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Geology

Selected Works

2012

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Articles 1 - 30 of 86

Full-Text Articles in Physical Sciences and Mathematics

Kernel Density Estimation Of Traffic Accidents In A Network Space, Zhixiao Xie, Jun Yan Dec 2012

Kernel Density Estimation Of Traffic Accidents In A Network Space, Zhixiao Xie, Jun Yan

Dr Jun Yan

A standard planar Kernel Density Estimation (KDE) aims to produce a smooth density surface of spatial point events over a 2-D geographic space. However, the planar KDE may not be suited for characterizing certain point events, such as traffic accidents, which usually occur inside a 1-D linear space, the roadway network. This paper presents a novel network KDE approach to estimating the density of such spatial point events. One key feature of the new approach is that the network space is represented with basic linear units of equal network length, termed lixel (linear pixel), and related network topology. The use …

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Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe Sep 2012

Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe

Ann Blythe

Application of thermochronological techniques to major normal fault systems can resolve the timing of initiation and duration of extension, rates of motion on detachment faults, timing of ductile mylonite formation and passage of rocks through the crystal-plastic to brittle transition, and multiple events of extensional unroofing. Here we determine the above for the top-to-the-east Raft River detachment fault and shear zone by study of spatial gradients in 40Ar/39Ar and fission track cooling ages of footwall rocks and cooling histories and by comparison of cooling histories with deformation temperatures. Mica 40Ar/39Ar cooling ages indicate that extension-related cooling began at ∼25–20 Ma, …

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Yellow-Fluorescing Calcite From Sterling Hill, James A. Van Fleet, E. R. Verbeek Aug 2012

Yellow-Fluorescing Calcite From Sterling Hill, James A. Van Fleet, E. R. Verbeek

James A. Van Fleet

No abstract provided.

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Interdisciplinary Science Applications To Glacier And Alpine Hazards In Relation To Development And Habitation In The Hindu Kush-Himalaya: Servir Science Team Project., Umesh Haritashya Jul 2012

Interdisciplinary Science Applications To Glacier And Alpine Hazards In Relation To Development And Habitation In The Hindu Kush-Himalaya: Servir Science Team Project., Umesh Haritashya

Umesh Haritashya

National Aeronautics and Space Administration (NASA). Total Amount $999,886. Role: Co-I. Project duration: Aug 2012 – Aug 2016.

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Preliminary Lineament Analysis Within The Vicinity Of Kainji Dam, Nigeria Using Ers-1 Sar Image, M S. Kolawole, E G. Ameh, A Daniel Jul 2012

Preliminary Lineament Analysis Within The Vicinity Of Kainji Dam, Nigeria Using Ers-1 Sar Image, M S. Kolawole, E G. Ameh, A Daniel

Confluence Journal Environmental Studies (CJES), Kogi State University, Nigeria

Various affordable, operational technologies such as remote sensing, Geographic Information Systems (GIS) can significantly contribute to improved efficiency. The main focus of the project has been directed to the use of remote sensing to gain geological and geohazard information. This study examines the use of Remote Sensing (RS) technology in geological studies of Kainji area. Radar SAR images were used to classify the various geological fractures found in the area located in the Northern part of Nigeria. A wide variety of digital image processing techniques were applied such as the Principal Components (PC) analysis and ratioing. ERS-1 SAR image that …

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Two Modes Of Accelerated Glacier Sliding Related To Water, J. T. Harper, Neil Humphrey, W. T. Pfeffer, B. Lazar Jun 2012

Two Modes Of Accelerated Glacier Sliding Related To Water, J. T. Harper, Neil Humphrey, W. T. Pfeffer, B. Lazar

Neil Humphrey

We present the first glacier-wide detailed measurement of basal effective pressure and related observations including bed separation to elucidate the role of water in sliding. The hard bedded glacier instrumented in our study exhibited two phases of accelerated sliding motion apparently driven by separate mechanisms. The first acceleration phase ( up to 5 fold increase in speed) was closely tied to an increase in bed separation. The faster second phase ( up to 9 fold increase in speed) was related to an unusually high level of connectivity of subglacial waters. We infer the first mode was related to cavity opening …

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Topographic Control Of Asynchronous Glacial Advances: A Case Study From Annapurna, Nepal, B. Pratt-Sitaula, D. W. Burbank, A. M. Heimsath, Neil Humphrey, M. Oskin, J. Putkonen Jun 2012

Topographic Control Of Asynchronous Glacial Advances: A Case Study From Annapurna, Nepal, B. Pratt-Sitaula, D. W. Burbank, A. M. Heimsath, Neil Humphrey, M. Oskin, J. Putkonen

Neil Humphrey

Differences in the timing of glacial advances, which are commonly attributed to climatic changes, can be due to variations in valley topography. Cosmogenic Be-10 dates from 24 glacial moraine boulders in 5 valleys define two age populations, late-glacial and early Holocene. Moraine ages correlate with paleoglacier valley hypsometries. Moraines in valleys with lower maximum altitudes date to the late-glacial, whereas those in valleys with higher maximum altitudes are early Holocene. Two valleys with similar equilibrium-line altitudes (ELAs), but contrasting ages, are aspect, such that spatial differences in climate can be excluded. A glacial mass-balance cellular automata model of these two …

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Depth-Varying Constitutive Properties Observed In An Isothermal Glacier, H. P. Marshall, J. T. Harper, W. T. Pfeffer, Neil Humphrey Jun 2012

Depth-Varying Constitutive Properties Observed In An Isothermal Glacier, H. P. Marshall, J. T. Harper, W. T. Pfeffer, Neil Humphrey

Neil Humphrey

[1] Detailed three-dimensional in-situ measurements of deformation at depth are used to examine the rheology of a 6 x 106 m3 block of temperate glacier ice. Assuming that the viscosity of this ice is primarily dependent on stress, the relationship between inferred stress and measurements of strain-rate above similar to 115 m depth suggest a constitutive relationship with a stress exponent n similar to 1. Deformation below 115 m is described by a non-linear flow law with a power exponent of approximately 3-4. A sharp transition between the two flow regimes is likely caused by a change in the dominant …

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High Altitude Himalayan Climate Inferred From Glacial Ice Flux, J. T. Harper, Neil Humphrey Jun 2012

High Altitude Himalayan Climate Inferred From Glacial Ice Flux, J. T. Harper, Neil Humphrey

Neil Humphrey

[1] Glaciological processes are modeled to investigate precipitation patterns and the resulting mass flux of snow and ice across Himalayan topography. Our model tracks the accumulation and ablation of snow and ice and the transport of snow and ice across the topography by glacier motion. We investigate high elevation precipitation on the Annapurna Massif by comparing the existing ice cover with model-simulated glaciers produced by a suite of different precipitation scenarios. Our results suggest that precipitation reaches a maximum level well below the elevation of the highest peaks. Further, essentially no snow accumulates on the topography above an elevation of …

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Thermal Tracking Of Meltwater Retention In Greenland's Accumulation Area, Neil Humphrey, J. T. Harper, W. T. Pfeffer Jun 2012

Thermal Tracking Of Meltwater Retention In Greenland's Accumulation Area, Neil Humphrey, J. T. Harper, W. T. Pfeffer

Neil Humphrey

Poorly understood processes controlling retention of meltwater in snow and firn have important implications for Greenland Ice Sheet's mass balance and flow dynamics. Here we present results from a 3 year (2007-2009) field campaign studying firn thermal profiles and density structure along an 85 km transect of the percolation zone of west Greenland. We installed one or two thermistor strings at 14 study sites, each string having 32 sensors spaced between 0 and 10 m depth. Data from our network of over 500 sensors were collected at 15-60 min intervals for 1-2 years, thereby recording the thermal signature of meltwater …

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Cooling Rates And The Depth Of Detachment Faulting At Oceanic Core Complexes: Evidence From Zircon Pb/U And (U-Th)/He Ages, C. B. Grimes, Michael Cheadle, Barbara John, P. W. Reiners, J. L. Wooden Jun 2012

Cooling Rates And The Depth Of Detachment Faulting At Oceanic Core Complexes: Evidence From Zircon Pb/U And (U-Th)/He Ages, C. B. Grimes, Michael Cheadle, Barbara John, P. W. Reiners, J. L. Wooden

Barbara John

Oceanic detachment faulting represents a distinct mode of seafloor spreading at slow spreading mid-ocean ridges, but many questions persist about the thermal evolution and depth of faulting. We present new Pb/U and (U-Th)/He zircon ages and combine them with magnetic anomaly ages to define the cooling histories of gabbroic crust exposed by oceanic detachment faults at three sites along the Mid-Atlantic Ridge (Ocean Drilling Program (ODP) holes 1270D and 1275D near the 15 degrees 20'N Transform, and Atlantis Massif at 30 degrees N). Closure temperatures for the Pb/U (similar to 800 degrees C-850 degrees C) and (U-Th)/He (similar to 210 …

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2.685-2.671 Ga Himalayan-Type Orogeny In The Northern Teton Range, Wyoming, Usa, B R. Frost, Susan Swapp, Carol Frost Jun 2012

2.685-2.671 Ga Himalayan-Type Orogeny In The Northern Teton Range, Wyoming, Usa, B R. Frost, Susan Swapp, Carol Frost

Carol Frost

Meeting abstract for “2.685-2.671 Ga Himalayan-Type Orogeny in the Northern Teton Range, Wyoming, USA,” June 2009.

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Preservation Of Fe Isotope Compositions Of Iron Formation During Contact Metamorphism, Carol Frost, F. Von Blanckenburg, R. Schoenberg, B R. Frost, Susan Swapp Jun 2012

Preservation Of Fe Isotope Compositions Of Iron Formation During Contact Metamorphism, Carol Frost, F. Von Blanckenburg, R. Schoenberg, B R. Frost, Susan Swapp

Carol Frost

Meeting abstract for “Preservation of Fe Isotope Compositions of Iron Formation During Contact Metamorphism,” May 2005.

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Cooling History Of Atlantis Bank Oceanic Core Complex: Evidence For Hydrothermal Activity 2.6 Ma Off Axis, J. J. Schwartz, Barbara John, Michael Cheadle, P. W. Reiners, A. G. Baines Jun 2012

Cooling History Of Atlantis Bank Oceanic Core Complex: Evidence For Hydrothermal Activity 2.6 Ma Off Axis, J. J. Schwartz, Barbara John, Michael Cheadle, P. W. Reiners, A. G. Baines

Michael Cheadle

We report 26 (U-Th)/He zircon ages from Atlantis Bank, Southwest Indian Ridge, which constrain time scales and rates of lower crustal cooling in ultraslow spreading oceanic crust in this setting. Samples from the detachment fault surface indicate that denuded oceanic crust cooled rapidly (< 1 Ma), yielding cooling rates > 1200 degrees C/Ma, consistent with existing models for the cooling of oceanic crust. (U-Th)/He zircon ages from samples collected along N-S and E-W trending faults scarps record young ages inconsistent with standard cooling models for lower oceanic crust. These samples have a mean (U-Th)/He zircon age 2.6 Ma younger than their corresponding igneous crystallization ages and …

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Evolution Of The Southwest Indian Ridge From 55 Degrees 45 ' E To 62 Degrees E: Changes In Plate-Boundary Geometry Since 26 Ma, A. G. Baines, Michael Cheadle, H.J.B. Dick, A. H. Scheirer, Barbara John, N. J. Kusznir, T. Matsumoto Jun 2012

Evolution Of The Southwest Indian Ridge From 55 Degrees 45 ' E To 62 Degrees E: Changes In Plate-Boundary Geometry Since 26 Ma, A. G. Baines, Michael Cheadle, H.J.B. Dick, A. H. Scheirer, Barbara John, N. J. Kusznir, T. Matsumoto

Michael Cheadle

[1] From 55 degrees 45'E to 58 degrees 45'E and from 60 degrees 30'E to 62 degrees 00'E, the ultraslow-spreading Southwest Indian Ridge (SWIR) consists of magmatic spreading segments separated by oblique amagmatic spreading segments, transform faults, and nontransform discontinuities. Off-axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the SWIR. Individual magmatic segments show varying magnitudes and directions of asymmetric spreading, which requires that the shape of the plate boundary has changed significantly over time. In particular, since 26 Ma the Atlantis II transform fault grew by 90 km to reach 199 km, …

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Protracted Construction Of Gabbroic Crust At A Slow Spreading Ridge: Constraints From (206)Pb/(238)U Zircon Ages From Atlantis Massif And Iodp Hole U1309d (30 Degrees N, Mar), C. B. Grimes, Barbara John, Michael Cheadle, J. L. Wooden Jun 2012

Protracted Construction Of Gabbroic Crust At A Slow Spreading Ridge: Constraints From (206)Pb/(238)U Zircon Ages From Atlantis Massif And Iodp Hole U1309d (30 Degrees N, Mar), C. B. Grimes, Barbara John, Michael Cheadle, J. L. Wooden

Michael Cheadle

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages of 24 samples from oceanic crust recovered in Integrated Ocean Drilling Program (IODP) Hole U1309D and from the surface of Atlantis Massif, Mid-Atlantic Ridge (MAR) (30 degrees N) document a protracted history of accretion in the footwall to an oceanic detachment fault. Ages for 18 samples of evolved Fe-Ti oxide gabbro and felsic dikes collected 40-1415 m below seafloor in U1309D yield a weighted mean of 1.20 +/- 0.03 Ma (mean square of weighted deviates = 7.1). However, the ages range from 1.08 +/- 0.07 Ma and 1.28 +/- 0.05 Ma indicating …

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U-Pb Discordance In Archean Detrital Quartzites, Central Wyoming: Implications For Pb Loss Mechanisms, Carol Frost, C. M. Allen, Susan Swapp, B R. Frost Jun 2012

U-Pb Discordance In Archean Detrital Quartzites, Central Wyoming: Implications For Pb Loss Mechanisms, Carol Frost, C. M. Allen, Susan Swapp, B R. Frost

Susan Swapp

Meeting abstract for "U-Pb Discordance in Archean Detrital Quartzites, Central Wyoming: Implications for Pb Loss Mechanisms," June 2010.

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2.685-2.671 Ga Himalayan-Type Orogeny In The Northern Teton Range, Wyoming, Usa, B R. Frost, Susan Swapp, Carol Frost Jun 2012

2.685-2.671 Ga Himalayan-Type Orogeny In The Northern Teton Range, Wyoming, Usa, B R. Frost, Susan Swapp, Carol Frost

Susan Swapp

Meeting abstract for “2.685-2.671 Ga Himalayan-Type Orogeny in the Northern Teton Range, Wyoming, USA,” June 2009.

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A Mesoarchean Rifted Continental Margin In The Wyoming Province: Evidence For Supercontinent Breakup, Susan Swapp, Carol Frost, B R. Frost Jun 2012

A Mesoarchean Rifted Continental Margin In The Wyoming Province: Evidence For Supercontinent Breakup, Susan Swapp, Carol Frost, B R. Frost

Susan Swapp

Meeting abstract for "A Mesoarchean Rifted Continental Margin in the Wyoming Province: Evidence for Supercontinent Breakup."

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Preservation Of Fe Isotope Compositions Of Iron Formation During Contact Metamorphism, Carol Frost, F. Von Blanckenburg, R. Schoenberg, B R. Frost, Susan Swapp Jun 2012

Preservation Of Fe Isotope Compositions Of Iron Formation During Contact Metamorphism, Carol Frost, F. Von Blanckenburg, R. Schoenberg, B R. Frost, Susan Swapp

Susan Swapp

Meeting abstract for “Preservation of Fe Isotope Compositions of Iron Formation During Contact Metamorphism,” May 2005.

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In Situ Sims, Micro-Baddeleyite U-Pb Dating Method For Mafic Rocks, K. R. Chamberlain, T. M. Harrison, A. K. Schmitt, L. M. Heaman, Susan Swapp, A. K. Khudoley Jun 2012

In Situ Sims, Micro-Baddeleyite U-Pb Dating Method For Mafic Rocks, K. R. Chamberlain, T. M. Harrison, A. K. Schmitt, L. M. Heaman, Susan Swapp, A. K. Khudoley

Susan Swapp

Meeting abstract for “In Situ Sims, Micro-Baddeleyite U-Pb Dating Method for Mafic Rocks,” June 2008.

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Structural Evolution Of Djebel-Debadib Anticline : A Clue To The Regional Tectonic Style Of The Tunisian Atlas, Art Snoke, S. Schamel, R. M. Karasek Jun 2012

Structural Evolution Of Djebel-Debadib Anticline : A Clue To The Regional Tectonic Style Of The Tunisian Atlas, Art Snoke, S. Schamel, R. M. Karasek

Art Snoke

Djebel Debadib is a northeast trending anticline in the Tunisian Atlas, near El Kef, Tunisia. The core of the anticline consists of a deformed Triassic, gypsum-matrix breccia containing clasts of supratidal dolomite, terrigeneous clastic rocks, and ophites (metabasites). Locally, low-grade metasedimentary rocks, occurring as clasts in the evaporite, may represent fragments of basement rock plucked from salt subcrop during deep-seated flowage. The multiply deformed Triassic rocks are juxtaposed against Cretaceous or younger rocks, and Jurassic and Neocomian strata are not present in outcrop. These characteristics have been cited in many studies to suggest a history of diapirism to explain both …

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Nature And Origin Of Seismic-Reflection Fabric, Ruby East Humboldt Metamorphic Core Complex, Nevada, P. A. Valasek, Art Snoke, C. A. Hurich, S. B. Smithson Jun 2012

Nature And Origin Of Seismic-Reflection Fabric, Ruby East Humboldt Metamorphic Core Complex, Nevada, P. A. Valasek, Art Snoke, C. A. Hurich, S. B. Smithson

Art Snoke

Seismic reflection profiling across exposed upper and middle crustal rocks of the Ruby-East Humboldt metamorphic core complex delineates important characteristics of the crustal structure developed during Tertiary extensional deformation. The goals of this study were to trace a Tertiary extensional shear zone from mylonitic surface outcrops into a seismic section and to characterize the deeper crustal fabric associated with the polyphase deformational history of the complex. Reflections in the shallow surface correlate with a plastic to brittle shear zone that formed during the tectonic unroofing of the middle crustal rocks. Constructive interference from strong planar layering in the mylonitic shear …

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The Mesozoic-Cenozoic Tectonothermal Evolution Of The Ruby Mountains, East Humboldt Range, Nevada : A Cordilleran Metamorphic Core Complex, R. D. Dallmeyer, Art Snoke, E. H. Mckee Jun 2012

The Mesozoic-Cenozoic Tectonothermal Evolution Of The Ruby Mountains, East Humboldt Range, Nevada : A Cordilleran Metamorphic Core Complex, R. D. Dallmeyer, Art Snoke, E. H. Mckee

Art Snoke

A combined K-Ar and 40Ar/39Ar geochronological study of the Ruby Mountains-East Humboldt Range, Nevada, a Cordilleran metamorphic core complex, has revealed a complex tectonothermal history. The three structural subdivisions of the core complex (migmatitic core, mylonitic zone, and cover) share magmatic and deformational histories in part, but also display important contrasts in structural style, metamorphic paragenesis, and thermal history. During the Late Jurassic (ca 160 Ma), miogeoclinal rocks were polyphase-deformed, metamorphosed under amphibolite facies conditions, and pervasively intruded by peraluminous granitic magmas, thereby forming an igneous and metamorphic complex. Late Jurassic muscovite granite porphyry plugs also intruded unmetamorphosed cover rocks. …

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Differential Stress, Strain Rate, And Temperatures Of Mylonitization In The Ruby Mountains, Nevada: Implications For The Rate And Duration Of Uplift, B. R. Hacker, A. Yin, J. M. Christie, Art Snoke Jun 2012

Differential Stress, Strain Rate, And Temperatures Of Mylonitization In The Ruby Mountains, Nevada: Implications For The Rate And Duration Of Uplift, B. R. Hacker, A. Yin, J. M. Christie, Art Snoke

Art Snoke

Knowledge of the magnitude of the differential stress during the formation of mylonitic rocks provides constraints on mechanical and thermal models for the exhumation of the metamorphosed foot walls of major low-angle detachment faults. We have analyzed the differential flow stress during the mylonitization of quartzose rocks in the Ruby Mountains, Nevada, using grain-size piezometers and kinetic laws for grain growth. Quartzites from mylonitic shear zones in Lamoille Canyon and Secret Creek gorge have grain sizes of 91–151 μm and 42–64 μm, respectively. The peak temperature during mylonitization was 630°±50°C, and analysis of grain-growth kinetics indicates that mylonitization continued during …

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Thermochronologic Evidence Of Major Tectonic Denudation Associated With Detachment Faulting, Northern Ruby Mountains : East Humboldt Range, Nevada, R. K. Dokka, M. J. Mahaffie, Art Snoke Jun 2012

Thermochronologic Evidence Of Major Tectonic Denudation Associated With Detachment Faulting, Northern Ruby Mountains : East Humboldt Range, Nevada, R. K. Dokka, M. J. Mahaffie, Art Snoke

Art Snoke

Fission track (FT) thermochronology studies on igneous and metamorphic rocks from the Ruby Mountains-East Humboldt Range metamorphic core complex provide important constraints on the timing and nature of major mid-Tertiary extension in northeast Nevada. Rocks from within the Ruby-East Humboldt detachment (brittle-ductile normal-sense shear) zone were analyzed; the dominant lithology studied was variably mylonitic mafic orthogneiss. Nonmylonitic amphibolite from the top of the structurally lower migmatitic core and porphyritic biotite granodiorite from the Oligocene (circa 36 Ma) Harrison Pass pluton were also studied. FT ages on apatite, zircon, and sphene (except one 18.4-Ma apatite from the basal portion of the …

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Understanding Melt Generation Beneath The Slow-Spreading Kolbeinsey Ridge Using (238)U, (230)Th, And (231)Pa Excesses, L. J. Elkins, Ken Sims, J. Prytulak, T. Elliott, N. Mattielli, J. Blichert-Toft, J. Blusztajn, N. Dunbar, C. Devey, D. F. Mertz, J. G. Schilling, M. Murrell Jun 2012

Understanding Melt Generation Beneath The Slow-Spreading Kolbeinsey Ridge Using (238)U, (230)Th, And (231)Pa Excesses, L. J. Elkins, Ken Sims, J. Prytulak, T. Elliott, N. Mattielli, J. Blichert-Toft, J. Blusztajn, N. Dunbar, C. Devey, D. F. Mertz, J. G. Schilling, M. Murrell

Ken Sims

To examine the petrogenesis and sources of basalts from the Kolbeinsey Ridge, one of the shallowest locations along the global ridge system, we present new measurements of Nd, Sr, Hf, and Pb isotopes and U-series disequilibria on 32 axial basalts. Young Kolbeinsey basalts (full-spreading rate = 1.8 cm/yr; 67 degrees 05'-70 degrees 26'N) display (230Th/238U) < 1 and (230Th/238U) > 1 with (230Th/238U) from 0.95 to 1.30 and have low U (11.3-65.6 ppb) and Th (33.0 ppb-2.40 ppm) concentrations. Except for characteristic isotopic enrichment near the Jan Mayen region, the otherwise depleted Kolbeinsey basalts (e. g. 87Sr/86Sr = 0.70272-0.70301, epsilon(Nd) = 8.4-10.5, epsilon(Hf) = 15.4-19.6 …

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Temporal Isotope Variations In Glacial-Postglacial Lavas From Northern Iceland, E. M. Mervine, Ken Sims, J. Blichert-Toft, J. Maclennan, J. Blusztajn, K. Gronvold Jun 2012

Temporal Isotope Variations In Glacial-Postglacial Lavas From Northern Iceland, E. M. Mervine, Ken Sims, J. Blichert-Toft, J. Maclennan, J. Blusztajn, K. Gronvold

Ken Sims

Meeting abstract for “Temporal Isotope Variations in Glacial-Postglacial Lavas from Northern Iceland,” June 2010.

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Combined U-Th/He And (40)Ar/(39)Ar Geochronology Of Post-Shield Lavas From The Mauna Kea And Kohala Volcanoes, Hawaii, S. M. Aciego, F. Jourdan, D. J. Depaolo, B. M. Kennedy, P. R. Renne, Ken Sims Jun 2012

Combined U-Th/He And (40)Ar/(39)Ar Geochronology Of Post-Shield Lavas From The Mauna Kea And Kohala Volcanoes, Hawaii, S. M. Aciego, F. Jourdan, D. J. Depaolo, B. M. Kennedy, P. R. Renne, Ken Sims

Ken Sims

Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the 40Ar/39Ar and U–Th/He methods. The objective of the study is to compare the recently demonstrated U–Th/He age method, which uses basaltic olivine phenocrysts, with 40Ar/39Ar ages measured on groundmass from the same samples. As a corollary, the age data also increase the precision of the chronology of volcanism on the Big Island. For the U–Th/He ages, U, Th and He concentrations and isotopes were measured to account for U-series disequilibrium and initial He. Single analyses U–Th/He ages for …

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Insight Into Volatile Behavior At Nyamuragira Volcano (D.R. Congo, Africa) Through Olivine-Hosted Melt Inclusions, E. M. Head, A. M. Shaw, P. J. Wallace, Ken Sims, S. A. Carn Jun 2012

Insight Into Volatile Behavior At Nyamuragira Volcano (D.R. Congo, Africa) Through Olivine-Hosted Melt Inclusions, E. M. Head, A. M. Shaw, P. J. Wallace, Ken Sims, S. A. Carn

Ken Sims

We present new olivine-hosted melt inclusion volatile (H(2)O, CO(2), S, Cl, F) and major element data from five historic eruptions of Nyamuragira volcano (1912, 1938, 1948, 1986, 2006). Host-olivine Mg#'s range from 71 to 84, with the exception of the 1912 sample (Mg# = 90). Inclusion compositions extend from alkali basalts to basanite-tephrites. Our results indicate inclusion entrapment over depths ranging from 3 to 5 km, which agree with independent estimates of magma storage depths (3-7 km) based on geophysical methods. Melt compositions derived from the 1986 and 2006 Nyamuragira tephra samples best represent pre-eruptive volatile compositions because these samples …

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