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- Submarine basaltic glass (3)
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Articles 1 - 21 of 21
Full-Text Articles in Earth Sciences
Assessing New And Old Methods In Paleomagnetic Paleothermometry: A Test Case At Mt. St. Helens, Usa, Julie A. Bowles, Devin Gerzich, Mike J. Jackson
Assessing New And Old Methods In Paleomagnetic Paleothermometry: A Test Case At Mt. St. Helens, Usa, Julie A. Bowles, Devin Gerzich, Mike J. Jackson
Geosciences Faculty Articles
Paleomagnetic data can be used to estimate deposit temperatures (Tdep) of pyroclastic density currents (PDCs) by finding the laboratory temperature at which a PDC-associated thermal remanence is removed. Paleomagnetic paleothermometry assumes that (1) blocking (Tb) and unblocking (Tub) temperatures are equivalent, and (2) the blocking spectrum remains constant through time. The first assumption fails for multidomain (MD) grains, and recent evidence shows that the second is violated in many titanomagnetites, where Tc is a strong function of thermal history. Here we assess the extent to which the standard paleomagnetic method may be biased …
Geology Of The Alarcon Rise, Southern Gulf Of California, David A. Clague, David W. Caress, Brian M. Dreyer, Lonny Lundsten, Jennifer B. Paduan, Ryan A. Portner, Ronald Spelz-Madero, Julie A. Bowles, Paterno R. Castillo, Rigoberto Guardado-France, Morgane Le Saout, Julie F. Martin, Miguel A. Santa Rosa-Del Río, Robert A. Zierenberg
Geology Of The Alarcon Rise, Southern Gulf Of California, David A. Clague, David W. Caress, Brian M. Dreyer, Lonny Lundsten, Jennifer B. Paduan, Ryan A. Portner, Ronald Spelz-Madero, Julie A. Bowles, Paterno R. Castillo, Rigoberto Guardado-France, Morgane Le Saout, Julie F. Martin, Miguel A. Santa Rosa-Del Río, Robert A. Zierenberg
Geosciences Faculty Articles
Abstract Meter-scale AUV bathymetric mapping and ROV sampling of the entire 47 km-long Alarcon Rise between the Pescadero and Tamayo transforms show that the shallowest inflated portion of the segment hosts all four active hydrothermal vent fields and the youngest, hottest, and highest effusion rate lava flows. This shallowest inflated part is located ~1/3 of the way between the Tamayo and Pescadero transforms and is paved by a 16 km2 channelized flow that erupted from 9 km of en echelon fissures and is larger than historic flows on the East Pacific Rise or on the Gorda and Juan de …
Malleable Curie Temperatures Of Natural Titanomagnetites: Occurrences, Modes, And Mechanisms, Mike J. Jackson, Julie A. Bowles
Malleable Curie Temperatures Of Natural Titanomagnetites: Occurrences, Modes, And Mechanisms, Mike J. Jackson, Julie A. Bowles
Geosciences Faculty Articles
Abstract Intermediate-composition titanomagnetites have Curie temperatures (Tc) that depend not only on composition but also on thermal history, with increases of 100°C or more in Tc produced by moderate-temperature (300–400°C) annealing in the laboratory or in slow natural cooling and comparable decreases produced by more rapid cooling (“quenching”) from higher temperatures. New samples spanning a range of titanomagnetite compositions exhibit reversible changes in Tc comparable to those previously documented for pyroclastic samples from Mt. St. Helens and Novarupta. Additional high- and low-temperature measurements help to shed light on the nanoscale mechanisms responsible for the observed changes …
Effects Of Titanomagnetite Reordering Processes On Thermal Demagnetization And Paleointensity Experiments, Julie A. Bowles, Mike J. Jackson
Effects Of Titanomagnetite Reordering Processes On Thermal Demagnetization And Paleointensity Experiments, Julie A. Bowles, Mike J. Jackson
Geosciences Faculty Articles
Titanomagnetite (Fe3-xTixO4, 0≤x≤1) is a common, naturally occurring magnetic mineral critical to many paleomagnetic studies. Underlying most interpretations is the assumption that, lacking chemical alteration, Curie temperature (Tc) remains constant. However, recent work has demonstrated that Tc of many natural titanomagnetites varies strongly as a function of thermal history, independent of chemical alteration. This is inferred to arise from reordering of cations and/or vacancies in the crystal structure, and changes occur at temperatures and times relevant to standard paleomagnetic thermal treatments. Because changes take place at Tc, …
Geomagnetic Paleointensity In Historical Pyroclastic Density Currents: Testing The Effects Of Emplacement Temperature And Postemplacement Alteration, Julie A. Bowles, Jeffrey S. Gee, Mike J. Jackson, Margaret S. Avery
Geomagnetic Paleointensity In Historical Pyroclastic Density Currents: Testing The Effects Of Emplacement Temperature And Postemplacement Alteration, Julie A. Bowles, Jeffrey S. Gee, Mike J. Jackson, Margaret S. Avery
Geosciences Faculty Articles
Thellier-type paleointensity experiments were conducted on welded ash matrix or pumice from the 1912 Novarupta (NV) and 1980 Mt. St. Helens (MSH) pyroclastic density currents (PDCs) with the intention of evaluating their suitability for geomagnetic paleointensity studies. PDCs are common worldwide, but can have complicated thermal and alteration histories. We attempt to address the role that emplacement temperature and postemplacement hydrothermal alteration may play in nonideal paleointensity behavior of PDCs. Results demonstrate two types of nonideal behavior: unstable remanence in multidomain (MD) titanomagnetite, and nonideal behavior linked to fumarolic and vapor phase alteration. Emplacement temperature indirectly influences MSH results by …
Full Vector Low-Temperature Magnetic Measurements Of Geologic Materials, Joshua M. Feinberg, Peter A. Solheid, Nicholas L. Swanson-Hysell, Mike J. Jackson, Julie A. Bowles
Full Vector Low-Temperature Magnetic Measurements Of Geologic Materials, Joshua M. Feinberg, Peter A. Solheid, Nicholas L. Swanson-Hysell, Mike J. Jackson, Julie A. Bowles
Geosciences Faculty Articles
The magnetic properties of geologic materials offer insights into an enormous range of important geophysical phenomena ranging from inner core dynamics to paleoclimate. Often it is the low-temperature behavior (<300 K) of magnetic minerals that provides the most useful and highest sensitivity information for a given problem. Conventional measurements of low-temperature remanence are typically conducted on instruments that are limited to measuring one single-axis component of the magnetization vector and are optimized for measurements in strong fields. These instrumental limitations have prevented fully optimized applications and have motivated the development of a low-temperature probe that can be used for low-temperature remanence measurements between 17 and 300 K along three orthogonal axes using a standard 2G Enterprises SQuID rock magnetometer. In this contribution, we describe the design and implementation of this instrument and present data from five case studies that demonstrate the probe’s considerable potential for future research: a polycrystalline hematite sample, a polycrystalline hematite and magnetite mixture, a single crystal of magnetite, a single crystal of pyrrhotite, and samples of Umkondo Large Igneous Province diabase sills.
Contribution Of Multidomain Titanomagnetite To The Intensity And Stability Of Mars Crustal Magnetic Anomalies, Stefanie A. Brachfeld, David Cuomo, Lisa Tatsumi-Petrochilos, Julie A. Bowles, Deepa Shah, Julie E. Hammer
Contribution Of Multidomain Titanomagnetite To The Intensity And Stability Of Mars Crustal Magnetic Anomalies, Stefanie A. Brachfeld, David Cuomo, Lisa Tatsumi-Petrochilos, Julie A. Bowles, Deepa Shah, Julie E. Hammer
Geosciences Faculty Articles
Two basalts with compositions relevant to the crusts of Mars and Earth were synthesized at igneous temperatures and held at 650°C for 21 to 257 days under quartz-fayalite-magnetite ƒO2 buffer conditions. The run products are germane to slowly cooled igneous intrusions, which might be a significant volumetric fraction of the Martian crust and carriers of magnetic anomalies in the Southern Highlands. Both basalts acquired intense thermoremanent magnetizations and intense but easily demagnetized anhysteretic remanent magnetizations carried by homogeneous multidomain titanomagnetite. Hypothetical intrusions on Mars composed of these materials would be capable of acquiring intense remanences sufficient to generate the …
Curie Temperatures Of Titanomagnetite In Ignimbrites: Effects Of Emplacement Temperatures, Cooling Rates, Exsolution, And Cation Ordering, Mike J. Jackson, Julie A. Bowles
Curie Temperatures Of Titanomagnetite In Ignimbrites: Effects Of Emplacement Temperatures, Cooling Rates, Exsolution, And Cation Ordering, Mike J. Jackson, Julie A. Bowles
Geosciences Faculty Articles
Pumices, ashes, and tuffs from Mt. St. Helens and from Novarupta contain two principal forms of titanomagnetite: homogeneous grains with Curie temperatures in the range 350–500°C and oxyexsolved grains with similar bulk composition, containing ilmenite lamellae and having Curie temperatures above 500°C. Thermomagnetic analyses and isothermal annealing experiments in combination with stratigraphic settings and thermal models show that emplacement temperatures and cooling history may have affected the relative proportions of homogeneous and exsolved grains and have clearly had a strong influence on the Curie temperature of the homogeneous phase. The exsolved grains are most common where emplacement temperatures exceeded 600°C, …
Eruptive Timing And 200 Year Episodicity At 92°W On The Hot Spot-Influenced Galapagos Spreading Center Derived From Geomagnetic Paleointensity, Julie A. Bowles, Alice Colman, J. Timothy Mcclinton, John Sinton, Scott M. White, Kenneth H. Rubin
Eruptive Timing And 200 Year Episodicity At 92°W On The Hot Spot-Influenced Galapagos Spreading Center Derived From Geomagnetic Paleointensity, Julie A. Bowles, Alice Colman, J. Timothy Mcclinton, John Sinton, Scott M. White, Kenneth H. Rubin
Geosciences Faculty Articles
Eruptive timing in mid-ocean ridge systems is relatively poorly constrained, despite being an important variable in our understanding of many mid-ocean ridge processes, including volcanic construction; magma recharge, flux, and storage; and the stability of hydrothermal systems and biological communities. Only a handful of absolute eruption chronologies exist, yet they are essential in understanding how eruptive timing varies with important controlling variables. To construct an eruptive history at one location on the Galapagos Spreading Center, we present age determinations derived from geomagnetic paleointensity. To aid interpretation of the paleointensity data, we also present results from on-bottom magnetic anomaly measurements and …
Multicomponent Cubic Oxide Exsolution In Synthetic Basalts: Temperature Dependence And Implications For Magnetic Properties, Julie A. Bowles, Lisa Tatsumi-Petrochilos, Julie E. Hammer, Stefanie A. Brachfeld
Multicomponent Cubic Oxide Exsolution In Synthetic Basalts: Temperature Dependence And Implications For Magnetic Properties, Julie A. Bowles, Lisa Tatsumi-Petrochilos, Julie E. Hammer, Stefanie A. Brachfeld
Geosciences Faculty Articles
Although the compositional unmixing of cubic-structured iron oxides has profound effects on the magnetic properties of rocks that contain them, a basic understanding of the kinetics and thermodynamics of this process has not been achieved in experimental studies due to sluggish reaction rates in binary oxide phases. Exploiting the fact that many natural Fe-oxides contain multiple additional cations, including Ti, Mg and Al, we perform novel “forward” laboratory experiments in which cubic-cubic phase exsolution proceeds from initially homogeneous multicomponent oxides. A variety of Fe-Ti-Mg-Al cubic iron oxides were nucleated and grown in synthetic, multicomponent basalt under different ƒO2 environments, and …
Snowmelt Runoff Modeling: Limitations And Potential For Mitigating Water Disputes, Jonathan Kult, Woonsup Choi, Anke Petra Maria Keuser
Snowmelt Runoff Modeling: Limitations And Potential For Mitigating Water Disputes, Jonathan Kult, Woonsup Choi, Anke Petra Maria Keuser
Geography Faculty Articles
No abstract provided.
Timing Of Magnetite Formation In Basaltic Glass: Insights From Synthetic Analogs And Relevance For Geomagnetic Paleointensity Analyses, Julie A. Bowles, Jeffrey S. Gee, Katherine Burgess, Reid F. Cooper
Timing Of Magnetite Formation In Basaltic Glass: Insights From Synthetic Analogs And Relevance For Geomagnetic Paleointensity Analyses, Julie A. Bowles, Jeffrey S. Gee, Katherine Burgess, Reid F. Cooper
Geosciences Faculty Articles
Absolute paleointensity estimates from submarine basaltic glass (SBG) typically are of high technical quality and accurately reflect the ambient field when known. SBG contains fine-grained, low-Ti magnetite, in contrast to the high-Ti magnetite in crystalline basalt, which has lead to uncertainty over the origin of the magnetite and its remanence in SBG. Because a thermal remanence is required for accurate paleointensity estimates, the timing and temperature of magnetite formation is crucial. To assess these factors, we generated a suite of synthetic glasses with variable oxygen fugacity, cooling rate, and FeO* content. Magnetic properties varied most strongly with crystallinity; less crystalline …
Effects Of Open And Closed System Oxidation On Texture And Magnetic Response Of Remelted Basaltic Glass, Katherine Burgess, Reid F. Cooper, Julie A. Bowles, Jeffrey S. Gee, Daniele J. Cherniak
Effects Of Open And Closed System Oxidation On Texture And Magnetic Response Of Remelted Basaltic Glass, Katherine Burgess, Reid F. Cooper, Julie A. Bowles, Jeffrey S. Gee, Daniele J. Cherniak
Geosciences Faculty Articles
As part of an experimental and observational study of the magnetic response of submarine basaltic glass (SBG), we have examined, using ion backscattering spectrometry (RBS), transmission and scanning electron microscopy, energy dispersive X-ray spectrometry, and surface X-ray diffraction, the textures wrought by the controlled, open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural SBG. Initial compositions with ~9 wt % FeO* were melted at 1430°C with the oxygen fugacity buffered at fayalite-magnetite-quartz; melts were cooled at a rate of 200°C min−1 near the glass transition (Tg = 680°C). In open …
Deconvolution Of U Channel Magnetometer Data: Experimental Study Of Accuracy, Resolution, And Stability Of Different Inversion Methods, Mike J. Jackson, Julie A. Bowles, Ioan Lascu, Peter A. Solheid
Deconvolution Of U Channel Magnetometer Data: Experimental Study Of Accuracy, Resolution, And Stability Of Different Inversion Methods, Mike J. Jackson, Julie A. Bowles, Ioan Lascu, Peter A. Solheid
Geosciences Faculty Articles
We explore the effects of sampling density, signal/noise ratios, and position-dependent measurement errors on deconvolution calculations for u channel magnetometer data, using a combination of experimental and numerical approaches. Experiments involve a synthetic sample set made by setting hydraulic cement in a 30-cm u channel and slicing the hardened material into ~2-cm lengths, and a natural lake sediment u channel sample. The cement segments can be magnetized and measured individually, and reassembled for continuous u channel measurement and deconvolution; the lake sediment channel was first measured continuously and then sliced into discrete samples for individual measurement. Each continuous data set …
Paleointensity Estimates From Ignimbrites: An Evaluation Of The Bishop Tuff, Jeffrey S. Gee, Yongjae Yu, Julie A. Bowles
Paleointensity Estimates From Ignimbrites: An Evaluation Of The Bishop Tuff, Jeffrey S. Gee, Yongjae Yu, Julie A. Bowles
Geosciences Faculty Articles
Ash flow tuffs, or ignimbrites, typically contain fine-grained magnetite, spanning the superparamagnetic to single-domain size range that should be suitable for estimating geomagnetic field intensity. However, ignimbrites may have a remanence of thermal and chemical origin as a result of the complex magnetic mineralogy and variations in the thermal and alteration history. We examined three stratigraphic sections through the ~0.76 Ma Bishop Tuff, where independent information on postemplacement cooling and alteration is available, as a test of the suitability of ignimbrites for paleointensity studies. Thermomagnetic curves suggest that low-Ti titanomagnetite (Tc = 560°C–580°C) is the dominant phase, with a …
Magnetic And Petrologic Characterization Of Synthetic Martian Basalts And Implications For The Surface Magnetization Of Mars, Julie A. Bowles, Julie E. Hammer, Stefanie A. Brachfeld
Magnetic And Petrologic Characterization Of Synthetic Martian Basalts And Implications For The Surface Magnetization Of Mars, Julie A. Bowles, Julie E. Hammer, Stefanie A. Brachfeld
Geosciences Faculty Articles
A suite of synthetic Martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data. We systematically evaluate the effects of major element composition, oxygen fugacity (ƒO2), and cooling rate on phase chemistry and magnetic mineralogy, grain size, and intensity of remanent magnetization. The range of experimental compositions and ƒO2 are chosen to bracket the range expected in the Martian crust; our results should therefore span the range of possible mineralogies, textures, and magnetic properties in rapidly cooled Mars crustal materials. Two starting compositions are used for …
On The Duration Of Magnetochrons C24r And C25n And The Timing Of Early Eocene Global Warming Events: Implications From The Ocean Drilling Program Leg 208 Walvis Ridge Depth Transect, Thomas Westerhold, Ursula Röhl, Jacques Laskar, Isabella Raffi, Julie A. Bowles, Lucas J. Lourens, James C. Zachos
On The Duration Of Magnetochrons C24r And C25n And The Timing Of Early Eocene Global Warming Events: Implications From The Ocean Drilling Program Leg 208 Walvis Ridge Depth Transect, Thomas Westerhold, Ursula Röhl, Jacques Laskar, Isabella Raffi, Julie A. Bowles, Lucas J. Lourens, James C. Zachos
Geosciences Faculty Articles
Five sections drilled in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge (SE Atlantic) during Ocean Drilling Program (ODP) Leg 208 resulted in the first complete early Paleogene deep-sea record. Here we present high-resolution stratigraphic records spanning a ~4.3 million yearlong interval of the late Paleocene to early Eocene. This interval includes the Paleocene-Eocene thermal maximum (PETM) as well as the Eocene thermal maximum (ETM) 2 event. A detailed chronology was developed with nondestructive X-ray fluorescence (XRF) core scanning records and shipboard color data. These records were used to refine the shipboard-derived spliced …
Paleointensity Applications To Timing And Extent Of Eruptive Activity, 9°–10°N East Pacific Rise, Julie A. Bowles, Jeffrey S. Gee, Dennis V. Kent, Michael R. Perfit, S. Adam Soule, S. Adam Soule
Paleointensity Applications To Timing And Extent Of Eruptive Activity, 9°–10°N East Pacific Rise, Julie A. Bowles, Jeffrey S. Gee, Dennis V. Kent, Michael R. Perfit, S. Adam Soule, S. Adam Soule
Geosciences Faculty Articles
Placing accurate age constraints on near-axis lava flows has become increasingly important given the structural and volcanic complexity of the neovolcanic zone at fast spreading ridges. Geomagnetic paleointensity of submarine basaltic glass (SBG) holds promise for placing quantitative age constraints on near-axis flows. In one of the first extensive tests of paleointensity as a dating tool or temporal marker we present the results of over 550 successful SBG paleointensity estimates from 189 near-axis (<4 km) sites at the East Pacific Rise, 9°–10°N. Paleointensities range from 6 to 53 µT and spatially correspond to the pattern expected from known temporal variations in the geomagnetic field. Samples within and adjacent to the axial summit trough (AST) have values approximately equal to or slightly higher than the present-day. Samples out to 1–3 km from the AST have values higher than the present-day, and samples farther off axis have values lower than the present-day. The on-axis samples (<500 m from the AST) provide a test case for using models of paleofield variation for the past few hundred years as an absolute dating technique. Results from samples collected near a well-documented eruption in 1991–1992 suggest there may be a small negative bias in the paleointensity estimates, limiting resolution of the dating technique. Possible explanations for such a bias include local field anomalies produced by preexisting magnetic terrain; anomalously high magnetic unblocking temperatures, leading to a small cooling rate bias; and/or the possibility of a chemical remanence produced by in situ alteration of samples likely to have complicated thermal histories. Paleointensity remains useful in approximating age differences in young flows, and a clear along-axis paleointensity contrast near 9°50’N is suggestive of a ~150–200 year age difference. Paleointensity values of off-axis samples are generally consistent with rough age interpretations based on side scan data. Furthermore, spatial patterns in the paleointensity suggest extensive off-axis flow emplacement may occur infrequently, with recurrence intervals of 10–20 kyr. Results of a stochastic model of lava emplacement show that this can be achieved with a single distribution of flows, with flow size linked to time between eruptions.
Cooling Rate Effects On Paleointensity Estimates In Submarine Basaltic Glass And Implications For Dating Young Flows, Julie A. Bowles, Jeffrey S. Gee, Dennis V. Kent, Eric Bergmanis, John Sinton
Cooling Rate Effects On Paleointensity Estimates In Submarine Basaltic Glass And Implications For Dating Young Flows, Julie A. Bowles, Jeffrey S. Gee, Dennis V. Kent, Eric Bergmanis, John Sinton
Geosciences Faculty Articles
Cooling rate effects on the intensity of thermoremanent magnetization (TRM) have been well documented in ceramics. In that case, laboratory cooling is generally more rapid than the initial cooling, leading to an overestimate of the paleofield by 5–10% in Thellier-type paleointensity experiments. The reverse scenario, however, has never been tested. We examine the effects of cooling rate on paleointensity estimates from rapidly quenched submarine basaltic glass (SBG) samples from 13 sites at 17°30′–18°30′S on the East Pacific Rise. Absolute cooling rates determined by relaxation geospeedometry at five of these sites range from ~10 to ~330°C min^-1 at the glass transition …
Source Of Tiny Wiggles In Chron C5: A Comparison Of Sedimentary Relative Intensity And Marine Magnetic Anomalies, Julie A. Bowles, Lisa Tauxe, Jeffrey S. Gee, David Mcmillan, Steve Cande
Source Of Tiny Wiggles In Chron C5: A Comparison Of Sedimentary Relative Intensity And Marine Magnetic Anomalies, Julie A. Bowles, Lisa Tauxe, Jeffrey S. Gee, David Mcmillan, Steve Cande
Geosciences Faculty Articles
In addition to the well-established pattern of polarity reversals, short-wavelength fluctuations are often present in both sea-surface data ("tiny wiggles") and near-bottom anomaly data. While a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles, anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations. Independent evidence from another geomagnetic recording medium such as deep-sea sediments is required to determine the true nature of the tiny wiggles. We present such independent evidence in the form of sedimentary relative paleointensity from Chron C5. We make the first comparison between …
Behavior Of Oceanic Crustal Magnetization At High Temperatures: Viscous Magnetization And The Marine Magnetic Anomaly Source Layer, Julie A. Bowles, H. Paul Johnson
Behavior Of Oceanic Crustal Magnetization At High Temperatures: Viscous Magnetization And The Marine Magnetic Anomaly Source Layer, Julie A. Bowles, H. Paul Johnson
Geosciences Faculty Articles
Although the source layer for marine magnetic anomalies has been assumed to be the extrusive basalts of uppermost ocean crust, recent studies indicate that lower crustal rocks may also contribute. Because the temperature at which magnetization of crustal rocks achieves long-term stability is crucial to any source layer contribution, we undertook high-temperature VRM (viscous remanent magnetization) experiments on samples of basalt, dike and gabbroic sections. Samples were heated at temperature intervals up to Tc, while a magnetic field was applied for periods between 6 hours and 28 days. Results show that the dike and gabbro samples achieve maximum …