Petrology of the Igneous Rocks from the West Gir Forest, Kathiawar, India

1932 ◽  
Vol 40 (2) ◽  
pp. 154-163 ◽  
Author(s):  
S. K. Chatterjee
Keyword(s):  
Igneous Rocks ◽  
The West

scholarly journals VII.—The Late Palæozoic Alkaline Igneous Rocks of the West of Scotland

1912 ◽  
Vol 9 (3) ◽  
pp. 120-131 ◽  
Author(s):  
G. W. Tyrrell
Keyword(s):  
Thin Section ◽  
Basic Type ◽  
Igneous Rocks ◽  
The West ◽  
Fine Grained ◽  
Late Palaeozoic

2. Essexite. (a) Carskeoch type.—A small boss of essexite, of rather basic type, pierces the agglomerate of the Carskeoch vent, near Patna, Ayrshire. Macroscopically it is light grey, compact, and fine-grained. In thin section it shows a plexus of fluxionally-arranged plagioclase laths of the composition Ab An, the interstices being filled with subhedral augite of a nearly colourless variety, and fresh olivine. Here and there minute angular interspaces are occupied with turbid isotropic matter, the form and arrangement of the particles of which suggest the former presence of nepheline. A few broad plates of pale augite and crystals of olivine interrupt the general trachytoid fabric. Ilmenite and biotite occur sparsely, and a little orthoclase may be detected on the margins of the plagioclases, extending irregularly into the interspaces. This rock has a distinct individuality, and resembles neither the essexites of Lochend and Craigleith in the Lothians, nor the Crawfordjohn type described below. It is poor in alkali-felspars and felspathoids, is devoid of purple augite, and has a well-developed trachytoid fabric.

scholarly journals IV.—The Glacial Deposits of Northern Pembrokeshire

1906 ◽  
Vol 41 (1) ◽  
pp. 53-87
Author(s):  
T. J. Jehu
Keyword(s):  
Igneous Rocks ◽  
Earth’S Crust ◽  
The West ◽  
Great Abundance ◽  
Glacial Deposits ◽  
North East ◽  
The North ◽  
Earth's Crust

The area embraced in this paper consists of that part of Pembrokeshire which lies to the north and north-east of St Bride's Bay. Bounded on the west by St George's Channel and on the north by Cardigan Bay, it extends to the north-east as far as the mouth of the river Teifi, near Cardigan.That part of the country which lies in the immediate neighbourhood of St David's has, through the laborious researches of the late Dr Hicks and others, become well-known to geologists, and may now be regarded as classic ground. The solid geology of this promontory has given rise to much discussion, and has, perhaps, attracted more attention than that of any other part of the Principality. The reason for this great interest is to be sought in the facts that the rocks of this area are of a very great antiquity, and that the sedimentary series contain the remains of some of the earliest organic forms yet found in the earth's crust, whilst the igneous rocks are also displayed in great abundance and variety, and present us, in the words of Sir Archibald Geikie, with “the oldest well-preserved record of volcanic action in Britain.”

IV.—Notes on the Arenig Rocks near Aberdaron, Carnarvonshire

1902 ◽  
Vol 9 (3) ◽  
pp. 118-122 ◽  
Author(s):  
Charles A. Matley
Keyword(s):  
Sedimentary Rocks ◽  
Igneous Rocks ◽  
The West

The geology of the Lleyn peninsula has from time to time attracted the attention of geologists, and several workers have added much to our knowledge of this district; but their researches have been mainly confined to (1) the strip of ancient rocks (usually assigned to the pre-Cambrian) in the west between Porth Dinlleyn and Bardsey Island, and (2) the igneous rocks lying in the Ordovician ground which occupies the eastern and larger portion of the peninsula. Thus the Ordovician sedimentary rocks have largely escaped attention, a result probably also due to their monotony, to the rarity of fossiliferous localities, and to the great extent to which the beds are concealed beneath accumulations of drift.

scholarly journals V.—Note on the Highland Border Series, near Aberfoyle

1914 ◽  
Vol 1 (9) ◽  
pp. 402-404 ◽  
Author(s):  
T. J. Jehu
Keyword(s):  
Igneous Rocks ◽  
Geological Survey ◽  
The West ◽  
Series Form ◽  
Lower Silurian ◽  
Close Resemblance ◽  
Southern Border

The rocks of this series form an interrupted belt along the southern border of the Highlands from Stonehaven on the east to the island of Arran on the west, and they appear again on a more extensive scale in Ireland. In Scotland the series consists of cherts or jaspers and shales, sometimes associated with limestones and with some peculiar igneous rocks. The age of the series has been for years a matter of controversy. Many geologists have held that these rocks are of pre-Cambrian age, but Messrs. Peach & Horne in their volume on The Silurian Rocks of Britain (Mem. Geol. Surv., 1899) remarked on the close resemblance of the rocks of this belt to some of the Arenig rocks in the Southern Uplands of Scotland, and the belt has been marked on the Geological Survey maps as doubtfully Lower Silurian.

Late Cenozoic, post-collisional Aegean igneous rocks: Nd, Pb and Sr isotopic constraints on petrogenetic and tectonic models

2001 ◽  
Vol 138 (6) ◽  
pp. 653-668 ◽  
Author(s):  
GEORGIA PE-PIPER ◽  
DAVID J. W. PIPER
Keyword(s):  
Partial Melting ◽  
Lithospheric Mantle ◽  
Igneous Rocks ◽  
Alkaline Basalt ◽  
Carbonate Sediments ◽  
Late Cenozoic ◽  
The West ◽  
Aegean Area ◽  
Terrigenous Sediment ◽  
Isotope Data

Nd isotopic composition has been determined for 16 igneous rocks, representing the wide geochemical, spatial and temporal range of post-collisional, late Cenozoic magmas in the Aegean area. Nd isotopes are used to further interpret previously published Pb and Sr isotope data. The overall pattern of late Cenozoic volcanism resulted from rapid extension, with thermal effects causing melting of hydrated, enriched, subcontinental lithosphere to produce widespread K-rich magmas. Slab break-off and intrusion of hot asthenosphere caused partial melting of rift-related continental margin basalts at the detachment point to generate adakitic magmas. Further outboard, mafic magma from enriched lithospheric mantle melted thickened lower crust to produce the granitoid plutons of the Cyclades. Nd isotopic variation in these varied rock types correlates with pre-Cenozoic palaeo-geography. Proterozoic subduction-related enrichment in Th and U, together with other large-ion lithophile elements, produced distinctive Pb isotope composition. This was later modified where Mesozoic subduction of terrigenous sediment was important, whereas subduction of oceanic carbonate sediments produced enrichment in radiogenic Sr and low Ce/Sr ratios. Late Cenozoic magmas sourced in eastern Pelagonian zone sub-continental lithospheric mantle have Nd model ages of about 1.0 Ga, and generally high 87Sr/86Sr and high 207Pb/204Pb (∼ 15.68) and 208Pb/204Pb (∼ 39.0) for low 206Pb/204Pb (∼ 18.6), but rocks to the west have more radiogenic Pb and higher Ce/Sr as a result of greater subduction of terrigenous sediment from the northern Pindos ocean. Magmas sourced from sub-continental lithosphere beneath the Apulian continental block were strongly influenced by subduction of oceanic crust and sediments north of the passive margin of north Africa. Subduction of Nile-derived terrigenous sediment in the east resulted in Nd model ages of 0.7 to 0.8 Ga and radiogenic Pb isotopes. Greater subduction of oceanic carbonate in the west resulted in magmas with higher 87Sr/86Sr and lower Ce/Sr. The strongly negative εNd for adakites in the central Aegean rules out a source from subducted oceanic basalt, and the adakite magma was probably derived from melting of hydrated Triassic sub-alkaline basalt of continental origin. Where trachytic rocks are succeeded by nepheline-normative basalts (e.g. Samos), Nd isotope data imply that early partial melting of the enriched subcontinental lithospheric mantle involved hydrous amphibole and phlogopite, but once these minerals were consumed, younger magmas were produced by partial melting dominated by olivine and orthopyroxene.

The Start-Dodman-Lizard Boundary-Zone in Relation to the Alpine Structure of Cornwall

1939 ◽  
Vol 76 (9) ◽  
pp. 385-402 ◽  
Author(s):  
E. M. Lind Hendriks
Keyword(s):  
Recent Work ◽  
Middle Devonian ◽  
Igneous Rocks ◽  
Boundary Zone ◽  
The West ◽  
South West ◽  
Entire Line ◽  
South West England

Previous opinion sums up in favour of the continuity of the three boundaries, the entire line being one of dislocation in the east, dislocation and intrusion in the west. Previous opinion also favours the view that, inside the boundary-zone, not only are the Start-Lizard schists continuous, but they have features comparable with some of the Alpine “Schistes lustrés”, with recumbent folding at the Lizard.The boundary-zone is defined as a belt of variolite (ophiolite), exotic blocks, and serpentine intrusive in, and contemporaneous with, a great thrust.Recent work by the writer has shown that some of the beds outside the boundary-zone are a “facies flysch”. Younger beds come in towards the west, in association with the westerly pitch visible in the older beds in South Devonshire; geanticlines occur in the Lower and Middle Devonian respectively, of South Devon and South Cornwall. In an area further north some of the beds show an accumulation of folds comparable with those of the “autochthonous sedimentary” in front of some of the great Alpine nappes; recumbent folding is prevalent in both Devon and Cornwall. The Cornish Flysch was deposited under conditions such as might have preceded a great nappe movement; it is described in relation to the exotic blocks and serpentine in the fracture.The much younger Alpine Flysch also includes ophiolites and exotic blocks, with serpentine intrusive in the fractures upon which the great nappes advanced. According to some authors, the nappes arose from recumbent folds based on geanticlines.The similar direction of both the Cornish (Variscan) and the Alpine movements makes possible a comparison in certain effects as, for instance, the southward increase in albitization and metamorphism, between the great Alps and the similar but older, comparatively tiny, flattened, and denuded relic in south-west England.These cases are also strikingly paralleled by a zone of basic igneous rocks and exotic blocks which overlies the Himalayas.The evidence appears sufficient basis for the suggestion that the Start-Dodman-Lizard boundary-zone may be the relic of a great Variscan nappe, associated with the fan-structure of Cornwall.

scholarly journals Preliminary account of the geology of south-east Renland, Scoresby Sund, East Greenland

1971 ◽  
Vol 34 ◽  
pp. 1-32
Author(s):  
B Chadwick
Keyword(s):  
Large Scale ◽  
Orogenic Belt ◽  
Igneous Rocks ◽  
Normal Faults ◽  
The West ◽  
East Greenland ◽  
Granite Intrusion ◽  
Internal Position ◽  
Preliminary Account ◽  
The Many

South-east Renland occupies an internal position in the Caledonian orogenic belt of East Greenland. The area comprises migmatised paragneisses ofCaledonian supracrustal origin intruded by concordant sheets of garnetiferous augen granite in the west. The gneisses and granites are folded in large-scale, tight to isoc1inal folds. Intermediate igneous rocks with charnockitic affinity were intruded after the folding. The principal intrusion is an extensive, concordant sheet delimiting an area of gneisses in the east that have undergone further migmatisation and granite intrusion. Prominent among the many fractures are normal faults with downthrow to the east. No indications of economic mineralisation were observed.

Extension of the melilite-carbonatite province in the Apennines of Italy: the kamafugite of Grotta del Cervo, Abruzzo

2002 ◽  
Vol 66 (4) ◽  
pp. 555-574 ◽  
Author(s):  
F. Stoppa ◽  
A. R. Woolley ◽  
A. Cundari
Keyword(s):  
Trace Element ◽  
Volcanic Field ◽  
Igneous Rocks ◽  
Bulk Rock ◽  
The West ◽  
Pyroclastic Rocks ◽  
Ultramafic Xenoliths ◽  
Bulk Rock Chemistry ◽  
Italian Apennines

AbstractA new occurrence of a rare kamafugite near L'Aquila, Abruzzo, is described in detail to characterize its paragenesis and to establish possible genetic links with similar alkaline mafic igneous rocks from the Oricola-Camerata Nuova (OC) volcanic field, ˜20 km to the west. Both occurrences belong to the Umbria-Latium-Ultralkaline-District (ULUD), an igneous district represented by rare kamafugites and carbonatites and distinct from the much more voluminous Roman Region (RR) rocks. The new kamafugite was found in a cave known as Grotta del Cervo (GC), associated with epiclastic and pyroclastic rocks. In the latter, lapilli ash tuff, welded lapilli, ultramafic xenoliths, cognate lithics and pelletal lapilli have been identified. The mineralogy of the welded lapilli comprises, in order of decreasing abundance, diopside, leucite, haüyne, Mg-mica, andraditic garnet, apatite, magnetite, kalsilite and olivine. The rock is carbonate-free. Based on bulk-rock chemistry it is classified as a kamafugite, closely approaching the composition of ULUD kamafugites, according to Sahama's (1974) criteria. Separate lapilli ash tuff, characterized by the same silicate mineralogy as that of the welded lapilli, plus modal carbonate exceeding 10 wt.%, is classified as a carbonatitic kamafugite. Bulk-rock and trace-element compositions confirm that the Grotta del Cervo rocks closely approach the ULUD analogues.The Grotta del Cervo occurrence partially fills the geographical and compositional gap between ULUD rocks and the rocks from the Vulture Complex, also a carbonatite and melilitite locality ˜200 km south of GC, and adds considerably to the bulk of kamafugitic and related rocks lying along the Italian Apennines. The petrogenesis of these kamafugites rocks is discussed and possible mineralogical similarities with the Roman Region rocks are highlighted.

Geological Interpretation of Airborne Magnetometer Observations from Nelson to Waikato River, New Zealand

1959 ◽  
Vol 96 (2) ◽  
pp. 118-124 ◽  
Author(s):  
H. W. Wellman
Keyword(s):  
New Zealand ◽  
West Coast ◽  
Axial Plane ◽  
Igneous Rocks ◽  
The South ◽  
The West ◽  
Geological Interpretation ◽  
The North ◽  
Cook Strait ◽  
Waikato River

AbstractA map is presented showing a series of airborne magnetometer profiles from the north end of the South Island of New Zealand to the mouth of Waikato River. The two southern profiles are related to the exposed Upper Palaeozoic igneous rocks which are considered to extend north across Cook Strait and along the west coast of the North Island to cause the anomalies in the northern profiles. The North Island profiles are considered to reflect the Kawhia Syncline and a major anticline to the east. The eastward displacement of the magnetic low relative to the synclinal axis at the surface is considered due to the eastward dip of the axial plane of the syncline.

IV.—The Plutonic Rocks of Garabal Hill

1913 ◽  
Vol 10 (11) ◽  
pp. 499-508 ◽  
Author(s):  
B. K. N. Wyllie ◽  
Alexander Scott
Keyword(s):  
Igneous Rocks ◽  
The West ◽  
Porphyritic Granite ◽  
North East ◽  
Loch Lomond ◽  
The Subject ◽  
Plutonic Rocks

This complex of igneous rocks lies between Ardlui, at the head of Loch Lomond, and the head of Loch Fyne. In 1892 it was the subject of a fairly exhaustive paper by Teall & Dakyns, but in view of a number of new facts which we have discovered we venture to submit a re-examination of the problems connected with the complex. The mass is broken by a north-east fault. The country to the west of this fault is mainly porphyritic granite and tonalite; to the east there is tonalite and also more basic diorite and ultrabasic rocks. We shall concern ourselves mainly with the basic and ultrabasic groups, as they are somewhat unusual in the “Newer Plutonic Rocks of the Highlands”.

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