Over one hundred and fifty basanite features are located in a 12.1 square kilometer (4.73 square mile) area on the north rim of the Grand Canyon National Monument, at the southern edge of the Toroweap Valley. Thirty-six of these were analyzed to determine their origin. The features, previously described as "Pressure blisters" (Hamblin and Best, 1970), are believed to be direct mantle orifices that have erupted under an ash or lava cover. Green and red colored peridotite xenoliths of varying dimensions are found enclosed within these features on the Toroweap Valley as well as on the adjacent cinder cone Vulcan's Throne. The unique red coloring, observed primarily in forsteritic olivine (Fo90-92), is believed to be a result of precipitation of a ferric rich phase within individual olivine grains. Results obtained from a theoretical single-pyroxene geothermobarometer (Mercier, 1980) suggest pressures of at least 15 kilobars and temperatures of at least 940°C, corresponding to a depth of origin of at least 52 kilometers for the Toroweap Valley features. A genetic model developed suggests that the basanite lava carrying green colored olivine originated from a magma chamber at least 52 kilometers below the ground surface, transected a shallower magma chamber in which red colored xenoliths are suspended and punctured the crust in the Toroweap Valley.

A long, narrow, straight belt of closely spaced Bouguer gravity contours and lithologic boundaries coincides with the Martic shear zone, southeastern Pennsylvania. The most likely cause of the steep gravity gradient is sought by checking the influence of the density of surface lithologies, mass distribution associated with the topography, and the isostacy model. 15-20 km difference in crustal thickness across the Martic Zone is calculated using Sharma's data and maximum depth equation. Based on a shear zone geometry, gravity anomaly parallelism, and crustal thickness contrast, the Martic Zone is proposed to be the western boundary of the Piedmont terrane. The Martic Zone is compared with other areas such as the San Andreas Fault and the Alpine Fault to evaluate possible plate boundary features. This tectonic interpretation of the Martic Zone may contribute to a new view on the central Appalachian orogenic belt.

Basalt from the Cohassett flow of the Columbia River Basalt Group (Southeast Washington) was reacted with synthetic Hanford groundwater in Dickson rocking autoclaves at 200° and 300°C, 30 MPa, with initial water:rock mass ratios of 50. During the experiments fresh solutions were re-injected into the reaction cells using a high-pressure chromatography pump. The re-injection experiments are intermediate between closed-system Dickson experiments and flow-through tests in that the fluid and solids can remain in contact for extended periods of time before the solution is replaced. This allows more time for equilibrium to be approached. Data from these experiments suggest the following interpretations: (1) After re-injection many solution parameters quickly (hrs-days) return to near pre-injection values. (2) The redox buffer capacity of the basalt was not exceeded, i.e. fO2 values remained near magnetite-hematite, although nominal water:rock mass ratios as high as ca. 140 were achieved by re-injection. (3) After re-injection the stable high-temperature pH value was only slightly less than the initial pH value, particularly at 300°C. (4) The silica concentration stabilized near apparent quartz saturation in one 300°C experiment, rather than the cristobalite saturation value found in closed-system experiments. (5) Ca­Na-K, quartz, and alpha-cristobalite geothermometer values from the re-injection experiments more closely model the actual experiment temperature than do values from closed­ system Dickson experiments. (6) Short-term relationships between cations appeared to be controlled by ion-exchange between the solutions and secondary clay minerals. Reaction products identified from the re-injection experiments include: Fe-smectite, illite, hematite, very minor cristobalite and possibly Ti-maghemite at 300°C, plus K-spar and analcime in 200°C and variable temperature (300° to 200°C) experiments.

An application of the Hypothesis of Punctuated Aggradational Cycles to the Upper Silurian-Lower Devonian carbonate sequence (Tonoloway and Keyser formations) at seven localities in central Pennsylvania reveals that the interval is entirely divisible into as many as 22 PACs which are correlative throughout the study area. Of these 22 PACs, 5 groups of PACs of similar facies are recognized in the interval. These groups of PACs are initiated and terminated by major deepening events which produce the primary surfaces of correlation in the interval. Paleoenvironments develop episodically throughout the interval, each punctuation event initiating and terminating a unique spectrum of small-scale environments. The Tonoloway portion of the interval represents a sequence of tidal-flat PACs. The transition to the shelf environments of the Lower Keyser Formation occurs episodically through 2 PACs consisting of nearshore, subtidal facies. The Upper Keyser is a shallowing sequence of PACs representing the episodic return from shelf to tidal-flat facies. Correlations reveal that as much as 13.5 meters of stratigraphic section, representing seven PACs, is missing at the Tonoloway-Keyser formation boundary at Tyrone, Pennsylvania. This missing section is interpreted to be the result of non-deposition because of differential uplift to the north of a proposed crustal-block boundary, represented by the Tyrone-Mt. Union lineament, while the basin to the south was differentially subsiding and PACs 1-7 were being deposited. Recognition of two paleoisotopographic surfaces (sea-level surfaces) at the base of PAC 1 and the top of PAC 22 facilitates the discernment of 17.5 meters of stratigraphic thickness difference attributable to differential subsidence between Tyrone and Cessna, Pennsylvania.

Composite ultramafic xenoliths were collected at Peridot Mesa, San Carlos, Arizona. These nodules were analyzed petrographically, by electron microprobe, and for intrinsic oxygen fugacity (IOF). Textures proved to be transitional between those of igneous and those of metamorphic petrogenetic environments. Phase chemistry interpretations were not totally consistent with either igneous or metamorphic models of formation. IOF data could not be used to unravel equilibrium relationships between solid phases, but were overprinted by reactions with volatiles contained in the minerals, chiefly CO2. These results indicate that the nodules were derived from a complex upper-mantle source region characterized by multi-phase igneous events with important intervening, probably sub-solidus, i.e. metamorphic, reactions between phases.

The determination of the aquifer parameters of transmissivity and storativity from pump test data of a two layer confined aquifer system is not possible due to the indeterminacy of the discharge from each aquifer to the pumping well bore. To resolve this theoretical problem and analyze pump test data from a groundwater system in the Triassic Brunswick Formation of northeastern Montgomery County, Pennsylvania, the Darcy Weisbach model of turbulent flow in pipes or conduits was coupled with the Theis model of confined aquifer flow to produce a mathematical model that simulates the distribution of discharge within a pumping well bore and the accompanying distribution of hydraulic head throughout the two aquifer layers. Two analytic models and one finite difference model were developed, tested and applied to the analysis of the study area pump test data. Analysis of the models showed that approximations of the transmissivities of the two aquifer layers could be determined from pump test data via a method similar to the Jacob straight line method. The models demonstrated that the distribution of discharge between the two aquifer layers is a variable function of time, that the change in the distribution of discharge over time is small in reference to the initial distribution and decreases in magnitude over time. Model simulation runs based on the transmissivity (T) calculation and a range of storativities (S) and boundary conditions yielded a good fit to pump test drawdown data for lower aquifer layer values of 4900 gal/ft/day (T) and 5.SE-6 (S) and upper aquifer layer values of 400 gal/ft/day (T) and lE-4 (S), plus a single barrier boundary in the lower aquifer located 2500 feet updip from the pumping well. The simulation results provide theoretical evidence in support of the interpretation of the study area groundwater system as a two layer system. The models demonstrated theoretically that two layer aquifer systems can produce distributions of drawdown data in observation wells that appear to evidence non-Theisian conditions, though in fact the individual layers are Theisian aquifers. As such, pump test data from Triassic Brunswick aquifers that exhibit non-Theisian distributions of drawdown may result from the distribution of pump discharge within the pumping well bore to vertically separated Theisian aquifer layers.

Application of the Hypothesis of Punctuated Aggradational Cycles to the stratigraphic analysis of the Binnewater Sandstone in southeast­ern New York reveals that the formation was deposited as a sequence of PACs (thin shallowing-upward cycles) in response to a series of six small-scale transgressive episodes. Each successive transgression ex­tended farther to the northeast resulting in an onlapping sequence which is conformable with the High Falls Formation to the southwest and unconformable with the Ordovician Normanskill Formation to the northeast. Within the study area the Binnewater Sandstone sequence is unconforma­bly overlain by the Rondout Formation. At each locality the Binnewater Sandstone consists of PACs repres­enting nearshore, shallow subtidal to high intertidal elastic paleo­environments. These PACs are laterally traceable and can be correlated amongst localities. To the southwest at High Falls the sequence consists of six PACs; to the northeast at South Wilbur the sequence is much thinner because only the third and fourth PACs in the sequence were deposited and preserved. That is, deposition did not begin in the northeast until the area was inundated by the third transgressive event. Then, following deposition of PACs 4, 5 and 6, the sequence was differentially truncated by erosion which eliminated PACs 5 and 6 at Wilbur. Following erosion of the Binnewater sequence the resulting erosional surface was flooded throughout the area by the first Rondout trangressive event indicating the near horizontality of this surface. These detailed strat­igraphic relationships of the Binnewater Sandstone between High Falls and Wilbur can be explained either by differential subsidence of a few meters accompanied by a minor sea-level fall or by differential uplift of a few meters causing greater erosion to the northeast.

The facies mosaic within the Thacher Member of the Manlius Forma­tion in central New York State can be subdivided into a sequence of ten upward-shallowing carbonate units. Each unit or Punctuated Aggradational Cycle (PAC), is bounded by non-depositional transgressive (deepening) surfaces. Between these surfaces, basal subtidal facies grade upward into shallow subtidal, intertidal and/or supratidal facies. These PACs exhibit facies which were deposited in several environments including an open shelf, a subtidal stromatoporoid patch reef, a restricted shelf, a bioclastic sand shoal and sand shoal fringe, and gradational shallow subtidal environments into intertidal and supratidal flat environments. Each PAC can be correlated between closely spaced outcrops by tracing key beds, facies lithosomes, cycles of similar thickness and internal facies arrangement. Longer distance correlation across the study area can be accomplished by matching shallowing sequences of PACs, matching major vertical facies changes across transgressive surfaces (indicating major deepening events) and by matching laterally persistent facies lithosomes. Analysis of the facies mosaic within a PAC provides a detailed interpretation of the paleogeographic changes accompanying its deposition. The Thacher Member consists of a sequence of ten paleo­environmental units consisting of facies which exhibit gradational transitions within and distinct facies changes at their boundaries.

Oxygen, iron, magnesium, and carbon are the principal geochemical parameters employed to elucidate the chemical relationship between the Bushveld Merensky Reef and associated structures termed "potholes". Potholes are large (hundreds of meters wide and tens of meters deep) depressions in the footwall filled with Merensky equivalent materials. Three potholes were analyzed in this study. The concentration of inorganic carbon was found to range from 1,835 ppm to 131 ppm. The fO2 analyses at 1150 C have a range from 10^-11.9 to 10^-13.9 atmospheres. In particular, stratigraphically equivalent basal chromites show a decrease from 10^-12.1 in the Normal Merensky Reef to 10^-13.9 in the pothole bottom. The ratios of Total Fe (as FeO/MgO + Total Fe (as FeO)) in these basal chromites show a range of 0.779 to 0.839 from pothole bottom to Normal Merensky Reef, respectively. Finally, Fe^+3 concentration in basal chromites, relative to Fe^+2 concentration, shows a depletion in the bottom of potholes. Parameter analyses indicate that geochemical gradients not only exist along stratigraphically equivalent horizons (lateral gradients) but also exist along stratigrpahic units (vertical gradients). Various hypotheses which address the genesis of pothole formation are reviewed in light of the above mentioned gradients. The author has found that the plutonic fumarole hypothesis as proposed in Ulmer et al. (1981) is best suited to explain the lateral and vertical geochemical gradients. Potholes acting as plutonic fumaroles releasing reducing carbonaceous and/or sulfurous gases are discussed as a possible mechanism for Merensky Reef petrogenesis. The author's geochemical data and published research from the literature are integrated into a discussion of new ideas for the platinum-reef petrogenesis in the Bushveld Complex.

Northerly dipping compositional layering in the central and western portions of the Stillwater Igneous Complex, the moderate northward slope of the Beartooth Front north of these outcrops, as well as gravity data (Bonini, 1981) provide structural evidence for the continuation at depth of the Complex north of the middle Cambrian unconformity along its northern boundary. The Lodgepole, Enos Mountain and Susie Peak plutons represent multiple intrusions of intermediate magmas at emplacement depths ranging from 2 km to near-surface conditions during late Cretaceous time. These intrusions lie respectively 8, 9, and 12 km north of the nearest outcrops of the Stillwater Complex. The Lodgepole Intrusion consists of an early dacite phase and a later diorite phase, the latter containing abundant xenoliths (up to 31 cm in diameter) in the area north of Clover Basin near its western margin. These xenoliths include foliated mafic amphibolites, gneisses, Paleozoic sediments, and cumulate textured basic rocks. Smaller xenoliths of similar lithologies are found in the Enos Mountain and Susie Peak intrusions. The cumulate textured xenoliths have magmatic textures, basic silica contents, and tholeiitic normative rnineralogies. The euhedral to subhedral, medium to coarse grained, tabular plagioclase in the xenolith sample suite has a total span of An62 to An86 (mole %) with variability in a single sample generally 1 to 5 mole % An. Minor primary-appearing augite is found in anorthositic specimens, but most of the primary mafic minerals have been altered to calcic amphibole and chlorite. The external habit and mineralogy of some mafic mineral domains suggest that they are pseudomorphic after primary pyroxenes and olivine. Based on interpretation of mineralogy and texture, cumulate xenoliths were classified as anorthosites, gabbros, norites, gabbronorites, troctolites, and altered ultramafic lithologies. One xenolith contained chromite, one contained graphite, and a few contained minor Fe and Cu sulfides. Mineral compositions and textures lead this author to conclude that the xenoliths were brought up from the underlying Stillwater Complex. Based on estimate of the fluid properties of the andesitic magma above its liquidus, ascent rates of greater than 1.7 m/second were needed to have raised the cumulate xenoliths. The lack of xenoliths with plagioclase compositions <An62, as well as structural space constraints imposed by the existence of non-cumulate basement lithologies north of the East Boulder Fault lead this author to question the existence of the thick differentiated Hidden Zone postulated by Hess (1960).