ATTILA: atmospheric tracer transport in a Lagrangian model

The model ATTILA has been developed to treat the global-scale transport of passive trace species in the atmosphere within the framework of a general circulation model (GCM). ATTILA runs online within the GCM ECHAM4 and advects the centroids of 80.000 to 190.000 constant mass air parcels. Each trace constituent is thereby represented by a mass mixing ratio in each parcel. ATTILA contains state-of-the-art parameterizations of convection, turbulent boundary layer mixing and inter-parcel transport, and provides an algorithm to map the tracer concentrations from the trajectories to the ECHAM model grid. The transport characteristics of ATTILA are evaluated against observations and the standard semi-Lagrangian transport scheme of ECHAM by two experiments. (1) We simulate the distribution of the short-lived tracer radon (²²²Rn) in order to examine fast vertical transport over continents, and long-range transport from the continents to remote areas. (2) We simulate the distribution of radiocarbon (¹⁴C) from nuclear weapon tests in order to examine upper tropospheric and stratospheric transport characteristics. Contrary to the semi-Lagrangian scheme, ATTILA shows a greatly reduced meridional transport in the upper troposphere and lower stratosphere, and a reduced downward flux from the stratosphere to the troposphere, especially in mid-latitudes. Since ATTILA is a numerically non-diffusive scheme, it is able to maintain steep gradients, which compare better to the observations than the rather smooth gradients produced by the semi-Lagrangian scheme.     

The role of the Mediterranean region in the development of sedimentary geology: a historical overview

The Mediterranean region, source of so much knowledge in the world, is the site of major advances in sedimentary geology. In addition to its economic and cultural richness, the geological and geographic diversity of the region, plus its active geological processes, have long stimulated indigenous scholars, along with attracting talented outsiders such as Steno, Lyell, Walther, Kuenen and Bagnold. Since classical Hellenic times, debates about the origin of fossils and the changing positions of sea-level served as catalysts for studies of sediments, sedimentary rocks and ancient life. The presence of geologically young and easily interpreted marine shell beds in many Mediterranean coastal areas adjacent to their modern analogues was a particular stimulus for progress in sedimentary geology, for example, the very advanced stratigraphic ideas of Leonardo da Vinci, expressed solely in his unpublished notebooks. Impeding progress was the geological complexity of facies, faunas and structure in the circum-Mediterranean Alpine belts. Once the secrets of these were unlocked, however, the Mediterranean region became the source of major discoveries about syn-sedimentary tectonics, carbonate platforms, pelagic and anoxic sediments, turbidites, evaporites, aeolian processes, cyclostratigraphy, magnetic stratigraphy and impact events. In many of these Mediterranean discoveries, the critical element is the occurrence of extensive Mesozoic-Cenozoic pelagic successions whose precise age dating was made possible by pioneering biostratgraphic studies using microfossils.     

IN THE WAY OF DEVELOPMENT: INDIGENOUS LAND‐RIGHTS ISSUES IN MALAYSIA*

The Malaysian government regards the country's indigenous peoples as “backward” and in need of “modernization.” It aims to assimilate them into the so‐called mainstream society and to incorporate their lands and resources into national and global markets. These policy objectives leave little scope for indigenous groups to pursue their own life projects. Indigenous communities want to share in the benefits of economic development, but they are not prepared to give up their lands, cultures, and identities to obtain them. They have attempted to ward off the negative consequences of development projects by forming advocacy nongovernmental organizations, engaging in various forms of resistance, and seeking redress of their grievances in the courts. Most of all, they want recognition of their rights to land and place. The efficacy of their agency is severely hampered by a battery of repressive laws and by their own political weakness.     

The Geochemistry of Lavas from the Gomores Archipelago, Western Indian Ocean: Petrogenesis and Mantle Source Region Characteristics

New mineral and bulk-rock analyses, as well as Nd, Sr and Pbisotope compositions are presented for lavas from Grande Comore,Moheli and Mayotte, thru of the four main islands of the ComoresArchipelago in the western Indian Ocean, and these data an usedto evaluate the petrogenesis, evolution and mantle source regioncharacteristics of Comorean lavas. The typically silica-undersaturated,alkaline lavas from all three islands can be grouped into twodistinct types: La Grille-type (LGT) lavas, which display strongrelative depletions in K, and Karthala-type (KT) lavas, whichdo not. With the exception of the lavas erupted by La Grillevolcano on Grande Comore, which exhibit the petrographic andgeochemical characteristics expected of primary mantle-derivedmagmas, all Comorean lavas analysed have experienced compositionalmodifications after they segregated from their source regions.Much of this variation can be explained quantitatively by fractionalcrystallization processes dominated by the fractionation ofolivineand clinopyroxene. Semi-quantitative modelling shows that theconsistent and fundamental difference in composition betweenK-depleted LGT lavas and normal KT lavas can be attributed topartial melting processes, provided amphibole is a residualmantle phase after extraction of LGT magmas at low degrees ofmelting. Low absolute abundances of the heavy rare earth elementsin LGT magmas are interpreted to reflect partial melting withinthe garnet stability field In contrast, KT magmas, which donot show relative K depletions, are considered to be the productsof somewhat larger degrees of partial melting of an amphibolefreesource at comparatively shallower depths. Whereas the Nd andSr isotopic compositions of Comorean lavas (which show a significantrange: ⁸⁷Sr/⁸⁶Sr = 0.70319–0.70393; ¹⁴³Nd/Nd = 0.51263–0.51288)bear evidence for a time-averaged depletion in incompatibleelements, the high incompatible element abundances of the lavasare interpreted to reflect the effects of a recent mantle enrichmentevent. At depths well within the garnet stability field thismantle enrichment is interpreted to have taken the form of modalmetasomatism with the introduction of amphibole (giving riseto the source of LGT magmas), whereas cryptic metasomatism tookplace at shallower levels (giving rise to the source of KT lavas).The Nd, Sr and Pb isotope signature of the majority of Comoreanlavas (both LGT and KT) is proposed to be the result of predominant4contributions from a somewhat heterogeneous source4 4 4 presentativeof the ambient sub-Comorean mantle, comprising a mixture betweena HIMU component and a component on the depleted portion ofthe mantle array (possibly the source of Indian Ocean MORB),with only limited contributions from an EM I plume component.The lavas erupted by Karthala volcano (the youngest Comoreanlavas), however, have significantly different isotopic compositionsfrom all other Comorean lavas (lower ¹⁴³Nd/¹⁴⁴Nd and higher⁸⁷Sr/⁸⁶Sr), suggesting increased contributions from the EM Icomponent. KEY WORDS: basalt petrogenesis; Comores; mantle geochemistry; ocean island basalts ^*Telephone: 27-21-6502921. Fax: 27-21-6503781 e-mail: alr{at}geology.uct.ac.za.     

Potassic Volcanic Rocks in NE China: Geochemical Constraints on Mantle Source and Magma Genesis

Potassic volcanic rocks from the Wudalianchi, Erkeshan and Keluo(WEK) fields in NE China are located between the Mesozoic SongliaoBasin and the Palaeozoic Xing'am Mountains fold belt. Theserocks erupted during three main eruptive episodes-Miocene (9•6–7•0Ma), Pleistocene (0•56–0•13 Ma) and Recent (AD1719–1721)-and are subdivided into three types-olivineleucitite, leucite basanite and trachybasalt—on the basisof modal composition. In comparison with Cenozoic alkaline basaltsfrom East China that are similar to oceanic island basalts (OIBs),WEK volcanic rocks are lower in Al₂O₃, CaO, Fe₂O3 and Sc, buthigher in K₂O (3•5–7•1 wt %), K₂O/Na₂O (>1)and incompatible elements. High ⁸⁷Sr/⁸⁶Sr (0•7050–0•7056),low ¹⁴³Nd/¹⁴⁴Nd (0•51238–0•51250) and ²⁰⁶Pb/²⁰⁴Pb(17•06–16•61) ratios also distinguish them fromoceanic and Chinese basalts. Trace element and isotope dataindicate that a post-Archaean subcontinental lithospheric mantlesource similar to the postulated EM1 component (enriched mantlewith low ^l43Nd/¹⁴⁴Nd and moderate high ⁸⁷Sr/⁸⁶Sr) must haveplayed a significant role in magma generation. The source rockis considered to be refractory phlogopite-bearing garnet peridotiteheterogeneously enriched in both large ion lithophile elementsand light rare earth elements by ancient metasomatism duringProterozoic times. This source may have mixed recently withOIB-like melts, but has not been modified by subduction of theKula-Pacific plate. Primitive WEK potassic magma was generatedby a low degree of partial melting, initiated by an extensionalphase beginning in the late Tertiary, at pressures of 20–45kbar and in the presence of mixed volatile components of H₂O,CO₂ and halogens. KEY WORDS: potassic volcanic rocks; NE China; geochemistry; montle sourc ^*Corresponding author. Present address: Centre for Petrology and Lithoipheric Studies, School of Earth Sciences, Macquarie University, NSW 2109, Australia     

Experimental verification of aeolian saltation and lee side deposition models

We report results of experiments intended to test the validity of a model for aeolian saltation and the resulting pattern of deposition on the lee side of aeolian dunes. In steady sea-breeze conditions on a 3-m-tall dune at Point Año Nuevo, California, we measured simultaneously the near-brink wind speed and the deposition on both horizontal and lee face collector platforms. We then used the details of the deposition patterns to constrain approximate values of parameters in a numerical model of the deposition rate that incorporates the essence of the saltation process. Best fits to the data constrain a parameter that controls the probability distribution of liftoff speeds. In addition, the total vertical number flux of grains is constrained to roughly 10⁷?10⁸ grains m^?2 s^?1 at shear velocities of 0.33–0.40 m s^?1. The lee side deposition pattern, which shows the expected maximum in deposition rate at a distance of several decimetres from the brink, is also well fit by the model. In addition, simultaneous collection of horizontal and lee deposition patterns, along with the numerical simulation of these patterns, strongly implies that the windfield in the lee of this particular dune is best described as a non-recirculating wake. Grainflows on the lee face are caused by failure of grainfall depositional bumps. Our results suggest that the principal effect of increased wind speed is to increase the frequency of grainflows. rather than to increase their size, implying that very large, thick grainflows require a different mechanism.     

Petrogenesis of the Labrieville Alkalic Anorthosite Massif, Grenville Province, Quebec

The Labrieville massif (     

Synthetic fluid inclusions - VI. Quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure

ABSTRACT The decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure H₂O synthetic inclusions formed by healing fractures in natural quartz. Three different modes of non-elastic deformation, referred to as stretching, leakage or partial decrepitation, and total decrepitation have been observed. The internal pressure required to initiate non-elastic deformation is inversely related to inclusion size according to the equation: internal pressure (kbar) = 4.26 D^-0.423 where D is the inclusion diameter in microns. Regularly shaped inclusions require a higher internal pressure to initiate non-elastic deformation than do irregularly shaped inclusions of similar size. Heating inclusions through the α/β quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion. Long-term heating experiments (∼2 years) suggest that the internal pressure required to initiate non-elastic deformation does not decrease significantly with time and indicates that short-lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature. Inclusions that do exhibit decreased density (higher homogenization temperature) are, however, always accompanied by a change in shape from irregular to that of a negative crystal. Observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals. These results indicate that an inclusion will not be influenced by a neighbouring inclusion, or other defect in the host phase, as long as the distance between the two is >2–4 diameters of the larger of the two inclusions.     

Petrogenesis of Ultramafic Xenoliths from the 1800 Kaupulehu Flow, Hualalai Volcano, Hawaii

The 1800 Kaupulehu flow on Hualalai Volcano, Hawaii, containsabundant xcnoliths of dunitc, wehrlite, and olivine clinopyroxenitewith minor gabbro, troctolite, anorthosite, and wcbstcrite.The petrography and mineral compositions of 41 dunite, wehrlite,and olivine clinopyroxenite xenoliths have been studied, andclinopyroxene separates from eight of these have been analyzedfor Ba, K, Rb, Sr, rare earth elements, ⁸⁷Sr/⁸⁶Sr, and ¹⁴³Nd/¹⁴⁴Nd.Temperatures of equilibration obtained by olivine-spinel andpyroxene geothermometry range from 1000 to 1200 C. Mineralogicaldata combined with published fluid inclusion data indicate depthsof origin in the range of 8–30 km. The rarity of orthopyroxene, the presence of Fe-rich olivine(Fo⁸¹–⁸⁹) and clinopyroxene (Fs⁵–¹²), and the occurrenceof high TiO² in spinel (0.9–2.8 wt.%) and clinopyroxene(035–1.33 wt%) all indicate that the xenoliths are cumulates,not residues from partial fusion. The separated clinopyrox-eneshave ⁸⁷Sr/⁸⁶Sr (0-70348.0-70367) and ¹⁴³Nd/¹⁴⁴Nd (0.51293–0.51299)values that are different from Sr and Nd isotope ratios of Pacificabyssal basalts (>0.7032 and >0-5130, respectively). Also,clinopyroxenes and spinels in the xenoliths have generally higherTiO₂ contents (>O.35 and >0.91 wt.%, respectively) thantheir counterparts in abyssal cumulates (<0.40 and <0.70wt%,respectively). These differences indicate that the xenolithsare not a normal component of oceanic crust. Because the xenoliths and alkalic to transitional Hualalai lavashave similar values for Cr/(Cr + Al) and Cr/(Cr + Al + Fe³⁺)of spinels, ⁸⁷Sr/⁸⁶Sr of clinopyroxenes, and whole-rock ³He/⁴He,we conclude that the xenoliths are cumulates from such magmas.Multiple parental magmas for the xenoliths are indicated byslightly heterogeneous ⁸⁷Sr/⁸⁶Sr of clinopyroxene separates.Depths of formation of the xenoliths are estimated to be {smalltilde}8–30 km. Extensive crystallization of olivine in the absence of pyroxenesand plagioclase is a characteristic and prominent feature ofHawaiian tholeiitic magmatism. Dunite xenoliths crystallizedfrom alkalic magmas have previously been reported from MaunaKea Volcano (Atwill & Garcia, 1985) and Loihi Seamount (Clague,1988). Our finding of an alkalic signature for dunite xenolithsfrom a third Hawaiian volcano, Hualalai, shows that early olivinecrystallization should be considered a characteristic not justof Hawaiian tholeiitic magmatism but also of Hawaiian alkalicmagmatism.     

Sedimentology of 40 000 year Milankovitch-controlled cyclothems from central Hawke's Bay, New Zealand

Cyclothemic sedimentary rocks of the Plio-Pleistocene Petane Group outcrop extensively in the Tangoio block of central Hawke's Bay, New Zealand. They are products of inner to mid-shelf sedimentation and were deposited during glacio-eustatic sea level fluctuations along the western margin of a shallow, pericontinental seaway located in a forearc setting. The succession consists of five laterally continuous cyclothems, each containing a fine grained interval of silt and a coarse grained interval of siliciclastic sand ± gravel or limestone. Five sedimentary facies assemblages comprising 20 separate facies have been recognized. Coarse grained intervals of cyclothems were deposited mostly during relative sea level lowstands and contain up to four facies assemblages: (1) a non-marine assemblage (with three component facies, representing braided river and overbank environments); (2) an estuarine assemblage (with three component facies, representing tidal flat and mud-dominated estuarine environments); (3) a siliciclastic shoreline assemblage (with six component facies, representing greywacke pebble beach, shoreface and inner shelf environments); and (4) a carbonate shelf assemblage (with four component facies, representing tide-dominated, inshore and shallow marine environments). Fine grained intervals of cyclothems were deposited during sea level highstands when the Tangoio area was generally experiencing mid-shelf sedimentation. This produced an offshore assemblage consisting of four component facies. The distribution of facies assemblages during relative sea level lowstands was dependent upon proximity to the shoreline, the type and rate of sediment supply to the basin, and shelf hydrodynamics. Carbonate shelf facies dominate coarse grained intervals in Cyclothems 3–5, but siliciclastic shoreline and non-marine facies dominate in Cyclothems 1 and 2. The abrupt change from siliciclastic to carbonate sedimentation during relative sea level lowstand deposition is thought to have been induced by rapidly falling interglacial to glacial sea level accentuated by regional tectonic shoaling. This caused most of the terrigenous sediment supply to bypass the Tangoio area. Consequently, carbonate sediment accumulated in inshore and shallow marine settings. Facies assemblages rarely show lateral interdigitation, but are vertically stratified over the entire Tangoio block. Facies successions in each cyclothem preserve a record of relative sea level change during deposition of the Petane Group and are consistent with a Plio-Pleistocene sea level change in eastern New Zealand of c. 75–150 m, i.e. approximately the magnitude suggested for Late Quaternary glacio-eustatic sea level changes.