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1.
The Vermilion district of northerneastern Minnesota is a classic example of a lower Precambrian greenstone-granite terrane. It is a complex volcanic-sedimentary pile, characterized by repeated periods of volcanism and the presence of intercalated pyroclastic, volcanoclastic and epiclastic rocks. The volcanic-sedimentary pile is surrounded and intruded by contemporaneous granitic batholiths. Several rock units from the district have been dated by the whole-rock Rb-Sr method. The isochron ages and the corresponding initial Sr87/Sr86 ratios (= I) are:
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2.
Delayed neutron measurements of U and Th in three meteorites yield the following values:
t(in b.y.) ± 2σ1 ± 2σ
Ely Greenstone2.69 ± 0.080.70056 ± 0.00026
Newton Lake Formation2.65 ±0.110.70086 ± 0.00024
Granitic pebbles2.69 ± 0.280.70078 ± 0.00058
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3.
Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using λ 87Rb = 1.42 · 10?11a?1, NBS 70A = 522 ppm Rb and 65.3 ppm Sr):
BruderheimU (ppb)Th(ppb)
Bruderheim14.5 ± 1.0171 ± 65
Peace River11.8 ± 0.796 ± 46
Stannern220 ± 6563 ± 190
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4.
Intercalibration of one intralaboratory and three interlaboratory standards used in 40Ar-39Ar dating has been carried out. In order to provide homogeneous values for 40Ar140K the standards were prepared by careful handpicking. To control the neutron fluence in the Herald Reactor (A.W.R.E.) 16 aliquots of the standards were arranged along 0.6 × 60 cm of a single silica tube. The corrections for all known interferences from K, Ca, Cl were carefully assessed. Two of the hornblende standards, Hb3gr and MMHb-1 appear homogeneous at the 0.1% level while the other two standards, LP-6 and FY12a are not completely homogeneous. The mean values of 40Ar140K when referenced to the previously determined value for Hb3gr (turner et al., 1971) are:
Ma87Sr/86Sr initial (IR)
(1) Differentiated gabbro-granophyre from a stratigraphically old (Kathleen Valley) greenstone sequence> 2718 ± 500.7007 ± 0.0004
(2) Voluminous tonalite, the Lawlers Tonalite2652 ± 200.70152 ± 0.00012
2576 ± 140.70218 ± 0.00021
(3) A less voluminous leucogranite, and a large complex pegmatite cutting the Perseverance nickel orebody2588 ± 180.7624 ± 0.0068
(4) Aplitic leucotonalite (very minor volumes but widespread)2474 ± 140.70193 ± 0.00012
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5.
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm2 total pressure.Complete solid solution of RbMg3AlSi3O10(OH)2 in KMg3AlSi3O10(OH)2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi3O8 in KAlSi3O8 has been found at all temperatures investigated.Distribution coefficients, expressed as Kd = (Rb/K) in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined KD values and their approximate Rb end-member mole fraction (XRM) ranges of constancy are summarized as follows: (°C)TKDPhlog/Vap.XRMKDSandi/Vap.Xrm
Hb3grhbld.08504 ± .05%(±lσ)1072. m.y.
MMHb-1hbld.03493 ± 05%518.9 m.y.
LP-6biot.007735 ± .13%128.5 m.y.
FY12ahbld.02858 ± .25%435.0 m.y.
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6.
A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data:
T(°C)=i=06aiXiKCl
where T is the liquidus temperature, XKCl is mole fraction of KCl, and ai (listed below) are the derived empirical constants.
(°C)TKDPhlog/Vap.XRMKDSanid/Vap.XRM
5000.64 ± 0.110–0.20.17 ± 0.040–0.07
7001.11 ± 0.110–0.20.33 ± 0.040–0.1
8001.28 ± 0.030–0.20.45 ± 0.060–0.1
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7.
Oxygen isotope fractionations between wollastonite, diopside, jadeite, hedenbergite and water have been experimentally studied at high pressures (1<- PH2O ≥ 24 kbar) and temperatures (400/dgT <- 800/dgC) using the three-isotope method (Matsuhisa et al., 1978). Initial 18O16O fractionations were made close to equilibrium and initial 17O16O ratios were well removed from equilibrium, allowing accurate determinations of the equilibrium 18O16O fractionations and of the extent of isotopic exchange. Scanning electron microscope and rate studies show that the wollastonite-water and diopside-water exchange reactions occur largely by solution-precipitation (Ostwald Ripening) mechanisms. Equilibrium 18O16O fractionations between water and the minerals wollastonite, diopside, and hedenbergite are in close agreement with one another, whereas significantly more positive fractionations are found for jadeite-water. These isotopic substitution effects can be ascribed to replacement of SiOM bonds (M is a divalent metal cation in octahedral coordination) by higher frequency SiOAl bonds. The fractionations determined in this study can be combined with quartz- and feldspar-water data of Matsuhisa et al. (1979) and revised magnetite-water data of O'NEIL (1963), to provide a coherent set of mineral-pair fractionations satisfactorily represented by straight lines through the origin on a conventional graph of In /ga versus T?2. Mineral-water data, on the other hand, cannot readily be fitted to the simple relationship suggested by Bottinga and Javoy (1973). Coefficients “A” for the mineral-pair fractionations 1000 ln α = A × 106T?2 are:
P (bars)aoa1a2a3a4a5a6
1 atm.800.1?334.2781.6?6490.317553.1?17638.46098.3
500813.5?354.9743.3?6011.716406.4?16516.35702.8
1000824.5?406.71446.8?8818.421253.5?20343.76839.4
1500838.6?418.71434.7?8819.021557.9?20908.47123.1
2000848.5?381.51246.9?8605.021785.8?21449.17375.8
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8.
E.C. Perry  S.N. Ahmad 《Lithos》1981,14(2):83-92
Oxygen and carbon isotope analyses of samples from three mines in the Krivoy Rog iron formation, Ukranian SSR, are reported here. Maximum and minimum quartz-magnetite fractionation values (ΔQM) and inferred temperature range in degrees centrigrade for each mine are:
AbJdAnDiWoMt
Q0.501.091.592.082.206.11
Ab0.591.091.581.705.61
Jd0.500.991.115.02
An0.490.614.52
Di0.124.03
Wo3.91
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9.
Self-diffusion of oxygen in adularia, anorthite, albite, oligoclase and labradorite has been measured by isotope exchange of oxygen between natural feldspars and hydrothermal water enriched in 18O. The analysis consisted of measuring the 18O/16O gradient inward from the feldspar surface using an ion microprobe, and fitting a solution of the diffusion equation to the data. Depth of the sputtered hole was measured with an optical interferometer. Linear Arrhenius plots were obtained:
MineΔQMCorresponding temperature
Sevgok9.4 to 14.2475° to 320°C
Ugok10.0 to 12.7450° to 355°C
Annovsky10.5 to 12.6430° to 360°C
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10.
Oxygen isotope fractionations between zoisite and water have been studied at 400–700°C, PH2O = 13.4 kbar, using the three-isotope method described by Matsuhisaet al. (1978) and Matthewset al. (1983a). The zoisite-waier exchange reaction takes place extremely slowly and consequently direct-exchange calibration of equilibrium 18O16O fractionation factors was possible only at 600 and 700°C. Fractionation factors at 400–600°C were determined from samples hydrothermally crystallized from a glass of the anhydrous zoisite composition. At 600°C, both exchange procedures gave identical fractionations within experimental error. Scanning electron microscope studies showed that the zoisite-water exchange reaction occurs largely by solution-precipitation mass-transfer mechanisms. The slow kinetics of zoisite-water exchange may be typical of hydrous silicates, since additional experiments on tremolite-water and chlorite-water exchange also showed very low rates. When the zoisite-water fractionation factors determined in this study are combined with the quartz and albite-water data of Matsuhisaet al. (1979) and the calcite-water data of O'Nellet al. (1969), mineral-pair fractionations are obtained for which the coefficients “A” in the equation 1000 In α = A × 106T?2 are:
d0 (cm2/sec)Q (kcal/g-atom O)T(°C)
Adularia (Or98)4.51 × 10?825.6350–700
Albite (Ab97, Ab99)2.31 × 10?921.3350–800
Anorthite (An96)1.39 × 10?726.2350–800
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AbCcZo
Q0.500.501.56
Ab0.001.06
Cc1.06
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