Proterozoic flood basalts of eastern Lake Superior: the Keweenawan volcanic rocks of Mamainse Point area, Ontario

Annells, Richard

doi:10.4095/102486

Cited by 15 publications

(4 citation statements)

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“…The Steens Basalt is known for conspicuous giant plagioclase laths (1-5 cm in diameter). Textures in these giant plagioclase basalts (GPB) are variable and include (1) distinctive radial, snowflake-like plagioclase clusters with olivine trapped at spoke apices (aka "daisy stone" of Annells, 1973;Fig. 7B), and (2) sandwich-structured glomerocrysts of plagioclase laths with micro phenocrystic olivine trapped between laths.…”

Section: Height (M)mentioning

confidence: 99%

The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafic intrusions

2018

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Section: Height (M)mentioning

confidence: 99%

The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafic intrusions

2018

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“…Although more highprecision dates are needed within these older sequences, the clustering of published ages for volcanic and intrusive rocks (Figure 2), as well as unpublished dates of reverse-magnetic polarity lavas from the North Shore Volcanic and Powder Mill groups (D. W. Davis, personal communication, 1993) between 1109 and 1105 Ma, suggests that perhaps most of the magmatism of this early stage was concentrated in the first 4 m.y. Evidence in support of this assertion includes the common occurrence of thick rhyolite flows and/or thick polymict conglomerates separating basalt sequences of distinct geochemistry in the upper portions of some of the reverse-polarity sequences Annells, 1973;Hubbard, 1975;Klewin and Berg, 1990]. Although dates are not available for these rhyolites, individual sedimentary zircons (presumably from rhyolitic lithologies) have been dated with ages typically between 1104 and 1106 Ma [Davis and Paces, 1990].…”

Section: Tectonomagmatic Evolution Of the Midcontinent Riftmentioning

confidence: 99%

Precise U‐Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift System

Paces¹,

Miller²

1993

J. Geophys. Res.

1,371

526

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Precise resolution of the timing of igneous activity is crucial to understanding the dynamic processes associated with continental rifting. Mafic intrusive rocks constitute a major portion of the exposed 1100 Ma (Keweenawan) Midcontinent Rift system in northeastern Minnesota; however, prior to this study, geochronological data were insufficient to allow rigorous interpretation of intrusive histories and their relationships to extrusive suites. Eight anorthositic and gabbroic intrusives were chosen to represent both the temporal and spatial ranges of plutonic activity that formed the Duluth Complex and related mafic intrusions. U‐Pb isotopic analyses from zircons and baddeleyites result in U‐Pb concordant ages with little or no ambiguity introduced by inherited components, Pb loss or common Pb. The earliest Keweenawan plutonism exposed in Minnesota occurs along the northeastern flank of the Duluth Complex as a series of layered gabbros (Nathan's layered series) emplaced at 1106.9 ± 0.6 Ma. This sequence of gabbro sheets shares temporal, spatial, and compositional similarities with the nearby Logan sills in Ontario. Four Duluth Complex anorthositic and troctolitic series samples from widely separated areas have unresolvable ages between 1099.3 ± 0.3 and 1098.6 ± 0.5 Ma, indicating a very short duration for peak intrusive activity (0.5–1 m.y.). The unresolvable ages between anorthositic and troctolitic plutons suggest that these two magma series are more closely related than previously modeled and argue strongly for the need to reexamine their fundamental petrogenetic relationships. These dates also imply that the major reverse‐to‐normal magnetic polarity switch, used throughout the rift system as an important correlation tool, occurred prior to 1099 Ma. This date is several million years earlier than previously suspected and emphasizes the need for further paleomagnetic and geochronological data from the overlying volcanics. Much of the hypabyssal intrusive suite within the volcanic pile overlying Duluth Complex plutons may be significantly younger than the main pulse of plutonic activity. Two hypabyssal bodies, the Sonju Lake intrusion and gabbro at Silver Bay, were emplaced at 1096.1 ± 0.8 Ma and 1095.8 ± 1.2 Ma, respectively. Dates reported here and in previous studies support the concept of episodic tectonomagmatic rift development where magmatism was apparently concentrated in episodes of short duration (<1–3 m.y.) interspersed with longer hiatuses (2–8 m.y.).

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“…), but emphasis is placed here on the pegmatitic rocks. For descriptions of other mafic flows exhibiting layering, the reader is referred to Emerson (1905), Annells (1973), Helz (1980), and Puffer and Horter (1991).…”

Section: Geology and Field Descriptionmentioning

confidence: 99%

Layered rhyolite bands in a thick North Mountain Basalt flow: the products of silicate liquid immiscibility?

Greenough

Dostál

1992

Mineral. mag.

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The upper 35 m of a thick (~<175 m) Early Jurassic North Mountain Basalt flow at KcKay Head contains 25 cm thick differentiated layers that are separated by 130 cm sections of basalt. The lower layers are mafic, pegmatitic, and contain thin (2 cm), fine-grained 'rhyolite' bands. Evidence that the rhyolite represents a Si-rich immiscible liquid includes: (1) textures such as fiine-grained globules of Ferich pyroxene (once Fe-rich liquid) bordering pegmatite feldspar grains; (2) structureless, microcrystalline, interstitial, polygonal patches of Si-rich minerals and similar areas of Fe-rich stilpnomelane surrounding skeletal Fe-Ti oxide grains, with bulk chemical compositions (to a first approximation), relative proportions and total modat percentages suggesting they were once Si-rich and Fe-rich glasses respectively; (3) basalt and pegmatite compositions (particularly their Fe, and Ti contents) similar to rocks known to contain immiscible liquids; (4) rhyolite major element compositions generally consistent with formation from an immiscible Si-rich liquid; (5) mineral compositions and temperature of pegmatite formation compatible with immiscibility; (6) the inability of mass balance calculations (crystal fractionation) to explain rhyolite formation unless mesostasis stilpnomelane (representing the Fe-rich liquid) is included in the caculations. If, as we suggest, these rocks are the result of immiscibility, they shed light on the incipient formation of granophyres in mafic intrusions and support liquid immiscibility as an important rock-forming process.

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Proterozoic flood basalts of eastern Lake Superior: the Keweenawan volcanic rocks of Mamainse Point area, Ontario

Cited by 15 publications

References 0 publications

The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafic intrusions

The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafic intrusions

Precise U‐Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift System

Layered rhyolite bands in a thick North Mountain Basalt flow: the products of silicate liquid immiscibility?

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