The magnetic fabrics of some slates from the borrowdale volcanic group in the English Lake District and their correlations with strains

Rathore, J.S.

doi:10.1016/0040-1951(80)90235-8

Cited by 47 publications

(14 citation statements)

References 11 publications

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“…AMS has also been used as a strain gauge, and several quantitative relationships have been reported from studies on different tectonic environments (Rathore 1980;Kligfield et al 1981, Hirt et al 1988Borradaile 1988;Hrouda 1982;Borradaile and Henry 1997). Despite a large number of useful publications, there appears to be a gap in understanding how AMS fabric develops during coseismic faulting, especially in trenched fault zone, which provides an opportunity to examine the deformation path in foldand-thrust belts (FTBs).…”

Section: Introductionmentioning

confidence: 98%

Magnetic fabrics indicating Late Quaternary seismicity in the Himalayan foothills

Jayangondaperumal

Dubey

Kumar³

et al. 2009

Int J Earth Sci (Geol Rundsch)

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The anisotropy of magnetic susceptibility (AMS) study was performed on soft sediment samples from a trenched fault zone across the Himalayan frontal thrust (HFT), western Himalaya. AMS orientation of K min axes in the trench sediments is consistent with lateral shortening revealed by geometry of deformed regional structures and recent earthquakes. Well-defined vertical magnetic foliation parallel to the flexure cleavage in which a vertical magnetic lineation is developed, high anisotropy, and triaxial ellipsoids suggest large overprinting of earthquake-related fabrics. The AMS data suggest a gradual variation from layer parallel shortening (LPS) at a distance from the fault trace to a simple shear fabric close to the fault trace. An abrupt change in the shortening direction (K min ) from NE-SW to E-W suggests a juxtaposition of pre-existing layer parallel shortening fabric, and bendingrelated flexure associated with an earthquake. Hence the orientation pattern of magnetic susceptibility axes helps in identifying co-seismic structures in Late Holocene surface sediments.

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Section: Introductionmentioning

confidence: 98%

Magnetic fabrics indicating Late Quaternary seismicity in the Himalayan foothills

Jayangondaperumal

Dubey

Kumar³

et al. 2009

Int J Earth Sci (Geol Rundsch)

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“…A regional study of 21 sites in 'andesites' of the Borrowdale Volcanic Group by Rathore (1980) probably sampled tuffaceous horizons because a relationship between AMS fabric and visible cleavage was sought. In each case k 1 and k 2 were observed to lie in the plane of cleavage with k 3 perpendicular to this plane.…”

Section: C Palaeomagnetic Results From the Borrowdale Volcanic Gromentioning

confidence: 99%

Palaeomagnetism of the Borrowdale and Eycott volcanic groups, English Lake District: primary and secondary magnetization during a single late Ordovician polarity chron

1997

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Late Ordovician volcanic rocks of the English Lake District typically have a magnetic remanence dominated by a single characteristic component. Previous investigations have interpreted this remanence as both of primary (pre-folding) and secondary origin. Palaeomagnetic field tests have been conducted on (a) andesite blocks from an autobrecciated lava top, (b) andesite blocks in mass-flow breccias, and (c) fault-blocks tilted during Ordovician caldera collapse to establish the time of remanence acquisition. All three tests show that the lavas retain a magnetization acquired during initial cooling: magnetizations of the breccias are coherent within clasts and random between clasts, whilst magnetizations of the tilted fault blocks converge with better that 95 % confidence when corrected for the effects of caldera collapse. In contrast, the volcaniclastic sedimentary and pyroclastic rocks possess an Ordovician secondary remanence acquired after strata had been tilted by volcano-tectonic subsidence. A distributed sample of 65 andesite and basalt sheets through the Borrowdale Volcanic Group has a mean remanence direction D/I = 341.9/-48.9°( α 95 = 4.0°) yielding a positive fold test and a palaeomagnetic pole at 12.7°E, 4.3°S (dp/dm = 3.5/5.3°). A progressive steepening of the palaeofield direction is recorded during emplacement of the Borrowdale Volcanic Group (~I = -39°to I = -51°) which continued into the interval of volcanotectonic overprinting (I = -62°); the equivalent motion of Eastern Avalonia is ~20°into higher southerly latitudes.Both the Eycott and Borrowdale volcanic groups exhibit uniform normal polarity throughout. Correlation with the geomagnetic time scale for the Ordovician restores the broad correlation between the two groups by constraining their emplacement and partial overprinting to a single long normal polarity chron occupying the Nemagraptus gracilis and earlier part of the Diplograptus multidens biozones (late Llandeilo and early Caradoc). All the volcanism, therefore, occurred within a period of no more than ~5 Ma. The palaeomagnetic evidence confirms that the Borrowdale Volcanic Group was affected by both syn-volcanic deformation (caldera collapse) and regional compressive deformation prior to deposition of the (late Ordovician-Silurian) Windermere Supergroup. The succession of primary and secondary Ordovician palaeomagnetic poles from the Lake District inlier defines an anticlockwise apparent polar wander (APW) loop with the apex correlating with 'soft' closure of the Iapetus Ocean and late Ordovician deformation. The APW paths from Avalonia and Baltica converge at this point as subduction ceased and the arc subsided beneath the sea after mid-Caradoc times.

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“…Garnet biotite gneiss shows lower values ranging from 1.02 to 1.5 (average = 1.09) as compared to massive charnockites and foliated charnockites. The anisotropy factor, P', is commonly used as strain intensity gauge which is indicative of the degree of deformation (Rathore, 1980;Tarling and Hrouda, 1993;Archanjo et al, 1995). Hrouda (1993) also investigated mathematically the relationship between strain and P' values for ductile, passive, plane and viscous models.…”

Section: Magnetomineralogy and Anisotropymentioning

confidence: 99%

Role of microfabrics and magnetic fabrics in the tectonic evolution of the Achankovil shear-zone, South India

Vikas

Prasannakumar

Pratheesh

2016

Journal of Asian Earth Sciences

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The magnetic fabrics of some slates from the borrowdale volcanic group in the English Lake District and their correlations with strains

Cited by 47 publications

References 11 publications

Magnetic fabrics indicating Late Quaternary seismicity in the Himalayan foothills

Magnetic fabrics indicating Late Quaternary seismicity in the Himalayan foothills

Palaeomagnetism of the Borrowdale and Eycott volcanic groups, English Lake District: primary and secondary magnetization during a single late Ordovician polarity chron

Role of microfabrics and magnetic fabrics in the tectonic evolution of the Achankovil shear-zone, South India

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