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.

scholarly journals Compressional origin of the Naxos metamorphic core complex, Greece: Structure, petrography, and thermobarometry

2019 ◽  
Vol 132 (1-2) ◽  
pp. 149-197 ◽  
Author(s):  
Thomas N. Lamont ◽  
Michael P. Searle ◽  
David J. Waters ◽  
Nick M.W. Roberts ◽  
Richard M. Palin ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Normal Faults ◽  
Crustal Extension ◽  
Core Complex ◽  
The Core ◽  
History Of ◽  
Metamorphic Core

Abstract The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the structural section, resulting in the juxtaposition of several distinct tectono-stratigraphic nappes that experienced contrasting metamorphic histories. The Cycladic Blueschists attained ∼14.5 kbar and 470 °C during attempted northeast-directed subduction of the continental margin. These were subsequently thrusted onto the more proximal continental margin, resulting in crustal thickening and regional metamorphism associated with kyanite-grade conditions of ∼10 kbar and 600–670 °C. With continued shortening, the deepest structural levels underwent kyanite-grade hydrous melting at ∼8–10 kbar and 680–750 °C, followed by isothermal decompression through the muscovite dehydration melting reaction to sillimanite-grade conditions of ∼5–6 kbar and 730 °C. This decompression process was associated with top-to-the-NNE shearing along passive-roof faults that formed because of SW-directed extrusion. These shear zones predated crustal extension, because they are folded around the migmatite dome and are crosscut by leucogranites and low-angle normal faults. The migmatite dome formed at lower-pressure conditions under horizontal constriction that caused vertical boudinage and upright isoclinal folds. The switch from compression to extension occurred immediately following doming and was associated with NNE-SSW horizontal boudinage and top-to-the-NNE brittle-ductile normal faults that truncate the internal shear zones and earlier collisional features. The Naxos metamorphic core complex is interpreted to have formed via crustal thickening, regional metamorphism, and partial melting in a compressional setting, here termed the Aegean orogeny, and it was exhumed from the midcrust due to the switch from compression to extension at ca. 15 Ma.

Accelerating exhumation in the Eocene North American Cordilleran hinterland: Implications from detrital zircon (U-Th)/(He-Pb) double dating

2019 ◽  
Vol 132 (1-2) ◽  
pp. 198-214 ◽  
Author(s):  
Andrew S. Canada ◽  
Elizabeth J. Cassel ◽  
Daniel F. Stockli ◽  
M. Elliot Smith ◽  
Brian R. Jicha ◽  
...  
Keyword(s):  
North American ◽  
Detrital Zircon ◽  
Sedimentary Basins ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Sediment Provenance ◽  
Core Complex ◽  
Extensional Faulting ◽  
Lag Times ◽  
Metamorphic Core

AbstractBasins in orogenic hinterlands are directly coupled to crustal thickening and extension through landscape processes and preserve records of deformation that are unavailable in footwall rocks. Following prolonged late Mesozoic–early Cenozoic crustal thickening and plateau construction, the hinterland of the Sevier orogen of western North America underwent late Cenozoic extension and formation of metamorphic core complexes. While the North American Cordillera is one of Earth’s best-studied orogens, estimates for the spatial and temporal patterns of initial extensional faulting differ greatly and thus limit understanding of potential drivers for deformation. We employed (U-Th)/(He-Pb) double dating of detrital zircon and (U-Th)/He thermochronology of detrital apatite from precisely dated Paleogene terrestrial strata to quantify the timing and magnitude of exhumation and explore the linkages between tectonic unroofing and basin evolution in northeastern Nevada. We determined sediment provenance and lag time evolution (i.e., the time between cooling and deposition, which is a measure of upper-crustal exhumation) during an 8 m.y. time span of deposition within the Eocene Elko Basin. Fluvial strata deposited between 49 and 45 Ma yielded Precambrian (U-Th)/He zircon cooling ages (ZHe) with 105–740 m.y. lag times dominated by unreset detrital ages, suggesting limited exhumation and Proterozoic through early Eocene sediment burial (<4–6 km) across the region. Minimum nonvolcanic detrital ZHe lag times decreased to <100 m.y. in 45–43 Ma strata and to <10 m.y. in 43–41 Ma strata, illustrating progressive and rapid hinterland unroofing in Eocene time. Detrital apatite (U-Th)/He ages present in ca. 44 and 39 Ma strata record Eocene cooling ages with 1–20 m.y. lag times. These data reflect acceleration of basement exhumation rates by >1 km/m.y., indicative of rapid, large-magnitude extensional faulting and metamorphic core complex formation. Contemporaneous with this acceleration of hinterland exhumation, syntectonic freshwater lakes developed in the hanging wall of the Ruby Mountains–East Humboldt Range metamorphic core complex at ca. 43 Ma. Volcanism driven by Farallon slab removal migrated southward across northeastern Nevada, resulting in voluminous rhyolitic eruptions at 41.5 and 40.1 Ma, and marking the abrupt end of fluvial and lacustrine deposition across much of the Elko Basin. Thermal and rheologic weakening of the lithosphere and/or partial slab removal likely initiated extensional deformation, rapidly unroofing deeper crustal levels. We attribute the observed acceleration in exhumation, expansion of sedimentary basins, and migrating volcanism across the middle Eocene to record the thermal and isostatic effects of Farallon slab rollback and subsequent removal of the lowermost mantle lithosphere.

Metamorphic evolution of a very low- to low-grade metamorphic core complex (Danubian window) in the South Carpathians

2008 ◽  
Vol 298 (1) ◽  
pp. 281-315 ◽  
Author(s):  
Magda Ciulavu ◽  
Rafael Ferreiro Mählmann ◽  
Stefan M. Schmid ◽  
Heiko Hofmann ◽  
Antoneta Seghedi ◽  
...  
Keyword(s):  
Metamorphic Core Complex ◽  
Low Grade ◽  
The South ◽  
Core Complex ◽  
Metamorphic Evolution ◽  
Metamorphic Core
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