Non-depleted sub-continental mantle beneath the Superior Province of the Canadian Shield: Nd-Sr isotopic and trace element evidence from Midcontinent Rift basalts

Journal Article · Tue Aug 01 00:00:00 EDT 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90322-0· OSTI ID:7266111

Paces, J B ^[1]; Bell, K ^[2]

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1. Michigan Technological Univ., Houghton (USA)
2. Carleton Univ., Ottawa, Ontario (Canada)

Midcontinent Rift flood basalts represent a sample of the relatively shallow, sub-continental upper mantle beneath the Canadian Shield at 1.1 Ga. A thick sequence of olivine tholeiite lavas, including minor intermediate to rhyolitic lavas, from the Portage Lake Volcanics (PLV) in northern Michigan have initial Nd and Sr isotopic compositions which cluster near Bulk Earth values. The effects of assimilation of old LREE-enriched continental crust into mantle-derived fractionating liquids are isotopically discernible in evolved lavas as well as in olivine tholeiites from the lowest portion of the volcanic pile. However, the effects of crustal contamination decrease with stratigraphic height and are absent in more primitive lavas in the upper half of the section. The source for PLV tholeiites is substantially less depleted than previously reported mantle values from the Superior Province. An origin for the PLV source is compatible with either of several mantle evolution models. The PLV source may have been associated with upwelling of a LIL element-enriched, asthenospheric plume which emplaced non-depleted material from deeper sources into the shallow sub-continental mantle beneath the Midcontinent Rift during continental break-up. Alternatively, the PLV source may have originated by enrichment of refractory sub-continental lithospheric mantle which was previously depleted in incompatible trace elements during Archean-aged melt extraction and continental crust formation. Concurrent generation of carbonatite magmas in other areas beneath the Superior Province indicates the widespread presence of sub-continental mantle with substantially higher {epsilon}{sub Nd}(T) and lower {epsilon}{sub Sr}(T) than the PLV source.

• OSTI ID: 7266111
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:8; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BASALT
PETROCHEMISTRY
PETROGENESIS
CHEMICAL ANALYSIS
EARTH MANTLE
GEOLOGIC HISTORY
ISOTOPE RATIO
LAVA
MAGMA
MAGMATISM
MICHIGAN
MINNESOTA
NEODYMIUM ISOTOPES
ONTARIO
RIFT ZONES
STRONTIUM ISOTOPES
ALKALINE EARTH ISOTOPES
CANADA
FEDERAL REGION V
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
ISOTOPES
NORTH AMERICA
ROCKS
USA
VOLCANIC ROCKS
580000* - Geosciences