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Accreted Terranes of the North Cascades Range, Washington: Spokane to Seattle, Washington, July 21 - 29, 1989, Volume T307

Accreted Terranes of the North Cascades Range, Washington: Spokane to Seattle, Washington, July 21 - 29, 1989, Volume T307

Rowland W. Tabor, Ralph A. Haugerud, Edwin H. Brown, R. Scott Babcock, Robert B. Miller

ISBN: 978-1-118-66671-5

Mar 2013, American Geophysical Union

62 pages

Select type: O-Book


Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 307.

The Cascade Range is an active north-trending volcanic arc at the western edge of North America (Figure 1). At the northern end of the range, between 47°N and 49°N, the average elevation increases, peaks become sharper, numerous small glaciers survive on the higher slopes, and volcanic rocks of the Cascade arc are scarce. This region is the North Cascades Range. The North Cascades are bounded on the west by the fore-arc basin of the Puget Lowland, on the south by the arc volcanic rocks of the Central Cascades, and on the southeast by the back-arc flood basalts of the Columbia Plateau. The geologic identity of the range is not so clearly defined to the north, but it is geographically bounded on the northeast by the Okanogan Ranges and on the northwest by the Fraser River, which separates the Cascades from the Coast Mountains.



Acknowledgments 1


Present topography and glaciation 2

(I) Pre-Late Cretaceous terranes 3

North American craton 3

Quesnellia 3

Pre-Late Cretaceous terranes east of the Straight Creek fault 3

Methow terrane 3

Hozameen terrane (Hozameen Group) 3

Little Jack terrane 4

Jack Mountain Phyllite 4

Elija Ridge Schist 4

North Creek Volcanics 4

Chelan Mountains terrane 7

Napeequa unit 7

Twisp Valley Schist 7

Cascade River unit 7

Marblemount Meta Quartz Diorite 7

Skagit Gneiss 8

Nason terrane 8

Chiwaukum Schist 8

Ingalls terrane 8

Swakane terrane 8

Pre-Late Cretaceous terranes west of the Straight Creek fault 8

Northwest Cascades system (NWCS) 8

Grandy Ridge terrane 9

Chilliwack Group and Cultus Formation 9

Wells Creek Volcanics and Nooksack Group 9

Easton terrane (Easton Metamorphic Suite) 9

Shuksan Greenschist 9

Darrington Phyllite 9

Yellow Aster terrane (Yellow Aster Complex) 9

Western and eastern melange belts (WEMB) 9

Eastern melange belt 10

Trafton sequence 10

Western melange belt 10

Helena-Haystack melange 10

(II) Late Cretaceous to Eocene(?) orogeny 11

Deformation 12

in Methow terrane 12

in Chelan Mountains and Nason terranes 12

in NWCS 12

Metamorphism 12

in Nason terrane 12

in Chelan Mountains terrane 12

in NWCS 12

in WEMB 13

Syn- to late-orogenic plutons 13

(Ill) The Eocene event 13

Eocene faulting 13

Straight Creek fault 13

Darrington-Devils Mountain fault zone (DDMFZ) 13

Entiat fault 13

Ross Lake fault zone (RLFZ) 13

Ross Lake fault sensu stricto I3

Gabriel Peak tectonic belt 15

Hozameen-North Creek and Foggy Dew faults 15

Twisp Valley fault 15

Thunder Lake fault 16

Chewack-Pasayten fault 16

Eocene deposition 16

Chuckanut Formation 16

Swauk Formation 16

Barlow Pass Volcanics 16

Eocene high-level deformation 16

Eocene magmatism 16

Golden Horn batholith 16

Late lineated dikes 16

Eocene ductile deformation 17

Eocene K-Ar cooling ages 17

(IV) Cascade magmatic arc I7

Indexfamily 17

Snoqualmie family I7

Cascade Passfamily I7


Day 1. Spokane to Twisp and Winthrop 34

Day 2. Winthrop to upper Eagle Creek 36

Day 3. Upper Eagle Creek to Lake Juanita 37

Day 4. Lake Juanita to Stehekin and Stehekin Valley Ranch 38

Day 5. Stehekin Valley to Skagit Valley 40

Day 6. Diablo Lake to Da"ington 43

Day 7. Darrington to Rat Trap Pass, Suiattl~ Mountain and return 48

Day 8. Darrington to Gee Point area, Deer Creek Pass and return 51

Day 9. Darrington to Helena Ridge, Barlow Pass and Seattle 55