Petrology of Mafic Plutons Associated with Calc-Alkaline Granitoids, Chilliwack Batholith, North Cascades, Washington

Tepper, Jeffrey H.

doi:10.1093/petrology/37.6.1409

Cited by 25 publications

(22 citation statements)

References 55 publications

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“…This association is observed in xenoliths from island arcs (Arculus and Wills, 1980;Conrad and Kay, 1984) as well as in Alaska-or Klamathtype mafi c-ultramafi c complexes (Irvine, 1974;Snoke et al, 1982;Saleeby, 1992) and early mafi c plutons of I-type granitoid batholiths in continental arcs (Smith et al, 1983;Beard and Day, 1988;Tepper, 1996). In contrast, plagioclase coexisting with olivine in Skymo troctolite and gabbro is signifi cantly more sodic (An 75-60 ), a paragenesis similar to that seen in gabbros from mid-ocean ridges, hotspots, and layered intrusions (Fig.…”

Section: La Ce Nd Smeu Gdmentioning

confidence: 75%

“…Relating processes documented in modern volcanic arcs to those inferred for ancient, exhumed arcs is, however, diffi cult because exhumed arcs are dominated by plutonic rocks of granitic to intermediate composition, and these provide more limited petrologic insights than the typical basalt-andesite-dacite suite. Exhumed arcs contain mafi c plutonic rocks, but these tend to be volumetrically minor constituents of granitic batholith complexes (Bateman, 1992;Lipman, 1992;Tepper, 1996). Large-scale mafi c intrusions in exhumed arcs are therefore of interest for the information they contain about the origin and evolution of magmas in continental arcs (e.g., Ratajeski et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

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Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

Tepper

Hirschmann

Hurlow

2008

Geological Society of America Bulletin

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The Skymo Complex in the North Cascades, Washington, is a layered mafi c intrusion within the Ross Lake fault zone, a major orogen-parallel structure at the eastern margin of the Cascades crystalline core. The complex is composed dominantly of troctolite and gabbro, both with inclusions of primitive olivine gabbro. Low-pressure minerals in the metasedimentary contact aureole and early crystallization of olivine + plagioclase in the mafi c rocks indicate the intrusion was emplaced at shallow depths (<12 km).The Skymo rocks have trace-element characteristics of arc magmas, but the association of Mg-rich olivine (Fo 88-80 ) with relatively sodic plagioclase (An 75-60 ) and the Al/Ti ratios of clinopyroxene are atypical of arc gabbros and more characteristic of riftrelated gabbros. A Sm-Nd isochron indicates crystallization in the early Tertiary (ca. 50 Ma), coeval with the nearby Golden Horn alkaline granite. Mantle melting to produce Skymo magma likely occurred in a mantle wedge with a long history of arc magmatism. The Skymo mafi c complex and the Golden Horn granite were emplaced during regional extension and collapse of the North Cascades orogen and represent the end of large-scale magmatism in the North Cascades continental arc.

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Section: La Ce Nd Smeu Gdmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

Tepper

Hirschmann

Hurlow

2008

Geological Society of America Bulletin

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“…However, the variation in Mg# was even higher between different samples (e.g., Samples 6104 and TCH 23, with Mg# = 69 80). The value of the Mg# of the clinopyroxenes and the range in silicon content (1.82 1.95 pfu) is typical of subalkaline gabbro (e.g., Tepper, 1996). The concentration of the minor elements, such as NiO, is very low (< 0.07 wt%), whereas the Cr 2 O 3 content showed more variation.…”

Section: Major Element Mineral Chemistrymentioning

confidence: 94%

Petrogenesis of the Neoproterozoic Bikilal-Ghimbi gabbro, Western Ethiopia

Woldemichael

Kimura²

2008

Journal of Mineralogical and Petrological Sciences

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The Western Ethiopian Shield is an exposed Neoproterozoic metamorphic belt and forms part of the Arabian Nubian Shield. The metamorphic belt consists of high grade biotite gneisses, low grade volcanogenic sediments, and mafic ultramafic complexes. The Bikilal Ghimbi gabbro is a mafic body surrounded by these gneissic rocks, and is located 440 km west of Addis Ababa. The gabbro is elliptical in shape and covers an area of 350 km 2 . It consists of olivine gabbro in its center and hornblende gabbro and hornblendite at the perimeter. The olivine gabbros are very fresh and undeformed, but hornblende bearing suites have deformational textures. Each rock type can be divided into apatite bearing and apatite free subtypes. The major element geochemistry shows that despite the differences between the olivine and the hornblende gabbros, there is no systematic chemical contrast between the lithotypes except for the fluid mobile elements, suggesting an origin from a common parental magma. Only the perimeter is affected by metasomatism. An estimation of the parental magma composition using the trace element abundance in fresh clinopyroxenes and fresh olivine gabbro bulk rock suggests an intraplate type tholeiite. Crystallization model calculations using a tholeiitic parental magma suggest that the gabbros crystallized in a manner where small amounts of interstitial melt were retained. The apatite bearing varieties are always associated with Mg rich mineral phases, suggesting an origin from the supercooling of replenished basalt into an evolved low temperature magma chamber. The supercooling caused saturation of the apatite in the basalt melt, along with Mg rich crystals, and these later mixed together with the more evolved crystals that had precipitated previously. The intraplate type tholeiitic parental magma suggests plume type magmatism for the origin of the Bikilal Ghimbi gabbro body.

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“…On the given spider diagrams (Fig. 13), the patterns of both metavolcanics and gabbroic rocks exhibit a diagnostic subduction-related Ta-Nb trough (Pearce 1983;Condi 1989;Tepper 1996;Ali-Bik et al 2014) in contrast to the continental-rift, within-plate basalts. In terms of maturity, the pattern of the studied metavolcanics matches that of the gabbroic rocks (Fig.…”

Section: Metavolcanics and Gabbroic Rocksmentioning

confidence: 99%

Late Neoproterozoic basement rocks of Kadabora-Suwayqat area, Central Eastern Desert, Egypt: geochemical and remote sensing characterization

2015

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Kadabora-Suwayqat area, in the Central Eastern Desert of Egypt, is built up by a wide variety of non-consanguineous, basement rock units, which represent a tectonostratigraphic suite within the frame of the Late Neoproterozoic, Pan-African Arabian-Nubian Shield. They were developed from different magma sources at varied tectonic settings through subsequent tectono-magmatic processes. They cover a wide compositional range of the Pan-African legend in the Eastern Desert of Egypt comprising ophiolitic, island-arc, and within-plate assemblages. The ophiolitic serpentinites were obducted onto arcrelated metavolcanics and intruded by gabbroic and syn-late to post tectonic granitoids. Geochemically, the precursor of the ophiolitic serpentinites seems to be peridotite (harzburgite). The basic, intermediate, and acidic metavolcanics imply a transitional stage between an island-arc and a proper active continental margin setting. They exhibit with the gabbroic rocks a diagnostic subduction-related island-arc, calc-alkaline affinity. The granitoids comprise both arc-related, calc-alkaline I-type and within-plate, anorogenic A-type varieties. These rocks have been successfully discriminated on Landsat 8 images including Minimum Noise Fraction (MNF; 4, 3, 7), Principal Component Analysis (PCA; PC6, PC2, PC7), and various band ratios (b6/ b2, b6/b7, b6/b5×b4b5) and (b7/b6, b7/b5, b5/b3). ASTER clay index (5×7/6) and silica index (10/13) discriminated the granitoid rocks, while the serpentinite-talc carbonate and metavolcanic rocks are distinguished on the ASTER images of amphibole index (6+9/7+8) and (6/8).

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Petrology of Mafic Plutons Associated with Calc-Alkaline Granitoids, Chilliwack Batholith, North Cascades, Washington

Cited by 25 publications

References 55 publications

Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

Petrogenesis of the Neoproterozoic Bikilal-Ghimbi gabbro, Western Ethiopia

Late Neoproterozoic basement rocks of Kadabora-Suwayqat area, Central Eastern Desert, Egypt: geochemical and remote sensing characterization

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