Tectonic implications of syn- and post-emplacement deformation of the Mount Stuart batholith for mid-Cretaceous orogenesis in the North Cascades

1992 ◽  
Vol 29 (3) ◽  
pp. 479-485 ◽  
Author(s):  
Robert B. Miller ◽  
Scott R. Paterson
Keyword(s):  
British Columbia ◽  
High Temperature ◽  
Main Part ◽  
North Cascades ◽  
Geochronological Data ◽  
The Core ◽  
The North ◽  
Crystalline Core ◽  
Thrust System ◽  
Unknown Period

The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting and folding, and west-northwest stretching. Contraction ended shortly after emplacement, as indicated by high-temperature recrystallization in thrust-related mylonites of the pluton and by geochronological data, whereas west-northwest stretching continued for an unknown period of time. This is the best documented mid-Cretaceous contractional belt in the main part of the crystalline core. The shortening direction and timing are identical to that of southwest-vergent thrusts in the offset continuation of the core in British Columbia. The contractional belt provides a link between thrusting in the Northwest Cascades thrust system and deformation in the crystalline core.

Tectono-stratigraphic terranes and the metamorphic history of the northeastern part of the crystalline core of the North Cascades: evidence from the Twisp Valley Schist

1993 ◽  
Vol 30 (7) ◽  
pp. 1306-1323 ◽  
Author(s):  
Robert B. Miller ◽  
Donna L. Whitney ◽  
Edward E. Geary
Keyword(s):  
Time History ◽  
Eastern Coast ◽  
North Cascades ◽  
Northeastern Part ◽  
The Core ◽  
Metamorphic History ◽  
The North ◽  
Crystalline Core ◽  
History Of ◽  
Geochemical Analyses

The Twisp Valley Schist (TVS) is important for both the correlation of terranes in the Cascades crystalline core and for the determination of the metamorphic pressure–temperature–time history of the northeastern part of the core. The TVS is a chaotically mixed unit of mainly siliceous schist (metachert) with significant amounts of metabasite, calc-silicate rock, and marble, and minor ultramafite and metapsammite. Geochemical analyses of metabasites indicate that the TVS contains both ocean-island basalts (OIB) and mid-ocean-ridge basalts (MORB). The TVS is lithologically similar to the Napeequa unit of the Chelan Mountains terrane in the Cascades core and is broadly correlative with units outside of the core, including the Mississippian–Jurassic Bridge River – Hozameen terrane of the eastern Coast belt, and coeval OIB-bearing terranes in the Northwest Cascades thrust system. Much of the northeastern Cascades core thus consists of oceanic rocks that probably originally lay between the Insular and the Intermontane superterranes, or were part of the latter superterrane.The TVS experienced polyphase deformation and greenschist to middle amphibolite facies metamorphism during the interval from 90 Ma (and possibly earlier) to ca. 50 Ma. Paleocene (ca. 65–58 Ma) dynamothermal metamorphism is the best documented event and in part resulted from forcible emplacement of plutons and from broadly distributed deformation in the Ross Lake fault zone. Major crustal loading of the TVS is inferred from the replacement of andalusite by kyanite, the presence of garnets that record an increase in pressure of 1.5–3.0 kbar (1 kbar = 100 MPa) from cores to rims, and the deeper emplacement levels of younger plutons. Loading may record thrusting in the northeastern core that is bracketed between 88 and 65 Ma and is younger than previously recognized, major contractional deformation in the North Cascades.

Intra-arc crustal loading and its tectonic implications, North Cascades crystalline core, Washington and British Columbia

Geology ◽  
1993 ◽  
Vol 21 (3) ◽  
pp. 255 ◽  
Author(s):  
Robert B. Miller ◽  
Edwin H. Brown ◽  
Daniel P. McShane ◽  
Donna L. Whitney
Keyword(s):  
British Columbia ◽  
North Cascades ◽  
Tectonic Implications ◽  
Crystalline Core

scholarly journals Deglaciation of the North Cascade Range, Washington and British Columbia, from the Last Glacial Maximum to the Holocene

2017 ◽  
Vol 43 (2) ◽  
pp. 467 ◽  
Author(s):  
J.L. Riedel
Keyword(s):  
British Columbia ◽  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Cascade Range ◽  
North Cascades ◽  
Alpine Glacier ◽  
The North ◽  
Alpine Glaciers ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Glacial retreat from the North Cascade Range after the Last Glacial Maximum (LGM) at approximately 21 ka until the end of the Pleistocene at 11.6 ka was complex and included both continental and alpine glaciers. Alpine valley glaciers reached their maximum extent before 21.4 ka, then underwent a punctuated retreat to valley heads. In the south, beyond the reach of ice sheet glaciation, several end moraines were deposited after the LGM. Moraines marking a re-advance of alpine glaciers to <5 km below modern glaciers were deposited from 13.7 to 11.6 ka.The Cordilleran Ice Sheet flowed south from near 52° north latitude in British Columbia into the North Cascades. At its maximum size the ice sheet covered more than 500 km2 and had a surface elevation of 2200 m in upper Skagit valley. Deglaciation commenced about 16 ka by frontal retreat of ice flanking the mountains. Surface lowering eventually exposed regional hydrologic divides and stranded ice masses more than 1000 m thick in valleys. Isolated fragments of the ice sheet disintegrated rapidly from 14.5 to 13.5 ka, with the pattern of deglaciation in each valley controlled by valley orientation, topography, and climate. Like alpine glaciers to the south, retreat of the ice sheet remnants was slowed by millennial scale climate fluctuations that produced at least one large recessional moraine, and multiple lateral moraines and kame terraces from elevations of 200-1400 m in most valleys. Large volumes of glacial meltwater flowed through the North Cascades and was concentrated in the Skagit and Methow rivers. Outburst floods from deep proglacial lakes spilled across divides and down steep canyons, depositing coarse gravel terraces and alluvial fans at valley junctions.Climate at the LGM was characterized by a mean summer temperature 6 to 7 ºC cooler than today, and 40% lower mean annual precipitation. Persistence of this climate for thousands of years before the LGM caused a 750-1000 m decrease in alpine glacier equilibrium line altitudes (ELA). In the southern North Cascades at 16 ka, glacial ELAs were 500-700 m lower than today, and during advances from 13.7 to 11.6 ka alpine glacier ELAs were 200-400 m lower.

Orogen-parallel extension in the North Cascades Crystalline Core, Washington

Tectonics ◽  
1989 ◽  
Vol 8 (6) ◽  
pp. 1105-1114 ◽  
Author(s):  
E. H. Brown ◽  
J. L. Talbot
Keyword(s):  
North Cascades ◽  
The North ◽  
Crystalline Core ◽  
Parallel Extension
Sign in / Sign up

Export Citation Format

Share Document