Late Cretaceous and early Tertiary plutonism and deformation in the Skagit Gneiss Complex, North Cascade Range, Washington and British Columbia

Haugerud, Ralph A.; Heyden, P van der; Tabor, R.W.; Stacey, J. S.; Zartman, Robert E.

doi:10.1130/0016-7606(1991)103<1297:lcaetp>2.3.co;2

Cited by 47 publications

(84 citation statements)

References 26 publications

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“…1b) at the southern end of the Chelan block (Haugerud et al 1991). It consists mainly of early Cretaceous metatonalite, metaplutonic migmatite, migmatitic amphibolite and hornblendite (Hopson and Mattinson 1994).…”

Section: Geological Settingmentioning

confidence: 99%

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

Dessimoz

Müntener

Ulmer

2011

Contrib Mineral Petrol

153

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Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U.S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of *1.0 GPa followed by isobaric cooling to 700°C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite.

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Section: Geological Settingmentioning

confidence: 99%

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

Dessimoz

Müntener

Ulmer

2011

Contrib Mineral Petrol

153

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“…An alternative interpretation is that the RLFZ is a continuous crustal section between two large-scale folds in the Skagit Gneiss Complex and Jurassic-Cretaceous Methow Basin (Kriens and Wernicke 1990). In the strike-slip scenario, the RLFZ accommodated dextral movement until about 45 Ma, when it was truncated by undeformed, posttectonic plutons with no observable displacement at their margins (Haugerud et al 1991b). The Eocene Cooper Mountain pluton (CMP;Figs.…”

Section: Introductionmentioning

confidence: 95%

“…By the early Tertiary, the orogeny had ceased in much of the North Cascades crystalline core. This study is focused on the western side of the CMP where it intrudes rocks of the Skagit Gneiss Complex (Haugerud et al 1991b) and Twenty-five Mile Creek unit (Figs. 1b,1c).…”

Section: Geologic Settingmentioning

confidence: 99%

“…One model to explain fabric orientation in the CMP involves shear, perhaps associated with displacements on the NW-SE faults in the region (i.e., the Ross Lake fault zone, RLFZ) or dextral transpression (Brown and Talbot 1989). The RLFZ is an early Tertiary fault, thought to be active until -45 Ma, exhibiting dextral strike-slip motion (Misch 1966;Haugerud et al 1991b). The younger age limit of fault movement was based on an interpretation that the Golden Horn batholith and the CMP were undeformed, posttectonic plutons that cut the fault trace and fabrics related to it (Haugerud et al 1991b).…”

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confidence: 99%

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Tectonic implications of magnetic fabrics and remanence in the Cooper Mountain pluton, North Cascade Mountains, Washington

et al. 2003

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Documenting the timing and kinematics of deformation in orogens is critical to unraveling their history. Anisotropy of magnetic susceptibility defines the orientation of magnetic fabrics in the Eocene Cooper Mountain pluton in the North Cascade Mountains of Washington. The magnetic foliation typically has a steep dip and a northwest strike; the magnetic lineation plunges moderately to shallowly northwest or southeast. The remanent magnetization was measured to determine if the Cooper Mountain pluton has been tilted following emplacement. The remanence has two components. The characteristic remanence typically unblocks at 370°C in most specimens, but at 580°C in others. The two components are carried by pyrrhotite and magnetite. Mean directions of these components are indistinguishable from each other and from the North American expected Eocene direction. The paleomagnetic results and -47 Ma 40 Ar-39 Ar total fusion ages from biotite suggest that there has been no remagnetization or significant reorientation of the pluton since emplacement. Therefore, the in situ magnetic fabrics from the pluton can be used to understand the kinematics. Discordance of the fabrics with the pluton margin and near concordance with regional structures suggests that they have a tectonic origin. Thus the Cooper Mountain pluton is syntectonic rather than posttectonic. The magmatic fabric is slightly oblique to the length of the Cascade orogen, which can be explained if it formed as a consequence of regional dextral shear during transpression.Résumé : Il est essentiel de documenter les facteurs temps et la cinématique de la déformation dans les orogènes afin de bien comprendre leur histoire. L'anisotropie de la susceptibilité magnétique définit l'orientation des fabriques magnétiques dans le pluton du mont Cooper (Éocène) dans les montages North Cascade de Washington. La foliation magnétique a typiquement un pendage abrupt et une direction nord-ouest; la linéation magnétique plonge modérément à légèrement vers le nord-ouest ou le sud-est. La magnétisation rémanente a été mesurée afin de déterminer si le pluton du mont Cooper a basculé depuis sa mise en place. La rémanence a deux composantes. La rémanence caractéristique typique dont la température de déblocage se situe à 370 ºC dans la plupart des spécimens mais à 580 ºC dans d'autres. Les deux composantes se retrouvent dans la pyrrhotite et la magnétite. Les directions moyennes de ces composantes ne peuvent être distinguées les unes des autres, ni de la direction attendue pour l'Amérique du Nord, à l'Éocène. Les résultats paléomagnétiques et les âges de fusion totale de 47 Ma 40 Ar-39 Ar d'échantillons de biotite suggèrent qu'il n'y a pas eu de remagnétisation ni de réorientation significative du pluton depuis sa mise en place. Donc, les fabriques magnétiques in situ du pluton peuvent être utilisées pour comprendre la cinématique. La discordance des fabriques avec la bordure du pluton et la quasi-concordance avec les structures régionales suggèrent une origine tectonique. Ainsi, le pluto...

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“…1). Oblique-slip faulting played a significant role in the Paleogene tectonic evolution of the Pacific Northwest, by disrupting and juxtaposing pre-Tertiary accreted terranes (Davis et al 1978;Johnson 1984a;Tabor et al 1989), by unroofing plutons and metamorphic complexes (Ewing 1980;Parrish et al 1988;Miller et al 1989;Miller and Bowring 1990;Haugerud et al 1991), and by initiating and deforming sedimentary basins (Gresens 1982;Tabor et al 1984;Johnson 1985;Evans 1994;Taylor et al 1988).…”

Section: Introductionmentioning

confidence: 97%

Depositional history of the southeastern outcrop belt of the Chuckanut Formation: implications for the Darrington – Devil's Mountain and Straight Creek fault zones, Washington (U.S.A.)

Evans¹,

Ristow²

1994

Can. J. Earth Sci.

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The southeastern outcrop belt of the Eocene Chuckanut Formation contains the erosional remnants of a larger depositional system. In the study area, the Chuckanut Formation can be split into four units based upon differences in age, lithology, sedimentology, paleocurrents, and provenance relationships. The Coal Mountain unit (Early Eocene) represents a southwest-flowing fluvial system that shows no evidence for fault control of drainage. The overlying Higgins Mountain unit (early Middle Eocene) represents a northeast-flowing fluvial system east of the Devil's Mountain fault zone (DMFZ), with lithologies derived from western source areas. The Sperry Peak unit (early Middle Eocene) represents a fluvial system with a wide dispersion of paleocurrent azimuths and a possible mixture of sediment source areas. We believe the Sperry Peak unit was deposited in a fault-wedge graben at the junction of the DMFZ and Straight Creek fault zone (SCFZ), with sediment sources from both east and west. The Grade Creek unit (age unknown) is a fluvial unit found along the trace of the SCFZ with paleo-flow subparallel to the fault zone. The sedimentary evidence suggests that onset of Paleogene faulting on the DMFZ and SCFZ was at about 50–48 Ma, while movement on the Darrington fault zone may have been later (post-42 Ma).

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Late Cretaceous and early Tertiary plutonism and deformation in the Skagit Gneiss Complex, North Cascade Range, Washington and British Columbia

Cited by 47 publications

References 26 publications

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

Tectonic implications of magnetic fabrics and remanence in the Cooper Mountain pluton, North Cascade Mountains, Washington

Depositional history of the southeastern outcrop belt of the Chuckanut Formation: implications for the Darrington – Devil's Mountain and Straight Creek fault zones, Washington (U.S.A.)

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