Kentallenite
Kentallenite: local term for a melanocratic variety of monzonite composed of olivine, augite, zoned plagioclase, brown and green micas and interstitial alkali feldspar. From Kentallen, Ballachulish, Scotland. Hill & Kynaston, 1900The Kentallen intrusion
The Kentallen intrusion is a member of the Duror of Appin cluster of appinitic diorite intrusions; appinites are melanocratic hornblende-rich syenite, monzonite, or diorite. The Kentallen intrusion is about 0.6 x 0.3 km (Fig.1), typical of many of the Appinite Suite plugs. The northern and southern contacts of the intrusion are grossly discordant to the strike of the host rocks while the eastern margin is broadly concordant. The body is thus a steeply plunging pipe. The bulk of the observed intrusion is emplaced in semipelite and quartzite of the Appin Phyllite and Limestone Formation but the eastern margin is in contact with a dolomitic member. The intrusion exhibits a relatively uniform interior but varied marginal rocks and structures.
Fig.1: Map of the Kentallen appinitic intrusion. From Platten (1991).
The interior of the intrusion is composed of a uniform melanocratic olivine monzonite (kentallenite) which is well exposed in the railway and road cuttings. The rock is composed of olivine, diopside, plagioclase, orthoclase, anorthoclase, phlogopite, magnetite and apatite. The olivine and diopside are coarse grained, most being 2-8 mm, but rare elongate olivine crystals may reach 20 mm. The crystals are euhedral to subhedral and are densely packed, approaching a grain-supported fabric. Plagioclase occurs as small interstitial tablets. Phlogopite crystals are large, 10 to 30 mm, and poikilitically enclose the plagioclase and mafic minerals. Alkali feldspar either overgrows plagioclase or forms poikilitic crystals.
Changes occur in the main olivine monzonite towards the contacts. The phlogopite shows a marked decrease in grain size (from > 10 mm to < 1 mm) and a change from poikilitic to interstitial texture. The olivine is much less abundant and the large (> 10 mm) olivine crystals are absent. This finer-grained margin abuts directly against country rock in the east but in the north and south is separated from the country rocks by sheets of diverse, earlier contact facies rocks. The early contact facies is best exposed on the coast just south of Sron Garbh (Fig.1). The earliest rock is a very fine-grained porphyritic kentallenite with pyroxene and olivine phenocrysts in a very fine-grained matrix.
Two marginal intrusions are emplaced between the country rock and the early contact facies rocks in the Sron Garbh section. The first is a medium-grained pyroxene-hornblende-biotite diorite that carries conspicuous xenoliths of the Appin Quartzite. The second is a pyroxene-biotite diorite with large (5 mm) pyroxenes that carries a rounded xenolith of chilled porphyritic kentallenite.
The olivine monzonite (kentallenite) is considered to be derived from magma represented by the porphyritic chill facies (the pyroxene-biotite diorite marginal facies), which are similar to other chilled rocks in the Appinite Suite. Following the interpretation of similar rocks by Platten (1991), in-situ wall crystallization from a convecting magma formed the pyroxenite and peridotite cumulates of the marginal zones. Temporary cessation of convection allowed crystallization of meladiorite at the walls. New, more mafic, magma was introduced into the pipe, displacing the existing magmas and triggering partial collapse and removal of the wall cumulates and initial chilled facies. This new magma quenched on the walls, forming the relatively fine-grained outer facies of the main intrusion. Settlement and accumulation of olivine and pyroxene phenocrysts in the center of the pipe led to the formation of the typical olivine monzonite (kentallenite) with its densely-packed olivine and pyroxene crystals.
Sample kindly given to me by Robert Gill.
Bibliography
• Bowes, D. R. (1962) Kentallenite–lamprophyre–granite age relations at Kentallen, Argyll. Geological Magazine, 99, 119-22.
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 2x (Field of view = 7mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
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Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
Olivine (high relief and fractured due to serpentinization), pyroxene, phlogopite and feldspar crystals in a kentallenite from Kentallen. XPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |
.jpg) Olivine (high relief and fractured due to serpentinization), pyroxene (beige), phlogopite (brown) and feldspar (colorless) crystals in a kentallenite from Kentallen. PPL image, 10x (Field of view = 2mm) |