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J. N. Grossman

Publications and source records attributed to J. N. Grossman.

32 records · Page 2Linked to original sources
USGS1992

Chemical fluxes and origin of a manganese carbonate-oxide-silicate deposit in bedded chert

Lens-like rhodochrosite-rich bodies within interbedded chert and shale are associated with basalt and/or graywacke in ophiolitic and orogenic zones. The Buckeye manganese mine in the Franciscan Complex of the California Coast Ranges is associated with metagraywacke. Despite blueschist-facies metamorphism, this deposit preserves the compositions and some textural features of its sedimentary protoliths. For this reason, it is a suitable deposit with which to compare more intensely altered deposits, or deposits originating in different paleoenvironments. Six Mn-rich and three Mn-poor minerals form monomineralic layers and mixtures: rhodochrosite, gageite, Mn-oxides (hausmannite, braunite), divalent Mn-silicates (caryopilite, taneyamalite), chlorite, quartz (metachert) and aegirine-augite. The Mn-rich protoliths have high Mn/Fe combined with relatively low concentrations of Ca, Al, Ti, Co, Ni, Cu, Th and REE. REE patterns of various protoliths are distinct. Rhodochrosite and gageite layers are depleted (seawater ?? 5 ?? 104) and flat, whereas patterns of metachert and the Mn-silicate-rich layers mimic the patterns of metashale and metagraywacke (seawater ?? 106). Hausmannite layers have flat patterns (seawater ?? 7 ?? 104) whereas braunite-rich layers are more enriched (seawater ?? 2 ?? 105) and show a distinct positive Ce anomaly. Factor analysis reveals components and fluxes attributed to sub-seafloor fluids (Ni, As, Zn, Sb, W, Mn), seawater (Mg, Au, V, Mo), detritus and veins (Ca, Ba, Sr). Silica is negatively correlated with the sub-seafloor factor. The observed variances indicate that water from the sediment column mixed with seawater, that deposition occurred near the sediment-seawater interface before mixtures of subsurface fluid and seawater homogenized, and that the system was not entirely closed during metamorphism. The variations in REE enrichment can be related to kinetics of deposition: rhodochrosite and gageite were precipitated most rapidly, and therefore were the protoliths that most effectively diluted the REE-rich background resulting from fine clastic material (derived from distal turbidites). The variation of the Ce anomaly and U/Th among diverse lithologies and the differences in Mn oxidation states are consistent with progressive dilution of reduced subsurface fluids with oxidized seawater. By this scheme, rhodochrosite, gageite and hausmannite were deposited from the most reduced fluids, braunite from intermediate mixtures, and Mn-silicates from the sub-seafloor fluids most diluted with fresh seawater. Comparison of the Buckeye with other lens-like and sheet-like deposits having high Mn/Fe and containing Mn3+ and/or Mn2+ suggests that each had three essential fluxes: a sub-seafloor source of Mn, a local source of very soluble silica and a source of relatively fresh, oxygenated water. Additional fluxes, such as clastics, appear to be more characteristic of the paleoenvironment than the three essential fluxes. ?? 1992.

Chemical Geology↗
USGS1992

Rhenium-osmium isotope constraints on the age of iron meteorites

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately ±31 million years for meteorites ∼4500 million years old. Although an absolute rheniumosmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of 187 Re, an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represented by these iron groups may have cooled significantly later than the parent body of the IIA irons.

Science↗
USGS1991

Iodine-xenon, chemical, and petrographie studies of Semarkona chondrules: Evidence for the timing of aqueous alteration

We have performed INAA, petrographie, and noble gas analyses on seventeen chondrules from the Semarkona meteorite (LL3.0) primarily to study the relationship of the I-Xe system to other measured properties. We observe a range of ≥10 Ma in apparent I-Xe ages. The three latest apparent ages fall in a cluster, suggesting the possibility of a common event. The initial 129 I/ 127 I ratio ( R 0 ) is apparently related to chondrule type and/or mineralogy, with nonporphyritic and pyroxene-rich chondrules showing evidence for lower R 0 'S (later apparent I-Xe ages) than porphyritic and olivine-rich chondrules. In addition, chondrules with sulfides on or near the surface have lower R 0 S than other chondrules. The 129 Xe/ 132 Xe ratio in the trapped Xe component anticorrelates with R 0 , consistent with evolution of a chronometer in a closed system or in multiple similar systems. On the basis of these correlations, we conclude that the variations in R 0 represent variations in ages, and that later event(s), possibly aqueous alteration, preferentially affected chondrules with nonporphyritic textures and/or sulfide-rich exteriors about 10 Ma after the formation of the chondrules.

Geochimica et Cosmochimica Acta↗
USGS1989

Enrichment of trace elements in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California

The abundance, P - T stability, solubility, and element-partitioning behavior of minerals such as rutile, garnet, sphene, apatite, zircon, zoisite, and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones. The influence of these minerals on the composition of subduction-related magmas has been inferred (and disputed) from inverse modelling of the geochemistry of island-arc basalt, or by experiment. Although direct samples of the dehydration + partial-melting region of a mature subduction zone have not been reported from subduction complexes, garnet amphibolites from melanges of circumpacific and Caribbean blueschist terranes reflect high T (>600°C) conditions in shallower regions. Such rocks record geochemical processes that affected deep-seated, high- T portions of paleo-subduction zones. In the Catalina Schist, a subduction-zone metamorphic terrane of southern California, metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta-ultramafic rocks. This mafic and ultramafic complex may represent either slab-derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab-mantle wedge contact, or both. The trace-element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by INAA, XRF, electron microprobe, and SEM. In order of increasing alteration from a probable metabasalt protolith, three common types of garnet amphibolite blocks in the Catalina Schist are: (1) non-migmatitic, clinopyroxene-bearing blocks, which are compositionally similar to MORB that has lost an albite component; (2) garnet-amphibolite blocks, which have rinds that reflect local interaction between metabasite, metaperidotite, and fluid; and (3) migmatites that are extremely enriched in Th, HFSE, LREE, and other trace elements. These trace-element enrichments are mineralogically controlled by rutile, garnet, sphene, apatite, zircon, zoisite, and allanite. Alkali and alkaline earth elements are much less enriched in the solid assemblage, and thus appear to be decoupled from the other elements in the inferred metasomatic process(es). The compositions of migmatitic garnet amphibolite blocks seem to complement that of “average” island-arc tholeiite. Trace-element metasomatism reflects fluid-solid, rather than melt-solid, interaction. The metasomatic effects indicate that H 2 O-rich fluid, perhaps with a significant component of Na-Al silicate and alkalis, carried Th, U, Sr, REE, and HFSE. Fractionations of LREE in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex. “Exotic” LREE deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment. If the paleo-subduction zone represented by the mafic and ultramafic complex of the Catalina Schist had continued its thermal and fluid evolution, a selvage of similarly enriched rocks might have been generated along the slab-mantle wedge contact between ~30 and 85 km depth. Rocks affected by “subduction-zone metasomatism,” although rarely recognized at the surface, could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments.

Geochimica et Cosmochimica Acta↗
USGS1988

ALH85085: A unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes

Allan Hills 85085 is a unique chondrite with affinities to the Al Rais-Renazzo clan of carbonaceous chondrites. Its constituents are less than 50 μm in mean size. Chondrules and microchondrules of all textures are present; nonporphyritic chondrules are unusually abundant. The mean compositions of porphyritic, nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements. Ca-, Al-rich inclusions are abundant and largely free of nebular alteration; they comprise types similar to those in CM and CO chondrites, as well as unique types. Calcium dialuminate occurs in several inclusions. Metal, silicate and sulfide compositions are close to those in CM-CO chondrites and Al Rais and Renazzo. C1-chondrite clasts and metal-rich “reduced” clasts are present, but opaque matrix is absent. Siderophile abundances in ALH85085 are extremely high (e.g., Fe/Si= 1.7 × solar), and volatiles are depleted (e.g., Na/Si= 0.25 × solar, S/Si= 0.03 × solar). Nonvolatile lithophile abundances are similar to those in Al Rais, Renazzo, and CM and CO chondrites.

Earth and Planetary Science Letters↗
USGS1987

Computer graphics for quality control in the INAA of geological samples

A data reduction system for the routine instrumental activation analysis of samples is described, with particular emphasis on interactive graphics capabilities for evaluating analytical quality. Graphics procedures have been developed to interactively control the analysis of selected photopeaks during spectral analysis, and to evaluate detector performance during a given counting cycle. Graphics algorithms are also used to compare the data on reference samples with accepted values, to prepare quality control charts to evaluate long term precision and to search for systematic variations in data on reference samples as a function of time. ?? 1987 Akade??miai Kiado??.

Journal of Radioanalytical and Nuclear Chemistry A↗
USGS1987

Compositional evidence regarding the origins of rims on Semarkona chondrules

The compositions of the interiors and abraded surfaces of 7 chondrules from Semarkona (LL3.0) were measured by neutron activation analysis. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors. Siderophile and chalcophile concentrations are much higher in the surfaces, whereas lithophile concentrations are similar in both fractions. Most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory, but for 3 or 4 chondrules the siderophile resemblance is inherent, implying that the surface and interior metal formed from a single precursor assemblage. Metal and sulfide-rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix-like material that had accreted onto the surface. The moderately-volatile to volatile elements K, As and Zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity; both enrichments and depletions are observed for other moderately volatile elements. A small fraction of chondrules experienced fractional evaporation while they were molten.

Geochimica et Cosmochimica Acta↗