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Thermobarometry of Mafic Igneous Rocks Based on Clinopyroxene-Liquid Equilibria, 0—30 Kbar

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Thermobarometry of Mafic Igneous Rocks Based on Clinopyroxene-Liquid Equilibria, 0—30 Kbar Contrib Mineral Petrol (1996) 123:92Ð108 ( Springer-Verlag 1996 Keith Putirka á Marie Johnson á Rosamond Kinzler á John Longhi á David Walker Thermobarometry of ma®c igneous rocks based on clinopyroxene-liquid equilibria, 0Ð30 kbar Received: 16 May 1994/Accepted: 15 June 1995 Abstract Models for estimating the pressure and tem- and diopside#hedenbergite (DiHd) components are perature of igneous rocks from co-existing clino- calculated from a normative scheme which assigns the pyroxene and liquid compositions are calibrated from lesser of Na or octahedral Al to form Jd; any excess AlVI existing data and from new data obtained from experi- forms Calcium Tschermak’s component (CaTs; CaAlAlSiO ); Ca remaining after forming CaTs and ments performed on several mafic bulk compositions 6 CaTiAl O is taken as DiHd. Experimental data not (from 8Ð30 kbar and 1100Ð1475¡ C). The resulting 2 6 geothermobarometers involve thermodynamic expres- included in the regressions were used to test models (i) sions that relate temperature and pressure to equili- and (ii). Error on predictions of ¹ using model (i) is brium constants. Specifically, the jadeite (Jd; $40 K. A pressure-dependent form of (i) reduces this NaAlSi O )Ðdiopside/hedenbergite (DiHd; Ca(Mg, Fe) error to $30 K. Using model (ii) to predict pressures, 2 6 the error on mean values of 10 isobaric data sets (0Ð25 Si2O6) exchange equilibrium between clinopyroxene and liquid is temperature sensitive. When composi- kbar, 118 data) is $0.3 kbar. Calculating thermodyn- tional corrections are made to the calibrated equili- amic properties from regression coe¦cients in (ii) gives $ $ brium constant the resulting geothermometer is V&J of 23.4 1.3 cm3/mol, close to the value anticip- ated from bar molar volume data (23.5 cm3/mol). Ap- 104 Jd19*Ca-*2*Fm-*2 plied to clinopyroxene phenocrysts from Mauna Kea, (i) "6.73!0.26* ln Hawaii lavas, the expressions estimate equilibration ¹ CDiHd19*Na-*2*Al-*2D depths as great as 40 km. This result indicates that Mg-*2 transport was su¦ciently rapid that at least some !0.86* ln #0.52*ln [Ca-*2] CMg-*2#Fe-*2D phenocrysts had insu¦cient time to re-equilibrate at lower pressures. an expression which estimates temperature to $27 K. Compared to (i), the equilibrium constant for jadeite formation is more sensitive to pressure resulting in a thermobarometer Overview ¹ ¹ Jd19 Thermobarometry applied to phenocrysts in volcanic (ii) P"!54.3#299* #36.4* ln 104 104 C[Si-*2]2*Na-*2*Al-*2D rocks provides a method for determining depths and -*2 -*2 temperatures of magma storage. If magma stalls at the #367*[Na *Al ] base of the crust prior to discharge, thermobarometry which estimates pressure to $ 1.4 kbar. Pressure is in constrains crustal thickness, and perhaps also the kbar, ¹ is in Kelvin. Quantities such as Na-*2 represent geothermal gradient at the time of eruption. Few means the cation fraction of the given oxide (NaO ) in the of temperature estimation widely applicable to basaltic 0.5 liquid and Fm"MgO#FeO. The mole fractions of Jd rocks exist and even fewer means of determining the pressures of phenocryst equilibration for such rocks K. Putirka ( ) á M. Johnson á R. Kinzler á J. Longhi á currently exist. The thermobarometers presented here D. Walker are calibrated using new experimental data and are Lamont-Doherty Earth Observatory of Columbia based on clinopyroxene-liquid equilibria. Equilibria in- University Palisades, NY 10964, USA volving clinopyroxene were chosen for two reasons. Editorial responsibility: T.L Grove (1) Clinopyroxene is a common phenocryst phase in 93 volcanic rocks; clinopyroxene-based thermobaro- smaller; these exchange-equilibria are temperature-de- meters will thus be of general applicability. (2) Forma- pendent and are calibrated as thermometers. Both ex- tion of the clinopyroxene component jadeite is accom- change equilibria, Jd-DiHd and CaTs-DiHd, require panied by a large change in molar volume and provides a pressure-dependent term for complete description. barometric information for igneous processes. The thermometers are presented both with and without The thermobarometers are thermodynamic rather pressure terms; ignoring the pressure term facilitates than empirical. They expand on the approaches taken application of the thermometers and results in only by Roeder and Emslie (1970) and Drake (1976). Equi- a slight increase in the uncertainty of the estimate. librium constants (K%2) describing pyroxene solution As many of the pertinent thermodynamic data are are calibrated for both pressure (P) and temperature lacking for the appropriate pyroxene and liquid com- (¹). The advantage of calibrating equilibrium con- ponents, the thermobarometers are constructed from stants is that thermodynamic relationships exist which regression analysis of experimental clinopyroxene- ¹ relate K%2 to and P. A thermodynamic approach also liquid equilibrium compositions. In an attempt to ex- allows extrapolation to pressures, temperatures, and plore compositional complexities, new experiments compositions outside the experimental range used for were performed in the melting interval 8Ð30 kbar at calibration. 2 kbar intervals on a range of natural basalt composi- The large partial molar volumes for Na and Al tions. Several solution models were tested. The result- oxides in basaltic liquid (Lange and Carmichael 1987) ing thermobarometers recover P and ¹ for combined with the small partial molar volume of clinopyroxene-liquid pairs synthesized from other labs jadeite (NaAlSi O ; Jd) result in a relatively large P- and yield thermodynamic quantities that compare well 2 6 dependency for jadeite formation compared to other with known values. mineral-liquid equilibria (Table 1; see also Robie et al. It is unclear whether mafic volcanic rocks are erup- 1979). The Jd-liquid equilibrium is also temperature- ted directly from substantial depths or are invariably sensitive and is thus calibrated as a thermobarometer. processed in shallow-level magma reservoirs. Also un- The volume changes for the solution of Jd and calcium- certain is the depth of stagnation during di¤erent stages Tschermak (CaAlAlSiO ; CaTs) into diopside-heden- of volcanism; are the parental magmas of alkalic and 6 bergite (Ca(Mg,Fe)Si O ; DiHd) are significantly tholeiitic suites extracted from di¤erent depths? Fur- 2 6 ther, what controls depth of magma ponding: density contrasts or mechanical behavior of the lithosphere? Table 1 Thermodynamic properties! These problems will be explored through application of Anticipated thermodynamic properties the thermobarometers to pyroxene-bearing rocks from Mauna Kea, Hawaii. Equilibrium S" S# V$ H% * * * 1573 * 1573 Jd-liq !120 !113 !23.5 !154 Di-Jd 56.7 47.1 !10.8 !7.7 Thermodynamic approach Di-CaTs 54.0 Ð !1.33 Ð Di-liq !63.3 !65.9 Ð !146 Below we present the equilibria and thermodynamic equations used for thermobarometry. The thermodyn- Thermodynamic properties recovered from models amic database is presently inadequate to yield all the K Model d *S *V *H coe¦cients appearing in these equations. The following %2 functions are thus used for regression analysis of ex- Jd-liq P1 !71.6 !23.2 !128 perimental equilibrium clinopyroxene-liquid composi- Jd-liq P2 !95.6 !23.4 !129 tions. Di-Jd T1 193 Ð 288 Di-CaTs T3 283 Ð 449 As anticipated from existing molar volume data, a useful equilibrium for barometry involves jadeite ! Crystalline data are from Robie et al (1979); crystal molar volumes formation (K[Jd-liq]). The exchange equilibria, diop- are corrected to 1573 K assuming aJ$"4.0]10~5/K and side-jadeite (K[DiHd-Jd]), and diopside-calcium- aD*@C!T4"3.0]10~5/K; *H is in kJ/mol, *S is in J/mol*K and Tschermak (K[DiHd-CaTs]), are less sensitive to P but volumes are cc/mol. SEE for model *H are $20 kJ/mol and for are sensitive to ¹, providing pressure-sensitive ther- model *S$5 J/mol*K " Calculation uses partial molar entropy of oxides at 298 K (Richet mometers. These equilibria may be expressed as et al. 1993), integrated to 1600 K using partial molar C1 data from Stebbins et al. (1984) who determined C with data ranging from 1 2SiO-*2 NaO-*2 AlO-*2 NaAlSi O19 (1) 1200Ð1850 K 2 # 1@2# 3@2" 2 6 # From C and S -S data of jadeite and diopside glass reported by 1 298 0 CaFmSi O19 NaO-*2 AlO-*2 NaAlSi O19 Richet et al. (1993, Table 7) 2 6 # 1@2# 3@2" 2 6 $ Uses partial molar oxide data of Lange and Carmichael (1987) % #CaO-*2#FmO-*2 (2) Derived from H7 and H& data of Navrotsky (1981) and molar volume of jadeite glass (Richet et al. 1993); the estimate for HJ$ assumes that H /H is the same for jadeite and diopside CaFmSi O19#2AlO-*2 "CaAlVIAlIVSiO19#FmO-*2#SiO-*2 (3) & &,T. 7,985 2 6 3@2 6 2 94 where superscripts denote the phase (liq"liquid; where the coe¦cient A is determined by multiple linear px"pyroxene) and the symbol FmO refers to total regression. Equation 9 is equivalent to Eq. 8 when (FeO#MgO). The methods used to calculate liquid A"0. and pyroxene components are discussed below. As equilibrium constants will vary with P and ¹, expressions must be developed to quantify these de- Activity modifying terms pendencies. The relationship between K%2 and Gibbs free energy may be written as Mixing properties of pyroxene and liquid components are unlikely to be perfectly ideal; such non-idealities !R¹ lnK " G0 (4) may reveal themselves as compositional dependencies %2 * 3 ¹ residual from the and P dependencies of K%2 antici- where R is the gas constant, ¹ is temperature (Kelvin) pated from the equations presented above. To compen- sate for non-ideality and to produce expressions that and *G30 is the Gibbs free energy change for the stoichiometric equilibrium at a reference pressure are useful as geothermobarometers for natural systems, P and temperature, ¹.
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  • Inosilicates (Chain Silicates)
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  • Minerals of Arizona Report
    MINERALS OF ARIZONA by Frederic W. Galbraith and Daniel J. Brennan THE ARIZONA BUREAU OF MINES Price One Dollar Free to Residents of Arizona Bulletin 181 1970 THE UNIVERSITY OF ARIZONA TUCSON TABLE OF CONT'ENTS EIements .___ 1 FOREWORD Sulfides ._______________________ 9 As a service about mineral matters in Arizona, the Arizona Bureau Sulfosalts ._. .___ __ 22 of Mines, University of Arizona, is pleased to reprint the long-standing booklet on MINERALS OF ARIZONA. This basic journal was issued originally in 1941, under the authorship of Dr. Frederic W. Galbraith, as Simple Oxides .. 26 a bulletin of the Arizona Bureau of Mines. It has moved through several editions and, in some later printings, it was authored jointly by Dr. Gal­ Oxides Containing Uranium, Thorium, Zirconium .. .... 34 braith and Dr. Daniel J. Brennan. It now is being released in its Fourth Edition as Bulletin 181, Arizona Bureau of Mines. Hydroxides .. .. 35 The comprehensive coverage of mineral information contained in the bulletin should serve to give notable and continuing benefits to laymen as well as to professional scientists of Arizona. Multiple Oxides 37 J. D. Forrester, Director Arizona Bureau of Mines Multiple Oxides Containing Columbium, February 2, 1970 Tantaum, Titanium .. .. .. 40 Halides .. .. __ ____ _________ __ __ 41 Carbonates, Nitrates, Borates .. .... .. 45 Sulfates, Chromates, Tellurites .. .. .. __ .._.. __ 57 Phosphates, Arsenates, Vanadates, Antimonates .._ 68 First Edition (Bulletin 149) July 1, 1941 Vanadium Oxysalts ...... .......... 76 Second Edition, Revised (Bulletin 153) April, 1947 Third Edition, Revised 1959; Second Printing 1966 Fourth Edition (Bulletin 181) February, 1970 Tungstates, Molybdates.. _. .. .. .. 79 Silicates ...
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  • Significant Lunar Minerals Mineral Names the Compositions of Minerals Naturally Fall Into Certain Groups
    Significant Lunar Minerals Mineral Names The compositions of minerals naturally fall into certain groups. A group shares a common anion and similarities in how the lattice of the minerals are structured. Plagioclase, olivine and pyroxene groups are silicates. Other groups of importance on the Moon are the oxides, of which the spinel group is a specific subset, the sulfides, the phosphates and the native (no anions) metals. In many cases within a group individual crystals may have quite a range of compositions. So for example a specimen in the olivine group may actually be half way between pure fayalite (Fe2SiO4) and pure forsterite (Mg2SiO4), or anywhere in between the end members. For mineral groups where this happens, geologists frequently will refer to the group name, rather than the mineral name. In such cases geologist will indicate the relative amount of each end member by giving the ratio of one end member to the total. For example an olivine that is half forsterite and half fayalite is described as Fo50, where Fo refers to the forsterite end member. This approach is also used for the plagioclase group, where the two end members are anorthite (CaAl2Si2O8) and albite (NaAlSi3O8). The relative amounts of these two end members in a crystal are expressed as An90. This is saying that 90% of the plagioclase is the anorthite end member. Lunar Abundance The terms indicating relative abundances in Table 1 are not formally defined. For this table the general concepts are as follows. Something that is Abundant is wide spread and usually more than ~33% of the material.
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