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scott bogue's research
abstracts of recent publications
list of selected publications
15 Oct 2017
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Correlated relative and absolute geomagnetic paleointensities from a Pliocene N-R polarity reversal record in basaltic lava flows on Kauai, Hawaii.

Scott Bogue Click here for a copy

New paleomagnetic results from basaltic lava flows erupted 4 my ago on Kauai (Hawaii) reveal how the geomagnetic intensity changed as the field switched from normal to reverse (N-R) polarity. Following stepwise alternating field (AF) demagnetization of each sample’s natural remanent magnetization, an anhysteretic remanent magnetization (ARM) was imparted in a 50 uT bias field and then AF demagnetized. Very similar behavior of the 35 mT to 90 mT coercivity fractions suggest that the NRM (interpreted to be a primary thermoremanent magnetization (TRM)) and ARM reside in the same subpopulation of magnetic grains. With the ARM intensity serving as an analog for TRM susceptibility, the ratio TRM/ARM provides a measure of relative paleointensity. Flow-averaged TRM/ARM ratios correlate with a small set of double-heating paleointensities determined on companion samples, allowing calibration of the ratios to absolute ancient field intensities. During the N-R transition, the field strength dropped by 77% to 91% compared to the maximum recorded by the flows. This decrease is comparable to that observed in other paleomagnetic studies and numerical simulations. During an interval of NE-down directional stasis recorded by ten flows in the lower half of the section, the geomagnetic intensity rose to 22 uT and then decreased to near 5 uT. This distinctive behavior could mark the waxing and waning of a stationary, inward-directed flux patch on the core mantle boundary centered NE of Kauai.

Directional change during a Miocene R-N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA

Scott Bogue, Jonathan Glen, and Nick Jarboe Click here for a copy

Recurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7N, 243.2E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30N in NE Africa. After jumping to 83N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core-mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.

Paleogeography of the Insular and Intermontane terranes reconsidered: Evidence from the southern Coast Mountains Batholith, British Columbia

Margaret Rusmore, Scott Bogue, and Glen Woodsworth

New geologic and paleomagnetic data from Knight Inlet in the southwestern Coast Mountains Batholith, British Columbia, support significant revision to the paleogeography of the Insular and Intermontane terranes. Recompilation of radiometric ages confirms that after 100 Ma, a magmatic arc migrated northeastward across the Coast Mountains Batholith at ~2 km/m.y. Magmatic age patterns suggest that plutons older than 100 Ma intruded the Intermontane terrane, not the expected Insular terrane. The distribution of brittle faults along Knight Inlet defines a structurally intact central domain, ~45 km wide, flanked to the SW and NE by faulted domains, with no evidence of the widespread Tertiary extension affecting the batholith farther north. Al-in-hornblende geobarometry yields emplacement depths of ~2.5–4 kbar and does not reveal systematic postemplacement tilting. Plutons in the central structural domain yield a consistently oriented paleomagnetic remanence presumably acquired as the Late Cretaceous arc cooled from ca. 110 to 85 Ma. In the absence of recognizable tilting, this result indicates ~1700 km of northward translation since ca. 85 Ma, which is significantly less than predicted for the Insular terrane in the “Baja British Columbia” model but similar to results from the Intermontane terrane. The pluton ages and the paleomagnetic results suggest that the Intermontane terrane, not the Insular terrane, underlies the southwestern flank of the Coast Mountains Batholith. This conclusion is compatible with a paleogeographic model in which the Vancouver Island fragment of Wrangellia was juxtaposed against the Intermontane terrane prior to ca. 120–100 Ma and emplaced in southern British Columbia after ca. 75 Ma

Very rapid geomagnetic field change recorded by the partial remagnetization of a lava flow (Click here for a reprint)

Scott W. Bogue and Jonathan M. G. Glen

A new paleomagnetic result from a lava flow with a distinctive, two-part remanence reinforces the controversial hypothesis that geomagnetic change during a polarity reversal can be much faster than normal. The 3.9-m-thick lava (“Flow 20”) is exposed in the Sheep Creek Range (north central Nevada) and was erupted during a reverse-to-normal (R-N) geomagnetic polarity switch at 15.6 Ma. Flow 20 began to acquire a primary thermoremanence while the field was pointing east and down but was soon buried, reheated, and partially-remagnetized in a north-down direction by the 8.2-m-thick flow that succeeded it. A simple conductive cooling calculation shows that the observed remagnetization could not have occurred unless Flow 20 was still warm (about 150°C near its base) when buried and that the 53° change from east-down to north-down field occurred at an average rate of approximately 1°/week, several orders of magnitude faster than typical of secular variation.

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Deformation of continental crust along a transform boundary, Coast Mountains, British Columbia

Margaret E. Rusmore, Scott W. Bogue, Karen Dodson, Kenneth A. Farley, and Glenn J. Woodsworth

New structural, paleomagnetic, and apatite (U-Th)/He results from the continental margin inboard of the Queen Charlotte fault (?54°N) delineate patterns of brittle faulting linked to transform development since ?50 Ma. In the core of the orogen, ?250 km from the transform, north striking, dip-slip brittle faults and vertical axis rotation of large crustal domains occurred after ?50 Ma and before intrusion of mafic dikes at 20 Ma. By 20 Ma, dextral faulting was active in the core of the orogen, but extension had migrated toward the transform, continuing there until <9 Ma. Local tilting in the core of the orogen is associated with glacially driven, post-4 Ma exhumation. Integration with previous results shows that post-50 Ma dextral and normal faulting affected a region ?250 km inboard of the transform and ?300 km along strike. Initially widespread, the zone of active extension narrowed and migrated toward the transform ?25 Ma after initiation of the transform, while dextral faulting continued throughout the region. Differential amounts of post-50 Ma extension created oroclines at the southern and northern boundaries of the deformed region. This region approximately corresponds to continental crust that was highly extended just prior to transform initiation. Variation in Neogene crustal tilts weakens interpretations relying on uniform tilting to explain anomalous paleomagnetic inclinations of mid-Cretaceous plutons. Similarities to the Gulf of California suggest that development of a transform in continental crust is aided by previous crustal extension and that initially widespread extension narrows and moves toward the transform as the margin develops.

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Structural correction of paleomagnetic vectors dispersed about two fold axes and application to the Duke Island (Alaska) ultramafic complex

Scott W. Bogue and C. Sherman Gromme

A new analysis of paleomagnetic data from the mid-Cretaceous (~110 Ma) ultramafic complex at Duke Island (southeast Alaska) supports large poleward transport of the Insular Superterrane relative to North America consistent with the Baja British Columbia hypothesis. Previous paleomagnetic work has shown that the characteristic remanence of the ultramafic complex predates kilometer-scale deformation of the very well developed cumulate layering but that the layering was not everywhere horizontal before the folding. It is possible, however, to estimate paleohorizontal for the Duke Island ultramafic complex because the post-remanence deformation of the intrusion occurred about two well defined and spatially separate fold axes. In such a case, the tectonically rotated paleomagnetic directions should be distributed along small circles centered on each of the two fold axes. The ancient field direction will lie on both small circles and therefore be identifiable as one of their two intersection points. Interpreted this way, the tectonically rotated remanence of the Duke Island ultramafic complex defines a mid-Cretaceous (i.e., ancient) field direction that is within 2° of the paleomagnetic direction found by assuming the cumulate layering was initially horizontal (despite the paleomagnetic evidence to the contrary) and performing the standard structure correction. The inferred mid-Cretaceous paleolatitude of Duke Island is 21.2° (2350 km) anomalous with respect to cratonic North America. This result is concordant with southerly paleolatitudes determined by many other workers from bedded rocks of terranes farther inboard in the Insular and Intermontane superterranes.

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Geomagnetic field behavior before and after the Kauai reverse-normal polarity transition

Scott W. Bogue

New paleomagnetic results from 4 m.y. old lava flows from Kauai, Hawaii, suggest that strong poloidal field is associated with an unusual state of the geodynamo that follows attempts at polarity reversal (successful or not). The new data comprise 50 paleomagnetic sites from superposed lava flows occurring just below and above the Kauai reverse-normal polarity transition. A composite record of 45 distinct field determinations was constructed by combining sites that record similar ancient field and correlating them to previously published results from Kauai. Of the 45 data, 25 include paleointensity estimates derived from double-heating experiments. A comparison of the composite record from Kauai with two similar data sets from volcanic sequences shows that field variability (in direction, intensity, or both) can change substantially across a polarity transition. These changes, however, do not appear to be systematic in sign or magnitude. The only feature common to all three records is high field strength in the posttransitional interval, interpreted here as a transient phenomenon associated with the reversal process.

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Bogue, S. W., 2018. Correlated relative and absolute geomagnetic paleointensities from a Pliocene N-R polarity reversal record in basaltic lava flows on Kauai, Hawaii. Geochem., Geophys., Geosystems doi: 10.1029/2018GC007748

Heermance, R. V., J. Pearson, A. Moe, A. L. Langtao, X. Jianhong, C. Jie, F. Richter, C. N.. Garzione, N. Junsheng, and S. W. Bogue; 2018. Erg deposition and development of the ancestral Taklimakan Desert (western China) between 12.2 and 7.0 Ma. Geology 46 (10): 919–922. doi:10.1130/G45085.1

Bogue, S. W., Glen, J. M. G., and Jarboe, N. A., 2017. Directional change during a Miocene R-N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA. Geochemistry, Geophysics, Geosystems 18(9), 3470-3488, doi:10.1002/2017GC007049

Rusmore, M. E., S. W. Bogue, and G. J. Woodsworth, 2013. Paleogeography of the Insular and Intermontane terranes reconsidered: Evidence from the southern Coast Mountains Batholith, British Columbia. Lithosphere, 5, p. 521-536, doi:10.1130/L288.1

Heermance, R. V., A. Pullen, P. Kapp, C. C. Garzione, C, S. Bogue, L. Ding, and P. Song, 2013. Climatic and tectonic controls on sedimentation and erosion during the Quaternary in the Qaidam Basin (China) – Pliocene, Geological Society of America Bulletin 125, 833-856 doi: 10.1130/B30748.1

Rood, D. H., D. W. Burbank, S. W. Herman, and S. Bogue (2011), Rates and timing of vertical-axis block rotations across the central Sierra Nevada-Walker Lane transition in the Bodie Hills, California/Nevada, Tectonics, 30, TC5013, doi:10.1029/2010TC002754.

Bogue, S. W., and J. M. G. Glen (2010), Very rapid geomagnetic field change recorded by the partial remagnetization of a lava flow, Geophys. Res. Lett., 37, L21308, doi:10.1029/2010GL044286.

Rusmore, M. E., S. W. Bogue, K. Dodson, K. A. Farley, and G. J. Woodsworth, 2010. Deformation of continental crust along a transform boundary, Coast Mountains, British Columbia, Tectonics, 29, TC4007, doi:10.1029/2009TC002502.

Bogue, S. W., and C. S. Gromme, 2004. Structural correction of paleomagnetic vectors dispersed about two fold axes and application to the Duke Island (Alaska) ultramafic complex. Journal of Geophyscial Research 119, B11102, doi:10.1029/2004JB002989.

Mukhopadhyay, S., J. C. Lassiter, K. A. Farley, and S. W. Bogue, Geochemistry of Kauai shield-stage lavas: Implications for the chemical evolution of the Hawaiian plume, Geochem. Geophys. Geosyst., 4(1), 1009, doi:10.1029/2002GC000342, 2003.

Farley, K. A, M.E. Rusmore, and S. W. Bogue, 2001. Post-10 Ma uplift and exhumation of the northern Coast Mountains, British Columbia. Geology 29, 99-102.

Bogue, S. W., 2001. Geomagnetic field behavior before and after the Kauai R-N polarity transition. Journal of Geophysical Research 106, 447-462.

Bogue, S. W. and E. Neroda, 1995. Intensity of the geomagnetic field during the Kauai N-R transition. EOS, Transactions, American Geophysical Union 76 (46), 170.

Bogue, S.W., C. S. Gromme, and J. W. Hillhouse, 1995. Paleomagnetism, magnetic anisotropy, and mid-Cretaceous paleolatitude of the Duke Island (Alaska) ultramafic complex. Tectonics 14, 1133-1152.

Bogue, S. W. and H. A. Paul, 1993. Distinctive field behavior following geomagnetic reversals. Geophysical Research Letters 20 (21), 2399-2402.

Bogue, S. W. and R. T. Merrill, 1992. The character of the field during geomagnetic reversals. Annual Review of Earth and Planetary Sciences 20, 181-219.

Bogue, S. W., D. S. Cowan, and J. I. Garver, 1989. Paleomagnetic evidence for poleward transport of Upper Jurassic rocks in the Decatur terrane, San Juan Islands, Washington, Journal of Geophysical Research 94, 10,415-10,427.

Bogue, S. W. and K. A. Hoffman, 1987. Morphology of geomagnetic reversals. Reviews of Geophysics 25, 910-916.

Bogue, S. W., 1987. Magnetostratigraphy of Kauai, Hawaii. Geological Society of America Abstracts with Programs 19, 359-360.

Bogue, S. W. and J. E. Evans, 1986. Discordant paleomagnetic component from the Eocene Chumstick Formation, central Washington State. Geological Society of America Abstracts with Programs 18, 88.

Bogue, S. W. and R. S. Coe, 1984. Transitional paleointensities from Kauai, Hawaii, and geomagnetic reversal models. Journal of Geophysical Research 89, 10,341-10,354.

Bogue, S. W. and R. S. Coe, 1982. Successive paleomagnetic reversal records from Kauai. Nature 295, 399-401.

Bogue, S. W. and R. S. Coe, 1981. Paleomagnetic correlation of Columbia River Basalt flows using secular variation. Journal of Geophysical Research 86, 11,883-11,897.

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Scott Bogue    email: bogue[at]oxy[dot]edu