Heavy carbon in individual oxide grains from the Murchison meteorite

The carbon isotopic composition of individual oxide grains from Murchison HF—HCl acid residue CFOc has been measured in the ion microprobe. Many grains (Mg-spinel, Cr-spinel, and Fe-oxide) contain carbon with large¹³C excesses ranging to 7000‰ (corresponding to¹²C/¹³C= 11). In most cases the carbon is present as micron-sized subgrains. The association of silicon with the anomalous carbon points towards SiC as carrier. If this tentative identification is correct then the SiC grains most likely originated in the circumstellar atmospheres of red giants. Oxide grains in which the ¹⁸O/¹⁶O ratio has also been measured show variable¹⁶O excesses which are not correlated with the¹³C excesses. This indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated.     

Pb-isotopic compositions of volcanic rocks in the West and East Philippine island arcs: presence of the Dupal isotopic anomaly

The Philippine islands are situated between two oppositely dipping zones of seismicity. With the exception of a few areas, such as in the west central Philippines where the North Palawan continental terrane (NPCT) has collided with the archipelago, these seismic zones are well defined to depths of 200 km. Active volcanic chains overlay segments in each of these zones, suggesting that subduction is presently taking place both east and west of the islands. Lavas we have studied are thus divided between what has been termed the West Philippine arc and the East Philippine arc.West Philippine arc volcanic rocks which were extruded before the Philippine archipelago collided with the NPCT, or which are younger than the collision but crop out hundreds of kilometers from the collision zone, and all but one of the rocks from the East Philippine arc fall in the MORB field on²⁰⁷Pb/²⁰⁴Pb versus²⁰⁶Pb/²⁰⁴Pb covariation diagrams. This is surprising considering the frequency with which arc materials have²⁰⁷Pb/²⁰⁴Pb ratios higher than those of MORB, the highBa/REE and Sr/REE ratios in the lavas and the possibility of sediment subduction given the small accretionary prisms. All of these rocks have high²⁰⁸Pb/²⁰⁴Pb ratios with respect to Pacific and Atlantic Ocean MORB, but are similar to Indian Ocean MORB and IOB. Thus the Philippines consist of island arcs with the peculiar Dupal isotopic anomaly documented between 0° and 60°S in the southern hemisphere and particularly in the Indian Ocean region. This demonstrates that the Dupal isotopic anomaly is not restricted to the southern hemisphere, or to MORB and OIB.Post-collision rocks cropping out near the NPCT, in the West Philippine arc, have elevated²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios that could be attributed to assimilation of the newly introduced continental crust (NPCT) by mantle-derived magmas or to the addition of a sedimentary component to mantle-derived magmas.     

Tectono-magmatic evolution of the 1.9-Ga great bear magmatic zone, Wopmay orogen, northwestern Canada

The 1875-1840-Ma Great Bear magmatic zone is a 100-km wide by at least 900-km-long belt of predominantly subgreenschist facies volcanic and plutonic rocks that unconformably overlie and intrude an older sialic basement complex. The basement complex comprises older arc and back-arc rocks metamorphosed and deformed during the Calderian orogeny, 5–15 Ma before the onset of Great Bear magmatism. The Great Bear magmatic zone contains the products of two magmatic episodes, separated temporally by an oblique folding event caused by dextral transpression of the zone: (1) a 1875-1860-Ma pre-folding suite of mainly calc-alkaline rocks ranging continuously in composition from basalt to rhyolite, cut by allied biotite-hornblende-bearing epizonal plutons; and (2) a 1.85-1.84-Ga post-folding suite of discordant, epizonal, biotite syenogranitic plutons, associated dikes, and hornblende-diorites, quartz diorites, and monzodiorites. The pre-folding suite of volcanic and plutonic rocks is interpreted as a continental magmatic arc generated by eastward subduction of oceanic lithosphere. Cessation of arc magmatism and subsequent dextral transpression may have resulted from ridge subduction and resultant change in relative plate motion. Increased heat flux due to ridge subduction coupled with crustal thickening during transpression may have caused crustal melting as evidenced by the late syenogranite suite. Final closure of the western ocean by collision with a substantial continental fragment, now forming the neoautochthonous basement of the northern Canadian Cordillera, is manifested by a major swarm of transcurrent faults found throughout the Great Bear zone and the Wopmay orogen.Although there is probably no single evolutionary template for magmatism at convergent plate margins, the main Andean phase of magmatism, exemplified by the pre-folding Great Bear magmatic suite, evolves as larger quantities of subduction-related mafic magma rise into and heat the crust. This results in magmas that are more homogeneous, siliceous, and explosive with time, ultimately leading to overturn and fractionation of the continental crust.     

A detailed magnetic study of Cobb Seamount

Results from a detailed magnetic survey and paleomagnetic measurements on oriented rock samples from the summit of Cobb Seamount indicate that the Seamount is complexly magnetized, recording at least one field reversal. The remanent magnetization probably resides in single-domain titanomagnetite (10 mole % ulvo¨spinel in solid solution with magnetite) which is unlike that found in dredged basalts. The simplest explanation for this difference is that the Seamount's pinnacle formed subaerially.     

Earthquake swarms of Mt Cameroon, West Africa

Historical and recent instrumental studies of the central region of the Cameroon Volcanic Line clearly indicate the occurrence of earthquake swarms of volcanic origin. Analyses of more than 3000 micro-earthquakes recorded between 1985 and 1992 show a well-defined seismic pattern characterised by single and swarm events with duration magnitudes between 2 and 3 at depths down to 20 km. On average, the earthquakes here occur at the rate of about 2 events every 3 days with occasional earthquake swarms, which greatly increase this number. The seismic swarms comprising felt earthquakes are shown to be sometimes preceded by, simultaneous with, or followed by swarms from Bimbia and Equatorial Guinea. Mapped epicentres of some of these swarms correspond to regions of volcanic gas emissions and are parallel to the fissures on Mt Cameroon and to the inferred direction of the underlying shear zone.The quiescent periods between swarms are seen to double each year since 1986. This observation was used to predict a major seismic swarm which occurred in 1993. The data coupled with historical data, are used to infer the involvement of a magma chamber in the generation of the earthquake swarms in the region. Since the installation of the network, no eruption has been observed on Mt Cameroon. This warrants more observation in order to study the seismicity that may precede, accompany or follow an eruption of the mountain.     

Aquaculture and the Postproductive Transition on the Maine Coast

Aquaculture is the global food system's fastest growing sector. The postproductive transition—the shift away from commodity production toward more consumption‐oriented land uses—is common in many coastal areas as well. This paper examines the intersection of these trends in a U.S. state, Maine, with expanding aquaculture and extensive coastal, rural economic and demographic change. It examines interactions between coastal landowners and aquaculture farmers at aquaculture lease hearings in the state's three main aquaculture regions. Landowners are often uncertain about aquaculture because it is new and unfamiliar. Farmers use lease hearings to educate coastal landowners about farm operations, and farmers respond to concerns by altering their operations to fit landowners’ priorities. However, comparative analysis of the three regions reveals divergent histories and geographies leading to different levels of conflict. This study shows the value of applying rural postproductive transition theory to coastal regions and aquaculture development.     

Influence of small-scale gold mining and toxic element concentrations in Bonsa river,Ghana: a potential risk to water quality and public health

A preliminary assessment of toxic element pollution caused by artisanal and small-scale gold mining in the Bonsa river of Ghana as well as the influence of TOC and SO₄ ^2? concentration on these traces in the sediment has been determined. With the exception of mercury (Hg), manganese (Mn), and arsenic (As), the concentration of aluminum (Al) in filtered river water exceeded the WHO guideline limit of 0.1 mg L^?1 in drinking water. Analyses of toxic element in sediment using Canadian Sediment Quality Criteria, contamination factor, geoaccumulation index, and enrichment factor indicate that river sediment is severely contaminated with Hg confirming the negative impact of the amalgamation technique in gold beneficiation in Ghana. The level of Hg in the surface water exceeded reported values from some rivers in Africa, Asia, and South America. The ranking order of the mean element concentration in both matrices followed the conservative order of traces found in the Earth crust except copper, which was below the detection limit of 0.01 mg kg^?1. A Pearson correlation matrix of the toxic element and geology of the river bedrock indicates that the Hg contamination is of anthropogenic origin whilst As, Mn, and Al are the result of natural enrichment. The partitioning of elements in the sediment compartments is independent of TOC and SO₄ ^2? concentration. Health-risk assessment based on average daily dose, hazard quotient, and cancer risk indicates that Hg is a health risk to the human population. In conclusion, the study has shown that there is a likely anthropic affection of the river and that this situation has worsened since earlier studies. In order to sustain aquatic life and to prevent future human health hazard, an immediate mercury remediation in the river is recommended.     

The effect of source area and atmospheric transport on mineral aerosol collected over the North Pacific Ocean

Aerosol samples collected on two North Pacific cruises were analyzed for rock-magnetic properties, grain size and <2 μm and 2–20 μm mineralogy. These sedimentological results were compared with isentropic air mass trajectories in order to study the effects of source region and atmospheric transport on the mineral aerosol. The results indicate that there are differences in the aerosol composition and grain size for two broad source regions. Aerosols which originate from west of the Pacific are characterized by abundant, fine-grained aerosol, which has a high coercivity magnetic composition, and is relatively enriched in kaolinite. Aerosols originating from continents to the north and east of the Pacific basin are much less abundant, contain coarse-grained material with a low coercivity magnetic component, and the mineralogy is relatively enriched in plagioclase. Comparison of the mineral aerosol from Asia with atmospheric transport time indicated that the concentration of the mineral aerosol decreases with increasing transport time. The mineral aerosol is compositionally fractionated as it moves away from the continental source region, with a relative decrease in the primary minerals quartz and plagioclase and an increase in the smectite, illite and chlorite concentration with increasing transport time.     

Planetary nebulae in planetary and binary systems

The problem of the survival of a low-mass secondary orbiting a primary that becomes a planetary nebula is studied. The values of the mass of the primary are 1.0, 1.5, and 2.0M ; the values of the mass of the secondary 0.001M , 0.01M and 0.1M . The orbital decay and mass of the secondary due to accretion and gravitational drag in the common envelope are presented. The possible application of the results to V471 Tau, UU Sge, WZ Sge and the Sun-Jupiter system are discussed.