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41.
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
42.
本研究量化了美国俄亥俄州橡树-山毛榉混交林森林碳储量,研究结果表明森林碳密度的增长率与其商品材积和总材积的增长率是一致的。橡树-山毛榉混交林连年增长量(CAI)和年平均增长量(MAI)高峰值分别出现在第23和46年。对于地上碳储量而言,其CAI和MAI最高值分别出现在第26年和53年。对于地上碳密度和地上商品材碳密度,其MAI高峰出现在第30年,与其同时间内总蓄积量和商品材的蓄积量出现的情况一致。了解了森林碳储量的增长和蓄积量的增加模式是相近的道理,有助于我们理解森林蓄积量增长的管理模式过渡到森林碳储量管理的模式。 相似文献
43.
Abstract— A new empirical cooling rate indicator for metal particles is proposed. The cooling rate indicator is based on the relationship between the size of the island phase in the cloudy zone, which abuts the outer taenite rim (clear taenite I), and the cooling rate of the host meteorite as obtained by conventional metallographic techniques. The size of the island phase was measured by high-resolution scanning electron microscopy (SEM) in 26 meteorites and decreases from 470 nm to 17 nm, while the cooling rate of the host meteorite increases from 0.5 K/Ma to 325 K/Ma. This island phase size vs. cooling rate relationship is independent of whether the host is an iron, stony-iron, or stony meteorite and can be used to estimate the low-temperature cooling rate of the host meteorite. The measurement of the size of the island phase in the cloudy zone can also be applied to a large number of meteorites. 相似文献
44.
45.
Ion microprobe UPb dating of a bimodal zircon populationfrom a graphitic schist from the basal section of the AlpineAlpujárride nappe complex in the Betic Cordilleras, southernSpain, has yielded different ages for zircons of contrastingmorphology and composition. Approximately half the grains arerounded and abraded, and have ages ranging from 相似文献
46.
SMITH M. P.; HENDERSON P.; JEFFRIES T. E. R.; LONG J.; WILLIAMS C. T. 《Journal of Petrology》2004,45(3):457-484
Garnets from skarns in the Beinn an Dubhaich granite aureole,Isle of Skye, Scotland, have a large range of concentrationsof uranium (0·2358 ppm) and the rare earth elements(REE) (234724 ppm). Variations in these concentrationscorrelate with major element zonation within the garnets, andwith changes in the shape of REE patterns. Typical patternsin most garnets display light REE (LREE) enrichment, flat heavyREE (HREE) distribution and a negative Eu anomaly. These patternsare interpreted to represent equilibrium trace element exchangebetween pre-existing pyroxene, hydrothermal fluid and calcicgarnets. Iron-rich zones are characterized by positive Eu anomaliesand an increase in the abundance of the LREE relative to theHREE. These patterns are interpreted as resulting from changesin REE speciation related to the introduction of externallybuffered fluid to the skarn system. Relatively Fe-poor zonesshow strongly HREE-enriched patterns with negative Eu anomaliesand in some instances depletions in Y relative to Ho and Dy,which are interpreted as resulting from surface sorption ofthe REE during rapid, disequilibrium garnet growth. Strong correlationsbetween U abundance and the REE patterns indicate that the sameprocesses have affected U distribution. Both types of patterncan be modified by the effects of closed-system crystallizationon REE abundance in the fluid, and changes in fluid major elementchemistry. KEY WORDS: fractionation; garnet; hydrothermal; rare earth elements; skarn 相似文献
47.
Deformation, metamorphism and imbrication of the Indian plate, south of the Main Mantle Thrust, north Pakistan 总被引:2,自引:0,他引:2
P. J. TRELOAR R. D. BROUGHTON M. P. WILLIAMS M. P. COWARD B. F. WINDLEY 《Journal of Metamorphic Geology》1989,7(1):111-125
ABSTRACT South of the Main Mantle Thrust in north Pakistan, rocks of the northern edge of the Indian plate were deformed and metamorphosed during the main southward thrusting phase of the Himalayan orogeny. In the Hazara region, between the Indus and Kaghan Valleys, metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically Barrovian sequence. Metamorphism was largely synchronous with early phases of the deformation. The metamorphic rocks were subsequently imbricated by late north-dipping thrusts, each with higher grade rocks in the hanging wall than in the footwall, such that the metamorphic profile shows an overall tectonic inversion. The rocks of the Hazara region form one of a number of internally imbricated metamorphic blocks stacked, after the metamorphic peak, on top of each other during the late thrusting. This imbrication and stacking represents an early period of post-Himalayan uplift. 相似文献
48.
Sigmoidal inclusion trails, punctuated fabric development, and interactions between metamorphism and deformation 总被引:2,自引:0,他引:2
M. L. WILLIAMS 《Journal of Metamorphic Geology》1994,12(1):1-21
Porphyroblast inclusion fabrics are consistent in style and geometry across three Proterozoic metamorphic field gradients, comprising two pluton-related gradients in central Arizona and one regional gradient in northern New Mexico. Garnet crystals contain curved ‘sigmoidal’ inclusion trails. In low-grade chlorite schists, these trails can be correlated directly with matrix crenulations of an older schistosity (S1). The garnet crystals preferentially grew in crenulation hinges, but some late crenulations nucleated on existing garnet porphyroblasts. At higher grade, biotite, staurolite and andalusite porphyroblasts occur in a homogeneous S2 foliation primarily defined by matrix biotite and ilmenite. Biotite porphyroblasts have straight to sigmoidal inclusion trails that also represent the weakly folded S1 schistosity. Staurolite and andalusite contain distinctive inclusion-rich and inclusion-poor domains that represent a relict S2 differentiated crenulation cleavage. Together, the inclusion relationships document the progressive development of the S2 fabric through six stages. Garnet and biotite porphyroblasts contain stage 2 or 3 crenulations; staurolite and andalusite generally contain stage 4 crenulations, and the matrix typically contains a homogeneous stage 6 cleavage. The similarity of inclusion relationships across spatially and temporally distinct metamorphic field gradients of widely differing scales suggests a fundamental link between metamorphism and deformation. Three end-member relationships may be involved: (1) tectonic linkages, where similar P-T-time histories and similar bulk compositions combine to produce similar metamorphic and structural signatures; (2) deformation-controlled linkages, where certain microstructures, particularly crenulation hinges, are favourable environments for the nucleation and/or growth of porphyroblasts; and (3) reaction-controlled linkages, where metamorphic reactions, particularly dehydration reactions, are associated with an increase in the rate of fabric development. A general model is proposed in which (1) garnet and biotite porphyroblasts preferentially grow in stage 2 or 3 crenulation hinges, and (2) chlorite-consuming metamorphic reactions lead to pulses in the rate of fabric evolution. The data suggest that fabric development and porphyroblast growth may have been quite rapid, of the order of several hundreds of thousands of years, in these rocks. These microstructures and processes may be characteristic of low-pressure, first-cycle metamorphic belts. 相似文献
49.
An efficient approach is proposed for analysing the non-stationary random responses of complex structures located in an evolutionary inhomogeneous stochastic field. The approach is a kind of complete CQC method because the cross-correlation terms both between the participant modes and between the ground joint excitations are included in the response calculations. The effect of the loss of coherency between ground joints is also taken into account. For non-proportionally damped structures with many degrees of freedom, the order of the equations of motion can be reduced by using only real modes while structural non-stationary random responses can still be computed conveniently and accurately. © 1997 by John Wiley & Sons, Ltd. 相似文献
50.