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.

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.

The early Palaeozoic evolution of northwest England

1993 ◽  
Vol 130 (5) ◽  
pp. 711-724 ◽  
Author(s):  
A. H. Cooper ◽  
D. Millward ◽  
E. W. Johnson ◽  
N. J. Soper
Keyword(s):  
Foreland Basin ◽  
Lake District ◽  
Volcanic Group ◽  
The North ◽  
Iapetus Ocean ◽  
Granitic Intrusions ◽  
Deformation Event ◽  
Lower Palaeozoic ◽  
Early Palaeozoic ◽  
Uplift And Erosion

AbstractThe Lake District and smaller Craven inliers of northwest England contain a Lower Palaeozoic sequence deposited on the Gondwanan side of the Iapetus Ocean, close to the junction with the Tornquist Sea. The Tremadoc to Llanvirn Skiddaw and Ingleton groups are deep water assemblages of turbidite, olistostrome and slump deposits, formed at a continental margin. They experienced uplift and erosion as a precursor to the eruption of two largely subaerial Llandeilo-Caradoc volcanic sequences: the tholeiitic Eycott Volcanic Group in the north and the calc–alkaline Borrowdale Volcanic Group in the central Lake District. The volcanic episodes are the earliest part of a major episode of magmatism, extending through to the early Devonian and responsible for a major batholith underpinning the Lake District. Subsidence in an intra-arc rift zone preserved the subaerial volcanic sequences. A marine transgression marks the base of the Windermere Group, which comprises a mixed carbonate–clastic shelf sequence of Ashgill age, passing upwards through the Silurian into a thick, prograding foreland basin sequence of Ludlow turbidites. Deformation of the Lower Palaeozoic sequences was possibly diachronous from north to south. It is attributed to the late Caledonian (Acadian) Orogeny and resulted in folding, cleavage and thrust development. Granitic intrusions, including those at Shap, Skiddaw and beneath the hydrothermal Crummock Water Aureole, are partly syntectonic and were therefore penecontemporaneous with this deformation event. Some thrust faulting post-dates the intrusive phase. Post-deformation Devonian conglomerates are also present locally.

Timing of magmatism, foreland basin development, metamorphism and inversion in the Anglo-Brabant fold belt

1997 ◽  
Vol 134 (5) ◽  
pp. 607-616 ◽  
Author(s):  
G. VAN GROOTEL ◽  
J. VERNIERS ◽  
B. GEERKENS ◽  
D. LADURON ◽  
M. VERHAEREN ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Foreland Basin ◽  
Fold Belt ◽  
East Anglia ◽  
Basin Inversion ◽  
Tectonic Model ◽  
The North ◽  
Basin Development ◽  
The North Sea ◽  
And Inversion

New data implying crustal activation of Eastern Avalonia along the Anglo-Brabant fold belt are presented. Late Ordovician subduction-related magmatism in East Anglia and the Brabant Massif, coupled with accelerated subsidence in the Anglia Basin and in the Brabant Massif during Silurian time, indicate a foreland basin development. Final collision resulted in folding, cleavage development and thrusting during the mid-Lochkovian to mid-Eifelian. In the southeast of the Anglo-Brabant fold belt, Acadian deformation produced basin inversion and the regional antiformal structure of the Brabant Massif. The uplift, inferred from the sedimentology, petrography and reworked palynomorphs in the Lower Devonian of the Dinant Synclinorium is confirmed by illite crystallinity studies. The tectonic model discussed implies the presence of two subduction zones in the eastern part of Eastern Avalonia, one along the Anglo-Brabant fold belt and another under the North Sea in the prolongation of the North German–Polish Caledonides.

scholarly journals Reactivated normal-sense shear zones in the core of the Greater Himalayan Sequence, Solukhumbu District, Nepal

2017 ◽  
Vol 53 ◽  
pp. 99-105
Author(s):  
Mary Hubbard ◽  
David R. Lageson ◽  
Roshan Raj Bhattarai
Keyword(s):  
Shear Zones ◽  
The North ◽  
Orogenic Wedge ◽  
Kinematic Models ◽  
Thrust System ◽  
Greater Himalayan Sequence ◽  
Displacement Based ◽  
Metamorphic Core ◽  
Normal Sense ◽  
Over Time

We present preliminary observations from the Solukhumbu region of Nepal, coupled with structures described in the literature, to suggest the importance of structural and metamorphic discontinuities within the Himalayan metamorphic core (Greater Himalayan Sequence) and reactivation of at least one of these thrust discontinuities with a normal (down-to-the-north) sense of displacement. Based on preliminary geochronologic data, development of these discontinuities may have evolved over time. In the Dudh Kosi Valley near Ghat, gneissic rocks and pegmatites exhibit tectonized fabrics and yield argon cooling ages of ~4 Ma for K-feldspar and ~9 Ma for biotite. Just north of Khumjung there is a prominent topographic break from which sheared gneissic rocks indicate a top-to-the-north, or normal, sense of shear. Near Pangboche, a repeated section of kyanitebearing rocks interleaved with sillimanite-muscovite schist suggests structural imbrication and/or interleaved retrograde metamorphism. Below the peaks of Nuptse and Lhotse, the Khumbu thrust (Searle 1999) appears to form the floor of a thick succession of leucogranite sills. We suggest that these discontinuities were formed over time, possibly from early MCT and STDS deformation at ~21 Ma to as recent as ~4 Ma, and need to be considered in kinematic models that combine channel flow with critical taper and tectonic denudation. Moreover, orogenic collapse in the Himalayan core may be migrating southward through time as the orogenic wedge continues to uplift in response to underthrusting of India and southward propagation of the Main Frontal Thrust system.

Crustal magnetization variations across the Iapetus Suture Zone

1995 ◽  
Vol 132 (5) ◽  
pp. 599-609 ◽  
Author(s):  
G. S. Kimbell ◽  
P. Stone
Keyword(s):  
Hanging Wall ◽  
Suture Zone ◽  
Lake District ◽  
The South ◽  
Long Wavelength ◽  
The North ◽  
Anomaly Pattern ◽  
Magnetic Basement ◽  
Crustal Magnetization ◽  
Structural Levels

AbstractThe Iapetus Suture (Solway) line coincides with a magnetic low, which lies between magnetic highs over southwestern Scotland and the Lake District-Isle of Man region. Although topography on deep magnetic basement can account for these long wavelength geophysical variations, an explanation which involves lateral basement magnetization contrasts is preferred on the basis of (a) correlations between inferred magnetization boundaries and major structures delineated from other evidence, and (b) the apparent westward continuation of the Solway low through Ireland and Newfoundland across areas with very different subsidence histories but similar position with respect to the collision of Laurentia and Avalonia. In the preferred model, relatively magnetic continental crust beneath the Southern Uplands and Lake District terranes is separated by a zone of less magnetic crust interpreted as sedimentary rock of Avalonian affinity carried to deeper structural levels within the Iapetus Suture Zone. The magnetic unit beneath the Southern Uplands is bounded to the south by the northward-dipping Iapetus Suture and to the north by a structure which may have been reactivated in late Caledonian times to produce the Moniaive Shear Zone in the overlying rocks; this unit may represent the ‘missing’ arc terrane inferred from provenance studies. Alternatively, the two magnetic basement domains may have originally been part of the same terrane, with that portion beneath the Southern Uplands rifting from the Avalonian continent during its northwards drift and being subsequently trapped in the hanging wall of the Iapetus Suture. The southern margin of the Lake District domain appears as a discontinuity in the magnetic anomaly pattern, with long wavelength anomalies to the south having a southeast ‘Tornquist’ trend.

scholarly journals Rapid Holocene bedrock canyon incision of Beida River, North Qilian Shan, China

2021 ◽  
Author(s):  
Yiran Wang ◽  
Michael E. Oskin ◽  
Youli Li ◽  
Huiping Zhang
Keyword(s):  
Average Rate ◽  
Foreland Basin ◽  
Uplift Rate ◽  
Field Surveys ◽  
Base Level ◽  
The North ◽  
River Incision ◽  
Mountain Front ◽  
The Relationship ◽  
North Qilian

Abstract. Located at the transition between monsoon and westerly dominated climate systems, major rivers draining the western North Qilian Shan incise deep, narrow canyons into latest Quaternary foreland basin sediments of the Hexi Corridor. Field surveys show that the Beida River incised 125 m at the mountain front over the Late Pleistocene and Holocene at an average rate of 6 m/kyr. We hypothesize that a steep knickzone, with 3 % slope, initiated at the mountain front and has since retreated to its present position, 10 km upstream. Terrace dating results suggest this knickzone formed around the mid-Holocene, over a duration of less than 1.5 kyr, during which incision accelerated to at least 25 m/kyr. These incision rates are much larger than the uplift rate across the North Qilian fault, which suggests a climate-related increase in discharge drove rapid incision over the Holocene and formation of the knickzone. Using the relationship between incision rates and the amount of base level drop, we show the maximum duration of knickzone formation to be 700 yr and the minimum incision rate to be 50 m/kyr. This period of increased river incision is the result of increasing excess discharge, which likely corresponds to a pluvial lake-filling event at the terminus of the Beida River and correlates with a wet period driven by strengthening of the Southeast Asian Monsoon.

Turbidite to storm transition in a migrating foreland basin: the Kendal Group (Upper Silurian), northwest England

1994 ◽  
Vol 131 (2) ◽  
pp. 255-267 ◽  
Author(s):  
Louisa M. King
Keyword(s):  
Lower Energy ◽  
Temporal Trend ◽  
Foreland Basin ◽  
Earthquake Activity ◽  
The North ◽  
Density Flow ◽  
Windermere Supergroup ◽  
Mountain Front ◽  
Basin Geometry ◽  
Upper Silurian

AbstractThe uppermost Windermere Supergroup (Kendal Group) of northwest England records the passage from Wenlock and lower Ludlow deep water ‘flysch’ deposits to upper Ludlow and Přídolí shallower water ‘molasse’ deposits within an evolving foreland basin. An upwards progression is preserved from oxygen-poor basin-slope turbidite deposits through more oxygenated, bioturbated dilute density flow deposits, to storm and wave-influenced sediments. The storm-influenced sediments display hummocky cross-stratification, a Skolithos ichnofacies, shelly lags, and symmetrical wave ripple cross-lamination. Convolute lamination increases in magnitude and frequency in the upper part of the sequence, apparently nucleated above ripple crests. Tropical hurricanes probably controlled storm deposition, as suggested by late Silurian palaeogeographic reconstructions. Structures in the heterolithic muddy siltstones suggest deposition in a lower energy, wave-influenced setting. Mud-drapes, short wavelength symmetrical ripples and multi-directional ripple cross-lamination are common. The Kendal Group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry, bounded to the northwest and northeast by topographic slopes. As well as a temporal trend, facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through Ludlow and Přídolí time, probably ahead of a rising mountain front to the north. The increase in pre-lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert.

Nd-isotope study of provenance patterns across the British sector of the Iapetus Suture

1995 ◽  
Vol 132 (5) ◽  
pp. 571-580 ◽  
Author(s):  
P. Stone ◽  
J. A. Evans
Keyword(s):  
Isotope Composition ◽  
Foreland Basin ◽  
Thrust Belt ◽  
Lake District ◽  
Nd Isotope ◽  
The North ◽  
Ancient Source ◽  
Provenance Areas ◽  
Windermere Supergroup ◽  
Isotope Study

AbstractThe Southern Uplands greywacke succession (Scotland) accumulated at the Laurentian margin of the Iapetus Ocean. It was sequentially incorporated into an imbricate, accretionary thrust complex until closure of the ocean. Thereafter the thrust belt propagated across the suture zone as a foreland thrust belt directed towards the hinterland of Avalonia. A foreland basin migrating ahead of the thrust belt was the depositional site for the southernmost Southern Uplands units and the Windermere Supergroup (English Lake District). A Nd-isotope study has shown that juvenile ophiolitic detritus was introduced into the oldest, mid-Ordovician, Southern Uplands greywackes before two distinct provenance areas evolved: one supplying juvenile andesitic detritus in addition to a quartzo-feldspathic component, the other Proterozoic and exclusively quartzo-feldspathic. Bimodal composition continued into the early Silurian but was overlapped from late in the Ordovician by greywackes with intermediate Nd-isotope composition. This was not a simple mixing effect since the andesitic component is not represented and the necessary juvenile component comes from granodioritic and felsitic lithologies. Intermediate eNd values are then a consistent feature through the Silurian both in the younger strata of the Southern Uplands and in the earliest foreland basin turbidites of the Windermere Supergroup. The transition suggests cessation of volcanicity and erosion of deeper levels of the provenance terrane(s), possibly linked to the evolution of the basin system from active margin, accretion-related, to a foreland setting. To the north of the Southern Uplands terrane, beyond the Southern Upland Fault, a Caradoc to Wenlock turbidite sequence occupies inliers within the Midland Valley. The older greywackes contain abundant juvenile ophiolite and plutonic detritus in addition to a quartzofeldspathic metamorphic component; there are similarities with the most northerly part of the Southern Uplands. From the late Ordovician, εNd values systematically decline so that early Llandovery Midland Valley greywackes are exclusively quartzo-feldspathic, derived from an ancient source indistinguishable in isotopic terms from that periodically supplying the Southern Uplands. In general the Llandovery Midland Valley provenance was significantly more mature than that contemporaneously supplying the Southern Uplands. Thereafter, the Midland Valley latest Llandovery and early Wenlock greywackes contain a higher proportion of a juvenile component, and by the early Wenlock, greywackes from the Midland Valley, Southern Uplands and Lake District terranes are similar in terms of εNd. A common provenance seems likely and suggests that by the mid-Silurian all three terrenes were in close proximity.

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.

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