Palaeomagnetism and chronology of Caledonian igneous episodes in the Cross Fell Inlier and northern Lake District

Piper, J. D. A.; Mccook, A. S.; Watkins, Keith P.; Brown, Geoff; Morris, William A.

doi:10.1002/gj.3350130108

Cited by 16 publications

(11 citation statements)

References 27 publications

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“…Such a hypothesis has been previously advanced to explain similar steeply inclined directions of Ordovician age from the Caledonian terranes of southern Britain (Thomas & Briden 1976;Piper et al 1978;Piper 1979). These authors favoured a long standing non-dipolar field, as opposed to a true intermediate field direction during a reversal, as a plausible explanation of their apparently anomalous Ordovician palaeomagnetic results.…”

Section: The a Component And Palaeopolementioning

confidence: 82%

A palaeomagnetic study of a Caledonian ophiolite

Taylor

1988

Geophys J Int

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A total of 89 sites have been sampled for palaeomagnetic studies from the Caledonian ophiolite complex of northeast Shetland (60.7'" 359.2"E) and a post-ophiolite emplacement suite of lamprophyre dykes. Of these only 35 sites from the ultramafite facies of the complex yielded statistically significant results. These sites define three distinct populations of magnetization directions which correspond to south palaeomagnetic poles at 47.2"s 244.2"E (A), 18.0"s 323.4"E (B), and 35.0"s 351.1"E (C). Of these only the C remanence can be assigned an unambiguous age of mid-Carboniferous; the ages of the other two poles remain ambiguous due to the uncertainty in the APW path and the complexity of the ophiolite history. Nevertheless palaeomagnetism is shown to be successful in detecting low temperature, low pressure, alteration events that have affected the complex and which hitherto have gone undetected.

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Section: The a Component And Palaeopolementioning

confidence: 82%

A palaeomagnetic study of a Caledonian ophiolite

Taylor

1988

Geophys J Int

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“…Notably, data from the Cader Idris Basalts (Thomas & Briden 1976) plot close to a PermoCarboniferous direction (in situ) and may therefore represent an overprint magnetization. We consider the high inclination results reported by Piper et al (1978) …”

Section: Cornroll 11967)mentioning

confidence: 97%

A revised Palaeozoic apparent polar wander path for Southern Britain (Eastern Avalonia)

Trench

Torsvik

1991

Geophysical Journal International

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S U M M A R Y A revised apparent polar wander path (APWP) is presented for Palaeozoic Southern Britain. The new path, based on a structural reinterpretation of existing data combined with new data from Wales, differs significantly from previous estimates in the following ways:(1) the 1,ocus of the Ordovician path segment is extended by approximately 25 degrees of arc;(2) revised time-calibration of the APWP suggests more Ordovician APW than previously calculated; and(3) the new path implies Middle Ordovician separation across the British sector of Iapetus to be greater than previous palaeomagnetic estimates based on APWP analyses (c. 3300 km; Northern Britain c. 133, Southern Britain c. 45s).

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“…15) Cross Fell Inlier (Piper et al 1978; D/I = 225/-84°). Unfortunately no field test is possible for this body.…”

Section: D Post-borrowdale Volcanic Group Igneous Eventsmentioning

confidence: 98%

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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Palaeomagnetism and chronology of Caledonian igneous episodes in the Cross Fell Inlier and northern Lake District

Cited by 16 publications

References 27 publications

A palaeomagnetic study of a Caledonian ophiolite

A palaeomagnetic study of a Caledonian ophiolite

A revised Palaeozoic apparent polar wander path for Southern Britain (Eastern Avalonia)

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

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