metamorphic Rocks

“Stone runs” is the Falklands vernacular term for openwork boulder accumulations, which include extensive blockstreams like the famous Darwin “stone-river” and associated features such as stone stripes. Since the early 20th century, they have been interpreted as the product of a suite of periglacial processes, including frost-wedging, gelifluction, frost heave, frost-sorting and snowmelt runoff. Following a literature review, the results of recent field investigations of the valley-floor blockstreams of East Falkland are presented. Access to the internal structure of these forms provides evidence for the existence of a three-fold profile, with clear vertical size gradation presenting striking similarities with an inverted weathering profile. Micromorphological analyses, SEM, XRD, thin sections and grain-size analyses lead to the hypothesis of an alternative model of stone run formation. It is suggested that the material forming the stone run profile lato sensu (including the superficial pavement) is not of periglacial origin, but derives directly from the stripping and accumulation downslope of a regolith, possibly Tertiary in age and formed under subtropical or temperate conditions. The valley-floor stone runs should, therefore, be considered as complex polygenetic landforms that may have formed according to a six-stage scenario, including in situ chemical weathering, regolith stripping by mass movements, soil formation, further regolith stripping, downslope accumulation and matrix washing-out (all phases possibly achieved by the Early Quaternary). Periglacial reworking of the stone run material would have operated at a “final” stage, i.e. during Quaternary cold stages, with boulder bioweathering and limonite-staining operating during the temperate intervals including the present one. The suggested antiquity of the Falklands blockstreams is in accordance with Caine's pioneer interpretation of Tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from Scandinavia and North America.

Basement rock reservoirs are a special type of oil and/or gas reservoir, which has been usually neglected until recently as a target for exploration. In this study, it is aimed to investigate the hydrocarbon potential of Niğde Massif. The n-alkane hydrocarbons found in the water samples collected are the mature petroleum hydrocarbons, which are the geochemical evidence for a working petroleum system in the study area. The dom structures in which they are suitable to be entrapped and protected for hydrocarbons in a predominantly SW-NE orientation, where metamorphic rocks in which granite has been located in its center have formed, is the possible hydrocarbon reservoir in the study area. The geochemical exploration methodology used in this study may be a new method that can eliminate the discovery of hydrocarbons in the metamorphic massif and granitic rocks by chance.

Keywords: Basement rock, Metamorphic rock, Granite, Reservoir-targeted oil and gas exploration, Hydrocarbon-rich water

Vertical electrical resistivity soundings were conducted in order to delineate groundwater potential aquifers in Peddavanka watershed, which is a catchment of about 398 km2 in Anantapur District, Andhra Pradesh, India. The main lithologic units in the watershed are quartzite, limestone, shale, and alluvium. Ninety-nine vertical electrical soundings were conducted using the Schlumberger configuration, covering the entire watershed. The data were interpreted with the help of master curves and auxiliary point charts. Interpretations of VES were used to generate a top layer apparent resistivity contour map and longitudinal conductance map. Isoresistivity contour maps were prepared and interpreted in terms of resistivity and thickness of various sub-surface layers using computer software (SURFER), and isocontour diagrams depicting the depth to bedrock were prepared. Resistivity results were correlated with the existing lithology. Based on the depth to bedrock, the thickness of the saturated layer and the resistivity of the second layer, a groundwater potential map has been prepared, in which good, moderate, and poor zones are classified. The study reveals that the weathered and fractured portions in shale and limestone that occur in the southernmost and central portions of the watershed area constitute the productive water-bearing zones categorized as good groundwater potential aquifers.

Koprubasi, located within Manisa Province near the Izmir, is the biggest uranium mine where uranium ores originate from Neogene aged altered sandstone and conglomerate layers. The main objective of this study is to determine the radiation hazard associated with radioactivity levels of uranium ores, and the rocks and sediments around Koprubasi. In this regard, measured activity levels of 226Ra, 232Th and 40K were compared with world averages. The average activity levels of 226 Ra, 232Th and 40K were measured to be 5369.75, 124.78 and 10.0 Bq/kg in uranium ores, 24.32, 52.94 and 623.38 Bq/kg in gneiss, 46.24, 45.13 and 762.26 Bq/kg in sandstone and conglomerate, 73.11, 43.15 and 810.65 Bq/kg in sediments, respectively. All samples have high 226Ra and 40K levels according to world average level. As these sediments are used as construction materials and in agricultural activities within the study area, the radiation hazard are calculated by using dose rate (D), annual effective dose rate (He), radium equivalent activity (Raeq) and radiation hazard index (Iyr). All the samples have Raeq levels that are lower than the world average limit of 370 Bq/kg. On the other hand, D, He and Iyr values are higher than world average values. These results indicate that the uranium ores in the Koprubasi is the most important contributor to the natural radiation level. The radioactivity levels of sediments and rocks make them unsuitable for use as agricultural soil and as construction materials. Moreover, it is determined that shallow groundwater in sediments and deep groundwater in conglomerate rocks and also surface water sources in the Koprubasi have high 226Ra content. According to environmental radioactive baseline, some environmental protection study must be taken in Koprubasi uranium site and the environment.

Field observations of pseudotachylites and experimental studies of high-speed friction indicate that melting on a slipping interface may significantly affect the magnitude of shear stresses resisting slip. We investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer, thermodynamics of phase transitions, and fluid mechanics. Results of laboratory experiments conducted at high (order of m/s) slip velocities but low (order of MPa) normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength, presumably due to viscous effects. However, extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses. When transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip, decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction, resulting in a nearly complete stress drop ("thermal runaway"). The amount of energy dissipation associated with the formation of pseudotachylites is governed by the temperature dependence of melt viscosity and the average clast size in the fault gouge prior to melting. Clasts from a coarse-grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of nonequilibrium overheating. The maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus (via viscous braking, and slip arrest) or liquidus (via thermal runaway and vanishing resistance to sliding). Our modeling results indicate that the thermally activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths but might be relevant for quartz-rich rocks, especially at shallow (<5-7 km) depths where the driving shear stress is relatively low.

Kulshan caldera (4.5×8 km), at the northeast foot of Mount Baker, is filled with rhyodacite ignimbrite (1.15 Ma) and postcaldera lavas and is only the third Quaternary caldera identified in the Cascade arc. A gravity traverse across the caldera yields a steep-sided, symmetrical, complete Bouguer anomaly of −16 mGal centered over the caldera. Density considerations suggest that the caldera fill,