Petrology of the Chilliwack batholith, North Cascades, Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity

The Holocene volumetric sediment budget is estimated for coarse textured sediments (sand and gravel) in a large, formerly glaciated valley in southwest British Columbia. Erosion is estimated by compiling volumetric loss estimated in digital elevation models (DEMs) of gullied topography and by applying a non-linear diffusion model on planar, undissected hillslopes. Estimates of steepland yield are based on estimates of post-glacial deposition volumes in fans, cones and deltas at the outlets of low-order tributary catchments. Erosion of post-glacial fans and tributary valley fills is estimated by reconstructing formerly continuous surfaces. Results are classed by catchment order and compared across scales of contributing area, revealing declining specific sediment yield (in m 3 km -2 a -1) with catchment area for the smaller tributaries (<10 km 2 ) and increasing specific sediment yield for larger tributaries and Chilliwack Valley itself. Approximately 60% of mobilized sediment is redeposited in first-to third-order catchments, with lesser proportions stored at the outlets of higher order catchments. A simple network routing model emphasizes the significant sediment flux contributions from colluvium, drift blankets and gullies in steeper terrain. As this material is deposited at junctions within the lower drainage network, an increasing proportion of material is derived from remnant valley fills and para-glacial fans in the major valleys. Yield from lower-order, steepland catchments tends to remain in storage, indefinitely sequestered on footslopes. These observations have implications for modelling the post-glacial sediment balance amongst catchments of varying size. After 10 4 years, the system remains in disequilibrium. The critical linkage lies between low-order, hillslope catchments (

show abstract

“…Chilliwack Valley has a contemporary glacier cover of roughly 2% of its basin area. (Richards and McTaggart, 1976;Tepper et al, 1993).…”

Section: Physical Environmentmentioning

confidence: 98%

Scale variation of post‐glacial sediment yield in Chilliwack Valley, British Columbia

Tunnicliffe

Church

2010

Earth Surf Processes Landf

View full text Add to dashboard Cite

show abstract

“…In addition, the melt composition resulting from the partial melting of the mafic lower crust is controlled by the water content, source composition, degree and P-T conditions of the melting (e.g., Rapp et al 1991;Sen and Dunn 1994;Wolf and Wyllie 1994;Rapp and Watson 1995;Winther 1996;Lopéz and Castro 2001). Recent experimental data have shown that regardless of the degree of partial melting, the partial melting of the mafic lower crust also could generate melts of metaluminous granitic composition (e.g., Rushmer 1991;Tepper et al 1993;Roberts and Clemens 1993;Wolf and Wyllie 1994;Rapp and Watson 1995). The most felsic sample, H3, is characterized by high silica (*76 wt%) and relatively low Mg# (11), while the evolved samples have higher I Sr (79 Ma) (0.70707), all of which would be consistent with melts derived from the lower crust.…”

Section: Source Featuresmentioning

confidence: 99%

“…This mechanism seems probable, as experimental studies show that underplating magma could provide the necessary heat source for the dehydration melting of lower crust (e.g., Rushmer 1991; Rapp and Watson 1995;Pedford and Gallagher 2001) and produce the granitic melt (e.g., Rushmer 1991;Tepper et al 1993;Roberts and Clemens 1993;Wolf and Wyllie 1994;Rapp and Watson 1995). Topuz et al (2005) and Karsli et al (2007) also showed that the underplating mechanism could result in granitic melt by the dehydration melting of the lower crust in the Eastern Pontides.…”

Section: Source Featuresmentioning

confidence: 99%

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Karslı

Dokuz

Uysal

et al. 2010

Contrib Mineral Petrol

147

View full text Add to dashboard Cite

We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (*79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO 2 = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO 2 = 54.95-56.32 wt%), and exhibits low Mg# (\46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb) 83. These geochemical data rule out pure crustalderived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved *65-75% of the lower crustal-derived melt and *25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Communicated by G. Moore. Electronic supplementary material 123Contrib Mineral Petrol (2010) 160:467-487 DOI 10.1007 Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least *79 Ma in the Eastern Pontides.

show abstract

“…Similar correlations between ƒH 2 O and ƒO 2 measured by Fe 3+ / Fe 2+ have been observed in granitoids (Czamanske and Wones, 1973;Tepper et al, 1993), therefore, the ƒH 2 O, is considered as the bridge to connect magma temperature and ƒO 2 . Specified mechanism between high ƒH 2 O and ƒO 2 , however, remains controversial, mainly including the H 2 separation and sulfur loss models proposed to explain the close association.…”

Section: Mechanism For High Oxidizing State Of Magmas At Halasumentioning

confidence: 50%

Magmatic sequences in the Halasu Cu Belt, NW China: Trigger for the Paleozoic porphyry Cu mineralization in the Chinese Altay–East Junggar

Chao

Chen

Hollings

et al. 2015

Ore Geology Reviews

View full text Add to dashboard Cite

Petrology of the Chilliwack batholith, North Cascades, Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity

Cited by 198 publications

References 48 publications

Scale variation of post‐glacial sediment yield in Chilliwack Valley, British Columbia

Scale variation of post‐glacial sediment yield in Chilliwack Valley, British Columbia

Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Magmatic sequences in the Halasu Cu Belt, NW China: Trigger for the Paleozoic porphyry Cu mineralization in the Chinese Altay–East Junggar

Contact Info

Product

Resources

About