VI.—The Picrite of Foel lwyd, Carnarvonshire

1913 ◽  
Vol 10 (3) ◽  
pp. 108-109
Author(s):  
J. E. Wynfield Rhodes
Keyword(s):  
Volcanic Rocks ◽  
Igneous Rocks ◽  
Geological Survey ◽  
The South ◽  
North Wales

During a short holiday to North Wales in Whit-week, 1910, I was investigating the igneous rocks to the south of Llanfairfechan, more particularly the intrusive greenstones of the Geological Survey map. Since the publication of this map, over fifty years ago, several districts within it have been investigated in greater detail, especially as to the volcanic rocks, but much remains to be done petrographically. One of these greenstones turned out to be of exceptional interest, being of a type of rock hitherto, I believe, unrecorded in North Wales, so another visit was made to it in August, 1912.

scholarly journals Tertiary volcanic rocks from Bontekoe Ø, East Greenland

1983 ◽  
Vol 116 ◽  
pp. 1-13
Author(s):  
A Noe-Nygaard ◽  
A.K Pedersen
Keyword(s):  
Volcanic Rocks ◽  
Igneous Rocks ◽  
Geological Survey ◽  
The South ◽  
East Greenland ◽  
The Third ◽  
The North

In East Greenland Tertiary igneous rocks are found from Kap Gustav Holm (66°30'N) in the south to Shannon (75°30'N) in the north. Within this region three areas are covered by plateau basalts; (a) south of Scoresby Sund (700N), (b) far inland on the nunataks at 74°N and (c) along the coast between 73° and 75°30'N. Bontekoe ø belongs to the third region (fig. 1). The geology of this part of East Greenland is largely known from the activities of Lauge Koch's expeditions during which, curiously enough, the areas dominated by Tertiary volcanism were almost neglected. To remedy this the Geological Survey of Greenland supported some reconnaissance work that was carried out in connection with other geological activity in the region over the last few years. Results of this work were given by NoeNygaard & Pedersen (1974), Upton & Emeleus (1977), Hald (1978), Brooks et al. (1979) and Upton et al. (1980, 1982, in press).

Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996

1997 ◽  
pp. 66-74
Author(s):  
Henrik Stendal ◽  
Wulf Mueller ◽  
Nicolai Birkedal ◽  
Esben I. Hansen ◽  
Claus Østergaard
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Field Work ◽  
Igneous Rocks ◽  
Border Zone ◽  
The South ◽  
East Greenland ◽  
North West ◽  
Arc Setting

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Mueller, W., Birkedal, N., Hansen, E. I., & Østergaard, C. (1997). Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 66-74. https://doi.org/10.34194/ggub.v176.5064 _______________ The multidisciplinary SUPRASYD project (1992–96) focused on a regional investigation of the Palaeoproterozoic Ketilidian orogenic belt which crosses the southern tip of Greenland. Apart from a broad range of geological and structural studies (Nielsen et al., 1993; Garde & Schønwandt, 1994, 1995; Garde et al., 1997), the project included a mineral resource evaluation of the supracrustal sequences associated with the Ketilidian orogen (e.g. Mosher, 1995). The Ketilidian orogen of southern Greenland can be divided from north-west to south-east into: (1) a border zone in which the crystalline rocks of the Archaean craton are unconformably overlain by Ketilidian supracrustal rocks; (2) a major polyphase pluton, referred to as the Julianehåb batholith; and (3) extensive areas of Ketilidian supracrustal rocks, divided into psammitic and pelitic rocks with subordinate interstratified mafic volcanic rocks (Fig. 1). The Julianehåb batholith is viewed as emplaced in a magmatic arc setting; the supracrustal sequences south of the batholith have been interpreted as either (1) deposited in an intra-arc and fore-arc basin (Chadwick & Garde, 1996), or (2) deposited in a back-arc or intra-arc setting (Stendal & Swager, 1995; Swager, 1995). Both possibilities are plausible and infer subduction-related processes. Regional compilations of geological, geochemical and geophysical data for southern Greenland have been presented by Thorning et al. (1994). Mosher (1995) has recently reviewed the mineral exploration potential of the region. The commercial company Nunaoil A/S has been engaged in gold prospecting in South Greenland since 1990 (e.g. Gowen et al., 1993). A principal goal of the SUPRASYD project was to test the mineral potential of the Ketilidian supracrustal sequences and define the gold potential in the shear zones in the Julianehåb batholith. Previous work has substantiated a gold potential in amphibolitic rocks in the south-west coastal areas (Gowen et al., 1993.), and in the amphibolitic rocks of the Kutseq area (Swager et al., 1995). Field work in 1996 was focused on prospective gold-bearing sites in mafic rocks in South-East Greenland. Three M.Sc. students mapped showings under the supervision of the H. S., while an area on the south side of Kangerluluk fjord was mapped by H. S. and W. M. (Fig. 4).

III.—A remarkable instance of Rock Differentiation

1908 ◽  
Vol 5 (8) ◽  
pp. 344-352
Author(s):  
Harford J. Lowe
Keyword(s):  
Igneous Rocks ◽  
Geological Survey ◽  
The South ◽  
Different Parts ◽  
The Hamlet

Upon Sheet 339 (Devonshire) of the new Geological Survey maps, one instance out of the very numerous outcrops of igneous rocks thereon indicated proves to be of unusual interest by reason of its peculiar constitutional modifications in different parts of the same mass. The rockin question occurs about four and a quarter miles 15° north of west from Newton Abbot, near to the hamlet of Bickington, within the limits of a farm named Lurcombe. It is an intrusive amidst the shales and grits of the Culm, occurring almost on the junction-line between that series and the Devonian, whose massive limestones and volcanics dominate it in elevation within a quarter of a mile on the south-east.

scholarly journals IX.—Firstfruits of a Geological Examination of Snowdon

1900 ◽  
Vol 7 (6) ◽  
pp. 267-273
Author(s):  
J. R. Dakyns
Keyword(s):  
Volcanic Rocks ◽  
Geological Survey ◽  
Lower Mass ◽  
Geological Investigation ◽  
Intermediate Band ◽  
Volcanic Material ◽  
North Wales ◽  
Great Mass

Ars longa, vita brevis. This is especially true when one reaches the age of 64. I therefore commit to paper some of the results of a geological investigation of Snowdon on which I am engaged. I start of course from the work of Messrs. Ramsay and Selwyn embodied in the Geological Survey Map of Snowdon and Ramsay's memoir on North Wales. To make what I have to say clear I may state that the rocks of Snowdon are by Ramsay and Selwyn divided into three principal groups, viz.: A, an upper felsitic lava ; an intermediate band (B) of bedded fossiliferous rocks of Bala age, containing much volcanic material, called the calcareo-felspathic ashy series ; and a lower mass (C) of felsitic rocks. This lower mass is in some places divided by sedimentary bands consisting of slates and grits. Below C come blue slates and grits, with occasional volcanic bands, D; and below D the great mass of volcanic rocks (E) which form Glyder Fach and Y Tryfan.

Radiolarian biostratigraphic constraints for latest Jurassic-earliest Cretaceous submarine volcanic activity in the Tethyan oceanic realm of the Sevan ophiolite (Armenia)

2012 ◽  
Vol 183 (4) ◽  
pp. 319-330 ◽  
Author(s):  
Gayané Asatryan ◽  
Taniel Danelian ◽  
Lilit Sahakyan ◽  
Ghazar Galoyan ◽  
Monique Seyler ◽  
...  
Keyword(s):  
Shallow Water ◽  
Volcanic Activity ◽  
Sedimentary Cover ◽  
Volcanic Rocks ◽  
Greenschist Facies ◽  
Igneous Rocks ◽  
The South ◽  
Lake Sevan ◽  
Northern Flank ◽  
Radiolarian Assemblages

AbstractBiostratigraphic constraints for the sedimentary cover of the ophiolites preserved in Armenia are of key importance for the palaeogeographic and geodynamic reconstruction of the greater area between Eurasia and the South-Armenian block, which is a micro-continent of Gondwanian origin. We present here radiolarian data obtained from radiolarites that are intercalated in a sequence of mafic volcanic rocks on the northern flank of the Dali valley (east of Lake Sevan), which is considered to be part of the Sevan ophiolite. Mafic sills and dykes with well-preserved igneous textures are probably part of the same sequence. The pseudomorphosis of primary phases indicates that the igneous rocks are strongly affected by alteration in the greenschist facies condition. The plagiogranites that are present in this locality appear to be intrusive into the mafic sequence. The radiolarian assemblages extracted from radiolarian cherts intercalated in the mafic volcanic rocks are dated as latest Tithonian-Late Valanginian; they contain metric rounded blocks of oolitic limestones with crinoid fragments, suggesting that these shallow water limestones slid during the Jurassic/Cretaceous transition into a rugged oceanic floor in which radiolarian ooze accumulated.

Volcanic pebbles from Pleistocene gravels in Norfolk and Essex

1977 ◽  
Vol 114 (3) ◽  
pp. 219-225 ◽  
Author(s):  
R. W. Hey ◽  
P. J. Brenchley
Keyword(s):  
Volcanic Rocks ◽  
Igneous Rocks ◽  
East Anglia ◽  
Source Areas ◽  
Fine Grained ◽  
North Wales ◽  
Almost All

SummaryIn the pre-Anglian Pleistocene of East Anglia and Essex are unfossiliferous gravels with pebbles of flint, quartz, quartzite, chert and volcanic rocks. All appear to belong to the Kesgrave Sands and Gravels of Rose & Allen (1976), which are largely or wholly fluviatile and probably of Beestonian age. Forty-six of the volcanic pebbles, from three different localities, have been examined microscopically. Almost all are fine-grained acid igneous rocks or vitric tuffs, evidently derived from a single suite. Various possible source-areas are considered, of which North Wales, with its Ordovician volcanics, is thought to be the most likely.

The sedimentology of the South Connemara Group, western Ireland – a possible Ordovician trench-fill sequence

1984 ◽  
Vol 121 (5) ◽  
pp. 505-514 ◽  
Author(s):  
G. D. Ffrench ◽  
D. Michael Williams
Keyword(s):  
Volcanic Rocks ◽  
Source Area ◽  
Igneous Rocks ◽  
Accretionary Wedge ◽  
Sedimentary Sequence ◽  
The South ◽  
Submarine Channels ◽  
Continental Source ◽  
Western Ireland ◽  
Sandstone Facies

AbstractThe stratigraphy of the ?Ordovician South Connemara Group is described. The group is approximately 3 km thick and includes sedimentary and volcanic rocks. The sedimentary elements of the succession include conglomerates, sandstones, shales, cherts and minor limestone breccias. The Lettermullen Formation exhibits the thickest continuous sedimentary sequence in the group. It is divided into five facies: a conglomerate facies, thick sandstone facies, medium sandstone facies, sandstone/siltstone facies, and chert facies. The sedimentary features of these rocks include channelling and grading and are described in terms of Bouma units where applicable. The coarse elements of the formation are thought to represent deposition in, or proximal to, submarine channels feeding a more distal depositional site represented by the finer elements. Igneous rocks of the group include pillowed and non-pillowed lavas, massive amphibolites and minor tuffs often in conformable contact with the sediments. Petrography of conglomerate clasts and sandstones indicates derivation from a continental source area. Palaeocurrent analysis reveals a primary easterly mode with a subsidiary northerly mode. It is suggested that the group exhibits some characteristics of trench-fill sequences and the succession may be related to similar environments within the Southern Uplands accretionary wedge.

Notes on the Petrology of the Bufumbira Volcanic Rocks of Uganda

1930 ◽  
Vol 67 (11) ◽  
pp. 491-499 ◽  
Author(s):  
W. C. Simmons
Keyword(s):  
Volcanic Rocks ◽  
Field Work ◽  
Volcanic Field ◽  
Geological Survey ◽  
The South ◽  
The West ◽  
South West ◽  
Short Summary ◽  
Belgian Congo

In view of the probability that there is likely to be some little delay in publishing the official Memoir on the Bufumbira volcanic rocks, which is in course of preparation by Mr. A. D. Combe and the writer, with, we hope, collaboration with authorities in England, permission has been given to publish a short summary of the results so far obtained in the investigation of these rocks. Mr. Combe has made a careful geological survey of the ground and has separated on his map forty-nine flows from nearly forty different centres situated at the south-west corner of the Uganda Protectorate. The remainder of this large volcanic field lies in the Belgian Congo to the west and south, and though all of those volcanoes, several of which are still active, have been visited by geologists and specimens of the rocks obtained, no very detailed field-work has been published on them, either by us or any other observers up to the present time; so far as is known to the writer.

scholarly journals III.—An Irish Augitite

1892 ◽  
Vol 9 (8) ◽  
pp. 348-350 ◽  
Author(s):  
Bernard Hobson
Keyword(s):  
Igneous Rocks ◽  
Geological Survey ◽  
The South ◽  
Isle Of Man ◽  
Coal Measures

When writing my paper “On the Igneous Rocks of the South of the Isle of Man,” I was led to compare a Manx melaphyre, from Scarlet Point, with a rock described by Prof. E. Hull as a melaphyre, occurring at Ballytrasna, near Limerick, and belonging to the “Upper Trap-band,” a little below the basal shales of the Coal-measures. Through the kindness of Prof. Hull, a chip of the rock was sent to me by the Irish Geological Survey. The specimen was black and basaltic-looking. I did not obtain satisfactory sections of it in time for my paper, but have since had excellent ones made. On examining them I was immediately struck by the resemblance of the rock to the augitite of Paschkapole, between Velmin and Boreslau, in Bohemia, with a section of which I compared it. Professor Hull describes the rock of Ballytrasna as containing “numerous large crystals and groups of banded felspar”; but I failed to find a single felspar in four sections, nor did I observe any in Allport's section, No. 1902, from the same locality, which agrees with my sections.

Sign in / Sign up

Export Citation Format

Share Document