| 000 -LEADER |
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| fixed length control field |
03663nab a2200241 4500 |
| 003 - CONTROL NUMBER IDENTIFIER |
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| control field |
GSMBLIc |
| 008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION |
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| fixed length control field |
210406b ||||| |||| 00| 0 eng d |
| 041 ## - LANGUAGE CODE |
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| Language code of text/sound track or separate title |
Einglish Language |
| 100 ## - MAIN ENTRY--PERSONAL NAME |
|---|
| Personal name |
Piper, J.D.A. |
| 9 (RLIN) |
8670 |
| 245 ## - TITLE STATEMENT |
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| Title |
Palaeomagnetism of the borrowdale and eycott volcanic groups, English Lake district : Primary and secondary magnetization during a single late ordovician polarity chron |
| 300 ## - PHYSICAL DESCRIPTION |
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| Extent |
481-506pp. |
| Other physical details |
Illustration |
| 520 ## - SUMMARY, ETC. |
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| Summary, etc. |
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° (α95=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.<br/><br/>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. |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
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| Topical term or geographic name entry element |
Borrowdale volcanic group |
| 9 (RLIN) |
10088 |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
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| Topical term or geographic name entry element |
Eycott volcanic group |
| 9 (RLIN) |
10089 |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
|---|
| Topical term or geographic name entry element |
Magnetostratigraphy |
| 9 (RLIN) |
10090 |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
|---|
| Topical term or geographic name entry element |
Paleomagnetism |
| 9 (RLIN) |
449 |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
|---|
| Topical term or geographic name entry element |
Volcanic rock - Europe |
| 9 (RLIN) |
10091 |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
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| Topical term or geographic name entry element |
Ordovician |
| 9 (RLIN) |
7840 |
| 700 ## - ADDED ENTRY--PERSONAL NAME |
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| Personal name |
Stephen, J.C. |
| 9 (RLIN) |
10092 |
| 700 ## - ADDED ENTRY--PERSONAL NAME |
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| Personal name |
Branney, M.J. |
| 9 (RLIN) |
10093 |
| 773 0# - HOST ITEM ENTRY |
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| Host Biblionumber |
1892 |
| Host Itemnumber |
2180 |
| Place, publisher, and date of publication |
London Cambridge University Press 1997 |
| Other item identifier |
002523 |
| Title |
Geological magazine : Vol. 134 Iss. 1-6 Year. 1997 |
| International Standard Serial Number |
00167568 |
| 942 ## - ADDED ENTRY ELEMENTS (KOHA) |
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| Source of classification or shelving scheme |
|
| Call number suffix |
{082b} |
| Koha item type |
Article |
