Intrusive Phenomena of the Whin Sill, East of the R. North Tyne

Summary Core from the Rookhope borehole and suites of samples from natural outcrops have been used in a detailed investigation of the petrology and chemistry of the Little Whin Sill. Orthopyroxene (Fs 23–27 ), plagioclase, clinopyroxene and olivine (Fa 15 ) occur as phenocrysts; this is the first report of fresh olivine. The groundmass is composed of clinopyroxene (Ca 45 Mg 51 Fe 4 -Ca 38 Mg 38 Fe 24 ), plagioclase (An 70–35 ) and iron-titanium ores. Eleven new analyses for major elements are presented, together with a new analysis of the White Whin. Statistical analysis of trace element data suggests that only Mn and Sr show significant variation within a given section across the sill, but these elements and Rb show significant variation between sections. A comparison of the chemistry of the Great and Little Whin Sills suggests that the latter is poorer in SiO 2 , K 2 O, and Rb than the Great Whin Sill but carries more CO 2 . The White Whin, consisting of Ca-Mg-Fe-carbonates, illite, kaolin, plagioclase, anatase and quartz, is shown to be chilled whin to which CO 2 , H 2 O and K 2 O have been added, and from which Na 2 O, CaO, MgO and Fe have been lost. It is suggested that the Little Whin Sill represents the initial magma of the whole Whin Sill complex, the high CO 2 content being a result of later alteration. The chemistry of the whin suite of intrusions has characteristics intermediate between tholeiitic and alkaline dolerites, and the initial magma may itself be a differentiate. Although crystal settling is absent, a trend towards iron enrichment is found, with an insrease in the ratio FeO : Fe 2 O 3 towards the centre of the Little Whin Sill. In addition there may be another trend toward silica enrichment in a lateral direction.

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Whin Sill in exploratory boreholes from Newbrough, Northumberland

Bateson

Johnson

1984

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SUMMARY Four exploratory boreholes at Newbrough near Hexham, Northumberland, intersected the Whin Sill and in three of the holes sections of extensively altered quartz-dolerite were observed with a small amount of Ba-Pb-Zn mineralisation. Chemical analyses (both trace and major oxide) of altered and unaltered quartz-dolerite are compared with results reported in previous investigations. Trends in the geochemistry between the extreme end members of fresh Whin Sill and ‘White Whin’ can be identified. Abnormal local features are attributed to interference with the normal sill development at this location.

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Intrusive Phenomena of the Whin Sill, East of the R. North Tyne

Cited by 7 publications

References 2 publications

Report of the 1976 summer field meeting in North East England

Report of the 1976 summer field meeting in North East England

The Petrology of the Little Whin Sill, County Durham

Whin Sill in exploratory boreholes from Newbrough, Northumberland

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