True polar wander in mantle convection models with multiple, mobile continents     

Benjamin R. Phillips  Hans-Peter Bunge  Katrin Schaber 《Gondwana Research》2009,15(3-4):288-296

The geologic record supports numerous instances during which continents apparently moved at speeds significantly faster than any of today's tectonic plates. While the time dependence of convective driving forces likely explains some such observations, rapid motions of large continents in particular are often attributed to true polar wander (TPW). In order to gauge the potential for connections between continents, mantle temperature anomalies, and polar motion, we present the first calculations of TPW derived from models that couple mantle convection with multiple, mobile continents. We find that the aggregation and dispersal of supercontinents can lead to two types of TPW, driven either by a well developed hot upwelling axis that creates a stable maximum moment of inertia, or by the homogenization of mantle thermal structure following continent dispersal that leads to destabilization of the principal axis and possible large magnitude polar wander. These supercontinent-modulated thermal heterogeneities drive model TPW events as large as 90° at rates of up to 2.5° Ma^− 1. Such magnitudes and speeds are greater than those attained in similar models lacking continents, but comparable to those for episodes inferred from paleomagnetic data for some large continents in the past.  相似文献   

From drought to flood: A water balance analysis of the Tuolumne River basin during extreme conditions (2015–2017)     

Andrew R. Hedrick  Danny Marks  Hans-Peter Marshall  James McNamara  Scott Havens  Ernesto Trujillo  Micah Sandusky  Mark Robertson  Micah Johnson  Kat J. Bormann  Thomas H. Painter 《水文研究》2020,34(11):2560-2574

The degree to which the hydrologic water balance in a snow-dominated headwater catchment is affected by annual climate variations is difficult to quantify, primarily due to uncertainties in measuring precipitation inputs and evapotranspiration (ET) losses. Over a recent three-year period, the snowpack in California's Sierra Nevada fluctuated from the lightest in recorded history (2015) to historically heaviest (2017), with a relatively average year in between (2016). This large dynamic range in climatic conditions presents a unique opportunity to investigate correlations between annual water availability and runoff in a snow-dominated catchment. Here, we estimate ET using a water balance approach where the water inputs to the system are spatially constrained using a combination of remote sensing, physically based modelling, and in-situ observations. For all 3 years of this study, the NASA Airborne Snow Observatory (ASO) combined periodic high-resolution snow depths from airborne Lidar with snow density estimates from an energy and mass balance model to produce spatial estimates of snow water equivalent over the Tuolumne headwater catchment at 50-m resolution. Using observed reservoir inflow at the basin outlet and the well-quantified snowmelt model results that benefit from periodic ASO snow depth updates, we estimate annual ET, runoff efficiency (RE), and the associated uncertainty across these three dissimilar water years. Throughout the study period, estimated annual ET magnitudes remained steady (222 mm in 2015, 151 mm in 2016, and 299 mm in 2017) relative to the large differences in basin input precipitation (547 mm in 2015, 1,060 mm in 2016, and 2,211 mm in 2017). These values compare well with independent satellite-derived ET estimates and previously published studies in this basin. Results reveal that ET in the Tuolumne does not scale linearly with the amount of available water to the basin, and that RE primarily depends on total annual snowfall proportion of precipitation.  相似文献   

FOREWORD     

Hans-Peter Plag  Steve Klosko 《Surveys in Geophysics》1997,18(2-3):129-130

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Marine ice-rafted debris records constrain maximum extent of Saalian and Weichselian ice-sheets along the northern Eurasian margin     

Jochen Knies  Hans-Peter Kleiber  Jens Matthiessen  Claudia Müller  Norbert Nowaczyk 《Global and Planetary Change》2001,31(1-4)

Ice-rafted debris (IRD) (>2 mm), input in eight sediment cores along the Eurasian continental margin (Arctic Ocean), have been studied over the last two glacial/interglacial cycles. Together with the revised chronologies and new micropaleontological data of two cores from the northern Barents Sea (PS2138) and northeastern Kara Sea (PS2741) spanning Marine Isotope Stages (MIS) 6 to 1, the IRD data give new insights into the glacial history of northern Eurasian ice-sheets over the last 150 ka. The chronologies of the cores are based on stable isotope records, AMS ¹⁴C datings, paleomagnetic and biostratigraphic data.Extensive episodes of northern Barents Sea ice-sheet growth, probably to the shelf edge, occurred during the late Weichselian (MIS 2) and the Saalian (MIS 6). Major IRD discharge at the MIS 4/3-transition hints to another severe glaciation, probably onto the outer shelf, during MIS 4. IRD-based instabilities of the marine-based ice margin along the northern Barents Sea between MIS 4 and 2 are similar in timing with North Atlantic Heinrich events and Nordic Seas IRD events, suggesting similar atmospheric cooling over a broad region or linkage of ice-sheet fluctuations through small sea-level events.In the relatively low-precipitation areas of eastern Eurasia, IRD peak values during Termination II and MIS 4/3-transition suggest a Kara Sea ice-sheet advance onto the outer shelf, probably to the shelf edge, during glacial MIS 6 and 4. This suggests that during the initial cooling following the interglacials MIS 5, and possibly MIS 7, the combined effect of sustained inflow of Atlantic water into the Arctic Ocean and penetration of moisture-bearing cyclones into easterly direction supported major ice build-up during Saalian (MIS 6) and Mid-Weichselian (MIS 4) glaciation. IRD peak values in MIS 5 indicate at least two advances of the Severnaya Semlya ice-sheet to the coast line during the Early Weichselian. In contrast, a distinct Kara Sea ice advance during the Late Weichselian (MIS 2) is not documented by the IRD records along the northeastern Kara Sea margin.  相似文献   

Li, Be, B concentrations and δ7Li values in plagioclase phenocrysts of dacites from Nea Kameni (Santorini, Greece)     

Joan Cabato  Rainer Altherr  Thomas Ludwig  Hans-Peter Meyer 《Contributions to Mineralogy and Petrology》2013,165(6):1135-1154

Li, Be, B and δ⁷Li SIMS analyses of plagioclase phenocrysts from the 1040–1941 Niki dacite lava (Nea Kameni, Santorini, Greece) exhibit varied processes. From their anorthite contents alone, the crystals may be segregated into four main types: type-N shows the normal decline in An during crystallisation (An_62–40); type-O has only oscillatory zoning accompanied by resorption surfaces (An_58–39); type-C is complex with high-An cores (subtype C1: An_64–58, subtype C2: An_88–73) and normal rims (An_55–42). Type-A plagioclase with high An content (An_92–82) is found within mafic enclaves. On the basis of their Li concentrations, type-O crystals may be subdivided into subtype O1 with flat Li concentration profiles and subtype O2 with decreasing Li concentration from core to rim. The concentrations of Be and B of all four types show a negative correlation with anorthite content (An), but Li concentration profiles differ amongst the different plagioclase types. Types N and O1, and the cores of type-C, are equilibrated in Li concentration. Types O2 and A, and the mantles of type-C display an initial enrichment in Li, probably from volatile influx into the melt. Consistent with the propensity towards equilibrium with the melt, these crystals display dramatic rim-ward declines in Li concentration. All analysed plagioclase crystals, except for the xenocrystic type-A, have nearly the same Li, Be and B concentrations at their rims. These coincide with the composition of plagioclase microlites in the groundmass, thereby affording estimates of plagioclase-melt partitioning for the light elements: K _Li = 0.19–0.28, K _Be = 0.24–0.38 and K _B = 0.007–0.009. δ⁷Li profiles in type-O2 and type-A phenocrysts manifest an unmistakable inverse relation to Li concentration, with variations of up to ~39 ‰, revealing preferential kinetic diffusion. This may have been driven by Li loss from the melt, most likely through degassing during decompression, perhaps in the course of magma ascent to subsequent eruption. Considering the rapid diffusion of Li in plagioclase, in situ phenocryst analyses may yield useful information about processes leading up to, or even causing, eruptions.  相似文献   

The crystal structure of galgenbergite-(Ce), CaCe2(CO3)4∙H2O     

Franz Walter  Hans-Peter Bojar  Christine E. Hollerer  Kurt Mereiter 《Mineralogy and Petrology》2013,107(2):189-199

Galgenbergite-(Ce) from the type locality, the railroad tunnel Galgenberg between Leoben and St. Michael, Styria, Austria, was investigated. There it occurs in small fissures of an albite-chlorite schist as very thin tabular crystals building rosette-shaped aggregates associated with siderite, ancylite-(Ce), pyrite and calcite. Electron microprobe analyses gave CaO 9.49, Ce₂O₃ 28.95, La₂O₃ 11.70, Nd₂O₃ 11.86, Pr₂O₃ 3.48, CO₂ 30.00, H₂O 3.07, total 98.55 wt.%. CO₂ and H₂O calculated by stoichiometry. The empirical formula (based on Ca + REE ∑3.0) is $ \mathrm{C}{{\mathrm{a}}_{1.00 }}{{\left( {\mathrm{C}{{\mathrm{e}}_{1.04 }}\mathrm{L}{{\mathrm{a}}_{0.42 }}\mathrm{N}{{\mathrm{d}}_{0.42 }}\mathrm{P}{{\mathrm{r}}_{0.12 }}} \right)}_{2.00 }}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ , and the simplified formula is $ \mathrm{CaC}{{\mathrm{e}}_2}{{\left( {\mathrm{C}{{\mathrm{O}}_3}} \right)}_4}\cdot {{\mathrm{H}}_2}\mathrm{O} $ . According to X-ray single crystal diffraction galgenbergite-(Ce) is triclinic, space group $ P\overline{1},a=6.3916(5) $ , b?=?6.4005(4), c?=?12.3898(9) Å, α?=?100.884(4), β?=?96.525(4), γ?=?100.492(4)°, V?=?483.64(6) ų, Z?=?2. The eight strongest lines in the powder X-ray diffraction pattern are [d _calc in Å/(I)/hkl]: 5.052/(100)/011; 3.011/(70)/0-22; 3.006/(66)/004; 5.899/(59)/-101; 3.900/(51)/1-12; 3.125/(46)/-201; 2.526/(42)/022; 4.694/(38)/-102. The infrared absorption spectrum reveals H₂O (OH-stretching mode at 3,489 cm^?1, HOH bending mode at 1,607 cm^?1) and indicates the presence of distinctly non-equivalent CO₃-groups by double and quadruple peaks of their ν1, ν2, ν3 and ν4 modes. The crystal structure of galgenbergite-(Ce) was refined with X-ray single crystal data to R1?=?0.019 for 2,448 unique reflections (I?>?2σ(I)) and 193 parameters. The three cation sites of the structure Ca(1), Ce(2) and Ce(3) have a modest mixed site occupation by Ca and small amount of REE (Ce, La, Pr, Nd) and vice versa. The structure is based on double layers parallel to (001), which are composed of Ca(1)Ce(2)(CO₃)₂ single layers with an ordered chessboard like arrangement of Ca and Ce, and with a roof tile-like stacking of the CO₃ groups. Perpendicular to (001) the double layers are connected to a triclinic framework structure with good cleavage parallel to (001) by a differently organized and more open part of the structure formed by Ce(3)(CO₃)₂(H₂O). Based on the topology of the CaCe(CO₃)₂ single layer in galgenbergite-(Ce), structural relationships to rutherfordine, to aragonite and ancylite type minerals, and to lanthanite are outlined.  相似文献   

Noble gas composition,cosmic-ray exposure age, 39Ar-40Ar,and I-Xe analyses of ungrouped achondrite NWA 7325          下载免费PDF全文

Jens Hopp  Natalie Schröter  Olga Pravdivtseva  Hans-Peter Meyer  Mario Trieloff  Ulrich Ott 《Meteoritics & planetary science》2018,53(6):1150-1163

Northwest Africa (NWA) 7325 is an anomalous achondrite that experienced episodes of large-degree melt extraction and interaction with melt under reducing conditions. Its composition led to speculations about a Mercurian origin and provoked a series of studies of this meteorite. We present the noble gas composition, and results of ⁴⁰Ar/³⁹Ar and ¹²⁹I-¹²⁹Xe studies of whole rock splits of NWA 7325. The light noble gases are dominated by cosmogenic isotopes. ²¹Ne and ³⁸Ar cosmic-ray exposure ages are 25.6 and 18.9 Ma, respectively, when calculated with a nominal whole rock composition. This ³⁸Ar age is in reasonable agreement with a cosmic-ray exposure age of 17.5 Ma derived in our ⁴⁰Ar/³⁹Ar dating study. Due to the low K-content of 19 ± 1 ppm and high Ca-content of approximately 12.40 ± 0.15 wt%, no reliable ⁴⁰Ar/³⁹Ar age could be determined. The integrated age strongly depends on the choice of an initial ⁴⁰Ar/³⁶Ar ratio. An air-like component is dominant in lower temperature extractions and assuming air ⁴⁰Ar/³⁶Ar for the trapped component results in a calculated integrated age of 3200 ± 260 (1σ) Ma. This may represent the upper age limit for a major reheating event affecting the K-Ar system. Results of ¹²⁹I-¹²⁹Xe dating give no useful chronological information, i.e., no isochron is observed. Considering the highest ¹²⁹Xe*/¹²⁸Xe_I ratio as equivalent to a lower age limit, we calculate an I-Xe age of about 4536 Ma. In addition, elevated ¹²⁹Xe/¹³²Xe ratios of up to 1.65 ± 0.18 in higher temperature extractions indicate an early formation of NWA 7325, with subsequent disturbance of the I-Xe system.  相似文献   

S velocity structure and radial anisotropy in the Aegean region from surface wave dispersion     

Brigitte Endrun  Thomas Meier  Sergei Lebedev  Marco Bohnhoff  George Stavrakakis  Hans-Peter Harjes 《Geophysical Journal International》2008,174(2):593-616

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Rock-weathering by lichens in Antarctic: patterns and mechanisms     

CHEN Jie  Hans-Peter Blume 《地理学报》2002,12(4):387-396

Saxicolous species of lichens are able to induce and accelerate weathering of their rock substrate, and effects of lichens on substrate can be attributed to both physical and chemical causes. This paper is focused on biotic weathering actions of epilithic and endolithic species on the different rock types (sandstones and volcanogenic rocks) in Antarctica. The patterns, mechanisms, processes and neoformations of rock-weathering resulting from lichen colonization are expounded in detail. Furthermore, it is pointed out that, for a better understanding of the impacts of lichens on environments, the studies on the rate of biotic weathering and the comprehensive involvement of the lichen effects on weathering of natural rocks remain to be carried out in Antarctica.  相似文献   

南极石生地衣主要生物风化作用研究进展与展望   总被引：1，自引：0，他引：1       下载免费PDF全文

陈杰  檀满枝 《极地研究》2003,14(1):65-72

地衣以物理、化学方式参与矿质基质的风化作用 ,诱导和加速岩石的风化过程。本文对南极地区表生和内生型地衣的生物风化作用进行了综合论述 ,详细阐述了不同地衣种类诱导和参与几种主要岩石类型 (砂岩类和火成岩类 )风化作用的模式、机制、过程以及产物。同时指出 ,地衣等其他生物因素间接参与的风化过程 ,地衣导致的岩石抗风化效应以及生物风化速率等方面的研究工作是目前南极生物风化作用研究方面的新领域。  相似文献