Calc-alkaline Suite Research Articles

The distribution of thorium, uranium, and potassium in Archean granites from northeastern Minnesota

The investigation of U, Th, and K distributions in 2700 m.y. old granitic rocks from northern Minnesota reveals the typical curvilinear increase in Th and U on Th and U versus K plots observed in most younger calc-alkaline suites.

The Feiran-Solaf gneiss belt, southwestern Sinai, Egypt

High-grade Archaean rocks of the remote Thrym Complex of southeastern Greenland expose a lower crustal section that formed at a depth of > 30 km at temperatures reaching 1000 °C and pressures approaching 1.5 GPa. The complex is part of the North Atlantic Craton, which is bound to the north by the Trans Hudson–Nagssugtoqidian–Ammassalik Orogen and to the south by the Makkovik–Ketilidian Orogen. The rocks in the complex include orthogneiss, migmatitic orthogneiss with banded or nebulitic fabrics, migmatite with a breccia-like structure (agmatite), and narrow bands of lensoidal mafic and ultramafic rocks (granulites) with associated widespread garnet-bearing mafic granulite, and a minor proportion of garnet–cordierite–sillimanite–biotite gneiss. The latter high-grade rocks form part of the substrate for the emplacement of the protoliths for orthogneiss that was synchronous with the ca. 2790–2700 Ma Skjoldungen Orogeny.At least two suites have been recognised in the Thrym Complex based on geochemistry. The oldest is a tholeiitic suite of mafic to ultramafic granulites, and the other is a calc-alkaline suite that includes felsic to intermediate orthogneiss. Most of the orthogneiss has a granodioritic (oldest) to quartz monzodioritic (younger) composition with rare monzogranitic, tonalitic, monzonitic and quartz dioritic protoliths. Historically, the orthogneiss units have been called TTGs, although monzogranite and tonalite are rare, and no trondhjemite is observed. In addition, they could also be called adakitic on geochemical grounds. Instead of using this terminology, which has genetic connotations, the orthogneiss is referred to as predominantly granodioritic to quartz-monzodioritic.Assuming that modern tectonics operated during the Neoarchaean, at least some of the mafic and ultramafic granulites and orthogneiss exposed in the Thrym Complex represent the root zone of a magmatic-arc that might have been relaminated around 2760 Ma during the collisional Skjoldungen Orogeny.

Calc-alkaline volcanic rocks from NW Sardinia: Evaluation of a fractional crystallization model

The volcanic centre of Monte Seda Oro, N. W. Sardinia, representative of a Cenozoic calc-alkaline andesitic suite of rocks is composed of a variety of rocks ranging from high alumina basalts to dacites. The minerals of basaltic, andesitic and dacitic rocks show only limited variation in chemical composition. The geochemical data suggest that the various rock-types are related by a crystal-liquid fractionation. Least-squate numerical calculations, using major element data, support the derivation of andesites with SiO3 content ranging from 53.8 to 59.0% from basalts having about 48.7% of SiO2 by low pressure crystal fractionation of the phenocryst phases present in these rocks. However, the origin of dacites cannot be readily explained by this mechanism.

Rare-earth elements in the Marda calc-alkaline suite: an Archaean geochemical analogue of Andean-type volcanism

REE, Th, U, Pb and Hf have been determined in nine selected samples from the Marda Archaean calc-alkaline suite. Data are consistent with field relationships and major and other trace element abundances, which suggest a crustal origin for the Marda magmas. REE patterns are analogous to continental margin (Andean) calc-alkaline volcanic suites and are not similar to those from other Archaean areas.

The geochemistry of the Archean Bourlamaque batholith, Abitibi, Quebec

The Bourlamaque batholith, of Archean age, outcrops in the Val d'Or mining camp of northwest Quebec. In order to describe its geochemistry and interpret its origin, 82 samples of the main igneous body, of synplutonic dykes, and of related later dykes were studied petrographically and analysed for 21 elements. Geochemical interpretation was based mainly on petrochemical variation (Larsen) diagrams and on abundance ratios calculated for several element pairs. The batholith is composed of at least two consanguineous and differentiated dioritic intrusions, probably introduced as sills into surrounding flat-lying volcanic rocks, and now metamorphosed to the greenschist facies. Local metamorphism appears to have been essentially isochemical except for CO2 and Cu. The redistribution of copper during metamorphism seems potentially important for mineral exploration. The Bourlamaque batholith, poor in K, Rb, Sr, Mg, Cr, and Ni, seems chemically very like the enclosing Archean volcanic rocks and similar but not identical to Phanerozoic calc-alkaline suites.

Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey

Analytical data for Sr, Rb, Cs, Ba, Pb, rare earth elements, Y, Th, U, Zr, Hf, Sn, Nb, Mo, Ni, Co, V, Cr, Sc, Cu and major elements are reported for eocene volcanic rocks cropping out in the Kastamonu area, Pontic chain of Northern Turkey. SiO2% versus K2O% relationship shows that the analyzed samples belong to two major groups: the basaltic andesitic and the andesitic ones. High-K basaltic andesites and low-K andesites occur too. Although emplaced on continental type basement (the North Anatolian Crystalline Swell), the Pontic eocene volcanics show elemental abundances closely comparable with typical island arc calc-alkaline suites, e.g. low SiO2% range, low to moderate K2O% and large cations (Cs, Rb, Sr, Ba, Pb) contents and REE patterns with fractionated light and almost flat heavy REE patterns. ΣREE and highly charged cations (Th, U, Hf, Sn, Zr) are slightly higher than typical calc-alkaline values. Ferromagnesian elements show variable values. Within the basaltic andesite group the increase of K%, large cations, ΣREE, La/Yb ratio and high valency cations and the decrease of ferromagnesian element abundances with increasing SiO2% content indicate that the rock types making up this group developed by crystalliquid fractionation of olivine and clinopyroxene from a basic parent magma. Trace element concentration suggest that the andesite group was not derived by crystal-liquid fractionation processes from the basaltic andesites, but could represent a distinct group of rocks derived from a different parent magma.

Origin of corundum-normative intrusive and extrusive magmas

MANY intrusive and extrusive calc-alkaline suites show a continuous trend from diopsode-normative basic magma to corundum normative acid magmas, that is, with an increasing SiO2 content there is an exceptional decrease in the Ca:Al ratio of the magma. A number of explanations have been proposed for these trends, including secondary alteration, vapour phase transfer, assimilation, crustal remelting, hydrous melting of the upper mantle and the fractional crystallisation of a variety of phases. We demonstrate here that corundum-normative magmas can be produced by the fractional crystallisation of a hornblendic amphibole from calc-alkaline magma under moderate water pressure.

3600-m.y. Rb [sbnd]Sr ages from very early Archaean gneisses from Saglek Bay, Labrador

Field studies in the vicinity of Saglek Bay, Labrador, demonstrated that it was possible to subdivide the Archaean gneiss complex into distinct lithologic units and erect a geologic chronology similar to that recognized in Godthaabsfjord, West Greenland. The Uivak gneisses are the oldest quartzo-feldspathic suite in the area and are distinguished from a younger gneissic suite in the field, the undifferentiated gneisses, by the presence of porphyritic basic dykes (Saglek dykes) within the Uivak gneisses. The Uivak gneisses range in composition from tonalites to granodiorites, with the two chemically distinct suites recognized: a grey granodioritic suite and an iron-rich plutonic igneous suite which locally intrudes or grades into a grey gneiss which strongly resembles the grey Uivak gneiss. Rb-Sr isotopic studies indicate an age of 3622 ± 72 m.y. (2σ) and initial Sr isotopic composition of 0.7014 ± 0.0008 (2σ) for the Uivak gneiss suite, i.e. grey gneiss plus iron-rich suite (λ Rb = 1.39 × 10 −11 yr −1). The grey Uivak gneiss suite, treated independently, defines a Rb-Sr isochron with an age of 3610 ± 144 m.y. (2σ) and initial Sr isotopic composition of 0.7015 ± 0.0014 (2σ) which is indistinguishable from the age and initial ratio of the total Uivak gneiss suite, grey gneisses plus iron-rich suite. The undifferentiated gneisses define a Rb-Sr isochron with an age of 3121 ± 160 m.y. (2σ), and initial Sr isotopic composition of 0.7064 ± 0.0012 (2σ). The isotopic data support field observations suggesting the undifferentiated gneisses were derived by local remobilization of the grey Uivak gneisses. The Uivak gneisses resemble the Amitsoq gneisses of Godthaabsfjord both chemically and isotopically. The interpretation of the initial Sr isotopic composition of the Uivak gneisses is interpreted as the time of regional homogenization rather than the initial ratio of the plutonic igneous parents of the Uivak gneisses as suggested for the Amitsoq gneisses. Although the undifferentiated gneisses are contemporaneous with the Nuk gneisses of West Greenland, they do not form a well-defined calc-alkaline suite and may not be associated with major crustal thickening in the Labrador Archaean.

Strontium isotopic studies of the volcanic rocks of the Saunda arc, Indonesia, and their petrogenetic implications

Pleistocene and Recent lavas from the Sunda arc range from those showing affinities with the island arc tholeiitic series, through a spectrum of calc-alkaline to high-K alkaline rocks. The tholeiitic rocks have relatively low 87Sr 86Sr ratios averaging 0–7043; the calc-alkaline rocks show a wide range (from 0.7038 to 0.7059, averaging 0.7048); the high-K alkaline rocks average 0.7045. A rhyolitic ignimbrite from Sumatra has an 87Sr 86Sr ratio of 0.7139. The relationship between 87Sr 86Sr and major and trace element geochemistry is variable and complex. Lavas from the same volcano sometimes show significant differences in 87Sr 86Sr despite close geochemical relationships. Rocks of the calc-alkaline suite show a regular decrease in 87Sr 86Sr from West Java to Bali and there is some evidence for increasing 87Sr 86Sr with increasing depth to the Benioff zone. Calc-alkaline and tholeiitic rocks from the Sunda arc have significantly higher 87Sr 86Sr ratios than those from other island arcs, except from those arcs where continental crustal involvement has been inferred (e.g. New Zealand). A model of 87Sr enrichment due to isotopic equilibration of oceanic crust with sea water and disequilibrium melting in the slab and/or mantle is favoured to explain the Sr isotopic composition of the tholeiitic and normal calc-alkaline lavas. Calc-alkaline lavas with high 87Sr 86Sr ratios are best explained by either sialic contamination, or the presence of alkali basalt as a component of the downgoing slab. The Sr isotopic data for the high-K alkaline lavas suggest a mantle origin. The high 87Sr 86Sr ratio in the Lake Toba rhyolite implies a crustal origin.

Subdivision of the Archean lavas of the Abitibi area, Canada, from Fe-Mg-Ni-Cr relations

The lavas of a part of the Archean Abitibi region may be divided into three stratigraphic levels in each of which FeO-MgO-Ni-Cr contents conform to certain broad differentiation trends. Within each stratigraphic level, there is a tendency for rocks to become more felsic upwards. The earliest and stratigraphically lowest subdivision is composed largely of magnesium-rich basaltic lavas called the magnesian suite. In the central part of the pile, where basalts predominate, the lavas contain intermediate MgO concentrations, and display pronounced Fe enrichment in intermediate members similar to conventional tholeiites. In the latest and stratigraphically highest lavas, where andesites predominate, Fe depletion is characteristic; these lavas are grouped into a primitive calcalkaline suite. All of the Abitibi lavas contain unusually high Ni and Cr. Other Archean lava piles appear to be similarly divisible, although all three suites are not always present. Mafic end-members of the three complete differentiation suites are viewed as possible source magmas derived by partial melting in a primitive, olivine-rich parent, probably the Archean mantle. The earliest, and highest temperature magmas precipitated olivine, Al-clinopyroxene, and minor Al-orthopyroxene, and display moderate FeO, TiO 2, MnO, Al 2O 3, and CaO enrichment in more felsic members. The intermediate age lavas, derived originally by less complete melting in the parent, precipitated plagioclase, olivine, and lesser clinopyroxene, and display, as a result, strong Fe enrichment until, in intermediate members, magma volumes became small enough to yield P f of levels sufficient to form clinopyroxene plus magnetite. The uppermost lavas, derived by relatively small volumetric melting in the parent, contain abundant Fe-Ti oxides in even the most mafic members, along with augite and plagioclase.

Geochemistry and tectonic setting of the late Precambrian Holyrood plutonic series of eastern Newfoundland

Major and trace element chemistry suggest that the Holyrood plutonic series is a co-magnetic calc-alkaline suite, formed at about 5 kb P H 2O by fractionation of plagioclase, amphibole and clinopyroxene from a gabbroic magma which was derived from the upper mantle. It appears unlikely that the series is genetically related to the Harbour Main volcanic rocks, either magmatically or by hybridization. Chemical comparison of the Holyrood series with suites from known tectonic environments suggest that this region approximated a ‘basin and range’ type of tectonic setting during formation of the Holyrood plutonic series.

Role of underthrust oceanic crust in the genesis of a Fijian calc-alkaline suite

A test of the proposition that calc-alkaline magmas are direct partial melts of underthrust oceanic crust is presented. It involves numerical evaluations of whether or not the major and trace element and isotopic composition of a Fijian calc-alkaline rock suite is consistent with these rocks representing unfractionated partial melts of oceanic crust at high pressures. Experimental data for one of the samples constrain the calculations. When compositions of liquidus minerals at 27 kb are combined with compositions of the volcanic rocks, close approximations can be made to the composition of oceanic crust only if the degree of partial melting is between ∼20% (dacite) and ∼45% (basaltic-andesite), and if accessory minerals are refractory phases. Concentrations of elements such as K, Rb, Sr, Pb, Th, and U, and 87Sr/86Sr ratios in the Fijian suite can be satisfactorily explained only if the parental material consisted of altered rather than fresh ocean floor basalt. Sediments are not likely to have been involved. Concentrations of Na, Ni, Co, Cr, Sc, V, the REE, Y, Zr, Hf, and Nb cannot be explained unless, or in some cases even if, several accessory phases are partially refractory. Therefore, partial melting of underthrust lithosphere does not seem likely to produce magmas with the composition of at least one quite typical calc-alkaline suite.

Geochemistry and Geochronology of the Southern Caribbean–Northern Venezuela Plate Boundary

Research Article| July 01, 1974 Geochemistry and Geochronology of the Southern Caribbean–Northern Venezuela Plate Boundary FRANCISCO SANTAMARÍA; FRANCISCO SANTAMARÍA 1Department of Geology, Rice University, Houston, Texas 77001 Search for other works by this author on: GSW Google Scholar CARLOS SCHUBERT CARLOS SCHUBERT 2Departamento de Ecología, Instituto Venezolano de Investigatións Cientificas, Apartado 1827, Caracas, 101, Venezuela Search for other works by this author on: GSW Google Scholar Author and Article Information FRANCISCO SANTAMARÍA 1Department of Geology, Rice University, Houston, Texas 77001 CARLOS SCHUBERT 2Departamento de Ecología, Instituto Venezolano de Investigatións Cientificas, Apartado 1827, Caracas, 101, Venezuela Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (7): 1085–1098. https://doi.org/10.1130/0016-7606(1974)85<1085:GAGOTS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation FRANCISCO SANTAMARÍA, CARLOS SCHUBERT; Geochemistry and Geochronology of the Southern Caribbean–Northern Venezuela Plate Boundary. GSA Bulletin 1974;; 85 (7): 1085–1098. doi: https://doi.org/10.1130/0016-7606(1974)85<1085:GAGOTS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The geochemistry and geochronology of the igneous rocks from the Venezuelan islands in the southern Caribbean, the Netherlands Leeward Islands, and the Caribbean Mountains of northern Venezuela were studied in an effort to test plate tectonics models for the evolution of that part of the Caribbean region. The continental platform north of Venezuela is underlain by an igneous and metamorphic complex that crops out on the Venezuelan islands. The older metamorphic rocks (lower to upper greenschist facies) are similar to those found in the Caribbean Mountains. These rocks were intruded by basic and granitic igneous rocks and andesitic to basaltic volcanic rocks during Early Cretaceous to early Tertiary time.Geochemically, the igneous rocks can be divided into two suites, a calc-alkaline suite consisting of quartz diorite, granodiorite, trondhjemite, and granite, and an olivine and ocean-floor tholeiitic suite consisting of gabbro, diabase, lamprophyre, and orthoamphibolite. The calc-alkaline affinity is shown by high Al2O3 and K2O, and low MgO and TiO2 contents. The K2O content increases southward from the Venezuelan islands toward the Caribbean Mountains. The tholeiitic affinity is shown by low Fe2O3/MgO ratios, low K2O and Sr contents, and high K/Rb ratios. K-Ar age determinations on these rocks show that the tholeiitic rock suite is the oldest, which confirms field relations, ranging between 114 m.y. and 130 m.y. (Early Cretaceous). The K-Ar ages of the calc-alkaline rock suite range between 30 m.y. and 84 m.y. (Late Cretaceous to Oligocene). These ages are interpreted to represent a Late Cretaceous–early Tertiary time of intrusion and later metamorphism and also support a late Eocene–Oligocene erogenic event that resulted in the present structural configuration of the central Caribbean Mountains. A dacite in the Carúpano area (Araya-Paria Península) yielded a K-Ar age of 5 m.y., or late Pliocene, which is the youngest evidence of igneous activity in northern Venezuela. The dacite is possibly related to the younger volcanic province of the Lesser Antilles.Our data support the hypothesis that the Aves Ridge represents a presently inactive volcanic arc prior to the Lesser Antilles arc. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Calc-Alkaline Volcanism and Plutonism from the Great Bear Batholith, N.W.T.

The Camsell River – Conjuror Bay area is a pendant of Aphebian intermediate and felsic volcanic rocks, lying in a granitic complex, and is part of the Great Bear batholith. This batholith complex has been interpreted as being the orogenic belt of the Coronation geosyncline.Twenty-four analyses of volcanic and plutonic rocks are presented; these show that, in spite of alteration, the rocks can be classified as comagmatic and part of an alkali-rich calc-alkaline suite. The suite is chemically similar to younger suites from continental-margin orogenic belts. These similarities support proposals that the Coronation geosyncline was of Andean type and that the magmas may have been generated by subduction.

Volcanism and orogenic belts — The origin of andesites

Since the early attempts of Bowen to account for the diversity of the igneous rocks, a number of proposals have been offered to explain the voluminous andesites of the continental orogenic belts. These include: 1. (1) contamination of basic magmas; 2. (2) anatexis of sialic crust; 3. (3) differentiation of basaltic magmas; 4. (4) anatexis of wet peridotite mantle; and 5. (5) anatexis of oceanic crust and mantle in subduction zones. This paper assembles some of the results of endeavors in experimental petrology and geochemistry to evaluate these proposals. The concept of contamination is supported by neither geologic occurrence nor isotope geochemistry. Similar judgements, together with the unrealistically high temperatures that are required, argue against anatexis of sialic crust to produce primary andesitic liquids. Differentiation of basic magmas to produce andesitic and other silica-rich melts unquestionably occurs. Recent experimental evidence on the hydrothermal melting of basalts reveals that fractionation of silica-poor amphiboles is probably a more efficacious mechanism for producing the calc-alkaline trend than is the early separation of magnetite. Nevertheless, it has yet to be demonstrated that such processes have operated to the extent necessary to produce the orogenic andesites. High-pressure melting experiments on wet synthetic peridotites disclose that quartz-normative liquids are the products of partial melting at pressures up to about 20 kbar. This suggests that andesites can develop from anatexis of water-bearing continental and oceanic mantle to depths of about 60 km, but this mechanism alone fails to account for the spatial distribution of the orogenic calc-alkaline suite. Armed with experimental data on melting and other phase relationships of basic and ultrabasic compositions, together with recent data on the abundances of trace and minor elements in andesites, the most attractive models involve anatexis of mantle peridotite or oceanic crust metamorphosed to amphibolite or eclogite in subducted lithosphere. Melting may also occur in rocks above the hanging wall of the Benioff zone as the result of incorporation of water released by dehydration of the descending slab. The fractionation of alkalis into amphiboles, and into micas at greater depths, may be responsible for the observed zoning of K 2O in surficial calc-alkaline rocks overlying the distal plate boundaries. However, this model is not in accord with the concept of generation of calc-alkaline magmas at depths of hundreds of kilometers proposed by some workers.

Les caract�res magmatiques du volcanisme plio-quaternaire des Andes dans le Sud du P�rou

Chemical data on late cenozoic lavas (83 new analyses) from southern of Peru indicate a zonal arrangement of lavas types according to their distance from the trench. The nearest belong to a calc-alkaline suite and the farthest are shoshonites rocks. The calc-alkaline rocks show progressive increase in K2O content and in K2O/Na2O ratio in northeastern direction. The shoshonitic rocks are more potassic and titaniferous, and the K2O/Na2O ratio is approximatively constant. The potash content of the two series correlate with the depth of the inclined seismic zone beneath the volcanoes, but this correlation is less well established than in island arcs.

Geochronology and petrology of recent volcanics in the eastern Aegean Sea (West Anatolia and Lesvos Island)

During the lower and middle Miocene the western Anatolia and the eastern Aegean Sea were dominated by a calcalkaline volcanism associated with minor acid and basic volcanics. The basic subcrustal volcanics consist mainly of alkali basalts and hawaiites (9.7–11.9 m.y.), nepheline hawaiites and nepheline trachyandesites (Kula area from 1.1 m.y. to the recent times). The rhyolitic volcanics (12.5 m.y.) derived by a partial melting process in the upper crust (87Sr/86Sr=0.7121). The calcalkaline suite (16.2–21.5 m.y., mean value87Sr/86Sr=0.708) shows a trend from latite-andesites to dacites and rhyodacites; a latite andesite system related to a sinking slab of lithosphere and constituted by a mixing of oceanic crust (tholeiite), oceanic sediments and/or tectonic fragments of sialic crust is envisaged.

The genesis of the calc-alkaline rock suite

The derivation of an island arc calc-alkaline suite from an alkaline parental magna source is suggested from petrological and mineralogical evidence in the Lesser Antilles. Possible sources are discussed, and a partial melt from the Upper Mantle, rather than a descending oceanic crustal plate preferred. The consequence of the incomplete melting of a plate in a subduction zone is the production of local heterogeneity in the Upper Mantle, leading to geographical chemical differences in magmas produced in partial melting episodes. The calc-alkaline trend apparently reflects the physical as much as the chemical environment of fractionation.

Melting Relations of Basalt with Equilibrium Water Pressure Less Than Total Pressure

Equilibrium H,O pressure (POH.O) was fixed at values less than total pressure (PT) in melting experiments on mixtures of 1921 Kilauea tholeiite, H,O, and CO, (58-5 mole per cent H,O, 41-5 mole per cent CO,), buffered by Ni+NiO. New determinations of the beginning of melting of mixtures of 1921 Kilauea tholeiite and H,O buffered by quartz+ fayalite+magnetite were made at 2 and 3 kb. Microprobe analyses of coexisting glass, clinopyroxene, ±olivine, ;£ amphibole were determined for several runs. Decreasing H,O fugacity (/H,O) to about six-tenths the fugacity of pure H,O ( /H,O) raises the solidus and the upper stability limit of plagioclase. Plagioclase and clinopyroxene coexist in equilibrium with liquid—a feature not observed in the pure H,O system. Amphibole is stable to about 970 °C at 2 kb, 1025 °C at 5 kb and 1060 °C at 8 kb. The Al (VI)+Ti contents of the amphibole increase with P, yielding kaersutite at 1050 °C and 8 kb. Calculated modes for the condensed phases reveal large differences in the amount of glass (liquid) present and large differences in liquid composition below and above the breakdown temperature of amphibole at 5 and 8 kb. Liquids coexisting with amphibole, clinopyroxene, olivine, and magnetite are dacitic near the solidus and silica-rich andesites around 1000 °C at 5 and 8 kb. The results of this study substantiate the model for the generation of the calcalkaline suite by partial melting of H,O-rich basalts.

The geochemistry and correlation of the Warren House, the Uriconian and the Charnian Volcanic Rocks from the English Pre-Cambrian

The Warren House, Uriconian and Charnian Volcanic Groups are poorly exposed remnants of the volcanic activity of the English Pre-Cambrian. The geological features of these rocks have lead to various correlations between these groups. Analyses of forty-one samples of these lavas, for major and trace elements, reveal considerable geochemical differences between these groups. It is therefore evident that these groups cannot be lateral equivalents. The evidence suggests that the Warren House lavas are a basaltic group while the Uriconian is a calc-alkaline suite. The Charnian porphyroids have unusual chemical features which suggest an origin by melting of pre-Charnian metamorphic basement. Recent suggestions on the tectonic situation of these rock groups are briefly discussed.