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Staudigel, H, Gee J, Tauxe L, Varga RJ.  1992.  Shallow Intrusive Directions of Sheeted Dikes in the Troodos Ophiolite - Anisotropy of Magnetic-Susceptibility and Structural Data. Geology. 20:841-844.   10.1130/0091-7613(1992)020<0841:sidosd>;2   AbstractWebsite

Sheeted dikes play a central role in the formation of oceanic crust. It is commonly assumed that sheeted dikes intrude vertically upward, from elongated mid-ocean ridge (MOR) magma chambers, but there are no direct observational data bearing on this hypothesis. This assumption contrasts with the intrusive behavior of subaerial volcanoes where magmas rise into shallow central magma chambers that laterally feed vertically oriented dikes. We have studied intrusive directions of sheeted dikes in a structural analogue to oceanic crust, the Troodos ophiolite. Structural and magnetic fabric data of 65 dikes provide consistent results and suggest a broad distribution of shallow (<20-degrees) to nearly vertical, upward magma-transport directions. These data suggest that horizontal emplacement has to be considered for sheeted dikes at MORs, implying more centralized MOR plumbing systems than previously thought. Such plumbing systems provide ample opportunity for complex mixing, fractionation, and contamination of MOR lavas in magma chambers and tabular magma-storage volumes. Whether the MOR magma supply is linear or centralized also has a fundamental effect on crustal accretion processes and the geometry of hydrothermal convection systems.

Gee, J, Meurer WP.  2002.  Slow cooling of middle and lower oceanic crust inferred from multicomponent magnetizations of gabbroic rocks from the Mid-Atlantic Ridge south of the Kane fracture zone (MARK) area. Journal of Geophysical Research-Solid Earth. 107   10.1029/2000jb000062   AbstractWebsite

[1] The remanent magnetization of gabbroic material of the Mid-Atlantic Ridge south of the Kane fracture zone (MARK) area provides constraints on both the thermal structure and tectonic history of the lower crust in this slow spreading environment. The remanence of these gabbroic samples is often complex, with the juxtaposition of intervals of apparently normal and reversed polarity rocks over small spatial scales (tens of centimeters to a few meters). Moreover, several samples when thermally demagnetized have a reversed polarity magnetization component between higher and lower stability normal polarity components. Given the nominal age (similar to1 Ma) of the crust, we suggest that this pattern of normal/reversed-normal polarity most plausibly reflects emplacement and/or cooling through three successive polarity intervals, Jaramillo normal polarity interval (1.07-0.99 Ma), a portion of the Matuyama reversed polarity interval (0.99-0.78 Ma), and the Brunhes normal polarity interval (0.78 Ma to present). A small number of samples with three well-defined magnetization components have magnetic characteristics compatible with a remanence carried by fine-grained, possibly single domain, magnetite. Laboratory unblocking temperatures in these samples therefore allow estimation of lower crustal temperatures at the time of the Jaramillo/Matuyama (0.99 Ma) and Matuyama/ Brunhes (0.78 Ma) polarity transitions. Together with depth estimates derived from fluid inclusion studies these results suggest that middle and lower crustal temperatures remained as high as similar to350degrees-475degreesC for a minimum of 0.21 m. y. after emplacement. We suggest that continued injection of liquid, in the form of sills or small magma bodies, over a broad region (half width of 3 km) is responsible for this slow cooling. In addition, inclinations of the highest stability component from these drill sites are remarkably similar to that expected from an axial geocentric dipole, suggesting that little, if any, resolvable tilt occurred during uplift of these rocks to the seafloor.

Winterer, EL, Gee JS, Van Waasbergen RJ.  1988.  The source area for Lower Cretaceous clastic sediments of the Galicia Margin : geology and tectonic and erosional history. Proceedings of the Ocean Drilling Program, Scientific Results. 103:697-732.   10.2973/   Abstract

Structural relations shown on seismic-reflection profiles of the Galicia margin indicate that during the Early Creta- ceous rifting of the margin, Galicia Bank and its southern extension (Galicia Ridge) were separated from the mainland of Iberia by a fault-controlled trough, and that the rift-stage sandy turbidite sediments in the fault troughs west of Gali- cia Bank were derived from the erosion of a narrow row of rugged hills that occupied the present area of Galicia Bank and Ridge. The volume and age span of rift-stage clastic sediments, estimated from drill and seismic data, imply rapid erosion of about 1 km of bedrock in the source area, suggesting that the source area was uplifted tectonically during the early stage of rifting. The composition of the sandstone indicates a source area dominated by granitic and schistose rocks, consistent with data from dredge hauls. The abundant fragmental plant debris in the sandstone indicates heavily wooded land, and regional sedimentological and paleobotanical data suggest warm rainy climatic conditions. A combi- nation of erosional lowering (largely compensated by isostatic rebound) and tectonic subsidence reduced most of the source area to sea level by the Aptian, and carbonate banks then flourished over the site of the former landmass.

Gee, JS, Kent DV.  2007.  Source of oceanic magnetic anomalies and the geomagnetic polarity timesale. Treatise on geophysics. 5( Kono M, Schubert G, Eds.).:455-507., Amsterdam ; Boston: Elsevier Abstract
Bowles, J, Tauxe L, Gee J, McMillan D, Cande S.  2003.  Source of tiny wiggles in Chron C5: A comparison of sedimentary relative intensity and marine magnetic anomalies. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000489   AbstractWebsite

[1] 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 a sedimentary relative paleointensity record (ODP Site 887 at 54degreesN, 148degreesW) and deep-tow marine magnetic anomaly data (43degreesN, 131degreesW) [ Bowers et al., 2001] for Chron C5. The sediment cores are densely sampled at similar to2.5 kyr resolution. The inclination record shows no evidence for reverse intervals within the similar to1 myr-long normal Chron C5n.2n. Rock magnetic measurements suggest that the primary magnetic carrier is pseudo-single domain magnetite. We choose a partial anhysteretic magnetization (pARM) as our preferred normalizer, and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization. We then compare the results of this model with the stacked deep-tow anomaly records. The two records show a significant degree of correlation, suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations. An analysis of our sampling density suggests that if any reverse intervals exist at this site, they are likely to be <5 kyr in duration. Furthermore, we suggest that reverse intervals during Chron C5n.2n documented in other locations are unlikely to be global.

Yu, YJ, Gee JS.  2005.  Spinel in Martian meteorite SaU 008: implications for Martian magnetism. Earth and Planetary Science Letters. 232:287-294.   10.1016/j.epsl.2004.12.015   AbstractWebsite

Shergotty-Nakhla-Chassigny (SNC) meteorites provide the only available samples of Martian material. The stable permanent magnetization of SNC meteorites has been traditionally attributed to magnetite (Fe3O4) or pyrrhotite (Fe7S8). On the basis of rock magnetic, microscopic, and electron microprobe analyses on rock chips and mineral separates, we suggest that a new material (Fe-Cr-Ti spinel) is responsible for the stable paleomagnetic record of Martian meteorite SaU 008. It is possible that SaU 008 acquired a primary remanence of thermal origin from the Martian crustal field. However, this proposition requires further testing because the effect of shock events on Fe-Cr-Ti spinel is unknown. (c) 2004 Elsevier B.V. All rights reserved.

Gee, JS, Cande SC.  2002.  A surface-towed vector magnetometer. Geophysical Research Letters. 29   10.1029/2002gl015245   AbstractWebsite

[1] We have tested the feasibility of using a commercial motion sensor as a vector magnetometer that can be towed at normal survey speeds behind a research vessel. In contrast to previous studies using a shipboard mounted vector magnetometer, the towed system is essentially unaffected by the magnetization of the towing vessel. Results from a test deployment compare favorably with an earlier vector aeromagnetic survey, indicating that the towed instrument can resolve horizontal and vertical anomalies with amplitudes >30-50 nT. This instrument should be particularly useful in equatorial regions, where the vector anomalies are substantially greater than the corresponding total field anomalies.