Carboniferous dykes as monitors of post-Caledonian fluid events in West Connacht, Ireland

AbstractThe causes of hydrothermal alteration in dolerite dykes intruding Caledonian rocks of W Connacht are investigated using stable isotope, water content and K–Ar data for whole rocks and mineral separates. Using an isochron approach the Logmór dyke in the north is re-dated to 308±4 Ma; previously determined older whole-rock ages reflect excess 40Ar. The ∼ 305 Ma age previously proposed for the Teach Dóite suite in the south is reinforced by a 305 Ma age on a pyroxene separate, although the severe resetting of most samples is emphasised by other pyroxene and plagioclase ages of ∼210 Ma. Pyroxene δ18O values for these Upper Carboniferous dykes are mostly 5·5 to 6·1%, indicating negligible crustal contamination. Logmór whole-rock samples have water contents of 1·7–2·1 wt.%, δ5D= 59 to –47‰ and δ18O = 9·4 to 9·6‰; plagioclase shows little mineralogical alteration but its δ18O is 9·7‰. Hydrothermal alteration involving a local formation or metamorphic water took place at high fluid/rock ratios and high temperature during cooling after intrusion, most probably in a thermally-driven convection system. Teach Dóite dykes have water contents of 2·0–4·2 wt.%. δD= –58 to –38‰ and δ18O = 3·6 to 9·2‰, and were mostly altered in two stages; hydration upon intrusion to ∼ 2 wt.% water by contemporaneous meteoric water at low fluid/rock ratios was followed by extensive chemical and isotopic alteration at ∼210 Ma (Upper Triassic) by surface waters. This latter event could also have caused the extensive alteration observed in the host rocks.

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A review of the tectonics of the northern Middle East region

Geological Magazine ◽

10.1017/s0016756800030727 ◽

1984 ◽

Vol 121 (6) ◽

pp. 577-587 ◽

Cited By ~ 99

Author(s):

P. E. R. Lovelock

Keyword(s):

Late Cretaceous ◽

Kinematic Model ◽

Continental Collision ◽

Dead Sea ◽

Plate Motion ◽

Arabian Plate ◽

Southern Boundary ◽

The North ◽

The Dead ◽

Two Stages

AbstractThe structure of the northern part of the Arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region. The Palmyra and Sinjar zones share a common history of development involving two stages of rifting, one in the Triassic–Jurassic and the other during late Cretaceous to early Tertiary times. Deformation of the Palmyra zone during the Mio-Pliocene is attributed to north–south compression on the eastern block of the Dead Sea transcurrent system which occurred after continental collision in the north in southeast Turkey. The asymmetry of the Palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow Triassic evaporites. An important NW-SE cross-plate shear zone has been identified, which can be traced for 600 km and which controls the course of the River Euphrates over long distances in Syria and Iraq. Transcurrent motion along this zone resulted in the formation of narrow grabens during the late Cretaceous which were compressed during the Mio-Pliocene. To a large extent, present day structures in the region result from compressional reactivation of old lineaments within the Arabian plate by the transcurrent motion of the Dead Sea fault zone and subsequent continental collision.

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Mineralization of the South Pennine Orefield, UK—A Review

Proceedings of the Yorkshire Geological Society ◽

10.1144/pygs2015-364 ◽

2016 ◽

Vol 61 (1) ◽

pp. 55-86 ◽

Cited By ~ 3

Author(s):

T.D. Ford ◽

N.E. Worley

Keyword(s):

Wall Rock ◽

Hydraulic Gradient ◽

Mississippi Valley ◽

The South ◽

The North ◽

East Midlands ◽

Ore Minerals ◽

Placer Deposits ◽

Fractured Limestone ◽

Host Rocks

This review of the South Pennine Orefield (SPO) draws together the findings from many years of underground field observations and petrographical study. Mineralization is of the Mississippi Valley-type (MVT) and is concentrated within an area of some 200 km2, mainly along the eastern margins of a large inlier, the Derbyshire High, in Carboniferous platform carbonate host rocks. The inlier covers some 390 km2, forms an up-dip promontory of a larger structure, the East Midlands Shelf, and is surrounded by shales and sandstones of the Millstone Grit and Pennine Coal Measures groups. Mineralization probably began during the late Westphalian (Moscovian, Mid Pennsylvanian), when subsidence due to thermal sag resulted in the limestone being buried to depths of c. 4 km beneath younger strata. A palaeohydraulic reconstruction is presented from analysis of mineralized palaeokarst features, which are interpreted as representing hypogenic or deep-seated karst formed by the interstratal circulation of hydrothermal water in a mostly confined hydrodynamic setting. It is reasoned that Variscan inversion of N–S faults to the east of the SPO resulted in erosion of Namurian and Westphalian (Upper Mississippian–Middle Pennsylvanian) rocks and created a hydraulic gradient inclined towards the south-west. Acidic F-Ba-Pb-Zn enriched fluid evolved in the Namurian basinal rocks and migrated into fractured limestone. The resultant wall-rock dissolution along existing wrench faults led to the formation of a maze of stratiform mineral deposits (flats) and more irregular spongework-shaped structures (pipes). The presence of hydrocarbon accumulations in the limestones and evidence from fluid inclusions indicates that the mineralizing fluids were chloride/fluoride-rich and compositionally typical of oilfield brine. Isotope evidence demonstrates a sulphate evaporite source of sulphur, mainly from the Chadian (Visean, Middle Mississippian) Middleton Anhydrite Formation. By the late Cenozoic, karstification of exposed carbonate rocks began and the current pattern of epigenic karst drainage started to develop as the regional hydraulic gradient reversed, assuming its present eastward inclined attitude. The mineralized hypogenic karst was overprinted by later drainage systems as the hydraulic gradient changed, and placer deposits were formed from the erosion of existing mineralization. This was accompanied by circulation of meteoric water and resulted in the supergene weathering of the sulphide ore minerals. Eastward underflow of meteoric groundwater also exploited the same mineralization flow paths. There is evidence that pre-mineralization hypogenic karst was also significant in the formation of orebodies in the North Pennine Orefield and the Halkyn–Minera Orefield of NE Wales.

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First Permo-Carboniferous conodonts from North Greenland

Geological Magazine ◽

10.1017/s0016756800007834 ◽

1996 ◽

Vol 133 (5) ◽

pp. 553-564 ◽

Cited By ~ 5

Author(s):

Jan Audun Rasmussen ◽

Eckart Håkansson

Keyword(s):

Early Permian ◽

Upper Carboniferous ◽

The North ◽

First Time ◽

North Greenland

AbstractUpper Palaeozoic conodonts are described for the first time from the North Greenland Wandel Sea Basin. In eastern Peary Land, the Moscovian species Idiognathodus incurvus and the Kasimovian—Gzhelian I. magnificus occur in the Upper Carboniferous Foldedal Formation, while an assemblage from the lower part of the succeeding Kim Fjelde Formation suggests deposition in the Upper Artinskian Neostreptognathodus pequopensis—N. clarki Zone. These datings confirm the existence in the northern part of the Wandel Sea Basin of the pronounced early Permian hiatus previously recognized in Holm Land and Amdrup Land in the southern part of the basin. The single conodont specimen found at Prinsesse Ingeborg Halvø further corrobates the local absence of this regional hiatus in the central part of the Wandel Sea Basin.

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Mineralogical and Fluid Inclusions Study of Epithermal Type Veins Intruding the Volcanic Rocks of the Kornofolia Area, Evros, NE Greece.

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.20755 ◽

2019 ◽

Vol 55 (1) ◽

pp. 202

Author(s):

Foteini Aravani ◽

Lambrini Papadopoulou ◽

Vasileios Melfos ◽

Triantafillos Soldatos ◽

Triantafillia Zorba ◽

...

Keyword(s):

Crystal Structure ◽

Fluid Inclusion ◽

Hydrothermal Alteration ◽

Fluid Inclusions ◽

Volcanic Rocks ◽

The Other ◽

Calc Alkaline ◽

Ft Ir ◽

Host Rocks

The volcanic rocks of Kornofolia area, Evros, host a number of epithermal-type veins. The host rocks are Oligocene calc-alkaline andesites to rhyo-dacites. The andesites form hydrothermal breccias and show hydrothermal alteration. The veins comprise mainly silica polymorphs such as quartz, chalcedony and three types of opal (milky white, transparent and green). Amethyst also forms in veins at the same area. Apart from the silica polymorphs, the veins are accompanied by calcite and zeolites. The main aim of this study is the characterization of the silica polymorphs. Using FT-IR analyses, variations in the crystal structure of the three opals were recognized. The green opal is found to be more amorphous than the other two types. Fluid-inclusion measurements were performed in calcite and were compared with amethyst from previous studies. The Th is between 121-175 °C and the Te between -22.9 and -22.4 °C. The salinities range from 0.9 to 4.5 wt % NaCl equiv.

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Field work in the north of the Ivisârtoq region, inner Godthåbsfjord, southern West Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v115.7830 ◽

1983 ◽

Vol 115 ◽

pp. 49-56

Author(s):

B Chadwick ◽

M.A Crewe ◽

J.F.W Park

Keyword(s):

Field Work ◽

Geological Survey ◽

West Greenland ◽

North West ◽

The North ◽

Field Investigations ◽

New Findings ◽

Host Rocks

The programme of field investigations in the north of the Ivisartoq region begun in 1981 by Chadwick & Crewe (1982) was continued in 1982. Julia Park began mapping the Taserssuaq granodiorite, its host rocks and the Ataneq fault in the north-west. Dur team was joined by D. Bellur, Geological Survey of India, nominally as an assistant. In this report we present only summary notes of new findings relevant to the interpretation of the geometry and chronology of this segment of the Archaean crust in southern West Greenland. We use the established terminology for the Archaean rocks of the Godthåbsfjord region.

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Himalayan and Trans Himalayan granitic rocks in and adjacent to Nepal and their mineral potential

Journal of Nepal Geological Society ◽

10.3126/jngs.v1i1.32668 ◽

1981 ◽

Vol 1 (1) ◽

Author(s):

A. H. G. Mitchell

Keyword(s):

Root Zone ◽

Porphyry Copper ◽

Tectonic Setting ◽

Granitic Rocks ◽

Main Central Thrust ◽

Southern Tibet ◽

Late Mesozoic ◽

The North ◽

Augen Gneiss ◽

Host Rocks

Granitic rocks occupying eight distinct tectonic settings can be recognized in the Himalayas and Transhimalayas. In the Lower Himalayas geographical belt a few plutons of two-mica granite intrude the lowest unit of the Nawakot Complex or Midland Group. More extensive are sheet- like lies of augen gneiss intrusive within a possibly thrust bounded succession carbonates and graphitic schists beneath the Main Central Thrust to the north. The most abundant granites in the Lower Himalayas are the two- mica cordierite- bearing granite within klippen; minor tin and tungsten mineralization is associated with these plutons, which are of late Cambrian age. Within the Higher Himalayas above the Main Central Thrust, the ‘Central Crystallines’ or Central Gneisses include pegmatites and pegmatitic granites intrusive into gneisses of probable early Proterozoic age; these have same potential for ruby, sapphire, aquamarine and possibly spodumene. Further north within the Higher Himalayan succession a southern belt of anatectic two- mica granites and leucogranites of mid-Tertiary age is favorable for tin, tungsten and uranium mineralization; a northern belt of granites or gneisses is of uncertain age and origin. North of the Indus Suture in the Transhimalayas extensive batholiths of hornblende granodiorite representing the root zone of a late Mesozoic to early Eocene volcanic arc are associated with porphyry copper deposits. Further north in southern Tibet the tectonic, setting for reported granitic bodies of Tertiary age is uncertain; their location suggests that they could be favorable host rocks for tin, uranium and porphyry molybdenum mineralization.

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IV.—On the Denudation of Western Brittany

Geological Magazine ◽

10.1017/s0016756800163046 ◽

1869 ◽

Vol 6 (64) ◽

pp. 442-446

Author(s):

G. A. Lebour

Keyword(s):

Sedimentary Rocks ◽

The South ◽

Upper Carboniferous ◽

The North ◽

Upper Silurian ◽

East And West

Geology.—Stated roughly, the geology of the Department of Finistère may be said to consist of two masses of granite, one to the north and one to the south, enclosing between them nearly the whole of the sedimentary rocks of the district. These consist of Cambrian slates and gneiss, Lower, Middle, and Upper Silurian slates and grits, and very small and unimportant patches of Upper Carboniferous shales. The entire mass of these deposits has an east and west direction, and occupies the central part of the Department.

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Signs of polichnous deformations in microstructures of carbonate rocks of the Katav-Yuryuzan zone of transpression (Southern Urals)

Moscow University Bulletin. Series 4. Geology ◽

10.33623/0579-9406-2020-4-13-21 ◽

2020 ◽

pp. 13-21

Author(s):

A. V. Tevelev ◽

A. A. Borisenko ◽

M. I. Erokhina ◽

S. S. Popov ◽

I. A. Kosheleva ◽

...

Keyword(s):

Simple Shear ◽

Carbonate Rocks ◽

Pure Shear ◽

Southern Urals ◽

Second Stage ◽

The Third ◽

The North ◽

Third Stage ◽

Three Stages ◽

Two Stages

The Katav-Ivanovsk transpression zone experienced at least two stages of tectonic deformations, and the sequence of deformations was approximately the same throughout the entire zone — from the Bakal-Satka fault in the south to the Suleimsky fault in the north. Three stages of the formation of parageneses were identified. The parageneses of the first and the second stages were formed in a pure shear environment, and the paragenesis of the third stage — in a simple shear environment. There are stylolites (S1) parallel to bedding, and mineral veins (V1) in the paragenesis of the first stage. Paragenesis of the second stage combines stylolites (S2), mineral veins (V2) and intergranular cleavage (S2). In paragenesis of the third stage were distinguished schistosity (S3), milonites (S3), cataclasites, mica packets (SC-textures), and the rotation structures of porphyroblasts.

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