Thin silty deposits are widespread in N. E. Essex. They are thickest on the coast at-the Naze where they reach nearly 1.5 m. These deposits overlie fluvial sands and gravels though in a number of localities there is a layer of aeolian sand (cover-sand) between the silt and the gravel. Up to 70% of the particle size distribution is within the silt fraction (2-63 um) which is consistent with aeolian transport and so these deposits are probably of loessial origin. Although the majority are classified as sandy loess, the loessial , sediments of N. E. Essex are a textural continuum ranging from loess to sediments approaching aeolian sand in composition. This reflects the degree of inter-mixing of overlying loessial silt with underlying cover-sand. The loess is texturally similar to that in Kent but the sandy loess, typical of inland parts, resembles deposits in Norfolk. The heavy mineral content of loessial sediments is uniform throughout N. E. Essex and the mineralogical similarity of the loess to underlying aeolian sand indicates the same sources supplied the silt and sand fractions of both sediments. The coarse silt fraction of N. E. Essex loess is like that of loesses elsewhere in Eastern England and those of the Netherlands and Belgium which suggests a common origin. The North Sea Basin is the likely source and a possible deflation area north-east of the Dogger Bank is suggested. Differences in the heavy mineral content of the sand fractions of loesses from N. E. Essex and Norfolk probably reflects their derivation from more local sources. N. E. Essex loess is Devensian and accumulation probably commenced at about the maximum extent of Devensian ice (about 18,000 Yr. B. P. ) and continued until about 14,000 Yr. B. P. A correlation with Cover-Loams I and II of Belgium which are -Pleniglacial B of the Weichselian, (Devensian) is suggested.

Metamorphosed pelitic rocks from the Eastern Dalradian (Scotland) contain Al₂SiO₅-bearing quartz veins. The veins formed during amphibolite-grade regional metamorphism. Veins occur in both Barrovian and Buchan-type terranes. Staurolite-grade pelitic schists in the Buchan region (Whitehills and Boyndie Bay) contain numerous pegmatitic quartz-and alusite-biotite veins. Optically strain-free quartz inclusions located within vein andalusite contain primary CO₂-CH₄/N₂ fluid inclusions (Type Aqz). Several generations of secondary H₂O-NaCl (Type B) fluid inclusions have also been identified in vein quartz. A number of Type Aqz inclusions have densities appropriate to the peak-metamorphic conditions calculated for the surrounding host rock and appear to indicate a CO₂-rich fluid was present during vein genesis. Post-entrapment modification however may have occurred during uplift as the mean Type Aqz isochore lies outside peak P-T conditions calculated, possibly suggesting some compositional modification. Kyanite-grade pelitic schists in the Sandend and Glen Esk areas (Barrovian-terranes) host pegmatitic kyanite-quartz veins. Pegmatitic kyanite crystals contain CO₂-bearing fluid inclusions (Type AkY); however, densities calculated lie outside the stability field of kyanite indicating either the Type Aky inclusions have been subjected to post-entrapment modification or the inclusions formed during the later stages of uplift. A source for the CO₂-rich fluid is enigmatic. The possible sources of CO₂ identified in Type A fluid inclusions are: 1) decarbonation reactions; 2) oxidation of carbonaceous or graphitic matter; and 3) deep-seated origin, ultimately from degassing of the mantle. Calc-silicate horizons and graphite-bearing schists are found within the Eastern Dalradian providing a source for both 1 and 2, with the gabbros of the 'Younger Basics', emplaced between the regional D₁ and D₃ events, providing a source for 3. The Portsoy Gabbro (component of the 'Younger Basics') appears to have altered the ¹³C isotope value of carbonate rocks structurally above the gabbro and may therefore be the source for the CO₂-CH₄/N₂ (Type Aqz) inclusions identified in veins from the Buchan-type terrane. Metamorphosed pelitic rocks of the Betic Cordillera (southern Spain) contain Al₂SiO₅-bearing quartz veins. The veins commonly contain all three Al₂SiO₅ polymorphs. Two vein types are recognised based on mineralogy. Fluid inclusion analysis shows that vein-forming fluids were predominantly CO₂-H₂O mixtures produced during devolatilisation of the local graphite-bearing pelitic host rocks. Spectacular post-entrapment modification textures attest to the rapid uplift path proposed for the Al₂SiO₅-bearing quartz veins and host rocks.

The Mull Tertiary igneous complex is characterised by large numbers of cone-sheets of a wide range of compositions (45-75% 5i02). Over 200 samples have been analysed for major and trace elements. Some were selected for further detailed chemistry and isotopic analysis. These new data have been combined with recent publ ished and unpublished work of others to propose an evolutionary model for the complex. The petrology and geochemistry of each of the three centres is evaluated in turn. Centre I has a considerable number of the early acid and intermediate suite of conesheets as well as the earliest of the early basic conesheets. It appears that these two suites are chemically related by two main magma chamber processes, crystal fractionation and hybridisation of which the latter is the more important. On REE and isotope evidence the magmas of this centre are shown to have been contaminated by both Lewisian granulites and Moine meta_$ediments. Centre 2 is dominated by the effects of crystal fractionation though hybridisation is also evident. During this period the early magma-type was replaced by one which was moderately more enriched in incompatible elements. The evolution of this late magma-type is characterised by extreme Fe-enrichment (~18%) in the intermediate range, largely due to the late crystallisation of magnetite under conditions of lower f02 than previously. The Fe-rich nature of the late magma-type was firmly established by Centre 3 times. The composition of the cone-sheets from this centre is mainly restricted to ferrodiorite. It is suggested that frequent replenishment by more primitive magma, with crystal fractionation, buffered the magma composition. Mixing between this and any granitic magma was probably inhibited by density differences. Thus the complex resulted from three cycles of activity during which hybridisation was gradually replaced by crystal fractionation as the more dominant magma chamber process, oxygen fugacity levels fell and crustal contamination decreased with time. The basic magmas of the Mull cone-sheet complex are high in calcium and low in alkalis and thus similar to the Preshal Mhor magma-type found in other centres, dykes, and occasional lava flows of the British Tertiary Volcanic Province.

No description available.

No description available.

No description available.

The Mount Tawai peridotite is a batholith, elongate north-south, situated between the Kinabatangan and Labuk rivers in the North Borneo ultrabasic belt. The surrounding country rocks are Upper Cretaceous and Tertiary sediments and volcanics which strike predominantly E.N.E. They are separated from the peridotite by a fault breccia which contains inclusions of metamorphic rocks. The batholith comprises at least three partially separated tectonic units, the largest of which is the Main Tawai block. Theouter parts of the tectonic units exhibit a crude gneissose foliation and peripheral serpentinization. The batholith is composed mainly of harzburgite with scarce dunite, pyroxenite and gabbro phases. The dunite occurs in lenticular pods which dip steeply westward in the Main Tawai block. Some of the dunite lenses contain thin chromite bands showing evidence of rudimentary gravity stratification. The harzburgite is composed mainly of forsterite and enstatite with only minor endiopside. The alumina content of the enstatite varies from 1.3 to 7.4 per cent and that of the endiopside from 2.9 to 7.2 per cent. The dunite bandscontain forsterite and chrome spinel, the composition of the latter varying from cr(_65.5) AL(_32.2) (Mg(_68.1)) to cr(__32.6) AL(_66 .9) (Mg(_63.8)) on Thayer's (1946) shortened formula. The gabbroic rocks are irregularly distributed within the batholith occurring mainly as tectonic inclusions. Both the ultrabasic and basic rocks are considered to have been derived from the same parent magma. The absence of anorthite from the ultrabasic assemblages is explained by an initial phase of differentiation at very high temperature and pressure which suppressed the precipitation of plagioclase but favoured the introduction of alumina into the pyroxenes. During the initial phase of differentiation only olivine, enstatite, endiopside, and spinel were precipitated, but there must have been frequent but short-lived intervals in which only olivine and spinel were precipitated; these are thought to have accumulated in hollows and channels on the floor of a crystal pile. A systematic increase of alumina in the pyroxenes and spinels of the Main Tawai block has been traced and is attributed to a crystallisation sequence. A gabbroic phase is thought to have been precipitated on top of the ultrabasic crystal pile following a drop in temperature which resulted in the precipitation of plagioclase and the lowering of the Mg/Fe ratio in the pyroxene and olivine. A calculation of the average composition of the rocks of the North Borneo belt is in close agreement with the average mantle composition suggested by Ringwood (1959). This evidence together with the high temperature and pressure conditions needed to explain the ultrabasic assemblages has led to the conclusion that the parent magma of the Mount Tawai complex was derived by fusion of upper mantle material. After or during the final stages of differentiation the gabbroic fraction was injected into the crust creating a pre-heated path up which the hot, already-differentiated peridotite rose as a series of almost crystalline units. During this stage a gneissose folliation developed roughly parallel to the sides of the intrusive units. Thermal metamorphism of the country rocks to garnet amphibolite fades accompanied the process. After cooling beneath the surface the intrusive units were serpentinised and emplaced in their present position by faulting, which also disrupted the thermal metamorphic aureole. Late lime bearing solutions, deposited calc-silicate veins and altered some of the gabbro to rodingite. The final emplacement had profound effects on the drainage system and occurred in late or post Pleistocene.

No description available.

No description available.

No description available.