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1.
A number of archeological features, including in‐filled irrigation canals of uncertain prehistoric age, occur within the Holocene floodplain of the Salt River at Phoenix, Arizona. In the first attempt to date irrigation‐canal sediments using luminescence methods, we obtained age estimates of 1640 ± 190 yr B.P. (1σ) (multi‐aliquot or MA) and 1621 ± 95 yr B.P. (post‐IR single‐aliquot‐regenerative‐dose or SAR) for a single sample from the base of the oldest canal‐infilling deposits (all IR‐PSL ages reported in this article are in calendar years before A.D. 2001). For the remaining canal samples, weighted mean luminescence ages of 819 ± 45 yr (MA) and 826 ± 32 yr (post‐IR SAR) were obtained. Thus from photonic dating we can resolve the first and last phases of canal use at this Phoenix site: initiation at ca. 1600 years ago and final use at ca. 800 years ago. These results demonstrate the power of SAR luminescence sediment dating to enhance our understanding of prehistoric irrigation‐canal development and usage here and elsewhere in the world. © 2004 Wiley Periodicals, Inc.  相似文献   

2.
 Land subsidence in the form of sinks has occurred on and near farmlands near Tucson, Pima County, Arizona, USA. The sinks occur in alluvial deposits along the flood plain of the Santa Cruz River, and have made farmlands dangerous and unsuitable for farming. More than 1700 sinks are confined to the flood plain of the Santa Cruz River and are grouped along two north-northwestward-trending bands that are approximately parallel to the river and other flood-plain drainages. An estimated 17,000 m3 of sediment have been removed in the formation of the sinks. Thirteen trenches were dug to depths of 4–6 m to characterize near-surface sediments in sink and nonsink areas. Sediments below about 2 m included a large percentage of dispersive clays in sink areas. Sediments in nonsink areas contain a large component of medium- to coarse-grained, moderately to well sorted sand that probably fills a paleochannel. Electromagnetic surveys support the association of silts and clays in sink areas that are highly electrically conductive relative to sand in nonsink areas. Sinks probably are caused by the near-surface process of subsurface erosion of dispersive sediments along pre-existing cracks in predominantly silt and clay sediments. The pre-existing cracks probably result from desiccation or tension that developed during periods of water-table decline and channel incision during the past 100 years or in earlier periods. Submitted, April 1997 · Revised, November 1997 · Accepted, April 1998  相似文献   

3.
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4.
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5.
W. Chen  R. J. Arculus 《Lithos》1995,36(3-4):203-225
A wide variety of xenoliths has been entrained in Miocene-to-Recent alkali olivine and hypersthene-normative basalts in the San Francisco Volcanic Field (SFVF), northern Arizona, U.S.A. Based on petrography, mineralogy, bulk rock chemistry and Sr-Nd isotopic characteristics, SFVF xenoliths can be divided into two major groups: cumulates and granulites. The cumulates are genetically related to the Cenozoic volcanic rocks and represent under- and/or intraplated additions to the crust of the Colorado Plateau. Assemblages are mafic to ultramafic and are dominated by clinopyroxene-orthopyroxene-plagioclase-spinel-amphibole-olivine. The granulites are probably Proterozoic in age, mafic-to-intermediate/felsic in bulk composition, either two pyroxene-plagioclase-spinel or plagioclase-alkali feldspar-quartz-magnetite-amphibole-biotite assemblages. Many of the granulites show evidence of partial melting. Some high SiO2, very high Rb/Sr glasses are close in composition to erupted rhyolites, and probably represent end-member melts that have interacted with basalt to produce a variety of hybrid intermediate lavas. The major element, trace element and Sr-Nd isotope geochemistry is highly variable in the SFVF xenoliths. Extremely high Ba contents and Ba/Nb of a number of the granulites are equivalent to values characteristics of modern supra-subduction zone magmas. The considerable variation of chemical and isotopic composition depends upon mineral proportions, assemblages and chemistry. Isotopically, three end-members can be identified within the granulites: (i) lowest 87Sr/86Sr (0.702870) with low 143Nd/144Nd (0.511541, εNd-21.4); (ii) high 87Sr/86Sr (0.711069) with the lowest 143Nd/144Nd (0.511434, εNd-23.5); (iii) highest 87Sr/{86}Sr (0.715306) with low 143Nd/144Nd (0.511793, εNd-16.5). Two important age ranges deduced from the isotopic data probably relate to episodes of crustal-growth beneath the SFVF (1.88 ± 0.33 Ga and Cenozoic). Thermobarometric calculations assuming equilibrium show that the xenoliths are derived from the lower crust (0.6–1.3 GPa, 850–1050 °C). The average SFVF lower crust is mafic in composition. In the absence of partial lithospheric delamination, the lower crust may become mafic with time due to under- and intraplating of continental crust by mafic magmas derived from the mantle.  相似文献   

6.
《Applied Geochemistry》1997,12(1):83-95
In a column experiment, acidic groundwater from Pinal Creek Arizona, a Cu mining area, was eluted through a composited alluvial sample obtained from a core that had been removed from a well downgradient of the acidic groundwater. The minerals present in typical grains and flakes in the alluvium before and after the elution were determined by X-ray diffraction (XRD), scanning electron microscopy, and energy dispersive multichannel analyses (EDX). The concentrations of Fe, Ti, Mn, Si, Al, Na, Ca, K, Mg and S in these grains and flakes and in their microcrystalline surface coatings were measured by EDX.In addition to magnetite, hematite, and Fe-Ti oxides, Fe was most concentrated in micas (especially biotite-like flakes) and in the microcrystalline coatings. The measured elements in these microcrystalline coatings were primarily K, Fe, Al, and Si. The microcrystalline coatings on the mica flakes also contained Mg. The approximate l:3 Mg:Si atomic ratios (ARs)_of the biotite-life flake both before and after the elution would suggest that the Fe deposited during the elution had not substituted for Mg in these flakes. As a result of the elution, assuming no loss of Si, the averaged recorded Fe:Si AR of the microcrystalline coatings increased from (0.46 to 0.58):3.00.Iron deposition on the typical grains and flakes may relate to the presence of Fe in the particle on which it is deposited or to the presence of Fe in the microcrystalline surface coatings before elution. The data here are not sufficient for a statistical evaluation, but elution caused the following trends: (l) The Fe:Si AR increased in the (K,Fe,Al,Si)-microcrystalline surface coatings; (2) For the mica flakes, there was more than a 2-fold increase in the Fe:Si AR for the microcrystalline surface coatings of the Fe-rich biotite-like flakes but no measurable increase of the Fe:Si AR for the microcrystalline surface coatings of the muscovite-like flakes that contained 3–5 times less Fe; (3) Also for the biotite-like flakes, the increase in Fe:Si AR was greater in the flakes that had a higher Fe:Si AR; (4) The Fe deposition on the Fe-rich microcrystalline surface coatings of the feldspar was much greater than on the Fe-poor, beige quartz and feldspar grains that, prior to elution, had only CaS04 microcrystalline coatings; and (5) No Fe was deposited on Fe-poor grains with no microcrystalline surface coating.  相似文献   

7.
Spinel lherzolite and pyroxenite inclusions from the Geronimovolcanic field, Arizona (and Dish Hill, California) record,in their constituent minerals, a chronology of diverse mantledepletion and enrichment events. Certain portions of the lithosphericmantle have remained relatively isolated for considerable periodsof time(1–4 b.y.) while wall rock adjacent to conduitsof basanite has been recently (< 0-2 b.y.) modified. Evidenceexists for a widespread ancient (1–4 b.y.) partial meltingresidue, now recognizable as MORB-like mantle below the southwesternU.S.A. Trace element enrichment (0?9 b.y.) has increased thelight rare earth element (LREE) and Sr content of many refractoryperidotites without any mineralogical changes to the host rock.The fluids/melt responsible for this enrichment have a complexhistory involving heterogeneous mantle sources. In contrast,modal metasomatism of the mantle (< 0.2 b.y.) in aureolesaround evolved derivatives of basanite has petrographicallyand chemically transformed this ancient partial melting residue.The metasomatic fluids responsible for such metasomatism havean asthenospheric mantle source identical to the host magma.It is proposed that modal metasomatism occurs in contact metamorphicaureoles that surround apophyses of basanitic silicate meltin the lithospheric mantle. The gradient in CO2/(CO2 ? H2O)ratio that must surround such veins in the upper mantle (<20 kb) may encourage the development of enrichment fronts. Immediatelyadjacent to the vein, a wet zone with a relatively low CO2/(CO2? H2O) ratio would allow a precipitation of mica ? amphibole.Beyond this a dry zone with a higher CO2/(CO2 ? H2O) ratio wouldhasten chemical but not petrographic transformation of the wallrock.  相似文献   

8.
This study examines the groundwater characteristics in the Silver Bell Mountains, Arizona, USA, using a numerical model. Groundwater modeling is developed to describe the flow pattern in the study area and subsequently explores the possible interaction with regional porphyry copper deposits. A conceptual model is developed for the study area and regional hydrogeological conditions are simulated using the finite-difference groundwater flow model, MODFLOW-2005. The model results show that groundwater flow in the Silver Bell Mountains is strongly influenced by topography and its velocity varies with depth. In addition, the numerical model supports the idea of a continuous sustained interaction between groundwater flow and porphyry copper deposits in the Silver Bell Mountains. This interaction may result in continuing leaching of trace elements from the ore deposit, an important implication for continuing supergene alteration and enrichment of the porphyry copper deposit.  相似文献   

9.
The development of irrigation agriculture on valley floors in the southwestern United States has substantially altered natural drainage systems. This study discusses five anthropogenic factors that have altered the hydrologic function of a dryland basin floor in south-central Arizona. These factors are: (1) upstream urbanization and channel entrenchment, (2) dam construction, (3) artificial diversion of drainage, (4) obstruction of flow by transportation routes, and (5) stream channelization. The first two factors have altered hydrologic inputs to the basin floor, the third and fourth factors have changed regional and local patterns of flooding, and the fifth factor has resulted in channel instability and reduced flood attenuation. These five factors, along with a recent increase in the frequency of incursions of tropical moisture into southern Arizona, have enhanced flow variability and the potential for devastating flooding on the basin floor. This research demonstrates the need for basin-wide approaches to stream management in drylands and illustrates the importance of basing management decisions on geomorphic information concerning fluvial forms and processes.  相似文献   

10.
Lignin derivatives have been isolated for the first time from carbonaceous sections of the silicified (~90% SiO2) conifer Araucarioxylon arizonicum. The products released by sequential high vacuum pyrolysis and identified by combined gas chromatography-mass spectrometry (GC-MS) include a wide variety of alkyl-substituted, phenolic and condensed aromatic compounds.Brauns spruce lignin was pyrolized and analyzed by GC-MS as a comparison for the fossil wood data. The primary pyrolyzates at the 300°C step were CO2, H2O, ethanol and propanol. The main product at 450°C was 4-methyl-2-methoxyphenol (methyl guaiacol), but at 600°C the pyrolyzates were similar both in product composition and in relative abundance to those from silicified wood. The results suggest that the fossil wood experienced a mild thermal event during which the ether bonds were ruptured and loss of oxygen occurred along with the rearrangement of the original wood into a highly stable polymer.  相似文献   

11.
A reconnaissance geochemical survey of stream drainages within 21,000 km2 of southeastern Arizona and southwestern New Mexico shows broad zones of low-level to moderate contrast anomalies, many associated with mid-Tertiary eruptive centers and Tertiary fault zones. Of these eruptive centers, few are known to contain metallic deposits, and most of those known are minor. This, however, may be more a function of shallow erosion level than an indication of the absence of mineralization, since hydrothermal alteration and Fe-Mn-oxide staining are widespread, and geochemical anomalies are pervasive over a larger part of the region than outcrop observations would predict. Accordingly, interpretations of the geochemical data use considerations of relative erosion levels, and inferred element zonalities, to focus on possible undiscovered deposits in the subsurface of base-, precious-, and rare-metal deposits of plutonic-volcanic association. In order to enhance the identification of specific deep targets, we use the empirically determined ratio: This ratio is based on reported metal contents of nonmagnetic heavy-mineral samples from the drainage sediment, determined by emission spectrographic analysis. Before the ratio was computed for each sample site, the data were normalized to a previously estimated regional threshold value. A regional isopleth map was then prepared, using a cell-averaging computer routine, with contours drawn at the 25th, 50th, 75th, 80th, 90th, 95th and 99th percentiles of the computed data.  相似文献   

12.
The crystal structure of four birefringent andradite samples (two from Arizona, one from Madagascar, and one from Iran) was refined with the Rietveld method, space group $Ia\overline{3} d$ , and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Each sample contains an assemblage of three different cubic phases. From the electron-microprobe (EMPA) results, fine-scale intergrowths in the Arizona-2 and Madagascar samples appear homogeneous with nearly identical compositions of {Ca2.99Mg0.01}Σ3[ ${\text{Fe}}_{1.99}^{3 + }$ ${\text{Mn}}_{0.01}^{3 + }$ ]Σ2(Si2.95Al0.03 ${\text{Fe}}_{0.02}^{3 + }$ )Σ3O12, Adr98 (Arizona-2), and Adr97 (Madagascar). Both samples are near-end-member andradite, ideally {Ca3}[ ${\text{Fe}}_{2}^{3 + }$ ](Si3)O12, so cation ordering in the X, Y, or Z sites is not possible. Because of the large-scale intergrowths, the Arizona-1 and Iran samples contain three different compositions. Arizona-1 has compositions Adr97 (phase-1), Adr93Grs4 (phase-2), and Adr87Grs11 (phase-3). Iran sample has compositions Adr86Uv12 (phase-1), Adr69Uv30 (phase-2), and Adr76Uv22 (phase-3). The crystal structure of the three phases within each sample was modeled quite well as indicated by the Rietveld refinement statistics of reduced χ2 and overall R (F 2) values of, respectively, 1.980 and 0.0291 (Arizona-1); 1.091 and 0.0305 (Arizona-2); 1.362 and 0.0231 (Madagascar); and 1.681 and 0.0304 (Iran). The dominant phase for each sample has the following unit-cell parameters (Å) and weight fractions (%): a = 12.06314(1), 51.93(9) (Arizona-1); 12.04889(1), 52.47(1) (Arizona-2); 12.06276(1), 52.21(8) (Madagascar); and 12.05962(2), 63.3(1) (Iran). For these dominant phases, the distances and site occupancy factors (sofs) in terms of neutral atoms at the Ca(X), Fe(Y), and Si(Z) sites are as follows: <Ca–O> = 2.4348, Fe–O = 2.0121(6), Si–O = 1.6508(6) Å; Ca(sof) = 0.955(2), Fe(sof) = 0.930(2), and Si(sof) = 0.917(2) (Arizona-1); <Ca–O> = 2.4288, Fe–O = 2.0148(7), Si–O = 1.6476(7) Å; Ca(sof) = 0.953(2), Fe(sof) = 0.891(2), and Si(sof) = 0.927(2) (Arizona-2); <Ca–O> = 2.4319, Fe–O = 2.0220(6), Si–O = 1.6460(6) Å; Ca(sof) = 0.955(2), Fe(sof) = 0.941(2), and Si(sof) = 0.939(2) (Madagascar); and <Ca–O> = 2.4344, Fe–O = 2.0156(8), Si–O = 1.6468(8) Å; Ca(sof) = 0.928(2), Fe(sof) = 0.908(2), and Si(sof) = 0.932(3) (Iran). The sofs based on the EMPA results are similar to those obtained from the Rietveld refinement. Each phase in the HRPXRD results can be correlated with a specific chemical composition. For example, the Iran sample composition Adr63Uv30 corresponds to phase-3 that has the smallest unit-cell parameter; Adr76Uv22 corresponds to phase-1 that has the intermediate cell value; and Adr86Uv13 corresponds to phase-2 that has the largest unit-cell parameter. The bond distances compare well with those obtained from radii sum. The three different cubic phases in each sample cause strain that arises from the mismatch of the cubic unit-cell parameters and give rise to birefringence.  相似文献   

13.
Eijun Onta 《Earth》1983,19(2):164-165
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14.
《Applied Geochemistry》1994,9(5):597-608
In Pacheta Lake, a high-elevation alkaline lake proximal to the smelting region of southern Arizona-New Mexico, concentrations of transition metal ions in pore waters and co-existing sediments were compared. Copper, Fe, Mn and Zn have been partitioned among operationally defined sediment solid phases (exchangeable sites, organic complexes, amorphous oxides, crystalline oxides, sulfides and residual silicates) and their concentrations in interstitial waters were measured. Concentrations are reported as a function of depth in the sediment column. The diagenetic environment is described and cycling mechanisms postulated for the above metals.Selective, sequential extraction of metals from lake sediments showed different binding mechanisms for Cu and Zn, the former most strongly associated with organic complexes, and the latter with iron oxyhydroxides. This difference has strong implications for selective metal remobilization under variable environmental conditions, both naturally and anthropogenically induced. Copper and zinc in porewaters were estimated to diffuse to overlying waters at 12.8 and 21.9 μg/cm2/a, respectively. These fluxes are large enough to account for observed concentrations of Cu and Zn in overlying waters. No sediment metal contamination was directly attributable to smelting activity. However, this study does document a flux from sediments, which have accumulated Cu and Zn, to overlying waters no longer receiving trace metal deposition from now inactive smelters.  相似文献   

15.
The Lower Cretaceous Mural Limestone marks the maximum marine incursion into southeast Arizona during Aptian-Albian time and records the middle Cretaceous transition from coral-dominated to rudist-bivalve dominated reefs. Upper Mural Limestone facies are most often dominated by corals. However, rudists form significant frameworks at some localities, one of which is described in this paper. The paleoenvironmental distribution of three potential reef-builders (corals, rudists, and ‘oysters’) were studied at this patch reef locality. Corals built the framework of the inner reef core. The rudist Petalodontia initially gained a foothold in sheltered areas among corals and subsequently built a framework in the outer reef core. Caprinid rudists formed mounds in the outer reef to back reef areas. The rudists Toucasia and Monopleura and the oyster-like bivalve Chondrodonta formed beds or were scattered in the reef-flank and shelf lagoon sediments and did not contribute to the reef framework.Upper Mural Limestone reefs are important examples of the coexistence of corals and rudists during this middle Cretaceous faunal transition period. This study supports the idea that rudist-bivalves initially colonized protected back-reef areas early in the Cretaceous and only later in the Cretaceous did rudists dominate reef frameworks.  相似文献   

16.
Abandoned fields in Colorado River alluvium in the eastern Grand Canyon show signs of primitive agriculture. Presence of maize pollen in association with buried soils near Comanche Creek suggests that farming began prior to 3130 yr B.P. Cotton pollen, identified in buried soils near Nankoweap Creek, dates to 1310 yr B.P., approximately 500 years earlier than previously reported anywhere on the Colorado Plateau. Farming spanned three millennia in this reach of the canyon. Entrenchment, starting approximately 700 yr B.P., making water diversion to fields infeasible, was likely responsible for field abandonment. © 2000 John Wiley & Sons, Inc.  相似文献   

17.
This work reports the results of noble gas (Ne, Ar, Kr, Xe) analyses of accidental mantle xenoliths from San Carlos, Arizona. Except for the addition of radiogenic 40Ar and mass fractionation effects, the isotopic structures of these gases are indistinguishable from atmospheric composition. The absence of 129Xe excesses in these rocks may reflect indirect mixing of atmospheric gases with the source region of the xenoliths. The dominant influence on the noble gas abundances in the San Carlos xenoliths appears to have been diffusive gas loss, which may have occurred in a mantle metamorphic event or during contact with the host basanite magma. Evidence is presented for the partitioning of significant amounts of the heavy noble gases into fluid inclusions in the xenolith minerals; the proportion of each gas in the inclusions increases with increasing atomic weight of the gas, possibly reflecting solubility effects. The noble gases are present in greater concentration in pyroxenes than in olivine, similar to the behavior of other incompatible elements.  相似文献   

18.
Mineral exploration programs commonly use a combination of geological, geophysical and remotely sensed data to detect sets of optimal conditions for potential ore deposits. Prospectivity mapping techniques can integrate and analyse these digital geological data sets to produce maps that identify where optimal conditions converge. Three prospectivity mapping techniques – weights of evidence, fuzzy logic and a combination of these two methods – were applied to a 32,000 km2 study area within the southeastern Arizona porphyry Cu district and then assessed based on their ability to identify new and existing areas of high mineral prospectivity. Validity testing revealed that the fuzzy logic method using membership values based on an exploration model identified known Cu deposits considerably better than those that relied solely on weights of evidence, and slightly better than those that used a combination of weights of evidence and fuzzy logic. This led to the selection of the prospectivity map created using the fuzzy logic method with membership values based on an exploration model. Three case study areas were identified that comprise many critical geological and geophysical characteristics favourable to hosting porphyry Cu mineralisation, but not associated with known mining or exploration activity. Detailed analysis of each case study has been performed to promote these areas as potential targets and to demonstrate the ability of prospectivity modelling techniques as useful tools in mineral exploration programs.  相似文献   

19.
The lower part of a 5-m core from Hay Lake (34°N, 109° 25′W) at 2780 m in east-central Arizona provides a pollen record for the middle Wisconsin. Identification of fossil pines is based on a key modified from Hansen and Cushing (1973, Geological Society of America Bulletin84, 1181–1200). Pinus edulis and P. monophylla are similar in size and morphology but are significantly different from P. flexilis. Haploxylon pines dominate the pollen record. The abundance of pinyon pines during the middle Wisconsin is interpreted as indicating that this group was widespread at lower elevations. The local vegetation was mixed conifer forest consisting of Picea, P. aristata, P. flexilis and/or P. strobiformis, and with P. ponderosa and/or P. contorta after about 26,000 yr B.P. Tree line was above the elevation of Hay Lake. The middle Wisconsin climate is inferred to have been cooler than today and is marked by more available moisture that permitted pinyon pines to grow at low elevations.  相似文献   

20.
Water storage reservoirs were an important feature of economic organization among ancient societies in the North American Southwest. Analyses of reservoir sediments from a Hohokam archaeological site in the Sonoran Desert yielded taxonomic species of ostracodes (microscopic crustaceans) and pollen grains that are indicative of a past water‐rich environment. The discovery that this reservoir was capable of storing water on a long‐term basis indicates that archaeological models for the region, which have relied on direct historic analogy, must be reexamined. In contrast to the local ethnographic record, paleoecological data generated by this study imply that the Hohokam could establish permanent desert settlements with water storage reservoirs away from perennial rivers and streams. Moreover, residents of these areas were geographically positioned to facilitate the circulation of marine resources (i.e., salt and shell) from the Gulf of California to territories within and beyond the Hohokam region. © 2004 Wiley Periodicals, Inc.  相似文献   

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