On the petrology of the ultrabasic and basic plutonic rocks of the Isle of Rum

1945 ◽  
Vol 27 (191) ◽  
pp. 127-136 ◽  
Author(s):  
S. I. Tomkeieff
Keyword(s):  
Quantitative Data ◽  
British Isles ◽  
Ring Fault ◽  
Ring Dike ◽  
On This Island ◽  
Igneous Activity ◽  
Plutonic Rocks ◽  
Western Side ◽  
Basic Rocks

The Isle of Rum contains one of the most interesting assemblages of plutonic rocks of Tertiary age in the British Isles. The pioneer work of Macculloch and the later exploratory efforts of Judd and Geikie were followed by an admirable account of the rocks by Harker, given with his usual lucidity and precision. In 1938 I spent a fortnight on this island, and this paper—the outcome of my visit—aims merely at supplementing Harker's petrographical description by certain quantitative data in respect of the ultrabasic and basic rocks found there and of recording certain observations relating to the igneous tectonics.The earliest phase of igneous activity on Rum was the eruption of doleritic and mugearitic lavas. As shown by Bailey the eruptive phase of igneous activity was followed or accompanied by the formation of a ring-fault and two subordinate vents iufilted with explosive breccia and intruded by felsite. The space inside the ring-fault was then intruded by a banded peridotite-allivalite complex and later by eucrite in the form of a semicircular ring-dike and associated sheets. Finally, a granophyre boss was intruded along the western side of the ultrabasic-basic complex.

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.

The Diorites and Associated Rocks of the Glen Tilt Complex, Perthshire

1938 ◽  
Vol 75 (4) ◽  
pp. 174-184 ◽  
Author(s):  
W. A. Deer
Keyword(s):  
Small Area ◽  
Biotite Granite ◽  
Reasonable Doubt ◽  
The South ◽  
The North ◽  
South West ◽  
Granitic Intrusion ◽  
Western Side ◽  
Basic Rocks ◽  
North Western

The Glen Tilt Complex, one of the larger masses of the Newer Granites of the Central Highlands, is included in sheet 64 of the Geological Survey of Scotland. The greater part of this complex is a granite which is bounded on the south-west and southeast by an earlier series of intermediate and basic rocks. The granites described in this contribution are restricted to a small area at the south-eastern margin of the large granitic intrusion generally known as the Beinn Dearc granite. The smaller and independent intrusion of the Sron a ‘Chro’ granite and a number of smaller masses of granite associated with the marginal strip of diorites on the north-western side of Glen Tilt have also been examined. These small isolated areas appear to be contemporaneous with the intrusion of the main Beinn Dearc mass and have been intruded between the earlier diorites and the margin of the intrusion, a feature not uncommon in many of the other Scottish Newer Granites. A small independent mass of muscovite-biotite-granite intruded into quartz-mica-diorite occurs on Conlach Mhor. Although these rocks are completely isolated from both the biotite- and muscovite-biotite-granites of the main Beinn Dearc intrusion their essential similarity with the latter leaves no reasonable doubt of their common origin.

scholarly journals Petrographic and Geochemical Studies of the Host Rock of the Chaghoo Copper Orebody in the Southwest of Karaj

2021 ◽  
Vol 34 (04) ◽  
pp. 1164-1179
Author(s):  
Alireza Rakhshani Moghadam ◽  
Mohammad Lotfi ◽  
Mohammad Reza Jafari ◽  
Afshin Ashja-Ardalan ◽  
Majid Pour Moghaddam ◽  
...  
Keyword(s):  
Host Rock ◽  
Homogenization Temperature ◽  
Low Grade ◽  
Magmatic Arc ◽  
Crustal Rocks ◽  
Enriched Mantle ◽  
Garnet Composition ◽  
Plutonic Rocks ◽  
Geochemical Studies ◽  
Basic Rocks

The study area is located 5 km southwest of Mahdasht city in Karaj on the Urmia-Dokhtar magmatic arc. In this area, Eocene volcanic and pyroclastic rocks are observed including basaltic andesite lavas, andesite, Trachyandesiticand trachyte lavas, tuff, and ignimbrite, along with plutonic rocks. There are two spectra of basic and acidic for the rocks in the area, of which basic rocks are chemically calc-alkaline in nature.Among the signs of subduction rocks in the area are enrichment in the Ta, Nb, and Ti lavas, as well as the anomaly of the HFSE index relative to the LILE of incompatible elements content. The geochemical and petrogenetic studies indicate the origin of the area’s plutonic rocks and the role of differential crystallization accompanied by the crustal rocks-contamination and digestion of magma in the evolution of the magma forming these rocks. This magma has been originated from the low-grade partial melting of an enriched mantle origin beneath the continental lithosphere with the lherzolite garnet composition at a depth of 100 to 110 km in a post-collision tensile environment. Investigating the fluids involved in the region, the homogenization temperature with the temperature of copper veins formation is between 120 to 306 ° C, with the salinity percentage varying between 6.45 to 15.96% of sodium chloride weight. Accordingly, this metamorphic hydrothermal orebodyis located in the mesothermal category. The presence of sub-faults, joints, and cracks in the host rock has provided a low-pressure environment for a proper place for copper mineralizationas veins.

A reassessment of the genera Chromatochlamys and Thelenella, and a new species of Strigula from the British Isles

2004 ◽  
Vol 36 (2) ◽  
pp. 89-95 ◽  
Author(s):  
Alan M. FRYDAY ◽  
Brian J. COPPINS
Keyword(s):  
New Species ◽  
New Combinations ◽  
British Isles ◽  
Basic Rocks ◽  
First Time ◽  
A New Species

Strigula confusa Fryday, Coppins & Common is described from the western British Isles, where it grows over bryophytes on mildly basic rocks. The concept of the genus Thelenella is expanded to include Chromatochlamys and the following new combinations are made: Thelenella larbalestieri (A. L. Sm.) Coppins & Fryday, Thelenella muscorum var. octospora (Nyl.) Coppins & Fryday, Thelenella vezdae (H. Mayrhofer & Poelt) Coppins & Fryday. Thelenella sordidula (Th. Fr.) H. Mayrhofer is reported for the first time from Europe (Svalbard).

A revision of the species of the Rhizocarpon hochstetteri group occurring in the British Isles

2002 ◽  
Vol 34 (6) ◽  
pp. 451-477 ◽  
Author(s):  
Alan M. Fryday
Keyword(s):  
North America ◽  
New Taxa ◽  
Distinct Species ◽  
Morphological Characters ◽  
British Isles ◽  
Green Is ◽  
Siliceous Rocks ◽  
Species Separation ◽  
Basic Rocks

AbstractRhizocarpon hochstetteri s. str. is shown to be an upland/montane species with relatively large ascospores. The name Rhizocarpon infernulum is resurrected for the species with smaller ascospores previously included within R. hochstetteri, but which is probably more closely related to R. cinereovirens. Lectotypes are chosen for a number of taxa, including R. cinereovirens and R. infernulum, and descriptions provided for two new taxa with small hyaline, 1–septate ascospores: R. caesium, which occurs on damp, mildly basic rocks in oceanic areas, and R. infernulum f. sylvaticum occurring on siliceous rocks in damp deciduous woodlands. All these taxa are known also from North America. Rhizocarpon discoense is shown to be a distinct species, not a synonym of R. cinereovirens. The different ascospore dimensions reported for R. hochstetteri by British and European authors are shown to be due to confusion between R. hochstetteri and R. polycarpum. A number of morphological characters are evaluated regarding their relevance to species separation in Rhizocarpon and the name Macrocarpa-green is proposed for the olivaceous pigment present in most species of Rhizocarpon and Porpidia. A key is provided for the species of Rhizocarpon with hyaline, 1– septate ascospores.

Phytogeographical and ecological relations of epiphytic lichens from Lewis and Harris with notes on other cryptogamic epiphytes

1979 ◽  
Vol 77 ◽  
pp. 295-304
Author(s):  
Harald Riedl
Keyword(s):  
Lichen Species ◽  
Epiphytic Lichens ◽  
British Isles ◽  
Epiphytic Algae ◽  
Epiphytic Lichen ◽  
Dwarf Shrubs ◽  
On This Island ◽  
Ecological Relations ◽  
First Time

SynopsisFifty-eight epiphytic lichen species are listed from Lewis and Harris, and their geographical connections are discussed. Twenty-nine of them were collected on this island for the first time. Judging from the occurrence of Lecanactis homalotropa, Pyrenula laevigata and Ramalina obtusata (which are confined to very few places in the British Isles today and may be regarded as relics) on a small number of old and mostly dying sycamores near Rodel at the southern end of Harris, there had been an older forest of which these trees form the last remnants and from which the colonization of Stornoway Woods may have originated. Some of the lichens also occur on dwarf-shrubs which have certainly been present all the time, or on rocks or ground. Man may have played a part in introducing lichen-species along with timber. A few notes on epiphytic algae, fungi, mosses and ferns are added.

Does the British Isles Paleocene dike swarm reflect the former location of the Iceland hotspot?

2022 ◽  
Author(s):  
Ian W.D. Dalziel ◽  
Lawrence A. Lawver
Keyword(s):  
Tectonic Setting ◽  
Three Dimensional ◽  
Ocean Basin ◽  
British Isles ◽  
Dike Swarm ◽  
Three Dimensional Modeling ◽  
The North ◽  
Magmatic Rocks ◽  
Igneous Activity ◽  
Distant Location

ABSTRACT The original location and tectonic setting of the prominent Paleocene dike swarm in the British Isles are reconstructed for a “tight fit” of the North Atlantic region prior to any Cenozoic opening of the ocean basin between Greenland and Europe. The present-day northwest-southeast–oriented swarm originally trended toward southern Greenland and the locations of magmatic rocks of comparable age along the eastern and western margins of Greenland and approximately the position of the Iceland hotspot at 70–60 Ma in a “fixed hotspot” model. This raises the possibility that the northeast-southwest–oriented extensional stress field in which the dikes and associated central igneous complexes were emplaced may have been generated by impingement on the base of the lithosphere by a rising plume beneath present-day West Greenland. It is speculated, on the basis of seismic tomography and three-dimensional modeling, that the Paleocene igneous activity in the British Isles may have resulted from flow of a hot “finger” of upper mantle outward from the plume, perhaps controlled by preexisting lithospheric structures and the distant location of a second Paleocene volcanic province in central Europe.

scholarly journals The Rum Igneous Centre, Scotland

2014 ◽  
Vol 78 (4) ◽  
pp. 805-839 ◽  
Author(s):  
C. H. Emeleus ◽  
V. R. Troll
Keyword(s):  
Crustal Contamination ◽  
Central Complex ◽  
Research Progress ◽  
Current Status ◽  
British Geological Survey ◽  
Ring Fault ◽  
Mixed Acid ◽  
Heating Event ◽  
Main Ring ◽  
Igneous Activity

AbstractThe publication of the British Geological Survey memoir on Rum and the Small Isles in 1997 was followed by a period of intense petrological and mineralogical research, leading to some 40 papers, books and other publications. The research progress since then is reviewed here and integrated with the information previously available to provide an overview of the current status of understanding of the centre. New data on the acidic and mixed acid/basic magmas of the early Rum caldera demonstrate that frequent mafic replenishments were the main driver for magmatic activity at Rum right from its initial stages. The caldera is bound by the Main Ring Fault, a structure which probably also exercised an influence on the emplacement of the subsequent basic and ultrabasic intrusions. The later emplacement of gabbros and ultrabasic rocks caused only limited thermal metamorphism of the surrounding Torridonian sandstones, contrasting markedly with the crustal isotope signatures of the early intracaldera ignimbrite magmas and the intense alteration of uplifted masses of Lewisian gneiss within the ring fault. Rare picritic dykes provide an indication of the possible parent magma for the mafic and ultrabasic rocks, but these, as with most other magmatic rocks on Rum, have undergone varying degrees of crustal contamination, involving both Lewisian granulite and amphibolite-type crust but, notably, no Moine metasedimentary compositions as is the case at the nearby Ardnamurchan centre. Detailed textural studies on the gabbroic and ultrabasic rocks allow a distinction between intrusive peridotites and peridotite that forms part of the classic layered cumulate units of Rum and, furthermore, this work and that on the chromite seams and veins in these rocks shows that movement of trapped magma and magma derived from later intrusions, may produce textures regarded previously as of primary cumulate origin. Sulfides in the chromitite seams and ultrabasic rocks, in turn, show possible influences from assimilated Mesozoic sediments. Igneous activity on Rum was short-lived, possibly only between 0.5 and 1 m.y. in duration and commenced at ∼60.5 Ma. The Rum Central Complex was extinct by the time the main activity at the nearby Skye Central Complex commenced (∼59 Ma). From recent apatite fission-track studies it seems probable that Rum, in common with other Palaeogene centres, underwent a brief, but significantly later heating event (∼45 Ma).

Tectonic setting of Avalonian volcanic and Plutonic rocks in the Caledonian Highlands, southern New Brunswick, Canada

1996 ◽  
Vol 33 (2) ◽  
pp. 156-168 ◽  
Author(s):  
S. M. Barr ◽  
C. E. White
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Continental Margin ◽  
Tectonic Setting ◽  
Sedimentary Rocks ◽  
Igneous Activity ◽  
Appalachian Orogen ◽  
Group Form ◽  
Plutonic Rocks ◽  
Clastic Sedimentary

The Caledonian Highlands of southern New Brunswick consist of Late Proterozoic to Cambrian rocks generally considered typical of the Avalon terrane of the northern Appalachian Orogen. Mainly tuffaceous volcanic and sedimentary rocks of the Broad River Group and cogenetic dioritic to granitic plutons with ages ca. 620 Ma form most of the eastern Caledonian Highlands. They have petrological features indicative of origin in a continental margin subduction zone. Significantly younger ca. 560–550 Ma dacitic to rhyolitic lapilli tuffs and flows, laminated tuffaceous siltstone, basaltic and rhyolitic flows, and clastic sedimentary rocks of the Coldbrook Group form most of the western highlands, and occur locally throughout the highlands. The mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group. This voluminous subaerial magmatism may have formed during postorogenic extension in the earlier ca. 620 Ma subduction zone complex represented by the Broad River Group and associated plutons. This tectono-magmatic model differs from other interpretations that related most of the igneous units to ca. 630–600 Ma subduction, and did not recognize the importance of ca. 560–550 Ma magmatism. The ca 620 Ma subduction-related volcanic and plutonic rocks of the Caledonian Highlands are comparable to units in other parts of the Avalon terrane, but voluminous ca. 560–550 Ma igneous activity like that represented by the Coldbrook Group and related plutons has not been documented yet in other Avalonian areas.

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