Pre-Acadian copper mineralization in the English Lake District

1999 ◽  
Vol 136 (2) ◽  
pp. 159-176 ◽  
Author(s):  
D. MILLWARD ◽  
B. BEDDOE-STEPHENS ◽  
B. YOUNG
Keyword(s):  
Quartz Crystal ◽  
Volcanic Rocks ◽  
Wall Rock ◽  
Lake District ◽  
Early Devonian ◽  
Rock Fragments ◽  
Copper Mineralization ◽  
English Lake District ◽  
Fibre Strain ◽  
Devonian Age

The Ordovician sedimentary and igneous rocks of the English Lake District host a widespread suite of epigenetic metalliferous veins dominated by copper sulphides with abundant arsenopyrite, pyrite and accessory galena and sphalerite. New field and microstructural evidence from examples of this suite at Coniston, Wasdale, Honister, Newlands and Borrowdale shows that the veins were strongly cleaved during the Early Devonian (Emsian) Acadian orogenic event. The principal evidence includes the continuity of wall-rock cleavage fabrics with pressure solution seams in the veins and consistently orientated cleavage through enclosed, rotated wall-rock fragments and chloritic mats. There is also widespread complex intracrystalline deformation in quartz, cataclasis of arsenopyrite and pyrite, fracturing and/or buckling of bladed hematite, and growth of quartz or mica-fibre strain fringes. Chalcopyrite was partially or totally remobilized, enabling it to migrate along quartz crystal boundaries, and invade brecciated pyrite. Previous K–Ar Early Devonian age determinations for the mineralization are considered to have been reset. The pre-Acadian age of this mineralization, its style and relationship to the volcanic rocks permits a genetic link with the final phases of Caradoc magmatism.

Controls of copper mineralization at Coniston, English Lake District

1977 ◽  
Vol 114 (3) ◽  
pp. 195-202 ◽  
Author(s):  
G. W. Dagger
Keyword(s):  
Regional Metamorphism ◽  
Fracture Pattern ◽  
Main Phase ◽  
Low Grade ◽  
Lake District ◽  
Granite Intrusion ◽  
Copper Mineralization ◽  
English Lake District ◽  
Textural Evidence ◽  
Volcanic Series

SummaryAnalysis of the fracture pattern in the Coniston area of the Lake District indicates that copper mineralization is localized in a series of fractures produced during the main phase of deformation affecting the Borrowdale Volcanic Series. Three events are recognized on the basis of field and textural evidence obtained from polished sections: an early haematite mineralization, correlated with the low grade regional metamorphism affecting the rocks; the main phase of sulphide mineralization, with zoning, which is correlated with a granite intrusion at depth; and a late renewed movement on the veins, with carbonate mineralization, believed to be related to uplift of the granite.

Relationship between metamorphism and structure in the Skiddaw Group, English Lake District

1993 ◽  
Vol 130 (5) ◽  
pp. 631-638 ◽  
Author(s):  
N. J. Fortey ◽  
B. Roberts ◽  
S. R. Hirons
Keyword(s):  
Cross Sections ◽  
Geothermal Gradient ◽  
Geological Structure ◽  
White Mica ◽  
Contact Metamorphism ◽  
Lake District ◽  
Illite Crystallinity ◽  
Directed Movement ◽  
Early Devonian ◽  
English Lake District

AbstractRegional variation of white mica (illite) crystallinity in the Skiddaw Group is set against the structural interpretation of Hughes, Cooper & Stone (1993, this issue) in which early- or pre-Ludlow deformation and slaty cleavage development (S1) were succeeded by southward thrusting and an associated development of S1 and S1 crenulation cleavages, possibly during early Devonian times. Kubier index (KI) values are plotted in relation to geological structure for a major part of the Skiddaw Group, and cross-sections constructed. The pattern is interpreted in terms of three processes: (1) diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late-arc stage (early to mid-Silurian) which preceded the orogenic phase and formation of S1; (2) upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre-Ludlow orogenic phase following closure of Iapetus; (3) late-tectonic uplift of already metamorphosed rocks by southward-directed movement on the Loweswater, Gasgale Gill and Causey Pike Thrusts possibly during early Devonian time. An analogous interpretation is made for the Skiddaw area, though with the addition of major post-S1 contact metamorphism.

VI.—A Cordierite-bearing Lava from the Lake District

1906 ◽  
Vol 3 (4) ◽  
pp. 176-177
Author(s):  
Alfred Harker
Keyword(s):  
Present Note ◽  
Volcanic Rocks ◽  
Wide Spread ◽  
Lake District ◽  
Systematic Account ◽  
Recent Contribution ◽  
Intrusive Rocks ◽  
English Lake District ◽  
Mode Of Occurrence ◽  
Volcanic Series

Although the volcanic rocks of the English Lake District have received notice from time to time, any systematic account of them from the petrographical side has yet to be written. The most recent contribution, by the late Mr. E. E. Walker, treated especially of the mode of occurrence of the garnet, which is so common a constituent, not only of the lavas and tuffs, but of the associated intrusive rocks, probably referable to the same Ordovician age. There can be no doubt that this mineral is sometimes a primary constituent, but very often a product of metamorphism. The object of the present note is to record the occurrence in one instance of a rarer mineral, which has not hitherto been observed in this series of rocks. Cordierite is found as a product of thermal metamorphism in the Coniston Flags near the Shap Granite, and in the Skiddaw Slates of the Skiddaw granite area. In the latter it is remarkably abundant and wide-spread. The mineral is now found to occur, as an exceptional constituent, in the volcanic series.

Age of the Eycott Volcanic Group and its conformable relationship to the Skiddaw Slates in the English Lake District

1972 ◽  
Vol 109 (3) ◽  
pp. 259-268 ◽  
Author(s):  
C. Downie ◽  
N. J. Soper
Keyword(s):  
Volcanic Rocks ◽  
Island Arc ◽  
Lake District ◽  
Volcanic Group ◽  
Volcanic Sequence ◽  
Volcanic Formation ◽  
English Lake District

SummaryAn earliest Llanvirn age is established on micropalaeontological grounds for the interbedded lava–pelite sequence at the base of the Binsey Volcanic Formation in the northern Lake District. The northern volcanic sequence, here termed the Eycott Volcanic Group, is earlier than, and chemically distinct from, the main Borrowdale Volcanic Group. The evidence precludes a regional unconformity between the Skiddaw Slates and the overlying volcanic rocks, but is compatible with the hypothesis that the vulcanicity occurred in an island arc environment.

IX.—Notes on the Occurrence of Chlorite among the Lower Silurian Volcanic Rocks of the English Lake District

1877 ◽  
Vol 1 (4) ◽  
pp. 119-122
Author(s):  
J. Clifton Ward
Keyword(s):  
Volcanic Rocks ◽  
Large Degree ◽  
Lake District ◽  
Geological Time ◽  
Volcanic Origin ◽  
Lower Silurian ◽  
Deep Burial ◽  
English Lake District

The Volcanic Rocks of Lower Silurian age in the Lake District are interesting in the highest degree on many accounts, and not least so on that of the extreme metamorphism which they have undergone, partly by the deep burial they suffered during the period between the close of the Lower Silurian and the Old Red, when they were once more largely uncovered, and partly by that neverceasing action of infiltration, decomposition, solution and replacement to which all rocks are subject during the course of geological time, but to which rocks of an originally volcanic origin seem specially subject.If there is one feature in this metamorphism of the Cumberland rocks more prorainent than another, it is the large degree to which chlorite has been developed among them, and the universality of its occurrence.

scholarly journals Primitive islandarc granitoids of the Schuchinskaya zone, the Polar Urals (SIMS U-Pb zircon dating)

2017 ◽  
pp. 22-32
Author(s):  
I. D. Sobolev ◽  
A. N. Shadrin ◽  
V. A. Rastorguev ◽  
D. A. Kozyreva
Keyword(s):  
Chemical Composition ◽  
Volcanic Rocks ◽  
Late Ordovician ◽  
Island Arc ◽  
Upper Ordovician ◽  
Early Devonian ◽  
Zircon Dating ◽  
Polar Urals ◽  
Devonian Age ◽  
The Polar Urals

In the Schuchinskaya Zone of the Polar Urals granitoids of the Rechnoy and Yalya-Pe paleovolcanoes have been studied. They were mapped as Khoimpeysky Complex of Silurian age. In addition, granitoids of the Nganotsky-1 and Nganotsky-2 plutons mapped as Yunyaginsky Complex of Early Devonian age have been investigated. It was found that based on the mineral and chemical composition the rocks of all plutons studied correspond to island arc I-type granitoids. U-Pb (SIMS) concordant ages of zircons from granitoids of the Rechnoy and Yalya-Pe paleovolcanoes, and of the Nganotsky-1 pluton are 456±6, 454±4 and 463±3 Ma, respectively, which implies the existence of an island arc in the Schuchinskaya Zone as early as the Middle-Late Ordovician. Establishing the age of granitoids allows to refer volcanic rocks cut by plutons to Syadayskaya Formation, and to clarify the upper stratigraphic limit of its sedimentation as Middle-Upper Ordovician.

The timing of Ordovician magmatism in the English Lake District and Cross Fell inliers

1993 ◽  
Vol 130 (3) ◽  
pp. 369-377 ◽  
Author(s):  
Richard A. Hughes ◽  
Peter Kokelaar
Keyword(s):  
Volcanic Rocks ◽  
Arc Magmatism ◽  
Lake District ◽  
Early Ordovician ◽  
Extensional Tectonic ◽  
English Lake District ◽  
Lower Palaeozoic ◽  
Ordovician Magmatism ◽  
Tectonic Style ◽  
Subduction System

AbstractVolcanic and hypabyssal intrusive rocks of the Lower Palaeozoic English Lake District and Cross Fell inliers are elements of the Ordovician destructive plate margin system of microcontinental Avalonia. Two igneous sheets within the marine sedimentary Skiddaw Group of these inliers, previously described as lavas, are reinterpreted as sills. Sedimentary rocks enclosing these sills are of late Tremadoc-early Arenig (c. 493 Ma) and early Llanvirn (> 476 Ma) age, and breccias along the upper contacts of both were produced by steam explosivity and fluidization ahead of theadvancing tips of the intrusions. Previous interpretation of the breccias on the older sheet, as sediment deposited on the eroded top of a lava flow, implied an early Ordovician onset of arc magmatism. Such early magmatism would have been virtually coincident with the latest Tremadoc initiation of arc magmatism in Wales, but evidence for such a near synchronous response tothe putative onset of subduction is lacking. Respective onsets of magmatismwere probably separated by at least 17 m.y., and possibly by as much as 29 m.y. The apparent contemporaneity of mid and late Ordovician volcanic episodes in England and Wales, and similarities in extensional tectonic style, suggest that the two areas then were part of the same subduction system responding similarly to plate-scale magma-generating and tectonic processes. The early Ordovician situation is uncertain, but the absence of arc volcanic rocks of this age in the English Lake District suggests that this area and Wales are not tectonically juxtaposed elements of a former simple linear arc.

scholarly journals The Mandalovoo–Gurvansayhan terranes in the southern Gobi of Mongolia: new insights from the Bayankhoshuu Ruins section

2021 ◽  
Author(s):  
A. Munkhjargal ◽  
P. Königshof ◽  
J. A. Waters ◽  
S. K. Carmichael ◽  
S. Gonchigdorj ◽  
...  
Keyword(s):  
Middle Devonian ◽  
Facies Analysis ◽  
Volcanic Rocks ◽  
Late Devonian ◽  
Basaltic Lava ◽  
Sedimentary Sequence ◽  
Early Devonian ◽  
Subaerial Exposure ◽  
Arc Setting ◽  
Devonian Age

AbstractThe Bayankhoshuu Ruins section in southern Mongolia is characterized by strongly thrusted and folded sequences. Overall, three sections ranging from Ordovician to Carboniferous rocks were studied. Facies analysis combined with stratigraphic data provide improved lithostratigraphic descriptions of Palaeozoic successions in the Mushgai region. The overall marine sedimentary sequence is punctuated by volcanic rocks–basaltic lava of Silurian and Middle Devonian age and volcaniclastic bentonite and tuff in the Middle to Late Devonian and Mississippian suggesting an island arc setting. The Minjin Member of the Botuulkhudag Formation (Middle Devonian to Late Devonian) is primarily composed of thick basaltic and subaerial volcanic rocks with minor silicified siltstone and chert inclusions. Thicker successions of limestone occur in the Ordovician/Silurian, Early Devonian, and the Mississippian. The macrofauna is scarce, except distinct limestone horizons where different fossil groups were recognized. Microfossils, such as radiolarians and conodonts, are scarce and generally poorly preserved. However, based on the re-study of collections from earlier publications and new conodont data, a more detailed biostratigraphic record of the Khoyormod, Botuulkhudag, and Arynshand formations of the Bayankhoshuu Ruins section can be developed. For instance, the Arynshand Formation likely ranges from the late Bispathodus ultimus conodont biozone to the Scaliognathus anchoralis–Doliognathus latus conodont biozone. A tectonic breccia occurs in the early Mississippian and is overlain by a red shale of remarkable thickness at the top of this formation which points to subaerial exposure in the early Mississippian (near the Tournaisian/Visean transition). Due to strong tectonic overprint and/or facies, some unconformities/hiatuses occur. Most strata are intensively folded and faulted, ranging from centimeter to meter scale. Overall, deposition likely occurred on either the Mandalovoo or Gurvansayhan Terrane.

Field and biostratigraphic evidence for an unconformity at the base of the Eycott Volcanic Group in the English Lake District

1992 ◽  
Vol 129 (1) ◽  
pp. 77-92 ◽  
Author(s):  
David Millward ◽  
Stewart G. Molyneux
Keyword(s):  
Volcanic Rocks ◽  
Tectonic Deformation ◽  
Lake District ◽  
Critical Data ◽  
Volcanic Group ◽  
Late Cambrian ◽  
Water Formation ◽  
English Lake District ◽  
Volcaniclastic Rocks ◽  
Lower Palaeozoic

AbstractThe Eycott Volcanic Group of the Lake District Lower Palaeozoic inlier consists of basaltic and andesite and and andesite sheets and associated, mainly coarse, volcaniclastic rocks. The volcanic rocks have been regarded previously as interdigitated with, and equivalent in age to, mudrocks of the upper part of the Skiddaw Group (Tremadoc–Llanvirn). Microfloral evidence has been quoted in support of this interpretation, but has not been substantiated by re-assessment of the critical data. Furthermore, a recent examination of the base of the Eycott Volcanic Group has shown that it rests with angular unconformity on the Skiddaw Group. Skiddaw Group rocks beneath the unconformity range in age from possible late Cambrian to early Llanvirn. The lowest part of the Eycott Volcanic Group, the Over Water Formation, consists of siltstones and tuffaceous sandstones yielding a diverse microflora, and is intercalated with two andesite sheets interpreted herein as sills. Since the currently accepted Llanvirn age for the Eycott Volcanic Group cannot be confirmed, the volcanism may have been penecontemporaneous with the Llandeilo–Caradoc Borrowdale Volcanic Group episode. There are implications for a pre-volcanic tectonic deformation episode.

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