Comment and Reply on "Discordant paleomagnetic poles from the Canadian Coast Plutonic Complex: Regional tilt rather than large displacement?"

Miller, Robert B.; Johnson, Samuel Y.; McDougall, James; Butler, Robert F.; Dickinson, William R.; Gehrels, George E.; McClelland, W.; May, Steven R.; Klepacki, D.

doi:10.1130/0091-7613(1990)018<1164:carodp>2.3.co;2

Cited by 9 publications

(6 citation statements)

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“…Butler et al (1989) arg u e d that southwest dipping sedimentary rocks of the Swauk Formation adjacent to the southwestern part of the batholith re q u i re post-early Eocene northeastside-up tilt which largely explains the discordant paleomagnetism. However, that interpretation was challenged by Miller et al (1990). Ague and Brandon (1996) applied aluminum-inh o rnblende barometry to infer a tilt of 8° northwest-side-up.…”

Section: The Moderate T R a N S L Ation A Lt E R Nat I V Ementioning

confidence: 99%

A Moderate Translation Alternative to the Baja British Columbia Hypothesis

Butler¹,

Gehrels²,

Kodama³

2001

Gsa Today

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Section: The Moderate T R a N S L Ation A Lt E R Nat I V Ementioning

confidence: 99%

A Moderate Translation Alternative to the Baja British Columbia Hypothesis

Butler¹,

Gehrels²,

Kodama³

2001

Gsa Today

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“…The southwestern margin of the batholith is in contact with southwesterly dipping clastic strata of the lower Eocene Swauk Formation. The nature of this contact-whether stratigraphic or structural-remains unresolved despite considerable debate (see Butler AGUE AND BRANDON et al, 1989;Miller et al, 1990;Umhoefer and Magloughlin, 1990;Tabor et al, 1993; Fig. 2A).…”

Section: Regional Tilt Mount Stuart Batholith Washingtonmentioning

confidence: 99%

Regional tilt of the Mount Stuart batholith, Washington, determined using aluminum-in-hornblende barometry: Implications for northward translation of Baja British Columbia

Ague

Brandon

1996

Geological Society of America Bulletin

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We have developed a new quantitative method to estimate paleohorizontal in granitic plutons using the aluminum-in-hornblende (AH) barometer. The method is used to correct previously published paleomagnetic data from the 93-96 Ma Mount Stuart batholith of the Cascades Mountains, Washington State, for the effects of postemplacement tilting. AH barometry was done on 46 samples from the batholith using the compositions of hornblende rims coexisting with the full mineral assemblage required for pressure estimation. High-contrast back-scattered electron imaging was used to ensure that the analyzed hornblendes were not significantly affected by subsolidus alteration. The success of the AH barometry is indicated by two observations. First, increases in the Al content of the hornblendes are governed almost entirely by a pressure-sensitive tschermak-type substitution. Second, amphibole-plagioclase thermometry indicates that assemblage equilibration occurred at or very near magmatic conditions (Ϸ650 ؇C) and that temperature has a negligible effect on our pressure estimates. AH barometry results indicate that the depth of crystallization across the batholith decreases systematically from Ϸ0.3 GPa in the northwest to Ϸ0.15 GPa in the southeast, consistent with independent barometry for the contact aureole of the batholith and regional structural and stratigraphic relations. Using a best-fit planar-tilt model and bootstrap analysis of uncertainties, we estimate that the paleohorizontal plane has a strike of 43؇ ؎ 30.4؇ and dip of 7؇ ؎ 2.0؇ southeast (؎95% confidence). Our estimated paleohorizontal allows us to restore the paleomagnetic data of Beck et al. (1981) and to estimate the original paleolatitude of the Mount Stuart batholith. Beck et al. found that the southern part of the batholith yielded a number of sites with a well-defined high-coercivity remanence. The carrier of this remanence was not resolved, but the following four lines of evidence strongly suggest that the published directions were acquired shortly after emplacement of the batholith. (1) The ''stable'' sites all came from the shallowest and most rapidly cooled portions of the batholith as indicated by our AH results and concordant K/Ar ages for hornblende/biotite pairs. (2) The high coercivity component was always normal in polarity, which is consistent with emplacement of the Mount Stuart batholith at the end of the Cretaceous long normal. (3) Sites from the batholith and the contact aureole gave similar directions. (4) The directions show no indication of tilt-related smearing. After restoration, the paleomagnetic data indicate 42؇ ؎ 11؇ clockwise rotation and 3100 ؎ 600 km of northward offset (؎95% confidence). This result verifies Beck et al.'s original interpretation that the Mount Stuart batholith originated at the paleolatitude of northern Mexico.

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“…1 in Paterson et al, 1994). We acknowledge that relationships are poorly exposed on the west side of the block and remain disputed (Miller et al, 1990;Butler et al, 1989Butler et al, , 1990Tabor et al, 1993). Nonetheless, the southern margin of the block is overlapped by a thick, wellstratified sequence of Paleogene sediments and volcanic rocks (e.g., Swauk Formation, Teanaway basalts, and Roslyn Formation described in Tabor et al, 1987).…”

Section: Regional Relationshipsmentioning

confidence: 89%

“…Taylor et al, 1988). Furthermore, significant segments of the Ingalls-Swauk contact have been modified by Eocene or younger faulting (Tabor et al, 1982;Miller et al, 1990). Thus, the Chiwaukum-Ingalls-Swauk complex is largely a structural sequence that in part reflects lateral variations in geology and may easily record effects other than tilting.…”

Section: Regional Relationshipsmentioning

confidence: 99%

“…However, it is important to note that available geologic data provide no hard evidence concerning the tilt geometry of the batholith. Many authors have attempted to deduce tilt of the batholith using the patterns of metamorphism and cooling ages within the Mount Stuart block Umhoefer and Magloughlin, 1990;Miller et al, 1990;Beck, 1991). We believe that these approaches are problematic because the Mount Stuart block has a complex metamorphic and thermal history.…”

Section: Regional Relationshipsmentioning

confidence: 99%

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