Export 3 results:
Sort by: Author Title Type [ Year  (Desc)]
Cheadle, MJ, Gee JS.  2017.  Quantitative textural insights into the formation of gabbro in mafic intrusions. Elements. 13:409-414.   10.2138/gselements.13.6.409   AbstractWebsite

Rock textures provide a key to deciphering the physical processes by which gabbro forms in mafic intrusions. Developments in both direct optical and crystallographic methods, as well as indirect magnetic fabric measurements, promise significant advances in understanding gabbroic textures. Here, we illustrate how bulk magnetic fabric data, particularly from intrusions with sparse silicate-hosted magnetite, may be used to extend direct crystallographic observations from thin sections. We also present a scheme for characterizing crystallographic foliation and lineation and use this to suggest that the strength of gabbro plagioclase foliations and lineations varies significantly with geodynamic environment.

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, J, Staudigel H, Tauxe L, Pick T, Gallet Y.  1993.  Magnetization of the La Palma Seamount Series - Implications For Seamount Paleoples. Journal of Geophysical Research-Solid Earth. 98:11743-11767.   10.1029/93jb00932   AbstractWebsite

Paleopoles determined from seamount magnetic anomalies constitute the major data source for the Pacific apparent polar wander path, but relatively little is known about the processes of remanence acquisition in seamounts. Since magnetic anomalies reflect both natural remanence (NRM) and the induced field, it is important first to assess whether the NRM is likely to represent an original field direction and second to constrain the magnitude of the induced component. To this end, we present paleomagnetic data from an uplifted, subaerially exposed section through a seamount on La Palma, Canary Islands. The Pliocene Seamount Series of La Palma comprises a >6 km sequence of alkalic extrusives and intrusives which includes all lithologies likely to be volumetrically important in seamounts. The structural tilt of the Seamount Series allows separation of early thermal or chemical remanence from magnetization components acquired after tilting (e.g., viscous remanence). The NRM provides a poor indication of the original magnetization direction, although the characteristic magnetization of many La Palma samples is compatible with the original pretilt direction. Hydrothermal alteration has resulted in the production of Ti-poor magnetite and an increasing contribution of hematite with increasing degree of alteration. More importantly, well-defined magnetization directions which deviate from any reasonable geomagnetic direction at La Palma can be attributed to hydrothermal alteration in a different polarity than prevalent during the original magnetization. Based on a comparison of the magnitude of low-stability components of magnetization and laboratory acquisition of viscous remanence and previous estimates of the induced magnetization, we conclude that viscous and induced magnetization probably account for 15-25% of the total magnetization of seamounts. The resulting paleopole bias is a function of the polarity and paleolatitude of the seamount and ranges from 4-degrees to 16-degrees for Cretaceous seamounts in the Pacific.