Association Of Volcanic Rocks Research Articles

The tectonic significance of Ordovician basic igneous rocks in the Southern Uplands, southwest Scotland

AbstractIn the northern part of the Southern Uplands, restricted volumes of basic igneous rocks occur at or near the base of the Ordovician sedimentary strata. These rocks have previously been interpreted as ocean-floor tholeiites representative of the subducted Iapetus oceanic plate, preserved as tectonic slivers in a fore-arc accretionary prism. The alternative, back-arc basin model proposed for the Southern Uplands on sedimentological evidence raises questions over the origin of these rocks. New geochemical data and previously published data clearly indicate that the volcanic material does not have a simple single source. The oldest (Arenig) volcanic rocks from the Moffat Shale Group associated with the Leadhills Fault include alkaline within-plate basalts and tholeiitic lavas which possibly display geochemical characteristics of midocean ridge basalts. In the northernmost occurrence, alkaline and tholeiitic basalts contained within the Caradoc Marchburn Formation are both of within-plate ocean island affinity. To the south, in the Gabsnout Burn area, the Moffat Shale Group contains lenticular bodies of dolerite and basalt which have characteristics of island-arc to transitional basalts. This complex association of basaltic volcanic rocks is, at the present time, difficult to reconcile with either a simple fore-arc or back-arc setting for the Southern Uplands. However, the increasing arc-related chemical influence on basic rock geochemistry towards the southeast may tentatively be used in support of a southern arc-terrane, and as a result, a back-arc situation for the Southern Uplands basin. An alternative is that these volcanic rocks may represent the local basement to the basin and include remnants of an arc precursor to the Southern Uplands basin.

Genesis of continental crust under island arc conditions

In the Japan context, the following characteristics of arc volcanic rocks are important for crustal growth: (1) intimate association of volcanic rocks of tholeiitic and calc-alkaline series; (2) repeated eruption of basaltic and dacitic lavas in a volcanic succession; (3) gradual change in chemistry from tholeiitic to calc-alkaline volcanic rocks; (4) crystallization differentiation which includes the crystallization of plagioclase along with other mafic minerals; (5) marked enrichment of K 2O associated with slight depletion of compatible elements; (6) an evolution limit represented by, for instance, Rb Sr ratios of 0.23–0.28 and SiO 2 contents of 60–66 wt.% and (7) repetitive magma mixing. Batch fractionation in refilled magma chambers best accounts for these characteristics, transforming mantlederived magmas through calc-alkaline magmas to magmas of composition very close to the bulk composition of the upper continental crust. Systems of periodically refilled magma chambers are general in the Japanese arcs. Differentiates and accumulated crystals may form the compositional stratification of the continental crust.

The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar, Xinjiang

Abstract The Middle Devonian volcanic rocks in the northern area of East Junggar, located between the Ertix and Ulungur rivers of northern Xinjiang, may be divided into basic and acid ones. It is evident that a compositional gap exists between the two groups so that the volcanic rocks are not in line with a calc‐alkaline series because the intermediate rocks are absent in the area. The fact shows that the volcanic rocks are a typical bimodal association. The formation of the bimodal association of volcanic rocks in the area was closely related to continental rifting or continental extension in the Middle Devonian. In such a tectonic setting, magmas were first produced by partial melting of the mantle. Where crustal thinning was greater, the magmas ascended and erupted on the surface directly so that the basic volcanic rocks formed, but olivine and / or partial pyroxene fractionation occurred in the magmas during their ascent through the thinning crust. On the other hand, where crustal thinning was less, ascending mantle‐derived magmas reached the lower crust and accumulated there, resulting in partial melting of the lower crust and thus giving rise to the contaminated magma which was consolidated as acid volcanic rocks on the surface.

The geological significance of manganese distribution in Jurassic-Cretaceous rocks of the Pindos Basin, Peloponnese, Greece

The Jurassic-mid-Cretaceous Radiolarite Series of the Pindos zone of the Peloponnese is a deep-water sediment sequence. It comprises Jurassic red mudstones, siliceous mudstones and ribbon-bedded cherts; and Cretaceous red mudstones, siliceous mudstones, cherts, calc-turbidites and terrigenous turbidites. Bedded manganese ores occur both in cherty calc-turbidites and ribbon-bedded cherts. In order to determine the origin of Mn enrichment, the transition element geochemistry and mineralogy has been determined for sediment samples from seven representative sections of the Radiolarite Series, representing an along and across strike section of the Pindos basin. Smectite and palygorskite are the principal clay minerals, with lesser mica, sepiolite and chlorite. Fe Al ratios in Jurassic rocks are close to values in continental detritus but increase upwards to the middle Cretaceous. Nevertheless, the association of volcanic rocks with Jurassic sediments is circumstantial evidence that the minor Mn enrichment is the result of hydrothermal processes. The hypothesis that high Fe Al in Cretaceous sediments is due to ophiolitic detritus is untenable in the Peloponnese, where sediment is derived from sources lacking ophiolites: the Fe enrichment must therefore result from hydrothermal processes, which may be related to formation of oceanic crust in the Pindos-Arvi zones. Mn concentrations are associated with diagenetic cherts at the top of calc-turbidites; in these settings, Mn correlates positively with Ca and negatively with Fe, suggesting that the concentration of beds of ore is diagenetic.

Evolution of the Early Proterozoic Colorado province: Constraints from U-Pb geochronology

The Colorado province represents an addition of a belt of rocks more than 500 km wide to the southern margin of the Archean Wyoming craton during the Early Proterozoic, between about 1790 and 1660 Ma. Correspondence in ages between metamorphism, deformation, and plutonism; association of volcanic rocks with comagmatic calc-alkalic plutons; and lack of older basement are all consistent with the interpretation that the rocks of the province are products of arc magmatism and cannibalistic sedimentation along a convergent margin at the southern edge of the craton.

Geochemical Evidence for the Tectonic Setting of Late Proterozoic Volcanic Suites in Central England

Summary The late Proterozoic basement of central England is largely concealed by a cover of Phanerozoic rocks. Proterozoic volcanic rocks are exposed as a result of localized uplift/folding in the eastern Midlands (the Charnian Supergroup) and adjacent to major crustal lineaments which include the Church Stretton and Pontesford-Linley Fault Zones (the Uriconian volcanic group) and the Malvern lineament (the Warren House volcanic group). The geochemistry of these volcanic associations has been examined through midocean ridge basalt (MORB)-normalized multi-element diagrams which emphasize the contrasted and variable relationships between large-ion lithophile (LIL) elements and high field strength (HFS) elements within/between these volcanic groups. The Charnian Supergroup comprises over 2.5 km of bedded volcaniclastic and sedimentary rocks locally with interbedded lavas and high-level intrusions (termed ‘porphyroids’) of andesitic to rhyodacitic composition. The more mafic lavas are characterized by enrichment of the LIL elements K, Rb, Ba and Th, while HFS elements (Nb, Ta, Zr and Y) are depleted relative to MORB, and suggest that the Charnian lavas resulted from calcalkaline volcanism in an island arc. The Charnwood diorites , a minor intrusive suite emplaced into the bedded series, reflect increasing maturity of this same arc. The Uriconian volcanic group comprises a bimodal association of volcanic and pyroclastic rocks ranging from basalt to rhyolite in composition. They are enriched in HFS elements relative to MORB, which may indicate a within-plate component to the source, although their high LIL/HFS element ratios imply a subduction-related environment. The tectonic environment of eruption may have been a post-subduction, ensialic faulted basin between the Church Stretton and Pontesford-Linley Fault Zones. The Warren House group is in tectonic contact with the Malvernian (calcalkaline) plutonic complex and has LIL-element concentrations enriched in relation to MORB, but shows slight depletion of HFS elements similar to that exhibited by some marginal basin basalts and island arc tholeiites. These lavas may represent relics of marginal basin lithosphere trapped and uplifted in a Proterozoic suture between the Uriconian and Charnian terranes. These new geochemical data suggest that the late Proterozoic basement of central England comprises a heterogeneous mosaic of geochemically-distinct volcanic terranes, formed in separate volcanic arc/marginal basin environments and juxtaposed by subsequent accretionary tectonism in the Avalonian/Cadomian Orogeny (cf. Thorpe et al. 1984).

Sedimentologic and Geochemical Evidence for Middle Ordovician Near-Trench Volcanism in the Central Appalachian Orogen

The Jonestown volcanic rocks are a minor but important component of the Greenwich slice of the Hamburg klippe of eastern Pennsylvania. Sedimentary rocks of the Greenwich slice are arranged in faultbounded, coarsening-upward sequences of pelagic deposits (Early to Middle Ordovician) overlain by hemipelagic and turbidite deposits (Middle Ordovician). Petrographic and geochemical characteristics of the sedimentary rocks indicate derivation from continental rather than volcanic sources. The coarsening-upward sequences of the Greenwich slice are inferred to record advance of a site on oceanic lithosphere toward, and ultimately into a trench by Middle Ordovician time. Rocks of the Jonestown volcanic suite were extruded onto and intruded into the inferred Middle Ordovician near-trench and trench axis mudstone and sandstone. Immobile element concentrations of the Jonestown suite are typical of mid-oceanic ridge basalts and, along with the lack of associated shallow-water and/or volcaniclastic sedimentary rocks, argue against magmatism related to an ocean island-trench encounter. Normal fault-related magmatism on the subducting plate seaward of the inner trench slope may explain some of the stratigraphic relations between the igneous and sedimentary rocks but raises more questions than it answers (e.g., mechanism of magma generation). The association of the MORB-like Jonestown volcanic rocks and near-trench sedimentary rocks of the Greenwich slice is best explained by either extension of a leaky transform fault into the trench or migration of a mid-oceanic ridge toward the trench. Geochemical and geological differentiation of these scenarios is not possible at the present time.

Mesozoic volcanic rocks in the lower reaches of the changjiang river

Mesozoic magmatic activities in the eastern part of China were closely related to the mutual movement of the Eurasian and Kula plates. Mesozoic volcanic rocks can be divided into the southern, central and northern petrological regions. The Changzhou-Yueyang deep fault in the south and the Baodi-Changli-Jinzhou fault in the north are the main boundaries between them and extend in a roughly NEE direction.Mesozoic volcanic basins distributed in the lower reaches of the Changjiang River are located near the boundary line between the southern and central petrological regions. Based on the association of volcanic rocks they can be divided into four volcanic belts. From south to north they are as follows: (I) Guangde-Liyang-Wuxi volcanic belt; (II) Fanchang-Lishui-Zhenjiang volcanic belt; (III) Huaining-Luzong-Ningwu volcanic belt; (IV) Chuxian-Jinhu volcanic belt. These volcanic belts are nearly parallel with the Changzhou-Yueyang deep fault.Their major-element chemical variation, strontium, oxygen and sulphur isotopes and REE suggest that the dacite-rhyolitic magma in volcanic belt (I) was generated by anatexis of the lower part of the continental crust, and the andesitic magma in the volcanic belts (III) and (IV) might be generated by fusion of the upper mantle mixed with some other materials in the subducted zone under great compression, at 1200°–1250°C, with sufficient water. The “trachyandesite-latite rock series” is very different from the shoshonitic one and, it might be the product of the interaction of alkali-enriched andesitic magma with gypsum-salt beds. The volcanic rocks in belt (II) exhibit a transitional character.

Geochemical evidence for the tectonic setting of the Coast Range ophiolite: A composite island arc–oceanic crust terrane in western California

The Middle to Late Jurassic age Coast Range ophiolite (CRO) of California contains two geochemically distinct volcanic rock associations that formed in different tectonic settings. Volcanic rocks from the southern CRO (Point Sal, Cuesta Ridge, Stanley Mountain, Llanada, Quinto Creek, and Del Puerto) and parts of the northern CRO (Healdsburg, Elder Creek) are similar to low-K tholeiites and calc-alkaline rocks of the island-arc suite. The thin volcanic sections of these ophiolite remnants suggest formation by intra-arc rifting. In contrast, volcanic rocks from Stonyford seamount and Paskenta in the northern CRO are transitional subalkaline metabasalts with geochemical characteristics similar to enriched mid-ocean ridge basalts or ocean-island tholeiites. These rocks are associated with Tithonian radiolarian cherts and may be part of the Franciscan Complex. Alternatively, they may represent a change in tectonic setting within the CRO during the Late Jurassic. Regardless, the CRO as currently conceived cannot be considered a single terrane with one mode of origin.

Ti-V plots and the petrogenesis of modern and ophiolitic lavas

Plots of Ti vs. V for many modern volcanic rock associations are diagnostic of tectonic setting and can be used to determine possible tectonic settings of ophiolites as well. The basis of this plot is the variation in the crystal/liquid partition coefficients for vanadium, which range with increasing oxygen fugacity from > 1 to ≪ 1. Since the partition coefficients for Ti are almost always ≪ 1, the depletion of V relative to Ti is a function of the fO2 of the magma and its source, the degree of partial melting, and subsequent fractional crystallization. Volcanic rocksfrom modern island arcs have Ti/V ratios of ⩽20, except for calc-alkaline volcanics which show the effects of magnetite fractionation. MORB and continental flood basalts have Ti/V ratios of about 20–50 and alkaline rocks have Ti/V generally >50. Back-arc basinbasalts may have either arc-like or MORB-like Ti/V ratios, and sample suites from single back-arc basins may have Ti/V ratios ranging from 10 to 50. This range in Ti/V ratios in samples from a restricted geographical area may be diagnostic of the back-arc setting. The Ti/V plot is applied here to published data on ophiolites from a variety of postulated settings and in general supports the conclusions of previous investigators. Ophiolites from the western Mediterranean (Corsica, northern Apennines) and the “lower” Karmoy volcanics have Ti/V trends similar to MORB; the “upper” Karmo'y volcanics have alkaline Ti/V ratios. Lavas and tonalites in the Papuan ultramafic belt, the high-Mg andesites of Cape Vogel, and the upper pillow lavas at Troodos all have Ti/V ratios < 20, consistent with formation in an island arc setting. More specific evaluation of the tectonic setting of these and otherophiolites requires application of detailed geologic and petrologic data as well as geochemistry. The Ti/V discrimination diagram, however, is a potentially powerful adjunct to these techniques.

Proterozoic mafic syenites from Baker Lake, N.W.T., Canada

The petrography and major-element chemistry of the Martell Syenite, a Paleohelikian sub-volcanic intrusion, and of some flows of the Christopher Island Formation of the Dubawnt Group, south of Baker Lake, are described. The chemical analyses were carried out using standard X-ray fluorescence techniques. The major-element chemistry of these rocks shows them to be only mildly alkalic. Elemental ratios K 2O/Na 2O, K/Rb, Rb/Ba, and elemental contents of CaO, Rb, Ba, Sr, Zr, U and Th suggest that the syenite has shoshonitic affinities. This is supported by the stratigraphic and structural relationships of the syenite with a volcanic sequence containing mafic trachyte and latite flows. It is concluded that the Martell Syenite is part of a shoshonitic association of volcanic rocks which erupted during the late stages of the Hudsonian Orogeny as the crust thickened and became stable. The chemical characteristics of these rocks suggest that they have been derived by partial melting of an ultramafic source material at mantle pressures. The rising magma may have become enriched in incompatible elements by the process of zone refining. It is suggested that the field relationships and composition of this rock suite indicate that processes similar in kind, but different in degree, to modern plate-tectonic processes were operational from the early Proterozoic.

Volcanic rock associations at convergent plate boundaries: Reappraisal of the concept using case histories from Papua New Guinea

Research Article| January 01, 1978 Volcanic rock associations at convergent plate boundaries: Reappraisal of the concept using case histories from Papua New Guinea R. W. JOHNSON; R. W. JOHNSON 1Bureau of Mineral Resources, P. O. Box 378, Canberra City, ACT 2601, Australia Search for other works by this author on: GSW Google Scholar D. E. MACKENZIE; D. E. MACKENZIE 1Bureau of Mineral Resources, P. O. Box 378, Canberra City, ACT 2601, Australia Search for other works by this author on: GSW Google Scholar I.E.M. SMITH I.E.M. SMITH 2Department of Geology, Australian National University, P. O. Box 4, Canberra, ACT 2600, Australia3Present address: Department of Geology, University of Toronto, Toronto, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information R. W. JOHNSON 1Bureau of Mineral Resources, P. O. Box 378, Canberra City, ACT 2601, Australia D. E. MACKENZIE 1Bureau of Mineral Resources, P. O. Box 378, Canberra City, ACT 2601, Australia I.E.M. SMITH 2Department of Geology, Australian National University, P. O. Box 4, Canberra, ACT 2600, Australia3Present address: Department of Geology, University of Toronto, Toronto, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1978) 89 (1): 96–106. https://doi.org/10.1130/0016-7606(1978)89<96:VRAACP>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 R. W. JOHNSON, D. E. MACKENZIE, I.E.M. SMITH; Volcanic rock associations at convergent plate boundaries: Reappraisal of the concept using case histories from Papua New Guinea. GSA Bulletin 1978;; 89 (1): 96–106. doi: https://doi.org/10.1130/0016-7606(1978)89<96:VRAACP>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 Three volcanic rock associations — identified by the geographic acronyms TLTF, MRB, and SBS — can be recognized in seven late Cenozoic provinces at convergent plate boundaries in Papua New Guinea. These associations are distinguished on a variation diagram showing the Differentiation Index relative to normative nepheline or to normative quartz plus the silica of normative hypersthene; this diagram serves as the basis for a preferred scheme of volcanic rock nomenclature for arc-trench systems. Rocks of the TLTF group constitute a dominantly alkalic (nepheline-normative) association. In contrast, the MRB and SBS groups do not correspond to any of the associations widely postulated for other circumoceanic regions. Calc-alkalic–type rocks, for example, are found in both associations: in the MRB group they form compositional continua with shoshonitic rocks, and in the SBS group they form continua with tholeiitic ones. We suggest that circumoceanic rocks should not be classified into these artificial, world-wide, “standard” associations; a more meaningful method is to identify associations on a regional basis. However, the most useful procedure would be to correlate the same ranges of rock compositions and relative abundances of rock types in individual tectonic provinces with specific geodynamic features or source-region compositions. These correlations may lead to the recognition of natural rock associations on a world-wide basis. This content is PDF only. Please click on the PDF icon to access. 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.

Operation Basement: Buried Precambrian Rocks of Missouri--their Petrography and Structure

The buried Precambrian basement of Missouri is described on the basis of data from 550 drillholes, petrographic analyses of more than 1,000 samples, and geophysical and structural data. Prominent topographic and probable structural highs are identified as (1) the Central Missouri high, (2) the Southeast Missouri high, (3) the Southwest Missouri high, and (4) the Northeast Missouri high. The first two of these underlie the Ozark dome. Basement rocks associated with the Central Missouri high and locally found elsewhere are gneissic granite, gneiss, and schist. These rocks formed at deeper crustal levels, subsequently have been upwarped to the basement surface, and may be part of an earlier orogenic period. They include lenses of infolded metamorphosed sediments, as well as intrusive granite and basic plutonic rocks. It is assumed that the crustal complex is older than late Precambrian igneous rocks exposed in southeast Missouri, and that regionally persistent prominent northwest trends observed on geophysical maps and in Paleozoic structures are related to structural belts of the crustal complex. In western Missouri a northwest-trending basement fault is defined and interpreted as the northern fault of a graben wher supracrustal Precambrian and possibly younger rocks locally are preserved and brought into contact with metamorphic rocks. The association of late Precambrian rhyolitic volcanic and related shallow intrusive rocks is referred to as the St. Francois terrane. These rocks are exposed in southeast Missouri and extend in the subsurface northwestward. They are associated with the Southwest Missouri high and the Northeast Missouri high. Volcanic rocks identified from southwest Missouri may be part of a volcanic terrane extending into southeast Kansas and northeast Oklahoma; rhyolite in northeast Missouri may extend into Illinois. The granitic rocks of the St. Francois terrane are interpreted as postorogenic subvolcanic massifs that are exposed at the basement surface where pre-Paleozoic uplift and erosion removed their supracrustal cover. Northeast-southwest structural trends are believed to be related in part t the evolution of the St. Francois terrane and are superimposed on the older trends. The youngest igneous rocks of the basement complex are dikes and sills of tholeiitic diabase intruded along both sets of pre-existing structural zones. Local accumulations of unmetamorphosed clastic sediments on the basement surface may be Precambrian or younger.

IV.—Drake's Island, Plymouth

The main feature of the geology of Drake's Island is the association of volcanic rocks with marine limestone of Mid-Devonian age. The Geological Survey memoir by Mr. W. A. E. Ussher attributes the discovery of the volcanic rocks to Mr. R. N. Worth. Mr. Ussher leaves their precise nature, “whether lavas or tuffs,” somewhat in doubt, but states that they are “most certainly contemporaneous”. As a matter of fact both lava and tuff occur, and are definitely distinguishable.