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Crystallographic–Magnetic Correlations In Single-Crystal Haemo-Ilmenite: New Evidence For Lamellar Magnetism, P. Robinson, F. Heidelbach, A. M. Hirt, S. A. Mcenroe, Laurie Brown
Crystallographic–Magnetic Correlations In Single-Crystal Haemo-Ilmenite: New Evidence For Lamellar Magnetism, P. Robinson, F. Heidelbach, A. M. Hirt, S. A. Mcenroe, Laurie Brown
Laurie Brown
17 single crystals were identified by electron backscatter diffraction (EBSD) and isolated from coarse massive haemo-ilmenite ore from South Rogaland, Norway. These were studied using the EBSD results, natural remanent magnetization (NRM), and anisotropy ofmagnetic susceptibility (AMS), to gain a better understanding of angular relationships between crystallographic axes and magnetic properties of haemo-ilmenite in relation to lamellar magnetism. Electron microprobe analyses gave the following average end-member compositions for ilmenite host: 21.1 per cent MgTiO3, 73.7 FeTiO3, 0.5 MnTiO3, 4.3 Fe2O3, 0.2 Cr2O3 and 0.3 V2O3; and for the coarsest (∼3 μm) haematite exsolution lamellae: 3.5 MgTiO3, 22.4 FeTiO3, 71.4 Fe2O3, …
The Relationship Between Exsolution And Magnetic Properties In Hemo-Ilmenite: Insights From Mössbauer Spectroscopy With Implications For Planetary Magnetic Anomalies, Laurie Brown, M. D. Dyar, S. A. Mcenroe, E. Murad, H. Schiellerup
The Relationship Between Exsolution And Magnetic Properties In Hemo-Ilmenite: Insights From Mössbauer Spectroscopy With Implications For Planetary Magnetic Anomalies, Laurie Brown, M. D. Dyar, S. A. Mcenroe, E. Murad, H. Schiellerup
Laurie Brown
Remanence properties of ilmenites with exsolved hematite have recently been the object of much study, because their high natural remanent magnetization (NRM) is greater than predicted for these two minerals. X-ray diffraction (XRD) and Mössbauer spectroscopy in conjunction with electron microprobe and NRM measurements were used to explore the possibility that single domain (SD) hematite lamellae in the ilmenite host could explain the observed remanence, and to determine if magnetite is present. XRD results show the presence of ilmenite and hematite. Mössbauer data show that only species assigned to hematite, ilmenite, and a small amount of tetrahedral Fe3+ are present. …
Paleomagnetic Directions And 40ar/39ar Ages From The Tatara-San Pedro Volcanic Complex, Chilean Andes: Lava Record Of A Matuyama-Brunhes Precursor?, Laurie Brown, J. C. Pickens, B. S. Singer, B. R. Jicha
Paleomagnetic Directions And 40ar/39ar Ages From The Tatara-San Pedro Volcanic Complex, Chilean Andes: Lava Record Of A Matuyama-Brunhes Precursor?, Laurie Brown, J. C. Pickens, B. S. Singer, B. R. Jicha
Laurie Brown
Lava flows within Quebrada Turbia valley of the Tatara San Pedro volcanic complex, in central Chile (36°S, 289°E), preserve a detailed record of what was presumed to be the Matuyama-Brunhes geomagnetic reversal. A sampling traverse in the central west wall of the valley yields reverse and transitional polarity flows of the Quebrada Turbia sequence. Two kilometers to the north, another section yields 17 transitional flows from the same volcanic sequence overlain by flows with normal polarity. The 40Ar/39Ar incremental heating experiments on lavas within the two sections provide nine independent age determinations and yield a weighted mean of 791.7 ± …
Magnetic Anomalies, Layered Intrusions And Mars, Laurie Brown, S. A. Mcenroe, J. R. Skilbrei, P. Robinson, F. Heidelbach, F. Langenhorst
Magnetic Anomalies, Layered Intrusions And Mars, Laurie Brown, S. A. Mcenroe, J. R. Skilbrei, P. Robinson, F. Heidelbach, F. Langenhorst
Laurie Brown
Studies of remanence-controlled magnetic anomalies on Earth provide possibilities to interpret the nature of crustal rocks that cause the large remanent anomalies on Mars. What types of conditions on Earth can create large remanent magnetic anomalies? Such an anomaly, extending for 20 km centered over a norite layer in the Bjerkreim-Sokndal (BKS) Intrusion, shows a minimum −13000 nT below background in the helicopter survey. Modeling of the anomaly requires a natural remanent magnetization (NRM) value of 24 A/m, similar to values measured in norite samples and to values invoked to explain the anomalies on Mars. Preliminary magnetic assessment considers the …
A Closer Look At Remanence-Dominated Aeromagnetic Anomalies: Rock Magnetic Properties And Magnetic Mineralogy Of The Russell Belt Microcline-Sillimanite Gneiss, Northwest Adirondack Mountains, New York, Laurie Brown, S. A. Mcenroe
A Closer Look At Remanence-Dominated Aeromagnetic Anomalies: Rock Magnetic Properties And Magnetic Mineralogy Of The Russell Belt Microcline-Sillimanite Gneiss, Northwest Adirondack Mountains, New York, Laurie Brown, S. A. Mcenroe
Laurie Brown
A large, distinct negative aeromagnetic anomaly of over 2000 nT associated with microcline-sillimanite-quartz gneisses in the Russell area, northwest Adirondack Mountains, was previously shown to be remanence-dominated, although the carriers of remanence were not well documented. Russell Belt gneisses have a strong natural rémanent magnetization with steep remanence directions, D = 263°, I = −58°, an average intensity of 3.6 A/m, and typical susceptibilities of 10−4 SI. The remanence is thermochemical in origin, acquired during cooling from peak metamorphic conditions of 650°–750°C during the Ottawan Orogen (1050–1080 Ma). The reversed polarity of remanence reflects a reversed paleofield, rather than self-reversed, …
Tectonic Stability Of The San Luis Hills, Northern Rio Grande Rift, Colorado: Evidence From Paleomagnetic Measurements, Laurie Brown, M. P. Golombek
Tectonic Stability Of The San Luis Hills, Northern Rio Grande Rift, Colorado: Evidence From Paleomagnetic Measurements, Laurie Brown, M. P. Golombek
Laurie Brown
The San Luis Basin is the largest of four tilted, fault bounded Neogene basins of the northern Rio Grande rift in New Mexico and Colorado. It formed during the second of two episodes of extension beginning in middle Oligocene and extending to the present. The San Luis Hills are an intrarift horst of Oligocene intermediate and basalt rocks preserved in the middle of the San Luis Basin. Previous paleomagnetic and structural studies in the Espanola Basin to the south indicate counterclockwise rotation of that region during the most recent extension. Paleomagnetic samples from the two exposed formations in the San …