Searchlight pluton, a steeply tilted, 10 km thick Miocene intrusion in southern Nevada, exposes a zone with abundant, 5-400 m long blocks of Proterozoic gneiss. Blocks are present within a pair of subparallel horizons that make up a 2 km thick zone and extend 5 km laterally away from the plutons N-margin, slightly oblique to the initially subhorizontal boundary between the pluton's middle granite and lower quartz monzonite units. Blocks are commonly polylithologic and well foliated, with long and intermediate dimensions parallel to their own foliation, the foliation of the host granitoid, and the orientation of flattened magmatic enclaves. Blocks have a sub-angular tabular geometry with an average aspect ratio of ~3.7. We interpret the blocks as stoped and emplaced after repeated wall collapse events onto a crystal-rich mush and transported laterally primarily by matrix-supported debris flows. SHRIMP ages of granitoid zircons constrain block emplacement between ~16.1-16.3 Ma, a small fraction of the lifetime of the pluton (15.8-17.7 Ma). Though blocks are locally abundant (~20% exposure over ~0.3 km2), they constitute <1% of the entire exposure, suggesting that stoping played a minor role in the emplacement process. LA-ICPMS analysis of zircons from host granitoids suggest minor host contamination by block disaggregation - a sample adjacent (15 cm) to a block contained ~8 % inherited Proterozoic zircons, while samples from elsewhere in the pluton yielded <<1%. Scaled settling experiments suggest tabular blocks deposit with their long and intermediate axes parallel to surfaces; blocks with a geometry controlled by foliation would on average possess a subparallel alignment of both their geometric shape and foliation. Experiments also show that fluid sublayers may become trapped beneath blocks and allow lateral transport by hydroplaning.

EARTH AND ENVIRONMENTAL SCIENCES MID-MIOCENE RHYOLITE SEQUENCE, HIGHLAND RANGE, NV: RECORD OF MAGMA EVOLUTION AND ERUPTION FROM THE SEARCHLIGHT PLUTON MAGMA CHAMBER LINDY L. COLOMBINI Thesis under the direction of Professor Calvin Miller The Highland Range in southern Nevada contains a ~3 km-thick sequence of pre- to synextensional volcanic rock that records both large-magnitude Miocene extension and the evolution of large magma system. A km-thick sequence of rhyolite in the southeast part of the range was emplaced above a thick section of trachyandesite and trachydacite at 16.2-16.0 Ma. The lower half of the sequence comprises trachydacite lavas, which abruptly give way to tuffs and inter-fingered rhyolite lavas that mark a transition to a more explosive period of eruption. The uppermost unit of the sequence is a rhyolite lava that is heavily contaminated by mafic enclaves, lithics, and xenocrysts. Basaltic trachyandesite overlies this upper rhyolite. SHRIMP analysis of Ti and other trace elements in zircon from two samples near the top of the sequence documents strongly fluctuating T (720-920°C) and evolution of melt compositions; generally, rims grew at lower T from more evolved melt. Zr-in-sphene thermometry indicates that these phenocrysts grew at the lower temperatures recorded by the zircon rims. The rhyolite sequence appears to have erupted from the middle granite zone of the nearby Searchlight pluton, which is the same age and similarly evolved toward highly silicic compositions, and overlies slightly older quartz monzonite (cf. Bachl et al. 2001; J Miller et al. 2007). MREE depletion in both the rhyolite lavas and in the high-silica granites of Searchlight pluton indicates sphene fractionation.

This study examines the effect that rainsplash-induced sediment mounds beneath desert shrubs have on sediment flux in semi-arid environments. Mounds form beneath shrubs by differential splash of particles beneath shrub canopies (i.e. a grain activity gradient). Measurements of mounds beneath rabbitbrush and broom snakeweed in New Mexico reveal that mounds range in volume from 1,000 to 16,000 cm3. Mound volume increases with increasing shrub size. A sediment transport model is developed to describe how mound development affects sediment flux by solving the Fokker-Planck Equation. Advection of sediment is determined by the local topographic gradient and mass diffusion is controlled by the activity gradient. Sediment stored in mounds is not available for downslope transport, so a local divergence of flux develops, whereby the land surface downslope of a mound experiences decreasing elevation. A decrease in sediment transport rates is observed up to two meters downslope of a mound during 40 years of shrub growth. After shrub mortality, local sediment flux increases due to the increased hillslope gradient of the mound. Within 100 years of simulated mound development, a mound persists for at least 60 years after shrub mortality, causing elevated local sediment flux. On a hillslope scale with a dynamic shrub population, these changes in sediment flux may lead to significant changes in topography over centuries to millennia. The additive effect of shrubs on sediment flux suggests that modeling larger hillslopes may not involve solving the Fokker-Planck Equation, but may be solved algebraically.

Gold mineralization in the moyar-bhavani shear zone around Nilambar, Kerala, India.

West bengal, India

Foraminiferal and biostratigraphical

Geophysical, geochemical & hydrological studies

Associated rock types, south west of Rajapalaiyam, Tamil Nadu.

Water quality in the river Arkavathi, Karnataka, India.

Around Biligiri-Rangan hill ranges Karnataka, India