Calc-alkaline volcanic rock series derived from alkali-olivine basalt magma

1966 ◽  
Vol 71 (24) ◽  
pp. 6127-6135 ◽  
Author(s):  
Ken-ichiro Aoki ◽  
Yoshio Oji
Keyword(s):  
Volcanic Rock ◽  
Olivine Basalt ◽  
Basalt Magma ◽  
Rock Series ◽  
Calc Alkaline ◽  
Alkali Olivine Basalt ◽  
Volcanic Rock Series

Exceptional REE-enrichment in apatite during the low pressure fractional crystallisation of alkali olivine basalt; an example from the British Tertiary Igneous Province

1999 ◽  
Vol 90 (4) ◽  
pp. 273-285 ◽  
Author(s):  
R.J. Preston ◽  
M.J. Hole ◽  
J. Still
Keyword(s):  
Olivine Basalt ◽  
Low Pressure ◽  
Basalt Magma ◽  
Accessory Phase ◽  
Igneous Province ◽  
Alkali Olivine Basalt ◽  
Typical Scheme ◽  
Common Variety ◽  
Fluor Apatite

AbstractThe Cnoc Rhaonastil dolerite boss on Islay, NW Scotland represents a body of alkali-olivine basalt magma which differentiated at low pressure and in situ, from dolerite through teschenite to minor nepheline-syenite. The syenites occur as isolated pods and pegmatitic schlieren within the leucodolerite, and have an exotic mineralogy including Zr-aegirine, Zr-arfvedsonite, Ca-catapleiite, zirconolite and aenigmatite. Fluor-apatite occurs as an accessory phase in the dolerite, but becomes more abundant within the teschenite and syenites. Total REE contents within apatites in the dolerites are typically low (σREE = 0·57–3·21 wt.% oxide), the highest REE contents occurring in irregular, deuterically altered rims and internal patches. The REE-enriched rims also have slightly elevated SiO2 contents at 0·81–0·95 wt.%, suggesting that the substitution scheme Ca2++P5+ ⇔ REE3++Si4+ was operating. These apatites have up to 0·08 wt.% Cl and 3·7 wt.% F, with most being almost pure end-member fluor-apatite. The majority of the teschenite apatites show the least REE-enrichment (σREE = 0·27–0·45 wt.%), coupled with low Na (<0·12 wt.%) and low SiO2 (<0·39 wt.%) contents. However, within the syenites two distinct populations of apatite exist. The first, most common, variety consists of unzoned, low-REE apatites (max. 3·1 wt.% σREE, again in irregular rims and patches), whereas the second variety is often complexly zoned, and has variably enriched zones up to a maximum σREE content of 42 wt.%; this is by far the most REE-enriched natural fluor-apatite so far reported from the British Isles. The REE-enriched zones are often less than 3 μm wide, and have Na content up to 5·4 wt.% Na2O, implying that the substitution scheme Na+ + REE3+⇔2Ca2+ dominated over the more typical scheme involving Si4+ which operated in the dolerites and teschenite. Other zones are either variably enriched in Y (up 2·1 wt.% Y2O3) or Th (up to 0·85 wt.% ThO2). However, there is no correlation between Y and REE contents, suggesting that crystallographic factors were involved in apatite Y and REE partitioning. The REE-rich apatites have very low Cl content (<0·04 wt.%), but high F concentrations (<2·8 wt.%). It is believed that these strongly enriched apatites crystallised under disequilibrium conditions from isolated, variably REE-enriched domains, within the fluid-rich residual syenitic magma. These domains may have been generated by the prior crystallisation of monazite, Ca-catapleiite or zirconolite, which can be found as small inclusions within albite and interstitial analcime. The dynamic process of slumping of the denser teschenite back into the leucodolerite crystal mush is believed to have played an important role in the release of deuteric fluids and the concentration of residual magmas.

scholarly journals Igneous stratigraphy and internal structure of the Little Minch Sill Complex, Trotternish Peninsula, northern Skye, Scotland

1991 ◽  
Vol 128 (1) ◽  
pp. 51-66 ◽  
Author(s):  
Sally A. Gibson ◽  
Adrian P. Jones
Keyword(s):  
Internal Structure ◽  
Magma Chamber ◽  
Thermal Gradient ◽  
Olivine Basalt ◽  
Small Scale ◽  
Basalt Magma ◽  
Alkali Olivine Basalt ◽  
Modal Layering ◽  
Crustal Magma

AbstractDetailed sampling of the Little Minch Sill Complex reveals that it is composed of both single and multiple sills. These are formed of three main, genetically related units: picrite, picrodolerite and crinanite, which are the result of differentiation of an alkali-olivine basalt magma (approximately 10% MgO) in an upper-crustal magma chamber. Variations in igneous stratigraphy and the presence of internal chills in the Trotternish sills suggest that they were emplaced by multiple intrusion and subsequently differentiated in situ. Changes in petrography adjacent to pegmatite veins and textures within picrite units indicate compaction and filter-pressing were important processes after emplacement. Rhythmic layering (1 cm to 1 m thick) is conspicuous in the sills near contacts but does not involve cryptic mineral variation. Such modal layering may be more common than realised in relatively small-scale intrusions and maybe modelled in terms of in situ differentiation under conditions of significant undercooling in a changing thermal gradient at the synthetic for-sterite-diopside-anorthite eutectic.

Fluid activity in the lower crust and upper mantle: mineralogical evidence bearing on the origin of amphibole and scapolite in ultramafic and mafic granulite xenoliths

1987 ◽  
Vol 51 (363) ◽  
pp. 719-732 ◽  
Author(s):  
A. J. Stolz
Keyword(s):  
Basaltic Magma ◽  
Olivine Basalt ◽  
Basalt Magma ◽  
Crust And Upper Mantle ◽  
Ultramafic Xenoliths ◽  
Basaltic Magmas ◽  
Alkali Olivine Basalt ◽  
Textural Evidence ◽  
Granulite Xenoliths ◽  
Mineralogical Evidence

AbstractXenoliths in an olivine nephelinite from the McBride Province, North Queensland, include Cr-diopside lherzolites, spinel and garnet websterites, felsic, 2-pyroxene and garnet granulites, and hornblendites. The spinel and garnet websterites are interpreted as crystal segregations from olivine basalt or alkali olivine basalt magma at ∼ 12 kbar followed by isobaric cooling (to approximately 900–1000°C) and subsolidus reequilibration. Garnet and 2-pyroxene granulites are mineralogically and texturally distinct and are considered to represent relatively large degrees of crystallization of basaltic magmas at comparable or slightly lower pressures (8–12 kbar). Mafic and ultramafic xenoliths have been modified to varying degrees following the relatively recent influx of a H2O- and CO2-bearing fluid. Variable amounts of amphibole and mica developed in response to the introduced fluid and it is argued that some hornblendites are the end-products of this process acting on spinel websterites. Felsic and 2-pyroxene granulite xenoliths display only minor evidence of increased PH2O. Mineralogical and textural evidence indicates high-sulphur Ca-rich scapolite in several garnet granulites did not form in response to the increased fluid activities. It is proposed the scapolite was a primary cumulate phase precipitated from alkali basaltic magma under elevated fo2 and fso2 conditions.

Discovery of Mg-righ volcanic rock series in western Altay area, Xinjiang and its geologic significance

1999 ◽  
Vol 44 (18) ◽  
pp. 1685-1688 ◽  
Author(s):  
Hecai Niu ◽  
Jifeng Xu ◽  
Xueyuan Yu ◽  
Fanrong Chen ◽  
Zouping Zheng
Keyword(s):  
Volcanic Rock ◽  
Rock Series ◽  
Volcanic Rock Series
Sign in / Sign up

Export Citation Format

Share Document