A Quartz-bearing Orthopyroxene-rich Websterite Xenolith from the Pannonian Basin, Western Hungary: Evidence for Release of Quartz-saturated Melts from a Subducted Slab

An unusual quartz-bearing orthopyroxene-rich websterite xenolithhas been found in an alkali basaltic tuff at Szigliget, Bakony–BalatonHighland Volcanic Field (BBHVF), western Hungary. Ortho- andclinopyroxenes are enriched in light rare earth elements (LREE),middle REE and Ni, and depleted in Nb, Ta, Sr and Ti comparedwith ortho- and clinopyroxenes occurring in either peridotiteor lower crustal granulite xenoliths from the BBHVF. Both ortho-and clinopyroxenes in the xenolith contain primary and secondarysilicate melt inclusions, and needle-shaped or rounded quartzinclusions. The melt inclusions are rich in SiO₂ and alkalisand poor in MgO, FeO and CaO. They are strongly enriched inLREE and large ion lithophile elements, and display negativeNb, Ta and Sr anomalies, and slightly positive Pb anomalies.The xenolith is interpreted to represent a fragment of an orthopyroxene-richbody that crystallized in the upper mantle from a hybrid meltthat formed by interaction of mantle peridotite with a quartz-saturatedsilicate melt that was released from a subducted oceanic slab.Although the exact composition of the slab melt cannot be determined,model calculations on major and trace elements suggest involvementof a metasedimentary component. KEY WORDS: quartz; mantle; silicate melt inclusion; SiO₂-rich melt; subduction; Carpathian-Pannonian Region     

Evolution of Mafic Alkaline Melts Crystallized in the Uppermost Lithospheric Mantle: a Melt Inclusion Study of Olivine-Clinopyroxenite Xenoliths, Northern Hungary

Olivine-clinopyroxenite xenoliths exhumed in alkali basalts(sensu lato) in the Nógrád–GömörVolcanic Field (NGVF), northern Hungary, contain abundant silicatemelt inclusions. Geothermobarometric calculations indicate thatthese xenoliths crystallized as cumulates in the upper mantlenear the Moho. These cumulate xenoliths are considered to representa period of Moho underplating by mafic alkaline magmas priorto the onset of Late Tertiary alkaline volcanism in the Carpathian–Pannonianregion. The major and trace element compositions of silicatemelt inclusions in olivine display an evolutionary trend characterizedby a strong decrease in CaO/Al₂O₃. The parental melt of thecumulates was a basanite formed by low-degree ( 2%) partialmelting of a garnet peridotite source. The compositional trendof the silicate melt inclusions, textural features, and modellingwith pMELTS show that the parental melt evolved by major clinopyroxeneand minor olivine crystallization followed by the appearanceof amphibole simultaneously with significant resorption of theearlier clinopyroxene and olivine. The resulting residual meltwas highly enriched in Al₂O₃, alkalis and most incompatibletrace elements. This type of melt is likely to infiltrate andreact with surrounding mantle peridotite as a metasomatic agent.It might also form high-pressure pegmatite-like bodies in themantle that might be the source of the amphibole and sanidinemegacrysts also found in the alkali basalts of the NGVF. Preferentialremelting of the later-formed (i.e. lower temperature) mineralassemblage (amphibole, sanidine, residual glass) might havesignificantly contaminated the host alkaline mafic lavas, increasingtheir Al₂O₃ and total alkali contents and, therefore, reducingtheir MgO, FeO and CaO content. KEY WORDS: silicate melt inclusions; geochemistry; petrogenesis; Nógrád–Gömör Volcanic Field; Pannonian Basin     

Uranium-Series Dating of Carbonate (Tufa) Deposits Associated with Quaternary Fluctuations of Pyramid Lake, Nevada

Uranium-series dating of dense tufa deposited in a small cave, at former lake margins, and in large tufa mounds clarifies the timing of lake-level variation during the past 400,000 yr in the Pyramid Lake basin. A moderate-sized lake occasionally overflowed the Emerson Pass sill at elevation of 1207 m between ca. 400,000 and 170,000 and from ca. 60,000 to 20,000 yr B.P., as shown by²³⁰Th/²³⁴U ages of the cave samples,²³⁰Th-excess ages of tubular tufas, and average isochron-plot ages of shoreline-deposited tufas. (By comparison, modern Pyramid Lake is 50 m below this sill). There is a lack of tufa record during the intervening period from ca. 170,000 to 60,000 yr B.P. After ca. 20,000 yr, Pyramid Lake underwent abrupt changes in level and, based on previous¹⁴C ages, reached its highest elevation (ca 1335 m) at ca. 14,000 yr B.P. The youngest uranium-series ages are comparable with previously reported¹⁴C ages.     

Prioritisation of sub-watersheds based on earth observation data of agricultural dominated northern river basin of India

The Upper Tons River Basin of North India has been selected for prioritisation of sub-watersheds (SW) based on morphometric parameters with respect to groundwater derived from topographic sheets and CARTOSAT data. There are 10 SW have been delineated in the region, high stream frequency (F_s) values of SW (1–5) and SW-9 indicated the occurrence of steep slopes, less permeable rocks, greater runoff, less infiltration possibility. Further, these regions have been predicted as poor groundwater potentialities. SW-2 has been identified as poorest groundwater potential zone, whereas SW-4 and SW (6–8) regions possess good permeable bed rocks. The Drainage density (D_d) map demonstrated that the middle south-west region possesses higher D_d whereas northeastern regions contain lower D_d. Further, the areal parameters indicate elongated shape of the basin, hilly region has moderate to steeper ground slope. The outcomes of work have potential to manage groundwater and to ameliorate the flash flood and droughts.     

The diet of deepwater sharks and the benefits of using DNA identification of prey

Stomachs from the sharks Dalatias licha, Centrophorus squamosus, Centroscymnus owstoni, Centroselachus crepidater, Proscymnodon plunketi, and Galeorhinus galeus were sampled from three research trawl surveys on Chatham Rise, east of New Zealand. Between 14 and 50 stomachs were examined for each species, of which 8–62% were empty. Prey were visually identified in 80 stomachs, and by DNA barcoding in a further 28 stomachs. The use of DNA methods allowed the identification of chunks of flesh found in the stomachs of D. licha and P. plunketi, and nearly doubled the rate of data accumulation for D. licha, C. squamosus, and C. owstoni. Between 84 and 223 stomachs were estimated to be needed to measure 90% of the extrapolated total prey richness. The prey of D. licha, C. squamosus, and P. plunketi were predominantly benthic or demersal fishes and cephalopods. The prey of C. owstoni and C. crepidater were predominantly mesopelagic fishes and squids. G. galeus foraged throughout the water column. Scavenging of discards from commercial fishing vessels was likely in C. squamosus, P. plunketi, and G. galeus. The diet of all species except C. crepidater was dominated by the commercially important benthopelagic species hoki Macruronus novaezelandiae.     

Understanding the Internal Magnetic Field Configurations of ICMEs Using More than 20 Years of <Emphasis Type="Italic">Wind</Emphasis> Observations

The magnetic topology, structure, and geometry of the magnetic obstacles embedded within interplanetary coronal mass ejections (ICMEs) are not yet fully and consistently described by in situ models and reconstruction techniques. The main goal of this work is to better understand the status of the internal magnetic field of ICMEs and to explore in situ signatures to identify clues to develop a more accurate and reliable in situ analytical models. We take advantage of more than 20 years of Wind observations of transients at 1 AU to compile a comprehensive database of ICMEs through three solar cycles, from 1995 to 2015. The catalog is publicly available at wind.gsfc.nasa.gov and is fully described in this article. We identify and collect the properties of 337 ICMEs, of which 298 show organized magnetic field signatures. To allow for departures from idealized magnetic configurations, we introduce the term “magnetic obstacle” (MO) to signify the possibility of more complex configurations. To quantify the asymmetry of the magnetic field strength profile within these events, we introduce the distortion parameter (DiP) and calculate the expansion velocity within the magnetic obstacle. Circular-cylindrical geometry is assumed when the magnetic field strength displays a symmetric profile. We perform a statistical study of these two parameters and find that only 35% of the events show symmetric magnetic profiles and a low enough expansion velocity to be compatible with the assumption of an idealized cylindrical static flux rope, and that 41% of the events do not show the expected relationship between expansion and magnetic field compression in the front, with the maximum magnetic field closer to the first encounter of the spacecraft with the magnetic obstacle; 18% show contractions (i.e. apparent negative expansion velocity), and 30% show magnetic field compression in the back. We derive an empirical relation between DiP and expansion velocity that is the first step toward improving reconstructions with possible applications to space weather studies. In summary, our main results demonstrate that the assumed correlation between expanding structure and asymmetric magnetic field is not always valid. Although 59% of the cases could be described by circular-cylindrical geometry, with or without expansion, the remaining cases show significant in situ signatures of departures from circular-cylindrical geometry. These results will aid in the development of more accurate in situ models to reconcile image.     

Comparison of the deflection of the vertical components computed by astro-geodetic, gravimetric and topographic-isostatic techniques

Three different types of deflection of the vertical components wre computed at a number of selected astronomical stations in the south central United States. Astro-geodetic deflections were obtained from the differences between the astronomical and geodetic coordinates of each station. Gravimetric deflections were computed from isostatic anomalies. The isostatic isoanomaly charts used in this computation were constructed from data obtained by correcting point values taken from existing free-air isoanomaly charts for the effects of the Bouguer reduction and the topographic-isostatic reduction. It is felt that this procedure substantially reduces the labor involved in making isostatic reductions without sacrificing accuracy appreciably. Topographic-isostatic deflections were computed by Hayford's Method as modified by Orlin. The differences between the three types of deflection components are compared and conclusions made concerning their accuracy and utility. Aerounautical Chart and Information Center     

Uranium-series dating of lacustrine limestones from pan deposits with final Acheulian assemblage at Rooidam,Kimberley district,South Africa

Lacustrine limestone samples from sedimentary pan deposits at Rooidam, near Kimberley, South Africa, that contain late Acheulian (Fauresmith) artifacts have been dated by ${}^{230}\text{Th}{}^{234}\text{U}$ and ${}^{231}\text{Pa}{}^{235}\text{U}$ methods. Results indicate a minimum age of about 200,000 yr B.P. for the terminal Acheulian in the interior of South Africa.     

Ages of subsurface stratigraphic intervals in the Quaternary of Enewetak Atoll,Marshall Islands

Drill cores of Enewetak Atoll, Marshall Islands, reveal six stratigraphic intervals, numbered in downward sequence, which represent vertical coral growth during Quaternary interglaciations. Radiocarbon dates indicate that the Holocene sea transgressed the emergent reef platform by about 8000 yr B.P. The reef grew rapidly upward (about 5 to 10 mm/yr) until about 6500 yr B.P. Afterward vertical growth slowed to about 0.5 mm/yr, then lateral development became dominant during the last several thousand years. The second interval is dated at 131,000 ± 3000 yr B.P. by uranium series. This unit correlates with oxygen-isotope substage 5e and with terrace VIIa of Huon Peninsula, New Guinea, and of Main Reef-2 terrace at Atauro Island. The third interval is not dated because corals were recrystallized and it is tentatively correlated with either oxygen-isotope stages 7 or 9. The age of the fourth interval is estimated at 454,000 ± 100,000 yr B.P. from measured ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios. This unit is correlated with either oxygen-isotope stage 9, 11, or 13.     

Large-scale structure of the sun's corona from radio observations using the Clark Lake Radioheliograph

We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona.