Evidence for late Ordovician amalgamation of volcanogenic terranes in the Iapetus suture zone, eastern Ireland

1987 ◽  
Vol 78 (3) ◽  
pp. 153-167 ◽  
Author(s):  
Finbarr C. Murphy
Keyword(s):  
Regional Scale ◽  
Late Ordovician ◽  
Suture Zone ◽  
Lake District ◽  
Early Devonian ◽  
Final Assembly ◽  
Form Part ◽  
Fault Trace ◽  
Transcurrent Faults ◽  
Wide Zone

ABSTRACTA major transcurrent fault in the zone of the Iapetus suture in eastern Ireland separates Ordovician (pre-Ashgill) terranes. The stratigraphy of each terrane belongs to a dismembered volcanic arc system: the northern terrane is characterised by acid plinian eruptions and derivative sediments which are displaced relative to the andesitic southern terrane volcanism. Each was a separate palaeoenvironment with its own lithostratigraphical character and faunal elements which were juxtaposed across the fault. However, the late Ashgill to Silurian sediments in both terranes form part of a regional overstep sequence which links across the suture zone, such that the palaeogeographical contrasts were eliminated by the Silurian. The inference is that the detached terranes were gradually amalgamated by late Ordovician transtensional movements. This occurred when regional scale subduction-related volcanism had ended. Final assembly by early Devonian sinistral transpressive movements juxtaposed a northern terrane, akin to the Lake District/SE Ireland calcalkaline volcanic province, with a southern terrane in the tholeiitic province of eastern Ireland. As distinct from a singular fault trace, the Iapetus suture is regarded as a 100 km wide zone of anastomosing late Caledonian transcurrent faults whose precursors were active during late Ordovician (i.e. Taconic) terrane amalgamation.

Foreland basin development and tectonics on the northwest margin of eastern Avalonia

1993 ◽  
Vol 130 (5) ◽  
pp. 691-697 ◽  
Author(s):  
B. C. Kneller ◽  
L. M. King ◽  
A. M. Bell
Keyword(s):  
Foreland Basin ◽  
Suture Zone ◽  
Lake District ◽  
Early Devonian ◽  
Basin Inversion ◽  
The North ◽  
Orogenic Wedge ◽  
Mountain Front ◽  
Thrust System ◽  
Early Palaeozoic

AbstractThe early Palaeozoic convergence of Avalonia and Laurentia created a foreland basin at the suture zone of the former lapetus Ocean. Sedimentological and stratigraphic evidence of shallowing and contemporaneous shortening suggests that the southern part of the basin (the Windermere Group) became detached from its basement in the late Ludlow, and began to invert. The detachment beneath the basin rooted into a northwest-dipping mid-crustal thrust system. Contemporaneous uplift to the north of the late Silurian basin involved shortening of the Avalonian foreland basement by thrusting. Basin inversion occurred ahead of a southeastward-advancing mountain front. We postulate a foreland (southeast) prograding sequence of thrusting through the Ludlow in the Lake District. The basin continued to migrate onto the Avalonian foreland through the early Devonian, ahead of an advancing orogenic wedge, finally coming to a stop in the Emsian.

Hirnantia Fauna from the Condroz Inlier, Belgium: another case of a relict Ordovician shelly fauna in the Silurian?

2021 ◽  
pp. 1-27
Author(s):  
Sofia Pereira ◽  
Jorge Colmenar ◽  
Jan Mortier ◽  
Jan Vanmeirhaeghe ◽  
Jacques Verniers ◽  
...  
Keyword(s):  
Sea Level ◽  
Mass Extinction ◽  
Late Ordovician ◽  
Lake District ◽  
Low Diversity ◽  
Hirnantia Fauna ◽  
And Sea Level

Abstract The end-Ordovician mass extinction, linked to a major glaciation, led to deep changes in Hirnantian–Rhuddanian biotas. The Hirnantia Fauna, the first of two Hirnantian survival brachiopod-dominated communities, characterizes the lower–mid Hirnantian deposits globally, and its distribution is essential to understand how the extinction took place. In this paper, we describe, illustrate, and discuss the first macrofossiliferous Hirnantia Fauna assemblage from Belgium, occurring in the Tihange Member of the Fosses Formation at Tihange (Huy), within the Central Condroz Inlier. Six fossiliferous beds have yielded a low-diversity, brachiopod-dominated association. In addition to the brachiopods (Eostropheodonta hirnantensis, Plectothyrella crassicosta, Hirnantia sp., and Trucizetina? sp.), one trilobite (Mucronaspis sp.), four pelmatozoans (Xenocrinus sp., Cyclocharax [col.] paucicrenulatus, Conspectocrinus [col.] celticus, and Pentagonocyclicus [col.] sp.), three graptolites (Cystograptus ancestralis, Normalograptus normalis, and ?Metabolograptus sp.), together with indeterminate machaeridians and bryozoans were identified. The graptolite assemblage, from the Akidograptus ascensus-Parakidograptus acuminatus Biozone, indicates an early Rhuddanian (Silurian) age, and thus, an unexpectedly late occurrence of a typical Hirnantia Fauna. This Belgian association may represent an additional example of relict Hirnantia Fauna in the Silurian, sharing characteristics with the only other known from Rhuddanian rocks at Yewdale Beck (Lake District, England), although reworking has not been completely ruled out. The survival of these Hirnantian taxa into the Silurian might be linked to delayed post-glacial effects of rising temperature and sea-level, which may have favored the establishment of refugia in these two particular regions that were paleogeographically close during the Late Ordovician–early Silurian.

II.—Note on the Recent Volcanic Eruption in New Zealand

1886 ◽  
Vol 3 (9) ◽  
pp. 398-402
Keyword(s):  
New Zealand ◽  
Early Morning ◽  
Considerable Change ◽  
Lake District ◽  
Historic Period ◽  
North East ◽  
The North ◽  
The One ◽  
Wide Zone ◽  
White Island

The “Lake District” of the North Island is too well known to all students of volcanic phenomena, especially of that branch comprising hydrothermal action, to need a detailed description. It will be sufficient to say that it forms a belt, crossing the island from north-east to south-west, and forms a portion of the Middle and Upper Waikato Basins of Hochstetter. The district has been recently brought into prominent notice by the disastrous eruption of Mount Tarawera, very full accounts of which have appeared in New Zealand papers lately received. The eruption commenced in the early morning of Thursday, June 10th, but premonitory symptoms showed themselves a few days before in a tidal wave, three feet high, on Lake Tarawera, great uneasiness of the springs at Ohinemutu, and the reported appearance of smoke issuing from Euapehu, the highest of the great trachytic cones at the extreme south-westerly end of the system. The belt of activity extends from Mount Tongariro at the one end to White Island, in the Bay of Plenty, at the other, a distance of about 150 miles. White Island has undergone considerable change from volcanic action during recent years, and Tongariro was last in eruption in July, 1871; whilst its snowclad sister cone Euapehu has never manifested volcanic action within the historic period until now. This wide zone in the centre of the North Island has, ever since the arrival of the Maoris, been the scene of such extraordinary phenomena, that it has of late been the resort of visitors from all quarters of the globe.

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.

The Antrim–Galway Line: a resolution of the Highland Border Fault enigma of the Caledonides of Britain and Ireland

1995 ◽  
Vol 132 (2) ◽  
pp. 171-184 ◽  
Author(s):  
P. D. Ryan ◽  
N. J. Soper ◽  
D. B. Snyder ◽  
R. W. England ◽  
D. H. W. Hutton
Keyword(s):  
Deep Structure ◽  
Sedimentary Basins ◽  
Strike Slip ◽  
Late Ordovician ◽  
Magnetic Data ◽  
The South ◽  
Early Devonian ◽  
Border Fault ◽  
Western Ireland

AbstractThe westward continuation of the Highland Border fault of Scotland (HBFZ) into Ireland is problematic. It is widely thought to follow a pronounced magnetic and gravity lineament, the Fair Head-Clew Bay Line (FCL). The advantage of this interpretation is that it places all the Ordovician ophiolitic complexes and associated sedimentary basins to the south of the FCL, which would represent the contact between Laurentia and the outboard terranes. Its main shortcomings are that both the deep structure and timing of strike-slip are different on the HBFZ and FCL. In Ireland the FCL is a north-dipping feature that can be traced to the Moho on BIRPS profiles, while the HBFZ has no such signature. Terrane amalgamation in western Ireland was completed by the late Ordovician, while in Scotland the Midland Valley terrane did not finally dock until the early Devonian. These considerations suggest that in western Ireland a branch of the HBFZ exists, which was active in post-Ordovician time and must lie south of Connemara. An examination of Irish geological, geophysical and image-processed magnetic data shows that a profound lineament can be traced from Antrim to Galway Bay (the Antrim–Galway Line). Stitching plutons date movement on it as pre-405 Ma. We propose that the Antrim–Galway Line represents the continuation of the Scottish HBFZ, while the FCL is a preserved Ordovician splay of the HBFZ system whose northdipping geometry is a product of Ordovician collapse of the orogen in western Ireland.

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.

An Acadian mountain front in the English Lake District: the Westmorland Monocline

1993 ◽  
Vol 130 (2) ◽  
pp. 203-213 ◽  
Author(s):  
B. C. Kneller ◽  
A. M. Bell
Keyword(s):  
Shear Zone ◽  
Foreland Basin ◽  
Lake District ◽  
Volcanic Group ◽  
The North ◽  
English Lake District ◽  
Mountain Front ◽  
Group A ◽  
Lower Palaeozoic ◽  
Wide Zone

AbstractThe structure of the southern and central English Lake District is that of a southeast-facing monocline, named here the Westmorland Monocline. This 10 km wide zone of highly cleaved, southeast-dipping rocks separates gently dipping, poorly cleaved Borrowdale Volcanic Group to the north from extensively folded but regionally subhorizontal Windermere Group (foreland basin) rocks to the south. The monocline formed early in the local Acadian deformation sequence, and accommodates at least 8 km of uplift. It coincides with the steep concealed margin of the Lake District batholith. A major northwest-dipping shear zone is revealed in the deepest levels now exposed within the monocline, in the Skiddaw Group rocks of the Black Combe inlier.The monocline has the characteristics of a mountain front, providing significant tectonic elevation across a foreland-dipping panel of rocks, with no hinterland-dipping thrust visible at the surface. We interpret the uplift as the consequence of a southeast-vergent thrust with a gently northwest-dipping ramp beneath the central Lake District, continuing southeastwards as a flat detachment beneath the Windermere Group. A displacement up the ramp of about 20 km is accommodated by backthrusting within the monocline and by shortening within the Windermere Group of the hangingwall southeast of the monocline. The tip lies beyond the limit of the Lower Palaeozoic inlier, beneath Carboniferous cover.

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