Late Quaternary vegetational changes on the east side of Yellowstone park,Wyoming     

Jean C.B. Waddington  H.E. Wright 《Quaternary Research》1974,4(2):175-184

A bog pond 4 km east of Yellowstone Lake has a pollen record starting with an Artemisia spruce assemblage, implying alpine vegetation. A layer of volcanic ash, dated as 14,360 ± 400 BP (probably Glacier Peak or Mt. St. Helens J), occurs within the zone, which terminates at 11,630 ± 180 BP. The rest of the pollen sequence is dominated by lodgepole pine, with reappearance of spruce pollen in modest quantities about 4500 BP, according to dating provided by a layer of Mt. Mazama ash (6600 BP). The present vegetation of the area is marked by forests of lodgepole pine with some stands of spruce and fir. The pollen sequence suggests that the upper treeline before 11,600 y. a. was perhaps 500 m lower than today. The climate then became warmer and/or drier than today (Altithermal interval). About 4500 y. a., a slight climatic reversal took place, roughly contemporaneous with the regrowth of glaciers in the western mountains (neoglaciation).  相似文献   

Preliminary petrographic description and geologic implications of the Apollo 17 Station 7 boulder consortium samples     

E.C.T. Chao  Jean A. Minkin  Carolyn L. Thompson 《Earth and Planetary Science Letters》1974,23(3):413-428

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Vesicles,water, and sulfur in Reykjanes Ridge basalts   总被引：1，自引：0，他引：1  

James G. Moore  Jean -Guy Schilling 《Contributions to Mineralogy and Petrology》1973,41(2):105-118

Dredge hauls of fresh submarine basalt collected from the axis of the Reykjanes Ridge (Mid-Atlantic Ridge) south of Iceland were taken aboard R/ V TRIDENT in 1967 and 1971. The samples show systematic changes as the water depth of collection (and eruption) decreases: radially elongate vesicles and concentric zones of vesicles appear at about 700 m depth and are conspicuous to shallow water; the smoothed volume percent of vesicles increases from 5% at 1000 m, 10% at 700 m, to 16% at 500 m, and the scatter in degree of vesicularity increases in shallower water; specific gravity decreases from 2.7±0.1 at 1000 m to 2.3±0.3 at 100 m. Bulk sulfur content for the outer 2 cm averages 843 ppm up to a depth of 200 m, then drops off rapidly in shallower water owing to degassing. Sulfur content below 200 m is independent of depth (or geographic position), and the melt is apparently saturated with sulfur, but the excess cannot escape the lava unless another vehicle carries it out. Only shallower than 200 m, where intense vesiculation of other gases occurs can excess sulfur be lost from the lava erupting on the sea floor. H₂O^+110° averages about 0.35 percent and H₂O^+150° about 0.25 percent, and both apparently decrease in water shallower than 200 m as a result of degassing. H₂O⁺ (below 200 m) decreases with distance from Iceland or increasing depth, presumably as a result of either adsorption of water on the surface of shallower, more vesicular rocks; or more likely due to the presence of the Iceland hot mantle plume supplying undifferentiated primordial material, relative to lavas of the Reykjanes Ridge supplied from the low velocity layer already depleted in volatiles and large lithophile elements. The H₂O^+110°/S ratio of lava erupting below 200 m water depth ranges from 3 to 5 which is comparable to reliable gas analyses from oceanic basaltic volcanoes. Publication authorized by the Director, U.S. Geological Survey.  相似文献   

Datation 87Rb-87Sr du massif granitique du Mendic et des porphyroïdes a l'est de la Montagne Noire —un exemple de relation entre pluton et volcans     

Jean Hamet  Claude J. Allègre 《Contributions to Mineralogy and Petrology》1973,38(4):291-298

In the East of Montagne Noire (South Massif Central), the granitic Mendic massif and the porphyroïds have been dated as 510±20 m.y. with a corresponding initial ratio of 0.706±0.001. Within the limits of the analytical errors, we cannot distinguish between two separate isochrons. The Mendic-porphyroïds represents a volcano-plutonic association. The age of 510 m.y. is somewhat younger than the one determined on the orthogneisses of the Central zone (530 m.y.). It can be connected to a post-orogenic magmatism of the cadomian orogenesis. At last the Sr of the minerals of the Mendic massif has been partially remobilised during the hercynian orogeny (285 m. y.).  相似文献   

Fractionnement dans les suites ignimbritiques de Toscane. Un example de rejuvenation crustale     

Claude Dupuy 《Geochimica et cosmochimica acta》1972

By means of flame spectrometry, K and Rb were measured in minerals and rocks belonging to several ignimbrite suite in Toscane, (Italy).  相似文献   

塔里木板块西南缘晚侏罗世古地磁研究   总被引：1，自引：0，他引：1       下载免费PDF全文

李永安  陈岩  Cogne Jean PASCAL  Gilder STUART  孙东江 《地质学报》2003,77(2):151-157

塔里木板块西南缘托云、奥依塔格晚侏罗世古地磁研究,获得了托云地区特征磁化方向:Ds=1.5°,Is=50.8°;古地磁极:λ=81.0°,ψ=247.0°,古纬度31.5°N。奥依塔格地区特征磁化方向:Ds=118.4°,Is=55.9°;古地磁极:λ=4.9°,ψ=120.6°,古纬度=36.4°N。从古地磁结果认为:①托云和奥依塔格相对托云地区产生顺时针旋转;②这两个地区古纬度为31°～36°左右,与塔里木平均古纬度30°N是基本一致的,但与现在纬度差达8°～10°左右,造成纬度差主要原因是构造运动造成的;③塔里木晚侏罗世古地磁亦与华北、华南基本一致,说明晚侏罗世塔里木、华北、华南三板块已联合成一个整体,拼合成统一的中国大陆,其位于热带—亚热带古气候环境。  相似文献   

A chlorine-36 study of regional groundwater flow and vertical transport in southern Nevada   总被引：1，自引：0，他引：1  

Jean E. Moran  Timothy P. Rose 《Environmental Geology》2003,43(5):592-605

Chlorine-36 data for groundwater from the Death Valley regional flow system is interpreted in the context of existing conceptual models for regional groundwater flow in southern Nevada. Chlorine-36 end member compositions are defined for both recharge and chemically evolved groundwater components. The geochemical evolution of ³⁶Cl is strongly controlled by water-rock interaction with Paleozoic carbonate rocks that comprise the regional aquifer system, resulting in chemically evolved groundwater that is characteristically low in ³⁶Cl/Cl and high in Cl. Groundwater from alluvial and volcanic aquifers that overlie the regional carbonate aquifer are generally characterized by high ³⁶Cl/Cl and low Cl signatures, and are chemically distinct from water in the regional carbonate aquifer. This difference provides a means of examining vertical transport and groundwater mixing processes. In combination with other geochemical and hydrogeologic data, the end members defined here provide constraints on aquifer residence times and mixing ratios.  相似文献   

Imagerie sismique de la zone de collision hercynienne dans le Sud-Est du Massif armoricain (projet Armor 2/programme Géofrance 3D)     

Adnand Bitri  Michel Ballèvre  Jean-Pierre Brun  Jean Chantraine  Denis Gapais  Paul Guennoc  Charles Gumiaux  Catherine Truffert 《Comptes Rendus Geoscience》2003,335(13):969-979

The structure of the Hercynian collision zone in the southeast of the Armorican Massif is illustrated by a 70-km long deep seismic profile acquired in September 2000. The profile images a previously unknown south-dipping thrust that brought the Champtoceaux Domain on top of the Central Armorican Domain during Carboniferous times. Dextral strike-slip motions along the South Armorican Shear Zone, which is downward cut by the thrust zone, are partly coeval with northward thrusting. A major discontinuity, hidden by the thrust front, is also imaged in the lower crust between the Champtoceaux area and the Central Armorican Domain. These new data lead to a structural and kinematic re-interpretation of this part of the Hercynian collision zone. To cite this article: A. Bitri et al., C. R. Geoscience 335 (2003).  相似文献   

Quantifying the effect of recent relief changes on age–elevation relationships     

Jean Braun   《Earth and Planetary Science Letters》2002,200(3-4):331-343

The effect that recent relief changes may have on the distribution of rock ages with elevation is investigated for a range of thermochronometers. From the solution of the heat transport equation in a crustal block undergoing uplift and surface erosion, the temperature history of rock particles that are exhumed at the Earth’s surface today is computed. These T-t paths are then used to calculate apparent isotopic ages for the (U–Th)/He system in apatite, characterized by a low (≈70°C) closure temperature. The results show that recent relief changes strongly affect the distribution of ages with elevation (notably the slope of the age–elevation relationship). The calculations presented here predict that, in most situations, regions that have undergone a steady decrease in surface relief in the recent past should be characterized by an inverted age–elevation relationship, that is older ages should be found near valley bottoms and younger ages near summit tops. It is also shown how the wavelength of the topography, the geothermal gradient, the exhumation rate and the duration of the relief reduction event affect this result.  相似文献   

Role of fluids in surface deformation caused by the 1999 Chi‐Chi earthquake in Taiwan     

Jiin‐Shuh Jean  Chuan‐Cheng Liu  Wei‐Teh Jiang  Jinder Chow  Ting‐To Yu  Ching‐Weei Lin  Shih‐Wei Huang 《地球表面变化过程与地形》2002,27(1):1-10

The 1999 Chi‐Chi earthquake significantly altered the landscape of central Taiwan. Surface deformation produced by the earthquake along the trace of the Chelungpu thrust can be classified into two styles: (1) uplift without significant surface rupture, and (2) uplift accompanied by surface rupture. Here we examine areas that exhibited the first style of deformation (e.g. Wufeng). Seismic stress at the time of the main shock may have been relieved by high pore‐fluid pressure in a 300‐m‐thick sand and gravel aquifer. Along the thrust fault, frictional heating of these sediments resulted in thermal expansion and an increase in pore‐fluid pressure. High pore‐fluid pressure damped seismic‐wave energy and enhanced intergranular slips of unconsolidated sandy and gravel sediments, which were possibly assisted by sulphuric acid corrosion, leading to a high sulphate content in the groundwater (c. 70 mg L^?1). These changes permitted surface folding and terrace‐style uplifting to occur without significant rupture. In contrast, other areas in which the second style of deformation is dominant (e.g. Fengyuen‐Shihkang) have thin (0–10 m) sand and gravel deposits and lower concentrations of sulphate (c. 30 mg L^?1) in groundwater. In these areas, sediments were heated but not sufficiently to produce significant thermal expansion and increase in pore‐fluid pressure; accumulation of stress in these locations led to rupture at the ground surface, with the formation of steep fault scarps. The areas exhibiting the first deformation style are characterized by the presence of high pore‐fluid pressure, frictional heat conduction, and possibly chemical corrosion related to sulphuric acid attack and formation of sulphate, in contrast to those involving significant uplift and surface rupture. The areal distribution of these two surface deformation styles suggests that the aforementioned fluid‐related subsurface processes may have altered the characteristics of sediments and caused diverse responses to the quake. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献