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Thomas L. Wright

Publications and source records attributed to Thomas L. Wright.

At least 37 records · Page 2Linked to original sources
USGS1987

The significance of observations at active volcanoes; A review and annotated bibliography of studies at Kilauea and Mount St. Helens

Study of active volcanoes yields information of much broader significance than to only the discipline of volcanology. Some applications are 1) interpretation of lava-flow structures, stratigraphic complexities, and petrologic relations in older volcanic units; 2) interpretation of bulk properties of the mantle and constraints on partial melting and deep magma transport; 3) interpretation of geophysical characteristics of potentially active volcanic systems; 4) direct determination of physical properties of molten and solidified basalt, and of intensive variables (e.g., oxygen fugacity and temperature) accompanying cooling and crystallization; 5) quantitative assessment of crystal fractionation and magma mixing, 6) tests of theoretical and experimental geochemical, geophysical, and rheologic models of volcanic behavior; and 7) confirmation in nature of laboratory experiments related to crystallization in igneous systems. The critical factors that make real-time study of volcanic activity valuable are that the location and timing of events are known, and that molten rock and gases are available for direct observation and sampling for subsequent study. Observations made over a period of time make it possible to calculate rates of magma transport, storage, and crystallization, as well as to quantitatively determine elastic and inelastic deformation and the build up and decay of stress within the active volcanic system. Discussion of these topics is keyed to an annotated bibliography from which quantitative information on properties and processes may be obtained. Emphasis is on Hawaii's active basaltic volcanoes for which the most information is available. Additional references are made to research at Mount St. Helens, one of the first real-time studies of an active volcano of dacitic composition.

Hawaii, Washington↗
USGS1986

Regional correlation of Grande Ronde basalt flows, Columbia River basalt group, Washington, Oregon, and Idaho (USA)

The tholeiitic flood basalts of the Columbia River Basalt Group of middle and late Miocene age cover more than 200,000 km 2 in Washington, Oregon, and Idaho. The most voluminous formation of the Group, the Grande Ronde Basalt, erupted for 2 m.y. from north-northwest-trending fissure systems concentrated in southeast Washington and adjacent Oregon and Idaho. Four magnetostratigraphic units (designated R 1 , N 1 , R 2 , and N 2 from oldest to youngest) are recognized on the basis of polarity in the Grande Ronde and provide the broad stratigraphic framework for the formation. In this study, major-element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the Grande Ronde Basalt on a regional scale. Systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings, which are distinguished primarily by small but significant variations in MgO, TiO 2 , and P 2 O 5 content. In addition, four minor chemical types local to the eastern part of the province have been identified. Feeder dikes of each chemical type have also been located. Flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical-stratigraphic subunits. These subunits consist of several flows collectively 30–150 m thick. Subunits of most chemical types are repeated at irregular intervals throughout the formation; no progressive chemical trend occurs within the Grande Ronde. Many of the chemical-stratigraphic subunits extend to the margins of the province, although most are confined to the source region in eastern Washington. Although the total number of subunits is less in the west away from the fissure systems, the total thicknesses of the N 2 and R 2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern Washington. The greatest thicknesses occur in the central part of the province within the Pasco basin. The distribution of basalt relative to the location of vents, as well as the relative east-west thicknesses, suggests that basalt flowed hundreds of kilometres westward during the most voluminous Grande Ronde eruptions, ponding against the irregular margin of the Cascade Range and being diverted through the ancestral Columbia Gorge toward the Washington-Oregon coast. Between these huge sheetflood events, smaller eruptions blanketed areas within the source region, and ongoing regional subsidence created a shallow westward-draining basin in the center of the province.

Idaho, Oregon, Washington↗
USGS1986

Volcano monitoring at the U.S. Geological Survey's Hawaiian Volcano Observatory

The island of Hawaii has one of the youngest landscapes on Earth, formed by frequent addition of new lava to its surface. Because Hawaiian are generally nonexplosive and easily accessible, the island has long attracted geologists interested in studying the extraordinary power of volcanic eruptions. The U.S. Geological Survey's Hawaiian Volcano Observatory (HVO), now nearing its 75th anniversary. has been in the forefront of volcanology since the 1900's. This issue of Earthquakes and volcanoes is devoted to the work of the Observatory and its role in studying the most recent eruptions of Hawaii's two currently active volcanoes, Kilauea and Mauna Loa.

Hawaii↗
USGS1978

A computer-assisted graphical method for identification and correlation of igneous rock chemistries

We have devised a computer-assisted graphical method for correlating chemical analyses in suites of related igneous rocks. The method provides a direct and empirical means of sample identification using all of the reported chemistry. In a study of basalt of the Columbia River plateau, the method has been used for (1) checking field identifications of rocks, (2) spotting analytical errors in analyses of samples of known chemical type, (3) identifying repetitions of chemistry in thick stratigraphic sections, and (4) matching analyses of dikes to those of flows that the dikes may have fed. Program OXVAR creates a set of oxide-oxide variation diagrams on a CALCOMP plotter; any oxide may be used as the base (for example, MgO, SiO 2 ). For each oxide-oxide variation diagram, program CTSET creates the smallest convex polygon that encloses all the data points as well as a larger polygon that takes into account the error in determination of each data point. A set of nested polygons, one for each oxide, then represents a chemical type. Program CTYPE identifies unknown analyses by comparing them with all defined chemical types. If all the elements or oxides of an analysis plot within the defined polygons for a given chemical type, then an identification is printed. If at least one element of an analysis falls outside the set of polygons defined for each chemical type, then “unidentified” is printed, and qualitative information on the amount of deviation from the defined chemical types is given.

Geology↗
USGS1976

Geologic interpretation of an aeromagnetic map of the west-central Columbia Plateau, Washington and Oregon

A low altitude, total intensity aeromagnetic map of the ?west-central Columbia Plateau, underlain principally by the Yakima Basalt,. shows Positive and negative anomalies that stand out from a moderate intensity .background reflecting .interbedded flows of normal and reversed magnetic polarity. One set of anomalies is related to anticlinal ridges, nother follows the traces of known or inferred faults, and a third set coincides with a swarm of feeder dikes for the Ice Harbor flows of Swanson and others (1975b), the youngest unit of basalt in the area. A fourth set of narrow, sinuous anomalies is related to flows that filled ancient valleys during the late stage of Yakima volcanism. The magnetic map suggests that the Ice Harbor dike swarm is offset by left-lateral strike-slip displacement along the Rattlesnake-Wallula fault, a segment of the Olympic-Wallowa lineament. The aeromagnetic map is of great help in delineating the extent of the dike swarm, mapping the ancient drainage system, and understanding the structural history of this part of the Columbia Plateau.

Oregon, Washington↗
USGS1975

Chemical compositions of Kilauea east-rift lava, 1968–1971

The major element chemical compositions of lava from four eruptions on the east rift zone of Kilauea between August 1968 and October 1971 reflect three petrologic processes: Production of chemically distinct batches of magma in the mantle. Separation of olivine, augite, and plagioclase from liquid during flow in the rift-zone conduits. Mixing of different magmas during ascent to the surface. Chemically none of the four Kilauea east-rift eruptions matches the preceding summit eruption in Halemaumau that ended in July 1968. The Mauna Ulu eruption, May 1969 to October 1971 (the last of flie east-rift eruptions), can be divided into five olivine-controlled and chemically distinct variants. Three of these characterize the first seven months of the eruption and are closest in composition to the 1967–8 Halemaumau eruption. Variants 4 and 5 were erupted later and have compositions that are distinctly different from that of the 1967–8 eruption. Major differences are higher Al 2 O 3 (0·15–0·23 per cent), and lower K 2 O (0·07–0·10 per cent) and TiO 2 (0·12–0·23 per cent) in variants 4 and 5 at the same MgO content. Some lavas from eruptions in August and October 1968 and February 1969, have olivine-controlled magma compositions that are identical to mixtures of Mauna Ulu variants 1–3 and the 1967–8 composition. This observation fits an hypothesis advanced earlier by T. L. Wright and R. S. Fiske that magmas in the central magma chamber become mixed with magmas in the rift zone and can be identified as mixing components of rift eruption magmas before they appear as distinctive magmas in summit eruptions. Lavas representing mixing of olivine-controlled magma with differentiated magma were erupted in October 1968, February 1969, and in May and December 1969. The changes in amount of K 2 O and TiO 2 during the latter part of the 1969–71 Mauna Ulu eruption are the reverse of the overall secular change in composition of Kilauea summit lavas from pre-1750 through 1967–8. The K 2 O and TiO 2 contents of the latest overflows during the 1969–71 Mauna Ulu eruption (April 1971) are comparable to that of lava erupted at Kilauea summit prior to 1750. The changing chemistry of Kilauea magma is found to be of use as a ‘tracer’ in the complex Kilauea conduit system. Application of these data to older lava sequences is difficul because of the complexity of the processes controlling lava composition and the absence of detailed information about the time-space chemical variation during individual eruptions.

Hawaii↗
USGS1973

Chemical variation related to the stratigraphy of the Columbia River basalt

Study of major element chemical analyses of Columbia River basalt leads to a grouping of most of the analyses into 11 chemical types which are distinguished with little overlap on a SiO 2 -MgO variation diagram. Other diagnostic variation diagrams are total iron (‘FeO’)-MgO, K 2 O-MgO, and TiO 2 -MgO. A four-unit informal stratigraphy has been adopted in order to define the relations between chemical composition and stratigraphic position. From oldest to youngest, the four stratigraphic units are (1) lower basalt of Bond (1963) and Picture Gorge basalt, (2) lower Yakima basalt, (3) middle Yakima basalt, and (4) upper Yakima basalt. Most of the Picture Gorge and lower basalt flows are relatively rich in MgO (approximately 4.5 to 7.1 percent) and are distinguished by intermediate SiO 2 relative to MgO. Furthermore, the Picture Gorge basalt generally has low K 2 O relative to MgO. The lower Yakima basalt consists almost entirely of flows with relatively low MgO content (approximately 3.0 to 5.5 percent) and with the highest SiO 2 relative to MgO of any flows of the Columbia River basalt. The middle Yakima basalt contains flows of three distinct chemical types, which together cover the same MgO range as the lower Yakima flows but which have considerably lower SiO 2 and higher ‘FeO’ and TiO 2 relative to MgO. Flows in the upper Yakima basalt are of diverse composition; two of the youngest flows are distinguished by having the lowest SiO 2 and highest ‘FeO’, TiO 2 , and P 2 O 5 relative to MgO of any analyzed Columbia River basalt. Flows of one or more chemical types may form the dominant lithology in a stratigraphic unit, but single flows of the same chemical types may occur in any stratigraphic unit. Some lava sampled in the eastern part of the plateau has more TiO 2 than does lava of otherwise similar composition sampled in the western part of the plateau. This is tentatively interpreted as reflecting a heterogeneous composition for the mantle beneath the Columbia Plateau.

Oregon, Washington↗
USGS1973

Magma Mixing as Illustrated by the 1959 Eruption, Kilauea Volcano, Hawaii

The 1959 eruption of Kilauea volcano is unique among recent Kilauea summit eruptions (1952 to 1968) in at least two respects: (1) a large collapse of Kilauea summit accompanied the eruption, and (2) the erupted lavas show a complex variation in their bulk chemical composition. Both features suggest that the 1959 eruption was fed from a source different from that which fed other summit eruptions in this period. The variations in chemical composition can be interpreted in terms of mixing chromite-bearing olivine with variable proportions of two “end-member” magmas represented by the composition of samples of pumice erupted during the first phase of the eruption. Mixing calculations show that the MgO content of olivine varies with the MgO content of the lava and thus with olivine percentage in the same manner as previously determined by Richter and Murata (1966) from petrographic study of hand samples. The calculations also show that the proportion of the two end-member magma types varies throughout the eruption. These results suggest that the eruption was fed from two separate magma batches, each of which was held in a reservoir with an olivine-poor top and olivine accumulation toward the bottom. There is also evidence that the two end-member magmas may be related by redistribution of clinopyroxene in a third hypothetical magma. The complex pre-eruption history implied by the chemical data is at present not satisfactorily explained by any physical model of fractionation, storage, and mixing that can be inferred from data on other well-studied Kilauea eruptions. The average MgO content (15.5 percent) of the 1959 eruption is estimated to be in minimum MgO content of magma produced by partial melting in the mantle beneath Kilauea.

Hawaii↗
USGS1972

Apollo 11 and 12 mare basalts and gabbros: Classification, compositional variations, and possible petrogenetic relations

On the basis of composition, it is possible to distinguish three major groups of Apollo 12 basaltic rocks: olivine-pigeonite basalts and gabbros, ilmenite-bearing basalts and gabbros, and feldspathic basalts. Two major groups of Apollo 11 basalts are also distinguishable: ophitic ilmenite basalts and intersertal ilmenite basalts. Compositional variations between samples within groups are generally dominated by MgO variations, whereas differences between groups are primarily inverse variations of TiO 2 and SiO 2 or Al 2 O 3 and FeO. Results of fractionation calculations indicate that the MgO variation trends are explained principally by low-pressure fractionation of early-crystallized olivine ± pigeonite ± chrome spinel. The Al 2 O 3 versus FeO trend in the basalts might possibly be explained by near-surface fractionation, but the TiO 2 versus SiO 2 trend is not explainable in this way. Investigations of the latter trend in terms of possible processes of high-pressure fractional melting or fractional crystallization indicate that the compositional variations cannot be the products of simple variations in depth or degree of fractionation. Our data are consistent with the view that the mafic magmas formed by partial melting in the lunar interior, and that near-surface fractionation, with the exception of removal or addition of olivine, has not been extensive.

GSA Bulletin↗