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

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.

Multiple Isotopic Components in Quaternary Volcanic Rocks of the Cascade Arc near Crater Lake, Oregon

1994 ◽  
Vol 35 (6) ◽  
pp. 1521-1556 ◽  
Author(s):  
C. R. BACON ◽  
S. H. GUNN ◽  
M. A. LANPHERE ◽  
J. L. WOODEN
Keyword(s):  
Crater Lake ◽  
Volcanic Rocks ◽  
Cascade Arc

The petrology of the basic and intermediate rocks of upper Swat, Pakistan

1973 ◽  
Vol 110 (3) ◽  
pp. 285-300 ◽  
Author(s):  
M. Qasim Jan ◽  
D. R. C. Kempe
Keyword(s):  
Volcanic Rocks ◽  
Age Determination ◽  
Tholeiitic Basalt ◽  
Amphibolite Facies ◽  
Igneous Rocks ◽  
Basalt Magma ◽  
Chemical Analyses

SummaryA series of metamorphosed (amphibolite facies) basic and intermediate igneous rocks from upper Swat, Pakistan, is described, with seven chemical analyses. The rocks intrude ?Palaeozoic metasediments and are partially bordered by other, later, intrusive and volcanic rocks. The group, now represented by, from S–N, epidote amphibolites, amphibolites, noritic and hypersthene gabbros, and quartz diorites, is considered to be derived from a series of plagioclase hypersthenites, norites, hypersthene gabbros, and hypersthene diorites. Variation diagrams are used to show that the series forms a differentiated sequence; FMA and lime-alkali diagrams suggest that it is similar to the rocks of the Garabal Hill–Loch Fyne area of Scotland. Some of the mineralogy of the group is briefly discussed, with five chemical analyses. A K/Ar age determination gives 67 Ma; thus the rocks probably derive from an early Himalayan (Alpine) tholeiitic basalt magma.

scholarly journals Geochemistry of Volcanic Rocks of Beka, North East of Ngaoundéré (Adamawa Plateau, Cameroon): Petrogenesis and Geodynamic Context

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Pauline Wokwenmendam Nguet ◽  
Benjamin Ntieche ◽  
Joseph Legrand Tchop ◽  
Bouba Christian Mana ◽  
Eddy Ferdinand Mbossi
Keyword(s):  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Parent Magma ◽  
Spinel Lherzolite ◽  
Chemical Analyses ◽  
Volcanic Zone ◽  
North East ◽  
Low Degree ◽  
Petrographic Study ◽  
Basaltic Lavas

Beka area is situated in the Adamaoua Plateau of Cameroon in central Arica. Lavas in this area has not been studied before the present work.The volcanism of Beka is characterized by basalt, trachyte and phonolite domes and flows. The petrographic study shows that basaltic lavas have porphyritic microlitic textures. The felsic lavas indicate trachytic textures.The rocks are composed of olivine, clinopyroxene, plagioclase and irontitanium oxide minerals for the basalts; clinopyroxene, alkali feldspar (including foids), sphene and titanomagnetite for the felsic lavas. Chemical analyses show that basaltic lavas are basanites. Felsic lavas contain modal feldspathoid (nepheline in phonolites). All these lavas belong to the same series, because the felsic lavas are derived from the differentiation of basaltic lavas by fractional crystallization. They show an alkaline nature according to their geochemistry. Trace elements including Rare Earth Elements characteristics show that rocks emplaced in the Winthin Plate volcanic zone. They derived from an evolved parent magma showing a low degree of partial melting and characteristics closer to a modified and evolved primitive spinel lherzolite.

scholarly journals The deformation and granitisation of Ketilidian rocks in the Nanortalik area, S. Greenland

1966 ◽  
Vol 59 ◽  
pp. 1-102
Author(s):  
A Escher
Keyword(s):  
Volcanic Rocks ◽  
Time Interval ◽  
Chemical Analyses ◽  
Intrusive Body ◽  
Major Phase ◽  
Fine Grained ◽  
Field Evidence ◽  
Rigid Mass ◽  
Metasomatic Replacement ◽  
Subsequent Replacement

The Nanortalik peninsula, situated between the fjords of Tasermiut and Sarqâ, is largely composed of Ketilidian schists, quartzites and volcanic rocks. All these rocks are more or less strongly folded. The folding took place probably in three successive phases during the Ketilidian period : A first deformation resulting in folds with NNE trending axes, was followed by a second major phase of folding with NW axes. This second folding was essentially plastic. A third deformation, acting probably on a more rigid mass, was characterised by the formation of fracturec1eavage. Third-period folds possess very long wavelengths; their axes are oriented NNE to NE. Migmatisation started probably during the second deformation period resulting in the formation of many dykes and veins of pegmatite and aplite. Four generations of Ketilidian pegmatites can be recognised. Most of them appear to have been formed by metasomatic replacement. It seems that during the Ketilidian orogeny, the evolution of the schists and gneissic schists tended to a granodioritic composition. Potassium metasomatism only became active at the end of the Ketilidian period. In the NE part of the Nanortalik peninsula, three Sanerutian granites can be observed. These granites are similar in composition (quartz-microline-biotite), but possess different ages and textures. The time interval between the last Ketilidian deformation and the emplacement of the first Sanerutian granite was marked by the intrusion of several metadoleritic dykes. The first and principal Sanerutian granite usually shows an indistinct foliation due to numerous oriented inc1usions. Field evidence indicates that this granite was formed mainly by replacement of volcanic rocks. Chemical analyses show that large amounts of K, Si and Na have been supplied to produce the granitisation of the volcanic rocks. The second Sanerutian granite is characterised by a coarse porphyroblastic texture and appears to have been emplaced partially by the intrusion of a melt and partially by a subsequent replacement of the host-rock. Finally, the last Sanerutian granite displays all the characteristics of a pure intrusive body. It is generally very fine-grained and forms many cross-cutting dykes.

Comparison of Conventional K–Ar and 40Ar/39Ar Dating of Young Mafic Volcanic Rocks

2000 ◽  
Vol 53 (3) ◽  
pp. 294-301 ◽  
Author(s):  
Marvin A. Lanphere
Keyword(s):  
Crater Lake ◽  
Volcanic Rocks ◽  
Snake River Plain ◽  
High Quality ◽  
Modern Equipment ◽  
Suitable Material ◽  
Mount Adams ◽  
River Plain ◽  
Isotope Correlation ◽  
Better Than

AbstractK–Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K–Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K–Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K–Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K–Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene.

The geochemistry of the Devonian lavas of the northern Lorne Plateau, Scotland

1974 ◽  
Vol 39 (306) ◽  
pp. 621-640 ◽  
Author(s):  
D. R. Groome ◽  
A. Hall
Keyword(s):  
Volcanic Rocks ◽  
Parent Magma ◽  
Igneous Rocks ◽  
Continuous Series ◽  
Chemical Analyses ◽  
Scottish Highlands ◽  
Igneous Activity ◽  
Common Parent ◽  
Short Time ◽  
Basic Rocks

SummaryChemical analyses of the Lorne volcanic rocks show that the basalts and andesites are a closely related suite of lavas, notably rich in alkalis, especially potassium. The rhyolites of the Lorne area do not appear to form a continuous series with the more basic rocks. The various lava types are compared with the plutonic rocks of the area, and a relationship is suggested between the basic lavas and appinitic intrusions. The acid lavas are not comparable to granites in the area.The late orogenic igneous activity in this part of the Caledonides therefore appears to involve three generations of magma, produced separately but within a short time of one another. The assumption that all the late Caledonian igneous rocks of the Scottish Highlands are differentiates of a common parent magma is not justified.

Observations on the Proterozoic Seton Formation, East Arm of Great Slave Lake, Northwest Territories

1972 ◽  
Vol 9 (9) ◽  
pp. 1110-1123 ◽  
Author(s):  
M. A. D. Olade ◽  
R. D. Morton
Keyword(s):  
Northwest Territories ◽  
Volcanic Rocks ◽  
Chemical Analyses ◽  
Quartz Porphyry ◽  
Shallow Marine ◽  
Hypabyssal Intrusions ◽  
Lake Region ◽  
Great Slave Lake ◽  
Marine Sedimentation ◽  
Partial Chemical

The Proterozoic (Aphebian) Seton Formation is shown to extend across almost the entire length of the East Arm structural subprovince of the Great Slave Lake region, Northwest Territories. Earlier described as greenstones or basalts and recently as an andesite–rhyolite suite, the volcanic rocks which characterize the Seton Formation are clearly of spilitic–keratophyric affinity. The formation is composed of a sequence of marine to subaerial, spilitic basalt flows, trachytic flows, quartz keratophyric–and spilitic–basic pyroclastics, volcanic sandstones, jasper, banded ironstones, and intercalated marine epiclastic sedimentary rocks. Small hypabyssal intrusions of albite granophyre, albite, and quartz porphyry represent minor subvolcanic phases. Petrographic descriptions of the lavas and pyroclastic rocks from Toopon Lake, the Fort Reliance area, and Seton Island are augmented by partial chemical analyses of 15 lavas from the latter locality. The volcanic–sedimentary Seton Formation, 1300 m thick in the SW of the East Arm, and 40 m thick in the Fort Reliance district, should be classified as a member of the Sosan Group, being in part laterally equivalent to the Akaitcho River Formation and the upper Kluziai Formation. The Aphebian Coronation Geosyncline during Seton times was thus characterized by effusive (partially submarine) island volcanism in the SW of the region, contemporaneous with shallow marine sedimentation towards the northeast part of the basin.

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