No abstract

Whether a significant thickness of Mesozoic cover rocks once rested upon the Palaeozoic rocks, which form the structural highs of the English Lake District and the Northern Pennines, is a subject of long debate which has been revived recently by apatite fission track analysis (AFTA) studies. Evidence from adjacent basins suggests that 1200–1750 m of Mesozoic cover was probably formerly present on the highs, prior to Cenozoic erosion. Higher estimates ( c . 3000 m) of cover thickness, based on such fission track-derived palaeotemperatures, result from underestimation of early Cenozoic surface temperatures and from not allowing for the relatively low thermal conductivity of the eroded cover rocks. For similar reasons, apatite fission track estimates of eroded cover rocks elsewhere in Britain may also prove to be overestimates.

-Late Carboniferous red-beds, < 700 m thick, at outcrop and in the subsurface

Summary The paper presents a revised and detailed correlation of Yoredale limestones, from the Jew Limestone to the Great Limestone, from the Alston area across Northumberland into southern Scotland. Stratigraphical and micro-palaeontological evidence suggests that the Scar Limestone of Alston is the lateral equivalent of the “Five-Yard” Limestone of Greenhead and consequently of the Eelwell Limestone of north-east Northumberland. Lower in the sequence the Jew Limestone appears to split northwards into the Oxford and Barrasford limestones of Northumberland. Apart from a narrow area of thicker strata on the southern margin of the Northumberland Trough, the higher Yoredale beds in the trough do not exceed greatly in thickness those of the Alston Block.

SUMMARY A granophyric microgranite has been proved in the sub-Carboniferous basement at Moorby, near Horncastle in south Lincolnshire. The microgranite is interpreted as a high level intrusion which has suffered strong alteration and deformation subsequent to emplacement, including the development of a spaced pressure-solution foliation and brecciation. The microgranite has yielded a U-Pb zircon age of 457 ± 20 Ma (late Ordovician) interpreted as the age of emplacement. A Rb-Sr whole-rock isochron age of 400 ± 9 Ma (early Devonian) is strongly discordant with the U-Pb age, and is interpreted to reflect thorough post-emplacement hydrothermal disturbance of the Sr isotope system, either associated with the development of the tectonic foliation during the Acadian phase of the Caledonian Orogeny or subsequent uplift. Geochemical data suggest that the affinities of the Moorby Microgranite lie with the arc-related Ordovician intrusions of the Lake District (e.g. the Ennerdale and Eskdale plutons) rather than with the early Devonian high heat production (HHP) granites such as Shap, Skiddaw and Weardale. While the physical properties of the Moorby Microgranite are comparable to those of the HHP granites, gravity modelling suggests that the microgranite is unlikely to be a major component of the inferred Caledonide Wash - north Norfolk Batholith.