Sector-zoned augite megacrysts in Aleutian high alumina basalts: implications for the conditions of basalt crystallization and the generation of calc-alkaline series magmas

1999 ◽  
Vol 135 (2-3) ◽  
pp. 277-290 ◽  
Author(s):  
Carla S. Whittington ◽  
Young-Rok Park ◽  
James G. Brophy
Keyword(s):  
High Alumina ◽  
Calc Alkaline ◽  
Basalt Crystallization

Chlorites in a spectrum of igneous rocks: mineral chemistry and paragenesis

1995 ◽  
Vol 59 (394) ◽  
pp. 129-141 ◽  
Author(s):  
Abdel-Fattah M. Abdel-Rahman
Keyword(s):  
Structural Type ◽  
Mineral Chemistry ◽  
Igneous Rocks ◽  
The Other ◽  
High Alumina ◽  
X Ray Diffraction ◽  
Calc Alkaline ◽  
Peralkaline Granite ◽  
Igneous Complexes ◽  
Data Points

AbstractThe chlorite data presented are from four igneous complexes covering the compositional spectrum of igneous rocks (gabbro to granite) of orogenic and anorogenic settings. The four igneous complexes are; early orogenic gabbro-diorite-tonalite (D-T) suite, late orogenic granodiorite-adamellite (G-A) suite (both are calc-alkaline suites), high-alumina trondhjemite (TR), and anorogenic peralkaline granite (PGR).Chlorites in these igneous rocks show characteristic compositional fields. The Mg vs Fe plot provides the best discriminant, as data points define three compositionally different groups. Phases in the PGR are Fe-rich, siliceous, interlayered chlorite-smectite (Fe/Mg = 8.6), and differ significantly from those in the calc-alkaline D-T and G-A rocks which are Mg-rich chlorites (Fe/Mg = 0.6–0.8). The X-ray diffraction data for the peralkaline granite samples show superlattice reflections at approximately 31 Å (air-dried) and 34 Å (ethylene glycollated), thus suggesting the presence of an expandable (smectite-like) component in this interlayered (chlorite-smectite) phyllosilicate phase. Chlorites in the peraluminous TR rocks contain Fe/Mg values intermediate between the other two types (Fe/Mg = 1.3). Tetrahedral Al (AlZ) values are remarkably low (0–0.5) in phyllosilicates in the PGR, but vary from 1.9–2.5 in chlorites from the other suites. Yet, these chlorite groups with their generally low AlZ values are distinct from the more stable (type IIb) metamorphic chlorites. Sedimentary chlorites are somewhat similar, in their low AlZ values and metastable structural type, to chlorites in igneous rocks.In the calc-alkaline rocks, chlorite may have been formed at the expense of both biotite [biotite + 3M + 3H2O = chlorite + A], and calcic amphibole [2 Ca-amphibole + 6H2O + 5O2 + 1.8Al = 1 chlorite + 8SiO2 + A], where M = Fe, Mg, Al, and A = K, Na, Ca. The alteration of alkali amphibole in the peralkaline rocks may have produced interlayered chlorite-smectite via this reaction; [1 Na-amphibole + 7H2O + 2.5O2 + M = 1 chlorite-smectite + A]. The presence of such interlayered chlorite-smectite which typically form at low T (150–200°C) suggests that the region was not affected by any major reheating events, which is consistent with the nature of the feldspars.

scholarly journals A Gondwana pre-break up related magmatism in Bafoussam area, west Cameroon: source characteristics and 40Ar/39Ar geochronology

2019 ◽  
Vol 7 (1) ◽  
pp. 23
Author(s):  
Gus Djibril Kouankap Nono ◽  
Pierre Wotchoko ◽  
Evine Laure Tanko Njiosseu ◽  
Sylvestre Ganno ◽  
Joelle Flore Tene Djoukam ◽  
...  
Keyword(s):  
High Temperature ◽  
Early Stage ◽  
Tectonic Setting ◽  
Central Africa ◽  
High Alumina ◽  
Primitive Mantle ◽  
Plate Tectonic ◽  
Calc Alkaline ◽  
Source Characteristics ◽  
Break Up

The Gondwana pre-break up related formations in Bafoussam area are transitional calc-alkaline doleritic dykes exhibiting high Alumina and low Ti-Mg contents. Their REE compositions are similar to those of E-MORB (Nd/Nb≈1, Zr/Nb≤20). A high partial melting of about 20% of Garnet peridotites source having primitive mantle composition, is inferred to the studied rocks. They are slightly evolved 50<Mg#<54, and its clinopyroxenes are augite of high temperature (600°C-1100°C). The studied dykes were emplaced in a within-plate tectonic setting and yield a 40Ar-39Ar plateau ages of 229±7Ma. These ages are slightly different from those of dolerites from the Oban-Obudu massif (Nigeria), from the basaltic dyke of the Cameroon Volcanic Line and from the Karoo-Ferrar mafic magmatism, all interpreted as magmatism that preceded the break-up of Gondwana. The emplacement age of 229±7Ma of dolerites from Bafoussam area relates them to the very early stage of Gondwana pre-break up magmatism in central Africa.    

Geology of the East Bull Lake gabbro–anorthosite pluton, Algoma District, Ontario

1989 ◽  
Vol 26 (2) ◽  
pp. 357-375
Author(s):  
G. F. D. McCrank ◽  
D. C. Kamineni ◽  
R. B. Ejeckam ◽  
R. Sikorsky
Keyword(s):  
High Alumina ◽  
Calc Alkaline ◽  
Plan View ◽  
Mafic Dykes ◽  
Water Interaction ◽  
Complex Fracture ◽  
Rock Water Interaction ◽  
Wide Range ◽  
Layered Gabbro ◽  
Dextral Strike Slip

The East Bull Lake Pluton, a layered gabbro–anorthosite intrusion 90 km west of Sudbury, Ontario, is in an inward-dipping lopolith and is 780 m thick in the centre and elliptical in plan view (13.5 km × 3.5 km). It intruded Archean metavolcanic and metaplutonic rocks of the Superior Province during the Early Proterozoic (2480 Ma).The intrusion consistes of a basal anorthositic unit, succeeded by rhythmic-layered gabbro, troctolite, layered gabbro, and massive and dendritic gabbro units. It is offset by the west-northwest-striking, subvertical Folson Lake fault. South of this fault, only anorthosite and massive and dendritic gabbro are exposed. North of the fault, subsurface lithologies intersected by me boreholes correlate with surface lithologies. Troctolite, the most distinctive marker that can be correlated between boreholes and surface exposures, confirms the general attitude and shape of the layers and lopolith.Chemical composition of the intrusion ranges from high-Mg tholeiite to calc-alkaline high-alumina basalts.Fractures occur in several preferred orientations, the most common being northwesterly, subparallel to the Folson Lake fault, numerous mafic dykes, and topographic lineaments. Complex fracture-filling and alteration mineralogies formed under a wide range of P–T conditions representative of epidote-amphibolite – greenschist facies, pumpellyite–prehnite facies, zeolite facies, and low-temperature rock–water interaction processes.The last movement on the Folson Lake fault was a dextral strike slip of up to 3.0 km that postdates most mafic dykes.

Geochemistry of Palaeozoic–Mesozoic Pacific rim orogenic magmatism, Thurston Island area, West Antarctica

1993 ◽  
Vol 5 (3) ◽  
pp. 281-296 ◽  
Author(s):  
Philip T. Leat ◽  
Bryan C. Storey ◽  
Robert J. Pankhurst
Keyword(s):  
Trace Element ◽  
High Alumina ◽  
Dyke Swarm ◽  
West Antarctica ◽  
Calc Alkaline ◽  
Magmatic Arc ◽  
Pacific Margin ◽  
Mafic Magmas ◽  
Oceanic Plates ◽  
End Members

Thurston Island, and the adjacent Eights Coast and Jones Mountains, record Pacific margin magmatism from Carboniferous to Late Cretaceous times. The igneous rocks form a uniformly calc-alkaline, high-alumina, dominantly metaluminous suite; some relatively fractionated granitoids are mildly peraluminous. The magmas were hydrous, a result of subduction. Gabbros have compositions outside the range of mafic volcanic and hypabyssal rocks, as a result of cumulate processes. Trace element compositions of the mafic magmas range from a low La/Yb, Th/Ta end-member close to E-MORB in composition, perhaps contaminated by crust, to a high La/Yb, Th/Ta end-member, close to shoshonite, with strong magmatic arc trace element character. This variation may be a result of mixing of tholeiitic and shoshonitic end-members. Most silicic rocks could have been generated batch-wise from mafic magmas by fractional crystallization of a phenocryst assemblage dominated by plagioclase, pyroxene ± amphibole, as seen in the cumulates. Cessation of magmatism at about 90 Ma approximately coincided with collison of a spreading centre between the Phoenix and Pacific oceanic plates with the continent margin subduction zone. The rifting of New Zealand from West Antarctica and associated extension probably was responsible for emplacement of a coast-parallel Cretaceous dyke swarm.

scholarly journals Plutonic development of the Ilordleq area, South Greenland. Part II: Late-kinematic basic dykes

1968 ◽  
Vol 70 ◽  
pp. 1-104
Author(s):  
J Watterson
Keyword(s):  
Water Pressure ◽  
Amphibolite Facies ◽  
High Alumina ◽  
Chemical Analyses ◽  
Calc Alkaline ◽  
Mineral Assemblages ◽  
Volcanic Suite ◽  
Characteristic Features

Basic dykes with primary amphibolite facies mineral assemblages were emplaced along active transcurrent fissures in the closing stages of a period of plutonic activity. The order of crystallisation, determined from petrographic evidence and from the composition of filter-pressed fractions, is consistent with consolidation of the magma at ca. 4000 bars water pressure at 800-850°C. The marked calc-alkaline trend of differentiation and the high-alumina characteristics of some dykes, illustrated by ten chemical analyses, is shown to be the likely result of a fractionation dominated by the separation of mafic from felsic phases. This type of fractionation is shown to be a consequence of the conditions under which the dykes crystallised, and is contrasted with fractionation taking place under conditions of low water pressure. The type of differentiation demonstrated by the dyke suite is shown to be capable of producing many of the characteristic features of the orogenic volcanic suite, including relatively large amounts of intermediate differentiates. Oblique foliation in the dykes is shown to be related to transcurrent movements and is interpreted by reference to a model of rotational homogenous strain.

Excelsior high-alumina clay deposit, Spokane, Washington

1954 ◽  
Author(s):  
V.E. Scheid ◽  
J.W. Hosterman ◽  
I.G. Sohn
Keyword(s):  
High Alumina ◽  
Clay Deposit
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