Middle Eocene sedimentary and volcanic infilling of an evolving supradetachment basin: White Lake Basin, south-central British Columbia

2005 ◽  
Vol 42 (1) ◽  
pp. 49-66 ◽  
Author(s):  
Jason D McClaughry ◽  
David R Gaylord
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Metamorphic Core Complex ◽  
Lake Basin ◽  
Alluvial Fans ◽  
Core Complex ◽  
South Central ◽  
Metamorphic Core ◽  
Okanagan Valley

The middle Eocene White Lake and Skaha formations in the White Lake Basin, British Columbia record the sedimentary and volcanic infilling of a supradetachment basin that developed during the latter stages of Shuswap metamorphic core complex exhumation. The 1.1-km-thick White Lake Formation is characterized by volcanogenic sediment gravity flow, fluvial, and sheetflood facies interbedded with volcanic deposits. Facies relations suggest White Lake strata accumulated on coalesced, west-sloping alluvial fans that drained an active volcanic center. The overlying 0.3-km-thick Skaha Formation records increased tectonism and mass-wasting. Pervasively shattered Skaha avalanche, slide, and sheetflood deposits accumulated on alluvial fans, shed from hanging-wall and footwall sources exposed along the Okanagan Valley fault. Clast compositions of the White Lake and Skaha formations record alluvial and tectonic stripping that locally eliminated hanging-wall blocks. Mylonite clasts in upper Skaha beds imply significant Okanagan Valley fault footwall uplift during the middle Eocene and syntectonic erosion of the Shuswap metamorphic core complex. The syntectonic sedimentary record preserved within the White Lake Basin elucidates the relations and timing between core complex exhumation and extensional tectonism in this region. The White Lake and Skaha formations are the apparent age equivalent of the Klondike Mountain Formation of northern Washington (USA.). White Lake Basin strata, however, are more complexly interstratified, post-depositionally disrupted, and contain a more complete record of core complex unroofing. Variations in the spatial distributions and textural and compositional character of middle Eocene strata in this area underscore the need to exercise care when developing regional-scale sedimentary–tectonic–volcanic models.

Permian inheritance : post-orogenic extension and metamorphic core complex formation (Western Pyrenees)

2020 ◽  
Author(s):  
Nicolas Saspiturry ◽  
Bryan Cochelin ◽  
Philippe Razin ◽  
Sophie Leleu ◽  
Benoit Issautier ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Structural Response ◽  
Metamorphic Core Complex ◽  
Rift System ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Core Complex ◽  
Domal Structure ◽  
Metamorphic Core ◽  
Western Pyrenees

<p>This study documents the sedimentary and structural response of continental crust in relatively hot lithosphere that is subjected to extension. We focus on the Permian rift system in the Western Pyrenees, where the narrow, post-orogenic intracontinental extensional Bidarray Basin is in contact with late Variscan granulites of the Ursuya massif. The western margin of the N-S trending Bidarray Basin preserves alluvial fans dominated by hyperconcentrated flows and interdigitating eastward into a N-S trending fluvial system. Structural analysis of the Ursuya granulites shows that they underwent orogen-parallel mid-crustal flow and were exhumed owing to strain localization during retrogressive metamorphism within an extensional shear zone flanking an E-W elongated domal structure. We show that the Bidarray Basin formed during Permian time on the hanging wall of a south-vergent detachment system that developed in response to the formation of an immature “a-type” metamorphic core complex (the Ursuya massif) under regional E-W extension, resulting in homogeneous thinning of the hot crust. This core complex was later exposed by denudation during Cenomanian time. The preservation of the Permian and Triassic paleogeography and structure indicates that there has been no lateral motion between Iberia and Europe in the study area. The Cretaceous Pamplona transfer zone, responsible for the shift of the Mesozoic rift axis, reactivated a N-S trending Permian crustal heterogeneity.</p>

P–T–t path for the lower plate of the Eocene Tatla Lake metamorphic core complex, southwestern Intermontane Belt, British Columbia

1992 ◽  
Vol 29 (5) ◽  
pp. 972-983 ◽  
Author(s):  
R. M. Friedman
Keyword(s):  
British Columbia ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Lower Plate ◽  
Normal Faults ◽  
Low Grade ◽  
Core Complex ◽  
T Path ◽  
C 50 ◽  
Metamorphic Core

The Tatla Lake metamorphic complex (TLMC) is a metamorphic core complex located along the western edge of the Intermontane Belt in southwestern interior British Columbia. Low- to moderate-angle normal faults separate lower plate greenschist- and amphibolite-grade, highly strained, commonly mylonitic rocks from unstrained to weakly deformed strata of the upper plate. The lower plate is divided into a core of granoblastic gneiss and migmatitic tonalite and an overlying, 1–2.5+ km thick mylonitic package called the ductilely sheared assemblage (DSA). Amphibolite-grade metamorphism of the gneissic core (Mc) largely accompanied the development and folding of gneissic layering (ca. 107–79 Ma). Eocene (ca. 55–47 Ma) fabric and mineral assemblages in the DSA (Ms) obscure any earlier history. Three metamorphic zones are observed within southern DSA metapelites with increasing structural depth: chlorite–biotite, garnet–staurolite, and garnet–staurolite–kyanite–sillimanite. The middle zone is about 300 m thick; the latter zone is now about 4 km below low-grade upper plate rocks, indicating late- or post-Ds metamorphic omission. DSA P–T conditions are calculated with the garnet–biotite thermometer and garnet–Al2SiO5–quartz–plagioclase (GASP) and total Al in hornblende barometers. Southern DSA metapelites record Eocene Ms conditions of 480–619 °C (± 50 °C), generally increasing with depth. One sample gave a calculated P–T of 0.72 ± 0.15 GPa and 500 ± 50 °C. P–T data from this area suggest that up to 10 km of structural section may be missing. Zoned garnet (pre-Ds) core to rim GASP pressures of 0.70–0.36 ± 0.15 GPa, for an outcrop-sized pelitic xenolith within a Late Cretaceous tonalitic body (U–Pb: 71 Ma) in the northwestern DSA, record its ascent during pluton emplacement and subsequent Eocene tectonic uplift. A total Al in hornblende crystallization pressure of 0.54 ± 0.1 GPa was calculated for the surrounding body. Biotite and hornblende K–Ar dates of 53.4–45.6 Ma for DSA and gneissic core rocks record cooling of the lower plate through the 530–280 °C (± 40 °C) interval. Mc metamorphism in the gneissic core is thought to have developed in response to crustal thickening and compression, beneath a regional mid-Cretaceous thrust belt. Characteristics of Eocene Ms metamorphism in the DSA, such as truncated and thinned metamorphic zones, are consistent with development during extensional tectonic exhumation of the lower plate.

18O/16O homogenization of the middle crust during anatexis: The Thor-Odin metamorphic core complex, British Columbia: Comment and Reply

Geology ◽  
1997 ◽  
Vol 25 (11) ◽  
pp. 1053 ◽  
Author(s):  
Georges Beaudoin ◽  
Bruce E. Taylor ◽  
Gregory J. Holk ◽  
Hugh P. Taylor, Jr.
Keyword(s):  
British Columbia ◽  
Metamorphic Core Complex ◽  
Core Complex ◽  
Middle Crust ◽  
Metamorphic Core

Thermal effects of exhumation of a metamorphic core complex on hanging wall syn-rift sediments: an example from the Rechnitz Window, Eastern Alps

1998 ◽  
Vol 297 (1-4) ◽  
pp. 31-50 ◽  
Author(s):  
István Dunkl ◽  
Bernhard Grasemann ◽  
Wolfgang Frisch
Keyword(s):  
Thermal Effects ◽  
Hanging Wall ◽  
Eastern Alps ◽  
Metamorphic Core Complex ◽  
Core Complex ◽  
Metamorphic Core

Tatla Lake Metamorphic Complex: An Eocene Metamorphic Core Complex on the southwestern edge of the Intermontane Belt of British Columbia

Tectonics ◽  
1988 ◽  
Vol 7 (6) ◽  
pp. 1141-1166 ◽  
Author(s):  
R. M. Friedman ◽  
Richard Lee Armstrong
Keyword(s):  
British Columbia ◽  
Metamorphic Core Complex ◽  
Metamorphic Complex ◽  
Core Complex ◽  
Metamorphic Core

scholarly journals Evidence of early Miocene synextensional volcanism and deposition in the northern Calico Mountains, central Mojave metamorphic core complex, southern California, USA

Geosphere ◽  
2021 ◽  
Author(s):  
Bryan P. Murray ◽  
Willis E. Hames
Keyword(s):  
Debris Flow ◽  
Southern California ◽  
Hanging Wall ◽  
Metamorphic Core Complex ◽  
Early Miocene ◽  
Core Complex ◽  
Alluvial Deposits ◽  
Mafic Lava ◽  
Lapilli Tuff ◽  
Metamorphic Core

The spatiotemporal link between large-scale continental crustal extension and magmatic activity has been identified by numerous past studies, yet commonly the details of these associations remain unresolved. This study in the central Mojave metamorphic core complex (CMMCC) of southern California (USA) presents new geologic mapping, stratigraphic interpretations, and 40Ar/39Ar geochronology of the Jackhammer and Pickhandle Formations in the northern Calico Mountains to provide additional age constraints on the relative timing of early Miocene volcanism, deposition, and extension. The Jackham­mer Formation, the oldest Tertiary stratigraphic unit, is nonconformable with pre-Cenozoic nonmylonitic metasedimentary and plutonic basement rocks and consists primarily of alluvial deposits and primary to reworked silicic tuffs, interbedded locally with basement-derived avalanche megabreccia, lacustrine limestone, and mafic lava; in addition, the “Mammut ignimbrite”, an ~130-m-thick crystal-rich welded lapilli tuff, is exposed only in the eastern part of the study area and appears to transition laterally into thinner, nonwelded lapilli tuff ~6 km to the west. The Pickhandle Formation conformably overlies the Jackhammer Formation and consists of: (1) a lower assemblage composed of reddish monomictic debris-flow breccias with porphyritic rhyodacitic clasts and silicic block-and-ash-flow deposits of sim­ilar composition; and (2) an upper assemblage of polymictic (metaplutonic basement and rhyodacite) alluvial deposits, primary to reworked lapilli tuff, and local rhyodacitic lava and block-and-ash flows. Rhyodacitic lava domes were emplaced during the final stages of Pickhandle Formation deposition, primarily intruded along preexisting normal fault zones. Sedimentary and volcanic lithofacies suggest that the Jackhammer and Pickhandle Formations were deposited in a volcanic vent–proximal alluvial fan system that formed within a half-graben basin bounded on the east by the southwest-dipping “Amphitheatre fault”. Growth strata within the hanging-wall deposits, primarily southwest-directed paleocurrents, and interbedded alluvial debris-flow, basement-derived megabreccia, and lacustrine deposits adjacent to this fault suggest synextensional deposition in an intra-hanging-wall basin that developed during upper-plate extension in the CMMCC. New 40Ar/39Ar ages for six samples of silicic pyroclastic flows and a lava dome from the synextensional Pickhandle and Jackhammer Formations in the Calico Mountains have a mean age of 20.10 ± 0.06 Ma. This age is 3–4 m.y. younger than the maximum age of initial extension determined by previous studies in other areas of the central Mojave, suggesting that CMMCC extension was not a synchronous large-magnitude regional event. Rather, extension and contemporaneous volcanism was more localized and asynchronous across the region, occurring in many smaller extensional basins that eventually culminated in exposure of the CMMCC mylonitic footwall rocks.

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