Paleomagnetic results from the Central Sierra Nevada: Constraints on reconstructions of the western United States

Frei, Leah S.; Magill, James R.; Cox, Allan

doi:10.1029/tc003i002p00157

Cited by 61 publications

(33 citation statements)

References 45 publications

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“…Evidently some plate-margin units are relatively uncomplicated and internally undeformed, but others have suspiciously large elongations. In Figure 11 Figure 13b shows the VGP distribution for the Grace Meadow pluton (SNY2) of the Yosemite Valley area [Frei et al, 1984]. This distribution also is elongate, in the same general sense as seen in Figure 13a.…”

Section: Cratonmentioning

confidence: 57%

On the shape of paleomagnetic data sets

Beck¹

1999

J. Geophys. Res.

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Abstract. A quick and easy method to analyze the shape of palcomagnetic data sets is described and illustrated. The elongation E of a set of directions of virtual geomagnetic poles VGP is defined as E = k2/k3, where k2 and k3 are the second and third eigenvalues of the Bingham distribution. It is shown that E<3 or so indicates that the distribution is significantly elongate, although the size of the sample and the palcolatitude both affect this conclusion. Because the azimuth of k2 gives the direction of elongation, it can be used to help determine why a particular distribution is elongate. It is shown that for most units from the eraton both directions and VGP are nearly circular, except for units magnetized at very low latitudes. In general, poles are more circular than directions. Some units formed in plate margin locations also are circular, but many are highly elongate. Many units from the western Cordillera of North America have highly elongate distributions that are compatible with origin within a shear zone; others are obviously underformed internally. Units formed during extension are less commonly elongate, but some show the probably effects of normal faulting. It is hoped that shape analysis will be part of any complete palcomagnetic study in the future.

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Section: Cratonmentioning

confidence: 57%

On the shape of paleomagnetic data sets

Beck¹

1999

J. Geophys. Res.

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“…Early work by GrommC andMerril (1965) andGrommC et al (1967) on plutons from the Sierra Nevada gave results that were generally consistent with those from cratonic North America. Recent detailed demagnetization studies by Frei et al (1984) of three plutons from the central Sierra Nevada showed a displacement of 8 2 10" from the south. Although the displacement is not significant at the 95% probability level, there is nevertheless a bias toward shallow inclinations, and a small poleward displacement of lower probability is indicated.…”

Section: Tectonic Implicationsmentioning

confidence: 98%

Paleomagnetic evidence for displacement from the south of the Coast Plutonic Complex, British Columbia

Irving¹,

Woodsworth²,

Wynne³

et al. 1985

Can. J. Earth Sci.

148

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The mid-Cretaceous Spuzzum and Porteau plutons of the Coast Plutonic Complex of British Columbia have two magnetizations, A and B. The A magnetization (eight sites, 83 specimens, D = 30.3", I = 56.7", ay, = 4.9", paleolatitude = 37 t SON, paleopole 65.0°N, 14.9OW, Ay, = 6.2") is considered to have been acquired in the age range 105-90 Ma. This result differs from the field established for cratonic North America in this time range. The difference could be caused either by previously undetected tilting about a horizontal axis of the plutons, or by their rotation about a vertical axis and lateral displacement relative to the craton. Previously observed mid-Cretaceous magnetizations from other rock units from the western Canadian Cordillera and the Cascades of Washington, United States, are similarly discordant with respect to the craton. This similarity over such a large area indicates that, although local undetected tilting could be partly responsible, it is unlikely to be the prime cause, and we argue therefore that lateral displacement and rotation have occurred. It would seem that much of the western part of the Canadian Cordillera has moved north by about 2400 km and rotated clockwise since the mid-Cretaceous. The paleolatitude of the southern Coast Plutonic Complex of British Columbia is statistically identical to that recently observed (39 * 3ON) for three plutons from the Central Sierra Nevada of California, which raises the possibility that the two complexes were much closer together at the time of their emplacement than at present. The second magnetization called B (four sites, 27 specimens, D = 5. lo, 1 = 67.6", a , , = 4.7", paleopole 86.S0N, 5 1.2"W) is parallel to the mid-Tertiary field, as previously determined from nearby intrusions, and is considered to be an overprint acquired during regional heating and low-grade metasomatism. Some earlier paleomagnetic studies of mid-Cretaceous rocks from the Coast Plutonic Complex indicated either an absence of displacement or uncertain evidence for it, and we attribute this to the nonrecognition, in this earlier work, of similar magnetically stable overprints of Tertiary age. Overprints in several Triassic rock units in the western Cordillera are parallel to the A magnetization, indicating that the mid-Cretaceous and the mid-Tertiary probably were periods of severe magnetic overprinting in British Columbia. Mid-Cretaceous and Late Triassic results from the western Cordillera of British Columbia are systematically different, indicating that movements relative to the craton occurred between these times.Les plutons de Spuzzum et de Porteau d'bge crktact moyen du Complexe plutonique cbtier de la Colombie-Britannique exhibent deux aimantations, A et B. L'aimantationA (huit sites, 83 spkcimens, D = 30,3", 1 = 56,7", ag5 = 4,9O, palkolatitude = 37 2 5"N, palkopole 65,0°N, 14,9"0, A,, = 6,2") semble avoir kt6 acquise entre 105 et 90 Ma. Ce rksultat differe du champ ktabli pour le craton de I'Amkrique du Nord relatif h cet Cpisode de temps. Cette diffkrence peut s'expli...

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“…Sources: 1) Magill et al (1982); 2) Sheriff (1984); 3) Wells et al (1989); 4) compilation of Gromme et al (1986); 5) Beck et al (1986); 6) compilation in Frei et al (1984), revised using N. Am. Cretaceous reference pole of Globerman and Irving (1988) (plat 71 N; plon 196 E; A95 = 4.9).…”

Section: Block Modelmentioning

confidence: 99%

Northward migration of the Cascadia forearc in the northwestern U.S. and implications for subduction deformation

Wells

Simpson

2014

Earth Planet Sp

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Geologic and paleomagnetic data from the Cascadia forearc indicate long-term northward migration and clockwise rotation of an Oregon coastal block with respect to North America. Paleomagnetic rotation of coastal Oregon is linked by a Klamath Mountains pole to geodetically and geologically determined motion of the Sierra Nevada block to derive a new Oregon Coast-North America (OC-NA) pole of rotation and velocity field. This long-term velocity field, which is independent of Pacific Northwest GPS data, is interpreted to be the result of Basin-Range extension and Pacific-North America dextral shear. The resulting Oregon Coast pole compares favorably to those derived solely from GPS data, although uncertainties are large. Subtracting the long-term motion from forearc GPS velocities reveals ENE motion with respect to an OC reference frame that is parallel to the direction of Juan de Fuca-OC convergence and decreases inland. We interpret this to be largely the result of subduction-related deformation. The adjusted mean GPS velocities are generally subparallel to those predicted from elastic dislocation models for Cascadia, but more definitive interpretations await refinement of the present large uncertainty in the Sierra Nevada block motion.

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Paleomagnetic results from the Central Sierra Nevada: Constraints on reconstructions of the western United States

Cited by 61 publications

References 45 publications

On the shape of paleomagnetic data sets

On the shape of paleomagnetic data sets

Paleomagnetic evidence for displacement from the south of the Coast Plutonic Complex, British Columbia

Northward migration of the Cascadia forearc in the northwestern U.S. and implications for subduction deformation

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