Bicyclic sesquiterpenoids and diterpenoids in Australian crude oils

Bicyclanes previously reported only in heavily biodegraded Texas Gulf Coast crudes have been found to be ubiquitous in Australian crude oils of non-marine origin from four different basins. The compounds are present in oils, thought to be derived from the same or similar sources, that have undergone varying degrees of biodegradation. They are also found to be present in oils of different geological age. In addition a series of tricyclic diterpenoid hydrocarbons was common to four oils from the Gippsland Basin. Four of these compounds had the molecular formula C₂₀H₃₄ and mass spectral fragmentation patterns suggested they were mono-unsaturated diterpenoids. The presence of unsaturated diterpenoids in crude oils appears to be a unique observation. It is proposed that the diterpenoids may be the source of the bicyclanes also observed in these oils.     

Apatite/liquid partition coefficients for the rare earth elements and strontium

Sixteen sets of apatite/liquid partition coefficients (D^ap/liq) for the rare earth elements (REE; La, Sm, Dy, Lu) and six values for Sr were experimentally determined in natural systems ranging from basanite to granite. The apatite + melt (glass) assemblages were obtained from starting glasses artificially enriched in REE, Sr and fluorapatite components; these were run under dry and hydrous conditions of 7.5–20 kbar and 950–1120°C in a solid-media, piston-cylinder apparatus. An SEM-equipped electron microprobe was used for subsequent measurement of REE and Sr concentrations in coexisting apatites and quenched glasses. The resulting partition coefficient patterns resemble previously determined apatite phenocryst/groundmass concentration ratios in the following respects: (1) the rare earth patterns are uniformly concave downward (i.e., the middle REE are more compatible in apatite than the light and heavy REE); (2) D_REE^ap/liq is much higher for silicic melts than for basic ones; and (3) strontium (and therefore Eu²⁺) is less concentrated by apatite than are the trivalent REE. The effects of both temperature and melt composition on D_REE^ap/liq are systematic and pronounced. At 950°C, for example, a change in melt SiO₂ content from 50 to 68 wt.% causes the average REE partition coefficient to increase from ～7 to ～30. A 130°C increase in temperature, on the other hand, results in a two-fold decrease in D_REE^ap/liq. Partitioning of Sr is insenstitive to changes in melt composition and temperature, and neither the Sr nor the REE partition coefficients appear to be affected by variations in pressure or H₂O content of the melt.The experimentally determined partition coefficients can be used not only in trace element modelling, but also to distinguish apatite phenocrysts from xenocrysts in rocks. Reported apatite megacryst/host basalt REE concentration ratios [12], for example, are considerably higher than the equilibrium partition coefficients, which suggest that in this particular case the apatite is actually xenocrystic.A reversal experiment incorporated in our study yielded diffusion profiles of REE in apatite, from which we extracted a REEαCa interdiffusion coefficient of 2–4×10^?14 cm²/s at 1120°C. Extrapolated downward to crustal temperatures, this low value suggests that complete REE equilibrium between felsic partial melts and residual apatite is rarely established.     

The role of sphene as an accessory phase in the high-pressure partial melting of hydrous mafic compositions

In a high-pressure experimental study of reactions and possible melt products occurring in the deep continental crust or in subducted oceanic crust, sphene has been identified over a pressure range of 10–18 kbar and to temperatures of 1020°C. Sphene may be a refractory phase with up to 60% partial melting for hydrous mafic compositions. Sphene breaks down at lower pressure than the maximum pressure stability of amphibole in hydrous mafic compositions, and rutile rather than sphene is the important Ti-bearing accessory phase at pressures greater than 16–18 kbar. Sphene and rutile coexist to pressures as low as 14 kbar. This implies that amphibole eclogites containing primary sphene and no rutile have most likely formed at depths less than 45 km.The presence of minor sphene as a residual phase in equilibrium with low-Ti silicic liquids may have a marked effect on the REE distribution in derivative liquids. Thus melts in equilibrium with a garnet and sphene-bearing residuum may have less light-REE-enriched patterns than those predicted when garnet is a residual phase without coexisting sphene. This effect is modelled using REE patterns for sphenes from high-grade metamorphic terrains of western Norway.Both the new REE data and the experimental study have important implications for the genesis of low-Ti magmas formed in continental margins and island arcs.     

The high pressure experimental crystallization of staurolite in hydrous mafic compositions

The experimental crystallization of staurolite in two mafic compositions at high pressures (24–26 kb) and temperatures (740 °–760 ° C) is reported. This, together with a recent report of staurolite from metamorphosed basic igneous rocks from Fiordland, New Zealand, leads to the conclusion that Staurolite may be an important subordinate phase in the subducted lithosphere. The synthesized staurolites are more magnesian than those occuring in natural metapelitic assemblages and are characterized by relatively high Si, Ti, Mg, Ca, and low Al, Fe.     

Heat flow and heat generation in the superior province of the canadian shield

Nine new heat flow determinations and several measurements of radioactive heat generation are presented for the Superior Province. The average value of twenty-one heat flows now published for the Superior, corrected for Pleistocene glaciation, is 40 ± 8 mW/m². Heat generation values are low generally less than 3 μWW/m³. Although individual values of the ratio of thorium to uranium vary considerably, the geometrical average of four is lower than results from other Archean rocks.A linear relation between the heat flow and radioactive heat generation may exist. The reduced heat flow, 21 mW/m², and the characteristic depth, 14 km, from this relation are quite different from other heat flow provinces. Since large thicknesses of the crust have been eroded away and since the original heat generation was much larger than the values measured now, a linear relation equivalent to those found in younger heat flow provinces is not expected.To account for the large differences in heat flow and heat generation observed in different Archean shields an Archean crustal model is proposed which includes thin (2–4 km) radioactive surface veneers over some areas.The thermal parameters of a young crust may well determine whether or not it will survive. Since Archean times the heat flow of each newly stabilized region has been a constant, and since the time of formation or last orogeny the heat flow in each province has steadily decreased. The geothermal gradients in Archean crust have decreased the most, causing significant underplating, and increasing the strength of the crust.     

Oil pollution on Israeli coasts

Israel has long experienced the effects of oil discharged offshore into the Eastern Mediterranean. A 7-week survey discovered that the country now faces an additional inshore problem resulting from the changing regional pattern of oil transportation.     

RAS National Astronomy Meeting 2005

Shortly after Easter, more than 430 registrants gathered at the the University of Birmingham for the Royal Astronomical Society's annual National Astronomy Meeting, held jointly this year with the UK Solar Physics Meeting. Trevor Ponman summarizes the lively discussion and debate at the NAM.     

The Clementine mission —A 10-year perspective

Clementine was a technology demonstration mission jointly sponsored by the Department of Defense (DOD) and NASA that was launched on January 25th, 1994. Its principal objective was to use the Moon, a near-Earth asteroid, and the spacecraft’s Interstage Adapter as targets to demonstrate lightweight sensor performance and several innovative spacecraft systems and technologies. The design, development, and operation of the Clementine spacecraft and ground system was performed by the Naval Research Laboratory. For over two months Clementine mapped the Moon, producing the first multispectral global digital map of the Moon, the first global topographic map, and contributing several other important scientific discoveries, including the possibility of ice at the lunar South Pole. New experiments or schedule modifications were made with minimal constraints, maximizing science return, thus creating a new paradigm for mission operations. Clementine was the first mission known to conduct an in-flight autonomous operations experiment. After leaving the Moon, Clementine suffered an onboard failure that caused cancellation of the asteroid rendezvous. Despite this setback, NASA and the DOD applied the lessons learned from the Clementine mission to later missions. Clementine set the standard against which new small spacecraft missions are commonly measured. More than any other mission, Clementine has the most influence (scientifically, technically, and operationally) on the lunar missions being planned for the next decade.