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Geology topics

Z. E. Peterman

Publications and source records attributed to Z. E. Peterman.

At least 37 records · Page 2Linked to original sources
USGS1996

Localized alteration of the paintbrush nonwelded hydrologic unit within the exploratory studies facility

The mound-like feature in the lower part of the PTn, composed of highly disrupted strata and open-system alteration were the result of intense water-rock interaction. This feature was formed by fumarolic activity during cooling of the 12.8 Ma Topopah Spring Tuff and prior to deposition of the pre-Pah Canyon bedded tuff. Evidence of vapor phase crystallization, commonly observed in fumaroles, is not pervasive but may have been destroyed by subsequent low-temperature water-rock interaction. The ESF has provided a unique opportunity to view the internal morphology and to sample the compositional variability of this feature, however, outcrop and borehole studies suggest that such localized occurrences of alterative are not uncommon phenomenon within the PTn Hydrology Unit.

Conference Paper↗
USGS1994

Isotopic tracers of gold deposition in Paleozoic limestones, southern Nevada

Strontium isotopic analyses of barren and mineralized Paleozoic carbonate rocks show that hydrothermal fluids added radiogenic strontium (87Sr) to the mineralized zones. At Bare Mountain, samples collected from mineralized areas have ??87Srt values (per mil deviation from primary marine values) ranging from +3.0 to +23.0 (mean of this log-normal distribution is +7.0), whereas unmineralized carbonate rocks have ??87Srt values of -0.6 to +2.9 (mean of +1.07??1.03). In other ranges (Striped Hills, Spring Mountains, and ranges in the vicinity of Indian Springs Valley), ??87Srt values of the unmineralized carbonate rocks are even lower and virtually indistinguishable from primary marine values. This correlation of elevated ??87Srt values with mineralized zones provided a useful technique for assessing the mineral potential of the Paleozoic basement beneath Yucca Mountain, and may find broader use in mineral exploration in the Basin and Range province as a whole.

Conference Paper↗
USGS1993

234U/238U as a ground-water tracer, SW Nevada-SE California

The 234U/238U ratio of uranium in oxidizing ground waters is potentially an excellent ground-water tracer because of its high solubility and insensitivity to chemical reactions. Moreover, recent advances in analytical capability have made possible very precise uranium-isotopic analyses on modest (approx.100 ml) amounts of normal ground water. Preliminary results on waters from SW Nevada/Se California indicate two main mixing trends, but in detail indicate significant complexity requiring three or more main components.

California, Nevada↗
USGS1993

Isotopic and trace element variability in altered and unaltered tuffs at Yucca Mountain, Nevada

Reference stratigraphic sections near Yucca Mountain, Nevada were established and sampled in outcrop areas where the volcanic rocks have been minimally altered. Isotopic and trace element analyses obtained for these reference sections are baseline data for assessing the degree and extent of element mobility attendant with past zonal alteration of the rock mass. In agreement with earlier studies, zeolitization is shown to have occurred under wholesale open-system conditions. Calcium was increased by two three times the baseline values and strontium up to twenty times. In contrast, barium displays less variability, and the high-field strength elements zirconium and titanium were the least mobile during zeolitization. The data reported here establish the usefulness of reference sections of assessing past elements mobility. The information gained will be helpful in predicting possible future element mobility induced by thermally activated fluids in the near field of a potential repository.

Conference Paper↗
USGS1991

U and Sr Isotopes in ground water and calcite, Yucca Mountain, Nevada: Evidence against upwelling water

Hydrogenic calcite and opaline silica deposits in fault zones at Yucca Mountain, Nevada, have created considerable public and scientific controversy because of the possible development of a high-level nuclear waste repository at this location. Strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep-seated waters. The vein deposits are isotopically distinct from ground water in the two aquifers that underlie Yucca Mountain, indicating that the calcite could not have precipitated from ground water. The data are consistent with a surficial origin for the hydrogenic deposits.

Nevada↗
USGS1991

Strontium isotopes in carbonate deposits at Crater Flat, Nevada

Strontium isotope studies of carbonates from soils, veins, eolian dust and Paleozoic basement sampled near Crater Flat, southwest of Yucca Mountain, provide evidence for the origins of these materials. Vein and soil carbonates have nearly identical ranges of 87Sr/86Sr, and eolian material has 87Sr/86Sr ratios at the lower end of the pedogenic range. The average 87Sr/86Sr of Paleozoic basement from Black Marble Hill is similar to the 87Sr/86Sr in the eolian dust, perhaps indicating a local source for this material. Possible spring deposits have generally higher 87Sr/86Sr than the other carbonates. These data are compared with similar data from areas east of Yucca Mountain.

Conference Paper↗
USGS1990

Origin of carbonate deposits in the vicinity of Yucca Mountain, Nevada. Preliminary results of strontium-isotope analyses

As part of the paleohydrology study of the Yucca Mountain Project, strontium-isotope analyses of carbonate deposits, ground water, and major rock reservoirs of strontium are in progress. This paper presents a summary of the strontium-isotope data obtained through 1989. Calcium carbonate is ubiquitous in the vicinity of Yucca Mountain, where it occurs as pedogenic horizons and rhizoliths, small veins and fracture fillings in Tertiary volcanic rocks, large veins and masses along faults, and freshwater and marine limestones. With the exception of marine limestones, which are Paleozoic, the calcium carbonate has been precipitated directly from water during the past 107 years. This paper reports strontium-isotope compositions of the following carbonate groups: 1) limestones of the Paleozoic basement, 2) calcite-silica veins, 3) small calcite veins, 4) pedogenic carbonate deposits, and 5) spring deposits (i.e., tufa). The authors have also analyzed the strontium from samples of Tertiary volcanic rocks and from ground water.

Conference Paper↗
USGS1989

Early Proterozoic activity on Archean faults in the western Superior province - evidence from pseudotachylite

Late Archean granitic plutons (∼2700 to 2665 Ma; U-Pb zircon) of the Superior structural province are cut by a variety of brittle discontinuities, including joints, fractures, and faults, the latter of which show evidence of cataclasis and meter to tens of meters displacements. Fluid circulation, alteration of wall rocks, and neomineralization of epidote, actinolite, and chlorite occurred under greenschist facies conditions in these structures at the time of their formation. The Rb-Sr ages of host rocks are ∼2650 Ma, and the fracture-zone materials are 2300 Ma, indicating that most of this activity occurred long after Archean plutonism and was concentrated in Early Proterozoic time. The brittle structures formed in response to horizontal compression on a regional scale, possibly caused by tectonic processes at margins of the craton. The structures are seen as important clues to the tectonic evolution of the Superior province.

Geology↗
USGS1989

Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine–Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860–1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835 – 1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subduction zone (Niagara fault zone), whereas the younger one developed as island arcs above a north-dipping subduction zone, the Eau Pleine shear zone. The northward subduction followed deformation related to arc–continent collision at the Niagara suture at about 1860 Ma. The southern Marshfield terrane contains remnants of mafic to felsic volcanic rocks about 1860 Ma that were deposited on Archean gneiss basement, foliated tonalite to granite bodies ranging in age from about 1890 to 1870 Ma, and younger undated granite plutons. Following amalgamation of the two arc terranes along the Eau Pleine suture at about 1840 Ma, intraplate magmatism (1835 Ma) produced rhyolite and anorogenic alkali-feldspar granite that straddled the internal suture.

Wisconsin↗
USGS1988

Sr and Nd isotopic variations in ferromanganese crusts from the Central Pacific: Implications for age and source provenance

Isotopic analyses of two hydrogenetic ferromanganese (Fe-Mn) crusts from volcanic edifices in the central Pacific Ocean reveal systematic variations in 87 Sr 86 Sr "> 87 Sr 86 Sr and 143 Nd 144 Nd "> 143 Nd 144 Nd , with both ratios decreasing as a function of depth into the Fe-Mn crusts. Leaching experiments suggest that Sr in the crusts is contained in at least two discrete sites. A loosely bound Sr, dominated by modern marine Sr, is removed by leaching with a 10 percent acetic acid solution. The 87 Sr 86 Sr "> 87 Sr 86 Sr ratio of the residue is significantly less than the 87 Sr 86 Sr "> 87 Sr 86 Sr ratio of the unleached material. The Sr-isotope ratios of leached samples are compared with the temporal variation in seawater to provide ages for layers within the Fe-Mn crusts. These data suggest that the oldest crust layers began to accrete in the early to middle Miocene. Correlated to the 87 Sr 86 Sr "> 87 Sr 86 Sr variations, 143 Nd 144 Nd "> 143 Nd 144 Nd ratios suggest that the Nd-isotope composition of central Pacific Ocean seawater also changed systematically over this time interval, or that the Fe-Mn crusts simply incorporated Nd from various parts of an isotopieally heterogeneous ocean as the crusts were carried along with the oceanic plate. In contrast to the layered ferromanganese crust, the phosphatized volcaniclastic substrates have Sr and Nd isotope compositions that are consistent with their volcanic origin.

Geochimica et Cosmochimica Acta↗