A.D. Evans

Provenance of glacial tills in Ong Valley, Antarctica, inferred from quartz cathodoluminescence imaging, zircon U/Pb dating, and trace element geochemistry

2014 AGU Fall Meeting (2014)

K. L. Edwards A. J. Padilla A.D. Evans D. J. Morgan Greg Balco

Trace element

Cathodoluminescence

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Geophysical survey of Precambrian terranes in SW Lleyn, Caernarvonshire, Wales

Geological Journal (1997)

R. J. E. Lodge Margaret Moore A.D. Evans N. R. Goulty

The geology of southwest Lleyn comprises two Late Precambrian terranes: the Gwna Mélange in the west and the Sarn Complex in the east, separated by the Lleyn Shear Zone. The location of the terrane boundary is poorly constrained due to the limited exposure. We undertook a ground magnetic survey and also measured four gravity profiles with the original intention of investigating the cause of a positive aeromagnetic anomaly previously recorded close to the terrane boundary at grid reference [SH 2200 3000]. This 'Sarn anomaly' appears to be associated with a shallow body within the Sarn Complex, which is known to be a heterogeneous plutonic igneous unit. Of greater interest was the identification of a much larger-amplitude magnetic anomaly striking roughly N–S for over 7 km close to the mapped position of the Lleyn Shear Zone. It can be modelled as a near-vertical discontinuous body of overall dyke-like form, and is too narrow to have been resolved by the aeromagnetic survey. We discovered a previously unreported outcrop of gabbro at Brynhunog Bach [2100 3127] located on this high-amplitude 'Brynhunog anomaly'. It seems likely that the whole anomaly is due to a gabbroic body which is an original constituent of the Sarn Complex, but an alternative possibility is that it is a later intrusion along the Lleyn Shear Zone. © 1997 John Wiley & Sons, Ltd.

Outcrop

Anomaly (physics)

10.1002/(sici)1099-1034(199709)32:3<265::aid-gj745>3.0.co;2-r

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Citations (1)

Geophysical survey of Precambrian terranes in SW Lleyn, Caernarvonshire, Wales

Geological Journal (1997)

R. J. E. Lodge Margaret Moore A.D. Evans N. R. Goulty

The geology of southwest Lleyn comprises two Late Precambrian terranes: the Gwna Mélange in the west and the Sarn Complex in the east, separated by the Lleyn Shear Zone. The location of the terrane boundary is poorly constrained due to the limited exposure. We undertook a ground magnetic survey and also measured four gravity profiles with the original intention of investigating the cause of a positive aeromagnetic anomaly previously recorded close to the terrane boundary at grid reference [SH 2200 3000]. This 'Sarn anomaly' appears to be associated with a shallow body within the Sarn Complex, which is known to be a heterogeneous plutonic igneous unit. Of greater interest was the identification of a much larger-amplitude magnetic anomaly striking roughly N–S for over 7 km close to the mapped position of the Lleyn Shear Zone. It can be modelled as a near-vertical discontinuous body of overall dyke-like form, and is too narrow to have been resolved by the aeromagnetic survey. We discovered a previously unreported outcrop of gabbro at Brynhunog Bach [2100 3127] located on this high-amplitude 'Brynhunog anomaly'. It seems likely that the whole anomaly is due to a gabbroic body which is an original constituent of the Sarn Complex, but an alternative possibility is that it is a later intrusion along the Lleyn Shear Zone. © 1997 John Wiley & Sons, Ltd.

Outcrop

Anomaly (physics)

10.1002/(sici)1099-1034(199709)32:3<265::aid-gj745>3.3.co;2-i

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Mineral investigations at Woodhall and Longlands in north Cumbria

A. J. Wadge J.D. Appleton A.D. Evans

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Geophysical investigations in Swaledale, north Yorkshire

A.D. Evans D.J. Patrick A. J. Wadge J.M. Hudson

An airborne geophysical survey was carried out over part of upper Swaledale and the adjacent moorland. The area has a long history of mining and the geology and style of mineralisation are representative of most of the north Pennine orefield. The survey employed magnetic, electromagnetic and radiometric methods, and provided a test of the applicability of airborne geophysical exploration in this environment. Eleven airborne electromagnetic anomalies were followed up with detailed ground surveys; more limited surveys were employed to check several smaller airborne indications. At two sites the follow-up surveys recorded anomalies sufficiently significant to be considered possible indications of mineralisation. One of these, at Oxnop Gill, was tested by core drilling, but no evidence of significant mineralisation was found. The other site, Whirley Gill, was not drilled, and the anomalies, although promising, remain unexplained. Of the remaining airborne anomalies, some were not detectable on the ground and others were considered to be due to stratigraphical or artificial conductors. It is concluded that the particular airborne EM system employed is not an effective tool in exploration for new mineral veins of the kind known in the northern Pennines.

Geophysical survey

Radiometric dating

Exploration geophysics

Mineral exploration

Magnetic survey

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The Mathry Dyke, a quartz-dolerite intrusion of probable Carboniferous age in southwest Wales

Geological Magazine (1989)

R. Cave J. D. Cornwell A.D. Evans

Abstract A previously unrecorded quartz-dolerite dyke some 40 km long and up to 15 m wide intrudes Lower Palaeozoic rocks in southwest Wales between Mathry and Llanboidy. It is of discontinuous subcrop but has an overall WNW trend. This crosscuts the Caledonian strike of the country rocks but is parallel with the line of the Hercynian front to the south. The dyke is probably related to the suite of Dinantian basalts and dolerites near the Bristol Channel, to the east of the South Wales Coalfield.

10.1017/s0016756800007020

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Palaeogene dyke swarm, NW Wales: evidence for Cenozoic sinistral fault movement

Journal of the Geological Society (1996)

R. E. Bevins Jana Horák A.D. Evans Richard Morgan

The Berw and Aber-Dinlle Faults represent the brittle manifestation of a major lineament, the Menai Strait Fault System, which is known to have been active intermittently since late Precambrian times. Documentation of historical seismicity in this area provides information on the most recent activity along this structure, although there is a paucity of field evidence to support conclusively Cenozoic or later movements. This work documents data from three separate aeromagnetic datasets, combined with field relationships, which reveal a well-defined Cenozoic dyke swarm traversing Anglesey and Snowdonia, showing clear sinistral offset (up to 1.5 km) along the Berw Fault, the most northwesterly component of the Menai Strait Fault System. These data provide conclusive evidence of Cenozoic (<65 Ma) strike-slip faulting in North Wales.

Paleogene

10.1144/gsjgs.153.2.0177

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Citations (18)

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