Chemical analyses of pre-Mazama silicic volcanic rocks, inclusions, and glass separates, Crater Lake, Oregon

1993 ◽  
Author(s):  
P.E. Bruggman ◽  
C.R. Bacon ◽  
J.S. Mee ◽  
S.T. Pribble ◽  
D.F. Siems
Keyword(s):  
Crater Lake ◽  
Volcanic Rocks ◽  
Chemical Analyses ◽  
Silicic Volcanic

scholarly journals Chemical analyses of volcanic rocks from monogenetic and shield volcanoes near Crater Lake, Oregon

1989 ◽  
Author(s):  
P.E. Bruggman ◽  
C.R. Bacon ◽  
J.S. Mee ◽  
S.T. Pribble ◽  
D.F. Siems
Keyword(s):  
Crater Lake ◽  
Volcanic Rocks ◽  
Chemical Analyses ◽  
Shield Volcanoes

Regionally continuous Miocene rhyolites beneath the eastern Snake River Plain reveal localized flexure at its western margin: Idaho National Laboratory and vicinity

2020 ◽  
Vol 57 (3) ◽  
pp. 241-270
Author(s):  
Kyle L. Schusler ◽  
David M. Pearson ◽  
Michael McCurry ◽  
Roy C. Bartholomay ◽  
Mark H. Anders
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
North American Plate ◽  
Snake River ◽  
Trace Element Geochemistry ◽  
Deep Borehole ◽  
Age Progression ◽  
Western Margin ◽  
Silicic Volcanic ◽  
River Plain

The eastern Snake River Plain (ESRP) is a northeast-trending topographic basin interpreted to be the result of the time-transgressive track of the North American plate above the Yellowstone hotspot. The track is defined by the age progression of silicic volcanic rocks exposed along the margins of the ESRP. However, the bulk of these silicic rocks are buried under 1 to 3 kilometers of younger basalts. Here, silicic volcanic rocks recovered from boreholes that penetrate below the basalts, including INEL-1, WO-2 and new deep borehole USGS-142, are correlated with one another and to surface exposures to assess various models for ESRP subsidence. These correlations are established on U/Pb zircon and 40Ar/39Ar sanidine age determinations, phenocryst assemblages, major and trace element geochemistry, δ18O isotopic data from selected phenocrysts, and initial εHf values of zircon. These data suggest a correlation of: (1) the newly documented 8.1 ± 0.2 Ma rhyolite of Butte Quarry (sample 17KS03), exposed near Arco, Idaho to the upper-most Picabo volcanic field rhyolites found in borehole INEL-1; (2) the 6.73 ± 0.02 Ma East Arco Hills rhyolite (sample 16KS02) to the Blacktail Creek Tuff, which was also encountered at the bottom of borehole WO-2; and (3) the 6.42 ± 0.07 Ma rhyolite of borehole USGS-142 to the Walcott Tuff B encountered in deep borehole WO-2. These results show that rhyolites found along the western margin of the ESRP dip ~20º south-southeast toward the basin axis, and then gradually tilt less steeply in the subsurface as the axis is approached. This subsurface pattern of tilting is consistent with a previously proposed crustal flexural model of subsidence based only on surface exposures, but is inconsistent with subsidence models that require accommodation of ESRP subsidence on either a major normal fault or strike-slip fault.

Geochemistry and eruptive environment of metavolcanic rocks from the Mona Complex of Anglesey, North Wales, U.K

1993 ◽  
Vol 130 (1) ◽  
pp. 85-91 ◽  
Author(s):  
R. S. Thorpe
Keyword(s):  
Volcanic Rocks ◽  
Fault Zones ◽  
Ultramafic Rocks ◽  
Chemical Analyses ◽  
Late Precambrian ◽  
Suprasubduction Zone ◽  
Metavolcanic Rocks ◽  
North Wales ◽  
Eruptive Environment ◽  
Early Palaeozoic

AbstractThe late Precambrian–early Palaeozoic Monian Supergroup of the Mona Complex is a thick sequence of flysch-type sediments and metavolcanic rocks which were deposited during the late Precambrian–early Palaeozoic and deformed during the late Precambrian and Caledonian (Ordovician/Silurian) orogenies. The Monian Supergroup includes tectonically emplaced, geographically separated outcrops of metabasalt/andesite, gabbro and serpentinized ultramafic rocks all of ophiolite affinity. The major units of the Mona Complex are separated by important faults/fault zones which may represent terrane boundaries. New chemical analyses, together with existing ones, show that the metabasalts and meta-andesites from the older New Harbour Group of north Anglesey have characteristics of suprasubduction zone arc eruptives whereas the metabasalts from the younger Gwna Group of south Anglesey and Lleyn have MORB geochemistry. It is suggested that these volcanic rocks were produced during the late Precambrian–early Palaeozoic development of the lapetus Ocean and emplaced as separate terranes during its closure.

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