Geology topics
Publications and source records attributed to J. J. Papike.
Three fossil fumaroles in rhyolite-rich ash-flow tuff from the lower Valley of Ten Thousand Smokes (VTTS) have been studied to ascertain chemical losses and gains and mineralogical evolution during fumarolic alteration and subsequent cooling and weathering processes. Major oxide and trace element data were interpreted using the isocon method of Grant (1986).
The great eruption of 1912 in the Aleutian Range of Alaska (Figure 1) is exceptional for both its size and relative simplicity. It was the largest eruption of this century and the largest rhyolitic outburst in almost 20 centuries. The 60-hour, 30-km 3 (ejecta volume) eruption produced extensive fallout deposits, an ash-flow sheet that gave rise to the Valley of Ten Thousand Smokes, and the 3-km-diameter Mt. Katmai caldera. Because magma reached the surface through uniform nonvolcanic basement and the vent underwent little or no collapse (unusual for such a large event), the site provides an ideal target for surface geophysical and subsurface coring exploration of structures and conditions produced by explosive volcanism [Panel on Volcanic Studies at Katmai, 1989]. A project to investigate upper crustal magmatic processes at Katmai is part of the U.S. Continental Scientific Drilling Program [Eichelberger and Hildreth, 1986]. The surface studies phase of this project was undertaken last summer and preliminary results are now emerging.
Samples from a fossil fumarole originating in the 1912 ash-flow tuffin the Valley of Ten Thousand Smokes have been analyzed to ascertain chemical changes resulting from high-temperature fumarolic alteration and subsequent cooling and weathering of the protolith. Samples of the underlying, dominantly leached, dacite-rich portion of the ash-flow tuff adjacent to the fumarolic conduit and samples of encrusted fallout from the shallow part of the fossil fumarole were interpreted using the isocon method of Grant (1986). The results show that, relative to unaltered l9l2 dacite, chosen as a standard composition for the protolith in this fossil fumarole, mass was conserved during the alteration reactions for most of the system, but mass gains of l4–2D% were determined for three samples in the leached ash-flow tuff Relative to unaltered dacite protolith, significant enrichments occurred in SO 3 , LOI (~H 2 O), Cl, F, Zn, Pb, Cu, Sn, Cr, Ni, As, Sb, Au, Br in various parts of the fossil fumarole. Some of these were during the high-temperature part of the alteration, and some were during cooling processes when acid alteration becomes prominent. The REEs indicate some depletion in highly altered samples relative to dacite protolith and differential mobility of Eu 2+ relative to trivalent REEs. This is manifested by positive Eu anomalies in REE patterns normalized against REE in the dacite protolith. Mineral phases introduced in the alteration assemblages include alunite reflecting high SO 3 , activity, hydrated aluminum hydroxy-fluoride (a ralstonite-like phase) and fluorite reflecting high F activity, smectite, magnetite, hematite, and goethite reflecting oxidation and hydration reactions. Opal and a portion of the α-cristobalite reflect SiO 2 , mobility; however, the abundance of α-cristobalite is formed from pumice leached during high-temperature vapor-phase processes and devitrification of the altered glass.
The Nd, O and Sr isotopic characteristics of Precambrian metasedimentary, metavolcanic and granitic rocks from the Black Hills of South Dakota are examined. Two late-Archean granites (2.5-2.6 Ga) have T dm ages of 3.05 and 3.30 Ga, suggesting that at least one of the granites was derived through the melting of significantly older crust. Early-Proterozoic metasedimentary rocks have T dm ages that range from 2.32 to 2.45 Ga. These model ages, in conjunction with probable stratigraphic ages ranging from 1.9 to 2.2 Ga, indicate that mantle-derived material was added to the continental crust of this region during the early-Proterozoic. Previous studies of the Harney Peak Granite complex have reported U-Pb and Rb-Sr ages of about 1.71 Ga and most granite samples examined in this study have Sr isotopic compositions consistent with that age. Two granite samples taken from the same sill, however, give two-point Rb-Sr and Sm-Nd ages of 2.08 ±0.08 and 2.20 ±0.20Ga (∑ 2200 Nd = −15.5), respectively. In addition, whole-rock and apatite samples of the spatially associated Tin Mountain pegmatite give a Sm-Nd isochron age of 2000 ±100 Ma (∑ 2200 Nd = −5.8 ±1.8). The Sm-Nd, O and Rb-Sr isotopic systematics of these granitic rocks have been complicated to some degree by both crystallization and post-crystallization processes, and the age of the pegmatite and parts of the Harney Peak Granite complex remain uncertain. Processes that probably complicated the isotopic systematics of these rocks include derivation from heterogeneous source material, assimilation, mixing of REE between granite and country rock during crystallization via a fluid phase and post-crystallization mobility of Sr. The Nd isotopic compositions of the pegmatite and the Harney Peak Granite indicate that they were not derived primarily from the exposed metasedimentary rocks.
The Jurassic Notch Peak granitic stock, western Utah, discordantly intrudes Cambrian interbedded pure limestones and calcareous argillites. Contact metamorphosed argillite and limestone samples, collected along traverses away from the intrusion, were analyzed for ??18O, ??13C, and ??D. The ??13C and ??18O values for the limestones remain constant at about 0.5 (PDB) and 20 (SMOW), respectively, with increasing metamorphic grade. The whole rock ??18O values of the argillites systematically decrease from 19 to as low as 8.1, and the ??13C values of the carbonate fraction from 0.5 to -11.8. The change in ??13C values can be explained by Rayleigh decarbonation during calcsilicate reactions, where calculated {Mathematical expression} is about 4.5 permil for the high-grade samples and less for medium and low-grade samples suggesting a range in temperatures at which most decarbonation occurred. However, the amount of CO2 released was not anough to decrease the whole rock ??18O to the values observed in the argillites. The low ??18O values close to the intrusion suggest interaction with magmatic water that had a ??18O value of 8.5. The extreme lowering of ??13C by fractional devolatilization and the lowering of ??18O in argillites close to the intrusion indicates oxgen-equivalent fluid/rock ratios in excess of 1.0 and X(CO2)F of the fluid less than 0.2. Mineral assemblages in conjunction with the isotopic data indicate a strong influence of water infiltration on the reaction relations in the argillites and separate fluid and thermal fronts moving thru the argillites. The different stable isotope relations in limestones and argillites attest to the importance of decarbonation in the enhancement of permeability. The flow of fluids was confined to the argillite beds (argillite aquifers) whereas the limestones prevented vertical fluid flow and convective cooling of the stock. ?? 1984 Springer-Verlag.
The Notch Peak granitic stock, western Utah, is comprised of three concentric sequentially intruded rock types, from granite at the rim, to quartz monzonite I, to quartz monzonite II at the core. The δ 18 O values of whole rocks vary about an average of 9.4 (SMOW), irrespective of the rock type and position relative to contact, suggesting that the three magmas had the same parent. The whole rock δD values in the stock range from −100 to −55. δD values increase toward the cores of both quartz monzonite I and quartz monzonite II, resulting in concentric contours. The δD contours of quartz monzonite II cross-cut those of quartz monzonite I, suggesting little isotopic interaction between these bodies and the absence of a late pervasive fluid phase. There is a positive correlation between δD values and water content of the samples, where samples from each body define a distinct field. The positive correlation is explained by isotopic fractionation attendant on vapor exsolution from the crystallizing magma. An observed increase in δD with the degree of chloritization, a trend opposite to that observed in systems where participation of meteoric water has been demonstrated, is the result of subsolidus interaction with the exsolved fluids. These results show that large variations in the hydrogen isotope ratios of a granitoid can arise by exsolution of a vapor phase from the melt on crystallization. In general, magmas with larger modal amount of primary hydrous phases will tend to have higher δD values than those with small amounts of hydrous phases. Furthermore, the relatively high δD values of chlorites at Notch Peak confirm the applicability of classical concepts of closed-system deuteric alteration to some granitoid bodies. Thus, meteoric water interaction need not be always invoked to explain hydrogen isotope variation and deuteric alteration in granitoids.
Single-crystal x-ray diffraction, microprobe, optical and electron optical examinations of clinopyroxenes from Apollo 11 lunar samples 10003, 10047, 10050, and 10084 show that generally the crystals are composed of (001) augite-pigeonite intergrowths in varying ratios. Transmission electron micrographs reveal abundant exsolution lamellae, many only 60 Å thick. In addition to the phase inhomogeneities, primary chemical inhomogeneities are clearly demonstrated. There are reciprocal relationships between calcium and iron and between Ti 4+ + 2Al and R 2+ + 2Si. Our evidence suggests that a chemically inhomogeneous subcalcic C 2/ c augite was the only primary pyroxene from which pigeonite later exsolved.
Four pairs of associated calcic and sodic amphiboles from blueschist facies metamorphic rocks were analyzed with the electron microprobe and studied by single-crystal X-ray diffraction techniques. Except for ranges in the ratios Mg/(Mg+Fe) and Fe 3+ /(Fe 3+ +Al+Ti), the sodic amphiboles are similar in chemical composition. The amount of calcium in the M(4)-site ranges only from 0·18 to 0·21 ion per formula unit. The calcic amphiboles, in addition to a range in Mg/(Mg+Fe), vary in Na/(Na+Ca) ratio (0·29–0·48). Three of the calcic amphiboles contain less than 1·5 calcium ions per formula unit, indicating a significant solid solution of sodic amphibole components in the calcic amphibole phase. The a and b unit-cell parameters of the calcic amphiboles decrease with increased content of the sodic component.
Protodolomite has been identified in the teeth of Recent echinoids by means of electron microprobe and X-ray diffraction analyses. The analyses demonstrate a high degree of heterogeneity with respect to magnesium carbonate content in these skeletal parts; the entire spectrum of compositions between magnesium calcite and protodolomite was encountered.
Bond distances and angles in isostructural, ordered clinopyroxenes are compared for eight compositions, based on five new and three published crystal-structure refinements from X-ray diffraction data. Unit-cell parameters and configuration of the silicate chains are directly correlated with cation composition and distribution in the M2 and M1 sites.
Alkali amphiboles from Type III and Type IV metamorphic zones in blueschist facies rocks of Cazadero, California, and from comparable New Caledonian rocks have been characterized by X-ray crystallographic, optical, and chemical methods. The composition of any particular alkali amphibole is strongly controlled by the bulk composition of the host rock. Within the blueschist facies, metamorphic zones are not characterized by changes in amphibole composition. All the alkali amphiboles studied herein belong to the C2/m space group and complete miscibility between glaucophane and riebeckite has been demonstrated for the conditions prevailing during metamorphism in the Cazadero and New Caledonian blueschists. Linear relationships are found between unit-cell dimensions and variations in composition between glaucophane and riebeckite. The alkali amphiboles of glaucophane compositions belong to the high pressure-low temperature series, glaucophane II-riebeckite. Limited miscibility of actinolite in glaucophane may be characteristic of blueschist facies metamorphism.
Twenty samples of hornblendes from rocks of 14 plutonic units in the central Sierra Nevada and Inyo Mountains, California, have been studied in detail. Optical, density, single-crystal and powder X-ray diffraction, and major and minor element chemical data are reported.The compositions of the hornblendes show only limited correlation with the chemistry of the rocks in which they occurred. Hornblendes from granitic rocks of the eastern Sierra Nevada and Inyo Mountains have a wide range of tetrahedral aluminum content which is often as low as three-quarters of an atom per formula unit, whereas hornblendes from younger granitic rocks elsewhere in the Sierra Nevada batholith contain more than one atom of tetrahedral aluminum per formula unit. Because an increase of aluminum in tetrahedral co-ordination is considered indicative of higher temperatures of crystallization, the observed differences in the hornblendes suggest that older plutonic rocks of the batholith may have been metamorphosed regionally or may have been affected by widespread hydrothermal action prior to consolidation of later granitic rocks.
Ten amphibole specimens from a variety of metamorphic rocks such as talc schists, eclogites, and metamorphosed iron formations contain lamellae of a second amphibole oriented parallel to (1̅01) or (100), or both, of the host. Tremolites, actinolites, and hornblendes commonly have lamellae of a calcium-poor clinoamphibole with P 2 1 / m space-group symmetry, or lamellae of cummingtonite with C 2/ m space-group symmetry. Likewise cummingtonites and P 2 1 / m clinoamphiboles commonly contain lamellae of calcium-rich C 2/ m amphiboles such as tremolite. Results of x-ray diffraction, electron-probe, and microscope studies indicate that most lamellae result from unmixing of a homogeneous amphibole. The P 2 1 / m clinoamphibole is analogous to the clinopyroxene pigeonite in agreement with the results of M. G. Bown.
X-ray diffraction crystal-structure analysis of omphacite from eclogite, Tiburon Peninsula, Marin County, California, shows that this clinopyroxene has P 2 symmetry with a nearly ordered distribution of the multiple cation content defined by its approximate formula: (Na 0.5 Ca 0.5 ) (Mg 0.4 Fe 2 + 0.1 Al 0.4 Fe 3 + 0.1 )Si 2 O 6 . Na+ and Ca 2+ tend to assume alternate locations in the structure, and (Mg,Fe 2+ ) octahedra alternate with Al 3+ or (Al,F 3+ ) octahedra in chains along c .