Bingfield Dyke

Location of the Bingfield dyke

Bingfield dyke is exposed in the Redhouse Burn limestone on the south bank of the Redhouse Burn south-east of Bingfield.

A Map of the Bingfield area showing the roads, position of the settlement, the burn, the bedrock and Bingfield dyke.

Location of the Bingfield dyke

Key to bedrock

The Redhouse Burn at NY972719 where tholeiite basalt stones and boulders lie in the stream bed

The Redhouse Burn at NY971719 where tholeiite basalt stones and boulders lie in the stream bed

Petrography and Petrology

Teall gave an excellent account of the dyke but mistakenly believed he was describing what Lebour had previously called the Brunton Dyke, a dyke now known as the St. Oswald’s Chapel Dyke, one of the Whin Sill-related Carboniferous dykes with typical quartz-dolerite features.
He described the ground-mass of the Bingfield dyke rock as being dark or greenish-grey and finely crystalline ‘portions of which bear a very close resemblance to the ground-mass of the Tynemouth dyke’. He estimated the width of the dyke to be 20 t0 25 feet with a 12 to 14 feet margin at the north-west that was highly altered with poorly crystallised feldspars, zones of iron oxide at bounding surfaces and joint planes, and abundant amygdaloids of calcite and chalcedony.
Feldspar crystals in the unaltered portions were seen to belong and narrow while the pyroxenes crystals wereirregular and almost colourless.
He noted that the iron-titanium oxides had remained part of the interstitial material.

Whole sample of tholeiite basalt from the Bingfield Dyke at NY972719 viewed in plane polarised light

Whole sample of tholeiite basalt from the Bingfield Dyke at NY972719 viewed in plane polarised light

Whole sample of tholeiite basalt from the Bingfield Dyke at NY972719 viewed with crossed polarising filters

Whole sample of tholeiite basalt from the Bingfield Dyke at NY972719 viewed with crossed polarising filters

Holmes and Harwood made the Bingfield dyke as the type-example of the ‘Brunton’ type of tholeiite basalt.
The comparatively small plagioclase phenocrysts that make up the few glomerocrystys in the rock show external zoning and an interior composition of approximately An<sub>88</sub>.
The many randomly distributed felspar laths in the rock matrix have an approx. An<sub>60</sub> composition at their centres of crystals ranging to approx. An<sub>40</sub> at their borders.
Holmes and Harwood wrote that the pyroxenes in the basalt were colourless to pale grey-green plates and interdigitated granules with augite prevalent and enstatite or hypersthene present in smaller quantities.
They agreed with Teall that the skeletal crystals and tapering rods of the iron-titanium oxides, along with some pyrites, appear only in the dark brown mesostasis that constitutes about a third of the rock.
They noted there were areas of the rock in which the mesostasis cleared to patches of calcite including or bordered by pyrite and also that calcite commonly occurred in the amygdaloids along with chalcedony and pyrite.

Their modal analysis of the Bingfield dyke established mineral proportions of:
34.7% Mesostasis
32.3% Pyroxene
24.6% Feldspar
– and a chemical composition that was very similar to the Kielderhead dyke.

Zoned plagioclase glomerocryst in Bingfield dyke basalt. Sample viewed in plane polarised light at x10

Zoned plagioclase glomerocryst in Bingfield dyke basalt
Sample viewed in plane polarised light at x10

Zoned plagioclase in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x10

Zoned plagioclase in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x10

The plagioclase in our samples is mostly in the form of broken, twinned laths with a very few plate-like crystalsand even fewer crystals that could be said to be glomerocrysts.
In common with the other glomerocryst-bearing tholeiite basalts of Northumberland, these are more calcium-rich than the laths and are clearly zoned.

Zoned plagioclase glomerocryst in Bingfield dyke basalt. Sample viewed with crossed polars at X25

Zoned plagioclase glomerocryst in Bingfield dyke basalt
Sample viewed with crossed polars at X25

The percentage of clinopyroxene is much greater than that of orthopyroxene in our samples. The former tends to be in granular masses that often show signs of alteration, while crystals of the latter are stumpyandrelatively unaltered.

Orthopyroxene in Bingfield dyke basalt. Sample viewed in plane polarised light at x25.

Orthopyroxene in Bingfield dyke basalt
Sample viewed in plane polarised light at x25

Orthopyroxene in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x25.

Orthopyroxene in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x25

Augite in Bingfield dyke basalt. Sample viewed in plane polarised light at x25.

Augite in Bingfield dyke basalt
Sample viewed in plane polarised light at x25

Augite in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x25.

Augite in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x25

The iron-titanium minerals tend to form clearly defined crystals in association with the brown mesostasis.
Amygdaloids are frequent and are composed of a mixture of calcite, a quartz mineral, possibly chalcedony, and an almost opaque mixture that is full of opaque particles, rods and micro-crystals.

Iron-titanium oxides in association with brown mesostasis in Bingfield dyke. Sample viewed in plane polarised light at  x10.

Iron-titanium oxides in association with brown mesostasis in Bingfield dyke
Sample viewed in p[lane polarised light at x10

Amygdaloid in Bingfield dyke basalt. Sample viewed in plane polarised light at x10

Amygdaloid in Bingfield dyke basalt
Sample viewed in plane polarised light at x10

Amygdaloid in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x10

Amygdaloid in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x10

Some of the minerals in the rock show signs of alteration with some crystals appearing as pseudomorphs, possiblyafter pyroxene.
The Bingfield dyke is intruded into limestone and number of calcite veinlets traversed our samples with some quartz, perhaps chalcedony, appearing towards the edges.

Alteration in Bingfield dyke basalt. Sample viewed in plane polarised light at x25.

Alteration in Bingfield dyke basalt
Sample viewed in plane polarised light at x25

Alteration in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x25.

Alteration in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x25

Calcite vein, with accompanying quartz, in Bingfield dyke basalt. Sample viewed in with crossed polarising filters at x10

Calcite vein, with accompanying quartz, in Bingfield dyke basalt
Sample viewed in with crossed polarising filters at x10

Fossils in the limestone in the banks of the Rehouse Burn at NY971719 viewed in plane polarised light

Fossils in the Redhouse Burn Limestone in the banks of the Rehouse Burn at NY971719 viewed in plane polarised light

Limestone with fossils and quartz grains in the banks of the Redhouse Burn at NY971720 viewed in plane polarised light

Limestone with fossils and quartz grains in the banks of the Redhouse Burn at NY971720 viewed in plane polarised light

References

Lebour, G A, 1878. Outlines Of The Geology Of Northumberland. M & M N W Lambert, Newcastle upon Tyne.
Teall, J J H. 1884. Peteological Notes On Some North-Of-England Dykes. The Quarterly Journal Of The Geological Society Of London, Vol. 40. Pp. 209-247.
Holmes, A and Harwood, H F. 1929. The Tholeiite Dikes Of The North Of England. The Mineralogical Magazine and Journal Of The Mineralogical Society, No. 124. Vol 22.
British Geological Society, Sheet 13 Bellingham, http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1001481

No vestige of a beginning, – no prospect of an end

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