Paleomagnetism of the Miocene Grotto and Snoqualmie Batholiths, Central Cascades, Washington

Beske, Suzanne J.; Beck, Myrl E.; Noson, Linda

doi:10.1029/jb078i014p02601

Cited by 20 publications

(3 citation statements)

References 16 publications

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“…The intrusion of the Chilliwack batholith and related plutons was the last important thermal event in the area. They have been studied paleomagnetically by Symons (1973~) and by Beck et al (1982).…”

Section: Fig 2 Sampling Sites In the Spuzzum Pluton Geology Adaptementioning

confidence: 99%

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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Section: Fig 2 Sampling Sites In the Spuzzum Pluton Geology Adaptementioning

confidence: 99%

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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“…As is frequently the case for plutonic rocks [e.g., Teissere and Beck, 1973;Beske et al, 1973;Wilson and Cox, 1980], stability of magnetization in the BVS pluton is variable. In general, magnetizations of these specimens are either highly stable with similar directions or highly unstable.…”

Section: Paleomagnetic Roesolts--bvs Plutonmentioning

confidence: 99%

Rotation of the southernmost Sierra Nevada, California

Kanter¹,

McWilliams²

1982

J. Geophys. Res.

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Structural, paleogeographic, and magmatic trends of the Sierra Nevada batholith swing from a characteristic NNW trend in the northern and central parts of the batholith to a nearly E‐W trend in the Tehachapi and San Emigdio mountains. Paleomagnetic results from eight sites in the upper Cretaceous (80–86 m.y.) Bear Valley Springs pluton in the Tehachapi Mountains yield a mean direction D = 022°, I = 56° (k = 97, α95 = 5.6°). This mean direction is significantly different from the expected late Cretaceous field direction for this locality and suggests that the pluton has undergone a clockwise rotation of 45° ± 14°, in accord with the change in structural trend in that area. Lower to middle Miocene volcanic and sedimentary rocks of the Kinnick Formation overlie the plutonic rocks and yield a mean direction D = 354°, I = 64°. A paleomagnetic pole derived from this mean direction is not significantly different from the expected Miocene pole for North America. This constrains the time of rotation of the pluton to be between about 80 and 20 m.y., probably predating establishment of the present San Andreas transform in this area. We suggest that the observed rotation is part of a large oroclinal bend affecting to different degrees the entire southern Sierra Nevada. The driving mechanism for such a bending may be right‐lateral shear along a proto‐San Andreas transform, for which there is now a significant body of evidence.

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“…Other than for some of the Teanaway dikes, there are insufficient data to restore potential tilt of bedding in host rocks. Paleomagnetic data are only available for the Corbaley Canyon swarm (Stauss, 1982), but results from six Eocene to Miocene plutons in the central and northern Washington Cascades do not indicate regional vertical axis rotation (within uncertainties) relative to North America in the last 47 Ma (Beske et al, 1973;Beck et al, 1982;Fawcett et al, 2003). In addition, some of the shallower dips may result from the inadvertent collection of data from steps in dikes, sills, or faulted surfaces, all of which have been observed.…”

Section: Field Methodsmentioning

confidence: 99%

Eocene dike orientations across the Washington Cascades in response to a major strike-slip faulting episode and ridge-trench interaction

et al. 2022

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The northern Cascade Mountains in Washington (USA) preserve an exceptional shallow to mid-crustal record of Eocene transtension marked by dextral strike-slip faulting, intrusion of dike swarms and plutons, rapid non-marine sedimentation, and ductile flow and rapid cooling in parts of the North Cascades crystalline core. Transtension occurred during ridge-trench interaction with the formation of a slab window, and slab rollback and break-off occurred shortly after collision of the Siletzia oceanic plateau at ca. 50 Ma. Dike swarms intruded a ≥1250 km2 region between ca. 49.3 Ma and 44.9 Ma, and orientations of more than 1500 measured dikes coupled with geochronologic data provide important snapshots of the regional strain field. The mafic Teanaway dikes are the southernmost and most voluminous of the swarms. They strike NE (mean = 036°) and average ~15 m in thickness. To the north, rhyolitic to basaltic dikes overlap spatially with 49.3–46.5 Ma, mainly granodioritic plutons, but they typically predate the nearby plutons by ca. 500 k.y. The average orientations of five of the six dike domains range from 010° to 058°; W-NW– to NW–striking dikes characterize one domain and are found in lesser amounts in a few other domains. Overall, the mean strike for all Eocene dikes is 035°, and the average extension direction (305°–125°) is oblique to the strike (~320°) of the North Cascades orogen. Extension by diking reached ~45% in one >7-km-long transect through the Teanaway swarm and ranged from ~5% to locally ~79% in shorter transects across other swarms, which corresponds to a minimum of ~12 km of extension. The dominant NE-striking dikes are compatible with the dextral motion on the N- to NW-striking (~355–320°) regional strike-slip faults. Some of the W–NW- to NW-striking dikes were arguably influenced by pre-existing faults, shear fractures, and foliations, and potentially in one swarm where both NE- and lesser W-NW–striking dikes are present, by a switch in principal stress axes induced by dike emplacement. Alternatively, the W-NW– to NW-striking dikes may reflect a younger regional strain field, as ca. 49.3–47.5 Ma U-Pb zircon ages of the NE-striking dikes are older than those of the few dated W-NW– to NW-trending dikes. In one scenario, NE-striking dikes intruded during an interval when strain mainly reflected dextral strike-slip faulting, and the younger dikes record a switch to more arc-normal extension. Diking ended as magmatism migrated into a N-S–trending belt west of the North Cascade core that marks the initiation of the ancestral Cascade arc.

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Paleomagnetism of the Miocene Grotto and Snoqualmie Batholiths, Central Cascades, Washington

Cited by 20 publications

References 16 publications

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

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

Rotation of the southernmost Sierra Nevada, California

Eocene dike orientations across the Washington Cascades in response to a major strike-slip faulting episode and ridge-trench interaction

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