共查询到20条相似文献,搜索用时 31 毫秒
1.
Hussain J. Alfaifi Mohammed S. Abdelfatah Kamal Abdelrahman Faisal K. Zaidi Elkhedr Ibrahim Nassir S. Alarifi 《Journal of the Geological Society of India》2017,89(6):669-674
Groundwater stored in the deep seated sedimentary aquifers is the most important source of water supply. The lack of sufficient groundwater recharge and the overdependence on groundwater might lead to unavailability of this precious natural resource if proper management practices are not adopted. Finite difference modelling using the MODFLOW program was carried out in the east of Riyadh city to simulate the groundwater level conditions under different abstraction scenarios. The simulated aquifer system combines the Wasia and Biyadh aquifer (composed of sandstone) and Aruma aquifer (limestone) which lies between 24°30'00"- 25°30'00" N and longitudes 47°00'00"- 48°00'00"E. The transmissivity and storage coefficient values of Biyadh aquifer are 7.0x10-3 to 7.0x10-2 m2/day and 3.7x10-4 to 9.4x10-4 respectively. The transmissivity and storage coefficient values of Wasia aquifer ranges from 6.7x10-3 to 8.5x10-2 m2/day and 2x10-4 to 2.3x10-4 respectively. The model calibration involved altering the values of model input parameters to match field conditions within certain acceptable limits to forecast the aquifer response over a period of 35 years (2015-2050). The modelling grid consisted of 20 and 24 columns with the grids spacing of 4 km for the small grids and 6 km for large grids. The results showed that though the Wasia aquifer was productive, it showed a large decline in water levels if water abstraction continued at the present rate. If the existing trends of groundwater withdraw continues; the piezometric heads in Wasia and Biyadh aquifers will decline by the year 2050. A reduction in 25% of the existing groundwater pumping rate in the well field will minimize the rate of groundwater decline in the aquifer to a considerable extent. 相似文献
2.
The investigated area is located south Egypt, between latitudes 22°00′N and 24°15′N, and longitudes 28°00′E and 30°00′E. It
covers a total area of about 95,000.17 km2. The area was remotely sensed to identify landscape and its land and water resources. A reconnaissance survey followed by
detailed one was done to verify the information resulted from satellite images. The prevailing deposits of the area could
be expressed as (1) the Nubian sandstone, (2) the Quaternary sediments, and (3) the sand dunes belt. Fourteen main and sub-main
landforms were recognized, i.e., sand sheets (high, moderately high, moderate, and low), depressions (high, moderately high,
moderate, and low), dry valleys, peniplains, footslopes, barchans, tablelands, and scattered hills. Associated soils were
distinguished and classified as Typic Torripsamments, Typic Haplocalcids, Typic Torrifluvents, and Typic Haplodurids. Spatial
variability of soil and water characteristics was identified through using ordinary Kriging interpolation method. Land surface
temperatures in both summer and winter seasons were derived from thermal band, and soil temperature regimes were defined digitally
as hyperthermic. Water potentiality was identified and classified according to salinity and sodicity hazards to C2-S1 and
C3-S1. Using GIS techniques, soil potentiality spatial model (SPSM) was designed to get potentiality classes, i.e., high,
moderately high, moderate, low, and very low. 相似文献
3.
This paper describes the morphology of the equatorial electrojet (EEJ) along 45°W longitude in east Brazil, where the ground
magnetic (dip) equator is associated with the largest declination in the world. Daily range of the horizontal field (ΔH), as expected, was largest at the station in the chain closest to the dip equator, Sao Luiz (inclination −0.25°S). ΔZ was largest positive at Eusebio (inclination 9.34°S) and largest negative at Belem (inclination 7.06°N); both near the fringe
of EEJ belt. ΔZ at Sao Luiz during the daytime was unexpectedly large negative in-spite of a small dip and also located south of the dip
equator where ΔZ should be positive. Center of EEJ was found to be shifted southward of the dip equator by about 1° in latitude. During southern
summer, ΔY started decreasing from 00 h and reached a minimum value in the afternoon, an abnormal feature not discussed for any station
so far. The mid-day value of the direction of ΔH vector was 22°–24°W compared to the declination of 19°–21°W in the region. 相似文献
4.
On the basis of mineral paragenesis and the chemistry and homogenization temperatures of fluid inclusions, the physicochemical
parameters were calculated for the formation of the Dalingkou Ag-Pb-Zn deposit in Zhejiang. From the early to the late stage
of mineralization the ore-forming temperature venation was found to be 298.5 °C → 267.0 °C → 217.6 °C → 167.3 °C, with a corresponding
pH change of 3.0 ∼ 5.8 → 6.1 → 6.7→ 5.0 ∼ 7.3. The pressure changed from 403.8 to 128.5 atm, andlogf S2-9.9 → -11.2 → < -15; logf o2< -44→ -45.6 ∼ -42.6 → > -44.2; and logf co2 around -1.55.
In conjunction with geological observations, the deposit is considered to be of meso-epithermal origin, i.e., it was formed
after continental volcanic-subvolcanic activity. The major factors affecting ore precipitation are the decreasing temperature
and the increasing pH of ore-forming solutions. 相似文献
5.
Angelika Kalt Fernando Corfu Jan R. Wijbrans 《Contributions to Mineralogy and Petrology》2000,138(2):143-163
A temperature–time path was constructed for high-temperature low-pressure (HT–LP) migmatites of the Bayerische Wald, internal
zone of the Variscan belt, Germany. The migmatites are characterised by prograde biotite dehydration melting, peak metamorphic
conditions of approximately 850 °C and 0.5–0.7 GPa and retrograde melt crystallisation at 800 °C. The time-calibration of
the pressure–temperature path is based on U–Pb dating of single zircon and monazite grains and titanite separates, on 40Ar/39Ar ages obtained by incremental heating experiments on hornblende separates, single grains of biotite and K-feldspar, and
on 40Ar/39Ar spot fusion ages of biotite determined in situ from sample sections. Additionally, crude estimates of the duration of peak
metamorphism were derived from garnet zoning patterns, suggesting that peak temperatures of 850 °C cannot have prevailed much
longer than 2.5 Ma. The temperature–time paths obtained for two areas approximately 30 km apart do not differ from each other
considerably. U–Pb zircon ages reflect crystallisation from melt at 850–800 °C at 323 Ma (southeastern area) and 326 Ma (northwestern
area). The U–Pb ages of monazite mainly coincide with those from zircon but are complicated by variable degrees of inheritance.
The preservation of inherited monazite and the presence of excess 206Pb resulting from the incorporation of excess 230Th in monazite formed during HT–LP metamorphism suggest that monazite ages in the migmatites of the Bayerische Wald reflect
crystallisation from melt at 850–800 °C and persistence of older grains at these temperatures during a comparatively short
thermal peak. The U–Pb ages of titanite (321 Ma) and 40Ar/39Ar ages of hornblende (322–316 Ma) and biotite (313–309 Ma) reflect cooling through the respective closure temperatures of
approximately 700, 570–500 and 345–310 °C published in the literature. Most of the feldspars' ages (305–296 Ma) probably record
cooling below 150–300 °C, while two grains most likely have higher closure temperatures. The temperature–time paths are characterised
by a short thermal peak, by moderate average cooling rates and by a decrease in cooling rates from 100 °C/my at temperatures
between 850–800 and 700 °C to 11–16 °C/my at temperatures down to 345–310 °C. Further cooling to feldspar closure for Ar was
probably even slower. The lack of decompressional features, the moderate average cooling rates and the decline of cooling
rates with time are not easily reconciled with a model of asthenospheric heating, rapid uplift and extension due to lithospheric
delamination as proposed elsewhere. Instead, the high peak temperatures at comparatively shallow crustal levels along with
the short thermal peak require external advective heating by hot mafic or ultramafic material.
Received: 7 July 1999 / Accepted: 28 October 1999 相似文献
6.
7.
S. W. Faryad F. Melcher G. Hoinkes J. Puhl T. Meisel W. Frank 《Mineralogy and Petrology》2002,74(1):49-73
Summary Retrograde eclogites and serpentinites from the Hochgr?ssen massif, Styria, are parts of the Speik complex in the Austroalpine
basement nappes of the Eastern Alps. They are in tectonic contact with pre-Alpine gneisses, amphibolites, and Permo-Triassic
quartz phyllites (Rannach Series). The eclogites are derived from ocean-floor basalts with affinities to mid-ocean ridge and
back-arc basin basalts. Fresh eclogites are rare and contain omphacite with a maximum of 39 mol% jadeite content, garnet (Py15–19) and amphibole. Retrograde eclogites consist of amphibole and symplectites of Na-poor clinopyroxene (5–8 mol% Jd) + albite ± amphibole.
Amphiboles are classified as edenite, pargasite, tschermakite, magnesiohornblende and actinolite. In relatively fresh eclogite,
edenite is a common amphibole and texturally coexists with omphacite and garnet. An average temperature of 700 °C was obtained
for eclogite facies metamorphism using garnet-pyroxene thermometry. A minimum pressure of 1.5 GPa is indicated by the maximum
jadeite content in omphacite. Thermobarometric calculations using the TWEEQ program for amphibole in textural equilibrium
with omphacite and garnet give pressures of 1.8–2.2 GPa at 700 °C. The equilibrium assemblage of Na-poor clinopyroxene, albite,
amphibole and zoisite in the symplectites gives a pressure of about 0.6–0.8 GPa at 590–640 °C. 40Ar/39Ar radiometric dating of edenitic amphibole in textural equilibrium with omphacite gave a plateau age of 397.3 ± 7.8 Ma, and
probably indicates retrograde cooling through the closure temperature for amphibole (∼500 °C). The age of the high-pressure
metamorphism thus must be pre-Variscan and points to one of the earliest metamorphic events in the Austroalpine nappes known
to date.
Received June 11, 2000; revised version accepted January 2, 2001 相似文献
8.
郑州邙山马兰黄土的光释光(OSL)测年初步研究 总被引:6,自引:1,他引:5
对郑州市西北邙山黄土塬赵下峪(34°58'N,113°22'E)剖面上部马兰黄土(厚约87m)不同层位的24个样品作了细颗粒(4-11μm)组分红外释光(IRSL)测年,其中8个样品同时进行了细颗粒组分绿光释光(GLSL)测年。样品的IRSL和GLSL信号强度都在Daybreak1100TL/OSL检测系统中测量。该系统的本底计数为70-80光子/秒。被检测的IRSL和GLSL波长分别为340-480nm和340±25nm;激发光束波长分别为880±80nm和514±14nm,功率为18mW和15-16mW。所有样品的等效剂量都用再生释光法测定;环境剂量率是通过测定样品的铀、钍和钾含量,按Aitken(1985)的转换系数确定的,考虑了含水量的影响及宇宙射线的贡献。从这批样品的光释光测年结果可得以下初步认识:(1)8个样品细颗粒组分的IRSL和GLSL测定的等效剂量和年龄值,除1个样品外,都在1-2σ范围内一致。这可能提供了沉积物光释光测年可靠性的一种自检方法。(2)邙山剖面马兰黄土不同层位段的沉积速率变化十分显著,从0.4m/ka到5.6m/ka,并与剖面上质量磁化率测定值的变化大致相吻合。该剖面马兰黄土至少有4个快速堆积层(沉积速率>3m/ka),其磁化率低而变化小;3个缓慢堆积层(沉积速率<0.5m/ka),其磁化率大或变化显著,它们之间有一系列过渡层。(3)邙山马兰黄土大体可三分即上部(L1-1)埋深2.7-27.5m,中部(L1-2)埋深27.5-57.9m)和下部(L1-3)埋深57.9-87.9m。它们的形成年代分别为10.8-36.2ka B P,36.2-70.3ka B P和70.3-80.2ka B P。较详细的黄土-古土壤序列年代表将在文中讨论 相似文献
9.
Over 800 paleomagnetic samples were collected from 79 sample localities, ranging in age from Devonian, Carboniferous, Permian
to Jurassic for paleo-latitude research on the Guizhou terrain. The area sampled covers 13 counties with an area of about
50000 km2. The paleomagnetic results obtained indicate that the Guizhou terrain was at 11.4°S in Devonian, 4.5°-9.3°S in Carboniferous,
2.6° − 4.5°S in Permian, 14.8°N in Triassic and 24.5° − 26.0°N in Jurassic. In the Cretaceous period, the paleo-latitude of
the area was at 22.4 − 23.6°N. Therefore, a variation curve of paleo-latitude is established in this paper for the Guizhou
terrain from Late Devonian to Late Cretaceous time. 相似文献
10.
Life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance. We were able to establish
the chronology and cooling history of the Zaldívar porphyry copper deposit (Northern Chile) by applying a combination of different
isotopic dating methods in minerals with different closure temperatures, including 40Ar/39Ar geochronology and zircon fission track thermochronology, together with fluid inclusion thermometry and previous published
U–Pb zircon geochronology. The hydrothermal mineralization in the Zaldívar deposit is genetically related to the Llamo Porphyry
unit. Samples of igneous biotites from this intrusion yielded 40Ar/39Ar plateau ages between 35.5 ± 0.7 and 37.7 ± 0.4 Ma defining a weighted average of 36.6 ± 0.5 Ma (2σ). In contrast, one sample from the Zaldívar porphyry, one from the andesites, and two from the Llamo porphyry yielded considerably
younger fission track ages of approximately 29 Ma with a weighted mean for all ages of 29.1 ± 1.7 Ma (2σ). Thermal and compositional constraints for the hydrothermal system in the Zaldívar deposit from fluid inclusions thermometry
show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit.
The main mineralization and alteration event is characterized by high temperature (above 320°C) hypersaline fluids (salinity
between 30 and 56 wt.% NaCl equivalents) coexisting with low-density gas-rich inclusions (salinity less than 17 wt.% NaCl
equivalents) that homogenizing into the gas phase at temperatures above 350°C. The second episode corresponds to a low-temperature
event which is characterized by liquid-rich fluid inclusions that homogenize into the liquid phase at temperatures ranging
from 200°C to 300°C with salinities lower than 10 wt.% NaCl equivalents. The 40Ar/39Ar data (36.6 ± 0.5 Ma, weighted average) obtained from igneous biotites represent the minimum age for the last high-temperature
(above 300°C) hydrothermal pulse. When compared with previously published U–Pb ages (38.7 ± 1.3 Ma) in zircons from the Llamo
porphyry, a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the
last high-temperature hydrothermal event is evident. Cooling took place from approximately 800°C (crystallization of the intrusive
complex defined by zircon U–Pb ages) to below 300 ± 50°C (biotite 40Ar/39Ar closure temperature) within approximately 1.5 m.y. Because the thermal annealing of fission tracks in zircons occurs at
temperatures of 240 ± 30°, the zircon fission track (ZFT) ages of 29.1 ± 1.7 Ma (2σ) mark the end of the thermal activity in the Zaldívar area, specifically the time when the whole area cooled below this temperature,
well after the collapse of the main hydrothermal event in the Zaldívar porphyry copper deposit. This cooling age roughly coincides
with the age defined for the emplacement of dacitic dikes at 31 ± 2.8 Ma (2σ) (published K–Ar whole rock), 5 km south of the Zaldívar deposit, in the Escondida area. This late magmatic pulse probably
is responsible for high heat flow in the Zaldívar deposit as late as 29 Ma. There is no evidence that the low temperature
hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event. The zircon fission track cooling
ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in
the geothermal field imposed by the intrusion of magmatic bodies, with or without any association with low temperature hydrothermal
activity. 相似文献
11.
Issanova Gulnura Jilili Abuduwaili Semenov Oleg 《Arabian Journal of Geosciences》2014,7(11):4513-4521
Deflation processes are important in arid environments such as deserts. The deserts of Kazakhstan mostly cover lowlands and extend from the eastern coast of the Caspian Sea to the piedmonts of the Tien-Shan Mountain. Desert areas are also major source areas of dust/sand storm activities. We considered deflation processes in the southern Pre-Balkhash deserts. In Kazakhstan, desertification processes due to wind erosion in the form of dust/sand storms were observed in semi-desert and desert landscapes. During analysis of numerous long-term meteorological data and cartographic materials, we revealed the sand movement directions which allow prediction of future potential sand movement patterns or processes in southern Pre-Balkhash deserts. The Taukum, Moiynkum deserts, Ili river deltas and valleys, and southern coastal of Lake Balkhash are most prone to dust/sand storms. The most frequent storms were observed in the Bakanas weather station (Ile river valley). Sand/dust transport occurs mainly in the east, south-east north-east direction in the southern Pre-Balkhash deserts. The high amount of sand transportation was observed at the Kuigan weather station; low amounts were encountered at the Naimansuiek weather station. The amount of airborne sand/dust varies in accordance with the general and local meteorological features, the complexity of relief forms, soil conditions and properties, lithology, and various contributions of the human activities. Thus, our study on deflation processes in the southern Pre-Balkhash deserts has great importance towards aiding in the prediction and monitoring of dust/sand storms and movement patterns. 相似文献
12.
Dmitry L. Lakshtanov Stanislav V. Sinogeikin Jay D. Bass 《Physics and Chemistry of Minerals》2007,34(1):11-22
The single-crystal acoustic velocities of α- and β-quartz were measured by Brillouin spectroscopy to a maximum temperature
>1,500°C at room pressure. From these velocities, the single-crystal elastic moduli were calculated up to 1,050°C, exceeding
the temperature range of previous measurements by 350°C for the elastic moduli and by 710°C for acoustic velocities. The ordinary
refractive index (n
o) of α- and β-quartz was measured from room temperature to 800°C. In the temperature interval from ∼950 to 1,000°C a subtle
change in the temperature derivative of the longitudinal acoustic velocity was observed in platelet geometry for all measured
directions. The high-temperature acoustic velocity data may indicate the presence of a second phase, presumably β-cristobalite,
that nucleates below 1,000°C.
相似文献
Dmitry L. LakshtanovEmail: |
13.
We present images of the star-forming regionG23.01–0.41 at 6.7GHz in the Class II methanol maser transition 51–60
A
+, produced from archival observations on the European VLBI Network. Our map of the source and its maser spots contains 24
maser components. The data for each spot—absolute coordinates, coordinates relative to the calibration feature, peak flux
and flux integrated over the spot, size, position angle, velocity along the line of sight, and line full width at half-maximum—are
collected in tabular form. The spatial region occupied by the maser spots is approximated by a 200×130 milliarcsec ellipse
in position angle PA = −0.40°, centered on the absolute coordinates α
0 = 18h34m40.282s, δ
0 = −09°00′38.27″ (J2000). If the source is a protoplanetary disk, then, for the distance estimate derived from trigonometric
parallax, its diameter is 1800 AU, and the mass of the central protostar is 23.5M
⊙. 相似文献
14.
Abhishek Saha Avik Dhang Jyotisankar Ray Suvankar Chakraborty David Moecher 《Journal of Earth System Science》2010,119(3):365-381
Field studies supplemented by petrographic analyses clearly reveal complete preservation of ophiolite suite from Port Blair
(11°39′N: 92°45′E) to Chiriyatapu (11°30′24″N: 92°42′30″E) stretch of South Andaman. The ophiolite suite reveals serpentinite
at the base which is overlain unconformably by cumulate ultramafic-mafic members with discernible cumulus texture and igneous
layering. Basaltic dykes are found to cut across the cumulate ultramafic-mafic members. The succession is capped by well exposed
pillow basalts interlayered with arkosic sediments. Olivine from the basal serpentinite unit are highly magnesian (Fo80.1–86.2). All clinopyroxene analyses from cumulate pyroxenite, cumulate gabbro and basaltic dyke are discriminated to be ‘Quad’ and
are uniformly restricted to the diopside field. Composition of plagioclase in different lithomembers is systematically varying
from calcic to sodic endmembers progressively from cumulate pyroxenite to pillow basalt through cumulate gabbro and basaltic
dyke. Plagioclase phenocrysts from basaltic dyke are found to be distinctly zoned (An60.7-An35.3) whereas groundmass plagioclase are relatively sodic (An33-An23.5). Deduced thermobarometric data from different lithomembers clearly correspond to the observed preservation of complete ophiolite
suite. 相似文献
15.
Arne P. Willner Axel Gerdes Hans-Joachim Massonne Alexander Schmidt Masafumi Sudo Stuart N. Thomson Graciela Vujovich 《Contributions to Mineralogy and Petrology》2011,162(2):303-327
The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is
composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde
garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf
mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are
followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration
of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained
at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx
at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica.
At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid
intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm
of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent
collisional setting. 相似文献
16.
M. Akaogi H. Takayama H. Kojitani H. Kawaji T. Atake 《Physics and Chemistry of Minerals》2007,34(3):169-183
The low-temperature isobaric heat capacities (C
p) of β- and γ-Mg2SiO4 were measured at the range of 1.8–304.7 K with a thermal relaxation method using the Physical Property Measurement System.
The obtained standard entropies (S°298) of β- and γ-Mg2SiO4 are 86.4 ± 0.4 and 82.7 ± 0.5 J/mol K, respectively. Enthalpies of transitions among α-, β- and γ-Mg2SiO4 were measured by high-temperature drop-solution calorimetry with gas-bubbling technique. The enthalpies of the α−β and β−γ
transitions at 298 K (ΔH°298) in Mg2SiO4 are 27.2 ± 3.6 and 12.9 ± 3.3 kJ/mol, respectively. Calculated α−β and β−γ transition boundaries were generally consistent
with those determined by high-pressure experiments within the errors. Combining the measured ΔH°298 and ΔS°298 with selected data of in situ X-ray diffraction experiments at high pressure, the ΔH°298 and ΔS°298 of the α−β and β−γ transitions were optimized. Calculation using the optimized data tightly constrained the α−β and β−γ transition
boundaries in the P, T space. The slope of α−β transition boundary is 3.1 MPa/K at 13.4 GPa and 1,400 K, and that of β−γ boundary 5.2 MPa/K at 18.7 GPa
and 1,600 K. The post-spinel transition boundary of γ-Mg2SiO4 to MgSiO3 perovskite plus MgO was also calculated, using the optimized data on γ-Mg2SiO4 and available enthalpy and entropy data on MgSiO3 perovskite and MgO. The calculated post-spinel boundary with a Clapeyron slope of −2.6 ± 0.2 MPa/K is located at pressure
consistent with the 660 km discontinuity, considering the error of the thermodynamic data. 相似文献
17.
Osvaldo M. Rabbia Laura B. Hernández David H. French Robert W. King John C. Ayers 《Mineralium Deposita》2009,44(8):849-866
Mineralogical, textural, and chemical analyses (EPMA and PIXE) of hydrothermal rutile in the El Teniente porphyry Cu–Mo deposit
help to better constrain ore formation processes. Rutile formed from igneous Ti-rich phases (sphene, biotite, Ti-magnetite,
and ilmenite) by re-equilibration and/or breakdown under hydrothermal conditions at temperatures ranging between 400°C and
700°C. Most rutile nucleate and grow at the original textural position of its Ti-rich igneous parent mineral phase. The distribution
of Mo content in rutile indicates that low-temperature (∼400–550°C), Mo-poor rutile (5.4 ± 1.1 ppm) is dominantly in the Mo-rich
mafic wallrocks (high-grade ore), while high-temperature (∼550-700°C), Mo-rich rutile (186 ± 20 ppm) is found in the Mo-poor
felsic porphyries (low-grade ore). Rutile from late dacite ring dikes is a notable exception to this distribution pattern.
The Sb content in rutile from the high-temperature potassic core of the deposit to its low-temperature propylitic fringe remains
relatively constant (35 ± 3 ppm). Temperature and Mo content of the hydrothermal fluids in addition to Mo/Ti ratio, modal
abundance and stability of Ti-rich parental phases are key factors constraining Mo content and provenance in high-temperature
(≥550°C) rutile. The initial Mo content of parent mineral phases is controlled by melt composition and oxygen fugacity as
well as timing and efficiency of fluid–melt separation. Enhanced reduction of SO2-rich fluids and sulfide deposition in the Fe-rich mafic wallrocks influences the low-temperature (≤550°C) rutile chemistry.
The data are consistent with a model of fluid circulation of hot (>550°C), oxidized (ƒO2 ≥ NNO + 1.3), SO2-rich and Mo-bearing fluids, likely exsolved from deeper crystallizing parts of the porphyry system and fluxed through the
upper dacite porphyries and related structures, with metal deposition dominantly in the Fe-rich mafic wallrocks. 相似文献
18.
The occurrence, movement and control of groundwater, particularly in hard-rock areas, are governed by different factors such
as topography, lithology, structures like fractures, faults and nature of weathering. An attempt is made in the present study
to investigate the extent of the influence of structures such as fractures and thereby delineate the nature of subsurface
lithology with the help of an electrical resistivity method. For this study, the Upper Gunjanaeru River basin, Cuddapah district
Andhra Pradesh was chosen to determine groundwater potentials. In order to understand the significance of the fracture pattern,
geological, hydrogeomorphological and lineament maps were prepared based on the field data and also from the LANDSAT TM imagery.
Further, electrical resistivity surveys were conducted to determine the subsurface lithology and also to confirm the studies
of LANDSAT imagery. The isoresistivity contour map has been prepared based on the 45 VES conducted to determine the resistivity
variations in the study area. The isoresistivity contours obtained were found to conform to the structural trends obtained
by geological studies and also confirm the relationship between the structure and secondary porosity present in the rocks.
The lineaments in the area have two preferred directions. One set is a NE-SW direction (N 30°–70° E; S 30°–70° W) and another
is a NW-SE direction (N 0°–30° W; S 0°–30° E and N 60°–80° W; S 60°–80° E). The water-table contour map shows that the direction
of groundwater flow is south to north.
Received: 3 March 1997 · Accepted: 17 June 1997 相似文献
19.
H. Fukui O. Ohtaka T. Nagai T. Katsura K. Funakoshi W. Utsumi 《Physics and Chemistry of Minerals》2000,27(6):367-370
Using the high-pressure differential thermal analysis (HP-DTA) system in a cubic multianvil high-pressure apparatus, we measured
the melting points of portlandite, Ca(OH)2, up to 6 GPa and 1000 °C. We detected endothermic behavior at the temperature and pressure conditions of 800 °C and 2.5 GPa,
769 °C and 3.5 GPa, 752 °C and 4.0 GPa, 686 °C and 5.0 GPa, and 596 °C and 6.0 GPa, respectively, due to melting of portlandite.
By in situ X-ray studies under pressure, the melting of portlandite was observed at 730 °C and 4.32 GPa and at 640 °C and 5.81 GPa,
respectively. Results of both HP-DTA and X-ray studies were consistent within experimental error. The melting is congruent
and has a negative Clapeyron slope, indicating that liquid Ca(OH)2 has higher densities than crystalline portlandite in this pressure range.
Received: 19 June 1999 / Revised, accepted: 11 September 1999 相似文献
20.
J. L. Rosenberg P. G. Spry C. E. Jacobson N. J. Cook F. M. Vokes 《Mineralium Deposita》1998,34(1):19-34
The Bleikvassli massive sulfide ore deposit is hosted by Proterozoic pelitic, quartzofeldspathic, and amphibolitic rocks
of the Uppermost Allochthon of the Scandinavian Caledonides. Staurolite-garnet-biotite and kyanite-staurolite-biotite assemblages
indicate that metamorphism reached the kyanite zone of the amphibolite facies. Geothermobarometry was conducted on rocks in
and around the deposit using a variety of silicate and sulfide calibrations. Temperature determinations are most reliant on
the garnet-biotite exchange reaction, with analyses obtained from 259 garnet rims and adjacent biotite. Results from nine
calibrations of the garnet-biotite geothermometer are considered, but compositional limitations of many calibrations involving
high Ca and Mn contents in garnet and AlVI and Ti in biotite make many of the coexisting mineral pairs unsuitable. Average temperatures calculated from the two calibrations
that most closely address the garnet-biotite compositions observed at Bleikvassli are 584 °C ± 49 °C and 570 °C ± 40 °C. The
application of two calibrations of the garnet-staurolite geothermometer on a limited number of samples yields 581 °C ± 2 °C
and 589 °C ± 12 °C, assuming a
H2O=0.84, based upon calculations of the modal proportions of gaseous species. Pressure determinations are less constrained.
Phengite and plagioclase-biotite-garnet-muscovite geobarometers give average pressures of approximately 5.0 kbar and 8.5 ± 1.2 kbar,
respectively. Pressures obtained from the sphalerite-hexagonal pyrrhotite-pyrite barometer average 7.7 ± 1.0 kbar. In consideration
of these results, the peak metamorphic conditions at the Bleikvassli deposit are estimated to be 580 °C and 8 kbar.
Received: 18 June 1997 / Accepted: 14 May 1998 相似文献