scholarly journals Petrogenesis of the tholeiitic basalt, calc-alkaline basaltic andesite and high magnesian andesite lava succession of the Oligo-Miocene Anamizu Formation in northeastern Noto Peninsula, central Japan.

2002 ◽  
Vol 97 (3) ◽  
pp. 85-113 ◽  
Author(s):  
Juan Carlos LÓPEZ ◽  
Akira ISHIWATARI
Keyword(s):  
Basaltic Andesite ◽  
Tholeiitic Basalt ◽  
Calc Alkaline ◽  
Central Japan ◽  
Andesite Lava

Early Miocene extrusives and shallow intrusives from Small Nggela, Solomon Islands

1980 ◽  
Vol 117 (6) ◽  
pp. 565-578 ◽  
Author(s):  
I. R. Plimer ◽  
G. Neef
Keyword(s):  
Shallow Water ◽  
Subduction Zone ◽  
Deep Water ◽  
Basaltic Andesite ◽  
Solomon Islands ◽  
Pillow Lava ◽  
Progressive Increase ◽  
Tholeiitic Basalt ◽  
Early Miocene ◽  
Calc Alkaline

SummaryChemically similar altered gabbro, tholeiitic basalt, basaltic andesite and calc-alkaline rhyolite of Early Miocene age is present on Small Nggela, Solomon Islands. Large vesicles are invariably lacking from the autochthonous basaltic pillow lava which has narrow chilled margins, but clasts of allochthonous basalt present in coeval Early Miocene sediment are commonly vesicular. This suggests that the autochthonous lava was deposited in deep water (> 2.5 km) whereas the allochthonous lava was formed upslope in shallow water. A progressive increase in the tholeiite in Zr, Ti, K2O/(K2O+Na2O), Rb/Sr and K2O/Rb from N to S confirms that an Early Miocene southward-descending subduction zone, postulated by some authors, was present. Its recognition implies that the subduction zone did not migrate far during the Early Miocene.

Robust 24±6 ka 40Ar/39 Ar Age of a Low-Potassium Tholeiitic Basalt in the Lassen Region of NE California

2007 ◽  
Vol 68 (1) ◽  
pp. 96-110 ◽  
Author(s):  
Brent D. Turrin ◽  
L.J. Patrick Muffler ◽  
Michael A. Clynne ◽  
Duane E. Champion
Keyword(s):  
Basaltic Andesite ◽  
Tholeiitic Basalt ◽  
Lava Flows ◽  
Firm Age ◽  
Low Potassium ◽  
Total Fusion ◽  
Low K ◽  
Additional Constraints ◽  
Andesite Lava

Abstract40Ar/39Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K2O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40Ar/39Ar ages of 38±7 ka (Cinder Butte; 1.65% K2O), 46±7 ka (Sugarloaf Peak; 1.85% K2O), 67±4 ka (Little Potato Butte; 1.42% K2O) and 77±11 ka (Potato Butte; 1.62% K2O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K2O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26"6 ka is seductively appealing. A second sample (0.17% K2O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26±18, 30±20 and 24±6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24"6 ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.

Ordovician volcanism in the Welsh Borderland

1986 ◽  
Vol 123 (6) ◽  
pp. 629-640 ◽  
Author(s):  
P. T. Leat ◽  
R. S. Thorpe
Keyword(s):  
Trace Element ◽  
Basaltic Andesite ◽  
Calc Alkaline ◽  
Basalt Flow ◽  
Chemical Alteration ◽  
Marginal Basin ◽  
Southeastern Margin ◽  
Trace Element Contents ◽  
Element Contents ◽  
Rhyolitic Volcanism

AbstractBasaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.

Constraints imposed by experimental petrology on possible and impossible magma sources and products

1984 ◽  
Vol 310 (1514) ◽  
pp. 439-456 ◽  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Basaltic Andesite ◽  
Subduction Zones ◽  
Mantle Peridotite ◽  
Experimental Petrology ◽  
Source Rocks ◽  
Calc Alkaline ◽  
Physical Constraints ◽  
Inverse Results

Experimental petrology can be used in forward and inverse approaches. The forward approach defines the compositions of liquids generated by partial melting of possible source rocks at various depths. The inverse approach determines conditions for multiple-mineral saturation at the liquidus of primitive magmas, correlates them with residual minerals of possible source rocks, and thus provides estimates of depths and temperatures required for their derivation. Review of a selection of forward and inverse results is followed by evaluation of petrological and geophysical processes in layered mantle and in subduction zones. Physical constraints imposed by solidus curves and geotherms present problems for models that derive basalts from deep mantle reservoirs, separated from overlying convecting layers. Magmas from mantle are limited to compositions less siliceous than basaltic andesite, with rare exceptions. Granite liquids cannot be generated from normal peridotite, nor from oceanic crust at mantle pressures in subduction zones. In continental crust, hydrous granite liquid is generated at depths of less than 30 km. Basaltic andesite and picritic basalt are parental magmas for the calc-alkaline series. Andesite is not primary from subcontinental depths, and can be generated as liquid in continental crust only if temperatures exceed about 1100°C. Calc-alkaline magmas may contain components from mantle peridotite, subducted oceanic crust, and continental crust.

The Southeastern Saurashtra dyke swarm, Deccan Traps: Magmatic evolution of a tholeiitic basalt–basaltic andesite–andesite–rhyolite suite

Lithos ◽  
2020 ◽  
Vol 376-377 ◽  
pp. 105759
Author(s):  
Ciro Cucciniello ◽  
Hetu Sheth ◽  
Raymond A. Duraiswami ◽  
Wencke Wegner ◽  
Christian Koeberl ◽  
...  
Keyword(s):  
Basaltic Andesite ◽  
Tholeiitic Basalt ◽  
Deccan Traps ◽  
Dyke Swarm ◽  
Magmatic Evolution

Petrography and mechanism of eruption of the Archean Dalembert tuff, Rouyn–Noranda, Quebec, Canada

1978 ◽  
Vol 15 (11) ◽  
pp. 1712-1723 ◽  
Author(s):  
Erich Dimroth ◽  
Janet Demarcke
Keyword(s):  
Basaltic Andesite ◽  
Pyroclastic Flows ◽  
Volatile Content ◽  
Volcanic Island ◽  
Terminal Stage ◽  
Local Variant ◽  
Andesite Lava

We investigated the petrography of the Dalembert tuff, an assemblage of pyroclastic flows, in two sections named the Dalembert and Reneault sections. Tuffs in the Dalembert section consist of pumice, plagioclase crystals, and a polymict assemblage of lithic fragments probably derived from sub-aerial lavas. The size of plagioclase quench crystals varies somewhat across a thick (about 15 m) graded unit, proving eruption of hot pumice flows, but the tuffs are unwelded. The features suggest the eruption of overflowing glowing avalanches, and emplacement of the cold tuff under the sea.Plagioclase-phyric basaltic andesite, very similar to the pumice of the Dalembert section except for its poor vesiculation, comprises more than 95% of the tuffs in the Reneault section. A few dacite fragments are the accessory component. These features suggest derivation from collapsing domes or spines.The Dalembert section is representative of the Dalembert tuff as a whole, whereas the facies exposed at Reneault is a local variant. We suggest that the eruption began with formation of an overflowing glowing avalanche from a fissure on a volcanic island. Volatile content of the magma decreased and viscosity increased during the eruption. Spines and domes of viscous andesite lava extruded in the terminal stage and their collapse produced a local mantle of debris represented by the tuffs at Reneault. The feeding fissure is located close to and south of the Reneault section.

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