Summary The Borrowdale Volcanic Series of this area have been sub-divided into six groups. The lowest group overlies the Skiddaw Slates and consists of up to 5500 feet of predominantly massive andesites. These Lower Andesites thin south-westward. Together with a small patch of tuffs near Wastwater, they are considered to have originated from a volcanic centre north-east of the area. All other groups probably originated from vents in the south-west. They range from sub-aerial andesitic and rhyolitic agglomerates to fine, delicately bedded tuffs which are thought to have been deposited in tranquil water. Rhyolites and andesites occur at several horizons in both types of tuff and a group of massive andesites comes in at the top of the succession. The pre-Bala movements tilted the area eastward and caused some gentle folding. During the Caledonian orogeny open folds trending north-east developed. Folding was most intense in the south-west and here the northern limb of the major syncline is vertical. Possibly the Eskdale Granite was involved in this folding. The rocks were later faulted and cleaved. Tear faults and normal faults affect both the granite and the volcanic rocks.
Of the several comprehensive geological reviews of the East Midlands, none makes more than a passing reference to the engineering or environmental geology. This paper is thus the first to attempt such a review, although only a brief appraisal is possible here.Earth tremors causing minor structural damage have occurred in the Nottingham region, although more damaging ground movements have usually resulted from natural subsidence, reactivation of Pleistocene landslips or collapse of old mines for lead ore and gangue minerals, limestone, coal and gypsum. More controlled and predictable subsidence is characteristic of modern coal mining although anomalous subsidence does still occur, as do slope failures in the numerous cuttings, quarries, and opencast workings for road metal, limestone, fluorspar, calcite, barytes, coal and gypsum. Mining, and to a lesser extent quarrying, has had profound effects on the underground movement of water, particularly in the Peak District where the water table has been permanently lowered as a result of centuries of lead mining. A similar lowering of the water table, now reversed, resulted from over pumping of the Sherwood Sandstones. The management, including recharge and pollution control, of this aquifer is of major importance to Nottingham.The wide range of foundation conditions reflects the range of rock types and problems vary from avoiding costly excavations for the M1 in hard Pre-Cambrian rocks to bridging the Trent over unconsolidated sands, gravels and peats. The extent of periglacial weathering is crucial in determining the foundation characteristics of Namurian, Westphalian, Mercia Mudstones and Jurassic strata and, as demonstrated by case histories, cannot be neglected in other formations.Throughout the region there are conflicting interests arising from exploitation of resources in areas of considerable amenity value. Satisfactory solutions have been found for some of these problems, for example, with the nature reserves and Water Sports Centre developed from gravel workings, but others, such as the proposals for disposing of nuclear waste, have attracted much attention, but though temporarily postponed, remain unsolved.
Minor fractures in the Eskdale Granite and adjacent Borrowdale Volcanic rocks have been investigated using a random sampling technique. One hundred joints were measured at each station and the data plotted on equal-area nets. The major concentrations are represented on maps in this paper. The distribution, dip and strike of the low-angled joints corresponds with that of the aplites and pegmatites and suggests that most of the low-angled joints were formed at an early stage in the emplacement of the granite. Very few of the high-angled joints show a similar correlation with aplites and pegmatites and the majority are thought to have been formed by a later north-to-south stress. Two types of joint pattern, with predominating high-angled joints, occur in the granite. One type is considered to consist of two near-vertical, shear-joint concentrations intersecting at about 60 o and bisected by two sets of tension-joints. These are attributed to irrotational fracturing resulting from an approximately north-to-south stress. The hypothetical shear-joints are parallel to sinistral and dextral faults and haematite veins. The other type is restricted to areas near the wrench-faults and haematite veins. Evidence is presented which suggests that these patterns are developed in zones of dextral and sinistral shearing and are due to rotational shear. Diffuse patterns in which low-angled joints predominate occur in both the granite and Borrowdale Volcanic rocks, only a few yards from normal faults. Although no satisfactory mechanical explanation of these patterns has been deduced, they are capable of empirical interpretation to give the approximate strike and direction of hade of the fault-plane. The structural history of the area is outlined.
Summary Localizod alterations in wall-rocks of a pre-granite joint system, and other fissures, in thermally metamorphosed andesites, rhyolites and tuffs have resulted in either epidotization or sericitization. Epidotization is often associated with the development of Ca-Fe garnets within the fissure and, more rarely, in the wall-rock. Later minerals, such as quartz, calcite, magnetite, haematite and metallic sulphides, occur filling cracks in the garnet in the centro of these garnet-bearing veins. The formation of epidote is attributed to silicification of the wall-rock followed by the introduction of Ca and OH from the granite. Al, Fe, Mg and some Ca migrated toward the fissure, where under higher temperatures in conditions of iron enrichment Ca-Fe garnets formed. Subsequently, movement of the granite mass cause deformation of the country rocks and also opened the garnet-bearing veins to fluids which precipitated to suite of hydrothermal minerals. Sericitization is associted with the formation of cordierite and is restricted to rocks adjacent to pyrite veins. Al, K, S and OH ions appear to have diffused into the wall-rocks, causing this alteration.
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