Geochemical and Re-Os isotope constraints on the origin and age of the Songshugou peridotite massif in the Qinling orogen, central China

NASA Astrophysics Data System (ADS)

Nie, Hu; Yang, Jianzhou; Zhou, Guangyan; Liu, Chuanzhou; Zheng, Jianping; Zhang, Wen-Xiang; Zhao, Yu-Jie; Wang, Hao; Wu, Yuanbao

2017-11-01

The Songshugou peridotite massif in the Qinling orogenic belt is one of the largest orogenic spinel peridotite bodies in central China, but its origin remains controversial and its age is poorly constrained. We have carried out an integrated study of major and trace element composition, mineral chemistry, platinum group elements (PGE), as well as Re-Os isotope systematics of 1 harzburgite and 12 dunites from the Songshugou peridotite massif. These samples contain high Mg# olivine (90.0-91.3) and Cr# spinel (83.4-96.0). The harzburgite and dunites are characterized by relatively low whole-rock Al2O3 (0.32-0.60 wt.%), CaO (0.26-1.57 wt.%), and Na2O (0.07-0.12 wt.%) concentrations. The studied samples have very low concentrations of middle and heavy rare earth elements and exhibit enrichments in iridium-group platinum-group elements (IPGE) relative to palladium-group PGE. The Songshugou peridotites exhibit variable enrichments of light rare earth elements, large ion lithophile elements, Re, Zr, and Hf, which resulted from reactions with melt after their isolation from the convecting mantle. Combined with previous results, our data suggest that the Songshugou peridotites are highly refractory mantle residues derived from a forearc mantle wedge. 187Os/188Os values of the studied samples vary from 0.12073 to 0.12390, and 187Re/188Os ratios are 0.005-0.081. The average Re-Os model ages (TMA) and maximum Re depletion model age (TRD) of the Songshugou peridotites are ca. 1.2-1.1 Ga, suggesting a tectonic affinity to the South China Block and that the peridotites formed during the assembly of the Rodinia supercontinent. The Songshugou peridotites were sourced from a mantle wedge above a subduction zone, and finally incorporated into the underlying continental lithosphere by exhumation.

Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont

USGS Publications Warehouse

Ratcliffe, N.M.; Harris, A.G.; Walsh, G.J.

1999-01-01

Middle Ordovician (late Arenigian - early Caradocian) conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the Pinney Hollow Formation in the Eastern Cover sequence near West Bridgewater, Vermont. These are the first reported fossils from the metamorphic cover sequence rocks east of the Green Mountain, Berkshire, and Housatonic massifs of western New England. The conodonts are recrystallized, coated with graphitic matter, thermally altered to a color alteration index (CAI) of at least 5, and tectonically deformed. The faunule is nearly monospecific, consisting of abundant Periodon aculeatus Hadding? and rare Protopanderodus. The preponderance of Periodon and the absence of warm, shallow-water species characteristic of the North American Midcontinent Conodont Province suggest a slope or basin depositional setting. The conodont-bearing carbonaceous schist is traceable 3 km southeast to the Plymouth area, where it had been designated the uppermost member of the Plymouth Formation, previously regarded as Early Cambrian in age. The age and structural position of the carbonaceous schist above dolostones of the Plymouth Formation but below the Pinney Hollow Formation (upper Proterozoic and Lower Cambrian?) suggest that this unit may be correlative or time transgressive with the Ira Formation, which underlies the Taconic allochthons in the Vermont Valley. Such a correlation supports the concept of placing the western limit of the root zone of the Taconic allochthons beneath the Pinney Hollow Formation. An approximate absolute age assignment for the conodont-bearing rock is between 470 and 454 Ma. This suggests that dynamothermal metamorphism during the Taconian orogeny on the east flank of the Green Mountains was younger than early Caradocian, which is in accord with the middle Caradocian age of the Ira Formation west of the Green Mountain massif.

IODP Expedition 340T: Borehole Logging at Atlantis Massif Oceanic Core Complex

NASA Astrophysics Data System (ADS)

Blackman, D.; Slagle, A.; Harding, A.; Guerin, G.; McCaig, A.

2013-03-01

Integrated Ocean Drilling Program (IODP) Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP). Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800-1400 meters below seafloor (mbsf) portion of the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offset now extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution. doi:10.2204/iodp.sd.15.04.2013

Stimulation Of The Methane Production With The Use Of Changing Of The Rock Massif Physical Conditions

NASA Astrophysics Data System (ADS)

Baev, Mikhail; Khyamyalyaynen, Veniamin; Shevtsov, Aleksandr

2017-11-01

The commercial coalbed methane production success is majorly defined by the effectiveness of the use of special gas inflow stimulation methods. The necessity of using of such methods issubject to the aspects of searching and displacement of methane within the coal compound. Theanalysis of the ways of methane production stimulation from virgin coal formations is given. The description of the process of hydraulic fracturing (fracturing) as the most common stimulation method during the commercial coalbed methane production as well as its major advantages are presented. The present work provides data about the initiated laboratory research of sands collected from Kemerovo region deposits for the purpose of finding of the most prospective samples by means of anchoring of fractures. The prospectivity and ability to implement the hydraulic fracturing with the use of locally available sands acting as proppants are shown. The influence of the strain-stress state of the rock massif on the alteration of permeability and the necessity of its extension study with respect to different technological features of hydraulic fracturing is shown

First insights on the molybdenum-copper Bled M'Dena complex (Eglab massif, Algeria)

NASA Astrophysics Data System (ADS)

Lagraa, Karima; Salvi, Stefano; Béziat, Didier; Debat, Pierre; Kolli, Omar

2017-03-01

Molybdenum-Copper showings in the Eglab massif (eastern part of the Reguibat rise of Algeria), are found in quartz-monzodiorite and granodiorite of the Bled M'Dena complex, a Paleoproterozoic circular structure of ∼5 km in diameter, comprising volcanic and intrusive suites. The latter consist of quartz-diorite, quartz-monzodiorite and granodiorite with a metaluminous normative composition. They display an "adakitic character" with moderate light rare-earth element (LREE) enrichment, minor Eu anomalies, high Sr/Y ratio and low Yb concentration, suggestive of a hydrous, arc magma of volcanic-arc affinity. The mineralization occurs mostly in quartz + molybdenite + chalcopyrite stockwork veins marked by widespread propylitic alteration along the selvages. Molybdenite and chalcopyrite are commonly associated with calcite, which precipitated at relatively late stages of the hydrothermal alteration. Fluid inclusions related to the mineralization stage, range from aqueous to aqueous-carbonic to solid bearing. The latter inclusions have the highest homogenization temperature (up to ∼400 °C), are salt saturated, and commonly contain molybdenite and/or chalcopyrite crystals. The petrology and geochemistry of the host rocks, the style of the hydrothermal alteration, the ore mineral associations, and the characteristics of the fluid inclusions, are all coherent in indicating that the Bled M'Dena represents a Paleoproterozoic porphyry style Mo mineralization, which is far unreported in the African continent.

Today's sediment budget of the Rhine River channel, focusing on the Upper Rhine Graben and Rhenish Massif

NASA Astrophysics Data System (ADS)

Frings, Roy M.; Gehres, Nicole; Promny, Markus; Middelkoop, Hans; Schüttrumpf, Holger; Vollmer, Stefan

2014-01-01

The river bed of the Rhine River is subject to severe erosion and sedimentation. Such high geomorphological process rates are unwanted for economical, ecological, and safety reasons. The objectives of this study were (1) to quantify the geomorphological development of the Rhine River between 1985 and 2006; (2) to investigate the bed erosion process; and (3) to distinguish between tectonic, hydrological, and human controls. We used a unique data set with thousands of bedload and suspended-load measurements and quantified the fluxes of gravel, sand, silt, and clay through the northern Upper Rhine Graben and the Rhenish Massif. Furthermore, we calculated bed level changes and evaluated the sediment budget of the channel. Sediment transport rates were found to change in the downstream direction: silt and clay loads increase because of tributary supply; sand loads increase because of erosion of sand from the bed; and gravel loads decrease because of reduced sediment mobility caused by the base-level control exerted by the uplifting Rhenish Massif. This base-level control shows tectonic setting, in addition to hydrology and human interventions, to represent a major control on morphodynamics in the Rhine. The Rhine bed appears to be in a state of disequilibrium, with an average net bed degradation of 3 mm/a. Sand being eroded from the bed is primarily washed away in suspension, indicating a rapid supply of sand to the Rhine delta. The degradation is the result of an increased sediment transport capacity caused by nineteenth and twentieth century's river training works. In order to reduce degradation, huge amounts of sediment are fed into the river by river managers. Bed degradation and artificial sediment feeding represent the major sources of sand and gravel to the study area; only small amounts of sediment are supplied naturally from upstream or by tributaries. Sediment sinks include dredging, abrasion, and the sediment output to the downstream area. Large uncertainties

Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

USGS Publications Warehouse

Davis, J.C.; Hausberger, G.; Schermann, O.; Bohling, G.

1995-01-01

The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik O??sterreich, and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types. ?? 1995 International Association for Mathematical Geology.

Alpine thermal events in the central Serbo-Macedonian Massif (southeastern Serbia)

NASA Astrophysics Data System (ADS)

Antić, Milorad D.; Kounov, Alexandre; Trivić, Branislav; Wetzel, Andreas; Peytcheva, Irena; von Quadt, Albrecht

2016-07-01

The Serbo-Macedonian Massif (SMM) represents a crystalline belt situated between the two diverging branches of the Eastern Mediterranean Alpine orogenic system, the northeast-vergent Carpatho-Balkanides and the southwest-vergent Dinarides and the Hellenides. We have applied fission-track analysis on apatites and zircons, coupled with structural field observations in order to reveal the low-temperature evolution of the SMM. Additionally, the age and geochemistry of the Palaeogene igneous rocks (i.e. Surdulica granodiorite and dacitic volcanic rocks) were determined by the LA-ICPMS U-Pb geochronology of zircons and geochemical analysis of main and trace elements in whole-rock samples. Three major cooling stages have been distinguished from the late Early Cretaceous to the Oligocene. The first stage represents rapid cooling through the partial annealing zones of zircon and apatite (300-60 °C) during the late Early to early Late Cretaceous (ca. 110-ca. 90 Ma). It is related to a post-orogenic extension following the regional nappe-stacking event in the Early Cretaceous. Middle to late Eocene (ca. 48-ca. 39 Ma) cooling is related to the formation of the Crnook-Osogovo-Lisets extensional dome and its exhumation along low-angle normal faults. The third event is related to regional cooling following the late Eocene magmatic pulse. During this pulse, the areas surrounding the Surdulica granodiorite (36 ± 1 Ma) and the slightly younger volcanic bodies (ca. 35 Ma) have reached temperatures higher than the apatite closure temperature (120 °C) but lower than ca. 250 °C. The geochemistry of the igneous samples reveals late- to post-orogenic tectonic setting during magma generation.

Latest Cambrian-Early Ordovician rift-related magmatic activity in the Kouřim Unit, Bohemian Massif

NASA Astrophysics Data System (ADS)

Soejono, Igor; Machek, Matej; Sláma, Jiří; Janoušek, Vojtěch

2017-04-01

Pre-collisional history of high-grade Variscan complexes is mostly difficult to reveal, due to intense reworking during the development of the orogenic belt. An ancient magmatism could provide a unique possibility to study it. The Kouřim Unit represents an extensive pre-Variscan plutonic body involved into the tectonic collage of the Kutná Hora Crystalline Complex, at the northern margin of the Moldanubian Domain in the Bohemian Massif. The LA-ICP-MS zircon ages and geochemical characteristics of (meta-)igneous rocks from the Kouřim Unit allow us to determine the timing and nature of magmatic activity within this part of the Bohemian Massif and thus to decipher its pre-Variscan evolution. The Kouřim Unit is composed of strongly metamorphosed and deformed sequence of magmatic rocks, dominated mainly by various types of migmatites, coarse-grained orthogneisses and minor metadiorites. The newly obtained LA-ICP-MS U-Pb zircon ages of four orthogneisses ranging between 486 ± 2 Ma and 484 ± 2 Ma are interpreted as timing the magma crystallization. The single metadiorite gave concordia age of 337 ± 2 Ma interpreted as the age of migmatitization. Few discordant older ages from metadiorite are considered as older xenocrysts more or less reset during the Variscan metamorphism. The orthogneisses are acid (SiO2 = 68.6-76.4 wt. %), exclusively subaluminous and seem to form a single calc-alkaline trend, whereas the metadiorite is intermediate (SiO2 = 54.3 wt. %; mg# = 61), distinctly metaluminous and displays tholeiitic character. The chondrite-normalized REE patterns for the orthogneisses show LREE enrichment (LaN/YbN = 1.5-8.9) and deep negative Eu anomalies (Eu/Eu* = 0.42-0.32); the NMORB-normalized spiderplots feature LILE/HFSE enrichment with deep negative Nb- Ta-Ti anomalies. In contrast, both patterns of metadiorite resemble those of NMORB (LaN/YbN = 0.5, Eu/Eu* = 0.96). The apparent magmatic arc-like geochemical signature of the orthogneisses is interpreted as

Alteration and chemical U-Th-total Pb dating of heterogeneous high-uranium zircon from a pegmatite from the Aduiskii massif, middle Urals, Russia

NASA Astrophysics Data System (ADS)

Zamyatin, Dmitry A.; Shchapova, Yuliya V.; Votyakov, Sergey L.; Nasdala, Lutz; Lenz, Christoph

2017-09-01

The U-Th-Pb isotope system in the accessory mineral zircon may be disturbed, as for instance by the secondary loss of radiogenic lead. The recognition of such alteration is crucial for the sound interpretation of geochronology results, in particular for chemical dating by means of an electron probe micro-analyser (EPMA). Here we present the example of high-U zircon samples from a granite pegmatite from the Aduiskii Massif, Middle Urals, Russia. The structural and chemical heterogeneity of samples was characterised by EPMA, including joint probability distribution (JPD) analysis of back-scattered electrons (BSE), cathodoluminescence (CL) and U M β images, and by Raman and photoluminescence (PL) spectroscopy. We found a high-U interior region (U up to 11.4 wt%) without any obvious indication of alteration. This domain has stoichiometric composition, and its Raman spectrum is similar to that of amorphous ZrSiO4. In addition, altered lower-U regions are present that are non-stoichiometric and contain non-formula elements such as Ca, Al, Fe, and water up to several wt%. Their Raman spectra yielded a band near 760-810 cm-1 which is not related to any ZrSiO4 vibration; we assign it tentatively to the symmetric stretching of (UO2)2+ groups. This assignment is supported by the observation of a fairly intense PL phenomenon whose spectral position and vibrational-coupling structure strongly indicates a uranyl-related emission. Altered zones were formed by both fluid-driven diffusion reaction and coupled dissolution-reprecipitation processes. The variation of BSE and CL intensities in amorphous high-U zircon is controlled by its chemical composition and the presence of water and uranyl groups. We have determined a weighted mean EPMA age of 246 ± 2 Ma, which agrees reasonably well with previous dating results for the Aduiskii Massif.

Late Cretaceous extensional denudation along a marble detachment fault zone in the Kırşehir massif near Kaman, central Turkey

NASA Astrophysics Data System (ADS)

Lefebvre, Côme; Barnhoorn, Auke; van Hinsbergen, Douwe J. J.; Kaymakci, Nuretdin; Vissers, Reinoud L. M.

2011-08-01

In the Central Anatolian Crystalline Complex (CACC), 100 km scale metamorphic domains were exhumed in a context of north-south plate convergence during late Cretaceous to Cenozoic times. The timing, kinematics and mechanisms of exhumation have been the focus of previous studies in the southern Niğde Massif. In this study, we investigate the unexplored northern area regarding the tectonic features preserved on the edges of the Kırşehir Massif, based on detailed field-mapping in the Kaman area where high-grade metasediments, non-metamorphic ophiolites and monzonitic plutons are locally exposed together. Close to the contact with the ophiolites, west-dipping foliated marble-rich rocks display mylonites and discrete protomylonites with normal shear senses indicating a general top-to-the W-NW direction. Both of these structures have been brittlely overprinted into cataclastic corridors parallel to the main foliation. The mylonite series and superimposed brittle structures together define the Kaman fault zone. The study of the evolution of calcite deformation fabrics along an EW section supported by Electron Back Scattered Diffraction measurements (EBSD) on representative fabrics indicates that the Kaman fault zone represents an extensional detachment. In Ömerhacılı, in the vicinity of the Baranadağ quartz-monzonite, the metamorphic sequence shows static annealing of the calcite mylonitic fabrics. This evidence suggests that intrusion took place at shallow depth (˜10 km) into an already exhuming metamorphic sequence. As a consequence for the Kaman area, buried metasediments have been rapidly exhumed between 84 and 74 Ma (˜1 km/Ma) where exhumation along a detachment zone, displaying a top-to-the W-NW shear motion, took place in the mid to upper crust prior to magmatic intrusion in the late Campanian. As the intrusion cut through the detachment fault, the main shearing deformation ceased. Brittle tectonics coupled with erosion likely took over during the final

Multi-response calibration of a conceptual hydrological model in the semiarid catchment of Wadi al Arab, Jordan

NASA Astrophysics Data System (ADS)

Rödiger, T.; Geyer, S.; Mallast, U.; Merz, R.; Krause, P.; Fischer, C.; Siebert, C.

2014-02-01

A key factor for sustainable management of groundwater systems is the accurate estimation of groundwater recharge. Hydrological models are common tools for such estimations and widely used. As such models need to be calibrated against measured values, the absence of adequate data can be problematic. We present a nested multi-response calibration approach for a semi-distributed hydrological model in the semi-arid catchment of Wadi al Arab in Jordan, with sparsely available runoff data. The basic idea of the calibration approach is to use diverse observations in a nested strategy, in which sub-parts of the model are calibrated to various observation data types in a consecutive manner. First, the available different data sources have to be screened for information content of processes, e.g. if data sources contain information on mean values, spatial or temporal variability etc. for the entire catchment or only sub-catchments. In a second step, the information content has to be mapped to relevant model components, which represent these processes. Then the data source is used to calibrate the respective subset of model parameters, while the remaining model parameters remain unchanged. This mapping is repeated for other available data sources. In that study the gauged spring discharge (GSD) method, flash flood observations and data from the chloride mass balance (CMB) are used to derive plausible parameter ranges for the conceptual hydrological model J2000g. The water table fluctuation (WTF) method is used to validate the model. Results from modelling using a priori parameter values from literature as a benchmark are compared. The estimated recharge rates of the calibrated model deviate less than ±10% from the estimates derived from WTF method. Larger differences are visible in the years with high uncertainties in rainfall input data. The performance of the calibrated model during validation produces better results than applying the model with only a priori parameter

Proterozoic Os model ages of sulfides in mantle peridotites from the Ronda massif (southern Spain): insights into the evolution of the W European subcontinental lithospheric mantle

NASA Astrophysics Data System (ADS)

Marchesi, Claudio; Griffin, William L.; Garrido, Carlos J.; Bodinier, Jean-Louis; O'Reilly, Suzanne Y.; Pearson, Norman J.

2010-05-01

The western part of the Ronda peridotite massif (southern Spain) consists mainly of highly foliated spinel-peridotite tectonites and undeformed granular peridotites that are separated by a recrystallization front. The spinel tectonites are interpreted as volumes of ancient subcontinental lithospheric mantle and the granular peridotites as a portion of lithospheric mantle that underwent partial melting and pervasive percolation of basaltic melts induced by Cenozoic asthenospheric upwelling. The Re-Os isotopic signature of sulfides from the granular domain and the recrystallization front mostly coincides with that of grains in the spinel tectonites. This indicates that the Re-Os radiometric system in sulfides was highly resistant to partial melting and percolation of melts induced by Cenozoic lithospheric thermal erosion. The Re-Os isotopic systematics of sulfides in the Ronda peridotites thus mostly conserve the geochemical memory of ancient magmatic events in the lithospheric mantle. Os model ages record two Proterozoic melting episodes at ~ 1.6-1.8 Ga and 1.2-1.4 Ga, respectively. The emplacement of the massif into the subcontinental lithospheric mantle probably coincided with one of these depletion events. A later metasomatic episode caused the precipitation of a new generation of sulfides at ~ 0.7-0.9 Ga. These Proterozoic Os model ages are consistent with results obtained for several mantle suites in central/western Europe and northern Africa as well as with the Nd model ages of the continental crust of these regions. This suggests that the events recorded in mantle sulfides of the Ronda peridotites reflect different stages of generation of the continental crust in the ancient Gondwana supercontinent

Evaluation of the Solar Water Disinfection Method Using an Ultraviolet Measurement Device

NASA Astrophysics Data System (ADS)

Leung, H.

2015-12-01

Drinking water security is a growing problem for the population of planet Earth. According to WHO, more than 750 million people on our planet lack access to safe drinking water, resulting in approximately 502,000 diarrhoea deaths in 2012. In order to solve this problem, the Swiss water research institute, Eawag, has developed a method of solar water disinfection, called, "SODIS" The theory of SODIS is simple to understand: a clear plastic bottle filled with water is placed under full sunlight for at least 6 hours. The ultraviolet radiation kills the pathogens in the water, making the originally contaminated water safe for drinking. In order to improve this method, Helioz, an Austrian social enterprise, has created the WADI, a UV measurement device which determines when water is safe for drinking using the SODIS method. When using the WADI, the device should be placed under the sun and surrounded with bottles of water that need to be decontaminated. There is a UV sensor on the WADI, and since the bottles of water and the WADI will have equal exposure to sunlight, the WADI will be able to measure the impact of the sunlight on the contaminated water. This experiment tests the accuracy of the WADI device regarding the time interval needed for contaminated water to be disinfected. The experiment involves using the SODIS method to purify bottles of water contaminated with controlled samples of E. coli. Samples of the water are taken at different time intervals, and the E. coli levels are determined by growing the bacteria from the water samples on agar plates. Ultimately, this helps determine when the water is safe for drinking, and are compared against the WADI's measurements to test the reliability of the device.

Migmatization and low-pressure overprinting metamorphism as record of two pre-Cretaceous tectonic episodes in the Santander Massif of the Andean basement in northern Colombia (NW South America)

NASA Astrophysics Data System (ADS)

Zuluaga, C. A.; Amaya, S.; Urueña, C.; Bernet, M.

2017-03-01

The core of the Santander Massif in the northern Andes of Colombia is dominated by migmatitic gneisses with a < 1.71 Ga protolith and was affected by continuous interactions of oceanic plates to the west and the northwestern corner of the South American continental plate. The exposed metamorphic core of the massif offers a unique opportunity to understand the tectonic evolution of northwestern South America. We present new metamorphic petrology and geochemistry data from the Bucaramanga Gneiss in the Santander Massif to document part of this tectonic evolution from late Proterozoic to Jurassic times. Metapelitic migmatite gneiss, quartz-feldspathic gneiss, and amphibolite from the Bucaramanga Gneiss recorded metamorphic peak conditions in the range of 660-850 °C at pressures of > 7.5 kbar. Lithologies are overprinted by low-pressure metamorphism, related to extensive Jurassic intrusions and linked with growth of cordierite and equilibration of low-pressure mineral assemblages, recorded metamorphic conditions are < 750 °C and < 6.5 kbar. Observed leucosomes display significant compositional variations and can be grouped in three groups: i) Group One leucosomes with high total REE content, high LREE/HREE, and negative Eu anomaly, ii) Group Two leucosomes with low total REE, low LREE/HREE, and positive Eu anomalies, and iii) Group Three leucosomes with relatively low LREE/HREE and strong positive Eu anomaly. Geochemical data support the interpretation that Group Two leucosomes crystallized from melts originated in a partial melting event affecting mostly pelitic and quartz-feldspathic lithologies with fluid-present melting reactions. The evaluation of mesosomes (amphibolite, pelitic and quartz-feldspathic rocks) as potential protoliths or restites indicates that at least two pelitic samples of the analyzed lithologies have characteristics consistent with the occurrence of fluid-present melting reactions involving quartz and feldspar. The leucosomes produced by

Preliminary geologic map of the Thaniyat Turayf Quadrangle, sheet 29C, Kingdom of Saudi Arabia

USGS Publications Warehouse

Meissner, C.R.; Dini, S.M.; Farasani, A.M.; Riddler, G.P.; Smith, G.H.; Griffin, M.B.; Van Eck, Marcel

1990-01-01

A new structural concept introduced in this report extends the Wadi as Sirhan graben complex southeastward into the An Nafud. This concept increases the size of the potentially oil-and-gas-bearing Wadi as Sirhan region to include the An Nafud.

Age and isotopic marks of K-rich Manning Massif trachybasalts: an evidence for Lambert-Amery rift-system initiation (East Antarctica)

NASA Astrophysics Data System (ADS)

Leitchenkov, German; Belyatsky, Boris; Lepekhina, Elena; Antonov, Anton; Krymsky, Robert; Andronikov, Alex; Sergeev, Sergey

2017-04-01

Volcanic rocks from the Manning Massif, which is situated in the western flank of the Paleozoic-Late Mesozoic Lambert Rift (East Antarctica), belong to a rare type of alkaline magmatism within the Precambrian East Antarctic Craton. K-rich olivine trachybasalts compose some flows resting upon a surface of Precambrian granulite terrain, each flow of 2.5-7 m in thickness and total section not less than 30 m. Each flow sequence comprises of glassy chilled base with vitroporphyritic texture, fine-plated vesicular basalt with interstitial texture, massive fine-grained basalt with porphyritic microlitic texture, amigdaloidal aphanitic basalt with poikilophytic texture, and vesicular mandelstone of slag crust with vitroporphyritic texture [Andronikov et al., 1998]. Rb-Sr and K-Ar isotopic age of this eruption was estimated as 40-50 Ma and the main reason for this Cenozoic continental volcanism was supposed the post-rift tectonic activity [Andronikov et al., 1998]. But the isotopic characteristics of these trachybasalts are very similar to those obtained for the part of spinel lherzolite and spinel-garnet lherzolite xenoliths from the Mesozoic alkaline picrite of the adjacent Jetty Peninsula region. That could be evidence of the trachybasalt mantle source in long-lived enriched upper mantle beneath the region, either under the lowermost levels of spinel lherzolite facies or on the highest levels of garnet lherzolite facies conditions. To reveal tectonic position of these enigmatic volcanics, we have studied 16 samples from different parts of basaltic flows for U-Pb geochronology and Pb-Sr-Nd-Os isotopic characteristics. U-Pb SIMS SHRIMP-II analysis was performed for 68 apatite grains from 5 samples. All obtained data-points are approximated by discordia line (MSWD=1.6) on Tera-Wasserburg diagram, corresponding to the age of 346±46 Ma. Common Pb isotope composition of these apatites differs from the model by increased 206Pb/204Pb (19.8) and 207Pb/204Pb (18.3) that means the

Tephras in lacustrine sediments of the Sarliève marsh (French Massif Central): age and preservation

NASA Astrophysics Data System (ADS)

Fourmont, Agathe; Macaire, Jean-Jacques; Bréhéret, Jean-Gabriel; Argant, Jacqueline; Prat, Béatrice; Vernet, Gérard

2006-12-01

The Sarliève marsh sediments (Massif Central, France) contain two tephras. The first tephra [ 13.7±0.4ka(2δ), ca. 12 000 BP], regionally well known, enables to date the beginning of lacustrine infill to the Lateglacial. The second tephra, the 'tephra de Sarliève', the emitting volcano of which is unknown, would be dated to around the Early Subboreal from pollen data. This occurrence, after the discovery of the 'tephra de Beaunit', emphasizes that volcanic eruption(s) occurred in the 'Chaîne des Puys' or in the volcanic Cézallier more than 1000 years after the last known eruption (Pavin) in the 'Chaîne des Puys' at around 6.6/6.7 ka (5800/5900 BP). In the Sarliève piles, these tephras, well preserved in thick and more silicated deposits of deltas, were not observed in carbonated basin sediments where they were altered. The abundance of authigenic zeolites formed during the Lateglacial in restricted depocentre lacustrine waters allows us to detect initial CF1 tephra occurrence. To cite this article: A. Fourmont et al., C. R. Geoscience 338 (2006).

A new genus and species of marine catfishes (Siluriformes; Ariidae) from the upper Eocene Birket Qarun Formation, Wadi El-Hitan, Egypt.

PubMed

El-Sayed, Sanaa E; Kora, Mahmoud A; Sallam, Hesham M; Claeson, Kerin M; Seiffert, Erik R; Antar, Mohammed S

2017-01-01

Wadi El-Hitan, the UNESCO World Heritage Site, of the Fayum Depression in the northeast part of the Western Desert of Egypt, has produced a remarkable collection of Eocene vertebrates, in particular the fossil whales from which it derives its name. Here we describe a new genus and species of marine catfishes (Siluriformes; Ariidae), Qarmoutus hitanensis, from the base of the upper Eocene Birket Qarun Formation, based on a partial neurocranium including the complete left side, partial right dentary, left suspensorium, two opercles, left pectoral girdle and spine, nuchal plates, first and second dorsal spines, Weberian apparatus and a disassociated series of abdominal vertebrae. All of the elements belong to the same individual and some of them were found articulated. Qarmoutus gen. nov. is the oldest and the most complete of the Paleogene marine catfishes unearthed from the Birket Qarun Formation. The new genus exhibits distinctive features not seen in other African Paleogene taxa, such as different sculpturing on the opercle and pectoral girdle with respect to that on the neurocranium and nuchal plates, denticulate ornamentation on the skull bones arranged in longitudinal rows and forming a radiating pattern on the sphenotic, pterotic, extrascapular and the parieto-supraoccipital, indentations or pitted ornamentation on the nuchal plates as well as the parieto-supraoccipital process, strut-like radiating pattern of ornamentation on the opercle from the proximal articulation to margins, longitudinal, curved, reticulate ridges and tubercular ornamentations on the cleithrum, sinuous articulation between the parieto-supraoccipital process and the anterior nuchal plate, long, narrow, and arrowhead shaped nuchal shield, very small otic capsules restricted to the prootic. Multiple parsimony and Bayesian morphological phylogenetic analyses of Ariidae, run with and without "molecular scaffolds", yield contradictory results for the placement of Qarmoutus; the genus is either

Preliminary geologic map of the Turayf Quadrangle, sheet 31C, and part of the An Nabk quadrangle, sheet 31B, Kingdom of Saudi Arabia

USGS Publications Warehouse

Meissner, C.R.; Riddler, G.P.; Van Eck, Marcel; Aspinall, N.C.; Farasani, A.M.; Dini, S.M.

1989-01-01

Oil shows have been reported in Cretaceous rocks of the Wadi As Sirhan depression, and oil has been discovered recently nearby in Jordan. Geologic and geophysical conditions are favorable for the entrapment of oil in the Wadi As Sirhan area and additional exploration is recommended.

Debris flows of the mountain massif of Hjorthfjellet and Adventtoppen, Svalbard: Implications for gullies on mountains in the Argyre basin, Mars

NASA Astrophysics Data System (ADS)

Reiss, D.; Hiesinger, H.; Zanetti, M.; Hauber, E.; Johnsson, A.; Carlsson, E.; Raack, J.; Olvmo, M.; Johansson, H. A. B.; Johansson, L.; Fredriksson, S.; Schmidt, H. T.; McDaniel, S.; Heldmann, J. L.; McKay, C. P.

2008-09-01

will focus on the regional distribution of gullies on the Hjorthfjellet and Adventtoppen mountain massif (Fig. 1, inset and Fig. 2), and detailed local studies of individual gullies on the same mountain massif are carried out as described by [8] and [9]. The Hjorthfjellet and Adventtoppen mountain massif consists of four stratigraphic units of sandstone and shales from the Tertiary and Mesozoic [10]. Several studies concerning talus slopes and debris flows on Svalbard have been performed in the last decades [e.g., 11, 12, 13, 14]. Regional studies of [14] using airborne imagery revealed that there are differences in the frequency and activity of debris flows on Svalbard between east- and west-facing slopes. Åkerman [14] suggested that differences in the solar radiation, the depth of the active layer and the amount of precipitation cause variances in the morphology and morphometry of the debris slopes as well as variances in the frequency and age of debris flows between east- and west-facing slopes. Studies and direct observations imply that debris flows on Svalbard are triggered by high intensity rainfall [e.g., 14, 15]. Gullies on mountains in Argyre basin, Mars For a comparative study on Mars we chose the Argyre region. Several isolated mountain massifs occur in the Nereidum and Charitum Montes (Fig. 3) with similar morphologies as the studied massif in Svalbard. A first data analysis with High Resolution Stereo Camera (HRSC) data revealed that gullies occur on the mountain slopes only at specific orientations. Fig. 4 shows an example of an isolated mountain, on which gullies only occur on west-facing slopes. Project Description The formation of gullies on Earth depends on several parameters, including rainfall and/or melting of snow, the presence of steep slopes, and sufficient amounts of fines/debris [e.g., 16]. As on Earth, the differences of slope angles and variabilities in bedrock and grain sizes influence the regional occurrence of gullies [17]. The main

Contribution of GIS to evaluate surface water pollution by heavy metals: Case of Ichkeul Lake (Northern Tunisia)

NASA Astrophysics Data System (ADS)

Yazidi, Amira; Saidi, Salwa; Ben Mbarek, Nabiha; Darragi, Fadila

2017-10-01

The concentrations of nutrients and heavy elements in the surface water of the lake Ichkeul, main wadis which feed directly and thermal springs that flow into the lake, are measured to evaluate these chemical elements. There are used to highlight the interactions between these different aquatic compartments of Ichkeul. All metal concentrations in lake water, except Cu, were lower than the maximum permitted concentration for the protection of aquatic life. The results show that the highest concentrations are located in the eastern and south-eastern part of the lake where the polluted water comes from the lagoon of Bizerte through the wadi Tinja as well as from the city of Mateur through the wadi Joumine. The pollution indices and especially the heavy metal evaluation index (HEI) show high pollution specially located at the mouths of wadis and an increase of heavy metal concentrations, as a result of uncontrolled releases of domestic and industrial wastewater.

Geotherms and heat flow estimates in the Odra Fault Zone (NE margin of Bohemian Massif, Central Europe) and its relationships to geological structure of NE termination of the European Variscan Orogen

NASA Astrophysics Data System (ADS)

Puziewicz, Jacek; Czechowski, Leszek; Majorowicz, Jacek; Pietranik, Anna; Grad, Marek

2017-04-01

The NE margin of Variscan Orogen in Europe comprises Sudety Mts., Fore-Sudetic Block, Odra Fault Zone and Fore-Sudetic Homocline. The Sudety Mts. together with the located to the NE Fore-Sudetic Block form NE part of the Bohemian Massif. The Variscan crystalline basement is exposed at the surface here. The Odra Fault Zone is situated further to the NE. It is a ca. 20 km wide horst of crystalline basement, hidden beneath relatively thin (< 1000 m) Permian-Mesozoic and Cenozoic sedimentary sequences and is called the Odra Horst in the following. This horst marks the margin of stretching to NE Fore-Sudetic Homocline, in which the crystalline basement is dipping to NE under thickening Permo-Mesozoic strata, covered by few hundred meter thick Cenozoic sedimentary layer (Żelaźniewicz et al. 2016 and references therein). The Odra Horst is possibly a continuation of the Mid German Crystalline High at the NE side of the Bohemian Massif (Dörr et al. 2006). The copper mines located at the central part of the Odra Horst at depth 600 - 1000 m enable the numerous high-quality temperature measurements. However, complicated geometry of geological units requires 3D simulations. We use 3D numerical thermal model for the considered region. The heat flow in the region is 80 mW/m2 (corrected for paleclimate). This value is higher than in the neighbouring parts of Sudetes and Fore-Sudetic Block ( 70 mW/m2) and compares rather to positive heat flow anomaly stretching NW-SE in Wielkopolska region north of the Dolsk Fault and continuing to NE Germany. This anomaly corresponds crudely to the extent of the Permian volcanic province of Polish and North-East German Basin. Unfortunately, preliminary results of the model are not conclusive, because they depend on many parameters, (compare e.g. Puziewicz et al 2012). It remains an open question if this anomaly could be related to the lithospheric mantle thermal anomalies (Tesauro et al. 2009) or is rather due to crustal rock contributions

The "Escarot" gas seep, French Massif Central: CO2 discharge from a quiescent volcanic system - Characterization and quantification of gas emissions

NASA Astrophysics Data System (ADS)

Gal, F.; Leconte, S.; Gadalia, A.

2018-03-01

Natural CO2 emissions from the volcanic rocks of the French Massif Central are poorly constrained. It is of interest better to assess the emission of such non-anthropogenic gases that may significantly contribute to the global carbon budget. We quantified the CO2 emissions to the atmosphere in a small area (0.052 km2) located in the Massif Central close to Lake Pavin, the most recent volcanic edifice in metropolitan France. The specific character of this area, known as the Escarot mofette, was earlier studied for soil-gas concentrations only. In June 2017, we used the accumulation chamber method for measuring CO2 flux and related O2 depletion in the gases emitted at the soil/atmosphere interface, resulting in 176 data acquisitions over four days. In addition, 44 soil-gas concentration measurements were made at selected locations. CO2 emission rates are estimated at 8100 ± 1800 tons/year of deep-seated CO2 and at 660 ± 440 tons/year of biologically produced CO2. The uncertainty on these evaluations comes from the high-frequency variability of CO2 efflux in the more emissive areas and from the occurrence of heavy precipitation events. Though unexpected, these events were used for quantifying the decreases in CO2 efflux, which were as high as 500% over a few hours or even days in some locations. However, repeat acquisitions performed under more favourable weather conditions showed errors of commonly accepted amplitude (±15%). The area showed several degassing centres aligned along a NNW-SSE direction that correlates well with known geological structures, proving the ability of soil-gas methods to map hidden faults. The whole area is characterized by strong CO2 enrichment and related O2 depletion, but it is nonetheless possible to detect areas influenced by the rise of deep-seated gases and a few peripheral areas where biological processes dominate (CO2 up to 10% vol.). This study of gas emissions in a non-urban area also provides complementary information that is

An Archaean Tonalite-Trondhjemite-Granodiorite Association of the Kursk Block (Voronezh Massif): Composition, Age, and Correlation with the Ukrainian Shield

NASA Astrophysics Data System (ADS)

Savko, K. A.; Samsonov, A. V.; Larionov, A. N.; Korish, E. Kh.; Bazikov, N. S.

2018-01-01

Framing of the Archaean greenstone belts of the Kursk Block (KB) of the East Sarmatia preserves rocks of the TTG association: those do not form massifs with distinct boundaries, but occur as fields gradually transiting into gneisses and migmatites. According to Sm-Nd isotope-geochemical data, the TTG are characterized by positive values of ɛNd(2960) = +0.3…+1.6 and protolith model ages of T Nd( DM) = 3100-3200 Ma. Magmatic protoliths of the Kursk Block TTG were formed about 2960 Ma by melting from a juvenile basite source. These age estimates are significantly younger than heterochronous (3.19, 3.13 and 3.07 Ga) TTGs of the Middle Dnieper granite-greenstone terrane. On the other hand, the similarity of ɛNd(T) implies a single source of their protoliths. Consequently, the KB TTGs, apparently, are a result of transformation of an older sial crust preserved within the Middle Dnieper Block.

Une complication rare des léiomyomes utérins: hémopéritoine massif par rupture de varices

PubMed Central

Ymele, Florent Fouelifack; Tsuala, Jovanny Fouogue; Fouedjio, Jeanne Hortence; Nangué, Charlette; De Kayo, Caroline Kayo; Dobgima, Pisoh Walter; Mbu, Robinson Enoh

2013-01-01

Les léiomyomes utérins sont des causes exceptionnelles d'hémopéritoine. Nous rapportons ici le cas d'une femme de 46 ans nullipare, en instance d'une hystérectomie totale indiquée pour utérus polymyomateux symptomatique. Elle a été opérée en urgence pour hémopéritoine aigu et massif compliqué de choc hémorragique. L'origine de l'hémopéritoine était la rupture spontanée d'une varice du léiomyome. Quoique rare l'éventualité d'un hémopéritoine causé par un fibrome utérin devrait être évoquée devant tout abdomen aigu spontané chez une femme en âge de procréer. La présence de varices sur les fibromes augmenterait le risque d'hémorragie spontanée. PMID:23717724

Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

USGS Publications Warehouse

Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

2002-01-01

The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

Age and geochemistry of Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Luan, Jin-Peng; Xu, Wen-Liang; Wang, Feng; Wang, Zhi-Wei; Guo, Peng

2017-10-01

This study presents new zircon U-Pb ages and geochemical data for Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif (SZRM) of NE China. This dataset provides insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent. The zircon U-Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages: (1) a ∼917-911 Ma suite of syenogranites and monzogranites, and (2) an ∼841 Ma suite of granodiorites. The 917-911 Ma granitoids contain high concentrations of SiO2 (67.89-71.18 wt.%), K2O (4.24-6.91 wt.%), and Al2O3 (14.89-16.14 wt.%), and low concentrations of TFe2O3 (1.63-3.70 wt.%) and MgO (0.53-0.88 wt.%). They are enriched in the light rare earth elements (LREE) and the large ion lithophile elements (LILE), are depleted in the heavy REE (HREE) and the high field strength elements (HFSE; e.g., Nb, Ta, and Ti), and have slightly positive Eu anomalies, indicating that they are geochemically similar to high-K adakitic rocks. They have zircon εHf (t) values and TDM2 ages from -4.4 to +1.5 and 1915 Ma to 1592 Ma, respectively, suggesting that they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material. In comparison, the 841 Ma granodiorites contain relatively low concentrations of Al2O3 (14.50-14.58 wt.%) and K2O (3.27-3.29 wt.%), relatively high concentrations of TFe2O3 (3.78-3.81 wt.%) and the HREE, have negative Eu anomalies, and have zircon εHf (t) values and TDM2 ages from -4.7 to +1.0 and 1875 to 1559 Ma, respectively. These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material. The ∼917-911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting, whereas the ∼841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic

A brief investigation of the surface-water hydrology of Yemen Arab Republic

USGS Publications Warehouse

Riggs, Henry Chiles

1977-01-01

Yemen, near the southwest tip of the Arabian Peninsula, is a mountainous country bordered by a desert on the east and a coastal plain on the west. Rainfall is low and seasonal; consequently, most streams (wadis) are ephemeral. The natural flow regimens of many of the smaller wadis are modified by terracing for agriculture. The only streamflow data available in Yemen are short records on four large wadis. A brief field investigation and application of reconnaissance techniques are the bases for the largely qualitative description of the hydrology, and for the proposal to collect streamflow data needed for orderly development of the expanding economy. (Woodard-USGS)

Distribution and PGE mineralization in the formation of chromitite in ophiolite complexes (Ospina-Kitoi Kharanur and ultrabasic massifs of Eastern Sayan, Sousern Siberia)

NASA Astrophysics Data System (ADS)

Kiseleva, Olga; Zhmodik, Sergei

2015-04-01

New study of PGE in restitic ultrabasic (Kharanur and Ospin-Kitoi) massifs from North and South branches (Dobretsov et al., 1985) of the ophiolite complexes in south-eastern part of the Eastern Sayan show their presence in chromitites of both branches belonging to the different geodynamic settings. Modern concepts model includes several mechanisms of podiform chromitite origin reflected in the chemistry of Cr-spinels (Arai, Yurimoto, 1994; Ballhaus, 1998; Uysal et al., 2009 et al.): 1) partial melting of upper mantle rocks, 2) mixing of primitive melts with melts enriched in SiO2, 3) melt-rock interaction. We estimated the types of interaction of mafic melts with mantle peridotites, with the formation of chromite bodies. For ore chrome spinelides from northern branch (Al2O3) melt = 8 - 14 wt%, (TiO2) melt = 0 - 0,4 wt%, (Fe/Mg) melt = 0,5 - 2,4; Southern branch (Al2O3) melt = 10 - 13 wt%, (TiO2) melt = 0,1 wt%, (Fe/Mg) melt = 0,3 - 1 (Kiseleva, 2014). There are two types of PGE distribution Os-Ir-Ru (I) and Pt-Pd (II). Type I chromitites (mid-Al#Cr-spinels) revealed only Os-Ir-Ru distributions; type II (low-Al#Cr spinelides) show both Os-Ir-Ru and (Pt-Pd) distributions (Kiseleva et al., 2012, 2014). PGE distribution in ultramafic peridotites and chromitites reflects PGE fractionation during partial melting (Barnes et al., 1985; Rehkämper et al., 1997). Processes bringing to extreme fractionation of PGE, may be associated with fluid-saturated supra subduction environment where melting degree near 20% and above is sufficient for the release of PGE from the mantle source (Dick, Bullen, 1984; Naldrett, 2010). Enrichment in PPGE together with a high content of IPGE in same chromite bodies is attributed to the second step of melting, and formation of S-enriched and saturated in PGE melts (Hamlyn, Keays, 1986; Prichard et al., 1996). For type I chromitites platinum group minerals (PGM) are presented by Os-Ir-Ru system. In type II chromitites PGM are represented by Os

Link of grabens and reactivated mantle boundaries in western Bohemian Massif

NASA Astrophysics Data System (ADS)

Babuska, Vladislav; Plomerova, Jaroslava; Vecsey, Ludek; Munzarova, Helena

2015-04-01

To study relations between mantle and crustal fabrics in the Bohemian Massif (BM), we model 3D anisotropy of the mantle lithosphere by inverting and interpreting jointly P-wave travel-time deviations and shear-wave splitting parameters of teleseismic waves recorded at portable and permanent stations operating in the BM for more than 20 years. Changes in orientation of the large-scale anisotropy in the mantle lithosphere, caused by systematic preferred orientation of olivine, identify boundaries of domains representing original micro-plates assembled during the Variscan orogeny. Consistent anisotropy of the mantle-lithosphere domains, with distinct changes at their boundaries, documents rigidity and a long memory of pervasive olivine fabrics. Some of the palaeo-plate boundaries represent weak elements of the assemblage that can be later rejuvenated. This is why graben structures in the western BM developed above the identified mantle boundaries. The Eger (Ohře) Rift (ER) originated above the ENE oriented mantle suture between the Saxothuringian (ST) in the north-west and the Moldanubian (MD) and Teplá-Barrandian (TB) in the south-east. The most significant graben structure, accompanied by a rich Cenozoic volcanic activity, developed above the central part of the ST/TB suture that witnessed a subduction down to ~150 km, as documented by findings of microdiamonds in ST granulites. The smaller-scale NNW oriented Cheb-Domažlice Graben (CDG) is located above the mantle boundary between the western rim of the TB and the MD. Unlike the suture beneath the ER, this boundary does not show any sign of a deep subduction and it is characterized by a less well developed graben structure and a weak volcanic activity. In both grabens we observe local shifts between the equivalent crustal and mantle boundaries of the units as large as ~20 km. The shift indicates a Variscan detachment of the crust from the mantle lithosphere. Cenozoic rifting and the graben structures developed

High morphogenic activity in the permafrost-affected rock walls of the Mont Blanc massif during the 2015 summer heat wave

NASA Astrophysics Data System (ADS)

Ravanel, Ludovic; Magnin, Florence; Deline, Philip

2016-04-01

In order to test the geomorphological hypothesis on the link between permafrost degradation and rock wall destabilisation, we survey all the rockfalls that occur in the central part of the Mont-Blanc massif using a network of observers since 2007. 511 rockfalls (100 < V < 45,000 m3) have been documented, year 2015 included. Between 2007 and 2014, the average number of destabilizations was 44 (from 17 in 2014 with a cold summer to 72 in 2009 with a relatively hot summer). In 2015, 160 events were recorded i.e. 4 times more than the annual average of the previous years. That makes the year 2015 similar to 2003 that was characterized by its summer heatwave triggering 152 rockfalls in the area currently covered by the network of observers, as shown by the analysis of a SPOT-5 image. Observations of 2015 are discussed and crossed with a statistical model of the Mean Annual Rock Surface Temperature (MARST) for the 1961-1990 period, implemented on a 4-m-resolution DEM of the Mont Blanc massif, and temperature measurements in three 10-m-deep boreholes at the Aiguille du Midi (3842 m a.s.l.), where the summer 2015 active layers have been the thickest since the start of measurements in 2009 (e.g. 3.6 m in the NE face against 2.9 m in average during the previous years). Before 2015, 90 % of the inventoried rockfalls occurred in areas where MARST is in the range -5 to 1°C, whereas only 50 % of the whole rock wall area above 2000 m a.s.l. covers this temperature range. With an air 0°C isotherm which sometimes exceeded the summit of Mont Blanc (4809 m a.s.l.) during the 2015 Summer, conditions were particularly unfavorable for mountaineering. Numerous rescues were carried out to climbers technically blocked by uncommon conditions or injured by rockfalls. On the normal route to the summit of Mont Blanc, two administrative closures of the Goûter hut (3835 m a.s.l.) were necessary to prevent climbers from the huge risk of rockfalls in the access couloir, known for its rockfall

Geochemistry and metamorphism of the Mouriscas Complex, Ossa-Morena/Central Iberian zone boundary, Iberian Massif, Central Portugal: Implications for the Cadomian and Variscan orogenies

NASA Astrophysics Data System (ADS)

Henriques, S. B. A.; Neiva, A. M. R.; Tajčmanová, L.; Dunning, G. R.

2018-01-01

The Mouriscas Complex is a deformed and metamorphosed predominantly mafic igneous complex of Ediacaran and Ordovician age and crops out at the Ossa-Morena/Central Iberian zone boundary in the Iberian Massif, Central Portugal. It comprises amphibolite with Neoproterozoic protoliths (ca. 544 Ma), protomylonitic felsic dykes derived from younger trondhjemitic protoliths (ca. 483 Ma) and garnet amphibolite derived of even younger dioritic protoliths (ca. 477 Ma). The protoliths of the Neoproterozoic amphibolites are calc-alkaline magmas of basic to intermediate compositions with intraplate and active continental margin affinities and are considered to represent the final phase of the Cadomian arc magmatism. They are interpreted to have originated as coarse-grained intrusions, likely gabbro or diorite and generated from the partial melting of meta-igneous lower crust and mantle. Their emplacement occurred near the Cadomian metamorphic event dated at ca. 540 Ma (P = 7-8 kbar and T = 640-660 °C) which is interpreted to represent a continental collision. During the Late Cambrian-Early Ordovician an extensional episode occurred in the central-southern Iberian Massif and was also observed in other areas of the Variscan Orogen. It led to mantle upwelling and to the development of an aborted intracratonic rift located at the Ossa-Morena/Central Iberian zone boundary and to the opening of the Rheic Ocean to the south of the area studied in present coordinates (i.e., between the Ossa-Morena and South Portuguese Zones). This event has been dated at ca. 477 Ma and was responsible for the melting of deep ancient mafic crust and mantle with formation of bimodal magmatism in an intra-plate setting, as indicated by the protoliths of the protomylonitic felsic dykes with trondhjemitic composition and of the garnet amphibolite. Subsequent Variscan metamorphism took place under amphibolite facies conditions (P = 4-5.5 kbar; T = 600-625 °C) at lower P-T conditions than the Cadomian

Alternations in burial and exhumation along the Selimiye (Kayabükü) shear zone in the Menderes Massif from detailed garnet pressure-temperature paths

NASA Astrophysics Data System (ADS)

Kelly, E. D.; Atakturk, K. R.; Catlos, E. J.; Lizzadro-McPherson, D. J.; Cemen, I.; Lovera, O. M.

2015-12-01

Pressure-temperature (P-T) paths derived from garnet chemical zoning and supported by thermal modeling record alternating burial and exhumation during Main Menderes Metamorphism in western Turkey. We studied six rocks along the Selimiye (Kayabükü) shear zone, three from the footwall (Çine nappe) and three from the hanging wall (Selimiye nappe). The shear zone bounds the southern Menderes Massif metamorphic core complex and has been suggested to record compression followed by extension. The rocks are lower-amphibolite facies garnet-bearing metapelites with nearly identical mineral suites. Retrograde overprinting hinders classical thermobarometry; to overcome this, preserved chemical zoning in garnet combined with a G-minimization approach was used to construct detailed P-T paths (e.g., 50 points in some paths). During continuous temperature increase, the Çine nappe paths show increasing, decreasing, and then increasing pressure (an N-shaped path) ending at 7-8 kbar and ~565-590 °C. The Selimiye nappe paths show a single increase in P-T ending at ~7.3 kbar and ~580 °C. Similar bulk-rock compositions in all samples and the separation by the shear zone suggest that garnets grew during distinct events in each nappe. The timing of garnet growth, and thus the P-T paths, is currently undetermined, as monazite inclusions in garnet appear secondary and complicated by excess common Pb. The Çine nappe N-shaped path describes alternations in burial and exhumation, possibly due to thrust motion along the shear zone. To demonstrate the physical plausibility of the P-T paths, a 2-D finite difference solution to the diffusion-advection equation was applied. The results of the thermal modeling suggest that thrusting, denudation, and renewed thrusting would produce similar changes in P-T to the N-shaped path. Thus, the Çine nappe N-shaped P-T path appears to record a gap in thrust motion along the Selimiye (Kayabükü) shear zone prior to ultimate unroofing of the massif.

A new genus and species of marine catfishes (Siluriformes; Ariidae) from the upper Eocene Birket Qarun Formation, Wadi El-Hitan, Egypt

PubMed Central

2017-01-01

Wadi El-Hitan, the UNESCO World Heritage Site, of the Fayum Depression in the northeast part of the Western Desert of Egypt, has produced a remarkable collection of Eocene vertebrates, in particular the fossil whales from which it derives its name. Here we describe a new genus and species of marine catfishes (Siluriformes; Ariidae), Qarmoutus hitanensis, from the base of the upper Eocene Birket Qarun Formation, based on a partial neurocranium including the complete left side, partial right dentary, left suspensorium, two opercles, left pectoral girdle and spine, nuchal plates, first and second dorsal spines, Weberian apparatus and a disassociated series of abdominal vertebrae. All of the elements belong to the same individual and some of them were found articulated. Qarmoutus gen. nov. is the oldest and the most complete of the Paleogene marine catfishes unearthed from the Birket Qarun Formation. The new genus exhibits distinctive features not seen in other African Paleogene taxa, such as different sculpturing on the opercle and pectoral girdle with respect to that on the neurocranium and nuchal plates, denticulate ornamentation on the skull bones arranged in longitudinal rows and forming a radiating pattern on the sphenotic, pterotic, extrascapular and the parieto-supraoccipital, indentations or pitted ornamentation on the nuchal plates as well as the parieto-supraoccipital process, strut-like radiating pattern of ornamentation on the opercle from the proximal articulation to margins, longitudinal, curved, reticulate ridges and tubercular ornamentations on the cleithrum, sinuous articulation between the parieto-supraoccipital process and the anterior nuchal plate, long, narrow, and arrowhead shaped nuchal shield, very small otic capsules restricted to the prootic. Multiple parsimony and Bayesian morphological phylogenetic analyses of Ariidae, run with and without “molecular scaffolds”, yield contradictory results for the placement of Qarmoutus; the genus is

Compositional and isotopic heterogeneities in the Neo-Tethyan upper mantle recorded by coexisting Al-rich and Cr-rich chromitites in the Purang peridotite massif, SW Tibet (China)

NASA Astrophysics Data System (ADS)

Xiong, Fahui; Yang, Jingsui; Xu, Xiangzhen; Kapsiotis, Argyrios; Hao, Xiaolin; Liu, Zhao

2018-06-01

The Purang harzburgite massif in SW Tibet (China) hosts abundant chrome ore deposits. Ores consist of 20 to >95% modal chromian spinel (Cr-spinel) with mylonitic fabric in imbricate shaped pods. The composition of Cr-spinel in these ores ranges from Al-rich [Cr#Sp or Cr/(Cr + Al) × 100 = 47.60-57.56] to Cr-rich (Cr#Sp: 62.55-79.57). Bulk platinum-group element (PGE) contents of chromitites are also highly variable ranging from 17.5 ppb to ∼2.5 ppm. Both metallurgical and refractory chromitites show a general enrichment in the IPGE (Os, Ir and Ru) with respect to the PPGE (Rh, Pt and Pd), resulting mostly in right-sloping primitive mantle (PM)-normalized PGE profiles. The platinum-group mineral (PGM) assemblages of both chromitite types are dominated by heterogeneously distributed, euhedral Os-bearing laurite inclusions in Cr-spinel. The Purang chromitites have quite inhomogeneous 187Os/188Os ratios (0.12289-0.13194) that are within the range of those reported for mantle-hosted chromitites from other peridotite massifs. Geochemical calculations demonstrate that the parental melts of high-Cr chromitites were boninitic, whereas those of high-Al chromitites had an arc-type tholeiitic affinity. Chromite crystallization was most likely stimulated by changes in magma compositions due to melt-peridotite interaction, leading to the establishment of a heterogeneous physicochemical environment during the early crystallization of the PGM. The highly variable PGE contents, inhomogeneous Os-isotopic compositions and varying Cr#Sp ratios of these chromitites imply a polygenetic origin for them from spatially distinct melt inputs. The generally low γOs values (<1) of chromitites indicate that their parental melts originated within different sections of a heterogeneously depleted mantle source region. These melts were most likely produced in the mantle wedge above a downgoing lithospheric slab.

Hydrochemical characteristics and spatial analysis of groundwater quality in parts of Bundelkhand Massif, India

NASA Astrophysics Data System (ADS)

Ali, Syed Ahmad; Ali, Umair

2018-03-01

The tribulations of water quality have become more serious than the quantity, as the environmental evils are getting more severe day by day in different parts of the world. Large number of components like soil, geology, sewage disposal, effluents and other environmental conditions in which the water tends to reside or move and interact with ground and biological characteristics, greatly persuade the groundwater quality. Therefore, hydrochemical study has been carried out graphically and spatially in GIS environment in part of Bundelkhand Massif. The hydrochemical study exposes the water quality by measuring the concentration of parameters and comparing them with the drinking water and irrigation standards. Groundwater samples have been collected and analysed for physiochemical characteristics in order to understand the hydrochemistry of the water. The results revealed that ground water is alkaline in nature and total hardness observed in all samples falls under moderately hard to very hard category. At some places higher concentration of Cl- could be dangerous from health point of view. Major hydrochemical facies were identified using Piper Trilinear diagram and Durov diagrams, etc. Analysis of different determinations such as sodium adsorption ratio, residual sodium carbonate and per cent sodium revealed that most of the samples are unsuitable for irrigation. It was also observed that the quality of groundwater was not suitable for drinking purpose in industrial and irrigation area. In the area, few sampling sites showed unsuitability because of influences of urban and industrial waste discharge, aquifer material mineralogy, other anthropogenic activities and increased human interventions.

Elastic and electrical properties and permeability of serpentinites from Atlantis Massif, Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Falcon-Suarez, Ismael; Bayrakci, Gaye; Minshull, Tim A.; North, Laurence J.; Best, Angus I.; Rouméjon, Stéphane

2017-11-01

Serpentinized peridotites co-exist with mafic rocks in a variety of marine environments including subduction zones, continental rifts and mid-ocean ridges. Remote geophysical methods are crucial to distinguish between them and improve the understanding of the tectonic, magmatic and metamorphic history of the oceanic crust. But, serpentinite peridotites exhibit a wide range of physical properties that complicate such a distinction. We analysed the ultrasonic P- and S-wave velocities (Vp, Vs) and their respective attenuation (Qp-1, Qs-1), electrical resistivity and permeability of four serpentinized peridotite samples from the southern wall of the Atlantis Massif, Mid-Atlantic Ridge, collected during International Ocean Discovery Program Expedition 357. The measurements were taken over a range of loading-unloading stress paths (5-45 MPa), using ∼1.7 cm length, 5 cm diameter samples horizontally extracted from the original cores drilled on the seafloor. The measured parameters showed variable degrees of stress dependence, but followed similar trends. Vp, Vs, resistivity and permeability show good inter-correlations, while relationships that included Qp-1 and Qs-1 are less clear. Resistivity showed high contrast between highly serpentinized ultramafic matrix (>50 Ω m) and mechanically/geochemically altered (magmatic/hydrothermal-driven alteration) domains (<20 Ω m). This information together with the elastic constants (Vp/Vs ratio and bulk moduli) of the samples allowed us to infer useful information about the degree of serpentinization and the alteration state of the rock, contrasted by petrographic analysis. This study shows the potential of combining seismic techniques and controlled source electromagnetic surveys for understanding tectonomagmatic processes and fluid pathways in hydrothermal systems.

Formation of pyroxenite layers in the Totalp ultramafic massif (Swiss Alps) - Insights from highly siderophile elements and Os isotopes

NASA Astrophysics Data System (ADS)

van Acken, David; Becker, Harry; Walker, Richard J.; McDonough, William F.; Wombacher, Frank; Ash, Richard D.; Piccoli, Phil M.

2010-01-01

Pyroxenitic layers are a minor constituent of ultramafic mantle massifs, but are considered important for basalt generation and mantle refertilization. Mafic spinel websterite and garnet-spinel clinopyroxenite layers within Jurassic ocean floor peridotites from the Totalp ultramafic massif (eastern Swiss Alps) were analyzed for their highly siderophile element (HSE) and Os isotope composition. Aluminum-poor pyroxenites (websterites) display chondritic to suprachondritic initial γOs (160 Ma) of -2 to +27. Osmium, Ir and Ru abundances are depleted in websterites relative to the associated peridotites and to mantle lherzolites worldwide, but relative abundances (Os/Ir, Ru/Ir) are similar. Conversely, Pt/Ir, Pd/Ir and Re/Ir are elevated. Aluminum-rich pyroxenites (clinopyroxenites) are characterized by highly radiogenic 187Os/ 188Os with initial γOs (160 Ma) between +20 and +1700. Their HSE composition is similar to that of basalts, as they are more depleted in Os, Ir and Ru compared to Totalp websterites, along with even higher Pt/Ir, Pd/Ir and Re/Ir. The data are most consistent with multiple episodes of reaction of mafic pyroxenite precursor melts with surrounding peridotites, with the highest degree of interaction recorded in the websterites, which typically occur in direct contact to peridotites. Clinopyroxenites, in contrast, represent melt-dominated systems, which retained the precursor melt characteristics to a large extent. The melts may have been derived from a sublithospheric mantle source with high Pd/Ir, Pt/Ir and Re/Os, coupled with highly radiogenic 187Os/ 188Os compositions. Modeling indicates that partial melting of subducted, old oceanic crust in the asthenosphere could be a possible source for such melts. Pentlandite and godlevskite are identified in both types of pyroxenites as the predominant sulfide minerals and HSE carriers. Heterogeneous HSE abundances within these sulfide grains likely reflect subsolidus processes. In contrast, large grain

The Variscan evolution in the External massifs of the Alps and place in their Variscan framework

NASA Astrophysics Data System (ADS)

von Raumer, Jürgen F.; Bussy, François; Stampfli, Gérard M.

2009-02-01

In the general discussion on the Variscan evolution of central Europe the pre-Mesozoic basement of the Alps is, in many cases, only included with hesitation. Relatively well-preserved from Alpine metamorphism, the Alpine External massifs can serve as an excellent example of evolution of the Variscan basement, including the earliest Gondwana-derived microcontinents with Cadomian relics. Testifying to the evolution at the Gondwana margin, at least since the Cambrian, such pieces took part in the birth of the Rheic Ocean. After the separation of Avalonia, the remaining Gondwana border was continuously transformed through crustal extension with contemporaneous separation of continental blocks composing future Pangea, but the opening of Palaeotethys had only a reduced significance since the Devonian. The Variscan evolution in the External domain is characterised by an early HP-evolution with subsequent granulitic decompression melts. During Visean crustal shortening, the areas of future formation of migmatites and intrusion of monzodioritic magmas in a general strike-slip regime, were probably in a lower plate situation, whereas the so called monometamorphic areas may have been in an upper plate position of the nappe pile. During the Latest Carboniferous, the emplacement of the youngest granites was associated with the strike-slip faulting and crustal extension at lower crustal levels, whereas, at the surface, detrital sediments accumulated in intramontaneous transtensional basins on a strongly eroded surface.

Methane- and Hydrogen-Influenced Microbial Communities in Hydrothermal Plumes above the Atlantis Massif, Mid Atlantic Ridge

NASA Astrophysics Data System (ADS)

Stewart, C. L.; Schrenk, M.

2017-12-01

Ultramafic-hosted hydrothermal systems associated with slow-spreading mid ocean ridges emit copious amounts of hydrogen and methane into the deep-sea, generated through a process known as serpentinization. Hydrothermal plumes carrying the reduced products of water-rock interaction dissipate and mix with deep seawater, and potentially harbor microbial communities adapted to these conditions. Methane and hydrogen enriched hydrothermal plumes were sampled from 3 sites near the Atlantis Massif (30°N, Mid Atlantic Ridge) during IODP Expedition 357 and used to initiate cultivation experiments targeting methanotrophic and hydrogenotrophic microorganisms. One set of experiments incubated the cultures at in situ hydrostatic pressures and gas concentrations resulting in the enrichment of gammaproteobacterial assemblages, including Marinobacter spp. That may be involved in hydrocarbon degradation. A second set of experiments pursued the anaerobic enrichment of microbial communities on solid media, resulting in the enrichment of alphaproteobacteria related to Ruegeria. The most prodigious growth in both case occurred in methane-enriched media, which may play a role as both an energy and carbon source. Ongoing work is evaluating the physiological characteristics of these isolates, including their metabolic outputs under different physical-chemical conditions. In addition to providing novel isolates from hydrothermal habitats near the Lost City Hydrothermal Field, these experiments will provide insight into the ecology of microbial communities from serpentinization influenced hydrothermal systems that may aid in future exploration of these sites.

Protracted construction of gabbroic crust at a slow spreading ridge: Constraints from 206Pb/238U zircon ages from Atlantis Massif and IODP Hole U1309D (30°N, MAR)

USGS Publications Warehouse

Grimes, Craig B.; John, Barbara E.; Cheadle, Michael J.; Wooden, Joseph L.

2008-01-01

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages of 24 samples from oceanic crust recovered in Integrated Ocean Drilling Program (IODP) Hole U1309D and from the surface of Atlantis Massif, Mid-Atlantic Ridge (MAR) (30°N) document a protracted history of accretion in the footwall to an oceanic detachment fault. Ages for 18 samples of evolved Fe-Ti oxide gabbro and felsic dikes collected 40–1415 m below seafloor in U1309D yield a weighted mean of 1.20 ± 0.03 Ma (mean square of weighted deviates = 7.1). However, the ages range from 1.08 ± 0.07 Ma and 1.28 ± 0.05 Ma indicating crustal construction occurred over a minimum of 100–200 ka. The zircon ages, along with petrologic observations, indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka. The oldest ages are observed below 600 mbsf, an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault. The data are most consistent with a “multiple sill” model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1.4 km. Zircon ages from broadly spaced samples collected along the southern ridge of Atlantis Massif yield a detachment fault slip rate of 28.7 ± 6.7 mm/a and imply significant asymmetric plate spreading (up to 100% on the North American plate) for at least 200 ka during core complex formation.

The Krásná Hora, Milešov, and Příčovy Sb-Au ore deposits, Bohemian Massif: mineralogy, fluid inclusions, and stable isotope constraints on the deposit formation

NASA Astrophysics Data System (ADS)

Němec, Matěj; Zachariáš, Jiří

2018-02-01

The Krásná Hora-Milešov and Příčovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks. Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krásná Hora-Milešov) or are associated with local strike-slip faults (Příčovy). Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 °C and gold at 200 to 130 °C from low-salinity aqueous fluids. The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 °C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature ( 250 MPa, 400 °C). The estimated oxygen isotope composition of the ore-bearing fluid (4 ± 1‰ SMOW; based on post-ore calcite) suggests its metamorphic or mixed magmatic-metamorphic origin and excludes the involvement of meteoric water. Rapid cooling of warm hydrothermal fluids reacting with "cold" host rock was probably the most important factor in the formation of both stibnite and gold.

Regional setting and characteristics of the Neoproterozoic Wadi Hamama Zn-Cu-Ag-Au prospect: evidence for an intra-oceanic island arc-hosted volcanogenic hydrothermal system

NASA Astrophysics Data System (ADS)

Abd El-Rahman, Yasser; Surour, Adel A.; El-Manawi, Abdel Hamid W.; El-Dougdoug, Abdel-Monem A.; Omar, Sayed

2015-04-01

The Wadi Hamama area is a volcanogenic Zn-Cu-Au-Ag prospect. It is hosted by a Neoproterozoic bimodal-mafic sequence, which comprises basalt, dacite and rhyolite along with volcaniclastic rocks. The rocks have a low-K tholeiitic affinity and are enriched in large ion lithophile elements over high field strength elements, which indicated their formation in an intra-oceanic island arc tectonic setting. The area was intruded by a tonalite-trondhjemite body, which has an intra-oceanic island arc affinity and later by diorite, which has a cordilleran-margin geochemical affinity. These rock units were intruded by post-tectonic granite dykes, which have a within-plate geochemical signature. There is a quartz-carbonate horizon extending along the contact between the basalt and the volcaniclastic rocks, mainly banded and lapilli tuffs. This horizon is of exhalative origin and is underlain by a mushroom-shaped alteration zone extending from the horizon down to the massive basalt. The footwall alteration is characterized by a silica-rich core surrounded by a thick chlorite sheath. Both the quartz-carbonate horizon and the footwall-altered rocks enclose historical trenches and pits. Sulfide-rich core samples are enriched in Zn, relative to Cu, and in Ag, which indicates the low-temperature nature of the hydrothermal system. The prospect was affected by supergene processes, which led to the widespread occurrence of secondary copper minerals and gold enrichment relative to the leached base metals, especially Zn. The prospect formed through a limited rifting of an intra-oceanic island arc which resulted in the formation of a small-scale volcanogenic Zn-Cu-Ag-Au prospect.

Evidence of Variscan and Alpine tectonics in the structural and thermochronological record of the central Serbo-Macedonian Massif (south-eastern Serbia)

NASA Astrophysics Data System (ADS)

Antić, Milorad D.; Kounov, Alexandre; Trivić, Branislav; Spikings, Richard; Wetzel, Andreas

2017-07-01

The Serbo-Macedonian Massif (SMM) represents a composite crystalline belt within the Eastern European Alpine orogen, outcropping from the Pannonian basin in the north to the Aegean Sea in the south. The central parts of this massif (south-eastern Serbia) consist of the medium- to high-grade Lower Complex and the low-grade Vlasina Unit. Outcrop- and micro-scale ductile structures in this area document three major stages of ductile deformation. The earliest stage D1 is related to isoclinal folding, commonly preserved as up to decimetre-scale quartz-feldspar rootless fold hinges. D2 is associated with general south-eastward tectonic transport and refolding of earlier structures into recumbent metre- to kilometre-scale tight to isoclinal folds. Stages D1 and D2 could not be temporally separated and probably took place in close sequence. The age of these two ductile deformation stages was constrained to the Variscan orogeny based on indirect geological evidence (i.e. ca. 408-ca. 328). During this period, the SMM was involved in a transpressional amalgamation of the western and eastern parts of the Galatian super-terrane and subsequent collision with Laurussia. Outcrop-scale evidence of the final stage D3 is limited to spaced and crenulation cleavage, which are probably related to formation of large-scale open upright folds as reported previously. 40Ar/39Ar thermochronology was applied on hornblende, muscovite, and biotite samples in order to constrain the age of tectonothermal events and activity along major shear zones. These 40Ar/39Ar data reveal three major cooling episodes affecting the central SMM. Cooling below greenschist facies conditions in the western part of the Vlasina Unit took place in a post-orogenic setting (extensional or transtensional) in the early Permian (284 ± 1 Ma). The age of activity along the top-to-the-west shear zone formed within the orthogneiss in the Božica area of the Vlasina Unit was constrained to Middle Triassic (246 ± 1 Ma). This

Copper isotope fractionation during partial melting and melt percolation in the upper mantle: Evidence from massif peridotites in Ivrea-Verbano Zone, Italian Alps

NASA Astrophysics Data System (ADS)

Huang, Jian; Huang, Fang; Wang, Zaicong; Zhang, Xingchao; Yu, Huimin

2017-08-01

To investigate the behavior of Cu isotopes during partial melting and melt percolation in the mantle, we have analyzed Cu isotopic compositions of a suite of well-characterized Paleozoic peridotites from the Balmuccia and Baldissero massifs in the Ivrea-Verbano Zone (IVZ, Northern Italy). Our results show that fresh lherzolites and harzburgites have a large variation of δ65Cu ranging from -0.133 to 0.379‰, which are negatively correlated with Al2O3 contents as well as incompatible platinum-group (e.g., Pd) and chalcophile element (e.g., Cu, S, Se, and Te) contents. The high δ65Cu can be explained by Cu isotope fractionation during partial melting of a sulfide-bearing peridotite source, with the light isotope (63Cu) preferentially entering the melts. The low δ65Cu can be attributed to precipitation of sulfides enriched in 63Cu during sulfur-saturated melt percolation. Replacive dunites from the Balmuccia massif display high δ65Cu from 0.544 to 0.610‰ with lower Re, Pd, S, Se, and Te contents and lower Pd/Ir ratios relative to lherzolites, which may result from dissolution of sulfides during interactions between S-undersaturated melts and lherzolites at high melt/rock ratios. Thus, our results suggest that partial melting and melt percolation largely account for the Cu isotopic heterogeneity of the upper mantle. The correlation between δ65Cu and Cu contents of the lherzolites and harzburgites was used to model Cu isotope fractionation during partial melting of a sulfide-bearing peridotite, because Cu is predominantly hosted in sulfide. The modelling results indicate an isotope fractionation factor of αmelt-peridotite = 0.99980-0.99965 (i.e., 103lnαmelt-peridotite = -0.20 to -0.35‰). In order to explain the Cu isotopic systematics of komatiites and mid-ocean ridge basalts reported previously, the estimated αmelt-peridotite was used to simulate Cu isotopic variations in melts generated by variable degrees of mantle melting. The results suggest that high

Identification of remagnetization processes in Paleozoic sedimentary rocks of the northeast Rhenish Massif in Germany by K-Ar dating and REE tracing of authigenic illite and Fe oxides

NASA Astrophysics Data System (ADS)

Zwing, A.; Clauer, N.; Liewig, N.; Bachtadse, V.

2009-06-01

This study combines mineralogical, chemical (rare earth elemental (REE)) and isotopic (K-Ar) data of clay minerals as well as chemical compositions (major and REE) of Fe oxide leachates from remagnetized Palaeozoic sedimentary rocks from NE Rhenish Massif in Germany, for which the causes of remagnetization are not yet clear. The dominant carrier of the syntectonic, pervasive Carboniferous magnetization is magnetite. The Middle Devonian clastic rocks record an illitization event at 348 ± 7 Ma probably connected to a major magmatic event in the Mid-German Crystalline Rise, whereas a second illitization episode at 324 ± 3 Ma is coeval to the northward migrating deformation through the Rhenish Massif, being only detected in Upper Devonian and Lower Carboniferous rocks. The age of that younger illitization is not significantly different from that of the remagnetization, which, however, is not restricted to the upper part of the orogenic belt, but affects also the Middle Devonian strata. The REE patterns of the Fe-enriched leachates support two mineralization episodes with varied oxidation-reduction conditions outlined by varied Eu and Ce anomalies. This is not compatible with a unique, pervasive migration of orogenic fluids on a regional scale to explain the remagnetization in the studied region. While clay diagenesis and remagnetization are time-equivalent in Upper Devonian and Lower Carboniferous rocks, they are not so in Middle Devonian rocks. Transformation of smectite into illite cannot, therefore, account for the growth of associated authigenic magnetite, which must have been triggered by a different process. Since remagnetization and deformation ages are similar, the mechanism could relate to local physical conditions such as pressure solution and changing pore fluid pressure due to tectonic stress as well as to chemical conditions such as changing composition of the pore fluids.

Seismic Reflection Transect across the Central Iberian Zone (Iberian Massif): The ALCUDIA project

NASA Astrophysics Data System (ADS)

Carbonell, R.; Simancas, F.; Martinez-Poyatos, D.; Ayarza, P.; Gonzalez, P.; Tejero, R.; Martín-Parra, L.; Matas, J.; Gonzalez-Lodeiro, F.; Pérez-Estaún, A.; García-Lobon, J.; Mansilla, L.; Palomeras, I.

2007-12-01

The lithosphere of the Central Iberian Zone (CIZ) differs from that of the southwestern Iberian Massif. They are limited by a suture zone. The seismic reflection profile IBERSEIS suggested that the activity of a Carboniferous mantle plume resulted in abundant intrusions of mafic magmas in the mid-to-lower crust which resulted in a singular crustal evolution. The current knowledge of the area based mostly in surface geological mapping suggests that basic magmatism continues further towards the north, indicating that the mantle plume may have affected a bigger area up to the Tajo depression. Furthermore, the existence of the Almadén mine, one of the largest mercury mine in the world within the CIZ, favour that the crust in this area is the result of anomalous lithospheric processes. Accordingly, the ALCUDIA project has been lauched aiming to study the structure and nature of the lithosphere of the CIZ. It includes the acquisition of a deep high resolution seismic reflection transect, detailed geological mapping, kinematic, petrologic and geochemical studies, and other geophysical studies (potential field methods). This new profile extends the previous IBERSEIS Transect towards the northeast, completing almost 600 km of deep seismic profiles, crossing the southern half of the Iberian Variscides. The transect crosses some important structures, such as the Toledo fault, Santa Elena Fault, Alcudia anticline, Almadén syncline, and some major magnetic anomalies. The preliminary results reveal that the crust is 30 km thick in average, with a horizontal Moho, a highly reflective mid-to-lower crust with a few mantle reflectors and well defined features in the upper crust with the indication of detachments zones that might link to the mid- crustal reflective zone.

Textural Variations during Antigorite Dehydration as Markers for Fluid Release Mechanisms in Subduction Zones: Constrains from the Cerro del Almirez Ultramafic Massif (Betic Cordillera, SE Spain)

NASA Astrophysics Data System (ADS)

Dilissen, N. M.; Garrido, C. J.; Lopez Sanchez-Vizcaino, V.; Jabaloy-Sánchez, A.; Padrón-Navarta, J. A.

2015-12-01

Subduction zones are dynamic convergent plate boundaries associated with arc volcanism and earthquakes, which are believed to be controlled by fluids released during devolatilization reactions from the downgoing slab. The high-pressure breakdown of antigorite serpentinite to prograde chlorite-harzburgite is considered to be the most significant source of water in subduction zones. The Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain) is a unique exhumed subduction terrane that preserves this dehydration reaction as a sharp front. Chl-harzburgite in this massif displays two differentiated textures-granofels and spinifex-like- indicating that antigorite breakdown occurred at different overstepping of the dehydration reaction. Detailed mapping of textural variations in chl-harzburgite unveils a network of granofels and spinifex-like lenses. These lenses have triaxial ellipsoid shapes with average axial ratios of 16:7:1 and 19:8:1, respectively, with the shorter axis nearly perpendicular to the serpentine-out isograd, and the longest axis ranging from 23 to 190 meters. We calculated the volume of water release per lens using the modal amount of olivine according to the model reaction 1Atg = 4Clin + 6Fo + 6En + 15H2O. The growth time and water flux per lens was computed using experimental olivine growth rates for granular and dendritic, spinifex-like olivine. Preliminary results show that formation of spinifex and granofels lenses imply temporal variations of the volumetric water fluxes ranging from 0.12 to 0.02 m3m-2yr-1, respectively. If the time of formation of lenses is inversely proportional to its relative distance to the dehydration front, the 52m thick, chl-harzburgite lens network in Almirez records ca. 315 yrs of antigorite dehydration. Our results show that antigorite dehydration in subduction zones occurs in a highly non-steady regime with yearly to decadal variations of water fluxes that record variations in the dynamics of slab and fluid

Spatial evaporation patterns within a small drainage basin in the Negev Desert

NASA Astrophysics Data System (ADS)

Kidron, Giora J.; Zohar, Motti

2010-01-01

SummaryAlthough important, data regarding the spatial distribution of evaporation are scarce. With the development of a small reference atmometer (RAM), studying the spatial distribution of evaporation was made more feasible and consequently carried out at the hilltops (TOP), wadi beds (WADI) and along the northern (NF), southern (SF), eastern (EF) and western (WF) aspects within a second order drainage basin in the Negev Desert Highlands during June 2004 to May 2006. Evaporation rates showed high variability in accordance with season and aspect following the order: TOP > SF ⩾ EF ⩾ WF > WADI > NF. The data showed (a) an increase in evaporation with elevation; (b) that the average evaporation rates of the stations located at the slopes and the wadi beds were respectively ˜14% and ˜23% lower than that of the hilltop stations; (c) that while insignificant differences characterized the eastern and the western aspects during summer and winter, significant differences characterized the northern and the southern aspects, and (d) that the ratio obtained between the northern and southern aspects is significantly different from that calculated based on direct-beam shortwave radiation. The findings were explained by the effects of sun and wind upon evaporation, with each factor explaining up to ˜45-50% of the results. The findings are in agreement with the dense vegetation at the north-facing footslope and at the wadi bed, and may have important implications towards the understanding of microorganism and plant distribution as well as geomorphological and pedological topics such as weathering rates and soil forming processes.

Rock Magnetic Properties of Remagnetised Devonian and Carboniferous Carbonate and Clastic Rocks From The NE Rhenish Massif, Germany

NASA Astrophysics Data System (ADS)

Zwing, A.; Matzka, J.; Bachtadse, V.; Soffel, H. C.

Previous studies on remagnetised carbonate rocks from the North American and Eu- ropean Variscides reported characteristic rock magnetic properties which are thought to be diagnostic for a chemical remagnetisation event. Their hysteresis properties with high ratios of Mrs/Ms and Hcr/Hc indicate the presence of a mixture of single-domain and superparamagnetic magnetite (Jackson, et al. 1990). In order to test if this fin- gerprint can be identified in remagnetised carbonate and clastic rocks from the NE Rhenish Massif, Germany, a series of rock magnetic experiments has been carried out. The hysteresis properties of the remagnetised clastic rocks indicate the domi- nance of large MD particles, as can be expected for detrital sediments. The carbon- ates yield significantly higher ratios of Mrs/Ms and Hcr/Hc than the clastic rocks, but only partly correspond to the characteristic properties of remagnetised carbon- ates described above. The latter might be attributed to detrital input into the carbonate platforms. Additional low-temperature remanence measurements show a wide vari- ety of phenomena, including Verwey transitions and indications for the presence of superparamagnetic grains. However, the low-temperature experiments do not allow a straightforward discrimination between the clastic and carbonate rocks and suggest more complex magnetomineralogies than expected from the hysteresis measurements alone.

Geochemical processes leading to the precipitation of subglacial carbonate crusts at Bossons glacier, Mont Blanc Massif (French Alps)

NASA Astrophysics Data System (ADS)

Thomazo, Christophe; Buoncristiani, Jean-Francois; Vennin, Emmanuelle; Pellenard, Pierre; Cocquerez, Theophile; Mugnier, Jean L.; Gérard, Emmanuelle

2017-09-01

Cold climate carbonates can be used as paleoclimatic proxies. The mineralogy and isotopic composition of subglacially precipitated carbonate crusts provide insights into the subglacial conditions and processes occurring at the meltwater-basement rock interface of glaciers. This study documents such crusts discovered on the lee side of a gneissic roche moutonnée at the terminus of the Bossons glacier in the Mont Blanc Massif area (France). The geological context and mineralogical investigations suggest that the Ca used for the precipitation of large crystals of radial fibrous sparite observed in these crusts originated from subglacial chemical weathering of Ca-bearing minerals of the local bedrock (plagioclase and amphibole). Measurements of the carbon and oxygen isotope compositions in the crusts indicate precipitation at, or near to, equilibrium with the basal meltwater under open system conditions during refreezing processes. The homogeneous and low carbonate δ13C values (ca. -11.3‰) imply a large contribution of soil organic carbon to the Bossons subglacial meltwater carbon reservoir at the time of deposition. In addition, organic remains trapped within the subglacially precipitated carbonate crusts give an age of deposition around 6500 years cal BP suggesting that the Mid-Holocene climatic and pedological optima are archived in the Bossons glacier carbonate crusts.

Analysis of the upper massif of the craniofacial with the radial method – practical use

PubMed Central

Lepich, Tomasz; Dąbek, Józefa; Stompel, Daniel; Gielecki, Jerzy S.

2011-01-01

Introduction The analysis of the upper massif of the craniofacial (UMC) is widely used in many fields of science. The aim of the study was to create a high resolution computer system based on a digital information record and on vector graphics, that could enable dimension measuring and evaluation of craniofacial shape using the radial method. Material and methods The study was carried out on 184 skulls, in a good state of preservation, from the early middle ages. The examined skulls were fixed into Molisson's craniostat in the author's own modification. They were directed in space towards the Frankfurt plane and photographed in frontal norm with a digital camera. The parameters describing the plane and dimensional structure of the UMC and orbits were obtained thanks to the computer analysis of the function recordings picturing the craniofacial structures and using software combining raster graphics with vector graphics. Results It was compared mean values of both orbits separately for male and female groups. In female skulls the comparison of the left and right side did not show statistically significant differences. In male group, higher values were observed for the right side. Only the circularity index presented higher values for the left side. Conclusions Computer graphics with the software used for analysing digital pictures of UMC and orbits increase the precision of measurements as well as the calculation possibilities. Recognition of the face in the post mortem examination is crucial for those working on identification in anthropology and criminology laboratories. PMID:22291834

Evolution of hut access facing glacier shrinkage in the Mer de Glace basin (Mont Blanc massif, France)

NASA Astrophysics Data System (ADS)

Mourey, Jacques; Ravanel, Ludovic

2016-04-01

Given the evolution of high mountain environment due to global warming, mountaineering routes and huts accesses are more and more strongly affected by glacial shrinkage and concomitant gravity processes, but almost no studies have been conducted on this relationship. The aim of this research is to describe and explain the evolution over the last century of the access to the five alpine huts around the Mer de Glace glacier (Mont Blanc massif), the larger French glacier (length = 11.5 km, area = 30 km²), a major place for Alpine tourism since 1741 and the birthplace of mountaineering, by using several methods (comparing photographs, surveying, collecting historical documents). While most of the 20th century shows no marked changes, loss of ice thickness and associated erosion of lateral moraines generate numerous and significant changes since the 1990s. Boulder falls, rockfalls and landslides are the main geomorphological processes that affect the access, while the glacier surface lowering makes access much longer and more unstable. The danger is then greatly increased and the access must be relocated and/or equipped more and more frequently (e.g. a total of 520 m of ladders has been added). This questions the future accessibility to the huts, jeopardizing an important part of mountaineering and its linked economy in the Mer de Glace area.

The carbon-isotopic composition of Proterozoic carbonates: Riphean successions from northwestern Siberia (Anabar Massif, Turukhansk Uplift)

NASA Technical Reports Server (NTRS)

Knoll, A. H.; Kaufman, A. J.; Semikhatov, M. A.

1995-01-01

Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks.

Pyroclastic chronology of the Sancy stratovolcano (Mont-Dore, French Massif Central): New high-precision 40Ar/39Ar constraints

NASA Astrophysics Data System (ADS)

Nomade, Sébastien; Scaillet, Stéphane; Pastre, Jean-François; Nehlig, Pierre

2012-05-01

The Sancy (16 km2) is the youngest of the two stratovolcanoes that constitute the Mont-Dore Massif (Massif Central, France). The restricted number of high precision radio-isotopic ages currently limits our knowledge of the pyroclastic chronology of this edifice which is the source of many tephra layers detected in middle Pleistocene sequences in southeast Europe. To improve our knowledge of the building phases of this stratovolcano, we collected thirteen pyroclastic units covering the entire proximal record. We present 40Ar/39Ar single grain laser dating performed in the facility hosted at the LSCE (Gif-sur-Yvette, France). The 40Ar/39Ar ages range from 1101 ± 11 ka to 392 ± 7 ka (1σ external). Four pyroclastic cycles lasting on average 100 ka were identified (C. I to C. IV). C. I corresponds to the earlier explosive phase between 1101 ka and 1000 ka and starts about 100 ka earlier than previously thought. The second pyroclastic cycle (C. II) is the main pyroclastic episode spanning from 818 to 685 ka. This cycle is constituted of a minimum of 8 major pyroclastic eruptions and includes a major event that corresponds to a large plinian eruption at 719 ± 10 ka (1σ external) and recorded as a 1.4 m thick layer 60 km south-east of the Sancy volcano. The link between this large eruption and formation of a caldera stays however, hypothetical. The third pyroclastic cycle (C. III) found in the northeastern part of the Sancy (Mont-Dore valley) spanned from 642 to 537 ka. Finally, the youngest pyroclastic cycle (C. IV) starts at 392 ka and probably ends around 280 ka. The age versus geographic location of each pyroclastic cycle indicates three preferential directions of channeling of the pyroclastic events and/or collapse of the volcanic edifice: northwest to west (C. I), southeast (C. II) and finally north to northeast (C. III and IV). The new high precision 40Ar/39Ar age for the Queureuilh bas pyroclastic unit (642 ± 9 ka) is identical within error with the U/Pb age

Monitoring and assessment of the groundwater quality in wadi Al-Arish downstream area, North Sinai (Egypt)

NASA Astrophysics Data System (ADS)

Masoud, Alaa A.; Meswara, Ebtesam A.; El Bouraie, Mohamed M.; Kamh, Samir Z.

2018-04-01

At a rate of 3 samples a year over 7 years (2008-2014), groundwater quality indicators for 294 samples from 14 groundwater supply wells located on the delta of Wadi Al-Arish, North Sinai (Egypt) were measured and analyzed. The prime objective was to characterize significant and sustained trends in the concentrations of the pH, TDS, Total Alkalinity, Fe2+, Mn2+, Zn2+, NO3-, K+, Pb2+, Al3+, and fecal coliform (FC). Detection and estimation of trends and magnitude were carried out applying the nonparametric Mann-Kendall and Thiel-Sen trend statistical tests, respectively. Geostatistical kriging implemented in ArcGIS 10× was appraised for the spatial distribution of the indicators and their sustained trends. Factor analysis was applied to identify significant sources of quality variation and their loads. Average contents of all indicators exceeded the permissible limits except for Mn. Violation of groundwater quality standards clarified emergence of FC (99.6%), Pb2+ (76.8%), TDS (60.2%), Al3+ (56.6%), NO3- (46.5%), Fe2+ (37.5%), and Mn2+ (14%). Out of the 14 wells, notable upward trends (deterioration) were significant (>95% level) for Mg2+ (100%), TDS (78.5%), NO3- (71.42%), Zn2+ (42.85%), pH (14.28%), K+ (14.28%), and 7.14% for Al3+ and FC. Ranges of attenuation rates (mg/l/year) varied for TDS (52.61-37.59), Mg2+ hardness (3.81-0.14), K+ (0.58-1), pH (0.004-0.027), total alkalinity (-1.89-13.18), NO3- (1.47-0.69), Al3+ (0.002-0.011), Fe2+ (-0.001-0.016), Mn2+ (-0.00004-0.01), Pb2+ (-0.00001-0.002), Zn2+ (0.049-0.018), and FC (5.25-22) in cfu/100 ml. Out of the 14 wells, well no. 9 showed the largest increasing attenuation rates (mg/l/year) that marked NO3- (1.47), K+ (0.58), pH (0.004), and Al3+ (0.002). TDS showed the largest rates of increase of 52.61, and 28.26 for well nos. 5 and 9, respectively. FC showed the highest rate of deterioration of 5.25 in well no. 10. Zn2+ recorded strong deterioration rates of 0.049, and 0.046 for well nos. 12 and 9, respectively

Déformation et cinématique de mise en place du dôme de la zone axiale de la Montagne Noire: signification des nodules à quartz-sillimanite (Massif central français)

NASA Astrophysics Data System (ADS)

Brunel, Maurice; Lansigu, Christophe

1997-10-01

Sillimanite nodules of the Espinouse massif are imponant features for describing the strain that prevailed at the climax of metamorphism. At this stage, the Axial Zone was already an antiformal structure affected by extensional unroofing. Occurrence of the sillimanite nodules mostly in the aureole zone of a granite recently dated at 327 ± 5 Ma, implies that extensional deformation defined by sillimanite nodules and low-angle shear zones was active at the end of the Visean and consequently, contemporaneous with the latest stage of nappe overthrusting and stacking in the southern limb of the Montagne Noire.

Age and evolution of the lithospheric mantle beneath the Khanka Massif: Geochemical and Re-Os isotopic evidence from Sviyagino mantle xenoliths

NASA Astrophysics Data System (ADS)

Guo, Peng; Xu, Wen-Liang; Wang, Chun-Guang; Wang, Feng; Ge, Wen-Chun; Sorokin, A. A.; Wang, Zhi-Wei

2017-06-01

New geochemical and Re-Os isotopic data of mantle xenoliths entrained in Cenozoic Sviyagino alkali basalts from the Russian Far East provide insights into the age and evolution of the sub-continental lithospheric mantle (SCLM) beneath the Khanka Massif, within the Central Asian Orogenic Belt (CAOB). These mantle xenoliths are predominantly spinel lherzolites with minor spinel harzburgite. The lherzolites contain high whole-rock concentrations of Al2O3 and CaO, with low forsterite content in olivine (Fo = 89.5-90.3%) and low Cr# in spinel (0.09-0.11). By contrast, the harzburgite is more refractory, containing lower whole rock Al2O3 and CaO contents, with higher Fo (91.3%) and spinel Cr# (0.28). Their whole rock and mineral compositions suggest that the lherzolites experienced low-degree (1-4%) batch melting and negligible metasomatism, whereas the harzburgite underwent a higher degree (10%) of fractional melting, and experienced minor post-melting silicate metasomatism. Two-pyroxene rare earth element (REE)-based thermometry (TREE) yields predominant equilibrium temperatures of 884-1043 °C, similar to values obtained from two-pyroxene major element-based thermometry (TBKN = 942-1054 °C). Two lherzolite samples yield high TREE relative to TBKN (TREE - TBKN ≥ 71 °C), suggesting that they cooled rapidly as a result of the upwelling of hot asthenospheric mantle material that underplated a cold ancient lithosphere. The harzburgite with a low Re/Os value has an 187Os/188Os ratio of 0.11458, yielding an Os model age (TMA) relative to the primitive upper mantle (PUM) of 2.09 Ga, and a Re depletion ages (TRD) of 1.91 Ga; both of which record ancient melt depletion during the Paleoproterozoic ( 2.0 Ga). The 187Os/188Os values of lherzolites (0.12411-0.12924) correlate well with bulk Al2O3 concentrations and record the physical mixing of ancient mantle domains and PUM-like ambient mantle material within the asthenosphere. This indicates that the SCLM beneath the Khanka

The magmatic history of the Vetas-California mining district, Santander Massif, Eastern Cordillera, Colombia

NASA Astrophysics Data System (ADS)

Mantilla Figueroa, Luis C.; Bissig, Thomas; Valencia, Víctor; Hart, Craig J. R.

2013-08-01

The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U-Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ˜1240 and 957 Ma; (2) early Ordovician calc-alkalic magmatism, which was synchronous with the Caparonensis-Famatinian Orogeny (˜477 Ma); (3) middle to late Ordovician post-collisional calc-alkalic magmatism (˜466-436 Ma); (4) late Triassic to early Jurassic magmatism between ˜204 and 196 Ma, characterized by both S- and I-type calc-alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc-alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic-hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic-early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204-199 Ma), Intermediate rocks (199-198 Ma), and late leucogranites, herein referred to as Alaskites-II (198-196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins.

Integration of remote sensing and GIS for studying a short-term flashflood in the El Arish Catchment (Egypt)

NASA Astrophysics Data System (ADS)

Badawy, M.

2012-04-01

Wadi El Arish is the largest drainage system in Sinai Peninsula, Egypt. The Wadi was subject to severe thunderstorms on 17 and 18 January 2010 followed by an extreme and violent flood that had not been known in Sinai since 1980. The flood claimed six victims, injured tens of people, and devastated vital infrastructure and hundreds of houses. Hydrologic characteristics of the Wadi are not fully understood due to substantial lack of the detailed hydro-meteorological information. Hence, remote sensing and GIS techniques were used to provide better spatial understanding of rainfall characteristics and drainage basin response. The study was based on the analysis of the TRMM images and 6 hourly average HYDIS data of rainfall analyses. A hydrological model was constructed using ASTER DEMs. The empirical black box model was used depending on the curve number approach to predict stream runoff. Landcover and hydrological soil groups were identified from the Landsat ETM+ mosaic using multispectral supervised classification. The curve numbers were adjusted to ARC I (dry condition) as the total rain in a 5-day period preceding the storm were very low (≤5 mm). We found, that the Wadi received a total rain volume of 665.4 x 106 m3. Most of it fell on 17 January, when the rain intensity ranged between 4-8 mm/hr. The estimated total surface runoff Q was 123.3 x 103 mm and the total runoff volume was 124 x 106 m3 that constitutes 18.8 % of the total rain volume. The results are in agreement with the observed values in the Wadi and highly required for many applications related to water harvesting and flood protection studies.

Oman Drilling Project Phase I Borehole Geophysical Survey

NASA Astrophysics Data System (ADS)

Matter, J. M.; Pezard, P. A.; Henry, G.; Brun, L.; Célérier, B.; Lods, G.; Robert, P.; Benchikh, A. M.; Al Shukaili, M.; Al Qassabi, A.

2017-12-01

The Oman Drilling Project (OmanDP) drilled six holes at six sites in the Samail ophiolite in the southern Samail and Tayin massifs. 1500-m of igneous and metamorphic rocks were recovered at four sites (GT1, GT2, GT3 and BT1) using wireline diamond core drilling and drill cuttings at two sites (BA1, BA2) using air rotary drilling, respectively. OmanDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, NASA, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, and with in-kind support in Oman from Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University and the German University of Technology. A comprehensive borehole geophysical survey was conducted in all the OmanDP Phase I boreholes shortly after drilling in April 2017. Following geophysical wireline logs, using slim-hole borehole logging equipment provided and run by the Centre National De La Recherche Scientifique (CNRS) and the Université de Montpellier/ Géosciences Montpellier, and logging trucks from the Ministry of Regional Municipalities and Water Resources, were collected in most of the holes: electrical resistivity (dual laterolog resistivity, LLd and LLs), spectral gamma ray (K, U, and Th contents), magnetic susceptibility, total natural gamma ray, full waveform sonic (Vp and Vs), acoustic borehole wall imaging, optical borehole wall imaging, borehole fluid parameters (pressure, temperature, electrical conductivity, dissolved oxygen, pH, redox potential, non-polarized spontaneous electrical potential), and caliper (borehole diameter). In addition, spinner flowmeter (downhole fluid flow rate along borehole axis) and heatpulse flow meter logs (dowhole fluid flow rate along borehole axis) were collected in BA1 to characterize downhole fluid flow rates along borehole axis. Unfortuantely, only incomplete wireline logs are available for

Teachers' views of using e-learning for non-traditional students in higher education across three disciplines [nursing, chemistry and management] at a time of massification and increased diversity in higher education.

PubMed

Allan, Helen T; O'Driscoll, Mike; Simpson, Vikki; Shawe, Jill

2013-09-01

The expansion of the higher educational sector in the United Kingdom over the last two decades to meet political aspirations of the successive governments and popular demand for participation in the sector (the Widening Participation Agenda) has overlapped with the introduction of e-learning. This paper describes teachers' views of using e-learning for non-traditional students in higher education across three disciplines [nursing, chemistry and management] at a time of massification and increased diversity in higher education. A three phase, mixed methods study; this paper reports findings from phase two of the study. One university in England. Higher education teachers teaching on the nursing, chemistry and management programmes. Focus groups with these teachers. Findings from these data show that teachers across the programmes have limited knowledge of whether students are non-traditional or what category of non-traditional status they might be in. Such knowledge as they have does not seem to influence the tailoring of teaching and learning for non-traditional students. Teachers in chemistry and nursing want more support from the university to improve their use of e-learning, as did teachers in management but to a lesser extent. Our conclusions confirm other studies in the field outside nursing which suggest that non-traditional students' learning needs have not been considered meaningfully in the development of e-learning strategies in universities. We suggest that this may be because teachers have been required to develop e-learning at the same time as they cope with the massification of, and widening participation in, higher education. The findings are of particular importance to nurse educators given the high number of non-traditional students on nursing programmes. Copyright © 2012 Elsevier Ltd. All rights reserved.

Apatite-hosted melt inclusions in Damiao massif anorthosite complex, North China

NASA Astrophysics Data System (ADS)

Wang, M.; Veksler, I. V.; Zhang, Z.

2014-12-01

Models for the nelsonite formation are currently highly contentious, with liquid immiscibility and fractional crystallization as frequently proposed formation mechanisms. The nelsonites in the Damiao massif anorthosite complex in the North China Craton and experimental evidence are revisited for the existence of silica-free CaO-FeO-Fe2O3-TiO2-P2O5 immiscible nelsonitic liquids. Our results of differential scanning calorimetry (DSC) demonstrate that nelsonite with the composition of one-third apatite and two-thirds Fe-Ti oxides by weight completely melts well above 1450 ºC, which is in good agreement with numerous experimental studies of the CaO-P2O5-FexO system in connection to metallurgy. Thus, the composition cannot be molten at temperatures relevant for crystallization of the Damiao magma. A review of experimental studies of liquid immiscibility and analyses of natural immiscible glasses show that all the liquids on the Fe- and P-rich side of the miscibility gap have at least 20 wt. % of aluminosilicate components. Main results of this study come from the analyses of apatite-hosted melt inclusions in Damiao nelsonite. The inclusions range from ~3 to 200 μm in diameter. They are ubiquitous and meet all the morphological criteria of primary melt inclusions crystallised into assemblages of daughter minerals. Almost all of them contain vermiculite and chlorite, and some contain biotite, amphibole, phlogopite and Fe-Ti oxides. Out of dozens analysed inclusions, only three have high contents of SiO2 (62.1-73.8 wt. %) and low contents of FeO (0.25-2.35 wt. %). Bulk compositions of other inclusions show large variations in SiO2 (20.79-50.16 wt. %) and FeOt (13.44-32.78 wt. %). With a few exceptions, the inclusions are very low in CaO (0.04-1.51 wt. %, and high in Al2O3 (10-21.17 wt. %). Despite the high Fe content, the compositions differ from those of the typical immiscible Fe-rich melts. It appears that the cumulus apatite crystallised from Fe-rich, hydrated

Volcanic avalanche fault zone with pseudotachylite and gouge in French Massif Central

NASA Astrophysics Data System (ADS)

Bernard, Karine; van Wyk de Vries, Benjamin

2017-11-01

Structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non-depositional to depositional conditions during volcanic avalanche emplacement. In the well-exposed impact-sheared contact along volcanic avalanche fault zone in the French Massif Central, we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress. Sequential events of basal aggradation along avalanche fault zone have been established related to fractal D-values, temperature pressure regime and oscillatory stress during slow wave velocity. A typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge. A cataclastic gradient is characterised by the fractal D-values from 2.7 in jigsaw breccias with pseudotachylite partial melt, to 2.6 in the polymodal gouge. Shock, brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris-avalanche deposit. Gouge microstructures show granular segregation, cataclasis with antithetic rotational Riedel shear, and an arching effect between the Riedel shear bands. X-ray microtomography provided 3D microfabrics along the clastic vein in the sandy-gouge. From the available statistical dataset, a few equations have been developed implicating the same cataclastic origin with a co-genetic evolution of lithofacies. An impact wave during primary shear propagation may contribute to produce hydroclastic matrix, pseudotachylite partial melt and proximal gouge thixotropy with v 50m/s and a T < 654 °C. The interseismic period with oscillatory stress is related to crushed clasts and basaltic melt around 800 °C, Riedel shear bands with granular segregation along the fault gouge. The secondary shock by matrix-rich avalanche (ΔP = 10GPa, T ≥ 1000-1500 �

Behavior of MORB magmas at uppermost mantle beneath a fast-spreading axis: an example from Wadi Fizh of the northern Oman ophiolite

NASA Astrophysics Data System (ADS)

Akizawa, Norikatsu; Arai, Shoji; Tamura, Akihiro

2012-10-01

Relationships of lithologies in uppermost mantle section of Oman ophiolite are highly complicated, harzburgites especially being closely associated with dunites, wehrlites, and gabbros. The petrology and geochemistry of the uppermost mantle section provide constrains on how MORB (mid-ocean ridge basalt) magmas migrate from the mantle to crust. We conducted detailed sampling at the uppermost mantle section of the northern Oman ophiolite (along Wadi Fizh), and it provides us with centimeter-scale lithological and mineral chemical heterogeneity. In particular, we found peculiar plagioclase-free harzburgites that have not been recorded from the current ocean floor, which contain high-Mg# [Mg/(Mg + Fe2+) atomic ratio] clinopyroxenes that are almost in equilibrium (saturated) with MORB in terms of REE concentrations. They are from the uppermost mantle section underlying the wehrlite-dunite layer (=Moho transition zone; MTZ) just beneath the layered gabbro. MORBs cannot be in equilibrium with harzburgites; however, we call the peculiar harzburgites as "MORB-saturated harzburgite" for simplicity in this paper. The MORB-saturated harzburgites exhibit slightly enriched mineralogy (e.g., spinels with higher Ti and ferric iron, and clinopyroxenes with higher Ti and Na) and contain slightly but clearly more abundant modal clinopyroxene (up to 3.5 vol.%) than ordinary Oman depleted harzburgites (less than 1 vol.% clinopyroxene), which are similar to abyssal harzburgites. Gabbro-clinopyroxenite bands, which were melt lenses beneath the ridge axis, are dominant around the MTZ. Detailed sampling around the gabbro-clinopyroxenite bands revealed that the MORB-saturated harzburgites appear around the bands. The interaction between a melt that was MORB-like and an ordinary harzburgite induced incongruent melting of orthopyroxenes in harzburgites, and the melt chromatographically intruded into the wall harzburgite and was modified to coexist with olivine and two pyroxenes at low melt

A Crystallization-Temperature Profile Through Paleo-Oceanic Crust (Wadi Gideah Transect, Oman Ophiolite): Application of the REE-in-Plagioclase-Clinopyroxene Partitioning Thermometer

NASA Astrophysics Data System (ADS)

Mueller, S.; Hasenclever, J.; Garbe-Schönberg, D.; Koepke, J.; Hoernle, K.

2017-12-01

The accretion mechanisms forming oceanic crust at fast spreading ridges are still under controversial discussion. Thermal, petrological, and geochemical observations predict different end-member models, i.e., the gabbro glacier and the sheeted sill model. They all bear implications for heat transport, temperature distribution, mode of crystallization and hydrothermal heat removal over crustal depth. In a typical MOR setting, temperature is the key factor driving partitioning of incompatible elements during crystallization. LA-ICP-MS data for co-genetic plagioclase and clinopyroxene in gabbros along a transect through the plutonic section of paleo-oceanic crust (Wadi Gideah Transect, Oman ophiolite) reveal that REE partitioning coefficients are relatively constant in the layered gabbro section but increase for the overlying foliated gabbros, with an enhanced offset towards HREEs. Along with a systematic enrichment of REE's with crustal height, these trends are consistent with a system dominated by in-situ crystallization for the lower gabbros and a change in crystallization mode for the upper gabbros. Sun and Liang (2017) used experimental REE partitioning data for calibrating a new REE-in-plagioclase-clinopyroxene thermometer that we used here for establishing the first crystallization-temperature depth profile through oceanic crust that facilitates a direct comparison with thermal models of crustal accretion. Our results indicate crystallization temperatures of about 1220±8°C for the layered gabbros and lower temperatures of 1175±8°C for the foliated gabbros and a thermal minimum above the layered-to-foliated gabbro transition. Our findings are consistent with a hybrid accretion model for the oceanic crust. The thermal minimum is assumed to represent a zone where the descending crystal mushes originating from the axial melt lens meet with mushes that have crystallized in situ. These results can be used to verify and test thermal models (e.g., Maclennan et al

Geological setting and petrogenesis of symmetrically zoned, miarolitic granitic pegmatites at Stak Nala, Nanga Parbat - Haramosh Massif, northern Pakistan

USGS Publications Warehouse

Laurs, B.M.; Dilles, J.H.; Wairrach, Y.; Kausar, A.B.; Snee, L.W.

1998-01-01

Miarolitic granitic pegmatites in the Stak valley in the northeast part of the Nanga Parbat - Haramosh Massif, in northern Pakistan, locally contain economic quantities of bi- and tricolored tourmaline. The pegmatites form flat-lying sills that range from less than 1 m to more than 3 m thick and show symmetrical internal zonation. A narrow outer or border zone of medium-to coarse-grained oligoclase - K-feldspar - quartz grades inward to a very coarse-grained wall zone characterized by K-feldspar - oligoclase - quartz - schorl tourmaline. Radiating sprays of schorl and flaring megacrysts of K-feldspar (intermediate microcline) point inward, indicating progressive crystallization toward the core. The core zone consists of variable mixtures of blocky K-feldspar (intermediate microcline), oligoclase, quartz, and sparse schorl or elbaite, with local bodies of sodic aplite and miarolitic cavities or "pockets". Minor spessartine-almandine garnet and lo??llingite are disseminated throughout the pegmatite, but were not observed in the pockets. The pockets contain well-formed crystals of albite, quartz, K-feldspar (maximum microcline ?? orthoclase overgrowths), schorl-elbaite tourmaline, muscovite or lepidolite, topaz, and small amounts of other minerals. Elbaite is color-zoned from core to rim: green (Fe2+- and Mn2+-bearing), colorless (Mn2+-bearing), and light pink (trace Mn3+). Within ???10 cm of the pegmatites, the granitic gneiss wallrock is bleached owing to conversion of biotite to muscovite, with local quartz and albite added. Schorl is disseminated through the altered gneiss, and veins of schorl with bleached selvages locally traverse the wallrock up to 1 m from the pegmatite contact. The schorl veins can be traced into the outer part of the wall zone, which suggests that they formed from aqueous fluids derived during early saturation of the pegmatite-forming leucogranitic magma rich in H2O, F, B, and Li. Progressive crystallization resulted in a late-stage sodic

Climatic, eustatic, and tectnoic controls on Quarternary deposits and landforms, Red Sea coast, Egypt

NASA Technical Reports Server (NTRS)

Arvidson, Raymond; Becker, Richard; Shanabrook, Amy; Luo, Wei; Sturchio, Neil; Sultan, Mohamed; Lofty, Zakaria; Mahmood, Abdel Moneim; El Alfy, Zeinhom

1994-01-01

The degree to which local climatic variations, eustatic sea level fluctuations, and tectonic uplift have influenced the development of Quaternary marine and fluvial landforms and deposits along the Red Sea coast, Eastern Desert, was investigated using a combination of remote sensing and field data, age determinations of corals, and numerical simulations. False color composites generated from Landsat Thematic Mapper and SPOT image data, digital elevation models derived from sterophotogrammetric analysis of SPOT data, and field observations document that a approximately 10-km wide swath inland from the coast is covered in many places with coalescing alluvial fans of Quaternary age. Wadis cutting through the fans exhibit several pairs of fluvial terraces, and wadi walls expose alluvium interbedded with corraline limestone deposits Further, three distinct coral terraces are evident along the coatline. Climatic, eustatic, and tectonic uplift controls on the overall system were simulated using a cellular automata algorithm with the following characteristics: (1) uplift as a function of position and time, as defined by the elevations and ages of corals; (2) climatic variations driven by insolation changes associated with Milankovitch cycles; (3) sea level fluctuations based on U/Th ages of coral terraces and eustatic data; and (4) parametrized fluvial erosion and deposition. Results imply that the fans and coralline limestones were generated in a setting in which the tectonic uplift rate decreased over the Quarternary to negligible values at present. Coralline limestones formed furing eustatic highstands when alluvium was trapped uspstream and wadis filled with debris. During lowstands, wadis cut into sedimentary deposits; coupled with continuing uplift, fans were dissected, leaving remnant surfaces, and wadi-related terraces were generated by down cutting. Only landforms from the past three to four eustatic sea level cycles (i.e., approximately 300 to 400 kyr) are likely

Kinematics and thermal conditions in the permafrost-affected rockwalls of the Aiguille du Midi (3842 m a.s.l., Mont Blanc massif, France)

NASA Astrophysics Data System (ADS)

Ravanel, Ludovic; Grangier, Germain; Weber, Samuel; Beutel, Jan; Magnin, Florence; Gruber, Stefan; Deline, Philip

2016-04-01

Processes that control climate-dependent rockfall from permafrost-affected rock slopes are still poorly understood. In this study, we present the results of a Wireless Sensor Network, integrated within the Swiss project PermaSense and developed in 2012, to measure rock temperature and geotechnical parameters in the steep rockwalls of the Aiguille du Midi (AdM, 3842 m a.s.l., Mont Blanc massif, France). Accessible year round by cable car, the AdM comprises two main peaks: (i) the Piton Nord with the cable car arrival station, where 4 crack-meters are placed on four major fractures, and (ii) the Piton Central with many touristic infrastructure, equipped with three 10-m-deep boreholes with 15 temperatures sensors since 2009, and where 2 crack-meters are installed along a major fracture. Three major kinematic regimes are observed: (i) opening of clefts when the rock temperature becomes positive, followed by closing during the cold period, (ii) summer opening continued by a winter opening, and (iii) closing during the warm period followed by opening in winter.

Chemical composition and osmium-isotope systematics of primary and secondary PGM assemblages from high-Mg chromitite of the Nurali lherzolite massif, the South Urals, Russia

NASA Astrophysics Data System (ADS)

Malitch, K. N.; Anikina, E. V.; Badanina, I. Yu.; Belousova, E. A.; Pushkarev, E. V.; Khiller, V. V.

2016-01-01

The isotopic and geochemical characteristics of PGE mineralization in high-Mg chromitite from the banded dunite-wehrlite-clinopyroxenite complex of the Nurali lherzolite massif, the South Urals, Russia is characterized for the first time. Electron microprobe analysis and LA MC-ICP-MS mass spectrometry are used for studying Cr-spinel and platinum-group minerals (PGM). Two processes synchronously develop in high-Mg chromitite subject to metamorphism: (1) the replacement of Mg-Al-rich Cr-spinel, orthopyroxene, and diopside by chromite, Cr-amphibole, chlorite, and garnet; (2) the formation of a secondary mineral assemblage consisting of finely dispersed ruthenium or Ru-hexaferrum aggregate and silicate-oxide or silicate matter on the location of primary Ru-Os-sulfides of the laurite-erlichmanite solid solution series. Similar variations of Os-isotopic composition in both primary and secondary PGM assemblages are evidence for the high stability of the Os isotope system in PGM and for the possibility of using model 187Os/188Os ages in geodynamic reconstructions.

The dynamics of serpentinite dehydration reactions in subduction zones: Constrains from the Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain)

NASA Astrophysics Data System (ADS)

Dilissen, Nicole; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Padrón-Navarta, José Alberto

2015-04-01

Arc volcanism, earthquakes and subduction dynamics are controlled by fluids from downgoing slabs and their effect on the melting and rheology of the overlying mantle wedge. High pressure dehydration of serpentinite in the slab and the subduction channel is considered as one of the main sources of fluids in subduction zones. Even though this metamorphic reaction is essential in subduction activities, the behavior of the fluids, the kinetics and thermodynamics during the breakdown reaction are still poorly understood. The Cerro del Almirez (Nevado-Filábride Complex, Betic Cordillera, SE Spain) uniquely preserves the dehydration front from antigorite serpentinite to chlorite-harzburgite and constitutes a unique natural laboratory to investigate high-pressure dehydration of serpentinite. This reaction occurred in a subduction setting releasing up to 13 wt% of water, contributing significantly to the supply of fluids to the overlying mantle wedge. A key to the understanding of the metamorphic conditions prevailing during serpentinite dehydration is to study the two prominent textures -granofels and spinifex-like chlorite harzburgite- occurring in this reaction product. The detailed texture differences in the Chl-harzburgite can provide insights into diverse kinetic and thermodynamic conditions of this dehydration reaction due to variations in effective pressure and drainage conditions. It has been proposed that difference in overpressure (P') and deviation from growth equilibrium, i.e. overstepping, is responsible for these two types of textures [Padrón-Navarta et al., 2011]. The magnitude and duration of P' is highly dependent on dehydration kinetics [Connolly, 1997]. The fast pressure drop, with spinifex-texture as a product, can be linked to draining events expected after hydrofracturing, which are recorded in grain size reduction zones in this massif. According to this hypothesis, mapping of textural variation in Chl-harzburgite might be used as a proxy to

Characterization of the paleo-hydrothermal fluids flow in the geothermal province of Limagne. (French Massif Central).

NASA Astrophysics Data System (ADS)

Fréville, K.; Sizaret, S.

2017-12-01

Exploitation of the geothermal energy is a prime target to future energy supply. Understanding the nature and the flow of geothermal fluids is a key objective for describe the functioning of current hydrothermal systems. Located in the French Massif Central, the Limagne basin is a tertiary hemi-graben characterized by a high thermal gradient with numerous occurrences of CO2-rich thermo-mineral waters. This basin has potential for high-temperature geothermal energy, expressed by numerous natural high temperature water sources, as well as at Royat and Vichy were the surface temperature of the water can reach 33°C and 27°C, respectively. In order to better localize this potential, the geological evolution has to be deciphered. In this aim we study the flow processes of the paleo-fluids and estimate the direction and the velocity of the hydrothermal flow from the studies of the growth bands of comb quartz grain localized in vein. In a second time, the studies fluids inclusions within the quartz grain are used to characterize the nature of the fluids involved. Preliminary results show that the flow is discontinuous over the time with changes in velocities and directions during the growth of a single quartz grain. Two main flows were identified, i) a relatively fast upward flow at 10-6,-5 m.s-1; ii) a downward flow at about 10-5,-4 m.s-1. The results allow: (i) to discuss the processes controlling the fluids flow in the Limagne basin; and (ii) to suggest to delimitate the areas with high geothermal potential which integrate the flow variation in time.

Geology of the epithermal Ag-Au Huevos Verdes vein system and San José district, Deseado massif, Patagonia, Argentina

NASA Astrophysics Data System (ADS)

Dietrich, Andreas; Gutierrez, Ronald; Nelson, Eric P.; Layer, Paul W.

2012-03-01

The San José district is located in the northwest part of the Deseado massif and hosts a number of epithermal Ag-Au quartz veins of intermediate sulfidation style, including the Huevos Verdes vein system. Veins are hosted by andesitic rocks of the Bajo Pobre Formation and locally by rhyodacitic pyroclastic rocks of the Chon Aike Formation. New 40Ar/39Ar constraints on the age of host rocks and mineralization define Late Jurassic ages of 151.3 ± 0.7 Ma to 144.7 ± 0.1 Ma for volcanic rocks of the Bajo Pobre Formation and of 147.6 ± 1.1 Ma for the Chon Aike Formation. Illite ages of the Huevos Verdes vein system of 140.8 ± 0.2 and 140.5 ± 0.3 Ma are 4 m.y. younger than the volcanic host rock unit. These age dates are among the youngest reported for Jurassic volcanism in the Deseado massif and correlate well with the regional context of magmatic and hydrothermal activity. The Huevos Verdes vein system has a strike length of 2,000 m, with several ore shoots along strike. The vein consists of a pre-ore stage and three main ore stages. Early barren quartz and chalcedony are followed by a mottled quartz stage of coarse saccharoidal quartz with irregular streaks and discontinuous bands of sulfide-rich material. The banded quartz-sulfide stage consists of sulfide-rich bands alternating with bands of quartz and bands of chlorite ± illite. Late-stage sulfide-rich veinlets are associated with kaolinite gangue. Ore minerals are argentite and electrum, together with pyrite, sphalerite, galena, chalcopyrite, minor bornite, covellite, and ruby silver. Wall rock alteration is characterized by narrow (< 3 m) halos of illite and illite/smectite next to veins, grading outward into propylitic alteration. Gangue minerals are dominantly massive quartz intergrown with minor to accessory adularia. Epidote, illite, illite/smectite, and, preferentially at deeper levels, Fe-chlorite gangue indicate near-neutral pH hydrothermal fluids at temperatures of >220°C. Kaolinite occurring with

Occurrence of springs in massifs of crystalline rocks, northern Portugal

NASA Astrophysics Data System (ADS)

Pacheco, Fernando António Leal; Alencoão, Ana Maria Pires

2002-02-01

An inventory of artesian springs emerging from fractures (fracture springs) was conducted in the Pinhão River Basin and Morais Massif, northern Portugal, comprising an area of approximately 650 km2. Over 1,500 springs were identified and associated with geological domains and fracture sets. Using cross-tabulation analysis, spring distributions by fracture sets were compared among geological environments, and the deviations related to differences in rock structure and, presumably, to differences in deformational histories. The relation between spring frequencies and rock structures was further investigated by spectral determination, the model introduced in this study. Input data are the spring frequencies and fracture lengths in each geological domain, in addition to the angles between fracture strikes and present-day stress-field orientation (θ). The model's output includes the so-called intrinsic densities, a parameter indexing spring occurrence to factors such as fracture type and associated deformational regime and age. The highest densities (12.2 springs/km of lineament) were associated with young shear fractures produced by brittle deformation, and the lowest (0.1) with old tensional and ductile fractures. Spectral determination also relates each orientation class to a dominant structural parameter: where spring occurrence is controlled by θ, the class is parallel to the present-day stress-field orientation; where the control is attributed to the length of fractures, the spring occurrence follows the strike of large-scale normal faults crossing the region. Résumé. Un inventaire des sources artésiennes émergeant de fractures (sources de fractures) a été réalisé dans le bassin de la rivière Pinhão et dans le massif de Morais, dans le nord du Portugal, dans une région couvrant environ 650 km2. Plus de 1,500 sources ont été identifiées et associées à des domaines géologiques et à des ensembles de fractures. Grâce à une analyse de tableaux

Intrusive rocks of the Wadi Hamad Area, North Eastern Desert, Egypt: Change of magma composition with maturity of Neoproterozoic continental island arc and the role of collisional plutonism in the differentiation of arc crust

NASA Astrophysics Data System (ADS)

Basta, Fawzy F.; Maurice, Ayman E.; Bakhit, Bottros R.; Azer, Mokhles K.; El-Sobky, Atef F.

2017-09-01

The igneous rocks of the Wadi Hamad area are exposed in the northernmost segment of the Arabian-Nubian Shield (ANS). These rocks represent part of crustal section of Neoproterozoic continental island arc which is intruded by late to post-collisional alkali feldspar granites. The subduction-related intrusives comprise earlier gabbro-diorites and later granodiorites-granites. Subduction setting of these intrusives is indicated by medium- to high-K calc-alkaline affinity, Ta-Nb troughs on the spider diagrams and pyroxene and biotite compositions similar to those crystallized from arc magmas. The collisional alkali feldspar granites have high-K highly fractionated calc-alkaline nature and their spider diagrams almost devoid of Ta-Nb troughs. The earlier subduction gabbro-diorites have lower alkalis, LREE, Nb, Zr and Hf values compared with the later subduction granodiorites-granites, which display more LILE-enriched spider diagrams with shallower Ta-Nb troughs, reflecting variation of magma composition with arc evolution. The later subduction granitoids were generated by lower degree of partial melting of mantle wedge and contain higher arc crustal component compared with the earlier subduction gabbro-diorites. The highly silicic alkali feldspar granites represent extensively evolved melts derived from partial melting of intermediate arc crustal sources during the collisional stage. Re-melting of arc crustal sources during the collisional stage results in geochemical differentiation of the continental arc crust and the silicic collisional plutonism drives the composition of its upper part towards that of mature continental crust.

Long-term dynamics of soil chemical properties after a prescribed fire in a Mediterranean forest (Montgrí Massif, Catalonia, Spain).

PubMed

Alcañiz, M; Outeiro, L; Francos, M; Farguell, J; Úbeda, X

2016-12-01

This study examines the effects of a prescribed fire on soil chemical properties in the Montgrí Massif (Girona, Spain). The prescribed forest fire was conducted in 2006 to reduce understory vegetation and so prevent potential severe wildfires. Soil was sampled at a depth of 0-5cm at 42 sampling points on four separate occasions: prior to the event, immediately after, one year after and nine years after. The parameters studied were pH, electrical conductivity (EC), total carbon (C), total nitrogen (N), available phosphorus (P), potassium (K + ), calcium (Ca 2+ ) and magnesium (Mg 2+ ). All parameters (except pH) increased significantly immediately after the fire. One year after burning, some chemical parameters - namely, EC, available P and K + - had returned to their initial, or even lower, values; while others - pH and total C - continued to rise. Total N, Ca 2+ and Mg 2+ levels had fallen one year after the fire, but levels were still higher than those prior to the event. Nine years after the fire, pH, total C, total N and available P are significantly lower than pre-fire values and nutrients concentrations are now higher than at the outset but without statistical significance. The soil system, therefore, is still far from being recovered nine years later. Copyright © 2016 Elsevier B.V. All rights reserved.

Cyclostratigraphic analysis of the Middle to lower Upper Ordovician Postolonnec Formation in the Armorican Massif (France): integrating pXRF, gammay-ray and lithological data

NASA Astrophysics Data System (ADS)

Sinnesael, Matthias; Loi, Alfredo; Dabard, Marie-Pierre; Vandenbroucke, Thijs; Claeys, Philippe

2017-04-01

The Middle to lower Upper Ordovician sections of the Crozon Peninsula area (Postolonnec Formation, Armorican Massif, western France) show multi-order eustatic sea-level changes (Dabard et al., 2015). The sections are characterized by siliciclastic facies, which were deposited in tidal to storm-dominated shelf environments. Dabard et al. (2015) analysed the facies, their stacking patterns, and gamma-ray data and applied backstripping to identify subsidence and several orders of sea-level change. The main stratigraphic constraints are coming from (chitinozoan) biostratigraphy. The 3th to 5th orders changes are hypothesized to correspond to various frequencies related to astronomical forcing. This study investigates the potential added value of portable X-Ray Fluorescence (pXRF) and the application of spectral analyses. High-resolution (cm-scale) non-destructive pXRF and natural gamma-ray measurements were carried out on 14 m of section that was equally logged on a cm resolution. The pXRF measurements on the surface of the outcrops are compared with earlier results of wavelength dispersive XRF spectrometry and ICP-MS. The potassium records of the pXRF and gamma-ray logs are comparable and essentially reflect lithological variations (i.e., between mudstone and coarse sandstones). Other reliably measured elements also reflected lithological aspects such as clay-sandstone alternations (e.g. K, Rb, Ti), placer locations (Zr, Ce, Ti) and potentially clay mineralogy and condensation horizons (Ni, Zn, Co, Mn). Spectral analyses of the various proxies (lithology, natural gamma-ray and pXRF) are compared with each other. Both the new high-resolution data (14 m of section) as well as the published low-resolution data (which span almost 400 m of Darriwilian-Sandbian) were analyzed. The study reveals strong indications for the imprint of obliquity, precession and eccentricity. Obtaining age constraints, in addition to the existing biostratigraphical framework is a challenge in

Variable viral and grazer control of prokaryotic growth efficiency in temperate freshwater lakes (French Massif Central).

PubMed

Ram, A S Pradeep; Palesse, S; Colombet, J; Sabart, M; Perriere, F; Sime-Ngando, T

2013-11-01

The effects of viral lysis and heterotrophic nanoflagellate grazing (top down forces) on prokaryotic mortality and their subsequent impact on their metabolism were estimated in the upper euphotic and deeper aphotic depth of 11 freshwater lakes located in the French Massif Central. The standing stocks of viruses (VA) and heterotrophic nanoflagellate (HNF) varied significantly (p < 0.05) with sampled depth. VA was substantially (twofold on an average) and significantly higher (p < 0.03) at the aphotic compared to euphotic depth, whereas the reverse was true (p < 0.02) for HNF. Among the prokaryote subgroup, high nucleic acid content prokaryotes explained for significant variability in the total VA and served as principle host target for viral proliferation. Like standing stocks, flagellate grazing and viral infection rates also followed similar patterns. In the investigated lakes, the mechanism for regulating prokaryotic production varied with sampled depth from grazing control in the euphotic to control due to viral lysis in the aphotic. We also tested the hypothesis of top down control on prokaryotic growth efficiency (PGE, which we used as an index of prokaryotic physiological and energetic status at the community level) at both depths. Overall, among the studied lakes, PGE varied widely (4-51 %) with significantly (p < 0.05) lower values in the aphotic (mean = 18 ± 4 %) than euphotic depth (mean = 32 ± 9 %). Contrasting observations on the top down control of PGE between sampled depths were observed. The presence of grazers was found to stimulate PGE at the euphotic, whereas viruses through their lytic infection had a strong negative impact on PGE at the aphotic depth. Such observed differences in PGE and the mechanism controlling prokaryotic production with depth could eventually have strong implication on carbon and nutrient flux patterns in the studied lakes.

Petrochemical and Mineralogical Constraints on the Source and Processes of Uranium Mineralisation in the Granitoids of Zing-Monkin Area, Adamawa Massif, NE Nigeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haruna, I. V., E-mail: vela_hi@yahoo.co.uk; Orazulike, D. M.; Ofulume, A. B.

Zing-Monkin area, located in the northern part of Adamawa Massif, is underlain by extensive exposures of moderately radioactive granodiorites, anatectic migmatites, equigranular granites, porphyritic granites and highly radioactive fine-grained granites with minor pegmatites. Selected major and trace element petrochemical investigations of the rocks show that a progression from granodiorite through migmatite to granites is characterised by depletion of MgO, CaO, Fe{sub 2}O{sub 3,} Sr, Ba, and Zr, and enrichment of SiO{sub 2} and Rb. This trend is associated with uranium enrichment and shows a chemical gradation from the more primitive granodiorite to the more evolved granites. Electron microprobe analysis showsmore » that the uranium is content in uranothorite and in accessories, such as monazite, titanite, apatite, epidote and zircon. Based on petrochemical and mineralogical data, the more differentiated granitoids (e.g., fine-grained granite) bordering the Benue Trough are the immediate source of the uranium prospect in Bima Sandstone within the Trough. Uranium was derived from the granitoids by weathering and erosion. Transportation and subsequent interaction with organic matter within the Bima Sandstone led to precipitation of insoluble secondary uranium minerals in the Benue Trough.« less

Fracture patterns of the drainage basin of Wadi Dahab in relation to tectonic-landscape evolution of the Gulf of Aqaba - Dead Sea transform fault

NASA Astrophysics Data System (ADS)

Shalaby, Ahmed

2017-10-01

Crustal rifting of the Arabian-Nubian Shield and formation of the Afro-Arabian rifts since the Miocene resulted in uplifting and subsequent terrain evolution of Sinai landscapes; including drainage systems and fault scarps. Geomorphic evolution of these landscapes in relation to tectonic evolution of the Afro-Arabian rifts is the prime target of this study. The fracture patterns and landscape evolution of the Wadi Dahab drainage basin (WDDB), in which its landscape is modeled by the tectonic evolution of the Gulf of Aqaba-Dead Sea transform fault, are investigated as a case study of landscape modifications of tectonically-controlled drainage systems. The early developed drainage system of the WDDB was achieved when the Sinai terrain subaerially emerged in post Eocene and initiation of the Afro-Arabian rifts in the Oligo-Miocene. Conjugate shear fractures, parallel to trends of the Afro-Arabian rifts, are synthesized with tensional fracture arrays to adapt some of inland basins, which represent the early destination of the Sinai drainage systems as paleolakes trapping alluvial sediments. Once the Gulf of Aqaba rift basin attains its deeps through sinistral movements on the Gulf of Aqaba-Dead Sea transform fault in the Pleistocene and the consequent rise of the Southern Sinai mountainous peaks, relief potential energy is significantly maintained through time so that it forced the Pleistocene runoffs to flow via drainage systems externally into the Gulf of Aqaba. Hence the older alluvial sediments are (1) carved within the paleolakes by a new generation of drainage systems; followed up through an erosional surface by sandy- to silty-based younger alluvium; and (2) brought on footslopes of fault scarps reviving the early developed scarps and inselbergs. These features argue for crustal uplifting of Sinai landscapes syn-rifting of the Gulf of Aqaba rift basin. Oblique orientation of the Red Sea-Gulf of Suez rift relative to the WNW-trending Precambrian Najd faults; and

Geochemistry of a Triassic dyke swarm in the North Patagonian Massif, Argentina. Implications for a postorogenic event of the Permian Gondwanide orogeny

NASA Astrophysics Data System (ADS)

González, Santiago N.; Greco, Gerson A.; González, Pablo D.; Sato, Ana M.; Llambías, Eduardo J.; Varela, Ricardo

2016-10-01

Permo-Triassic magmatism is widespread in the eastern North Patagonian Massif and has been related to the Gondwanide orogeny. Although a magmatic arc setting is widely accepted for the Permian plutonic rocks, the origin and geotectonic setting for the Triassic plutonic and volcanic rocks are still unknown. A NW-SE Triassic dyke swarm composed of andesites and latites with minor rhyolites was previously described in the Sierra Grande - Rincon de Paileman area. The dyke swarm was associated with extensional tectonics which was linked to a postorogenic process. In this paper we present new geochemical data of the rocks that form the swarm. Trachyandesites and rhyolites were separated based on their geochemical characteristics. Both groups may be considered originated from different sources. On the other hand, the content of incompatible elements (LILE and HFSE) indicates a strong relation between the swarm and an active continental margin. The samples also show a transitional signature between continental-arc and postcollisional or anorogenic settings. The new geochemical data on the dyke swarm support the idea of a magmatism that was linked to a postorogenic extensional tectonic regime related to a continental magmatic arc. Such an extension started in the Paleopacific margin of Pangea during the Anisian and might indicate the beginning of the Pangea break-up.

Remelting of nanogranitoids in UHP felsic granulites from Erzgebirge (Bohemian Massif, Germany)

NASA Astrophysics Data System (ADS)

Acosta-vigil, A.; Stöckhert, B.; Hermann, J.; Yaxley, G.; Cesare, B.; Bartoli, O.

2017-12-01

Crustal melting commonly takes place at pressures ≤ 1.5 GPa. Anatexis at UHP conditions, however, can occur during subduction of continental crust down to mantle depths. Understanding the timing, mechanisms and nature of this process is important as it has major mechanical and geochemical implications. One way to address this problem is through the novel studies of nanogranitoids in migmatites and granulites (Cesare et al. 2015). We have remelted crystallized former melt inclusions (nanogranitoids) trapped in garnets of diamond-bearing UHP felsic granulites from Erzgebirge, Bohemian Massif. These rocks are made of Qtz+Phe+Pl+Grt+Ky+Bt+Dia, and their peak conditions have been estimated at P≥4.5 GPa and T≥1000 ºC. Nanogranitoids appear homogeneously distributed throughout the entire garnet crystals, are 5-50 µm across and often isometric, with partially developed negative crystal shape, and were trapped during garnet growth in the presence of melt. The mineral assemblage within nanogranites consists of Qtz+Pl+Phe+Pg+Phl±Ky±Dia±Gr±Ap±Rt (Stöckhert et al. 2009). Fragments of nanogranitoids-bearing garnets were loaded inside gold capsules, enclosed in SiO2 or C powders that acted as cushion, either dry or with H2O in excess, and subjected to conditions between 975-1100 ºC and 2.5-4.5 GPa for 2-24 hrs. Re-homogenization has not been completely achieved. Nanogranitoids partially melt, melt often coexists with Als, diamond or Gr, and Grt grows into the melt to form a higher #Mg and Ti, ≈5 µm fringe. Preliminary EMP analyses indicate that melts are granitic sensu stricto, with low FeOt+MgO (≈2 wt%), moderate to high in ASI, and high in TiO2 (≈0.4-0.8 wt%), P2O5 (up to 1 wt%) and volatiles (100-EMP totals ≈ 10-15 wt%). These preliminary results suggest that (i) anatexis started in the presence of a H2O-rich fluid phase, (ii) melt was present and equilibrated at quite high T (>850-950 ºC, Hayden & Watson 2007) at or close to peak conditions, (iii) Als

Geomorphological map of glaciated gorges in a granitic massif (Gredos range, Central Spain).

NASA Astrophysics Data System (ADS)

Campos, Néstor; Tanarro, Luis Miguel; Palacios, David

2017-04-01

A detailed geomorphological map on a 1:10,000 scale is presented for a high mountain area in Gredos range (Iberian Central System), this area is located in a granitic massif 160 km West of Madrid and comprises three gorges : La Vega, Taheña-Honda and La Nava. Only few detailed geomorphological maps of the Gredos range are available despite the wide diversity of landforms, in order to improve the understanding of this zone, this geomorphological map of the area has been produced, showing in detail the geomorphologic diversity of these gorges. The map was created with the aid of 25 cm resolution aerial photographs, 25 cm resolution satellite images, Iberpix 3D images provided by the Spanish National Geographic Institute and verified with field work. The landforms were delimitated with a stereoscope and satellite image pairs and digitized using GIS and CAD software, in some areas 3D glasses has been used with 3D images and the software Esri ArcScene. The landforms resulting from interpretation of aerial photographs and satellite images were classified using the IGUL (Institute of Geography, University of Lausanne) legend system (developed at the end of the 1980s) combined with the legend proposed by Peña et al. (1997) and some personal adaptations. The map legend includes 45 landforms divided into seven sections: structural, hydrography, fluvial, gravitative, glacial, nival and anthropic landforms. The use of both legend systems allows us to represent the landform types distributed over an area of 40 km2 and to identify the geomorphic processes involved in their morphogenesis, this variety of processes and landforms identified demonstrated that geomorphological cartography obtained by combining traditional image interpretation and GIS technology facilitates the production of geomorphological maps and the obtaining of valuable data for identify and understand surface processes and landforms. References: Maillard, B., Lambiel, C., Martin, S., Pellitero, R., Reynard, E

Speleothem evidence for the greening of the Sahara and its implications for the early human dispersal out of sub-Saharan Africa

NASA Astrophysics Data System (ADS)

El-Shenawy, Mohammed I.; Kim, Sang-Tae; Schwarcz, Henry P.; Asmerom, Yemane; Polyak, Victor J.

2018-05-01

Although there is a consensus that there were wet periods (greening events) in the Sahara in the past, the spatial extent and the timing of these greening events are still in dispute, yet critical to our understanding of the early human dispersal out of Africa. Our U-series dates of speleothems from the Northeastern Sahara (Wadi Sannur cave, Egypt) reveal that the periods of speleothem growth were brief and restricted to the interglacial Marine Isotope Stages MIS 5.5, MIS 7.3, and the early MIS 9 with a remarkable absence of the Holocene deposition of speleothems. These growth periods of Wadi Sannur cave speleothems correspond to periods of high rainfall and spread of vegetation (green Sahara). Distinct low δ18O values of speleothems indicate a distal moisture source that we interpret to be the Atlantic Ocean. These two lines of evidence from the Wadi Sannur speleothems thus suggest that maximal northward shifts in the West African monsoon system occurred during the growth periods of the speleothems, leading to greening of the Sahara, facilitating human migration into Eurasia. The periods of speleothem growth at Wadi Sannur cave are contemporaneous with important archeological events: (1) the earliest occurrence of the Middle Stone Age assemblages and Homo sapiens in North Africa (Jebel Irhoud), suggesting wide spread of greening conditions over the East-West transect of the Sahara, (2) the sharp technological break between the Acheulo-Yabrudian and the Mousterian industries, and (3) the arrival of Homo sapiens in Levant, indicating a key role of the Sahara route in early human dispersal out of Africa.

Serpentinization and Synthesis: Can abiotic and biotic non-volatile organic molecules be identified in the subsurface of the Atlantis Massif?

NASA Astrophysics Data System (ADS)

Hickok, K.; Nguyen, T.; Orcutt, B.; Fruh-Green, G. L.; Wanamaker, E.; Lang, S. Q.

2016-12-01

The high concentrations of hydrogen created during serpentinization can promote the formation of abiotic organic carbon molecules such as methane, formate, short chain hydrocarbons and, in laboratory experiments, larger molecules containing up to 32 carbon atoms. Subsurface archaeal and bacterial communities can use these reduced compounds for metabolic energy. International Ocean Discovery Project Expedition 357 drilled into the Atlantis Massif with the goals of investigating carbon cycling and the presence of life in a zone of active serpentinization. The expedition recovered multiple rock lithologies including gabbros, basalts, carbonate sands, and serpentinites. A subset of these samples are being analyzed to determine if non-volatile organic molecules are produced abiotically in serpentinizing environments and to identify `hot spots' of microbial life in the subsurface. Rock samples of contrasting representative lithologies are being analyzed for the presence of n-alkanes and fatty acids. Preliminary results have so far indicated the presence of alkanes in some samples. The isotopic (13C, 2H) characteristics of these compounds are being compared to a suite of oils, greases, and drilling fluids used during sample collection to distinguish in situ abiotic and biotic signatures from contaminant compounds. Other initial results have shown the efficacy of various sample-handling procedures designed to reduce surface contamination. This study will contribute to the overall understanding of the role serpentinization plays in the global carbon cycle and its implications for pre-biotic chemistry.

The genus Macroocula Panfilov in Egypt, with two new species (Hymenoptera: Bradynobaenidae: Apterogyninae).

PubMed

Gadallah, Neveen S; Soliman, Ahmed M; Al-Shahat, Ahmed M; Hossni, Mohammed T

2015-09-16

The genus Macroocula Panfilov in Egypt is reviewed. Seven species were previously recorded from Egypt: M. magna (Invrea, 1965), M. mahunkai Argaman, 1994, M. morawitzi (Radoszkowski, 1888), M. nigriventris (Invrea, 1960), M. nitida (Bischoff, 1920), M. savignyi (Klug, 1829) and M. sinaica (Invrea, 1963). Macroocula brothersi Gadallah & Soliman, sp. nov. (Egypt, Wadi Shab, Red Sea) and M. salehi Gadallah & Soliman, sp. nov. (Egypt, Wadi Shaghab, Aswan) are described and illustrated. The subspecies M. nitida nitida (Bischoff, 1920) and M. nitida patrizii (Invrea, 1932) are raised to species level. An illustrated key and a faunistic list of Macroocula species are given.

A Search for Amino Acids and Nucleobases in the Martian Meteorite Roberts Massif 04262 Using Liquid Chromatography-Mass Spectrometry

NASA Technical Reports Server (NTRS)

Callahan, Michael P.; Burton, Aaron S.; Elsila, Jamie E.; Baker, Eleni M.; Smith, Karen E.; Glavin, Daniel P.; Dworkin, Jason P.

2013-01-01

The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of beta-alanine and gamma-amino-eta-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal eta-omega-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites. A carbon isotope ratio of -24(0/00) +/- 6(0/00) for beta-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of eta-omega-amino acids may be due to a high temperature Fischer-Tropschtype synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.

Polyphase deformation history and strain analyses of the post-amalgamation depositional basins in the Arabian-Nubian Shield: Evidence from Fatima, Ablah and Hammamat Basins

NASA Astrophysics Data System (ADS)

Hamimi, Zakaria; El-Fakharani, Abdelhamid; Abdeen, Mamdouh M.

2014-11-01

Post-amalgamation depositional basins <650 Ma (PADBs), dominated by volcano-sedimentary assemblages, unconformably overlying Neoproterozoic juvenile (mantle-derived) arcs, represent one of the main collage in the Arabian-Nubian Shield (ANS). In this work, three distinguished PADBs; namely Fatima, Ablah and Hammamat PADBs, are the subject matter of detailed field investigations and quantitative strain analysis in an attempt to highlight the polyphase deformation history of these PADBs and to discern whether the ANS's PADBs were deformed at the same time or not. The Fatima PADB is studied in its type locality along the northwestern flank of Wadi Fatima; between Jabal Abu Ghurrah and Jabal Daf, in Jeddah tectonic terrane. The Ablah PADB is examined around Wadi Yiba, further south of its type locality near Jabal Ablah in Al-Aqiq Quadrangle, in Asir tectonic terrane. The Hammamat PADB is investigated in Wadi Umm Gheig, Wadi Allaqi and Wadi Hodein in the Egyptian Eastern Desert tectonic terrane. It is supposed that the Fatima is a basin controlled by dextral transcurrent shearing occurred along the NE-oriented Wadi Fatima Shear Zone and the Ablah is a strike-slip pull-apart basin, and both basins were believed to be deposited during and soon after the Nabitah Orogeny (680-640 Ma) that marked suturing of the Afif terrane with the oceanic ANS terranes to the west. They were affected by at least three Neoproterozoic deformation phases and show geometric and kinematic relationships between folding and thrusting. The Hammamat PADB is a fault-bounded basin affected by a NW-SE- to NNW-SSE-oriented shortening phase just after the deposition of the molasse sediments, proved by NW- to NNW-verging folds and SE- to SSE-dipping thrusts that were refolded and thrusted in the same direction. The shortening phase in the Hammamat was followed by a transpressional wrenching phase related to the Najd Shear System, which resulted in the formation of NW-SE sinistral-slip faults associated

40 Ma of hydrothermal W mineralization during the Variscan orogenic evolution of the French Massif Central revealed by U-Pb dating of wolframite

NASA Astrophysics Data System (ADS)

Harlaux, Matthieu; Romer, Rolf L.; Mercadier, Julien; Morlot, Christophe; Marignac, Christian; Cuney, Michel

2018-01-01

We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically <10 ppm) and show significant variations in their radiogenic Pb isotopic compositions. The obtained U-Pb ages define three distinct geochronological groups related to three contrasting geodynamic settings: (i) Visean to Namurian mineralization (333-327 Ma) coeval with syn-orogenic compression and emplacement of large peraluminous leucogranites (ca. 335-325 Ma), (ii) Namurian to Westphalian mineralization (317-315 Ma) synchronous with the onset of late-orogenic extension and emplacement of syn-tectonic granites (ca. 315-310 Ma) and (iii) Stephanian to Permian mineralization (298-274 Ma) formed during post-orogenic extension contemporaneous with the Permian volcanism in the entire Variscan belt. The youngest ages (276-274 Ma) likely reflect the reopening of the U-Pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration (e.g. ferberitization). Our results demonstrate that W(±Sn) mineralization in the FMC formed during at least three distinct hydrothermal events in different tectono-metamorphic settings over a time range of 40 Ma.

Using airborne LiDAR in geoarchaeological contexts: Assessment of an automatic tool for the detection and the morphometric analysis of grazing archaeological structures (French Massif Central).

NASA Astrophysics Data System (ADS)

Roussel, Erwan; Toumazet, Jean-Pierre; Florez, Marta; Vautier, Franck; Dousteyssier, Bertrand

2014-05-01

Airborne laser scanning (ALS) of archaeological regions of interest is nowadays a widely used and established method for accurate topographic and microtopographic survey. The penetration of the vegetation cover by the laser beam allows the reconstruction of reliable digital terrain models (DTM) of forested areas where traditional prospection methods are inefficient, time-consuming and non-exhaustive. The ALS technology provides the opportunity to discover new archaeological features hidden by vegetation and provides a comprehensive survey of cultural heritage sites within their environmental context. However, the post-processing of LiDAR points clouds produces a huge quantity of data in which relevant archaeological features are not easily detectable with common visualizing and analysing tools. Undoubtedly, there is an urgent need for automation of structures detection and morphometric extraction techniques, especially for the "archaeological desert" in densely forested areas. This presentation deals with the development of automatic detection procedures applied to archaeological structures located in the French Massif Central, in the western forested part of the Puy-de-Dôme volcano between 950 and 1100 m a.s.l.. These unknown archaeological sites were discovered by the March 2011 ALS mission and display a high density of subcircular depressions with a corridor access. The spatial organization of these depressions vary from isolated to aggregated or aligned features. Functionally, they appear to be former grazing constructions built from the medieval to the modern period. Similar grazing structures are known in other locations of the French Massif Central (Sancy, Artense, Cézallier) where the ground is vegetation-free. In order to develop a reliable process of automatic detection and mapping of these archaeological structures, a learning zone has been delineated within the ALS surveyed area. The grazing features were mapped and typical morphometric attributes

Chemical profiles along olivine crystallographic axes: a record of the melt-rock interaction sequence forming Hole U1309D Olivine-rich troctolites (Atlantis Massif, MAR, 30°N)

NASA Astrophysics Data System (ADS)

Ferrando, Carlotta; Godard, Marguerite; Ildefonse, Benoit; Rampone, Elisabetta

2017-04-01

phases. Dunitic and troctolitic domains display different microstructural and geochemical signatures. Their mineral modal percentages and compositions are not correlated along typical trends of fractional crystallization. The dunitic domain has olivines showing lower Mg# (82-83, against 85-86 in troctolitic domain), higher Ni and Mn contents. In the dunitic domain olivine, plagioclase and clinopyroxene are more enriched in trace elements compared to those in the troctolitic domain. These compositions reveal reaction and re-equilibration processes of pre-existing mantle-derived olivine-rich rock with an infiltrating olivine-undersaturated MORB-type melt. Chemical traverses along principal crystallographic axes of olivine reveal flat cpxcore-cpxrim-olrim-olcore profiles for all major and trace elements with the exception of Ca and Y, which are modified due to late subsolidus re-equilibration. Flat profiles indicate either (i) slow olivine dissolution kinetics relative to equilibration of primary olivine with incoming melts or (ii) preservation of initial chemical signature and fast olivine dissolution kinetics. These two end-member scenarii are investigated using thermodynamic models to better constrain (dis-)equilibrium relationships between mineral phases and reactive percolation modeling to determine the contribution of advective and diffusive processes to local chemical signatures. Drouin, M., Godard, M., Ildefonse, B., Bruguier, O., Garrido, C.J. (2009): Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 30°N). Chem Geol 264, 71-88. Drouin, M., Ildefonse, B., Godard, M. (2010) A microstructural imprint of melt impregnation in slow-spread lithosphere: olivine-rich troctolites from the Atlantis Massif (Mid-Atlantic Ridge 30°N, IODP Hole U1309D). Geochem Geophys Geosyst 11:Q06003, doi:10.1029/2009GC002995. Godard, M., et al. (2009): Geochemistry of a long in-situ section

Multiphase formation of the Obří důl polymetallic skarn deposit, West Sudetes, Bohemian Massif: geochemistry and Re-Os dating of sulfide mineralization

NASA Astrophysics Data System (ADS)

Veselovský, František; Ackerman, Lukáš; Pašava, Jan; Žák, Karel; Haluzová, Eva; Creaser, Robert A.; Dobeš, Petr; Erban, Vojtěch; Tásler, Radko

2017-10-01

The Obří důl Fe-Cu-As polymetallic sulfide skarn deposit is developed in a metamorphic series in the West Sudetes, Bohemian Massif. It consists of lenses of marble, calc-silicate rocks, and skarns. We studied the Gustav orebody, which is located few hundred meters away from the contact with a large, late-orogenic Variscan Krkonoše-Jizera Plutonic Complex (KJPC) emplaced into shallow crust. Mineralogical and fluid inclusion study evidence indicates that the main sulfide stage, dominated by pyrrhotite, arsenopyrite, and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt% NaCl eq. with minimum homogenization temperatures ranging from 324 to 358 °C. These fluids mainly replaced carbonate-rich lithologies. Carbon, oxygen, and strontium isotope data in Ca-rich rocks imply total overprinting by channelized metasomatic fluid flow, which is most probably related to the intrusion of the KJPC, whereas δ34S values of sulfides argue for a magmatic source of sulfur. The Re-Os age of arsenopyrite overlaps published age data for the KJPC and suggests synchronous formation of the main sulfide mineralization and pluton emplacement.

Multiphase formation of the Obří důl polymetallic skarn deposit, West Sudetes, Bohemian Massif: geochemistry and Re-Os dating of sulfide mineralization

NASA Astrophysics Data System (ADS)

Veselovský, František; Ackerman, Lukáš; Pašava, Jan; Žák, Karel; Haluzová, Eva; Creaser, Robert A.; Dobeš, Petr; Erban, Vojtěch; Tásler, Radko

2018-06-01

The Obří důl Fe-Cu-As polymetallic sulfide skarn deposit is developed in a metamorphic series in the West Sudetes, Bohemian Massif. It consists of lenses of marble, calc-silicate rocks, and skarns. We studied the Gustav orebody, which is located few hundred meters away from the contact with a large, late-orogenic Variscan Krkonoše-Jizera Plutonic Complex (KJPC) emplaced into shallow crust. Mineralogical and fluid inclusion study evidence indicates that the main sulfide stage, dominated by pyrrhotite, arsenopyrite, and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt% NaCl eq. with minimum homogenization temperatures ranging from 324 to 358 °C. These fluids mainly replaced carbonate-rich lithologies. Carbon, oxygen, and strontium isotope data in Ca-rich rocks imply total overprinting by channelized metasomatic fluid flow, which is most probably related to the intrusion of the KJPC, whereas δ34S values of sulfides argue for a magmatic source of sulfur. The Re-Os age of arsenopyrite overlaps published age data for the KJPC and suggests synchronous formation of the main sulfide mineralization and pluton emplacement.

A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites

USGS Publications Warehouse

Woodruff, Laurel G.; Nicholson, Suzanne W.; Fey, David L.

2013-01-01

This descriptive model for magmatic iron-titanium-oxide (Fe-Ti-oxide) deposits hosted by Proterozoic age massif-type anorthosite and related rock types presents their geological, mineralogical, geochemical, and geoenvironmental attributes. Although these Proterozoic rocks are found worldwide, the majority of known deposits are found within exposed rocks of the Grenville Province, stretching from southwestern United States through eastern Canada; its extension into Norway is termed the Rogaland Anorthosite Province. This type of Fe-Ti-oxide deposit dominated by ilmenite rarely contains more than 300 million tons of ore, with between 10- to 45-percent titanium dioxide (TiO2), 32- to 45-percent iron oxide (FeO), and less than 0.2-percent vanadium (V). The origin of these typically discordant ore deposits remains as enigmatic as the magmatic evolution of their host rocks. The deposits clearly have a magmatic origin, hosted by an age-constrained unique suite of rocks that likely are the consequence of a particular combination of tectonic circumstances, rather than any a priori temporal control. Principal ore minerals are ilmenite and hemo-ilmenite (ilmenite with extensive hematite exsolution lamellae); occurrences of titanomagnetite, magnetite, and apatite that are related to this deposit type are currently of less economic importance. Ore-mineral paragenesis is somewhat obscured by complicated solid solution and oxidation behavior within the Fe-Ti-oxide system. Anorthosite suites hosting these deposits require an extensive history of voluminous plagioclase crystallization to develop plagioclase-melt diapirs with entrained Fe-Ti-rich melt rising from the base of the lithosphere to mid- and upper-crustal levels. Timing and style of oxide mineralization are related to magmatic and dynamic evolution of these diapiric systems and to development and movement of oxide cumulates and related melts. Active mines have developed large open pits with extensive waste-rock piles, but

Paleomagnetic evidence bearing on Tertiary tectonics of the Tihamat Asir coastal plain, southwestern Saudi Arabia

USGS Publications Warehouse

Kellogg, K.S.; Blank, H.R.

1982-01-01

Paleomagnetic directions determined for an upper Oligocene to lower Miocene dike swarm and from two lower Miocene layered gabbros in the Tihamat Asir coastal plain of southwestern Saudi Arabia are used to test several hypotheses concerning the tectonics of rifting along the eastern margin of the Red Sea. The dikes and gabbros were emplaced during the initial phases of Red Sea rifting and may mark the transition between continental and oceanic crust. Although these rocks have been hydrothermally altered to varying degrees, reliable remanent directions after alternating-field demagnetization were obtained for 23 dikes and for gabbros at Jabal at Tirf and Wadi Liyyah. Twelve of the dikes are reversely magnetized. After the directions of the reversely magnetized dikes are inverted 180?, the mean direction calculated for the normal dikes is approximately 24? more downward than that calculated for the reversed dikes. This result is similar to that found for the As Sarat volcanic field, 100 km to the north, and may be due to a displaced dipole source for the field. The unrotated mean remanent direction for the dikes (inverting reversed dike directions 180?) is D (declination) = 353.2? and I (inclination) = 6.8? with a95 (radius of the cone of 95 percent confidence) = 8.9? whereas directions from the Jabal at Tirf and Wadi Liyyah gabbros lie at D = 176.2?, I = -1.6? (a95 = 7 1 ?) and D = 17.1?, I = 16.3? (a 95 = 8.7?), respectively. Comparing these results with the results from the As Sarat volcanic field, all the paleomagnetic evidence supports a model for approximately 20 ? of westward tilting of the Wadi Damad and Wadi Jizan areas after the emplacement of the Jabal at Tiff gabbro. The Wadi Liyyah area may have been tilted even more toward the Red Sea. The paleomagnetic directions from three widely separated localities in the Jabal at Tirf gabbro are not significantly different, a fact which indicates that the body cooled in approximately its present bowl shape. Evidence

Petrogenesis, detrital zircon SHRIMP U-Pb geochronology, and tectonic implications of the Upper Paleoproterozoic Seosan iron formation, western Gyeonggi Massif, Korea

NASA Astrophysics Data System (ADS)

Kim, Chang Seong; Jang, Yirang; Samuel, Vinod O.; Kwon, Sanghoon; Park, Jung-Woo; Yi, Keewook; Choi, Seon-Gyu

2018-05-01

This study involves investigations on the Upper Paleoproterozoic iron formation (viz., Seosan iron formation) from the Seosan Group, Gyeonggi Massif of the southwestern Korean Peninsula. It occurs as thin banded layers within meta-arkosic sandstone, formed by alternating processes of chemical (hydrothermal) and detrital depositions under a shallow marine environment. It mainly consists of alternating layers of iron oxides, mostly hematite, and quartz. Minor amounts of magnetite surrounded by muscovite, clinopyroxene and amphibole indicate hydrothermal alteration since its formation. Meta-arkosic sandstone is composed of recrystallized or porphyroclastic quartz and microcline, with small amounts of hematite and pyrite clusters. The Seosan iron formation has high contents of total Fe2O3 and SiO2 with positive Eu anomalies similar to those of other Precambrian banded iron formations, and its formation is clearly related to hydrothermal alteration since its deposition. Detrital zircon SHRIMP U-Pb geochronology data from a meta-arkosic sandstone (SN-1) and an iron formation (SN-2) show mainly two age groups of ca. 2.5 Ga and ca. 1.9-1.75 Ga. This together with intrusion age of the granite gneiss (ca. 1.70-1.65 Ga) clearly indicate that the iron formations were deposited during the Upper Paleoproterozoic. The dominant Paleoproterozoic detrital zircon bimodal age peaks preserved in the Seosan iron formation compare well with those from the South China Craton sedimentary basins, reflecting global tectonic events related to the Columbia supercontinent in East Asia.

Prise en charge d’un afflux massif de brûles lors d’une situation de catastrophe par incendie au Maroc

PubMed Central

Siah, S.; Hatimi, E.M.; Ihrai, H.; Drissi Kamili, N.

2012-01-01

Summary La brûlure est l’une des lésions les plus fréquemment rencontrées lors de catastrophes naturelles ou lors de catastrophes d’origine humaine (incendies de lieux publics d’origine accidentelle, ou en temps de guerre ou encore lors d’attentats terroristes). La prise en charge et le triage de brûlés en nombre reste un problème difficile; ceci souligne la nécessité d’une réflexion et de prévisions de ces crises en insistant sur la formation des médecins et des soignants. Les défis à relever sont multiples: les soins aux brûlés requièrent un nombre important de personnel qualifié; les évacuations doivent être planifiées en fonction de la gravité de la brûlure et des lésions associées; les stocks et lots de dotation (en particulier en topiques anti-infectieux et en cristalloïdes) doivent être suffisants et adéquats. Les services hospitaliers de l’Hôpital Militaire d’Instruction Mohammed V de Rabat doivent pouvoir être rapidement adaptés pour accueillir et surtout isoler ces patients. L’hypothèse d’une catastrophe par incendie avec afflux massif de brûlés à l’hôpital militaire d’instruction Mohammed V de Rabat ne doit laisser place à aucune improvisation. PMID:23467075

Sedimentary patterns in perched spring travertines near Granada (Spain) as indicators of the paleohydrological and paleoclimatological evolution of a karst massif

NASA Astrophysics Data System (ADS)

Martín-Algarra, Agustín.; Martín-Martín, Manuel; Andreo, Bartolomé; Julià, Ramón; González-Gómez, Cecilio

2003-10-01

Perched spring travertines of the Granada basin (South Spain) constitute a perched system with four well-defined steps, which are formed by several facies associations deposited in different sub-environments (travertine pools, dams and cascades). These perched travertines are considered as a freshwater reef system with a facies zonation and stratigraphic architecture closely resembling that of marine reef terraces and prograding carbonate platforms. The travertine deposits have been dated by 230Th/ 234U and 14C methods. As in other Mediterranean areas, the travertine deposition occurred episodically during warm and wet interglacial periods coinciding with isotopic stages 9, 7 and 5, and with the transition between isotopic stages 2/1. During these periods, underground dissolution, large outflow in the springs and subsequent calcium carbonate precipitation occurred. In the same way that evolution of reef systems indicates sea level changes, the geomorphology, age and architecture of perched spring travertine systems may be used to interpret former climatically controlled changes in outflow, in base level marked by the altitude of springs and in the chemistry of spring waters. Thus, aggradation or climbing progradation may indicate an increase of outflow at the spring, progradation with toplap is due to a stable base level and, conversely, dowlapping progradation may signify that the base level was gradually dropping. Therefore, the travertines can be considered semiquantitative indicators of the paleohydrological evolution of karstic massifs and used as an important terrestrial proxy climate record.

Detachment Faulting, Serpentinization, Fluids and Life: Preliminary Results of IODP Expedition 357 (Atlantis Massif, MAR 30°N)

NASA Astrophysics Data System (ADS)

Fruh-Green, G. L.; Orcutt, B.; Green, S.; Cotterill, C.

2016-12-01

We present an overview of IODP Expedition 357, which successfully used two seabed rock drills to core 17 shallow holes at 9 sites across Atlantis Massif (Mid-Atlantic Ridge 30°N). A major goal of this expedition is to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration. The cores show highly heterogeneous rock type, bulk rock chemistry and alteration that reflect multiple phases of magmatism and fluid-rock interaction within the detachment fault zone. In cores along an E-W transect of the southern wall, recovered mantle peridotites are locally intruded by gabbroic and doleritic dikes and veins. The proportion of mafic rocks are volumetrically less than the amount of mafic rocks recovered previously in the central dome at IODP Site U1309, suggesting a lower degree of melt infiltration into mantle peridotite at the ridge-transform intersection. New technologies were developed and successfully applied for the first time: (1) an in-situ sensor package and water sampling system on each seabed drill measured real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential, temperature, and conductivity during drilling and took water samples after drilling; (2) a borehole plug system to seal the boreholes was successfully deployed at two sites to allow access for future sampling; and (3) delivery of chemical tracers into the drilling fluids for contamination testing. We will provide an overview of the drilling strategy and preliminary results of Expedition 357, and highlight the role of serpentinization in sustaining microbial communities in a region of active serpentinization and low temperature hydrothermal alteration.

Deformation Microstructures of the Yugu Peridotites in the Gyeonggi Massif, Korea: Implications for Olivine Fabric Transition in Mantle Shear Zones

NASA Astrophysics Data System (ADS)

Jung, H.; Park, M.

2017-12-01

Large-scale emplaced peridotite bodies may provide insights into plastic deformation process and tectonic evolution in the mantle shear zone. Due to the complexity of deformation microstructures and processes in natural mantle rocks, the evolution of pre-existing olivine fabrics is still not well understood. In this study, we examine well-preserved transitional characteristics of microstructures and olivine fabrics developed in a mantle shear zone from the Yugu peridotite body, the Gyeonggi Massif, Korean Peninsula. The Yugu peridotite body predominantly comprises spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We classified highly deformed peridotites into four textural types based on their microstructural characteristics: proto-mylonite; proto-mylonite to mylonite transition; mylonite; and ultra-mylonite. Olivine fabrics changed from A-type (proto-mylonite) via D-type (mylonite) to E-type (ultra-mylonite). Olivine fabric transition is interpreted as occurring under hydrous conditions at low temperature and high strain, because of characteristics such as Ti-clinohumite defects (and serpentine) and fluid inclusion trails in olivine, and a hydrous mineral (pargasite) in the matrix, especially in the ultra-mylonitic peridotites. Even though the ultra-mylonitic peridotites contained extremely small (24-30 μm) olivine neoblasts, the olivine fabrics showed a distinct (E-type) pattern rather than a random one. Analysis of the lattice preferred orientation strength, dislocation microstructures, recrystallized grain-size, and deformation mechanism maps of olivine suggest that the proto-mylonitic, mylonitic, and ultra-mylonitic peridotites were deformed by dislocation creep (A-type), DisGBS (D-type), and combination of dislocation and diffusion creep (E-type), respectively.

Mineralogical and geochemical features of the alteration processes of magmatic ores in the Beni Bousera ultramafic massif (north Morocco)

NASA Astrophysics Data System (ADS)

Hajjar, Zaineb; Gervilla, Fernando; Essaifi, Abderrahim; Wafik, Amina

2017-08-01

The Beni Bousera ultramafic massif (Internal Rif, Morocco) is characterized by the presence of two types of small-scale magmatic mineralizations (i) a mineralization consisting mainly of chromite and Ni arsenides associated to orthopyroxene and cordierite (Cr-Ni ores), and (ii) a mineralization mainly composed of magmatic Fe-Ni-Cu sulfides containing variable amounts of graphite and chromite associated to phlogopite, clinopyroxène and plagioclase (S-G ores). Theses ores underwent High-T (450-550 °C) and Low-T (150-300 °C) alteration processes. The High-T alteration processes are tentatively related to intrusion of leucogranite dykes. They are preserved in the Galaros Cr-Ni ore deposit where nickeline is partly dissolved and transformed to maucherite, and orthopyroxene alters to phlogopite. Ni and Co were mobilized to the fluid phase, rising up their availability and promoting their diffusion into chromite and phlogopite, which have significantly higher contents in Ni and Co in phlogopite-rich ores than in orthopyroxene- and nickeline-rich ones. The Low-T alteration processes are related to serpentinization/weathering spatially associated with a regional shear zone. They affected both the Cr-Ni and S-G ores. In the Cr-Ni ores, Ni-arsenides were completely leached out while chromite is fractured within a matrix of chlorite, vermiculite and Ni-rich serpentine. In S-G ores, the silicates were altered into amphibole, Fe-rich chlorite and pectolite in clinopyroxene- and plagioclase-bearing ores while sulfides were completely leached out in phlogopite-bearing ores where iron oxides and hydroxides, and Fe-rich vermiculite were deposited. Chromite composition is not affected by the Low-T alteration processes.

Volume gain during shearing of the Whatley Mill Gneiss, Pine Mountain Basement massif, eastern Alabama--A trace element approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salpas, P.A.; Daniell, N.

1993-03-01

The Whatley Mill Gneiss is the most voluminous exposure of the Pine Mountain Basement massif in eastern Alabama. Its type lithology is a proto-mylonitic gneiss composed of K-spar augen, up to 5 cm in diameter, in a finer matrix of biotite, microcline, and quartz. Granulite-facies mineral assemblages in the Whatley Mill Gneiss have been completely retrograded to amphibolite- and greenschist-facies assemblages in response to deformation that produced shear zones paralleling the foliation of the gneiss. The augen gneiss and its associated mylonites are well-exposed in a creek bed in Chewacla State Park. At this location the mineralogy of the mylonitesmore » is dominated by quartz indicating that shearing was associated with influx of a silica-rich fluid. A detailed geochemical study of these rocks shows that the augen gneiss displays relatively little variation in its major and trace element compositions while the quartz-rich mylonites display wider ranges, are enriched in SiO[sub 2] and depleted in the REE and other incompatible trace elements relative to the augen gneiss. When standard composition/volume calculations are applied to the mylonites the results show (1) the bulk of all of the elements, including the REE, were immobile during shearing with the exceptions of Si and Al which were added; and, (2) volume changes calculated using the REE as immobile elements range from +70% to +350%. Though these volume changes seem excessive, they apply to meter-thick shear zones which may actually represent only a small fraction of the total volume of the augen gneiss. Consistent with previous interpretations of these shear zones, the calculated volume gains imply shearing during extension.« less

Multistage magma emplacement and progressive strain accumulation in the shallow-level Krkonoše-Jizera plutonic complex, Bohemian Massif

NASA Astrophysics Data System (ADS)

Žák, Jiří; Verner, Kryštof; Sláma, Jiří; Kachlík, Václav; Chlupáčová, Marta

2013-09-01

relationships combined with new U-Pb zircon geochronology suggest that the shallow-level Krkonoše-Jizera plutonic complex, northern Bohemian Massif, was assembled successively from bottom to top, starting with emplacement of the separately evolved S-type Tanvald granite (317.3 ± 2.1 Ma), followed by at least two voluminous batches of the I-type porphyritic Liberec (319.5 ± 2.3 Ma) and Jizera (320.1 ± 3.0 Ma and 319.3 ± 3.7 Ma) granites. The intrusive sequence was completed by uppermost, minor intrusions of the equigranular Harrachov (315.0 ± 2.7 Ma) and Krkonoše granites. The I-type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility (AMS). The outer Liberec granite preserves margin-parallel foliations and lineations, interpreted to record emplacement-related strain captured by cooling from the pluton floor and walls. In contrast, the inner Jizera, Harrachov, and Krkonoše granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike-slip faults cutting the opposite ends of the plutonic complex. Late-stage felsic dikes in the Liberec and Jizera granites reorient from horizontal to vertical (lineation-perpendicular) attitude in response to changing the least principal stress direction, whereas mafic schlieren do not do so, representing only randomly oriented small-scale thermal-mechanical instabilities in the phenocryst framework. In general, this case example challenges the common approach of inferring pluton-wide magma flow from interpolated foliation, lineation, and schlieren patterns. More likely, magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales.

Taxonomical studies of ticks infesting wild rodents from Asir Province in Saudi Arabia.

PubMed

Al-Mohammed, Hamdan I

2008-04-01

Ticks infesting rodents in Asir Province, which is about 3000 meter above sea level, were surveyed in Wadi Dalaghan and Wadi Bin Hachbal. They were examined from September to December 2006, where ten local life baited traps were distributed for 3 days each month. The rodents were Acomys c. dimitatus (20), Meriones rex (19) & one Gerbillus cheesmani. Fifty three nymphs were dropped off from the rodents in the laboratory 3 to 12 days post-trapping. Forty eight nymphs were reared to adults for identification and 5 ones died. The reared ticks were Rhipicephalus turanicus and R. sanguineus. The medical and veterinary importance was discussed.

Morphology of Shatsky Rise oceanic plateau from high resolution bathymetry

NASA Astrophysics Data System (ADS)

Zhang, Jinchang; Sager, William W.; Durkin, William J.

2017-06-01

Newly collected, high resolution multi-beam sonar data are combined with previous bathymetry data to produce an improved bathymetric map of Shatsky Rise oceanic plateau. Bathymetry data show that two massifs within Shatsky Rise are immense central volcanoes with gentle flank slopes declining from a central summit. Tamu Massif is a slightly elongated, dome-like volcanic edifice; Ori Massif is square shaped and smaller in area. Several down-to-basin normal faults are observed on the western flank of the massifs but they do not parallel the magnetic lineations, indicating that these faults are probably not related to spreading ridge faulting. Moreover, the faults are observed only on one side of the massifs, which is contrary to expectations from a mechanism of differential subsidence around the massif center. Multi-beam data show many small secondary cones with different shapes and sizes that are widely-distributed on Shatsky Rise massifs, which imply small late-stage magma sources scattered across the surface of the volcanoes in the form of lava flows or explosive volcanism. Erosional channels occur on the flanks of Shatsky Rise volcanoes due to mass wasting and display evidence of down-slope sediment movement. These channels are likely formed by sediments spalling off the edges of summit sediment cap.

Three new endemic Aphyosemion species (Cyprinodontiformes: Nothobranchiidae) from the Massif du Chaillu in the upper Louessé River system, Republic of the Congo.

PubMed

Zee, Jouke R van der; Walsh, Gina; Mikembi, Valdie N Boukaka; Jonker, Michiel N; Alexandre, Marco P; Sonnenberg, Rainer

2018-01-02

Three new 'Aphyosemion' species are described from the upper Louessé River in the Massif du Chaillu, Republic of the Congo, based on a combination of DNA, habitat preference, male colour pattern, and morphological data. 'Aphyosemion' cyanoflavum, new species, is a member of the 'A'. ogoense group. It differs from its congeners by a unique colour pattern and cephalic sensory system which contains a wide supra-orbital groove with large, densely pigmented anterior neuromasts and dark frontal neuromasts housed in one pit with one central anterior lobe. 'Aphyosemion' mandoroense, new species, and 'A'. cryptum, new species, are members of the 'A'. coeleste group. 'Aphyosemion' cryptum, new species, is in appearance very similar to 'A'. coeleste, but lacks the typical post opercular metallic green blotch and is generally larger in body size. Initial DNA analyses demonstrate that 'A'. cryptum, new species, is more closely related to 'A'. mandoroense, new species, than to 'A'. coeleste, despite similarity in appearance. 'Aphyosemion' cryptum, new species, and 'A'. coeleste occur syntopic in several locations in a sub-catchment of the upper Louessé system, however differ in microhabitat preference. 'Aphyosemion' mandoroense, new species, differs by male body and fin colour pattern from all species of the 'A'. coeleste group except 'A'. citrineipinnis. From the latter, it can be distinguished by the absence of red pigmentation and a dark grey to black margin in the unpaired fins.

Artist's concept of topographical layout of Taurus-Littrow landing site

NASA Image and Video Library

1972-10-01

S72-49761 (October 1972) --- An artist's concept illustrating the topographical layout of the Taurus-Littrow landing site of the Apollo 17 lunar landing mission. The Lunar Module touchdown point is in the center of the smooth area in the middle of the picture. The imposing mountain in the center is South Massif. A portion of North Massif is in the lower right corner of the photograph. Note the ridge-like feature extending from South Massif to North Massif. The southern portion of the ridge is called Lee Scarp and the northerly portion Lincoln Scarp. (This concept is by JSC artist Jerry Elmore).

LANDING SITE - APOLLO XVII

NASA Image and Video Library

1972-09-28

S72-49760 (October 1972) --- An artist's concept illustrating the topographical layout of the Taurus-Littrow landing site of the Apollo 17 lunar landing mission. The Lunar Module touchdown point is in the center of the smooth area in the middle of the picture. The imposing mountain in the center is South Massif. A portion of North Massif is in the lower right corner of the photograph. Note the ridge-like feature extending from South Massif to North Massif. The southern portion of the ridge is called Lee Scarp and the northerly portion Lincoln Scarp. (This concept is by JSC artist Jerry Elmore).

The origin and geochemical characteristics of rutile in eluvial and fluvial-alluvial placers and quartz veins of the Menderes Massif from the Neoproterozoic Pan-African Belt, Western Turkey

NASA Astrophysics Data System (ADS)

Kuşcu, Mustafa; Cengiz, Oya; Işık, Kayhan; Gül, E. Kübra

2018-07-01

Rutile occur in important amounts within Quaternary detrital sediments, and quartz veins which cut down the Paleozoic aged Eşme formation in the Menderes Massif on the Neoproterozoic Pan-Afrikan Belt in the west of Turkey. As a result of erosion, transport and accumulation of rutile-bearing quartz veins in the mica schists of the Eşme formation outcropped between Eşme (Uşak) and Kula (Manisa), the placer rutile occurrences occur in terraces, fluvial-alluvial and eluvial deposits. This study investigates the element content of rutile, oxygen isotope ratios of rutile and quartz, and formation temperature of rutile related to titanium source rock. Field observations show that rutiles are located in quartz veins that cut the schists. After these veins were fragmented and eroded, blocks of quartz with rutile and rutile grains are transported into clastic sediments in slope debris (eluvial), terraces and recent fluvial-alluvial deposits. Whereas quartz, rutile, ilmenite, and albite are found in the paragenesis of the rutile-bearing quartz vein fragments, the placers forming the terraces and current fluvial-alluvial deposits contain quartz, albite, muscovite, orthoclase, kaolinite, rutile, dravite, ilmenite, and zircon. The rutile grains in the examined placers and quartz vein fragments have grain sizes ranging from mm fractions to 5-6 cm. The major oxide compositions of the rutile grains have average values of 94 wt.% TiO2, 1.5 wt.% Fe2O3, 0.5 wt.% SiO2, and 0.3 wt.% Al2O3. The rutile samples have average values Nb of 1424 ppm, V of 980 ppm, W of 192 ppm, Ta of 94 ppm, and Zr of 73 ppm. The rutiles in the study area are defined as iron-rich rutile "nigrine" due to high iron content. Quartz veins are host rocks of rutile grains in the terrace and fluvial-aluvial sediments. The rutile-bearing quartz veins may be sourced from the Lower-Middle Miocene aged granites which are intruded the rocks in the Menderes Massif. Based on the analysis results of the methods of Zr

Neotectonic and seismic activity in the Armorican and Cornubian Massifs: Regional stress field with glacio-isostatic influence?

NASA Astrophysics Data System (ADS)

Van Vliet-Lanoë, B.; Bonnet, S.; Hallegouët, B.; Laurent, M.

1997-09-01

Hercynian massifs resulting from a regional stress field especially from 400 ka to 200 ka BP. Stratigraphical, geodynamical and paleoclimatological implications are discussed.

Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria)

NASA Astrophysics Data System (ADS)

Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Vitale-Brovarone, Alberto; Fernandez, Laure; Hammor, Dalila; Laouar, Rabah; Ouabadi, Aziouz; Abdallah, Nachida; Mechati, Mehdi

2017-09-01

Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

Syntectonic Variscan magmatism in the Aguiar da Beira region (Iberian Massif, Portugal)

NASA Astrophysics Data System (ADS)

Mafalda Costa, Maria; Margarida Neiva, Ana; do Rosario Azevedo, Maria; Corfu, Fernando

2014-05-01

The Aguiar da Beira region (Portugal) is located in the core of the Iberian Massif, more precisely in the Central-Iberian Zone, which is dominantly composed by abundant volumes of plutonic rocks, emplaced into Late Proterozoic - Early Cambrian and Palaeozoic metasediments, mainly during or slightly after the third deformation phase of the Variscan Orogeny (D3). A considerable amount of these granites are syntectonic, intruded during the peak of this deformation event (D3). In particular, at the Aguiar da Beira region, two suites of syntectonic granitoids represent distinct magmatic series: a medium- to coarse-grained porphyritic biotite granodiorite-granite (322 Ma), which belongs to the early granodiorite series, and a medium-grained muscovite-biotite granite (317 Ma) that is part of the two-mica peraluminous leucogranites suite. The petrographic, geochemical (whole-rock and mineral compositions) and isotopic (Sr-Nd, δ18O-wr and δ18O-zr) study of the two intrusions reveals their remarkably different character. It is concluded that they correspond to two independent magma pulses, derived from distinct sources and/or petrogenetic processes. The biotite granodiorite-granite is a weakly peraluminous intrusion, characterized by intermediate to felsic SiO2 contents (66 - 68 %), high Ba, Sr and REE, and biotite with high Al and Mg contents, typical of the calc-alkaline associations. The Sr-Nd initial ratios are homogeneous (87Sr-86Sr322: 0.7070 - 0.7074; ɛNd322: -3.9 to -4.6) and overlap the isotopic signatures of lower crustal felsic metaigneous granulites (Villaseca et al. 1999). This similarity, which is further supported by δ18O-wr and δ18O-zr data, may indicate an origin by anatexis of lower felsic metaigneous rocks. Alternatively, the same data, allied to the presence of microgranular enclaves seen in this intrusion, can also be explained by the mixing of lower crustal derived magmas and mantle melts. By contrast, the muscovite-biotite granite has an entirely

Reconnaissance geology of the Manjamah Quadrangle, sheet 18/41 A, Kingdom of Saudi Arabia

USGS Publications Warehouse

Hadley, D.G.

1982-01-01

The Manjamah quadrangle (sheet 18/41 A) lies between lat 18?30' and 19?00' N. and long 41?00' and 41?30' E. and encompasses an area of 2,932 km2, of which about half is land and the remainder covered by the Red Sea. The geologic formations exposed in the quadrangle comprise Precambrian layered and intrusive rocks,. Tertiary layered rocks and gabbro dikes, and. Quaternary basaltic lavas, pyroclastic rocks, and surficial deposits. The Precambrian rocks are layered metasedimentary and metavolcanic rocks that have been assigned to the Baish and Bahah groups. These rocks are cut by Precambrian biotite quartz monzonite and by Miocene gabbro dikes that were intruded during the initial stages of the opening of the Red Sea rift. Tuffaceous siltstone of the Baid formation was also deposited during the Miocene, followed in the Pliocene by the polymict conglomerate of the Bathan formation. The Quaternary rocks include basalt that was extruded during a continuation of the opening of the Red Sea rift, after uplift of the escarpment parallel with the Red Sea but before the Holocene erosional cycle. The greater part of the land area of the quadrangle is covered by Quaternary coastal, pediment, and alluvial deposits of various kinds associated with the deltaic mouths of Wadi Hall and Wadi Yiba and their tributaries and with the development of fringing reefs and islands. The area also contains extensive Quaternary eolian deposits. The economic potential of the quadrangle lies essentially in the agricultural value .of its flood-plain deposits, which are frequently refreshed during flooding with the products of weathering and erosion of the Precambrian rocks in the valleys of Wadi Hal i and Wadi Yiba; coral reefs could possibly provide raw material for use in a cement industry, if any such industry were ever required in this area.

Developing a Vulnerability Mapping Methodology: Applying the Water-Associated Disease Index to Dengue in Malaysia

PubMed Central

Dickin, Sarah K.; Schuster-Wallace, Corinne J.; Elliott, Susan J.

2013-01-01

The Water-associated Disease Index (WADI) was developed to identify and visualize vulnerability to different water-associated diseases by integrating a range of social and biophysical determinants in map format. In this study vulnerability is used to encompass conditions of exposure, susceptibility, and differential coping capacity to a water-associated health hazard. By assessing these conditions, the tool is designed to provide stakeholders with an integrated and long-term understanding of subnational vulnerabilities to water-associated disease and contribute to intervention strategies to reduce the burden of illness. The objective of this paper is to describe and validate the WADI tool by applying it to dengue. A systemic ecohealth framework that considers links between people, the environment and health was applied to identify secondary datasets, populating the index with components including climate conditions, land cover, education status and water use practices. Data were aggregated to create composite indicators of exposure and of susceptibility in a Geographic Information System (GIS). These indicators were weighted by their contribution to dengue vulnerability, and the output consisted of an overall index visualized in map format. The WADI was validated in this Malaysia case study, demonstrating a significant association with dengue rates at a sub-national level, and illustrating a range of factors that drive vulnerability to the disease within the country. The index output indicated high vulnerability to dengue in urban areas, especially in the capital Kuala Lumpur and surrounding region. However, in other regions, vulnerability to dengue varied throughout the year due to the influence of seasonal climate conditions, such as monsoon patterns. The WADI tool complements early warning models for water-associated disease by providing upstream information for planning prevention and control approaches, which increasingly require a comprehensive and

Climatic, eustatic, and tectonic controls on Quaternary deposits and landforms, Red Sea coast, Egypt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arvidson, R.; Becker, R.; Shanabrook, A.

1994-06-10

The degree to which local climatic variations, eustatic sea level fluctuations, and tectonic uplift have influenced the development of Quaternary marine and fluvial landforms and deposits along the Red Sea coast, Eastern Desert, Egypt was investigated using a combination of remote sensing and field data, age determinations of corals, and numerical simulations. False color composites generated from Landsat Thematic Mapper and SPOT image data, digital elevation models derived from stereophotogrammetric analysis of SPOT data, and field observations document that a {approximately}10-km-wide swath inland from the coast is covered in many places with coalescing alluvial fans of Quaternary age. Wadis cuttingmore » through the fans exhibit several pairs of fluvial terraces, and wadi walls expose alluvium interbedded with coralline limestone deposits. Further, three distinct coral terraces are evident along the coastline. Climatic, eustatic, and tectonic uplift controls on the overall system were simulated using a cellular automata algorithm with the following characteristics: (1) uplift as a function of position and time, as defined by the elevations and ages of corals; (2) climatic variations driven by insolation changes associated with Milankovitch cycles; (3) sea level fluctuations based on U/Th ages of coral terraces and eustatic data; and (4) parameterized fluvial erosion and deposition. Results imply that the fans and coralline limestones were generated in a setting in which the tectonic uplift rate decreased over the Quaternary to negligible values at present. During lowstands, wadis cut into sedimentary deposits; coupled with continuing uplift, fans were dissected, leaving remnant surfaces, and wadi-related terraces were generated by down cutting. Only landforms from the past three to four eustatic sea level cycles (i.e., {approximately} 300 to 400 kyr) are likely to have survived erosion and deposition associated with fluvial processes. 33 refs., 18 figs., 2

Origin of the Okrouhlá Radouň episyenite-hosted uranium deposit, Bohemian Massif, Czech Republic: fluid inclusion and stable isotope constraints

NASA Astrophysics Data System (ADS)

Dolníček, Zdeněk; René, Miloš; Hermannová, Sylvie; Prochaska, Walter

2014-04-01

The Okrouhlá Radouň shear zone hosted uranium deposit is developed along the contact of Variscan granites and high-grade metasedimentary rocks of the Moldanubian Zone of the Bohemian Massif. The pre-ore pervasive alteration of wall rocks is characterized by chloritization of mafic minerals, followed by albitization of feldspars and dissolution of quartz giving rise to episyenites. The subsequent fluid circulation led to precipitation of disseminated uraninite and coffinite, and later on, post-ore quartz and carbonate mineralization containing base metal sulfides. The fluid inclusion and stable isotope data suggest low homogenization temperatures (˜50-140 °C during pre-ore albitization and post-ore carbonatization, up to 230 °C during pre-ore chloritization), variable fluid salinities (0-25 wt.% NaCl eq.), low fluid δ18O values (-10 to +2 ‰ V-SMOW), low fluid δ13C values (-9 to -15 ‰ V-PDB), and highly variable ionic composition of the aqueous fluids (especially Na/Ca, Br/Cl, I/Cl, SO4/Cl, NO3/Cl ratios). The available data suggest participation of three fluid endmembers of primarily surficial origin during alteration and mineralization at the deposit: (1) local meteoric water, (2) Na-Ca-Cl basinal brines or shield brines, (3) SO4-NO3-Cl-(H)CO3 playa-like fluids. Pre-ore albitization was caused by circulation of alkaline, oxidized, and Na-rich playa fluids, whereas basinal/shield brines and meteoric water were more important during the post-ore stage of alteration.

Description of Candidatus Bartonella fadhilae n. sp. and Candidatus Bartonella sanaae n. sp. (Bartonellaceae) from Dipodillus dasyurus and Sekeetamys calurus (Gerbillinae) from the Sinai Massif (Egypt)

PubMed Central

Alsarraf, Mohammed; Mohallal, Eman M.E.; Mierzejewska, Ewa J.; Behnke-Borowczyk, Jolanta; Welc-Falęciak, Renata; Bednarska, Małgorzata; Dziewit, Lukasz; Zalat, Samy; Gilbert, Francis; Behnke, Jerzy M.

2017-01-01

Abstract Bartonella spp. are parasites of mammalian erythrocytes and endothelial cells, transmitted by blood-feeding arthropod ectoparasites. Different species of rodents may constitute the main hosts of Bartonella, including several zoonotic species of Bartonella. The aim of this study was to identify and compare Bartonella species and genotypes isolated from rodent hosts from the South Sinai, Egypt. Prevalence of Bartonella infection was assessed in rodents (837 Acomys dimidiatus, 73 Acomys russatus, 111 Dipodillus dasyurus, and 65 Sekeetamys calurus) trapped in 2000, 2004, 2008, and 2012 in four dry montane wadis around St. Katherine town in the Sinai Mountains. Total DNA was extracted from blood samples, and PCR amplification and sequencing of the Bartonella-specific 860-bp gene fragment of rpoB and the 810-bp gene fragment of gltA were used for molecular and phylogenetic analyses. The overall prevalence of Bartonella in rodents was 7.2%. Prevalence differed between host species, being 30.6%, 10.8%, 9.6%, and 3.6% in D. dasyurus, S. calurus, A. russatus, and A. dimidiatus, respectively. The phylogenetic analyses of six samples of Bartonella (five from D. dasyurus and one from S. calurus) based on a fragment of the rpoB gene, revealed the existence of two distinct genetic groups (with 95–96% reciprocal sequence identity), clustering with several unidentified isolates obtained earlier from the same rodent species, and distant from species that have already been described (90–92% of sequence identity to the closest match from the GenBank reference database). Thus, molecular and phylogenetic analyses led to the description of two species: Candidatus Bartonella fadhilae n. sp. and Candidatus Bartonella sanaae n. sp. The identification of their vectors and the medical significance of these species need further investigation. PMID:28541836

A km-scale "triaxial experiment" reveals the extreme mechanical weakness and anisotropy of mica-schists (Grandes Rousses Massif, France)

NASA Astrophysics Data System (ADS)

Bolognesi, Francesca; Bistacchi, Andrea

2018-02-01

The development of Andersonian faults is predicted, according to theory and experiments, for brittle/frictional deformation occurring in a homogeneous medium. In contrast, in an anisotropic medium it is possible to observe fault nucleation and propagation that is non-Andersonian in geometry and kinematics. Here, we consider post-metamorphic brittle/frictional deformation in the mechanically anisotropic mylonitic mica-schists of the Grandes Rousse Massif (France). The role of the mylonitic foliation (and of any other source of mechanical anisotropy) in brittle/frictional deformation is a function of orientation and friction angle. According to the relative orientation of principal stress axes and foliation, a foliation characterized by a certain coefficient of friction will be utilized or not for the nucleation and propagation of brittle/frictional fractures and faults. If the foliation is not utilized, the rock behaves as if it was isotropic, and Andersonian geometry and kinematics can be observed. If the foliation is utilized, the deviatoric stress magnitude is buffered and Andersonian faults/fractures cannot develop. In a narrow transition regime, both Andersonian and non-Andersonian structures can be observed. We apply stress inversion and slip tendency analysis to determine the critical angle for failure of the metamorphic foliation of the Grandes Rousses schists, defined as the limit angle between the foliation and principal stress axes for which the foliation was brittlely reactivated. This approach allows defining the ratio of the coefficient of internal friction for failure along the mylonitic foliation to the isotropic coefficient of friction. Thus, the study area can be seen as a km-scale triaxial experiment that allows measuring the degree of mechanical anisotropy of the mylonitic mica-schists. In this way, we infer a coefficient of friction μweak = 0.14 for brittle-frictional failure of the foliation, or 20 % of the isotropic coefficient of internal

10Be exposure dating of the timing of Neoglacial glacier advances in the Ecrins-Pelvoux massif, southern French Alps

NASA Astrophysics Data System (ADS)

Le Roy, Melaine; Deline, Philip; Carcaillet, Julien; Schimmelpfennig, Irene; Ermini, Magali; Aster Team

2017-12-01

Alpine glacier variations are known to be reliable proxies of Holocene climate. Here, we present a terrestrial cosmogenic nuclide (TCN)-based glacier chronology relying on 24 new 10Be exposure ages, which constrain maximum Neoglacial positions of four small to mid-sized glaciers (Rateau, Lautaret, Bonnepierre and Etages) in the Ecrins-Pelvoux massif, southern French Alps. Glacier advances, marked by (mainly lateral) moraine ridges that are located slightly outboard of the Little Ice Age (LIA, c. 1250-1860 AD) maximum positions, were dated to 4.25 ± 0.44 ka, 3.66 ± 0.09 ka, 2.09 ± 0.10 ka, c. 1.31 ± 0.17 ka and to 0.92 ± 0.02 ka. The '4.2 ka advance', albeit constrained by rather scattered dates, is to our knowledge exposure-dated here for the first time in the Alps. It is considered as one of the first major Neoglacial advance in the western Alps, in agreement with other regional paleoclimatological proxies. We further review Alpine and Northern Hemisphere mid-to-high latitude evidence for climate change and glacier activity concomitant with the '4.2 ka event'. The '2.1 ka advance' was not extensively dated in the Alps and is thought to represent a prominent advance in early Roman times. Other Neoglacial advances dated here match the timing of previously described Alpine Neoglacial events. Our results also suggest that a Neoglacial maximum occurred at Etages Glacier 0.9 ka ago, i.e. during the Medieval Climate Anomaly (MCA, c. 850-1250 AD). At Rateau Glacier, discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders. Overall, this study highlights the need to combine several sites to develop robust Neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation.

Uranium-series dated authigenic carbonates and acheulian sites in southern Egypt

USGS Publications Warehouse

Szabo, B. J.; McHugh, W.P.; Schaber, G.G.; Haynes, C.V.; Breed, C.S.

1989-01-01

Field investigations in southern Egypt have yielded Acheulian artifacts in situ in authigenic carbonate deposits (CaCO3-cemented alluvium) along the edges of nowaggraded paleovalleys (Wadi Arid and Wadi Safsaf). Uranium-series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45, 141 and 212 ka (thousand years ago). Most of the carbonate appears to have been precipitated from groundwater, which suggests that these three episodes of deposition may be related to late Pleistocene humid climates that facilitated human settlement in this now hyperarid region. Carbonate cements from sediments containing Acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys.

Dating an actively exhuming metamorphic core complex, the Suckling Dayman Massif in SE Papua New Guinea

NASA Astrophysics Data System (ADS)

Oesterle, J.; Seward, D.; Little, T.; Stockli, D. F.; Mizera, M.

2016-12-01

Low-temperature thermochronology is a powerful tool for revealing the thermal and kinematic evolution of metamorphic core complexes (MCCs). Most globally studied MCCs are ancient, partially eroded, and have been modified by deformation events that postdate their origin. The Mai'iu Fault is a rapidly slipping active low-angle normal fault (LANF) in the Woodlark Rift in Papua New Guinea that has exhumed a >25 km-wide (in the slip direction), and over 3 km-high domal fault surface in its footwall called the Suckling-Dayman massif. Some knowledge of the present-day thermal structure in the adjacent Woodlark Rift, and the pristine nature of this active MCC make it an ideal candidate for thermochronological study of a high finite-slip LANF. To constrain the thermal and kinematic evolution of this MCC we apply the U/Pb, fission-track (FT) and (U-Th)/He methods. Zircon U/Pb analyses from the syn-extensional Suckling Granite that intrudes the footwall of the MCC yield an intrusion age of 3.3 Ma. Preliminary zircon FT ages from the same body indicate cooling below 300 °C at 2.7 Ma. Ages decrease to 2.0 Ma with increasing proximity to the Mai'iu Fault and imply cooling controlled by tectonic exhumation. Almost coincident zircon U/Pb and FT ages from the nearby syn-extensional Mai'iu Monzonite, on the other hand, record extremely rapid cooling from magmatic temperatures to 300 °C at 2 Ma. As apparent from the preliminary He extraction stage, these syn-extensional plutons have young zircon and apatite (U-Th)/He ages. These initial results suggest that the Mai'iu Fault was initiated as an extensional structure by 3.3 Ma. We infer that it reactivated an older ophiolitic suture that had emplaced the Papuan Ultramafic body in the Paleogene. Rapid cooling of the Mai'iu Monzonite indicates that it was intruded into a part of the MCC's footwall that was already shallow in the crust by 2 Ma. This inference is further supported by the mineral andalusite occurring in the contact

The Finero phlogopite-peridotite massif: an example of subduction-related metasomatism

NASA Astrophysics Data System (ADS)

Zanetti, Alberto; Mazzucchelli, Maurizio; Rivalenti, Giorgio; Vannucci, Riccardo

The Finero peridotite massif is a harzburgite that suffered a dramatic metasomatic enrichment resulting in the pervasive presence of amphibole and phlogopite and in the sporadic occurrence of apatite and carbonate (dolomite)-bearing domains. Pyroxenite (websterite) dykes also contain phlogopite and amphibole, but are rare. Peridotite bulk-rock composition retained highly depleted major element characteristics, but was enriched in K, Rb, Ba, Sr, LREE (light rare earth elements) (LaN/YbN=8-17) and depleted in Nb. It has high radiogenic Sr (87Sr/86Sr(270)=0.7055-0.7093), low radiogenic Nd (ɛNd(270)=-1 to -3) and EMII-like Pb isotopes. Two pyroxenite - peridotite sections examined in detail show the virtual absence of major and trace element gradients in the mineral phases. In both rock types, pyroxenes and olivines have the most unfertile major element composition observed in Ivrea peridotites, spinels are the richest in Cr, and amphibole is pargasite. Clinopyroxenes exhibit LREE-enriched patterns (LaN/YbN 16), negative Ti and Zr and generally positive Sr anomaly. Amphibole has similar characteristics, except a weak negative Sr anomaly, but incompatible element concentration 1.9 (Sr) to 7.9 (Ti) times higher than that of coexisting clinopyroxene. Marked geochemical gradients occur toward apatite and carbonate-bearing domains which are randomly distributed in both the sections examined. In these regions, pyroxenes and amphibole (edenite) arelower in mg## and higher in Na2O, and spinels and phlogopite are richer in Cr2O3. Both the mineral assemblage and the incompatible trace element characteristics of the mineral phases recall the typical signatures of ``carbonatite'' metasomatism (HFSE depletion, Sr, LILE and LREE enrichment). Clinopyroxene has higher REE and Sr concentrations than amphibole (amph/cpxDREE,Sr=0.7-0.9) and lower Ti and Zr concentrations. It is proposed that the petrographic and geochemical features observed at Finero are consistent with a subduction

Subduction Metamorphism of Ophicarbonates beyond the Stability of Antigorite: insights into Carbonate Dissolution vs. Decarbonation from the Almirez ultramafic massif (S. Spain)

NASA Astrophysics Data System (ADS)

Menzel, Manuel; Garrido, Carlos J.; López Sánchez Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

2017-04-01

Subduction zone processes play a key role in determining the time and length-scales of long-term element cycles like the deep carbon cycle. Recent improvements in thermodynamic modelling of fluid properties at high pressure and new experiments have underlined the importance of carbonate dissolution by subduction fluids from dehydration reactions for the transfer of carbon out of the subducting slab. However, natural case studies are scarce, in particular regarding the impact of fluids generated by serpentinite dehydration, which are considered as a major dissolution agent for carbon due to the high temperature of antigorite breakdown (about 650°C) and the potentially large volumes of hydrated peridotites occurring in the upper part of the subducting oceanic mantle lithosphere. Here we report the occurrence of meta-ophicarbonate lenses within prograde Chl-harzburgites in the Almirez ultramafic massif (Betic Cordillera, S. Spain). The presence of these lenses indicates that carbonate minerals were preserved beyond the stability conditions of antigorite and were not dissolved by deserpentinization fluids. The largest meta-ophicarbonate lens in the Almirez Chl-harzburgites measures 8 x 160 m and is composed of a high-grade assemblage of olivine, Ti-clinohumite, diopside, chlorite, dolomite, calcite and Cr-bearing magnetite with a granofelsic to banded appearance. In this assemblage we identified, for the first time in the Betic Cordillera, aragonite inclusions in olivine and diopside using coupled EBSD and chemical mapping. Calcite-dolomite thermometry and thermodynamic equilibrium modelling constrain the peak metamorphic conditions to 1.7 - 1.9 GPa and 680 °C at very low XCO2. These conditions compare well with P-T-estimates for the surrounding Chl-harzburgites. There is strong evidence that the protolith of the carbonate rocks within Chl-harzburgites was an ophicarbonate zone: bulk rock contents of Ni and Cr are similarly high in the carbonate rocks as in Atg

An integrated magnetic and geological study of cataclasite- dominated pseudotachylytes in the Chiapas Massif, Mexico: a snapshot of stress orientation following slip

NASA Astrophysics Data System (ADS)

Garza, Roberto S. Molina; Geissman, John; Wawrzyniec, Tim; Weber, Bodo; Martínez, Margarita López; Aranda-Gómez, Jorge

2009-06-01

The Permian age Chiapas Massif in southeast Mexico is locally host to well-exposed pseudotachylyte vein networks. The veins are black to dark grey and aphanitic in appearance, and consist mostly of microbreccia of angular fragments of plagioclase, K-feldspar, biotite and quartz, in a cryptocrystalline (microscopically irresolvable) matrix. Evidence of melting is present in the form of glass seams, dikelets, glass clasts included in cataclasite and a distinct chemistry in the pseudotachylite veins; pristine glass represents a relatively small volume of the pseudotachylite veins. At an exposure along the Tablón River valley, where the host rock is a medium to coarse-grained equigranular quartz diorite, individual veins are consistently oriented about 280°, are up to 16 mm wide, tens of cm apart, display a consistent left-lateral offset and can be traced for several metres. Individual pseudotachylyte veins rarely cross each other, and they cannot be directly linked to a regional-scale fault. Pseudotachylytes are apparently formed by a combination of crushing, comminution and frictional melting, but they are cataclasite dominated. Textures indicate that cataclasis continued after frictional melting had ceased. A 40Ar/39Ar age determination from whole rock chips of one vein shows a climbing Ar release spectrum with a date of ~114 Ma as the most reliable age estimate for Ar retention. This result is interpreted in the context of pseudotachylyte formation, recrystallization and resetting of K-bearing minerals for the K-Ar system in the late Early Cretaceous. Ten veins were sampled for palaeomagnetic and magnetic fabric studies, with samples collected from both the veins and their host rock. Remanence data give moderate natural remanent magnetization (NRM) intensities for both the veins (e.g. NRM mean 6.6 × 10-3 A m-1 σ = 5.5) and host rock (mean 7.7 × 10-3 A m-1 σ = 10.8). Many samples of host rock yield an ill-defined east-west directed and shallow magnetization

Geochronology and geochemistry of late Carboniferous-middle Permian I- and A-type granites and gabbro-diorites in the eastern Jiamusi Massif, NE China: Implications for petrogenesis and tectonic setting

NASA Astrophysics Data System (ADS)

Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Xu, Wen-Liang; Yang, Jin-Hui; Xing, De-He; Chen, Hui-Jun

2016-12-01

Late Carboniferous-middle Permian magmatism in the Jiamusi Massif of northeast China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), provides critical evidence regarding the tectonic history and geodynamic processes in the region. The gabbro-diorites of the Longtouqiao pluton and two groups of coeval granite in the study area comprise a bimodal magmatic suite. Precise LA-ICP-MS U-Pb zircon ages indicate that the granitoids and gabbro-diorites were emplaced in the late Carboniferous-middle Permian (302-267 Ma). Group I granites have high SiO2 (70.75-77.04 wt.%) and K2O (3.65-5.89 wt.%) contents, are enriched in LILEs (e.g., Rb, Th, and U) relative to HFSEs and LREEs, and have negative Nb, Ta, P, and Ti anomalies, which collectively indicate affinities with subduction-related magmas. Group II granites are weakly peraluminous (A/CNK = 1.03-1.07) and are characterized by enrichment in alkalis (Na2O + K2O = 8.22-8.90 wt.%), low MgO (0.04-0.09 wt.%) and P2O5 (0.01-0.04 wt.%) contents, high Zr and Nb contents, high 10,000 × Ga/Al ratios, and they are geochemically similar to aluminous A-type granites. All the magmatic zircons in these granitoids have great variations of εHf(t) (+ 7.89 to - 5.60) and two-stage Hf model ages (TDM2) of 0.8-1.7 Ga, which suggest that the precursor magmas originated from a heterogeneous source that involved juvenile components derived from a depleted mantle source during magma generation. The aluminous A-type granite magmas were probably derived by high-temperature partial melting of a felsic crustal source, whereas the other granite magmas probably resulted from partial melting of a mafic lower crust. The gabbro-diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for large positive anomalies in Ba, K, and Pb. These features reflect a limited degree of crustal contamination associated with the subduction-related magmatic processes. These data

Geochronology of high-pressure granulites from the Czech part of the Zlote Unit (Bohemian Massif)

NASA Astrophysics Data System (ADS)

Lange, U.; Bröcker, M.; Trapp, E.

2003-04-01

At the NE margin of the Bohemian Massif, granulites occur in the Zlote Unit which is exposed in the border region between Poland and the Czech Republic [e.g. 1, 3]. On the Polish side, outcrop conditions are rather poor. Besides some isolated blocks, granulites are restricted to a very small occurrence near Stary Gieraltow. This exposure has attracted much attention due to findings of presumed coesite pseudomorphs, as inferred from radial fractures around polycrystalline quartz inclusions in garnet [1]. Peak metamorphic conditions were estimated between 21 and 28 kbar at 800 to 1000 °C [2]. Better outcrop conditions of the same tectonic unit are found on the Czech side in the Rychleby Mts [3]. The focus of this study is on the geochronology of granulites from this occurrence. By means of Sm-Nd (garnet, cpx, whole rock) and single grain U-Pb dating of zircon, we have studied felsic and mafic granulites collected near the location Cerveny Dul. A felsic granulite yielded a Sm-Nd age of 337 +/- 4 Ma (two grain-size fractions of garnet, whole rock). Two mafic granulites provided Sm-Nd ages (two grain-size fractions of garnet, cpx and/or whole rock) of 357 +/- 10 Ma and 351 +/- 10 Ma, respectively. The new Sm-Nd results are in good agreement with metamorphic ages reported for other Bohemian granulites and further document the significance of HP-HT metamorphism at c. 350-340 Ma. Single-grain zircon dating of air-abraded grains provided concordant results. Zircons from a mafic granulite yielded an age of 362 +/- 1 Ma. A similar result was reported for a mafic granulite from Stary Gieraltow, based on conventional multigrain analyses of zircon [2]. This age is considered to approximate the timing of crystallisation from a melt. However, it remains unclear whether this process took place before or during early stages of high-pressure metamorphism. The studied felsic granulite yielded a range in zircon ages between 390 to 330 Ma, indicating the presence of inherited magmatic

Hydro-Geomorphic Connectivity in Arid Watershed: Anthropogenic Effects and Extreme Flash flood

NASA Astrophysics Data System (ADS)

Egozi, Roey

2017-04-01

Arid watersheds are excellent settings to study water and sediment connectivity because of spars vegetation and the possibility to make clearer links between climate parameters and topographical changes. However different flood event magnitudes may result in different degrees of connectivity. This even gets more complicated when man made modifications to the drainage system are done without considering the outcomes in terms of the potential of flood damage and risks, i.e. in the case of extreme flash floods. Herein we report on the results from two studies conducted in two different small catchments along the dead sea rift: Wadi A Dalia and Wadi Ras Moakif. The studies conducted as part of a larger project aimed at investigating the floods and damages triggered by a rare storm event occurred at the end of October 2015. This storm event covered all of Israel and characterized with rare rainfall depths and intensities as well as floods with rare pick discharges. Observations and field measurements of bed material, river cross sections and water elevation markers were done and statistical analysis has been performed to estimate the exceed probability of the different measured and estimated hydro-climatic values. In Wadi-A-Dalia the coupling of rare rainfall depths over the watershed area which itself was bare due to over grazing result in a major flood. The severe damage caused by this flood was intensified due to the increase of structural hydrologic connectivity, i.e. flood protection canal discharged higher volumes of water collected from small Wadi systems at the same time. In Wadi Ras Moakif the rainfall cells did not produced rare rainfall, but still a major flood occurred over a very short distance of the main channel transporting huge amount of bed material deposited and blocked the main road along the dead sea western coast. In this case the cause was similar - a modification to the drainage system result in increase structural hydrologic connectivity lead to

Apollo 17 materials viewed from 2 to 4 mm soil particles: Pre-serenitatis highlands components

NASA Technical Reports Server (NTRS)

Jolliff, Bradley L.; Bishop, Kaylynn M.

1993-01-01

Among the highland lithologies of 2-4 mm rock fragments in North Massif soil 76503, we have found a compositional group, low in incompatible element concentrations, that we interpret as representing the pre-Serenitatis surface. A component of these materials is an igneous-textured lithology that we believe formed in large impact melts. These are compositionally similar to, and possibly precursors of, many of the granulitic breccias that appear to be mixtures of ferroan and magnesian-suite rocks. The polymict, or old, upper-crustal breccias, along with granulitic breccias and the endogenous igneous lithologies found particularly at the North Massif stations, constitute the poorly consolidated portions of North Massif. Highland samples from the South Massif, on the other hand, are enriched in materials of the competent, impact-melt breccias formed by the Serenitatis impact. The competent melt-breccias contain clasts of most of the pre-existing surface materials, but they also contain components not found in the rocks of the poorly consolidated massif materials.

A model for Iapetan rifting of Laurentia based on Neoproterozoic dikes and related rocks

USGS Publications Warehouse

Burton, William C.; Southworth, Scott

2010-01-01

Geologic evidence of the Neoproterozoic rifting of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and rift-related clastic sedimentary sequences. The spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting. The most salient features include: (1) a rift-related magmatic event recorded in the French Broad massif and the southern and central Shenandoah massif that is distinctly older than that recorded in the northern Shenandoah massif and northward; (2) felsic volcanic centers at the north ends of both French Broad and Shenandoah massifs accompanied by dike swarms; (3) differences in volume between massifs of cover-sequence volcanic rocks and rift-related clastic rocks; and (4) WNW orientation of the Grenville dike swarm in contrast to the predominately NE orientation of other Neoproterozoic dikes. Previously proposed rifting mechanisms to explain these features include rift-transform and plume–triple-junction systems. The rift-transform system best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant rifting mechanism for most of the Laurentian margin. To explain feature 4, as well as magmatic ages and geochemical trends in the Northern Appalachians, we propose that a plume–triple-junction system evolved into the rift-transform system. A ca. 600 Ma mantle plume centered east of the Sutton Mountains generated the radial dike swarm of the Adirondack massif and the Grenville dike swarm, and a collocated triple junction generated the northern part of the rift-transform system. An eastern branch of this system produced the Long Range dike swarm in Newfoundland, and a subsequent western branch produced the ca. 554 Ma Tibbit Hill volcanics and the ca. 550 Ma rift-related magmatism of Newfoundland.

Evidence of Nb-Ta mobility in high temperature F-rich fluids evidenced by the La Bosse quartz-Nb-ferberite stockwork (Echassières, French Massif Central).

NASA Astrophysics Data System (ADS)

Marignac, C.; Cuney, M.

2012-04-01

In the Echassières district (northern French Massif Central), the 310 Ma Beauvoir granite (a P-rich peraluminous RMG) overprints a quartz-ferberite stockwork. The 900 m-deep GPF1 scientific hole shows that the stockwork is split into two parts by the gently dipping Beauvoir intrusion: the upper section (~ 100m thick) occurs in the La Bosse quarry, , and the lower section (≥ 60 m thick) below the granite floor. The root of the stockwork (hypothetic La Bosse granite) has not been reached. The stockwork comprises flat-lying quartz veins (≤ 0.6 m thick) concordant to the regional schistosity of surrounding micaschists, and steep N10-N50°E quartz veins (≤ 0.2 m thick). The two sets result from hydraulic fracturing, and consistently display crack seal features. A family of aplites and aplo-pegmatites dikes follow the same set of fractures, being either later (with partial dissolution of pre-existing quartz veins) or earlier, than the quartz veins. There is no alteration, nor associated mineral other than ferberite, at the La Bosse quarry, whereas micaceous selvages are observed in the lower section. Ferberite display a trend of ferberite enrichment with increasing depth (0.71 to 0.95 Fb mole%). In the La Bosse quarry, three ferberite habitus are present: acicular, lanceolate and prismatic. Acicular crystals are typically nicely zoned, with alternating Nb-rich (4.95±0.94 % Nb2O5) and Nb-poor (1.57±0.38 % Nb2O5) growth bands. Ta (up to 0.30 Ta2O5), Ti and Sn are also enriched in the Nb-rich bands. Nb and Ta incorporation into the ferberite is in the form of columbite, as either true solid solution or nanoinclusions. Lanceolate crystals have a similarly zoned acicular core and a Nb-poor rim (1.08±0.66 % Nb2O5). Prismatic crystals are unzoned and Nb-poor (0.67±0.20 % Nb2O5). In the lower part of the stockwork, the Nb contents are lower (2.17 % Nb2O5 in the Nb-rich bands, 1.36 % in the Nb-poor bands, 0.08 % in the unzoned cortex, 0.15 % in the unzoned prisms

Diverse subaerial and sublacustrine hot spring settings of the Cerro Negro epithermal system (Jurassic, Deseado Massif), Patagonia, Argentina

NASA Astrophysics Data System (ADS)

Guido, Diego M.; Campbell, Kathleen A.

2012-06-01

The Late Jurassic (~ 150 Ma) Cerro Negro volcanic-epithermal-geothermal system (~ 15 km2 area), Deseado Massif, Patagonia, Argentina, includes two inferred volcanic emission centers characterized by rhyolitic domes linked along NW-SE regional faults that are associated with deeper level Au/Ag mineralization to the NW, and with shallow epithermal quartz veins and mainly travertine surface hot spring manifestations to the SE. Some travertines are silica-replaced, and siliceous and mixed silica-carbonate geothermal deposits also are found. Five hot spring-related facies associations were mapped in detail, which show morphological and textural similarities to Pleistocene-Recent geothermal deposits at Yellowstone National Park (U.S.A.), the Kenya Rift Valley, and elsewhere. They are interpreted to represent subaerial travertine fissure ridge/mound deposits (low-flow spring discharge) and apron terraces (high-flow spring discharge), as well as mixed silica-carbonate lake margin and shallow lake terrace vent-conduit tubes, stromatolitic mounds, and volcano-shaped cones. The nearly 200 mapped fossil vent-associated deposits at Cerro Negro are on a geographical and numerical scale comparable with subaerial and sublacustrine hydrothermal vents at Mammoth Hot Springs, and affiliated with Yellowstone Lake, respectively. Overall, the Cerro Negro geothermal system yields paleoenvironmentally significant textural details of variable quality, owing to both the differential preservation potential of particular subaerial versus subaqueous facies, as well as to the timing and extent of carbonate diagenesis and silica replacement of some deposits. For example, the western fault associated with the Eureka epithermal quartz vein facilitated early silicification of the travertine deposits in the SE volcanic emission center, thereby preserving high-quality, microbial macro- and micro-textures of this silica-replaced "pseudosinter." Cerro Negro provides an opportunity to reconstruct

Evolution Process and Structural Analysis of Precambrian Jirisan Metamorphic and Sancheong Anorthosite Complexes in the Jirisan Province, Yeongnam Massif, Korea

NASA Astrophysics Data System (ADS)

Kang, J. H.; Lee, D. S.

2016-12-01

The Jirisan metamorphic complex consists mainly of schist, blastoporphyritic granite gneiss, granitic gneiss, leucocratic gneiss, biotite gneiss, banded gneiss, migmatitic gneiss and granite gneiss. The Paleoproterozoic (1.87 1.79 Ga) Sancheong anorthosite complex, which intrude it, is classified into massive-type and foliation-type Sancheong anorthosite, Fe-Ti ore body, and mafic granulite which were formed from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma. These complexes went at least through three times of ductile deformation during Early Proterozoic Late Paleozoic. The D1 deformation formed sheath or "A" type folds and its characteristic orientation was uncertain due to the intensive multi-deformation superimposed after that. The D2 deformation occurred under the EW- or WNW-directed tectonic compression, and formed a regional NS or NNE trend of isoclinal and intrafolial folds and an extensive ductile shear zone accompanied by mylonitization. The D3 deformation occurred under the NS- or NNW-directed tectonic compression environment, and formed an EW or ENE trend of open and tight folds and a partial semibrittle shear zone accompanied by mylonitization, and rearranged the NS-trend pre-D3 structural elements into (E)NE or (W)NW direction. The D2 deformation generally increases from the center toward the margin of Sancheong anorthosite complex but is more intensive in the eastern than western parts of Sancheong anorthosite complex. While the D3 deformation is inversely more intensive in the its western than eastern parts. The D2 and D3 deformations are closely related to the distribution features of Sancheong anorthosite complex. These three tectonic events are expected to give important information in understanding and reconstructing the tectonic movement after the formation of Columbia Supercontinent as well as the present NS-trend tectonic frame of the Jirisan province of the Yeongnam massif, the Korean Peninsula.

Sedimentological downstream effects of dam failure and the role of sediment connectivity: a case study from the Bohemian Massif, Austria

NASA Astrophysics Data System (ADS)

Wurster, Maria-Theresia; Weigelhofer, Gabriele; Pichler-Scheder, Christian; Hein, Thomas; Pöppl, Ronald

2017-04-01

Sediment connectivity describes the potential for sediment transport through catchment systems, further defining locality and characteristics of sedimentation in river channels. Dams generally decrease sediment connectivity and act as temporary sediment sinks. When dams are removed these sediments are being reworked and released downstream. During dam restoration works along a small-sized stream in the Bohemian Massif of Austria in December 2015 a dam failure occurred which led to the entrainment of several tons of fine-grained reservoir sediments further entering and depositing in the downstream channel reaches, located in the Thayatal National Park. Aiming to remove these fine sediment deposits the National Park Authority decided to initiate a flushing event in April 2016. The main aim of the present study was to investigate the effects of dam failure-induced fine sediment release and reservoir flushing on downstream bed sediment characteristics by applying geomorphological mapping (incl. volumetric surveys) and sedimentological analyses (freeze-core sampling and granulometry), further discussing the role of in-channel sediment connectivity. The obtained results have shown that immediately after the dam failure event a total of ca. 18 m3 of fine-grained sediments have accumulated as in-channel sediment bars which were primarily formed in zones of low longitudinal connectivity (e.g. in the backwater areas of woody debris jams, or at slip-off bank locations). The flushing event has been shown to have caused remobilization and downstream translocation of these deposits, further reducing their total volume by approx. 60%. The results of the granulometric analyses of the freeze-core samples have revealed fine sediment accumulation and storage in the upper parts of the channel bed, having further increased after the flushing event. Additionally, effects on chemical conditions and invertebrate community have been observed. These observations clearly indicate a

Early differentiation of the Moon: Experimental and modeling studies and experimental and modeling studies of massif anorthosites

NASA Technical Reports Server (NTRS)

Longhi, John

1994-01-01

NASA grant NAG9-329 was in effect from 3/1/89 to 8/31/94, the last 18 months being a no-cost extension. While the grant was in effect, the P.I., coworkers, and students gave 22 talks and poster sessions at professional meetings, published 12 articles in referred journals (one more is in press, and another is in review), and edited 2 workshop reports relevant to this project. Copies of all the publications are appended to this report. The major accomplishments during the grant period have derived from three quarters: 1) the application of quantitative models of fractional crystallization and partial melting to various problems in planetary science, such as the petrogenesis of picritic glasses and mare basalts and the implications of the SNC meteorites for martian evolution; 2) an experimental study of silicate liquid immiscibility relevant to early lunar differentiation and the petrogenesis of evolved highlands rocks; and 3) experimental studies of massif anorthosites and related rocks that provide terrestrial analogs for the proposed origin of lunar anorthosites by multistage processes. The low-pressure aspects of the quantitative models were developed by the P.I. in the 1980s with NASA support and culminated with a paper comparing the crystallization of terrestrial and lunar lavas. The basis for the high-pressure modifications to the quantitative models is a data set gleaned from high pressure melting experiments done at Lamont and is supplemented by published data from other labs that constrain the baric and compositional dependences of various liquidus phase boundaries such as olivine/orthopyroxene, relevant to the melting of the mantles of the terrestrial planets. With these models it is possible to predict not only the thermal and compositional evolution of magmatic liquids ranging in composition from lumar mare basalt to terrestrial calc-alkaline basalts, but also the small increments of fractional melting that are produced when mantle rises adiabatically

The destabilization of the Pilatte hut (2577 m a.s.l. - Ecrins massif, France), a paraglacial process?

NASA Astrophysics Data System (ADS)

Ravanel, Ludovic; Dubois, Laurent; Fabre, Sébastien; Duvillard, Pierre-Allain; Deline, Philip

2015-04-01

The Pilatte hut is located at 2572 m a.s.l. at Saint-Christophe-en-Oisans (south of the Ecrins Massif, France), at a 3-hours-walk from La Bérarde hamlet. Its capacity is 120 beds for hikers and climbers who are engaged in the ascent of Les Bans (3669 m a.s.l.). Built on a rocky ledge on the right side of the Pilatte Glacier (A = 2.64 km2; L = 2.6 km), it currently dominates the glacier by about 150 m. This relief results from the retreat of the glacier since the end of the Little Ice Age, as the till around the hut was deposited during this stage. The glacier has lost about 1.8 km in length during the same period. A first wooden hut was built in 1925 and presently serves as a winter refuge. In 1954, the growth of mountain activities led to the construction of a larger hut made of cemented stones. An extension to the west made of reinforced concrete was built in 1994. But in the late 1980s, severe damages to the 1954 part of the building were already recognized: vertical cracks lining the north and south facades, ,subsidence (c. 10 cm downstream) of the ground floor, cracked interior walls. Currently, the evolution of the instability is monitored by several methods: - since 2003, cracks in the building are surveyed by 25 Saugnac gauges, while an outside fracture in the rock is surveyed by a simple extensometer; - since 2009, 8 strain gauges allow to annually measure displacements along the main fractures that delimit the unstable rock mass; - a high-resolution topographic data set acquired by terrestrial laser scanning from the surface of the glacier in July 2014 has completed the monitoring. The acting process is a translational slide of a rock mass with a volume of about 300 000 m3, initiated by the glacier shrinkage. Therefore, it has to be considered as a paraglacial process. Even if the slide velocity is presently decreasing, a demolition project of the hut is under consideration in favor of a new building on the right side of the valley, 800 m downstream the

Contrasting thermal and melting histories for segments of mantle lithosphere in the Nahlin ophiolite, British Columbia, Canada

NASA Astrophysics Data System (ADS)

McGoldrick, Siobhan; Canil, Dante; Zagorevski, Alex

2018-03-01

The Permo-Triassic Nahlin ophiolite is the largest and best-preserved ophiolite in the Canadian Cordillera of British Columbia and Yukon, Canada. The ophiolite is well-exposed along its 150 km length with mantle segments divisible into the Hardluck and Menatatuline massifs. Both massifs comprise mostly depleted spinel harzburgite (< 2 wt% Al2O3 and 45 wt% MgO). Chondrite normalized REE abundances in clinopyroxene vary in (Gd/Yb)N from 0.2 to 1.1. Inversion modelling of clinopyroxene REE abundances requires 10-16% and 16-20% partial melting in the Hardluck and Menatatuline massifs, respectively. The two-pyroxene and Fe-Mg exchange temperatures in the mantle of the ophiolite also change systematically along strike with the degree of partial melt depletion. The temperatures recorded by REE and Ca-Mg exchange between coexisting pyroxenes require markedly higher peak temperatures and cooling rates for the Menatatuline massif (1250 °C, 0.1-0.01 °C/year) compared to the Hardluck massif (< 1100 °C, 10- 4 °C/year). The differences between these two contiguous massifs can be reconciled by their evolution as two separate segments along a ridge system having varying melt depletion, with contrasting cooling rates controlled by presence or absence of a crustal section above the mantle lithosphere, or by rapid exhumation along a detachment.

Petrology of spinel lherzolite xenoliths from Youkou volcano, Adamawa Massif, Cameroon Volcanic Line: mineralogical and geochemical fingerprints of sub-rift mantle processes

NASA Astrophysics Data System (ADS)

Njombie, Merlin Patrick Wagsong; Temdjim, Robert; Foley, Stephen F.

2018-02-01

The basaltic maar of Youkou, situated in the Adamawa Volcanic Massif in the eastern branch of the continental segment of the Cameroon Volcanic Line, contains mantle-derived xenoliths of various types in pyroclastites. Spinel-bearing lherzolite xenoliths from the Youkou volcano generally exhibit protogranular textures with olivine (Fo89.4-90.5), enstatite (En89 - 91Fs8.7-9.8Wo0.82-1.13), clinopyroxene, spinel (Cr#Sp = 9.4-13.8), and in some cases amphibole (Mg# = 88.5-89.1). Mineral equilibration temperatures in the lherzolite xenoliths have been estimated from three-two pyroxene thermometers and range between 835 and 937 °C at pressures of 10-18 kbar, consistent with shallow mantle depths of around 32-58 km. Trends displayed by bulk-rock MgO correlate with Al2O3, indicating that the xenoliths are refractory mantle residues after partial melting. The degree of partial melting estimated from spinel compositions is less than 10%: evidences for much higher degrees of depletion are preserved in one sample, but overprinted by refertilization in others. Trace element compositions of the xenoliths are enriched in highly incompatible elements (LREE, Sr, Ba, and U), indicating that the spinel lherzolites underwent later cryptic metasomatic enrichment induced by plume-related hydrous silicate melts. The extreme fertility (Al2O3 = 6.07-6.56 wt% in clinopyroxene) and the low CaO/Al2O3 ratios in the spinel lherzolites suggest that they could not be a simple residue of partial melting of primitive mantle and must have experienced refertilization processes driven by the infiltration of carbonatite or carbonated silicate melts.

Morphostructural context of gullies in Taroudant, Morocco

NASA Astrophysics Data System (ADS)

Hssaine, Ali Ait; Ghafrani, Hassan; Peter, Klaus Daniel; d'Oleire-Oltmanns, Sebastian; Ries, Johannes B.; Marzolff, Irene

2013-04-01

The Souss depression is wedged between the High Atlas to the north and the Anti-Atlas to the south. It corresponds to the south atlasic path and opens on the Atlantic Ocean. It is drained by the Souss wadi which flows into the ocean. This depression extends over 160 km in length from east to west and 40 km wide from north to south, its greatest extension is near the city of Taroudant. Morphologically, the Souss depression is a set of coalescing alluvial fans from the High Atlas and Anti-Atlas, their convergence is highlighted by the Souss or the very low Holocene terrace. Morphostructurally, the Souss depression is a broad Cretaceous syncline fault, filled with Plio-Quaternary deposits whose thickness can reach about 250 to 300 m near Taroudant. These deposits are in a stepped or inserted position at the outlets of the wadis of the Atlas area and contain coarse material. They become thin and layered (stacked) in the distal part of alluvial fans in the axis of the syncline due to subsidence. These superficial deposits of Holocene age support a speculative agriculture and are heavily used by large agricultural investors. Currently, at the historic town of Taroudant and around the Wadi el Ouaar, on these superficial deposits (sand, silt and clay) grows a spectacular landscape of gullies moving in all directions and leading to land abandonment. Two factors are responsible for triggering these gullies: the first is of tectonic order. It is linked to a hidden fault and active which affects the Cretaceous base. Its influence is expressed by the behaviour of the river system (deep-set of Wadi el Ouaar, dissymmetry of the morphological fan of Assif Irguitène). The second is the human factor, related to the introduction of sugar cane and its factories in Taroudant and in the Souss region in the 16th century (deforestation of the argan tree).

Challenges to estimate surface- and groundwater flow in arid regions: the Dead Sea catchment.

PubMed

Siebert, Christian; Rödiger, Tino; Mallast, Ulf; Gräbe, Agnes; Guttman, Joseph; Laronne, Jonathan B; Storz-Peretz, Yael; Greenman, Anat; Salameh, Elias; Al-Raggad, Marwan; Vachtman, Dina; Zvi, Arie Ben; Ionescu, Danny; Brenner, Asher; Merz, Ralf; Geyer, Stefan

2014-07-01

The overall aim of the this study, which was conducted within the framework of the multilateral IWRM project SUMAR, was to expand the scientific basement to quantify surface- and groundwater fluxes towards the hypersaline Dead Sea. The flux significance for the arid vicinity around the Dead Sea is decisive not only for a sustainable management in terms of water availability for future generations but also for the resilience of the unique ecosystems along its coast. Coping with different challenges interdisciplinary methods like (i) hydrogeochemical fingerprinting, (ii) satellite and airborne-based thermal remote sensing, (iii) direct measurement with gauging station in ephemeral wadis and a first multilateral gauging station at the river Jordan, (iv) hydro-bio-geochemical approach at submarine and shore springs along the Dead Sea and (v) hydro(geo)logical modelling contributed to the overall aim. As primary results, we deduce that the following: (i) Within the drainage basins of the Dead Sea, the total mean annual precipitation amounts to 300 mm a(−1) west and to 179 mm a(−1) east of the lake, respectively. (ii) The total mean annual runoff volumes from side wadis (except the Jordan River) entering the Dead Sea is approximately 58–66 × 10(6) m(3) a(−1) (western wadis: 7–15 × 10(6) m(3) a(−1); eastern wadis: 51 × 10(6) m(3) a(−1)). (iii) The modelled groundwater discharge from the upper Cretaceous aquifers in both flanks of the Dead Sea towards the lake amounts to 177 × 10(6) m(3) a(−1). (iv) An unexpected abundance of life in submarine springs exists, which in turn explains microbial moderated geo-bio-chemical processes in the Dead Sea sediments, affecting the highly variable chemical composition of on- and offshore spring waters.The results of this work show a promising enhancement of describing and modelling the Dead Sea basin as a whole. Copyright © 2014 Elsevier B.V. All rights reserved.

Discrimination of rock classes and alteration products in southwestern Saudi Arabia with computer-enhanced LANDSAT data

NASA Technical Reports Server (NTRS)

Blodget, H. W.; Gunther, F. J.; Podwysocki, M. H.

1978-01-01

Digital LANDSAT MSS data for an area in the southwestern Arabian Shield were computer-enhanced to improve discrimination of rock classes, and recognition of gossans associated with massive sulphide deposits. The test area is underlain by metamorphic rocks that are locally intruded by granites; these are partly overlain by sandstones. The test area further includes the Wadi Wassat and Wadi Qatan massive sulphide deposits, which are commonly capped by gossans of ferric oxides, silica, and carbonates. Color patterns and boundaries on contrast-stretched ratio color composite imagery, and on complementary images constructed using principal component and canonical analyses transformations, correspond exceptionally well to 1:100,000 scale field maps. A qualitative visual comparison of information content showed that the ratio enhancement provided the best overall image for identification of rock type and alteration products.

Insights into the evolution of an alkaline magmatic system: An in situ trace element study of clinopyroxenes from the Ditrău Alkaline Massif, Romania

NASA Astrophysics Data System (ADS)

Batki, Anikó; Pál-Molnár, Elemér; Jankovics, M. Éva; Kerr, Andrew C.; Kiss, Balázs; Markl, Gregor; Heincz, Adrián; Harangi, Szabolcs

2018-02-01

Clinopyroxene is a major constituent in most igneous rock types (hornblendite, diorite, syenite, nepheline syenite, camptonite, tinguaite and ijolite) of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. Phenocryst and antecryst populations have been distinguished based on mineral zoning patterns and geochemical characteristics. Major and trace element compositions of clinopyroxenes reflect three dominant pyroxene types including primitive high-Cr Fe-diopside, intermediate Na-diopside-hedenbergite and evolved high-Zr aegirine-augite. Clinopyroxenes record two major magma sources as well as distinct magma evolution trends. The primitive diopside population is derived from an early camptonitic magma related to basanitic parental melts, whilst the intermediate diopside-hedenbergite crystals represent a Na-, Nb- and Zr-rich magma source recognised for the first time in the Ditrău magmatic system. This magma fractionated towards ijolitic and later phonolitic compositions. Field observations, petrography and clinopyroxene-melt equilibrium calculations reveal magma recharge and mingling, pyroxene recycling, fractional crystallisation and accumulation. Repeated recharge events of the two principal magmas resulted in multiple interactions between more primitive and more fractionated co-existing magma batches. Magma mingling occurred between mafic and felsic magmas by injection of ijolitic magma into fissures (dykes) containing phonolitic (tinguaite) magma. This study shows that antecryst recycling, also described for the first time in Ditrău, is a significant process during magma recharge and demonstrates that incorporated crystals can crucially affect the host magma composition and so whole-rock chemical data should be interpreted with great care.

Carbonates in mantle xenoliths from French Massif Central: inference for carbonatite-related metasomatism.

NASA Astrophysics Data System (ADS)

Wagner, Christiane; Deloule, Etienne

2016-04-01

Mantle xenoliths from the sub-continental lithospheric mantle (SCLM) frequently display evidence of metasomatism by melts or fluids of variable composition, e.g. alkali-basaltic, alkali-carbonate or carbonate melts. Carbonate-bearing mantle xenoliths are particularly interesting as highly mobile carbonate melts are likely prominent metasomatic agents of the mantle. This study presents detailed petrographic descriptions and major and trace element compositions of minerals in protogranular spinel lherzolites from the Mont Coupet occurrence (Devès province, French Massif Central), with focus on the carbonate phases to discuss their possible link to carbonatite melt. Two representative samples are described here. MC9 shows no evidence for infiltration of the host basanitic magma. Carbonates occur (1) as large (100 μm - 200 μm) anhedral crystals in interstitial pockets at triple point of primary olivine grains, (2) in a few cross-cutting veins (up to 200 μm width), (3) along grain boundaries and (4) in composite carbonate-silicate pockets from well-developed reaction zones, in which carbonates fill globular vesicles. The reaction zone contains secondary subhedral to euhedral phases: Al- and Ti-rich clinopyroxene, Ca-rich olivine, Cr-rich spinel and quenched plagioclase and relict sieved-textured primary spinel. MC2 shows carbonate-bearing thin (< 50 μm width) interconnected veinlets and only a few poorly-developed reaction zones around primary spinel. Large carbonate crystals (1), as in sample MC9, occur associated with (2) fibrous carbonate with a well-formed meniscus at the boundary between the two carbonate types. In some reaction zones the carbonate patches (3) show well-developed concentric carbonate structures, similar to those observed in the globular vesicles from the host basanite. In sample MC9, the carbonate is an alkali-free Mg-poor calcite (XCa = 0.95 - 0.98; with 0.5 - 1.8 wt. % MgO) whatever the occurrence. In sample MC2, carbonates are Mg

The non-serpentine phases in serpentinites from the Braszowice-Brzeźnica Massif (SW Poland) as traces of magmatic processes within oceanic mantle

NASA Astrophysics Data System (ADS)

Wojtulek, Piotr; Puziewicz, Jacek; Ntaflos, Theodoros

2016-04-01

The Braszowice-Brzeźnica Massif - BBM (SW Poland) is a part of the Variscan Central-Sudetic Ophiolite. It is located at the southern termination of the Niemcza Shear Zone and consists of gabbros and serpentinites. The ultramafic rocks occurring in the BBM are (from E to W) serpentinites with abundant relics of olivine and tremolite, lizardite-chrysotile serpentinites and antigorite serpentinites. Clinopyroxene, olivine and zoned chromite grains were found in the central part of the BBM (Mnich Hill) within antigoritic serpentinites. The non-serpentine phases occur in the following microstructures: (1) olivine-chromite aggregates: olivine (Fo = 90.0-91.0) contains 0.35-0.44 wt.% NiO, elongated or amaeboidal chromite I (Cr# = 0.49-0.50, TiO2 = 0.14-0.15 wt.%) is rimmed by chromite II (Cr# = 0.98, TiO2 = 0.01 wt.%); (2) coarse and dismembered diopside grains (Cpx I, Mg# = 0.91-0.92) containing 0.70-0.80 wt.% TiO2, 3.0-4.0 wt.% Al2O3, 1.0-1.4 Cr2O3 and 0.3-0.5 wt.% Na2O; Cpx I is enriched in REE relative to primitive mantle, the REE pattern reveals HREE enrichment relative to LREE and negative Eu anomaly; (3) olivine-clinopyroxene aggregates: olivine (Fo = 90.4-91.3) contains 0.27-0.35 wt.% NiO, anhedral, often elongated clinopyroxene (Cpx II, Mg# = 0.91-0.92) has <0.1 wt.% TiO2, 3.00-4.00 wt.% Al2O3, 1.00-1.40 Cr2O3 and <0.20 wt.% Na2O, (4) magnetite-bearing olivine grains, locally in aggregates with minute clinopyroxene ones; olivine has variable Fo (86.0-96.0) and NiO concentration (0.02-0.55 wt.%), clinopyroxene (Cpx III, Mg# = 0.93-0.97) contains <0.40 wt.% Al2O3 and <0.20 Cr2O3. Cpx III rims also locally Cpx II. The non-serpentine phases from the BBM massif have various compositions and mode of occurrence, thus they record various crystallization events. Composition of chromite I is similar to primary chromite grains occurring in oceanic peridotites of the Romanche and Kurchatov F.Z. (Dick and Bullen, 1984), thus the olivine-chromite aggregates represent probably

Gypsum, jarosite, and hydrous iron-phosphate in Martian meteorite Roberts Massif 04262: Implications for sulfate geochemistry on Mars.

NASA Astrophysics Data System (ADS)

Greenwood, J. P.

2008-12-01

Gypsum has been identified on Mars by MEX OMEGA [1] and jarosite identified via MER-B lander [2] and both minerals are examples of the importance of calcium and iron sulfates in Martian weathering processes. The weathering of Martian basalt to form Ca and iron sulfates should be an important process on Mars. Martian jarosite has been identified in MIL 03346 [3] and Ca-sulfate has been identified in EETA 79001 [4], but both phases have yet to be identified in the same Martian sample. In Roberts Massif 04262, an olivine-phyric shergottite, iron-sulfide and calcium-phosphate minerals are undergoing reaction (dissolution and reprecipitation?) to form gypsum, jarosite, and an iron-phosphate phase, presumably during the meteorite's residence in Antarctica. If true, then an acidic and oxidizing fluid was present in this meteorite, due to the formation of jarosite which requires fluid of this type to form [5]. The weathering of iron-sulfides on Earth to form acidic and oxidizing fluids is common, thus this can be reconciled with the formation of an acidic fluid in a basic rock. Presumably, under more extensive weathering of silicate minerals in Martian basalt, the pH would be raised to values where jarosite would not be stable. While the weathering of RBT 04262 is likely occurring in Antarctica, a similar susceptibility of the apatite and pyrrhotite to incipient weathering on Mars may be expected. Oxidizing crustal fluids on Mars may attack iron- sulfides first in Martian basalts. The weathering of iron-sulfides leads to increasing acidity of fluids, which would enhance the dissolution of the calcium-phosphate minerals [6]. The formation of jarosite, gypsum, and iron-phosphate minerals during the early stages of weathering of Martian basalts may be an important process on Mars globally. [1] Gendrin, A. et al. (2005) Science, 307, 1587-1591. [2] Klingelhöfer et al. (2004) Science, 306, 1740- 1745. [3] Vicenzi E. P. et al. (2007) LPSC XXXVIII, Abstract 2335. [4] Gooding J

Green infrastructure development at European Union's eastern border: Effects of road infrastructure and forest habitat loss.

PubMed

Angelstam, Per; Khaulyak, Olha; Yamelynets, Taras; Mozgeris, Gintautas; Naumov, Vladimir; Chmielewski, Tadeusz J; Elbakidze, Marine; Manton, Michael; Prots, Bohdan; Valasiuk, Sviataslau

2017-05-15

The functionality of forest patches and networks as green infrastructure may be affected negatively both by expanding road networks and forestry intensification. We assessed the effects of (1) the current and planned road infrastructure, and (2) forest loss and gain, on the remaining large forest landscape massifs as green infrastructure at the EU's eastern border region in post-socialistic transition. First, habitat patch and network functionality in 1996-98 was assessed using habitat suitability index modelling. Second, we made expert interviews about road development with planners in 10 administrative regions in Poland, Belarus and Ukraine. Third, forest loss and gain inside the forest massifs, and gain outside them during the period 2001-14 were measured. This EU cross-border region hosts four remaining forest massifs as regional green infrastructure hotspots. While Poland's road network is developing fast in terms of new freeways, city bypasses and upgrades of road quality, in Belarus and Ukraine the focus is on maintenance of existing roads, and no new corridors. We conclude that economic support from the EU, and thus rapid development of roads in Poland, is likely to reduce the permeability for wildlife of the urban and agricultural matrix around existing forest massifs. However, the four identified forest massifs themselves, forming the forest landscape green infrastructure at the EU's east border, were little affected by road development plans. In contrast, forest loss inside massifs was high, especially in Ukraine. Only in Poland forest loss was balanced by gain. Forest gain outside forest massifs was low. To conclude, pro-active and collaborative spatial planning across different sectors and countries is needed to secure functional forest green infrastructure as base for biodiversity conservation and human well-being. Copyright © 2017. Published by Elsevier Ltd.

Geologic and tectonic characteristics of rockbursts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adushkin, V.V.; Charlamov, V.A.; Kondratyev, S.V.

1995-06-01

The modern mining enterprises have attained such scales of engineering activity that their direct influence to a rock massif and in series of cases to the region seismic regime doesn`t provoke any doubts. Excavation and removal of large volumes of rock mass, industrial explosions and other technological factors during long time can lead to the accumulation of man-made changes in rock massifs capable to cause catastrophic consequences. The stress state changes in considerable domains of massif create dangerous concentration of stresses at large geological heterogeneities - faults localized in the mining works zone. External influence can lead in that casemore » to such phenomena as tectonic rockbursts and man-made earthquakes. The rockbursts problem in world mining practice exists for more than two hundred years. So that its actuality not only doesn`t decrease but steadily mounts up as due to the mining works depth increase, enlargement of the useful minerals excavations volumes as due to the possibility of safe use of the rock massif potential energy for facilitating the mastering of the bowels of the Earth and for making that more cheap. The purpose of present work is to study the engineering activity influence to processes occurring in the upper part of Earth crust and in particular in a rock massif. The rock massif is treated in those studies as a geophysical medium - such approach takes into account the presence of block structure of medium and the continuous exchange of energy between parts of that structure. The idea ``geophysical medium`` is applied in geophysics sufficiently wide and stresses the difference of actual Earth crust and rock massifs from the continuous media models discussed in mechanics.« less

Statistical analysis and trends of wet snow avalanches in the French Alps over the period 1959-2010

NASA Astrophysics Data System (ADS)

Naaim, Mohamed

2017-04-01

Since an avalanche contains a significant proportion of wet snow, its characteristics and its behavior change significantly (heterogeneous and polydisperse). Even if on a steep given slope, wet snow avalanches are slow. They can flow over gentle slopes and reach the same extensions as dry avalanches. To highlight the link between climate warming and the proliferation of wet snow avlanches, we crossed two well-documented avalanche databases: the permanent avalanche chronicle (EPA) and the meteorological re-analyzes. For each avalanche referenced in EPA, a moisture index I is buit. It represents the ratio of the thickness of the wet snow layer to the total snow thickness, at the date of the avalanche on the concerned massif at 2400 m.a.s.l. The daily and annual proportion of avalanches exceeding a given threshold of I are calculated for each massif of the French alps. The statistical distribution of wet avalanches per massif is calculated over the period 1959-2009. The statistical quantities are also calculated over two successive periods of the same duration 1959-1984 and 1984-2009, and the annual evolution of the proportion of wet avalanches is studied using time-series tools to detect potential rupture or trends. This study showed that about 77% of avalanches on the French alpine massif mobilize dry snow. The probability of having an avalanche of a moisture index greater than 10 % in a given year is 0.2. This value varies from one massif to another. The analysis between the two successive periods showed a significant growth of wet avalanches on 20 massifs and a decrease on 3 massifs. The study of time-series confirmed these trends, which are of the inter-annual variability level.

Permafrost investigation in the Mont Blanc massif steep rock walls: a combined measurement, modelling and geophysical approach

NASA Astrophysics Data System (ADS)

Magnin, Florence; Deline, Philip; Ravanel, Ludovic; Gruber, Stephan; Krautblatter, Michael

2014-05-01

The steep rockwalls of the Mont Blanc massif have been affected by an increase in rockfall activity in the last decades. Permafrost degradation is suggested as the most likely triggering factor. To better understand geomorphic processes we investigate permafrost distribution and address questions on its pattern in steep alpine bedrock. We use GIS-modeling to simulate Mean Annual Rock Surface Temperature (MARST) distribution. Rock temperature measurements including three 10-m-deep borehole monitoring at the Aiguille du Midi (AdM, 3842 m a.s.l) serve to estimate the temperature offset (i.e. temperature difference between rock surface and depth of negligible inter-annual temperature varibility). The estimation of the lower extent of permafrost distribution is derived from a combination of both approaches and hypotheses on permafrost occurrence are evaluated with Electrical Resistivity Tomography (ERT) measurements. The MARST model indicates that the 0°C isotherm extends down to 2600 m a.s.l in the most shaded faces and rises up to 3800 m in the most sun-exposed areas. According to recent literature and the AdM borehole thermal profiles, we postulate that permafrost could extends down below MARST reaching up to 3°C due to temperature offset processes. ERT measurements performed along 160-m-long profiles at six different sites which the top are located from 3360 m a.s.l to 2760 m a.s.l and the MARST range from <-1°C to > 3°C are the first of this kind. Five of sites are located in the granite area making them directly comparable. They all show high resistivity values at depth (>200 kΩ) interpreted as permafrost bodies. Lower resistivity values (< 90 kΩ) are found either above the high resistivity bodies and interpreted as thawed active layer, or below MARST warmer than 2-3°C and interpreted as non-perenially frozen rock. Two sites were measured in autumn 2012 and autumn 2013 allowing for time-lapse investigation which demonstrates the change in resistivity in

GIS-based model of groundwater occurrence using geological and hydrogeological data in Precambrian Oban Massif southeastern Nigeria

NASA Astrophysics Data System (ADS)

Sikakwe, Gregory Udie

2018-06-01

This research modeled geological and hydrogeological controls on groundwater occurrence in Oban Massif and environs southeastern Nigeria. Topographical, hydrogeological, and structural maps, including lithology samples from drilled bores, well completion, and pumping test data in the study area were procured. Collection of coordinates of rock sample locations and structural data on strike and dip of rock exposures was collected. Geological and structural information collected was overlaid on the topographical, hydrogeological and structural map and digitized to produce the geological map of the study area. Thematic map on geological groundwater prospect map of the study was prepared using multicriteria evaluation. Relative weights were assigned to various rock types based on their relative contribution to groundwater occurrence and the map was reclassified using geographic information system (ArcGIS10.1) analysis. Depth ranges of the various lithologic units from drilled boreholes were used to construct lithologic correlation section of the boreholes across the study area using RockWorks16 Program software. Hydrogeological parameters such as storativity, specific capacity, transmissivity, drawdown, pumping rate, static water level, total depth, and well yield were computed from well completion reports and aquifer test. Results shows that the geologic groundwater prospect map was categorized into very good (28.73 m2), good (9.66 m2), moderate (35.08 m2), fair (49.38 m2), and poor (77.63 m2) zones. Aquifer parameters showed ranges such as (specific capacity (1.81-31.16 m2/day/m), transmissivity (0.0033-12 m2/day), storativity (9.4 × 10-3-2.3), drawdown (2.2-17.65 m), pumping rate (0.75-3.57 l/s), static water level (0-20.5 m), and total depth (3.3-61 m). Borehole depths obtained in the basement are shallower than those in the sedimentary area. Aquifer test parameters obtained from boreholes across the study indicate better correspondence with zones identified as

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

NASA Astrophysics Data System (ADS)

Paquette, J.-L.; Ballèvre, M.; Peucat, J.-J.; Cornen, G.

2017-12-01

In the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples. Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism.

Élaboration et performances de matériaux supraconducteurs {YBa_2Cu_3O_7} massifs texturés de taille croissante

NASA Astrophysics Data System (ADS)

Chaud, X.; Gautier-Picard, P.; Beaugnon, E.; Porcar, L.; Bourgault, D.; Tournier, R.; Erraud, A.; Tixador, P.

1998-03-01

Industrial applications of the bulk superconducting YBa_2Cu_3O_7 material imply to control the growth of large oriented monodomains in samples of big size (several centimeters). The laboratory EPM-Matformag is committed to produce such materials according to three different methods (zone melting, solidification controlled by a magnetic field, crystal growth from a seed). The results obtained show that it is possible by such methods to elaborate a material with high performances at the centimeter scale and to produce it in series. The availability of such materials allows the measure of physical properties on a large scale and the testing of prototypes for cryo-electrotechnical applications (magnetic bearing, flywheel, coupling device, current lead...). Les applications industrielles des matériaux supraconducteurs massifs YBa_2Cu_3O_7 impliquent de contrôler la croissance de larges monodomaines orientés dans des échantillons de grande taille (plusieurs centimètres). Le laboratoire EPM-Matformag s'est appliqué à produire de tels matériaux selon trois techniques différentes (fusion de zone, solidification contrôlée sous champ magnétique, croissance cristalline à partir d'un germe). Les résultats obtenus montrent qu'il est possible par de telles techniques d'obtenir un matériau performant à l'échelle des centimètres et de le produire en série. La disponibilité de tels matériaux permet de mesurer des propriétés physiques à grande échelle et de tester des prototypes d'applications cryo-électrotechniques (palier magnétique, volant d'inertie, coupleur, amenée de courant, limiteur de courant...).

Genome-Wide Association Analyses Highlight the Potential for Different Genetic Mechanisms for Litter Size Among Sheep Breeds

PubMed Central

Xu, Song-Song; Gao, Lei; Xie, Xing-Long; Ren, Yan-Ling; Shen, Zhi-Qiang; Wang, Feng; Shen, Min; Eyϸórsdóttir, Emma; Hallsson, Jón H.; Kiseleva, Tatyana; Kantanen, Juha; Li, Meng-Hua

2018-01-01

Reproduction is an important trait in sheep breeding as well as in other livestock. However, despite its importance the genetic mechanisms of litter size in domestic sheep (Ovis aries) are still poorly understood. To explore genetic mechanisms underlying the variation in litter size, we conducted multiple independent genome-wide association studies in five sheep breeds of high prolificacy (Wadi, Hu, Icelandic, Finnsheep, and Romanov) and one low prolificacy (Texel) using the Ovine Infinium HD BeadChip, respectively. We identified different sets of candidate genes associated with litter size in different breeds: BMPR1B, FBN1, and MMP2 in Wadi; GRIA2, SMAD1, and CTNNB1 in Hu; NCOA1 in Icelandic; INHBB, NF1, FLT1, PTGS2, and PLCB3 in Finnsheep; ESR2 in Romanov and ESR1, GHR, ETS1, MMP15, FLI1, and SPP1 in Texel. Further annotation of genes and bioinformatics analyses revealed that different biological pathways could be involved in the variation in litter size of females: hormone secretion (FSH and LH) in Wadi and Hu, placenta and embryonic lethality in Icelandic, folliculogenesis and LH signaling in Finnsheep, ovulation and preovulatory follicle maturation in Romanov, and estrogen and follicular growth in Texel. Taken together, our results provide new insights into the genetic mechanisms underlying the prolificacy trait in sheep and other mammals, suggesting targets for selection where the aim is to increase prolificacy in breeding projects. PMID:29692799

Applying a general triclinic transpression model to highly partitioned brittle-ductile shear zones: A case study from the Torcal de Antequera massif, external Betics, southern Spain

NASA Astrophysics Data System (ADS)

Díaz-Azpiroz, M.; Barcos, L.; Balanyá, J. C.; Fernández, C.; Expósito, I.; Czeck, D. M.

2014-11-01

Oblique convergence and subsequent transpression kinematics can be considered as the general situation in most convergent and strike-slip tectonic boundaries. To better understand such settings, progressively more complex kinematic models have been proposed, which need to be tested against natural shear zones using standardized procedures that minimise subjectivism. In this work, a protocol to test a general triclinic transpression model is applied to the Torcal de Antequera massif (TAM), an essentially brittle shear zone. Our results, given as kinematic parameters of the transpressive flow (transpression obliquity, ϕ; extrusion obliquity, υ; and kinematic vorticity number, Wk), suggest that the bulk triclinic transpressive flow imposed on the TAM was partitioned into two different flow fields, following a general partitioning type. As such, one flow field produced narrow structural domains located at the limits of the TAM, where mainly dextral strike-slip simple-shear-dominated transpression took place (Outer domains, ODs). In contrast, the remaining part of the bulk flow produced pure-shear-dominated dextral triclinic transpression at the inner part of the TAM (Inner domain, ID). A graphical method relating internal (ϕ, Wk) to far-field (dip of the shear zone boundary, δ; angle of oblique convergence, α) transpression parameters is proposed to obtain the theoretical horizontal velocity vector (V→), which in the case of the TAM, ranges between 099 and 118. These results support the applicability of kinematic models of triclinic transpression to brittle-ductile shear zones and the potential utility of the proposed protocol.

Paleoglacier reconstruction of the central massif of Gredos range during Last Glacial Maximum.

NASA Astrophysics Data System (ADS)

Campos, Néstor; Tanarro, Luis Miguel

2017-04-01

The accurate reconstruction of paleoglaciers require a well determined extent and morphology of them, one of the main problems is the absence of glacial geomorphic evidences which made possible the delimitation of the ice limits, for this reason physical-based models are useful for ice surface reconstruction in areas where geomorphological information is incomplete. A paleoglacier reconstruction during its maximum extension is presented for a high mountain area of the western part of the central massif of Gredos range, in the center of Iberian Peninsula, this area is located 30 km west of Almanzor (40˚ 14' 48? N; 5˚ 17' 52? W; 2596 m a.s.l.), the highest peak of Iberian Central System (ICS) and covers five gorges: La Nava, Taheña- Honda, La Vega, San Martín and Los Infiernos, the first three facing North, San Martin facing Northwest and Los Infiernos facing West. Despite the existence of some works analyzing the extension of paleoglaciers in the ICS during its maximum extension, there is still a need to improve the understanding of this zone, to provide a more detailed knowlegde of the evolution of the range and to know more in detail the full extent of paleoglaciers in this area. For delimitate the glaciated area the most distant frontal moraines with a larger geomorphological entity that indicates a great advance or a prolonged stay and stabilization which would presumably correspond with the maximum advance of the glaciers have been mapped, for that, photo interpretation of digital aerial photographs (25 cm resolution) has been done, in some areas where the location or limits of the moraines were not clear 3D images were used, all the work was complemented with detailed field surveys. Once the ice limits have been determined is necessary to estimate the topography of the paleoglaciers, for that purpose a simple steady-state models that assume a perfectly plastic ice rheology have been used, reconstructing the theoretical ice profiles and obtaining the extent

The age of deformations and composition inhomogeneities in Maxwell Montes on Venus.

NASA Astrophysics Data System (ADS)

Basilevskij, A. T.; Head, J. W.

1995-10-01

The photogeologic analysis of radar images of the Maxwell Montes massif and adjacent terrain, obtained by the Magellan spacecraft (SC), has shown that the northern part of this massif is disturbed by a fault, presumably classified as an upthrust with a left-side strike-slip component. This fault in strike merges into wide ridges that complicate the surface of Lakshmi Planum and Sedna and Snegurochka Planitias. Obviously, the upthrust with the strike-slip component is formed by the same compression deformations as the ridges, the latter being close in age to the average age of Venus' surface. This allows to conclude that the Maxwell Montes massif has existed in a state similar to the modern one, even for some hundreds of millions of years, which implies a low efficiency of gravitational relaxation of the massif at this stage of the planet's geologic history. This conclusion can probably be applied to the other prominent highlands and depressions in the Venusian relief. The areas in the northwestern part of Maxwell Montes found in the course of photogeologic analysis and possessing relatively low radiowave backscattering are, apparently, composed of rocks whose composition differs from that of the remaining part of the massif, which is characterized by very high radar brightness.

Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif

NASA Astrophysics Data System (ADS)

Ackerman, Lukáš; Bizimis, Michael; Haluzová, Eva; Sláma, Jiří; Svojtka, Martin; Hirajima, Takao; Erban, Vojtěch

2016-07-01

We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial εHf values ranging from - 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and εHf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial εHf of + 66 for a given εNd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Bečváry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial γOs. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor

3D modeling of the laterites on top of the Koniambo Massif, New Caledonia: refinement of the per descensum lateritic model for nickel mineralization

NASA Astrophysics Data System (ADS)

Quesnel, Benoît; de Veslud, Christian Le Carlier; Boulvais, Philippe; Gautier, Pierre; Cathelineau, Michel; Drouillet, Maxime

2017-10-01

Resulting from the weathering of the Peridotite Nappe, laterites are abundant in New Caledonia and host one of the largest nickel deposits worldwide. This work presents a 3D model of the Koniambo nickel laterite ore deposit. It shows that the laterites are located along the ridges of the massif and organized as hectometric-sized patches obliquely cut by the topography and distributed at various elevations. Three kinds of geometry were observed: (i) a thick laterite cover (between 20 and 40 m) overlying saprolite and mainly localized on topographic highs, (ii) a thin laterite cover (from a few meters to 20 m) mainly localized on areas with gentle slopes, and (iii) exposure of saprolite without laterite cover. Our data show that Ni-rich and Ni-poor areas are organized as hectometric-sized patches which broadly correlate with the distribution of the laterite thickness. The highest Ni areas are localized on slopes where laterite cover is thin or absent. The areas with lowest Ni are located in topographic highs under the thickest laterite cover. The vertical Ni mass balance for each borehole shows that, in areas with thick laterite cover, Ni is sub-equilibrated to slightly depleted whereas in areas with thin laterite cover, Ni is enriched. This suggests the existence of lateral infiltration of water rich in dissolved Ni, from areas such as topographic highs to downstream slope areas, in a process leading to enrichment of saprolite in Ni in slope areas. Mechanical transport and leaching of laterite material on slopes, including Ni-bearing material, could also contribute to local enrichment of Ni in the saprolite.

Subduction-related metasomatism in French Massif Central: evidence from secondary orthopyroxene in mantle xenoliths.

NASA Astrophysics Data System (ADS)

Wagner, Christiane

2017-04-01

Peridotite xenoliths from the French Massif Central (FMC) have undergone a complex mantle metasomatic history by percolation of various melts/ fluids from alkali basaltic to carbonatite composition. This contribution argues for the imprint of another type of metasomatism related to subduction-derived melts/fluids. The samples come from the Mont Coupet strombolian volcano, Devès, FMC. They are fresh protogranular spinel lherzolites, with no infiltration of the host basanitic magma, but with evidences of alkali and carbonate-related metasomatism discussed elsewhere [1-3]. This study focuses on secondary orthopyroxene (opx2). It occurs +/- minor secondary clinopyroxene (cpx2) in cross-cutting thin (10 µm-20 µm) veinlets, and also as discontinuous patches developed after primary clinopyroxene (cpx1) at the contact with primary olivine (ol1). Opx2 crystals do not form fibrous radial aggregates. Rare small (<1 µm) rounded chloroapatite is included in opx2 after cpx1. Small (2 µm) pores are observed throughout the veins, at the contact with ol1, along sub-grained boundaries between opx2 and cpx2 in the veinlets, and between opx2 and cpx1. The primary minerals crosscut by the veinlets do not show any compositional zoning and the different elements show sharp profiles between opx 2 and primary minerals. Compared to primary opx, opx2 are characterized by a lower content in Al2O3 (1.7-2.5 wt. %) / 3.2-4.0 wt. %). They are slightly MgO (XMg = 90-91/ 89-90) and CaO richer (0.5 wt. % / 0.3 wt. %), and contain slightly less Cr2O3 (<0.2 wt. % / 0.2-0.3wt. %) and TiO2 (<0.06 wt. % / 0.06-0.14 wt. %), although there is some crossover between the two data sets. Na2O contents (<0.05 wt. %) are comparable. Cpx2 and opx2 from the veinlets are in equilibrium (XMg = 90-92). Al and Ti contents in cpx2 exclude any influence of percolation of the host magma. Moreover, their high Al6/Al4 ratio points to an equilibration at higher pressure than igneous cpx, close to that of cpx1. These

Petrogenesis of fertile mantle peridotites from the Monte del Estado massif (southwest Puerto Rico): a preserved section of Proto-Caribbean oceanic lithospheric mantle?

NASA Astrophysics Data System (ADS)

Marchesi, Claudio; Jolly, Wayne T.; Lewis, John F.; Garrido, Carlos J.; Proenza, Joaquín. A.; Lidiak, Edward G.

2010-05-01

The Monte del Estado massif is the largest and northernmost serpentinized peridotite belt in southwest Puerto Rico. It is mainly composed of spinel lherzolite and minor harzburgite with variable clinopyroxene modal abundances. Mineral and whole rock major and trace element compositions of peridotites coincide with those of fertile abyssal peridotites from mid ocean ridges. Peridotites lost 2-14 wt% of relative MgO and variable amounts of CaO by serpentinization and seafloor weathering. HREE contents in whole rock indicate that the Monte del Estado peridotites are residues after low to moderate degrees (2-15%) of fractional partial melting in the spinel stability field. However, very low LREE/HREE and MREE/HREE in clinopyroxene cannot be explained by melting models of a spinel lherzolite source and support that the Monte del Estado peridotites experienced initial low fractional melting degrees (~ 4%) in the garnet stability field. The relative enrichment of LREE in whole rock is not due to secondary processes but probably reflects the capture of percolating melt fractions along grain boundaries or as microinclusions in minerals, or the presence of exotic micro-phases in the mineral assemblage. We propose that the Monte del Estado peridotite belt represents a section of ancient Proto-Caribbean (Atlantic) lithospheric mantle originated by seafloor spreading between North and South America in the Late Jurassic-Early Cretaceous. This portion of oceanic lithospheric mantle was subsequently trapped in the forearc region of the Greater Antilles paleo-island arc generated by the northward subduction of the Caribbean plate beneath the Proto-Caribbean ocean. Finally, the Monte del Estado peridotites belt was emplaced in the Early Cretaceous probably as result of the change in subduction polarity of the Greater Antilles paleo-island arc without having been significantly modified by subduction processes.

Using spatial metrics and surveys for the assessment of trans-boundary deforestation in protected areas of the Maya Mountain Massif: Belize-Guatemala border.

PubMed

Chicas, S D; Omine, K; Ford, J B; Sugimura, K; Yoshida, K

2017-02-01

Understanding the trans-boundary deforestation history and patterns in protected areas along the Belize-Guatemala border is of regional and global importance. To assess deforestation history and patterns in our study area along a section of the Belize-Guatemala border, we incorporated multi-temporal deforestation rate analysis and spatial metrics with survey results. This multi-faceted approach provides spatial analysis with relevant insights from local stakeholders to better understand historic deforestation dynamics, spatial characteristics and human perspectives regarding the underlying causes thereof. During the study period 1991-2014, forest cover declined in Belize's protected areas: Vaca Forest Reserve 97.88%-87.62%, Chiquibul National Park 99.36%-92.12%, Caracol Archeological Reserve 99.47%-78.10% and Colombia River Forest Reserve 89.22%-78.38% respectively. A comparison of deforestation rates and spatial metrics indices indicated that between time periods 1991-1995 and 2012-2014 deforestation and fragmentation increased in protected areas. The major underlying causes, drivers, impacts, and barriers to bi-national collaboration and solutions of deforestation along the Belize-Guatemala border were identified by community leaders and stakeholders. The Mann-Whitney U test identified significant differences between leaders and stakeholders regarding the ranking of challenges faced by management organizations in the Maya Mountain Massif, except for the lack of assessment and quantification of deforestation (LD, SH: 18.67, 23.25, U = 148, p > 0.05). The survey results indicated that failure to integrate buffer communities, coordinate among managing organizations and establish strong bi-national collaboration has resulted in continued ecological and environmental degradation. The information provided by this research should aid managing organizations in their continued aim to implement effective deforestation mitigation strategies. Copyright © 2016 Elsevier

Effect of deforestation on stream water chemistry in the Skrzyczne massif (the Beskid Śląski Mountains in southern Poland).

PubMed

Kosmowska, Amanda; Żelazny, Mirosław; Małek, Stanisław; Siwek, Joanna Paulina; Jelonkiewicz, Łukasz

2016-10-15

The purpose of the study was to identify the factors affecting stream water chemistry in the small mountain catchments deforested to varying degrees, from 98.7 to 14.1%, due to long-term acid deposition. Water samples were collected monthly in 2013 and 2014 from 17 streams flowing across three distinct elevation zones in the Skrzyczne massif (Poland): Upper, Middle and Lower Forest Zone. Chemical and physical analyses, including the pH, electrical conductivity (EC), total mineral content (Mt), water temperature, and the concentrations of Ca(2+), Mg(2+), Na(+), K(+), HCO3(-), SO4(2-), Cl(-), and NO3(-), were conducted. Based on Principal Component Analysis (PCA), the most important factor affecting water chemistry was human impact associated with changes in pH, SO4(2-) concentration, and the concentration of most of the main ions. The substantial acidity of the studied environment contributed to the exclusion of natural factors, associated with changes in discharge, from the list of major factors revealed by PCA. All of the streams were characterized by very low EC, Mt, and low concentrations of the main ions such as Ca(2+) and HCO3(-). This is the effect of continuous leaching of solutes from the soils by acidic precipitation. The lowest parameter values were measured for the streams situated in the Upper Forest Zone, which is associated with greater acid deposition at the higher elevations. In the streams located in the Upper Forest Zone, a higher percentage of SO4(2-) occurred than in the streams situated in the Middle and Lower Forest Zones. However, the largest share of SO4(2-) was measured in the most deforested catchment. The saturation of the studied deforested catchment with sulfur compounds is reflected by a positive correlation between SO4(2-) and discharge. Hence, a forest acts as a natural buffer that limits the level of acidity in the natural environment caused by acidic atmospheric deposition. Copyright © 2016 Elsevier B.V. All rights reserved.

Modelling rock wall permafrost degradation in the Mont Blanc massif from the LIA to the end of the 21st century

NASA Astrophysics Data System (ADS)

Magnin, Florence; Josnin, Jean-Yves; Ravanel, Ludovic; Pergaud, Julien; Pohl, Benjamin; Deline, Philip

2017-08-01

High alpine rock wall permafrost is extremely sensitive to climate change. Its degradation has a strong impact on landscape evolution and can trigger rockfalls constituting an increasing threat to socio-economical activities of highly frequented areas; quantitative understanding of permafrost evolution is crucial for such communities. This study investigates the long-term evolution of permafrost in three vertical cross sections of rock wall sites between 3160 and 4300 m above sea level in the Mont Blanc massif, from the Little Ice Age (LIA) steady-state conditions to 2100. Simulations are forced with air temperature time series, including two contrasted air temperature scenarios for the 21st century representing possible lower and upper boundaries of future climate change according to the most recent models and climate change scenarios. The 2-D finite element model accounts for heat conduction and latent heat transfers, and the outputs for the current period (2010-2015) are evaluated against borehole temperature measurements and an electrical resistivity transect: permafrost conditions are remarkably well represented. Over the past two decades, permafrost has disappeared on faces with a southerly aspect up to 3300 m a.s.l. and possibly higher. Warm permafrost (i.e. > - 2 °C) has extended up to 3300 and 3850 m a.s.l. in N and S-exposed faces respectively. During the 21st century, warm permafrost is likely to extend at least up to 4300 m a.s.l. on S-exposed rock walls and up to 3850 m a.s.l. depth on the N-exposed faces. In the most pessimistic case, permafrost will disappear on the S-exposed rock walls at a depth of up to 4300 m a.s.l., whereas warm permafrost will extend at a depth of the N faces up to 3850 m a.s.l., but possibly disappearing at such elevation under the influence of a close S face. The results are site specific and extrapolation to other sites is limited by the imbrication of local topographical and transient effects.

Brief communication: 3-D reconstruction of a collapsed rock pillar from Web-retrieved images and terrestrial lidar data - the 2005 event of the west face of the Drus (Mont Blanc massif)

NASA Astrophysics Data System (ADS)

Guerin, Antoine; Abellán, Antonio; Matasci, Battista; Jaboyedoff, Michel; Derron, Marc-Henri; Ravanel, Ludovic

2017-07-01

In June 2005, a series of major rockfall events completely wiped out the Bonatti Pillar located in the legendary Drus west face (Mont Blanc massif, France). Terrestrial lidar scans of the west face were acquired after this event, but no pre-event point cloud is available. Thus, in order to reconstruct the volume and the shape of the collapsed blocks, a 3-D model has been built using photogrammetry (structure-from-motion (SfM) algorithms) based on 30 pictures collected on the Web. All these pictures were taken between September 2003 and May 2005. We then reconstructed the shape and volume of the fallen compartment by comparing the SfM model with terrestrial lidar data acquired in October 2005 and November 2011. The volume is calculated to 292 680 m3 (±5.6 %). This result is close to the value previously assessed by Ravanel and Deline (2008) for this same rock avalanche (265 000 ± 10 000 m3). The difference between these two estimations can be explained by the rounded shape of the volume determined by photogrammetry, which may lead to a volume overestimation. However it is not excluded that the volume calculated by Ravanel and Deline (2008) is slightly underestimated, the thickness of the blocks having been assessed manually from historical photographs.

Soil seed bank in different habitats of the Eastern Desert of Egypt.

PubMed

Gomaa, Nasr H

2012-04-01

The floristic composition and species diversity of the germinable soil seed bank were studied in three different habitats (desert salinized land, desert wadi, and reclaimed land) in the Eastern Desert of Egypt. Moreover, the degree of similarity between the seed bank and the above-ground vegetation was determined. The seed bank was studied in 40 stands representing the three habitats. Ten soil samples (each 25 × 20 cm and 5 cm depth) were randomly taken per stand. The seed bank was investigated by the seedling emergence method. Some 61 species belonging to 21 families and 54 genera were identified in the germinable seed bank. The recorded species include 43 annuals and 18 perennials. Ordination of stands by Detrended Correspondence Analysis (DCA) indicates that the stands of the three habitats are markedly distinguishable and show a clear pattern of segregation on the ordination planes. This indicates variations in the species composition among habitats. The results also demonstrate significant associations between the floristic composition of the seed bank and edaphic factors such as CaCO3, electrical conductivity, organic carbon and soil texture. The reclaimed land has the highest values of species richness, Shannon-index of diversity and the density of the germinable seed bank followed by the habitats of desert wadi and desert salinized land. Motyka's similarity index between the seed bank and the above-ground vegetation is significantly higher in reclaimed land (75.1%) compared to desert wadi (38.4%) and desert salinized land (36.5%).

Holocene evolution of Dahab coastline - Gulf of Aqaba, Sinai Peninsula, Egypt

NASA Astrophysics Data System (ADS)

Magdy, Torab

2016-04-01

Dahab was a little Bedouin-village in Sinai Peninsula at the mid-western coast of Gulf of Aqaba approx. 90 km north of Sharm-el-Sheikh City and it means "gold" in Arabic language. But in the past 20 years ago it becomes one of the most tourist sites in Egypt. The basement complex is composed mostly of biotiteaplite-granite, mica-aplitegranite, granodiorite, quartzdiorite, alaskite, and diorite. Based on correlation with similar igneous in the most southern part of Sinai and the Red Sea area. Wadi Dahab composed of igneous and metamorphic rocks and the coastline is formed of the fragments of its rocks, mixed with fragments of coral reef and fluvial deposits of Wadi Dahab. The morphology of Dahab coastline is characterized by hooked marine spit, which composed of fluvial sediments carried by marine current from wadi Dahab mouth, this spit encloses shallow lagoon, but the active deposition on the lagoon bottom will evaluate it into saline marsh. This paper dealing with the evolution of Dahab spit and lagoon during the Holocene in addition to the recent time for last 100 years, and it impacts of the future management of the coast area. The coastline mapping during the period of study depends upon GIS technique for data were collected during field measuring by using total station, aerial photo and satellite image interpretation as well as soil sample dating. Suggested geomorphological evolution of Dahab area during the Holocene depending upon geomorphic investigation of the sedimentological process into 6 stages.

Contamination risk and drinking water protection for a large-scale managed aquifer recharge site in a semi-arid karst region, Jordan

NASA Astrophysics Data System (ADS)

Xanke, Julian; Liesch, Tanja; Goeppert, Nadine; Klinger, Jochen; Gassen, Niklas; Goldscheider, Nico

2017-09-01

Karst aquifers in semi-arid regions are particularly threatened by surface contamination, especially during winter seasons when extremely variable rainfall of high intensities prevails. An additional challenge is posed when managed recharge of storm water is applied, since karst aquifers display a high spatial variability of hydraulic properties. In these cases, adapted protection concepts are required to address the interaction of surface water and groundwater. In this study a combined protection approach for the surface catchment of the managed aquifer recharge site at the Wala reservoir in Jordan and the downstream Hidan wellfield, which are both subject to frequent bacteriological contamination, is developed. The variability of groundwater quality was evaluated by correlating contamination events to rainfall, and to recharge from the reservoir. Both trigger increased wadi flow downstream of the reservoir by surface runoff generation and groundwater seepage, respectively. A tracer test verified the major pathway of the surface flow into the underground by infiltrating from pools along Wadi Wala. An intrinsic karst vulnerability and risk map was adapted to the regional characteristics and developed to account for the catchment separation by the Wala Dam and the interaction of surface water and groundwater. Implementation of the proposed protection zones for the wellfield and the reservoir is highly recommended, since the results suggest an extreme contamination risk resulting from livestock farming, arable agriculture and human occupation along the wadi. The applied methods can be transferred to other managed aquifer recharge sites in similar karstic environments of semi-arid regions.

Combined garnet and zircon geochronology of the ultra-high temperature metamorphism: Constraints on the rise of the Orlica-Śnieżnik Dome, NE Bohemian Massif, SW Poland

NASA Astrophysics Data System (ADS)

Walczak, Katarzyna; Anczkiewicz, Robert; Szczepański, Jacek; Rubatto, Daniela; Košler, Jan

2017-11-01

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810-860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342-337 Ma which corresponds to a fast, nearly isobaric cooling.

Failed Silurian continental rifting at the NW margin of Gondwana: evidence from basaltic volcanism of the Prague Basin (Teplá-Barrandian Unit, Bohemian Massif)

NASA Astrophysics Data System (ADS)

Tasáryová, Zuzana; Janoušek, Vojtěch; Frýda, Jiří

2018-06-01

The Silurian volcanic rocks of the Prague Basin represent within-plate, transitional alkali to tholeiitic basalts, which erupted in a continental rift setting through the thick Cadomian crust of the Teplá-Barrandian Unit (Bohemian Massif). Despite the variable, often intense alteration resulting in post-magmatic replacement of the basalt mass due to carbonatization, the geochemical signatures of Silurian basalts are still sufficiently preserved to constrain primary magmatic processes and geotectonic setting. The studied interval of Silurian volcanic activity ranges from Wenlock (Homerian, 431 Ma) to late Ludlow (Gorstian, 425 Ma) with a distinct peak at the Wenlock/Ludlow boundary ( 428 Ma). Trace-element characteristics unambiguously indicate partial melting of a garnet peridotite mantle source. Wenlock basalts are similar to alkaline OIB with depleted radiogenic Nd signature compared to Ludlow basalts, which are rather tholeiitic, EMORB-like with enriched radiogenic Nd signature. The correlation of petrogenetically significant trace-element ratios with Nd isotopic compositions points to a mixing of partial melts of an isotopically heterogeneous, possibly two-component mantle source during the Wenlock-Ludlow melting. Lava eruptions were accompanied by intrusions of doleritic basalt and meimechite sills. The latter represent olivine-rich cumulates of basaltic magmas of probably predominantly Ludlow age. Meimechites with dolerites and, to a lesser extent, some lavas were subject to alteration due to wall-rock-fluid interaction. The trigger for the Wenlock-to-Ludlow (431-425 Ma) extension and related volcanism in the Prague Basin is related to far-field forces, namely slab-pull regime due to progressive closure of the Iapetus Ocean. The main stage of the Baltica-Laurentia collision then caused the Prague Basin rift failure at ca. 425 Ma that has never reached an oceanic stage.

Chronological constraints on the Holocene glacier dynamics of the Argentière Glacier (Mont Blanc massif, France) based on cosmogenic nuclide dating

NASA Astrophysics Data System (ADS)

Protin, Marie; Schimmelpfennig, Irene; Mugnier, Jean-Louis; Ravanel, Ludovic; Deline, Philip; Le Roy, Melaine; Moreau, Luc; Aster Team

2017-04-01

While reconstruction of glacier fluctuations during the Holocene provides important information about the glacier response to natural climate change, it is still a challenge to accurately constrain chronologies of past glacier advances and retreats. Moraine deposits and roches moutonnées represent valuable geomorphic markers of advanced glacier extensions, while the currently ongoing glacier melt uncovers proglacial bedrock that can be used as a new archive to investigate the durations when a glacier was in retreated position during the Holocene. Our study focuses on the Mont-Blanc massif (MBM), located in the Western Alps and hosting some of the largest glaciers of Europe. Chronologies of Holocene glacier fluctuations in this area are still sparse, even if recent studies considerably improved the temporal reconstruction of Holocene advances of some glaciers in the MBM and locations near-by (e.g. Le Roy et al., 2015). Here we present preliminary 10Be exposure ages obtained from moraine boulders, roches moutonnées and pro- and subglacial bedrock in the area of the Argentière Glacier, located on the north-western flank of the MBM. The ages of moraine boulders and roche moutonnée surfaces outboard of the investigated moraines suggest that the Early Holocene deglaciation of this area started around 11 ka ago. Also, 10Be measurements of recently deglaciated bedrock surfaces indicate that the glacier was at a position at least as retracted as today for a minimum duration of 7 ka throughout the Holocene. The 10Be measurement of one sample from a surface that is currently still covered by 60 m of ice suggests that the glacier was shorter than today for at least a duration of 3 ka. These first results will soon be completed with in situ 14C measurements, which will allow us to quantify and take into account subglacial erosion rates and thus to more accurately determine the cumulative duration of pro- and subglacial bedrock exposure during the Holocene.

Post-Hercynian subvolcanic magmatism in the Serre Massif (Central-Southern Calabria, Italy)

NASA Astrophysics Data System (ADS)

Romano, V.; Cirrincione, R.; Fiannacca, P.; Mazzoleni, P.; Tranchina, A.

2009-04-01

In the Serre Massif (Central-Southern Calabria, Italy) dykes and subvolcanic bodies intrude diffusively both Hercynian metamorphic rocks and late-Hercynian granitoids. They range in composition from basaltic andesites to dacite-rhyodacites and can be ascribed to the extensive magmatic activity that affects the entire Hercynian orogenic belt in late Paleozoic - early Mesozoic time. The geodinamic framework of the magmatic activity is still matter of debate, nevertheless most authors agree in correlating magmatism both to the late-orogenic collapse of the Hercynian belt and to the lithosphere thinning responsible for the subsequent continental rifting. In this work, we propose a petrogenetic model for acidic to basic hypabissal bodies from southern Calabria in order to define the nature of sources, discriminate magmatic processes and supply a contribution in the geodynamic reconstruction of the Late Palaeozoic in the Calabria-Peloritani Orogen. In relation to their geochemical affinity, studied dykes have been divided in two groups: a medium- to high-K calc-alkaline and a tholeiitic one. Dykes belonging to the former group, andesitic and dacitic-rhyodacitic in composition, show typical features of subduction-related magmatism, such as LILE and LREE enrichments, depletions in HFSE, peaks in Rb, Th and Ce, accentuated troughs in Ba, Nb-Ta, P and Ti (White and Dupré, 1986; McCulloch and Gamble, 1991), contrasting with the late Hercynian collisional context. On the other side, features typical of intra-plate magmatic activity, such as a moderate enrichment in Ta, Nb, Ce, P, Zr, Hf and Sm relative to MORB composition are also present in studied rocks (Shimizu & Arculus, 1975; Pearce, 1982). REE-patterns are strongly to weakly fractionated for the andesitic rocks (Lan/Ybn = 10.03-13.98) and the dacitic-rhyodacitic ones (Lan/Ybn = 6.00 to 2.82), respectively. The latter rocks exhibit a very slight negative Eu anomaly, whereas no Eu anomaly is recognizable in the andesite

Characteristics of Preservice Teachers in Multi-Campus Settings: Using Demographics and Epistemological Beliefs to Unpack Stereotypes

ERIC Educational Resources Information Center

Exley, Beryl; Walker, Sue; Brownlee, Joanne

2008-01-01

The last two decades have seen the massification of preservice teacher education and critiques of its quality in Australia and elsewhere. Part of the strategy of massification has been the establishment of satellite campuses in growth corridors. This paper enters the debate on the quality of preservice candidates. The purpose of this research is…

Geologic setting of Boulder 1, Station 2, Apollo 17 landing site

USGS Publications Warehouse

Wolfe, E.W.

1975-01-01

Boulder 1 at Station 2 is one of three boulders sampled by Apollo 17 at the base of the South Massif, which rises 2.3 km above the floor of a linear valley interpreted as a graben formed by deformation related to the southern Serenitatis impact. The boulders probably rolled from the upper part of the massif after emplacement of the light mantle. Orbital gravity data and photogeologic reinterpretation suggest that the Apollo 17 area is located approximately on the third ring of the southern Serenitatis basin, approximately 1.25 times larger than the analogous but fresher Orientale basin structure. The massif exposures are interpreted to represent the upper part of thick ejecta deposited by the southern Serenitatis impact near the rim of the transient cavity. Basin ring structure and the radial grabens that give the massifs definition were imposed on this ejecta at a slightly later stage in the basin-forming process. There is no clear-cut compositional, textural, or photogeologic evidence that Imbrium ejecta was collected at the Apollo 17 site. ?? 1975 D. Reidel Publishing Company, Dordrecht-Holland.

First Evidence of Middle Triassic Basic Magmatism in the Southwestern Part of the Dzhugdzhur-Stanovoi Superterrane (Ilikan Terrane)

NASA Astrophysics Data System (ADS)

Buchko, I. V.; Sorokin, A. A.; Rodionov, A. A.; Kudryashov, N. M.

2018-04-01

U-Pb ID-TIMS zircon analyses of the Dzhigda gabbro-gabbrodiorite Massif (Ilikan block in the southwestern part of the Dzhugdzhur-Stanovoi superterrane) have been carried out. The results demonstrate that the formation of the massif at 244 ± 5 Ma corresponds to one of the stages of formation of the Selenga-Vitim volcano-plutonic belt. The latter stretches along the southeastern margin of the North Asian Craton along its border with the Mongol-Okhotsk fold belt. This indicates that the Selenga-Vitim volcano-plutonic belt along with granitoids and volcanics comprises Permian-Triassic massifs and that this belt is superimposed onto structures of not only the Selenga-Stanovoi terrane but also the Dzhugdzhur-Stanovoi terrane.

The first polluted river? Repeated copper contamination of fluvial sediments associated with Late Neolithic human activity in southern Jordan.

PubMed

Grattan, J P; Adams, R B; Friedman, H; Gilbertson, D D; Haylock, K I; Hunt, C O; Kent, M

2016-12-15

The roots of pyrometallurgy are obscure. This paper explores one possible precursor, in the Faynan Orefield in southern Jordan. There, at approximately 7000cal. BP, banks of a near-perennial meandering stream (today represented by complex overbank wetland and anthropogenic deposits) were contaminated repeatedly by copper emitted by human activities. Variations in the distribution of copper in this sequence are not readily explained in other ways, although the precise mechanism of contamination remains unclear. The degree of copper enhancement was up to an order of magnitude greater than that measured in Pleistocene fluvial and paludal sediments, in contemporary or slightly older Holocene stream and pond deposits, and in the adjacent modern wadi braidplain. Lead is less enhanced, more variable, and appears to have been less influenced by contemporaneous human activities at this location. Pyrometallurgy in this region may have appeared as a byproduct of the activity practised on the stream-bank in the Wadi Faynan ~7000years ago. Copyright © 2016. Published by Elsevier B.V.

Modern dust aerosol availability in northwestern China.

PubMed

Wang, Xunming; Cheng, Hong; Che, Huizheng; Sun, Jimin; Lu, Huayu; Qiang, Mingrui; Hua, Ting; Zhu, Bingqi; Li, Hui; Ma, Wenyong; Lang, Lili; Jiao, Linlin; Li, Danfeng

2017-08-18

The sources of modern dust aerosols and their emission magnitudes are fundamental for linking dust with climate and environment. Using field sample data, wind tunnel experiments and statistical analysis, we determined the contributions of wadis, gobi (stony desert), lakebeds, riverbeds, and interdunes to modern dust aerosol availability in the three important potential dust sources including the Tarim Basin, Qaidam Basin, and Ala Shan Plateau of China. The results show that riverbeds are the dominant landscape for modern dust aerosol availabilities in the Qaidam Basin, while wadis, gobi, and interdunes are the main landscapes over the Ala Shan Plateau and Tarim Basin. The Ala Shan Plateau and Tarim Basin are potential dust sources in northwestern China, while the Qaidam Basin is not a major source of the modern dust aerosols nowadays, and it is not acting in a significant way to the Loess Plateau presently. Moreover, most of modern dust aerosol emissions from China originated from aeolian processes with low intensities rather than from major dust events.

Mineralogy and ore fluid chemistry of the Roc Blanc Ag deposit, Jebilet Hercynian massif, Morocco

NASA Astrophysics Data System (ADS)

Essarraj, Samira; Boiron, Marie-Christine; Cathelineau, Michel; Tarantola, Alexandre; Leisen, Mathieu; Hibti, Mohamed

2017-03-01

The Roc Blanc Ag deposit is located about 20 km north of Marrakesh city (Morocco) in the Jebilet Hercynian massif. The ore bodies consist of N-S to NE-SW quartz (±carbonates) veins hosted by the Sarhlef marine sediments. These series, deposited in a Devonian-Carboniferous rift basin context, were deformed during the Hercynian orogeny, and submitted to low-grade regional metamorphism. Two major stages of fluid circulation and metal deposition are distinguished on the basis of mineralogical and paleo-fluid studies carried out on quartz and dolomite (microthermometry, Raman spectroscopy, LA-ICP-MS on individual inclusions, and O, H stable isotope data): (i) an early Fe-As stage, characterized by the circulation of metamorphic aqueous-carbonic fluids, under P-T conditions lower than 200 MPa ± 20 MPa and 400 °C respectively, along N-S structures; (ii) the ore stage, characterized by the circulation of a Na-Mg-K ± Ca high salinity brine, poor in gas but rich in metals such as Fe, Sr, Ba, Zn, Pb, ± Cu (salinity ranging from 19.6 wt% to likely more than 30 wt% NaCl equiv.) and the deposition of a sphalerite/dolomite-calcite assemblage; such a fluid likely evolved to a Na-K-(Ca-Mg)-Ag brine, with significant Pb and Sb concentrations and lower Sr, Ba and Zn concentrations than in the preceding fluid (salinity up to 19.4 wt% NaCl equiv.). The Ag content of the second mineralizing brine ranges from 0.9 mmol/kg to 9.4 mmol/kg solution (100 ppm-1000 ppm), whereas the base metal brine is generally Ag poor (up to 1.3 mmol/kg solution: 140 ppm). Dilution of the Ag brine by low salinity fluids (<6 wt% NaCl equiv., and Th from 130° to 230 °C) seems to be the main driving mechanism for the Ag ore deposition at Roc Blanc, with a possible involvement of cooling and reduction reactions in black schists. Base metal and Ag fluids may have circulated at average temperatures around 200 ± 30 °C or slightly higher and under hydrostatic pressures, along dominant E-W structures. The ore

Fungi of Mt. Babia Gora. 2: Indicative value of macromycetes in forest associations. A: Initial considerations

NASA Technical Reports Server (NTRS)

Bujakiewicz, A.

1984-01-01

The role and value of fungi in forest associations of Mt. Babia Gora massif were determined. The general physiographic characteristics of the research terrain, the distribution of the fungi sites, a list of the 618 taxons noted in the subalpine forests of Mt. Babia Gora, and the initial characteristics of the forest mycoflora of this massif are presented.

Hyperextension of continental to oceanic-like lithosphere: The record of late gabbros in the shallow subcontinental lithospheric mantle of the westernmost Mediterranean

NASA Astrophysics Data System (ADS)

Hidas, Károly; Varas-Reus, Maria Isabel; Garrido, Carlos J.; Marchesi, Claudio; Acosta-Vigil, Antonio; Padrón-Navarta, José Alberto; Targuisti, Kamal; Konc, Zoltán

2015-05-01

We report gabbroic dikes in the plagioclase tectonite domains of the Ojén and Ronda massifs (Betic Cordillera, southern Spain), which record crystallization at low-pressure syn-, or slightly postkinematic to the late ductile history of the Betic Peridotite in the westernmost Mediterranean. We present mineral major and trace element compositional data of discordant gabbroic dikes in the Ojén massif and gabbroic patches in the Ronda massif, complemented by the whole rock and electron backscattered diffraction (EBSD) data of the Ojén occurrence. In the Ojén massif, gabbro occurs as 1-3 centimeter wide discordant dikes that crosscut the plagioclase tectonite foliation at high angle. These dikes are composed of cm-scale igneous plagioclase and clinopyroxene crystals that show shape preferred orientations subparallel to the lineation of the host peridotite and oblique to the trend of the dike. Intrusion of Ojén gabbro dikes is coherent with the stress field that formed the high temperature, ductile plagioclase tectonite foliation and then attests for a mantle igneous event prior to the intracrustal emplacement of the massif. In the Ronda massif, gabbroic rocks crystallized in subcentimeter wide anastomozing veins, or as interstitial patches in the host dunite. They are mostly composed of plagioclase and clinopyroxene. Plagioclase composition is bytownitic in the Ojén, and andesinic in the Ronda massif. Clinopyroxene in both places shows identical, light Rare-Earth Element (LREE) depleted trace element patterns. The calculated trace element composition of melts in exchange equilibrium with the studied igneous clinopyroxenes reflects LREE-enriched character coupled with negative Eu anomaly, and indicates that gabbro-forming melts in Ronda and Ojén share a common melt source with an island arc tholeiitic affinity. Geothermobarometric data and liquidus mineralogy indicate that gabbro crystallization occurred at shallow depths (0.2-0.5 GPa) in a 7-16 km thick

Slip-deficit on the Levant fault estimated by paleoseismological investigations

NASA Astrophysics Data System (ADS)

Lefevre, Marthe; Klinger, Yann; Al-Qaryouti, Mahmoud; Le Béon, Maryline; Moumani, Khaled; Thomas, Marion; Baize, Stephane

2016-04-01

The Levant fault is a major tectonic structure located east of the Mediterranean Sea. It is a 1200 km-long left-lateral strike-slip fault, which accommodates the northward movement of the Arabic plate relatively to the Sinai micro-plate, with a ˜ 5mm/year slip-rate. This slip-rate has been estimated over a large range of time scales, from a few years (gps) to several hundred thousands of years (geomorphology). The geometry of the southern part of the Levant fault, the Wadi Araba fault, is linear with only a few bends and steps. The Middle-East is a region where there is an important and complete historical record of past earthquakes. Nevertheless, due to the arid and unpopulated nature of the Wadi Araba, to constrain location and lateral extent of those past earthquake with accuracy remains challenging. We excavated a trench ˜ 100 km north of Aqaba in the wadi Musa alluvial fan, next to the largest compressional jog of the Wadi Araba. The stratigraphy contains three main units. Two units are coarse and channelized, and sandy flat layers form the third unit. In the trench the deformation is distributed over 15m, and is more pronounced in the eastern part. We can identify at least 12 earthquakes, based on upward terminations of ground ruptures. 14C dating of 28 charcoals distributed over the three documented trench walls, shows a 7000 year-long record and it allows us to match some events with historical earthquakes in AD1458, AD1293, AD748, AD114, BC31. For other dated events, matching with historical events remains more speculative considering the limited testimonies in old ages. As the last earthquake in the Wadi Araba occurred in AD1458, with an average slip rate of 5 mm/yr, about 2.7 m of slip-deficit have already accumulated, suggesting that this area might be ripe for a large earthquake. Some of the events recognized in our trench are attested north of the Dead Sea as well, such as the AD749 earthquake, suggesting that long sections of the Levant Fault might

Spatial Temporal Analysis Of Mine-induced Seismicity

NASA Astrophysics Data System (ADS)

Fedotova, I. V.; Yunga, S. L.

The results of analysis of influence mine-induced seismicity on state of stress of a rock mass are represented. The spatial-temporal analysis of influence of mass explosions on rock massif deformation is carried out in the territory of a mine field Yukspor of a wing of the Joined Kirovsk mine JSC "Apatite". Estimation of influence of mass explosions on a massif were determined based firstly on the parameters of natural seismicic regime, and secondly taking into consideration change of seismic energy release. After long series of explosions variations in average number of seismic events was fixed. Is proved, that with increase of a volume of rocks, involved in a deforma- tion the released energy of seismic events, and characteristic intervals of time of their preparation are also varied. At the same time, the mechanism of destruction changes also: from destruction's, of a type shift - separation before destruction's, in a quasi- solid heterogeneous massif (in oxidized zones and zones of actuated faults). Analysis of a database seismicity of a massif from 1993 to 1999 years has confirmed, that the response of a massif on explosions is connected to stress-deformations state a mas- sif and parameters of a mining working. The analysis of spatial-temporal distribution of hypocenters of seismic events has allowed to allocate migration of fissile regions of destruction after mass explosions. The researches are executed at support of the Russian foundation for basic research, - projects 00-05-64758, 01-05-65340.

Homogenity of geological units with respect to the radon risk in the Walloon region of Belgium.

PubMed

Tondeur, François; Cinelli, Giorgia; Dehandschutter, Boris

2014-10-01

In the process of mapping indoor radon risk, an important step is to define geological units well-correlated with indoor radon. The present paper examines this question for the Walloon region of Belgium, using a database of more than 18,000 indoor radon measurements. With a few exceptions like the Carboniferous (to be divided into Tournaisian, Visean and Namurian-Westphalian) and the Tertiary (in which all Series may be treated together), the Series/Epoch stratigraphic level is found to be the most appropriate geological unit to classify the radon risk. A further division according to the geological massif or region is necessary to define units with a reasonable uniformity of the radon risk. In particular, Paleozoic series from Cambrian to Devonian show strong differences between different massifs. Local hot-spots are also observed in the Brabant massif. Finally, 35 geological units are defined according to their radon risk, 6 of which still present a clear weak homogeneity. In the case of 4 of these units (Jurassic, Middle Devonian of Condroz and of Fagne-Famenne, Ordovician of the Stavelot massif) homogeneity is moderate, but the data are strongly inhomogeneous for Visean in Condroz and in the Brabant massif. The 35 geological units are used in an ANOVA analysis, to evaluate the part of indoor radon variability which can be attributed to geology. The result (15.4-17.7%) agrees with the values observed in the UK. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

U-Pb SHRIMP-RG zircon ages and Nd signature of lower Paleozoic rifting-related magmatism in the Variscan basement of the Eastern Pyrenees

USGS Publications Warehouse

Martinez, F.J.; Iriondo, A.; Dietsch, C.; Aleinikoff, J.N.; Peucat, J.J.; Cires, J.; Reche, J.; Capdevila, R.

2011-01-01

The ages of orthogneisses exposed in massifs of the Variscan chain can determine whether they are part of a pre-Neoproterozoic basement, a Neoproterozoic, Panafrican arc, or are, in fact, lower Paleozoic, and their isotopic compositions can be used to probe the nature of their source rocks, adding to the understanding of the types, distribution, and tectonic evolution of peri-Gondwanan crystalline basement. Using SHRIMP U-Pb zircon geochronology and Nd isotopic analysis, pre-Variscan metaigneous rocks from the N??ria massif in the Eastern Pyrenean axial zone and the Guilleries massif, 70km to the south, have been dated and their Nd signatures characterized. All dated orthogneisses from the N??ria massif have the same age within error, ~457Ma, including the Ribes granophyre, interpreted as a subvolcanic unit within Caradocian sediments contemporaneous with granitic magmas intruded into Cambro-Ordovician sediments at deeper levels. Orthogneisses in the Guilleries massif record essentially continuous magmatic activity during the Ordovician, beginning at the Cambro-Ordovician boundary (488??3Ma) and reaching a peak in the volume of magma in the early Late Ordovician (~460Ma). Metavolcanic rocks in the Guilleries massif were extruded at 452??4Ma and appear to have their intrusive equivalent in thin, deformed veins of granitic gneiss (451??7Ma) within metasedimentary rocks. In orthogneisses from both massifs, the cores of some zircons yield Neoproterozoic ages between ~520 and 900Ma. The age of deposition of a pre-Late Ordovician metapelite in the Guilleries massif is bracketed by the weighted average age of the youngest detrital zircon population, 582??11Ma, and the age of cross-cutting granitic veins, 451??7Ma. Older detrital zircons populations in this metapelite include Neoproterozoic (749-610Ma; n=10), Neo- to Mesoproterozoic (1.04-0.86Ga; n=7), Paleoproterozoic (2.02-1.59Ga; n=5), and Neoarchean (2.74-2.58Ga; n=3). Nd isotopic analyses of the N??ria and Guilleries

Space Radar Image of Wadi Kufra, Libya

NASA Image and Video Library

1998-04-14

The ability of a sophisticated radar instrument to image large regions of the world from space, using different frequencies that can penetrate dry sand cover, produced the discovery in this image: a previously unknown branch of an ancient river, buried under thousands of years of windblown sand in a region of the Sahara Desert in North Africa. This area is near the Kufra Oasis in southeast Libya, centered at 23.3 degrees north latitude, 22.9 degrees east longitude. The image was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture (SIR-C/X-SAR) imaging radar when it flew aboard the space shuttle Endeavour on its 60th orbit on October 4, 1994. This SIR-C image reveals a system of old, now inactive stream valleys, called "paleodrainage systems, http://photojournal.jpl.nasa.gov/catalog/PIA01310

Age and isotopic constraints on pleistocene pluvial episodes in the Western Desert, Egypt.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crombie, M. K.; Arvidson, R. E.; Sturchio, N. C.

1997-01-01

North Africa has undergone drastic climatic changes over the past several hundred thousand years. The timing of humid intervals called pluvials was investigated by uranium-series disequilibrium dating of travertines from the Kurkur Oasis, Western Desert, Egypt. The youngest and best dated travertines (70-160 ka) are found in Wadi Kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces. Travertines having an age of approximately 191-220 ka are exposed by differential erosion as linear mounds produced by spring systems over fracture zones in ancient wadis. The oldest travertines, having ages >260 ka, are extensive, cap limestonemore » units above the oasis, and were deposited in paludal and lacustrine environments. Oxygen isotope ratios were measured for the wadi travertines ({delta}{sup 18}O values ranging from 16.7 to 19.1{per_thousand} SMOW) and for spring mound travertines (18.5-20.5{per_thousand}). Equilibrium oxygen isotope fractionation calculations indicate that the Kurkur travertines were deposited from waters having {delta}{sup 18}O values similar to ancient Western Desert groundwaters ({approx} -11{per_thousand}). The ages of the travertines correspond to times of monsoonal maxima, eustatic sea level high stands and interglacial maxima. Rainfall producing these groundwaters (and travertines) was significantly fractionated during atmospheric transport, in contrast to modern meteoric waters (-2.09{per_thousand}), implying a distant source for the pluvial waters. Increased precipitation, recharge of Western Desert groundwaters, and resultant travertine deposition are interpreted to be consequences of Milankovitch insolation cycle forcing, through enhanced Atlantic and Indian Ocean monsoons during interglacial time periods.« less

Estimation of groundwater flow directions and the tensor of hydraulic conductivity in crystalline massif rocks using information from surface structural geology and mining exploration boreholes

NASA Astrophysics Data System (ADS)

Florez, C.; Romero, M. A.; Ramirez, M. I.; Monsalve, G.

2013-05-01

In the elaboration of a hydrogeological conceptual model in regions of mining exploration where there is significant presence of crystalline massif rocks., the influence of physical and geometrical properties of rock discontinuities must be evaluated. We present the results of a structural analysis of rock discontinuities in a region of the Central Cordillera of Colombia (The upper and middle Bermellon Basin) in order to establish its hydrogeological characteristics for the improvement of the conceptual hydrogeological model for the region. The geology of the study area consists of schists with quartz and mica and porphyritic rocks, in a region of high slopes with a nearly 10 m thick weathered layer. The main objective of this research is to infer the preferential flow directions of groundwater and to estimate the tensor of potential hydraulic conductivity by using surface information and avoiding the use of wells and packer tests. The first step of our methodology is an analysis of drainage directions to detect patterns of structural controls in the run-off; after a field campaign of structural data recollection, where we compile information of strike, dip, continuity, spacing, roughness, aperture and frequency, we built equal area hydro-structural polar diagrams that indicate the potential directions for groundwater flow. These results are confronted with records of Rock Quality Designation (RQD) that have been systematically taken from several mining exploration boreholes in the area of study. By using all this information we estimate the potential tensor of hydraulic conductivity from a cubic law, obtaining the three principal directions with conductivities of the order of 10-5 and 10-6 m/s; the more conductive joint family has a NE strike with a nearly vertical dip.

Origin of the Sinai-Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history

USGS Publications Warehouse

Muhs, Daniel R.; Roskin, Joel; Tsoar, Haim; Skipp, Gary; Budahn, James R.; Sneh, Amihai; Porat, Naomi; Stanley, Jean-Daniel; Katra, Itzhak; Blumberg, Dan G.

2013-01-01

The Sinai–Negev erg occupies an area of 13,000 km2 in the deserts of Egypt and Israel. Aeolian sand of this erg has been proposed to be derived from the Nile Delta, but empirical data supporting this view are lacking. An alternative source sediment is sand from the large Wadi El Arish drainage system in central and northern Sinai. Mineralogy of the Negev and Sinai dunes shows that they are high in quartz, with much smaller amounts of K-feldspar and plagioclase. Both Nile Delta sands and Sinai wadi sands, upstream of the dunes, also have high amounts of quartz relative to K-feldspar and plagioclase. However, Sinai wadi sands have abundant calcite, whereas Nile Delta sands have little or no calcite. Overall, the mineralogical data suggest that the dunes are derived dominantly from the Nile Delta, with Sinai wadi sands being a minor contributor. Geochemical data that proxy for both the light mineral fraction (SiO2/10–Al2O3 + Na2O + K2O–CaO) and heavy mineral fraction (Fe2O3–MgO–TiO2) also indicate a dominant Nile Delta source for the dunes. Thus, we report here the first empirical evidence that the Sinai–Negev dunes are derived dominantly from the Nile Delta. Linkage of the Sinai–Negev erg to the Nile Delta as a source is consistent with the distribution of OSL ages of Negev dunes in recent studies. Stratigraphic studies show that during the Last Glacial period, when dune incursions in the Sinai–Negev erg began, what is now the Nile Delta area was characterized by a broad, sandy, minimally vegetated plain, with seasonally dry anastomosing channels. Such conditions were ideal for providing a ready source of sand for aeolian transport under what were probably much stronger glacial-age winds. With the post-glacial rise in sea level, the Nile River began to aggrade. Post-glacial sedimentation has been dominated by fine-grained silts and clays. Thus, sea level, along with favorable climatic conditions, emerges as a major influence on the timing of dune

Late Cenozoic cooling history of the central Menderes Massif: Timing of the Büyük Menderes detachment and the relative contribution of normal faulting and erosion to rock exhumation

NASA Astrophysics Data System (ADS)

Wölfler, Andreas; Glotzbach, Christoph; Heineke, Caroline; Nilius, Nils-Peter; Hetzel, Ralf; Hampel, Andrea; Akal, Cüneyt; Dunkl, István; Christl, Marcus

2017-10-01

Based on new thermochronological data and 10Be-derived erosion rates from the southern part of the central Menderes Massif (Aydın block) in western Turkey, we provide new insights into the tectonic evolution and landscape development of an area that undergoes active continental extension. Fission-track and (U-Th)/He data reveal that the footwall of the Büyük Menderes detachment experienced two episodes of enhanced cooling and exhumation. Assuming an elevated geothermal gradient of 50 °C/km, the first phase occurred with an average rate of 0.90 km/Myr in the middle Miocene and the second one in the latest Miocene and Pliocene with a rate of 0.43 km/Myr. The exhumation rates between these two phases were lower and range from 0.14 to 0.24 km/Myr, depending on the distance to the detachment. Cosmogenic nuclide-based erosion rates for catchments in the Aydın block range from 0.1 to 0.4 km/Myr. The similarity of the erosion rates on both sides of the Aydın block (northern and southern flank) indicate that a rather symmetric erosion pattern has prevailed during the Holocene. If these millennial erosion rates are representative on a million-year timescale they indicate that, apart from normal faulting, erosion in the hanging wall of the Büyük Menderes detachment fault did also contribute to the exhumation of the metamorphic rocks.

Dating desert ground water

USGS Publications Warehouse

Thatcher, L.; Rubin, M.; Brown, G.F.

1961-01-01

Tritium in Arabian rainfall has followed the trend observed in North America with peaks in 1958 and the spring of 1959. These measurements will be useful for future hydrologie studies. Water from wadi gravels averages 10 yr old. Carbon-14 measurements of deep waters indicate ages of several thousand years.

Melt Transport and Mantle Assimilation at Atlantis Massif (IODP Site U1309): Evidence from Chemical Profiles along Olivine Crystallographic Axes

NASA Astrophysics Data System (ADS)

Ferrando, C.; Godard, M.; Ildefonse, B.; Rampone, E.

2017-12-01

Olivine-rich troctolites (Ol > 70%, Ol T) indicate that extensive melt impregnation of preexisting Ol rich lithologies participate to the building of slow spread crust. To constrain their origin and their impact on the structure and geochemistry of oceanic crust, we realized a multi-scale petro-structural, geochemical, and numerical modelling study of Ol T drilled at IODP Hole U1309D (Atlantis Massif, Exp. 304/305). Ol T display deformed (high temperature imprint) corroded coarse grained to undeformed fine grained Ol embayed in poikilitic Cpx and Plg. Ol crystallographic preferred orientations show [001] cluster suggesting formation after impregnation and assimilation of a deformed Ol rich matrix at high melt/rock ratios. Ol have variable major and minor element compositions, but similar fractionated REE (DyN/YbN = 0.04 - 0.11). Chemical traverses along principal crystallographic axes of Ol are flat suggesting local equilibrium between Ol and neighboring phases. 3 types of Ol T were distinguished. Ol T 1 - 2 display sharp contacts. Ol T 1 has Ol <75% (single grains) and primitive compositions (Mg# = 85-86; Ni = 1870-2840 ppm, Mn = 1570-1950 ppm; Li = 1.2 - 2.7 ppm). Ol T 2 have high Ol ( > 75%, dominantly aggregates) yet more evolved composition (Mg# = 83-84, Ni = 1790 - 2510 ppm, Mn = 1760 - 1990 ppm, Li = 1.5 - 3.9 ppm) in contrast to modal and composition trends predicted by MORB crystallization. Ol T 3 has diffusive contacts with gabbroic veins, variable modal Ol with the most evolved compositions and record late stages of Ol-T formation. Ol T compositions are best modelled assuming percolation of primitive MORB melts into Hole U1309B harzburgite, triggering Opx dissolution, followed by Ol assimilation and Plg + Cpx crystallization. Modelling shows that Ol Ni variations at constant Mg# in Ol T are mantle inherited. Ol T 1 compositions were fitted assuming higher Ol assimilation (Ma = 0.06 - 0.13) in contrast to Ol T 2 -3 (Ma = 0.01 - 0.02). Ol T 3 was `buffered

Petrological evolution of subducted rodingite from seafloor metamorphism to dehydration of enclosing antigorite-serpentinite (Cerro del Almirez massif, southern Spain)

NASA Astrophysics Data System (ADS)

Laborda-López, Casto; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Gómez-Pugnaire, María Teresa; Garrido, Carlos J.; Jabaloy-Sánchez, Antonio; Padrón-Navarta, José Alberto

2016-04-01

Rodingites are common rocks associated with serpentinites in exhumed terrains that experienced subduction and high pressure metamorphism. However, the response of these rocks to devolatilization and redox reactions in subduction settings is not well constrained. In the Cerro del Almirez ultramafic massif (southern Spain) rodingites constitute about 1-2% of the total volume of exposed rocks. Metarodingites are enclosed in antigorite-serpentinite and chlorite-harzburgite separated by a transitional zone that represents the front of prograde serpentinite-dehydration in a paleo-subduction setting (Padrón-Navarta et al., 2011). Metarodingites occur as boudin lenses, 1 to 20 m in length and 30 cm to 2 m in thickness. During serpentinization of peridotite host rocks, dolerites and basalts precursor of rodingites underwent intense seafloor metasomatism, causing the enrichment in Ca and remobilization of Na and K. Subsequent metamorphism during subduction transformed the original igneous and seafloor metamorphic mineralogy into an assemblage of garnet (Ti-rich hydrogrossular), diopside, chlorite, and epidote. During prograde metamorphism, garnet composition changed towards higher andradite contents. High-pressure transformation of enclosing antigorite-serpentinite to chlorite-harzburgite released fluids which induced breakdown of garnet to epidote in metarodingites. Ti liberation by this latter reaction produced abundant titanite. Released fluids also triggered the formation of amphibole by alkalis addition. Highly recrystallized metarodingites in chlorite-harzburgite present a new generation of idiomorphic garnet with composition equal to 10-30% pyrope, 30-40% grossular and 35-55% almandine + spessartine. This garnet has titanite inclusions in the core and rutile inclusions in the rim. The contact between metarodingites and ultramafic rocks consists of a metasomatic zone (blackwall) with variable thickness (7 to 40 cm) constituted by chlorite, diopside, and titanite

Environmental evolution in the Picos de Europa (Cantabrian Mountains, SW Europe) since the Last Glaciation

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesús; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Freitas, Maria da Conceição; Andrade, César; García-Hernández, Cristina; López-Sáez, José Antonio; Geraldes, Miguel

2016-04-01

The Western Massif of the Picos de Europa (latitude 43° N, longitude 4-5° W) includes some of the highest peaks in the Cantabrian Mountains. This massif was heavily glaciated during the Last Glaciation, though the post-glacial environmental evolution is still poorly understood. Using a complementary geomorphological and sedimentological approach, we have reconstructed the environmental events occurred in this massif since the last Pleistocene glaciation. The geomorphological distribution of glacial landforms suggests the occurrence of four main glacial stages: maximum glacial advance, glacial expansion after the maximum advance, Late Glacial and Little Ice Age. Moreover, a 5.4-m long sedimentary sequence was retrieved from the karstic depression of Belbín providing a continuous record of the paleoenvironmental conditions in this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, periglacial processes prevailed in the mid lands of the massif until glaciers expanded between 22.5 and 18.7 ka cal BP. Following the melting of the glaciers, a shallow lake appeared in the Belbín depression. Lake sediments do not show evidence of a cold stage during the Late Glacial, when moraine systems formed at higher locations. The terrestrification of this lake started at 8 ka cal BP and the area turned into grassland. At 4.9 ka cal BP the existence of charcoal particles in the sediments of Belbín sequence reveals the onset of human occupation in the massif through the use of fire activity for grazing purposes. Finally, the presence of moraines inside the highest northern cirques shows evidence of the last glacial phase that occurred during the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers and periglacial processes prevail in the high lands of the massif.

Chromium-rich lawsonite in high-Cr eclogites from the Făgăras Massif (South Carpathians)

NASA Astrophysics Data System (ADS)

Negulescu, E.; Săbău, G.

2012-12-01

Lawsonite is a relatively rare phase in natural rocks, because of its thermal decomposition during exhumation, and Cr-bearing lawsonite being restricted to only a few occurrences worldwide. Here we report Cr-lawsonite in eclogites hosted in a medium-grade metamorphic complex. Several high-Cr eclogite lenses occur in the Topolog Complex (Făgăras Massif) of dominantly gneissic-amphibolitic composition. High Cr contents are the result of emerald-green mm-sized nodules containing Cr-rich minerals, embedded in a gray-green matrix of kyanite, clinopyroxene, garnet, amphibole, zoisite, and rutile. Garnets occur as porphyroblasts or in coronas around clinopyroxene aggregates probably replacing former magmatic pyroxene. Relict gabbroic textures (sometimes pegmatoid) and whole rock geochemistry indicate a gabbroic cumulate origin. The REE pattern, displaying a slight positive Eu anomaly and a tea spoon-shaped LREE depletion is also indicative of a cumulate origin, as also noted by Pe Piper & Piper (2002) for the Othrys gabbro (as well as others in the Vourinos and Pindos ophiolitic suites) with the same unusual REE-pattern. The emerald-green Cr-rich nodules are unevenly distributed in the rock, and always enclosed in Cr-rich clinopyroxenes (up to 5.46% Cr2O3) which may exhibit Cr-diffusion haloes towards normal Cr-free matrix pyroxene. The nodules consist of diablastic chromite, rutile and Cr-rich kyanite of up to 15.67 wt% Cr2O3, Cr-bearing epidote, to which Cr-rich staurolite (up to 10.45% Cr2O3; XMg up to 0.68) and Cr-rich lawsonite (up to 9.17% Cr2O3) may exceptionally associate. Cr concentrations in kyanite and lawsonite are, to our knowledge, the highest reported so far. Cr-lawsonite was identified in a single sample, as small single phase inclusions armoured in Cr-kyanite. Equilibrium PT-conditions of 2.6 GPa and 610o C were derived from the garnet-mantled clinopyroxene aggregates using multi-equilibria calculation with the PTGIBBS routine of Brandelik & Massonne

80 Million Years of Prolonged and Localized Fluid flow on Shatsky Rise

NASA Astrophysics Data System (ADS)

Vermillion, K. B.; Koppers, A.; Heaton, D. E.; Harris, R. N.

2017-12-01

Shatsky Rise is a large igneous province (LIP) in the northwest Pacific Ocean, which formed at an unstable ridge-ridge-ridge (RRR) triple junction at the Jurassic-Cretaceous boundary. High resolution 40Ar/39Ar incremental heating analyses of samples from TAMU and Ori Massif, the two largest volcanic features on Shatsky Rise, yield mixing ages between fresh plagioclase and sericite alteration phases. Mixing ages range from several million years younger to 75 Myr younger than the eruption ages of 147 (TAMU Massif) and 140 Ma (Ori Massif). Sericitic alteration in plagioclase from IODP (Integrated Ocean Drilling Program) Expedition 324 Holes U1347A, U1349A, U1350A and U1346A on TAMU, Ori and Shirshov Massifs suggests pervasive fluid flow throughout Shatsky Rise in the first million years after eruption. Sericitic alteration in plagioclase from ODP (Ocean Drilling Program) Hole 1231B on the flanks of the TAMU Massif also suggests fluid flow. However, localized and very late stage fluid flow is found in the deepest highly altered pillow basalt sequence (Unit IV) of IODP Hole U1350A, where sericitic plagioclase samples is dated to be 65.8, 70.2 and 82.1 Ma. Since the sericite 40Ar/39Ar ages obtained are a mixture between fresh plagioclase and sericite alteration in the plagioclase, we estimate the true age of alteration, using the Verati and Jourdan (Geological Society, London, 2015) mixing model, showing that in IODP Hole U1350A (140 Ma eruption age) the sericite formed around 127 Ma or much later between 85 and 60 Ma. Thermal modeling suggests that throughout Shatsky Rise sustained fluid flow may occur and could be responsible for sericite alteration up to approximately 22 Myr after eruption. During this initial Shatsky Rise cool down phase, the natural geothermal gradient remains high enough to form sericite at temperatures of 100-215 °C. However, the same model shows that the conductive geothermal gradient alone does not sustain enough heat to form sericite 80 Myr

Plume-related mantle source of super-large rare metal deposits from the Lovozero and Khibina massifs on the Kola Peninsula, Eastern part of Baltic Shield: Sr, Nd and Hf isotope systematics

NASA Astrophysics Data System (ADS)

Kogarko, L. N.; Lahaye, Y.; Brey, G. P.

2010-03-01

The two world’s largest complexes of highly alkaline nepheline syenites and related rare metal loparite and eudialyte deposits, the Khibina and Lovozero massifs, occur in the central part of the Kola Peninsula. We measured for the first time in situ the trace element concentrations and the Sr, Nd and Hf isotope ratios by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometer) in loparite, eudialyte an in some other pegmatitic minerals. The results are in aggreement with the whole rock Sr and Nd isotope which suggests the formation of these superlarge rare metal deposits in a magmatic closed system. The initial Hf, Sr, Nd isotope ratios are similar to the isotopic signatures of OIB indicating depleted mantle as a source. This leads to the suggestion that the origin of these gigantic alkaline intrusions is connected to a deep seated mantle source—possibly to a lower mantle plume. The required combination of a depleted mantle and high rare metal enrichment in the source can be explained by the input of incompatible elements by metasomatising melts/fluids into the zones of alkaline magma generation shortly before the partial melting event (to avoid ingrowth of radiogenic isotopes). The minerals belovite and pyrochlore from the pegmatites are abnormally high in 87Sr /86Sr ratios. This may be explained by closed system isotope evolution as a result of a significant increase in Rb/Sr during the evolution of the peralkaline magma.

Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks of Burpala massi, Northern Baikal folded zone

NASA Astrophysics Data System (ADS)

Sotnikova, Irina; Vladykin, Nikolai

2015-04-01

Burpalinsky rare metal alkaline massif in the Northern Baikal folded zone in southern margin of Siberian Platform, is a of intrusion central type, created 287 Ma covering area of about 250 km2. It is composed of nepheline syenites and pulaskites grading to quartz syenites in the contacts. Veines and dykes are represented by shonkinites, sodalite syenite, leucocratic granophyres, alkali granites and numerous rare metal alkaline syenite pegmatites and two dykes of carbonatites. All rocks except for granites are cut by a large apatite-fluorite dyke rocks with mica and magnetite, which in turn is cut by alaskite granites dyke. The massif has been studied by A.M. Portnov, A.A. Ganzeev et al. (1992) Burpalinsky massif is highly enriched with trace elements, which are concentrated in pegmatite dykes. About 70 rare-metal minerals we found in massif. Zr-silicates: zircon, eudialyte, lovenite, Ti-lovenite, velerite, burpalite, seidozerite, Ca- seidozerite, Rosenbuschite, vlasovite, katapleite, Ca-katapleite, elpidite. Ti- minerals:- sphene, astrophyllite, ramsaite, Mn-neptunite bafertisite, chevkinite, Mn-ilmenite, pirofanite, Sr-perrerit, landauite, rutile, anatase, brookite; TR- minerals - loparite, metaloparite, britolite, rinkolite, melanocerite, bastnesite, parisite, ankilite, monazite, fluocerite, TR-apatite; Nb- minerals - pyrochlore, loparite. Other rare minerals leucophanite, hambergite, pyrochlore, betafite, torite, thorianite, tayniolite, brewsterite, cryolite and others. We have proposed a new scheme massif: shonkinites - nepheline syenites - alkaline syenite - quartz syenites - veined rocks: mariupolites, rare-metal pegmatites, apatite, fluorite rock alyaskite and alkaline granites and carbonatites (Sotnikova, 2009). Apatite-fluorite rocks are found in the central part of massif. This is a large vein body of 2 km length and a 20 m width cutting prevailing pulaskites. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and