共查询到20条相似文献,搜索用时 31 毫秒
1.
J.C. de WIT C.M. van der STRAATEN W.G. MOOK 《Geostandards and Geoanalytical Research》1980,4(1):33-36
By mixing 1 H2 O and 2 H2 O, both with accurately known purity, samples were prepared with 2 H/1 H ratios close to those of the international isotopic water standards: V-SMOW and SLAP. A mass spectrometrical comparison of these calibration samples with the actual water standards revealed:
2 H/1 H of V-SMOW = (155.95 ± 0.08) × 10−6
2 H/1 H of SLAP = (89.12 ± 0.07) × 10−6
δ2 HV-SMOW (SLAP) =−428.5 ± 0.5 % 相似文献
δ
2.
Abstract: The Hishikari deposits comprise the Honko (Main), Yamada, and Sanjin deposits. The horizontal strain in the direction (approx. N40°W normal to the general NE-SW strike of the Hishikari vein system was calculated, based on the measured total vein widths to the distance along three crosscuts. Veins were assumed to accompany no significant fault displacement in the calculation. Veins in the eastern and the middle parts of the Honko-Sanjin deposits spatially occupy 3. 2% and 1. 3%, respectively, and veins in the Yamada deposit occupy 6. 7%. Significant local variation of strain is observed in some areas. Reported K-Ar ages on adularia-quartz veins indicate the duration of vein opening to be 2. 6 × 105 yr in the Honko-Sanjin deposits and 5. 9 × 105 yr in the Yamada deposit. Horizontal strain rates were calculated to be 5. 0–12 × 10-8 yr-1 through the Hishikari deposits. The calculated strain rates at the Hishikari deposits are roughly comparable to the regional horizontal strain rate in the Recent. Widespread extensional movement in southern Kyushu seems to have been able to provide sufficient strain for the formation of the Hishikari deposits, rather than contribution of local movements. 相似文献
3.
Diffusion-controlled corona reaction and overstepping of equilibrium in a garnet granulite, Yenisey Ridge, Siberia 总被引:2,自引:1,他引:1
J. R. ASHWORTH V. S. SHEPLEV N. A. BRYXINA V. Yu. KOLOBOV & V. V. REVERDATTO 《Journal of Metamorphic Geology》1998,16(2):231-246
Diffusion modelling is applied to layered garnet–pyroxene–quartz coronas, formed by a pressure-induced reaction between plagioclase and primary pyroxene in a metabasic granulite. The reconstructed reaction involves some change in composition of reactant minerals. The distribution of minerals between layers is satisfactorily explained by diffusion-controlled reaction with local equilibrium, in which the diffusion coefficient for Al was smaller than those for Fe, Mg and Ca by a factor of approximately four. Diffusion of Mg towards plagioclase implies a chemical-potential gradient for MgO component in a direction opposite to the changing Mg content of garnet; this is explained by the influence of Al2 O3 on the chemical potential of the pyrope end-member. Grain-boundary diffusion is suggested to have operated, possibly with composition gradients different from those in the bulk minerals. Chemical-potential differences across the corona are estimated from the variation in garnet composition, enabling affinity (the free energy change driving the reaction) to be estimated as 6.9±1.8 kJ per 24-oxygen mole of garnet produced. This implies that the pressure for equilibrium among the minerals was overstepped by 1.4±0.4 kbar. The probable P–T conditions of reaction were in the range 650–790 °C, 8–10 kbar. Assuming a timescale of reaction between 106 and 108 years, estimated diffusion coefficients for Fe, Mg and Ca are in the range 9×10−23 to 5×10−20 m2 s−1 . These are consistent with experimental values in the literature for solid-state diffusion, including grain-boundary diffusion. 相似文献
4.
LARS FORSSTROM 《Boreas: An International Journal of Quaternary Research》1984,13(3):301-318
The Quaternary stratigraphy in Finland is discussed on the basis of an example from the Oulainen area of Ostrobothnia. Organogenic deposits found beneath till at this site are correlated with the Eemian Interglacial on biostratigraphical evidence. This is confirmed by TL dates of 97,000 ± 18,000 B.P. and 150,000 ± 30,000 B.P., whereas a finite radiocarbon date of 63,200 +5500 -3200 B.P. is probably too young. Correlation of the Weichselian stratigraphy is based on deep-sea oxygen isotope data, in which the variations in isotope ratios are assumed to reflect global changes in climate and fluctuations in the volume of the ice-caps. It is concluded on the latter grounds that Finland must have been free of ice at two periods during the Early Weichselian but at least for the most part covered by ice thereafter up to the final deglaciation. The sediments attributed to the only known Weichselian interstadial in Finland, the Perapohjola Interstadial, are taken to correspond most probably to the Brørup, although some may represent the Odderade, Information on the Weichselian till stratigraphy in the Oulainen area is largely confined to the deglaciation phase, the relatively complex nature of which suggests that complete reconstruction of the earlier phases of the Weichselian in an area such as Finland, located towards the centre of the ice sheet, is scarcely feasible by the methods currently available. 相似文献
5.
Leif Kullman 《Boreas: An International Journal of Quaternary Research》1980,9(2):101-106
Wood samples from above the present-day pine limit were collected from within a limited area in central Sweden. New dates from an intensively investigated part of that area all fall within the period 8550 ± 110 to 4270 ± 90 14 C years B. P. No evidence at present exists to suggest that any drastic change, or fluctuations, in the pine tree-limit, took place within that period. Some dates support the view that the present-day altitude of the pine tree-limit was established during the historic period and perhaps is still declining. 相似文献
6.
Preparation and Certification of Re-Os Dating Reference Materials: Molybdenites HLP and JDC 总被引:27,自引:1,他引:27
Andao Du Shuqi Wu Dezhong Sun Shuxian Wang Wenjun Qu Richard Markey Holly Stain John Morgan Dmitry Malinovskiy 《Geostandards and Geoanalytical Research》2004,28(1):41-52
Two Re-Os dating reference material molybdenites were prepared. Molybdenite JDC and molybdenite HLP are from a carbonate vein-type molybdenum-(lead)-uranium deposit in the Jinduicheng-Huanglongpu area of Shaanxi province, China. The samples proved to be homogeneous, based on the coefficient of variation of analytical results and an analysis of variance test. The sampling weight was 0.1 g for JDC and 0.025 g for HLP. An isotope dilution method was used for the determination of Re and Os. Sample decomposition and pre-concentration of Re and Os prior to measurement were accomplished using a variety of methods: acid digestion, alkali fusion, ion exchange and solvent extraction. Negative thermal ionisation mass spectrometry and inductively coupled plasma-mass spectrometry were used for the determination of Re and 187 Os concentration and isotope ratios. The certified values include the contents of Re and Os and the model ages. For HLP, the Re content was 283.8 ± 6.2 μg g−1 , 187 Os was 659 ± 14 ng g−1 and the Re-Os model age was 221.4 ± 5.6 Ma. For JDC, the Re content was 17.39 ± 0.32 μg g−1 , 187 Os was 25.46 ± 0.60 ng g−1 and the Re-Os model age was 139.6 ± 3.8 Ma. Uncertainties for both certified reference materials are stated at the 95% level of confidence. Three laboratories (from three countries: PR. China, USA, Sweden) joined in the certification programme. These certified reference materials are primarily useful for Re-Os dating of molybdenite, sulfides, black shale, etc. 相似文献
7.
Marinella A. Laurenzi Maria Laura Balestrieri Giulio Bigazzi Julio C. Hadler Neto Pedro J. Iunes Pio Norelli Massimo Oddone Ana Maria Osorio Araya José G. Viramonte 《Geostandards and Geoanalytical Research》2007,31(2):105-124
New analyses have been performed in order to enhance the data-set on the independent ages of four glasses that have been proposed as reference materials for fission-track dating. The results are as follows. Moldavite - repeated 40 Ar/39 Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the 40 Ar/39 Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) -four K-Ar ages ranging from 5.44 ± 0.06 to 5.72 ± 0.12 Ma have been published previously. New 40 Ar/39 Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission-track ages determined using the IRMM-540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new 40 Ar/39 Ar ages than the previously published ages. Roccastrada glass (Italy) - a new 40 Ar/39 Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm-2 ). Defects that might produce "spurious" tracks are virtually absent. An independent 40 Ar/39 Ar age of 8.77 ± 0.09 Ma was determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission-track groups, will be very useful for testing system calibrations and experimental procedures. 相似文献
8.
MEREDITH A. KELLY SUSAN IVY-OCHS PETER W. KUBIK FRIEDHELM VON BLANCKENBURG CHRISTIAN SCHLÜCHTER 《Boreas: An International Journal of Quaternary Research》2006,35(4):634-643
Surface exposure dating, using in situ produced cosmogenic 10 Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine 10 Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four 10 Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three 10 Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two 10 Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of 10 Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions. 相似文献
9.
ATLE NYGÅRD HANS PETTER SEJRUP HAFLIDI HAFLIDASON MARCELLO CECCHI DAG OTTESEN 《Boreas: An International Journal of Quaternary Research》2004,33(1):1-17
Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14 C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14 C ka BP. On the shallow Måløy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c. 15 14 C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15–13.3 14 C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1. 相似文献
10.
Measurement of SIMS Instrumental Mass Fractionation of Pb Isotopes During Zircon Dating 总被引:8,自引:0,他引:8
Richard A. Stern Simon Bodorkos Sandra L. Kamo Arthur H. Hickman Fernando Corfu 《Geostandards and Geoanalytical Research》2009,33(2):145-168
An igneous zircon reference material (OG1) was characterised for U-Pb isotopes by ID-TIMS, and utilised to evaluate SIMS (SHRIMP) instrumental mass fractionation (IMF) of radiogenic Pb isotopes (207 Pb*/206 Pb*). The TIMS 207 Pb*/206 Pb* reference value for OG1 was 0.29907 ± 0.00011 (95% confidence limit), 3465.4 ± 0.6 Ma. The high 207 Pb* (∼ 30 μg g−1 ), negligible common Pb, and isotopic homogeneity permitted precise (± 1–2‰) 207 Pb*/206 Pb* measurements within the analytical sessions. External reproducibility of mean 207 Pb*/206 Pb* ratios between sessions was demonstrated for one instrument, yielding a mean IMF of +0.87 ± 0.49‰. The mean 207 Pb*/206 Pb* ratios between instruments were dispersed beyond uncertainties, with session IMF values from +3.6 ± 1.7‰ to −2.4 ± 1.3‰, and a grand mean IMF value (twenty-six sessions) of +0.70 ± 0.52‰, indicating a tendency towards elevated 207 Pb*/206 Pb*. The specific causes of variability in IMF are unclear, but generally reflect subtle differences in analytical conditions. The common practice in SIMS of assuming that IMF for Pb+ is insignificant could result in systematic age biases and underestimated uncertainties, of critical importance for precise correlation of Precambrian events. Nevertheless, a zircon RM such as OG1 can be readily incorporated into routine dating to improve 207 Pb*/206 Pb* accuracy and external reproducibility. 相似文献
11.
This brief contribution presents new boron isotopic data for a set of proposed borosilicate reference minerals, most of which are described in the companion paper by Dyar et al.2001 . The results for a variety of minerals (tourmalines, danburite, prismatine, serendibite, ferroaxinite and a Li mica) show that it is generally possible to reproduce the 11 B/10 B ratio within ± 0.5 per mil with replicate chemistry and mass spectrometry over long time spans. Because the accuracy of boron isotopic analysis is commonly determined by reference to secondary standards, it is suggested that some of the samples used in this study be adopted for interlaboratory comparisons and for quality control on boron isotopic analyses produced by a variety of analytical methods. 相似文献
12.
DAVID J. LUBINSKI SERGEY KORSUN LEONID POLYAK STEVEN L. FORMAN SCOTT J. LEHMAN FRANCES A. HERLIHY GIFFORD H. MILLER 《Boreas: An International Journal of Quaternary Research》1996,25(2):89-100
A study of two piston cores and a 3.5 kHz seismic profile from the Franz Victoria Trough provides new stratigraphic, stable isotopic and foraminiferal AMS 14 C data that help constrain the timing of ice-sheet retreat in the northern Barents Sea and the nature of the deglacial marine environment. Silty diamicton at the base of each core, interpreted as till or ice-marginal debris flow, suggests that the Barents ice sheet was grounded at the core sites (470 m water depth). Eight AMS 14 C dates on sediment overlying the diamicton indicate that the ice sheet retreated from both core sites by 12.9 ka and that postglacial sedimentation began 10 ka ago. These dates, combined with a recently published 14 C date from a nearby core, suggest that the Franz Victoria Trough may not have been deglaciated until c . 13 ka, 2000 years later than modeled ice-sheet reconstructions indicate. In the trough, oxygen isotopic ratios in planktonic foraminifera N . pachyderma (sinistral) were 0.5–0.750, lower during deglaciation than after, probably as a result of ice-sheet and/or iceberg melting. Foraminiferal assemblages suggest that Atlantic-derived intermediate water may have begun to penetrate the trough c . 13 ka ago. 相似文献
13.
Stanislaw Halas Janina Szaran Maciej Czarnacki Ahmad Tanweer 《Geostandards and Geoanalytical Research》2007,31(1):61-68
Refinements have been made to achieve over 99% yield in the conversion of CO to CO2 in order to improve the reproducibility and accuracy of δ18 O measurements in sulfates. BaSO4 (10-15 mg) was mixed with an identical amount of spectrographic-grade graphite and loaded into a Pt boat. The mixture was gradually heated to 1100 °C to reduce sulfate to CO and CO2 ; the former gas was simultaneously converted to CO2 by a glow discharge between Pt electrodes immersed in a magnetic field (produced by a pair of external neodymium magnets). A small memory effect was noticed during the analysis (less than 0.3‰ per 10‰ difference in δ18 O between two subsequently analysed samples). The memory effect, however, was suppressed by repetitive preparation of the same specimen. CO2 produced in this way from sulfate reference samples was analysed on a dual inlet and triple collector mass spectrometer along with CO2 equilibrated with VSMOW, GISP and SLAP water reference samples. To avoid large departures of measured isotope ratios from 18 O/16 O of the working calibrator we used CO2 gas prepared from ocean water sulfate for this purpose. The calibrated δ18 O values (in ‰) obtained in this way for NBS-127, IAEA SO-5 and IAEA SO-6 reference materials were 8.73 ± 0.05, 12.20 ± 0.07 and -10.43 ± 0.12, respectively. 相似文献
14.
Radiocarbon dating of marine shells, including a discussion of apparent age of Recent shells from Norway 总被引:1,自引:0,他引:1
JAN MANGERUD 《Boreas: An International Journal of Quaternary Research》1972,1(2):143-172
General problems in determining and interpreting shell C14 dates are discussed: calculation methods, factors influencing primary activity (apparent age), and determination of contamination. It is concluded that shell dates are reliable when handled carefully. Measurements on ten shells, collected between 1898 and 1923 on the Norwegian coast, gave apparent ages from 340±75 to 550±80 years, indicating that apparent age is not a significant problem in dating of Norwegian shells. 相似文献
15.
Re-Os Dating of Sulfides from the Volcanogenic Massive Sulfide Deposit at Gacun, Southwestern China 总被引:1,自引:0,他引:1
Abstract. The Re-Os isotopic compositions of sulfide ores were analyzed for the Gacun, a volcanogenic massive sulfide deposit in southwestern China, to constrain the timing of mineralization. Sulfide ores from the deposit have a wide range of Re and Os concentrations, varying from 80.2 to 1543.2 ppb and from 0.307 to 8.83 ppb, respectively, and yielded a limited field of high 187 Re/188 Os and high 187 Os/188Os ratios, ranging from 1452 to 3309 and from 5.77 to 13.24, respectively. All sulfide samples yielded an isochron with an age of 217±28 Ma and an initial 187 Os/188 Os ratio of around 0.52±0.73. The Re-Os isochron age agrees with ages previously constrained by the other isotopic dating of the host rocks and fossil strata for the deposit. The rhythmic variation in 187 Os/188 Os and 187 Re/188 Os ratios within massive sulfide zone records a complicated process for ore-forming fluids episodically vented into the brine pool on the Mesozoic seafloor. 相似文献
16.
ÁRNÝ E. SVEINBJÖRNSOTTIR JÓN EIRÍKSSON ÁSLAUG GEIRSDÓTTIR JAN HEINEMEIER NIELS RUD 《Boreas: An International Journal of Quaternary Research》1993,22(2):147-157
An exhaustive 14 C dating programme of molluscs from the Fossvogur sediments in Reykjavik. Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm earlier conclusions of a widespread occurrence of marine sediments of Allerød age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow 14 C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional 14 C age is 11,400 BP. Assuming a reservoir effect of 400 years. this corresponds to a reservoir-corrected age of I1,000 BP. i.e. the Allerød- Younger Dryas transition for the sampled units, These new 14 C dates from Fossvogur confirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The dates suggest that the marine units in Fossvogur accumulated within a restricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explain anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. δ13 C and δ18 O results suggest that temperatures may have ranged up to 60°C. 相似文献
17.
Chemical Separation and Isotopic Variations of Cu and Zn From Five Geological Reference Materials 总被引:6,自引:0,他引:6
John B. Chapman Thomas F.D. Mason Dominik J. Weiss Barry J. Coles Jamie J. Wilkinson 《Geostandards and Geoanalytical Research》2006,30(1):5-16
This paper presents an adapted anion exchange column chemistry protocol which allowed separation of high-purity fractions of Cu and Zn from geological materials. Isobaric and non-spectral interferences were virtually eliminated for consequent multiple-collector ICP-MS analysis of the isotopic composition of these metals. The procedure achieved ∼ 100% recoveries, thus ensuring the absence of column-induced isotopic fractionation. By employing these techniques, we report isotopic analyses for Cu and Zn from five geological reference materials: BCR-027 blende ore (BCR), δ65 Cu = 0.52 ± 0.15‰ (n = 10) and δ66 Zn = 0.33 ± 0.07‰ (n = 8); BCR-030 calcined calamine ore (BCR), δ66 Zn = -0.06 ± 0.09‰ (n = 8); BCR-1 basalt (USGS), δ66 Zn = 0.29 ± 0.12‰ (n = 8); NOD-P-1 manganese nodule (USGS), δ65 Cu = 0.46 ± 0.08‰ (n = 10) and δ66 Zn = 0.78 ± 0.09‰ (n = 9); SU-1 Cu-Co ore (CCRMP), δ65 Cu = -0.018 ± 0.08‰ (n = 10) and δ66 Zn = 0.13 ± 0.17‰ (n = 6). All uncertainties are ± 2s; copper isotope ratios are reported relative to NIST SRM-976, and zinc isotope ratios relative to the Lyon-group Johnson Matthey metal (batch 3-0749 L) solution, JMC Zn. These values agree well with the limited data previously published, and with results reported for similar natural sample types. Samples were measured using a GVi IsoProbe MC-ICP-MS, based at the Natural History Museum, London. Long-term measurement reproducibility has been assessed by repeat analyses of both single element and complex matrix samples, and was commonly better than ± 0.07‰ for both δ66 Zn and δ65 Cu. 相似文献
18.
Ore-Forming Fluid Characteristics of the Dayingezhuang Gold Deposit, Jiaodong Gold Province, China 总被引:27,自引:0,他引:27
Liqiang Yang Jun Deng Chunying Guo Jing Zhang Shaoqing Jiang Bangfei Gao Qingjie Gong Qingfei Wang 《Resource Geology》2009,59(2):181-193
The Dayingezhuang gold deposit is located in the central part of the Zhaoping Fault Zone, which is one of the most important gold-hosting faults in the Jiaodong gold province of China. Dayingezhuang is a typical large-scale shear zone-hosted disseminated gold deposit with superimposed silver mineralization. Fluid inclusion (FI) petrography and microthermometry, and analysis of oxygen and hydrogen isotopes for fluid inclusions were conducted to determine the characteristics of the ore-forming fluids and the processes of silver mineralization. Microthermometry data of FI indicated that ore-forming fluids are characterized by low salinity and low density. Homogenization pressures of FI are estimated at 20 × 105 –220 × 105 Pa. The change in ore-forming fluids from K2 SO4 type to NaCl type indicates the superposition of two hydrothermal mineralizing events. Ore-forming fluids were dominated by magmatic components in the early mineralization period, and affected by meteoric waters in the late period. Gold may have been transported as Au-S or Au-Cl complexes, whereas silver was transported as Ag-Cl complexes. Early fluid boiling and later fluid mixing are thought to be two of the main factors causing the deposition and superimposing of gold and silver to form the large deposit. 相似文献
19.
Younger Dryas end moraines between Hardangerfjorden and Sognefjorden, Western Norway 总被引:1,自引:0,他引:1
End moraines (called the Herdla Moraines) from the Younger Dryas Stadial arc morphologically mapped along the western coast of Norway, from Hardangerfjorden to north of Sognefjorden. The submarine position of the moraines are found by means of a conventional echo sounder. Stratigraphieal studies with many C14 datings are used for age determination, giving Late Younger Dryas (10,000–10,500 C14 years B.P.) for the Herdla Moraines. The moraines are correlated with the Ra-Salpausselkä Moraines. Isobases for the Younger Dryas are obtained from marine terraces formed contemporaneously with the moraines. 相似文献
20.
YEONG BAE SEONG LEWIS A. OWEN HYOUN SOO LIM HO IL YOON YEADONG KIM YONG IL LEE MARC W. CAFFEE 《Boreas: An International Journal of Quaternary Research》2009,38(2):207-213
Glacial landforms on the Barton and Weaver peninsulas of King George Island in the South Shetland Islands, West Antarctica were mapped and dated using terrestrial cosmogenic 36 Cl methods to provide the first quantitative terrestrial record for late Quaternary deglaciation in the South Shetland Islands. 36 Cl ages on glacially eroded and striated bedrock surfaces range from 15.5±2.5 kyr to 1.0±0.7 kyr. The 36 Cl ages are younger with decreasing altitude, indicating progressive downwasting of the southwestern part of the Collins Ice Cap at a rate of ∼12 mm yr−1 since 15.5±2.5 kyr ago, supporting the previously published marine records for the timing and estimate of the rate of deglaciation in this region. 相似文献