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Dive into the research topics where Barry L. Weaver is active.

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Featured researches published by Barry L. Weaver.


Earth and Planetary Science Letters | 1991

The origin of ocean island basalt end-member compositions: trace element and isotopic constraints

Barry L. Weaver

Abstract Ocean island basalt (OIB) suites display a wide diversity of major element, trace element, and isotopic compositions. The incompatible trace element and isotopic ratios of OIB reflect considerable heterogeneity in the mantle source regions. In addition to the distinctive Sr, Nd and Pb isotopic signatures of the HIMU, EMI and EMII OIB end-members, differences in incompatible trace element ratios among these end-members are of great help in identifying the nature and origin of their sources. Examination of trace element and isotopic constraints for the three OIB end-members suggests a relatively simple model for their origin. The dominant component in all OIB is ancient recycled basaltic oceanic crust which has been processed through a subduction zone, and which carries the trace element and isotopic signature of a dehydration residue (enrichment in HFSE relative to LILE and LREE, low Rb/Sr, but high U/Pb and Th/Pb ratios leading to the development of radiogenic Pb isotope compositions). HIMU OIB are derived from such a source, with little contamination from other components. Both the EMI and EMII OIB end-members are also dominantly derived from this source, but they contain significant proportions (up to 5–10%) of sedimentary components derived from the continental crust. In the case of EMI OIB, ancient pelagic sediment with high LILE/HFSE, LREE/HFSE, Ba/Th and Ba/La ratios, and low U/Pb ratios, is the contaminant. EMII OIB are also contaminated by a sedimentary component, in the form of ancient terrigenous sediment with high LILE/HFSE and LREE/HFSE ratios, but lacking relative Ba enrichment, and with higher U/Pb and Rb/Sr ratios. A model whereby the source for all OIB is ancient (1–2 Ga old) subducted oceanic crust ± entrained sediment (pelagic and/or terrigenous) is therefore consistent with the trace element and isotopic data. Although subducted oceanic lithosphere will accumulate and be dominantly concentrated within the mesosphere boundary layer, forming the source for hot-spots, such material may also become convectively dispersed within the depleted upper mantle as blobs or streaks, giving rise to small-scale chemical heterogeneities in the upper mantle.


Earth and Planetary Science Letters | 1993

Os isotope systematics in ocean island basalts

Laurie Reisberg; Alan Zindler; Franco Marcantonio; William D. White; Derek Wyman; Barry L. Weaver

New ReOs isotopic results for Os-poor basalts from St. Helena, the Comores, Samoa, Pitcairn and Kerguelen dramatically expand the known range of initial 186Os/187Os ratios in OIBs to values as high as 1.7. In contrast to the Os isotopic uniformity of Os-rich basalts from the HIMU islands of Tubuai and Mangaia found by Hauri and Hart [1], our values for St. Helena span most of the known range of Os isotopic variability in oceanic basalts (initial 187Os/186Os ranges from 1.2 to 1.7). Generation of such radiogenic Os in the mantle requires melting of source materials that contain large proportions of recycled oceanic crust. The very low Os concentrations of most of the basalts analyzed here, however, leave them susceptible to modification via interaction with materials containing radiogenic Os in the near-surface environment. Thus the high 186Os/187Os ratios may result from assimilation of radiogenic Os-rich marine sediments, such as Mn oxides, within the volcanic piles traversed by these magmas en route to the surface. Furthermore, the Os isotopic signatures of Os-rich, olivine-laden OIBs may reflect the accumulation of lithospheric olivine, rather than simply their mantle source characteristics. The extent to which these processes alter the view of the mantle obtained via study of ReOs systematics in oceanic basalts is uncertain. These effects must be quantified before ReOs systematics in OIBs can be used with confidence to investigate the nature of mantle heterogeneity and its causes.


Geology | 1991

Trace element evidence for the origin of ocean-island basalts

Barry L. Weaver

Ocean-island basalt (OIB) suites display significant and consistent differences in highly incompatible trace element ratios between islands which have end-member radiogenic isotope signatures. OIB derived from sources with a high U/Pb ratio have trace element characteristics consistent with a source dominated by recycled ancient oceanic crust. OIB derived from the isotopically distinct enriched mantle sources have trace element characteristics best interpreted in terms of sources which are mixtures of high U/Pb OIB with minor amounts (a few percent) of recycled sedimentary (pelagic and terrigenous) components.


Geology | 1986

Role of subducted sediment in the genesis of ocean-island basalts: Geochemical evidence from South Atlantic Ocean islands

Barry L. Weaver; David Wood; John Tarney; Jean Louis Joron

The South Atlantic Ocean islands of Ascension, Bouvet, St. Helena, Gough, and Tristan da Cunha display considerable inter-island (and to a variable extent intra-island) heterogeneity in ratios of highly incompatible trace elements. Basaltic and hawaiitic lavas from Ascension, Bouvet, and St. Helena have consistent trace-lenient ratios (e.g., La/Nb, Ba/Nb, Ba/La, Ba/Th, Rb/Th). In contrast, Tristan da Cunha and Gough (and Walvis Ridge) lavas are depleted in Nb and enriched in Ba relative to other highly incompatible trace elements as compared to the other islands. The trace-element and Pb isotopic geochemistry of these lavas is explicable by contamination of the ocean-island basalt source that gave rise to Ascension, Bouvet, and St. Helena lavas by variable, but small (about 1%), amounts of ancient (1.5–2.0 Ga) pelagic sediment.


Contributions to Mineralogy and Petrology | 1990

Geochemistry of highly-undersaturated ocean island basalt suites from the South Atlantic Ocean: Fernando de Noronha and Trindade islands

Barry L. Weaver

The volcanic rocks of the South Atlantic Ocean islands of Fernando de Noronha and Trindade comprise a diverse magmatic series ranging from nephelinites and basanites to phonolites and, on Fernando de Noronha, trachytes. All rock types are highly silica undersaturated with the exception of Fernando de Noronha trachytes_, and have high abundances of incompatible trace elements and strongly LREE (light rare earth element)-enriched REE patterns. Crystal fractionation of parental basanitic magmas produced evolved phonolites and trachytes which display severe trace-element fractionation, even among trace elements (Nb, Ta, Zr, Hf) which normally behave highly incompatibly during crystallisation of alkaline magmas. Moderately to highly evolved compositions develop strongly MREE (middle REE)-depleted REE patterns, and become increasingly depleted in elements such as Nb and, in particular, Ta. Ratios of Nb/Ta and Zr/Hf are highly fractionated in phonolites (60–65, 64–77 respectively in Fernando de Noronha phonolites) compared to ratios in basanites (14, 45 respectively). The compatibility of Nb, Ta, and the REE, and the strong fractionation of Nb/Ta and Zr/Hf ratios and the MREE, during crystallisation from basanite to phonolite are attributable to the crystallisation of small amounts (<5%) of sphene. Trace-element behaviour is relatively insensitive to the major phenocryst phases, and is controlled by minor phases in highly undersaturated alkaline suites. Incompatible trace-element ratios (e.g. La/Nb, Th/Ta) in nephelinites and basanites from Fernando de Noronha and Trindade are generally comparable with those in basaltic and hawaiitic OIB (ocean island basalt) lavas from other South Atlantic islands, but are distinct from those of Gough and Tristan da Cunha OIB. The mantle source for the highly undersaturated volcanism on Fernando de Noronha and Trindade is similar in trace-element characteristics to the “typical” OIB source which produces alkaline lavas with significant relative enrichment in Nb and Ta compared to other trace elements (as expressed by low La/Nb, Ba/Nb and Th/Ta ratios). The highly undersaturated nature of the magmas and the slight fractionation of some incompatible-element ratios (elevated Ba/Nb, Ba/Rb, Ba/Th etc.) is consistent with a smaller degree of melting of a “typical” OIB source, but with residual phlogopite in the source to account for significant K depletion and LIL-element fractionation.


Geological Society of America Bulletin | 2000

Beyond whole-rock geochemistry of shales: The importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the Ouachita Mountain flysch deposits

Matthew W. Totten; Mark A. Hanan; Barry L. Weaver

The origin of the Ouachita Mountains has been the focus of significant debate for decades. Considerable confusion also exists concerning the provenance of the Carboniferous flysch of the Ouachitas. Trace-element geochemistry of shales from the Stanley Group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during Mississippian time. Th/Sc and Cr/Th ratios indicate a cratonic source for the majority of the Stanley Group sedimentary rocks. However, in several samples, low Th/Sc ratios and high Cr/Th ratios suggest a contribution from a mafic source. Using element ratio diagrams, all of the samples plot along a curve consistent with a two-component mixing model, consisting of a dominant felsic and a subordinate mafic source. The heavy-mineral fraction of these shales sequester many of the trace elements used in whole-rock studies. Monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock. The occurrence of monazite almost exclusively in sialic igneous rocks implies that Sm/Nd isotopic signatures are not sensitive to sediment input from more mafic sources. In some Stanley shale samples, chromite and Mn oxides were identified and positively identify an oceanic crustal component as a source of Stanley Group sediment. The results of this study emphasize the importance of determining the mineralogic sites of trace elements, and realization of specific mineralogic contributions from mafic or sialic tectonic provenances.


Geothermics | 1996

Geochemical characteristics of volcanic rocks from ascension island, South Atlantic Ocean

Barry L. Weaver; Aditya Kar; Jon P. Davidson; Mike Colucci

Abstract The volcanic rocks of Ascension Island are a transitional to mildly alkaline basalt-hawaiite-mugearite-benmoreite-trachyte-rhyolite suite. Although the overall major element variations in the suite are consistent with derivation of the more evolved compositions by crystal fractionation from parental basalt magma, trace element variations among basalt and hawaiite compositions define four distinct magma types. Three of these types are discriminated by variations in Zr/Nb. A number of hawaiite scoria cones and associated flows restricted to the southwestern part of the island have low Zr/Nb (4.1), whereas basalt scoria and flows distributed over the southeastern part of the island have high Zr/Nb (≈6.0), and basalt and hawaiite scoria cones and associated flows widely distributed over the remainder of the island have intermediate Zr/Nb (≈ 5.0). The fourth magma type is a subset of the intermediate Zr/Nb group, but has high Ni and Sr relative to Zr compared to the rest of the group; the flows defining this magma type are related to a single vent, Dark Slope Crater, in the southwestern part of the island. The mugearite and benmoreite flows and scoria are exclusively derived by crystal fractionation of intermediate Zr/Nb group parent basalt magma. Field relationships suggest non-overlapping phases of eruption of the different mafic magma types. The oldest exposed mafic lava flows are of high Zr/Nb basalt; limited KAr age data suggest that this magma type may have erupted between ca 0.66 and 0.35 Ma. Subsequently, there was localised eruption of the Dark Slope Crater magma type, followed by equally localised eruption of the low Zr/Nb magma type. The most recent eruptions (which have continued to possibly within the last few hundred years) have been much more widespread and of the intermediate Zr/Nb magma type.


Geological Society of America Bulletin | 1994

Geochemistry of Mississippian tuffs from the Ouachita Mountains, and implications for the tectonics of the Ouachita orogen, Oklahoma and Arkansas

Jennifer Loomis; Barry L. Weaver; Harvey Blatt

The Ouachita orogeny was the result of plate convergence at the southern margin of the North American continent, although the nature of the converging southern plate and the direction of subduction remain uncertain. The presence of areally extensive tuff layers interbedded with shale in the Mississippian Stanley Group of the Ouachita Mountains, Oklahoma and Arkansas, provides the potential to define the tectonic environment of volcanism from the geochemistry of the tuffs and thereby delimit the subduction configuration. The tuffs contain relic primary magmatic quartz, plagioclase, and alkali feldspar and range from crystal- to vitric-rich. Mineralogical sorting and diagenetic effects have caused chemical variability within individual tuff units, but overall the tuffs have retained their primary igneous geochemical characteristics. The Beavers Bend and Hatton tuffs are geochemically very similar and are more evolved (higher SiO2, Rb, Th, REE; lower Sr, Ba) than the Mud Creek tuff. The stratigraphically equivalent Sabine Rhyolite is geochemically distinct from the tuffs, having less fractionated rare earth element (REE) patterns and different trace element ratios. Both the Ouachita tuffs and Sabine Rhyolite have the geochemical characteristics of subduction-related magmas (for example, strong depletion of Nb and Ta relative to other incompatible trace elements). Consideration of trace element systematics in the tuffs compared to those of modern high-silica volcanic rocks from different subduction-related tectonic settings suggests a continental arc origin and implies southward subduction beneath a southern continent during Carboniferous ocean basin closure.


Lithos | 1998

Evidence for an enriched mantle source for jøtunite (orthopyroxene monzodiorite) associated with the St. Urbain anorthosite, Quebec

Jonathan P. Icenhower; Robert F. Dymek; Barry L. Weaver

Abstract Mafic orthopyroxene monzodiorite (jotunite) lithologies are exposed in the St. Urbain plutonic suite as a marginal facies to quartz mangerite and massif anorthosite intrusive bodies and as dikes within a variety of host rocks. High concentrations of Ti, Fe, P, K, Ba, Nb, La, Ce, Zn, Ga, Zr and Y characterize these rocks and are distinctive of many mafic lithologies associated with anorthosite massifs worldwide. Characteristically low concentrations of Ni and Cr, in conjuction with low Mg numbers, have been used by previous investigators as evidence for either partial melting of mafic granulitic lower crust or extensive fractional crystallization of a mantle-derived magma. In an attempt to distinguish between these competing models, we note that jotunite display many features that bear a strong resemblance to continental tholeiitic flood basalts, including chemical signatures on normalized multi-element (‘spider’) diagrams. Ratios of incompatible trace elements and patterns on rare earth and ‘spider’ diagrams collectively indicate that the jotunite rocks were derived from an enriched, rather than depleted, mantle source. Enrichment may have occured by subduction-derived fluids or by mixture with a plume component prior to partial melting so that isotopic and trace-element compositions are decoupled. Small amounts of partial melting of mafic granulite has been advanced as an alternative model; we show, however, that the experimental data on which this model is built are not applicable. Our preferred model begins with partial melting of a trace-element enriched mantle source that fractionates olivine at high to moderate pressures. Increasing concentrations of P (and Ti) eventually caused a contraction of the olivine stability field in favor of orthopyroxene. Fractional crystallization may yield the series of rocks from anorthosite, leuconorite, oxide-apatite gabbronorite, to jotunite. Mafic magmas emplaced into continental crust are typically attributed to incipient rifting or mantle upwelling, which are features common to many models for the genesis of anorthosite and related rocks.


Geological Society of America Bulletin | 2015

Paleomagnetic and petrologic study of the age, origin, and significance of early and late Paleozoic events in the Long Mountain Granite, Wichita Mountains, Oklahoma

Evan Matthew Hamilton; R. Douglas Elmore; Barry L. Weaver; Shannon Dulin; Jacob Jackson

The Cambrian Long Mountain Granite, exposed in the western Wichita Mountains, Oklahoma, is red, granophyric, alkali feldspar granite. The red granite abruptly transitions into a green granite in the subsurface; both red and green granites have similar geochemical signatures. Anisotropy of magnetic susceptibility analysis shows that the green granite retains a primary magnetic fabric that is consistent with the sill-like emplacement of the Wichita Granite Group. Demagnetization of green granite specimens yields a characteristic remanent magnetization (ChRM) residing in magnetite with east declinations and moderate down inclinations. The paleopole (9.0°N, 314.6°E) is interpreted as a primary Cambrian thermal remanent magnetization or an early magnetization related to deuteric/hydrothermal alteration. The paleopole position is consistent with some other poles for Cambrian igneous rocks in southern Oklahoma but is to the southwest of the Cambrian part of the apparent polar wander path. The red granite contains abundant secondary hematite that occurs in fractures, as grain boundary coatings, and along cleavage and exsolution planes in alkali feldspars. The iron in the hematite appears to be sourced from the oxidation of primary magnetite and ilmenite and the breakdown of silicate ferromagnesian minerals. The red granite has about two orders of magnitude lower magnetic susceptibility and natural remanent intensity than the green granite. The magnetic fabric is interpreted as an alteration fabric. The ChRM of red granite has southeast declinations and shallow inclinations and is interpreted as a chemical remanent magnetization (CRM) residing in hematite. The paleopole (44.9°S, 304.9°E) falls near the 290–300 Ma segment of the North American apparent polar wander path, which is consistent with inferred timing of exposure of the Long Mountain Granite. The CRM is interpreted to have been acquired during alteration by low-temperature weathering fluids near the surface during the late Paleozoic. The results from the red granite are not consistent with alteration caused by widespread paleoclimatic conditions in the Late Permian, and they are interpreted as related to local tectonic and/or weathering events.

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Aditya Kar

University of Oklahoma

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Jacob Jackson

University of Texas at Dallas

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Mark A. Hanan

University of New Orleans

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Mike Colucci

Southern Methodist University

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