Petrology and Geochemistry of basaltic rocks from north western Ethiopian Plateau Continental Flood Basalt

Abstract The Miocene Columbia River Basalt Group (CRBG) is the youngest and best studied continental flood basalt province on Earth. The 210,000 km3 of basaltic lava flows in this province were fed by a series of dike swarms, the largest of which is the Chief Joseph dike swarm (CJDS) exposed in northeastern Oregon and southwestern Washington. We present and augment an extensive data set of field observations, collected by Dr. William H. Taubeneck (1923–2016; Oregon State University, 1955–1983); this data set elucidates the structure of the CJDS in new detail. The large-scale structure of the CJDS, represented by 4279 mapped segments mostly cropping out over an area of 100 × 350 km2, is defined by regions of high dike density, up to ∼5 segments/km−2 with an average width of 8 m and lengths of ∼100–1000 m. The dikes in the CJDS are exposed across a range of paleodepths, from visibly feeding surface flows to ∼2 km in depth at the time of intrusion. Based on extrapolation of outcrops, we estimate the volume of the CJDS dikes to be 2.5 × 102–6 × 104 km3, or between 0.1% and 34% of the known volume of the magma represented by the surface flows fed by these dikes. A dominant NNW dike segment orientation characterizes the swarm. However, prominent sub-trends often crosscut NNW-oriented dikes, suggesting a change in dike orientations that may correspond to magmatically driven stress changes over the duration of swarm emplacement. Near-surface crustal dilation across the swarm is ∼0.5–2.7 km to the E-W and ∼0.2–1.3 km to the N-S across the 100 × 350 km region, resulting in strain across this region of 0.4%–13.0% E-W and 0.04%–0.3% N-S. Host-rock partial melt is rare in the CJDS, suggesting that only a small fraction of dikes were long-lived.

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Relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the Deccan Traps of the Western Ghats, India

Earth and Planetary Science Letters ◽

10.1016/0012-821x(87)90176-2 ◽

1987 ◽

Vol 84 (1) ◽

pp. 59-68 ◽

Cited By ~ 76

Author(s):

C.W. Devey ◽

K.G. Cox

Keyword(s):

Special Reference ◽

Western Ghats ◽

Crustal Contamination ◽

Flood Basalt ◽

Deccan Traps ◽

Continental Flood Basalt ◽

The Western Ghats

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The Paraná-Etendeka Continental Flood Basalt Province: A historical perspective of current knowledge and future research trends

Journal of Volcanology and Geothermal Research ◽

10.1016/j.jvolgeores.2017.11.011 ◽

2018 ◽

Vol 355 ◽

pp. 287-303 ◽

Cited By ~ 6

Author(s):

Edgardo Cañón-Tapia

Keyword(s):

Historical Perspective ◽

Current Knowledge ◽

Flood Basalt ◽

Research Trends ◽

Future Research ◽

Continental Flood Basalt

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A simple recipe for red bole formation in continental flood basalt provinces: weathering of flow-top and flow-bottom breccias

Arabian Journal of Geosciences ◽

10.1007/s12517-020-05973-9 ◽

2020 ◽

Vol 13 (18) ◽

Author(s):

Raymond A. Duraiswami ◽

Hetu Sheth ◽

Purva Gadpallu ◽

Nasrrddine Youbi ◽

El Hassane Chellai

Keyword(s):

Flood Basalt ◽

Continental Flood Basalt

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The early tectono-magmatic evolution of the Southern Province: implications from the Agnew Intrusion, central Ontario, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e98-031 ◽

1998 ◽

Vol 35 (7) ◽

pp. 854-870 ◽

Cited By ~ 11

Author(s):

D C Vogel ◽

R S James ◽

R R Keays

Keyword(s):

Parental Magma ◽

Structural Data ◽

Flood Basalt ◽

Incompatible Trace Element ◽

Superior Province ◽

Magmatic Evolution ◽

Layered Intrusions ◽

Continental Flood Basalt ◽

Southern Province ◽

Field Evidence

The Palaeoproterozoic Southern Province comprises a thick, continental rift related volcanic-sedimentary sequence along the southern margin of the Archaean Superior Province. The Agnew Intrusion (50 km2), which is a member of the East Bull Lake suite of layered intrusions, occurs adjacent to the Superior Province - Southern Province boundary in central Ontario, Canada, and provides an opportunity to examine the early tectono-magmatic evolution of a Palaeoproterozoic rifting event. The Agnew Intrusion is a well-exposed, 2100 m thick, layered gabbronoritic to leucogabbronoritic pluton. It was the product of at least four recognizable, but chemically similar, high-Al2O3 and low-TiO2 magma pulses. Structural data, coupled with excellent stratigraphic correlations between the Agnew Intrusion and other East Bull Lake suite layered intrusions, suggest that these plutons are erosional remnants of one or more sill-like bodies that may originally have formed an extensive, subhorizontal mafic sheet. We argue on the basis of field evidence that the early evolution of the Southern Province was characterized by a large, mantle plume induced magmatic event that gave rise to a Palaeoproterozoic continental flood basalt province. However, the incompatible trace element characteristics of the Agnew Intrusion parental magma (i.e., large ion lithophile and light rare earth element enrichment and high field strength element depletion) are more typical of modern subduction-modified subcontinental lithospheric mantle. Given that this is a prevailing geochemical signature of mafic rocks in the Archaean-Palaeoproterozoic, we suggest that there was a fundamental difference in both the composition and structure between the ancient and more modern mantle. "Subduction-like" geochemical signatures may have been imparted to the entire developing mantle during early Earth differentiation.

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