20th-CENTURY CHANGES OF TEMPERATURE IN THE MOUNTAIN REGIONS OF CENTRAL EUROPE

Daily maximum and minimum temperatures from 29 low-lying and mountain stations of 7 countries in Central Europe were analyzed. The analysis of the annual variation of diurnal temperature range helps to distinguish unique climatic characteristics of high and low altitude stations. A comparison of the time series of extreme daily temperatures as well as mean temperature shows a good agreement between the low-lying stations and the mountain stations. Many of the pronounced warm and cold periods are present in all time series and are therefore representative for the whole region. A linear trend analysis of the station data for the period 1901–1990 (19 stations) and 1951–1990 (all 29 stations) shows spatial patterns of similar changes in maximum and minimum daily temperatures and diurnal temperature range. Mountain stations show only small changes of the diurnal temperature range over the 1901–1990 period, whereas the low-lying stations in the western part of the Alps show a significant decrease of diurnal temperature range, caused by strong increase of the minimum temperature. For the shorter period 1951–1990, the diurnal temperature range decreases at the western low-lying stations, mainly in spring, whereas it remains roughly constant at the mountain stations. The decrease of diurnal temperature range is stronger in the western part than in the eastern part of the Alps.     

REE Variations Across the Peninsular Ranges Batholith: Implications for Batholithic Petrogenesis and Crustal Growth in Magmatic Arcs

Rare earth element (REE) patterns of plutonic rocks across theCretaceous Peninsular Ranges batholith vary systematically westto east, transverse to its long axis and structural trends andgenerally parallel to asymmetries in petrologic, geochronologicand isotopic properties. The batholith can be ivided into threedistinct parallel longitudinal regions, each defined by distinctREE pattern types. An abrupt transition occurs between rockswith slightly fractionated REE patterns in the western (coastal)region and rocks with middle to heavy REE fractionated and depletedpatterns in the central region. Further to the east a secondtransition to strongly light REE enriched rocks occurs. Theslopes of the REE patterns within each of these regions arelargely independent of rock type. The first REE transition isclosely coupled to regional discontinuities in other parameters:elimination of negative Eu anomalies, an increase in Sr content,and a marked restriction in petrologic diversity. This transitionoccurs over a range of initial ⁸⁷Sr/⁸⁶Sr ratios and ¹⁸O values,but approximately correlates to a major shift in the emplacementstyle of the batholith from a stationary arc to a rapidly eastward-migrating(cratonward) arc. The sense of the regionally consistent REE trends cannot beexplained by crystallization, assimilation, combined crystallization-assimilation,or mixing processes. The consequences of assimilation and high-leveldifferentiation are not observed generally, despite the sensitivityof the REE to these processes. Geochemical and petrologicalfeatures argue that the partial melting of mafic source rocksin which plagioclase-rich (gabbroic) residual assemblages abruptlygave way laterally and downward to garnet-bearing (eclogitic)residual assemblages produced all the changes associated withthe first REE transition. The change in residual assemblagesfrom gabbroic to eclogitic was superimposed on source regionsalready zoned in light REE abundances, ⁸⁷Sr/⁸⁶Sr and ¹⁸O. Temperatureand pressure constraints on the source regions place them ina subcrustal location. The calcic nature of the batholith andthe dominance of tonalite and low-K²O granodiorite in all itsregions argue that the source materials are broadly basalticin composition. Experimental studies are consistent with thegeneration of the abundant tonalitic magmas by the partial meltingof basalt under both low and high pressure conditions. Arc basaltssuch as those commonly erupted in modern island arcs and continentalmargins are inferred to have provided much of the source materialand the heat. Additional high-¹⁸O components are needed in themore easterly source regions. These materials must be distributedso as to contribute equally to the range of magmas that occurin a given local region, and must preserve the calcic natureof batholithic sources. Altered basalts of ancient oceanic crustand possibly their associated metasediments, previously incorporatedinto the lithosphere beneath the continental margin during earliercycles of subduction, most readily satisfy these constraints. The REE geochemistry of the central and eastern regions of thebatholith differs from that of oceanic island arcs in the presenceof strongly heavy REE depleted and fractionated magmas. A modelis proposed in which arc basalts accumulate beneath a crustallayer. Melting of accumulated material at low pressure producesmagmas of the western region. Where thickening of the basalticunderplate is sufficient to form eclogitic assemblages, eclogite-derivedmagmas of the central and eastern region are produced. The abrupttransition to eclogite-derived magmas that suggests a processdriven by a density instability is responsible for their origin. The Peninsular Ranges batholith appears to be representativeof a major differentiation process in which mantle-derived basaltis remelted, contributing its more sialic fractions to the continentalcrust and leaving its mafic to ultramafic residues in the mantle.This process preserves the sialic character of the continentalcrust and may play a significant role in its growth and evolution.The batholith and the processes that produced it may be a moreappropriate basis than immature oceanic island arcs on whichto construct models of continental growth and evolution.     

The Substitution of Al and F in Titanite at High Pressure and Temperature: Experimental Constraints on Phase Relations and Solid Solution Properties

Experimental studies were carried out to evaluate phase relationsinvolving titanite–F–Al-titanite solid solutionin the system CaSiO₃–Al₂SiO₅–TiO₂–CaF₂. Theexperiments were conducted at 900–1000°C and 1·1–4·0GPa. The average F/Al ratio in titanite solid solution in theexperimental run products is 1·01 ± 0·06,and X_Al ranges from 0·33 ± 0·02 to 0·91± 0·05, consistent with the substitution [TiO²⁺]_–1[AlF²⁺]₁.Analysis of the phase relations indicates that titanite solidsolutions coexisting with rutile are always low in X_Al, whereasthe maximum X_Al of titanite solid solution occurs with fluoriteand either anorthite or Al₂SiO₅. Reaction displacement experimentswere performed by adding fluorite to the assemblage anorthite+ rutile = titanite + kyanite. The reaction shifts from 1·60GPa to 1·15 ± 0·05 GPa at 900°C, from1·79 GPa to 1·375 ± 0·025 GPa at1000°C, and from 1·98 GPa to 1·575 ±0·025 GPa at 1100°C. The data show that the activityof CaTiSiO₄O is very close to the ideal molecular activity model(X_Ti) at 1100°C, but shows a negative deviation at 1000°Cand 900°C. The results constrain     

Effects of uranium mining discharges on water quality in the Puerco River basin,Arizona and New Mexico

Abstract

From 1967 until 1986, uranium mine dewatering increased dissolved gross alpha, gross beta, uranium and radium activities and dissolved selenium and molybdenum concentrations in the Puerco River as indicated by time trends, areal patterns involving distance from the mines and stream discharge. Additionally, increased dissolved uranium concentrations were identified in groundwater under the Puerco River from where mine discharges entered the river to approximately the Arizona-New Mexico State line about 65 km downstream. Total mass of uranium and gross alpha activity released to the Puerco River by mine dewatering were estimated as 560 Mg (560 × 10⁶ g) and 260 Ci, respectively. In comparison, a uranium mill tailings pond spill on 16 July 1979, released an estimated 1.5 Mg of uranium and 46 Ci of gross alpha activity. Mass balance calculations for alluvial ground water indicate that most of the uranium released did not remain in solution. Sorption of uranium on sediments and uptake of uranium by plants probably removed the uranium from solution.     

Liquid Immiscibility in the Join NaAlSi3O8-CaCO3 to 2.5 GPa and the Origin of Calciocarbonatite Magmas

Field evidence from intrusive and effusive carbonatites supportsthe existence of calciocarbonatite magmas. Published experimentalevidence in the model system Na₂O–CaO–Al₂O₃–SiO₂–CO₂indicated the formation of nearly pure (99%) CaCO₃ immiscibleliquids from a carbonated silicate liquid. This evidence hasbeen used to support interpretations of extremely CaCO₃-richcalciocarbonatite magmas, and immiscible liquids with compositionsof almost pure CaCO₃ in metasomatized mantle peridotite andeclogite. Detailed phase relationships are constructed in themodel system, based on phase fields intersected by the joinNaAlSi₃O₈–CaCO₃ (Ab-CC) at 1.0, 1.5, and 2.5 GPa between1100 and 1500C, and analyzed immiscible liquids. The miscibilitygap between silicate-rich liquid and carbonate-rich liquid intersectedby the join Ab-CC contracts considerably with decreasing pressure:2.5 GPa, between Ab₁₀CC₉₀ (by wt%) and Ab₆₅CC₃₅ above 1310C;1.5 GPa, betweenAb₂₃CC₇₇ and Ab₄₃CC₅₇ above 1285C; 1.0 GPa,not intersected. The liquidus piercing point between calciteand silicates becomes enriched in CaCO₃ with decreasing pressure,from Ab₈₀CC₂₀ at 2.5 GPa to Ab₄₇CC₅₃ at 1.0 GPa. No immiscibleliquid contains more than 80% dissolved CaCO₃, and all containat least 5% Na₂CO₃. A round CaCO₃ phase exhibiting morphologysimilar to that displayed by immiscible liquid globules is determinedto be crystalline calcite under experimental conditions. Thetopology of the phase fields and field boundaries illustratesthe kinds of processes and controls existing in magmatic systems.Calciocarbonatite magmas cannot be produced by equilibrium immiscibilityprocess in the mantle. Carbonated silicate magmas in the crustyield residual calciocarbonatite magmas by fractionation alongthe silicate-calcite field boundary, reached either directlyfrom the silicate liquidus or more commonly via the miscibilitygap. Immiscible carbonaterich magmas when freed from the silicateparent cool down a sleep silicate liquidus until they reacha silicate-carbonate field boundary. There is no experimentalevidence for immiscible calciocarbonatite magmas with > 80%CaCO₃, and calcite lapilli cannot be formed from 99% CaCO₃ magmas.Sovites are surely cumulates. KEY WORDS: carbonatite; join NaAlSi₃O₈–CaCO₃; liquid immiscibility; sovite ^* Corresponding author. Telephone: (818)-395–6239. Fax: (818)-568–0935. e-mail: wjl{at}gpi.caltech.edu     

Isotopic Evolution of the Tonga Arc during Lau Basin Rifting; Evidence from the Volcaniclastic Record

New Pb, Sr and Nd isotope data from volcaniclastic sedimentsrecovered from the Tonga forearc and Lau Basin permit the isotopicevolution of a section of this arc system, next to the modernisland of Ata, to be traced through the backarc basin riftingprocess from 7.0 Ma to the present. The new data suggest thatthe isotopic character of the mantle wedge remains constant,and of Pacific mid-ocean ridge basalt (MORB) character, duringthe early rifting phase. The isotopic evidence supports traceelement data in showing an increase in the sediment contributionto arc petrogenesis about 2–3 m.y. after the start ofLau Basin rifting. Since 0.45 Ma the sediment contribution decreasedto pre-rift values with the initiation of spreading in the adjacentbackarc basin, where the high sediment influence is not seenin the isotopes. The isotopes show a relative increase in thevolcaniclastic compared with pelagic sediment involvement duringrifting. The inferred peak in sediment subduction is probablythe result of a decoupling of the two plates owing to roll-backof the Pacific lithosphere at the time of arc rifting. KEY WORDS: isotopes; Pacific; rifting; subduction; volcanism ^*Corresponding author. Telephone: (508) 289 3437. Fax: (508) 457 2187. e-mail: pclift{at}whoi.edu     

In situ acoustic measurements of marine gravel threshold and transport

Measurements of the nearbed turbulent current flow and the bedload transport of marine gravel have been made over three tidal cycles. The turbulence in the bottom boundary layer was measured using two electromagnetic current meters, and the gravel transport was measured using a passive acoustic system which monitored the interparticle collision noise of locally mobile material. Visual estimates of bedload were also obtained with an underwater TV camera. The acoustic technique, unlike a conventional bedload sampler, has allowed estimates of transport to be obtained with a temporal resolution comparable with the turbulence data collected. This has enabled a detailed comparison to be made between the turbulent flow and the sediment response to the instantaneous flow conditions. The results of the study show that of the turbulent bursting events which contribute towards the Reynolds stress, only the sweeps and outward interactions play a significant role in the transport of coarse sedimentary material. The measurements show that it is the instantaneous increases in the horizontal turbulent velocity fluctuations that generate excess shear stresses which drive the transport process.