Generation of felsic rocks of bimodal volcanic suites from thinned and rifted continental margins

Geochemical and Nd, Sr, Pb-isotopic evidence from Haida Gwaii, British Columbia, Canada

Jaroslav Dostal, Tark S. Hamilton, J.g  Shellnutt

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The compositionally bimodal volcanic rocks of the Eocene–Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust (~ 19–24 km thick), with volcanism persisting for ~ 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic ~ 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd–Sr–Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin.

Original languageEnglish
Pages (from-to)146-160
Number of pages15
JournalLithos
Volume292-293
DOIs
Publication statusPublished - 2017 Nov 1

Fingerprint

felsic rock
continental margin
Rocks
rare earth element
basalt
fractional crystallization
Crystallization
Bearings (structural)
mid-ocean ridge
Plumbing
dacite
Volcanic rocks
mafic rock
chondrite
magma chamber
peridotite
spinel
pyroxene
Mineralogy
continental crust

Keywords

  • Bimodal volcanism
  • Eocene–Miocene
  • Fractional crystallization
  • Rhyolite
  • Thinned continental margin

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

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title = "Generation of felsic rocks of bimodal volcanic suites from thinned and rifted continental margins: Geochemical and Nd, Sr, Pb-isotopic evidence from Haida Gwaii, British Columbia, Canada",
abstract = "The compositionally bimodal volcanic rocks of the Eocene–Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust (~ 19–24 km thick), with volcanism persisting for ~ 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic ~ 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd–Sr–Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin.",
keywords = "Bimodal volcanism, Eocene–Miocene, Fractional crystallization, Rhyolite, Thinned continental margin",
author = "Jaroslav Dostal and Hamilton, {Tark S.} and J.g  Shellnutt",
year = "2017",
month = "11",
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doi = "10.1016/j.lithos.2017.09.005",
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T1 - Generation of felsic rocks of bimodal volcanic suites from thinned and rifted continental margins

T2 - Geochemical and Nd, Sr, Pb-isotopic evidence from Haida Gwaii, British Columbia, Canada

AU - Dostal, Jaroslav

AU - Hamilton, Tark S.

AU -  Shellnutt, J.g

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N2 - The compositionally bimodal volcanic rocks of the Eocene–Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust (~ 19–24 km thick), with volcanism persisting for ~ 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic ~ 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd–Sr–Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin.

AB - The compositionally bimodal volcanic rocks of the Eocene–Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust (~ 19–24 km thick), with volcanism persisting for ~ 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic ~ 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd–Sr–Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin.

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KW - Rhyolite

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