Structural development of the Tso Morari ultra-high pressure nappe of the Ladakh Himalaya

A continental subduction-related and multistage exhumation process for the Tso Morari ultra-high pressure nappe is proposed. The model is constrained by published thermo-barometry and age data, combined with new geological and tectonic maps. Additionally, observations on the structural and metamorphic evolution of the Tso Morari area and the North Himalayan nappes are presented. The northern margin of the Indian continental crust was subducted to a depth of > 90 km below Asia after continental collision some 55 Ma ago. The underthrusting was accompanied by the detachment and accretion of Late Proterozoic to Early Eocene sediments, creating the North Himalayan accretionary wedge, in front of the active Asian margin and the 103–50 Ma Ladakh arc batholith. The basic dikes in the Ordovician Tso Morari granite were transformed to eclogites with crystallization of coesite, some 53 Ma ago at a depth of > 90 km (> 27 kbar) and temperatures of 500 to 600 °C. The detachment and extrusion of the low density Tso Morari nappe, composed of 70% of the Tso Morari granite and 30% of graywackes with some eclogitic dikes, occurred by ductile pure and simple shear deformation. It was pushed by buoyancy forces and by squeezing between the underthrusted Indian lithosphere and the Asian mantle wedge. The extruding Tso Morari nappe reached a depth of 35 km at the base of the North Himalayan accretionary wedge some 48 Ma ago. There the whole nappe stack recrystallized under amphibolite facies conditions of a Barrovian regional metamorphism with a metamorphic field gradient of 20 °C/km. An intense schistosity with a W–E oriented stretching lineation L₁ and top-to-the E shear criteria and crystallization of oriented sillimanite needles after kyanite, testify to the Tso Morari nappe extrusion and pressure drop. The whole nappe stack, comprising from the base to top the Tso Morari, Tetraogal, Karzok and Mata–Nyimaling-Tsarap nappes, was overprinted by new schistosities with a first N-directed and a second NE-directed stretching lineation L₂ and L₃ reaching the base of the North Himalayan accretionary wedge. They are characterized by top-to-the S and SW shear criteria. This structural overprint was related to an early N- and a younger NE-directed underthrusting of the Indian plate below Asia that was accompanied by anticlockwise rotation of India. The warping of the Tso Morari dome started already some 48 Ma ago with the formation of an extruding nappe at depth. The Tso Morari dome reached a depth of 15 km about 40 Ma ago in the eastern Kiagar La region and 30 Ma ago in the western Nuruchan region. The extrusion rate was of about 3 cm/yr between 53 and 48 Ma, followed by an uplift rate of 1.2 mm/yr between 48 and 30 Ma and of only 0.5 mm/yr after 30 Ma. Geomorphology observations show that the Tso Morari dome is still affected by faults, open regional dome, and basin and pull-apart structures, in a zone of active dextral transpression parallel to the Indus Suture zone.     

Abnormal development of Dentalium due to the Amoco Cadiz oil spill

A comparison was made between the development of Dentalium eggs, spawned by animals, collected before and after the Amoco Cadiz oil spill. Development of eggs from animals collected before the oil spill was significantly better than development of eggs from animals collected after the oil spill. It is suggested that development is affected by oil hydrocarbons, accumulated during oogenesis in the lipidrich phases of the oocytes.     

Mass spectrometric evidence for organic constituents in tektites

Since the physical and chemical events leading to the formation of organic molecules in numerous carbon-containing meteorites (e.g. paraffins, alcohols and aromatics have been identified) have been studied in considerable detail, it becomes important to compare and relate similar studies with tektites. For this purpose, various tektite specimens were heated to temperatures up to 1500°C and the vaporizing molecular species identified with a mass spectrometer. In this technique, volatile constituents are selectively vaporized from the sample, ionized to electrically charged positive particles by bombardment with high energy electrons, and separated in an electric and magnetic field according to their respective molecular weights. Mass spectra for the direct volatilization of individual tektites from the Philippine Islands, Viet Nam, Thailand, Australia, Czechoslovakia and Texas were compared with those obtained from the carbonaceous Pueblito de Allende chondrite and terrestrial obsidian.     

Late Holocene temperature record from southwestern Australia: evidence of global warming from deep boreholes*

A ground surface temperature history for the last 500 years was created from the inversion of geophysical temperature logs in four deep (?>?1400?m) boreholes on the Blackwood Plateau in southwestern Australia. Modelled temperature changes show close agreement with ground surface temperature histories from elsewhere in the world for this period and indicate that the Blackwood Plateau has experienced a 0.4 K increase in mean temperature between the beginning of the sixteenth century and the 1980s, with more than half of the increase having taken place after 1900. The modelling indicates that the highest temperatures in the region for the last 500 years were recorded during the twentieth century, and that the current rate of temperature change of more than 0.5° K per century is higher than at any other time during this time period.     

Aspects of the differences in the erodibility of the waste rock dump and natural surfaces, Ranger Uranium Mine, Northern Territory, Australia

Small-scale flume experiments on the waste rock dump of Ranger Uranium Mine, Northern Territory, Australia, show that the unmanaged surface of the dump is 10–100 times more erodible than adjacent natural hillslopes. Silt and clay are preferentially removed and their proportion of the total sediment load is enhanced over their content in surface sediment. There is strong evidence that a low threshold of erosion does not exist and that even the smallest of flows across the waste rock dump can erode and transport some surface material. The erodible dump surface and the preferential removal of silt-clay could degrade ecosystems both on the dump and off-site. Rehabilitation of the waste rock dump will require special attention to erosion and its management.