Title:
 Layered mafic sill complex beneath the eastern Snake River plain;evidence from cyclic geochemical variations in basalt 
Reference Number:
 2542 
ISSN:
 0091-7613
Publication Year:
 2006
GeoREF Number:
 2006-049735 (View Original Data File)
Authors:
 Shervais, John W; Vetter, Scott K; Hanan, Barry B
Descriptors:
 alkaline earth metals; assimilation; basalts; chemical fractionation;cores; crust; crystal fractionation; cycles; electron probe data;geochemical cycle; geochemistry; granitic layer; Idaho; igneous rocks;INEEL; intrusions; isotope ratios; isotopes; lava; layered intrusions;lead; mafic composition; magmas; major elements; metals; middle crust;Pb-208/Pb-204; radioactive isotopes; rhyolites; sills; Snake Riverplain; southern Idaho; Sr-87/Sr-86; stable isotopes; strontium; traceelements; United States; volcanic rocks; volcanism
Source:
 Geology (Boulder), vol.34, no.5, pp.365-368, May 2006
Abstract:
 The eastern Snake River plain in southern Idaho, Western UnitedStates, is characterized by 1-2 km of Pleistocene to late Pliocenebasalt overlying rhyolite caldera complexes. Cyclic variations in thechemical composition of basalts from 1136 m of scientific drill coreshow that the parent magmas of these lavas evolved by crystalfractionation at shallow to intermediate crustal depths, punctuated byepisodic recharge with more primitive compositions and assimilation ofadjacent wall rock. We have identified 10 upward fractionation cyclesand four reversed cycles; assimilation of sialic crust was limited andmainly affects the oldest basalts, which directly overlie rhyolites.We infer that the crystal fractionation and/or recharge cycles tookplace in a series of sill-like intrusions at intermediate crustaldepths that now form a layered mafic intrusion that underlies theeastern Snake River plain at depth. This layered sill complex isrepresented by the approximately 10-km-thick basaltic sill that hasbeen imaged seismically at approximately 12-22 km depth. Theassociation of this mid-crustal sill complex with geochemicalfractionation cycles in basalt supports the concept that exposedlayered mafic intrusions may be linked to overlying basalt provincesthat have since been removed by erosion.
Notes:
 With GSA Data Repository Item 2006072
Copyright:
 GeoRef, Copyright 2006, American Geological Institute. Referenceincludes data supplied by the Geological Society of America, Boulder,CO, United States

Sample Summary:
Sample ID: Major Data: Trace Data: Isotope Data:
20 Yes Yes No
77 Yes Yes No
90 Yes Yes Yes
188 Yes Yes Yes
349 Yes Yes Yes
431 Yes Yes Yes
626 Yes Yes No
655 Yes Yes No
705 Yes Yes Yes
786 Yes Yes No
860 Yes Yes No
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944 Yes Yes No
998 Yes Yes No
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1054 Yes Yes No
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1136 Yes Yes Yes
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1378 Yes Yes Yes
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1541 Yes Yes Yes
1565 Yes Yes Yes
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1632 Yes Yes No
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1805 Yes Yes Yes
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2190 Yes Yes Yes
2198 Yes Yes No
2325 Yes Yes No
2458 Yes Yes Yes
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2611 Yes Yes Yes
2707 Yes Yes Yes
2782 Yes Yes Yes
2878 Yes Yes No
3000 Yes Yes No
3079 Yes Yes Yes
3193 Yes Yes Yes
3242 Yes Yes Yes
3341 Yes Yes Yes
3409 Yes Yes Yes
3606 Yes Yes Yes
3645 Yes Yes Yes
3740 Yes Yes Yes