Cretaceous intrusions in the Commerce Mountain and adjacent areas of southeastern British Columbia and southwestern Alberta

1999 ◽  
Vol 36 (12) ◽  
pp. 1939-1956 ◽  
Author(s):  
R J Goble ◽  
S B Treves ◽  
V M Murray
Keyword(s):  
Continental Crust ◽  
Upper Mantle ◽  
Normative Data ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Upper Crust ◽  
Metasomatic Alteration ◽  
Isotopic Data ◽  
Lower Continental Crust ◽  
Low Pressures

An older oversaturated monzonitic and a younger undersaturated syenitic suite of Cretaceous igneous rocks are present at Commerce Mountain and adjacent areas of the southern Canadian Rockies. The undersaturated suite consists of foid-bearing alkali feldspar syenite and trachyte, with lesser amounts of phonolite and foid syenite. Normative data indicate a higher degree of undersaturation attributable to the presence of garnet. Sr and Nd isotopic data are consistent with generation of the magma by partial melting of an enriched source in the upper mantle or the lower continental crust; Pb isotopic data are more consistent with a source in the lower continental crust. High Sr and Ba concentrations in analcime-bearing alkali feldspar megacrysts support early crystallization at high pressure. Replacement of the analcime by muscovite suggests emplacement and continued crystallization at shallow depth under low pressures, at which the analcime was unstable. Prior to emplacement in the upper crust, the Commerce Mountain suite evolved in composition from mafic analcime-bearing perthite syenite to felsic analcime-nepheline-bearing perthite syenite to nepheline (micro)monzosyenite and to analcime (micro)syenite compositionally similar to analcime phonolites found in adjacent areas. Extensive metamorphic-metasomatic alteration suggests that Commerce Mountain was a volcanic center, possibly associated with the eruption of the Crowsnest Formation volcanic rocks.

scholarly journals Microcontinent subduction and S-type volcanism prior to India–Asia collision

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zongyao Yang ◽  
Juxing Tang ◽  
M. Santosh ◽  
Xiaoyan Zhao ◽  
Xinghai Lang ◽  
...  
Keyword(s):  
Continental Crust ◽  
Late Stage ◽  
Volcanic Rocks ◽  
Isotope Ratios ◽  
Lower Continental Crust ◽  
Nd Isotope ◽  
Magmatic Rocks ◽  
Upper Continental Crust ◽  
Volcanic Succession

AbstractContinental crust has long been considered too buoyant to be subducted beneath another continent, although geophysical evidence in collision zones predict continental crust subduction. This is particularly significant where upper continental crust is detached allowing the lower continental crust to subduct, albeit the mechanism of such subduction and recycling of the upper continental crust remain poorly understood. Here, we investigate Paleocene S-type magmatic and volcanic rocks from the Linzizong volcanic succession in the southern Lhasa block of Tibet. These rocks exhibit highly enriched 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb together with depleted 143Nd/144Nd isotope ratios. The geochemical and isotopic features of these rocks are consistent with those of modern upper continental crust. We conclude that these Paleocene S-type volcanic and magmatic rocks originated from the melting of the upper continental crust from microcontinent subduction during the late stage of India–Asia convergence.

Water-assisted production of late-orogenic trondhjemites at magmatic and subsolidus conditions

2019 ◽  
Vol 491 (1) ◽  
pp. 147-178 ◽  
Author(s):  
Patrizia Fiannacca ◽  
Miguel A. S. Basei ◽  
Rosolino Cirrincione ◽  
Antonino Pezzino ◽  
Damiano Russo
Keyword(s):  
Genetic Relationships ◽  
Alkali Feldspar ◽  
Magma Source ◽  
High Grade ◽  
Upper Crust ◽  
Dehydration Melting ◽  
Metasomatic Alteration ◽  
Granitoid Magmatism ◽  
Granite Emplacement ◽  
Peraluminous Granites

AbstractPeraluminous granites and trondhjemites make up small plutonic bodies intruded into high-grade paragneisses in the Peloritani Mountains, marking the beginning of late Variscan granitoid magmatism in southernmost Italy. The granites range from low-Ca monzogranites to alkali feldspar granites, while the trondhjemites vary from trondhjemites s.s. to low-Ca trondhjemites. Relatively high radiogenic (87Sr/86Sr)i ratios (mostly from 0.7073 to 0.7125) and negative εNd values (mostly from −5.66 to −8.73) point to crustal sources for all the granitoids. Major and trace element compositions indicate an absence of genetic relationships between the trondhjemites s.s. and the low-Ca granitoids, but possible relationships between the low-Ca trondhjemites and the granites. All of the studied granitoids have near-pure melts compositions, consistent with H2O-fluxed and dehydration melting of metasediments for the trondhjemites and the granites, respectively. However, the unusual compositions of the low-Ca trondhjemites and microstructural evidence in these rocks for pervasive subsolidus replacement of magmatic feldspars by secondary sodic plagioclase indicate that they were derived instead from metasomatic alteration of the granites. Thus, water may be involved in the production of trondhjemites in two different ways, driving water-fluxed melting in the magma source and driving alkali metasomatism at the sites of granite emplacement in the upper crust.

U–Pb and Rb–Sr geochronology of Acadian plutonism in the Dunnage zone of the southeastern Quebec Appalachians

1990 ◽  
Vol 27 (7) ◽  
pp. 881-892 ◽  
Author(s):  
Antonio Simonetti ◽  
Ronald Doig
Keyword(s):  
Continental Crust ◽  
Host Rock ◽  
Crustal Thickening ◽  
Metasomatic Alteration ◽  
Calc Alkaline ◽  
Lower Continental Crust ◽  
Isotopic Heterogeneity ◽  
Acadian Orogeny

U–Pb zircon and (or) titanite or monazite ages have been obtained for five major, undeformed, calc-alkaline plutons of the Appalachians of southeastern Quebec. These are interpreted as ages of crystallization for the Scotstown (384 ± 2 Ma), Lac aux Araignées (383 ± 3 Ma), Winslow (377 ± 7 Ma), Aylmer (375 ± 3 Ma), and Ste-Cécile (374 ± 2 Ma) plutons. Many other titanite samples gave 206Pb/238U dates that are 2–16 Ma younger than the concordant zircon dates from the same samples, and this is probably the result of Pb loss. Variation in 207Pb/206Pb ages of titanite from some samples is attributed to incorrect common Pb correction.Rb–Sr data for the same plutons show considerable isotopic heterogeneity and correspondingly high errors in ages. The isotopic heterogeneity is likely caused by postsolidification metasomatic alteration by host rock fluids. Where the scatter is least (Ste-Cécile), the Rb–Sr age (364 ± 14 Ma) is similar to the U–Pb mineral age (374 ± 2 Ma). The 87Sr/86Sr initial ratios range from 0.7065 to 0.710 and are probably related to the source of the magmas. The relatively high initial ratios and the peraluminous nature of the plutons preclude a significant mantle contribution to the magmas. These undeformed plutons are probably the result of melting of the lower continental crust near the end of crustal thickening caused by compression during the Acadian Orogeny.

Supplemental Material: Tectonic origin of the Bainaimiao arc terrane in the southern Central Asian orogenic belt: Evidence from sedimentary and magmatic rocks in the Damao region

2020 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
et al.
Keyword(s):  
Volcanic Rocks ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Isotopic Data ◽  
Magmatic Rocks ◽  
Central Asian ◽  
Southern Central ◽  
Samples And Sampling ◽  
Tectonic Origin

Table S1: Summary of the samples and sampling positions in this study (sampling sites are marked in Fig. 3); Table S2: U-Pb age data for zircons of (meta-)sedimentary and volcanic rocks in this study; Table S3: Lu-Hf isotopic data for zircons of (meta-)sedimentary and volcanic rocks in this study.

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