Petrochemical Data Research Articles

Chemical differentiation of the Bishop Tuff and other high-silica magmas through crystallization processes

Re-examination of petrochemical data for high-silica ash-flow tuffs suggests that crystal-liquid fractionation plays a major role in the differentiation of high-silica magmas. For the high-silica Bishop Tuff, the enrichment and depletion of 27 major and trace elements correlates with the bulk crystal-liquid partition coefficients (calculated from the data of Hildreth) in ways that are consistent with crystal fractionation. Comparison of the Bishop Tuff with other high-silica tuffs and rhyolites with different compositional variations and different phenocryst assemblages shows the correspondence of chemical gradients with mineralogy. Crystal zoning studies in the Cordillera Paine granite in southern Chile suggest that the evolution of differentiated liquids similar to those in the Bishop Tuff results from crystal fractionation. The physical mechanisms of separation of liquid and crystals for the Paine granite and Bishop Tuff were quite different, however. Differentiation of the high-silica ash flows might result from advection of a less dense liquid from a crystallizing boundary into the top of the magma chamber.

Chemical composition of magmatic rocks in a certain region and its regional geochemical characteristics

Based on a review of the available petrological and petrochemical data on magmatic rocks in a certain region in China, the average chemical composition of them has been calculated, and the frequency distribution of elements in the rocks, the mineralization of rock bodies and the regional geochemical characteristics have been discussed. In response to temporal and spatial variations during the evolutionary process of magmatic activity, a systematic variation is obvious from this study in the chemical composition of magmatic rocks, the frequency distribution patterns of elements, the concentration levels of various elements and the calc-alkali index of the rocks as well as in the average atomic weight and average atomic valence. Particularly, different geochemical indicators have been established for mineralized and barren rock bodies, respectively. Crystallization-differentiation and post-magmatic metasomatism constitute the most important mechanism controlling mineralization.

Volcanism and the Tectonic Development of the Rio Grande Rift and Environs, New Mexico - Colorado, from Analysis of Petrochemical Data

A computerized data bank of over 1200 published major element analyses has been created, listing volcanic rocks from the Rio Grande rift and its flanks in New Mexico, Colorado and Texas. In this preliminary study, the data for each of the major volcanic fields, summarized on histograms and binary and triangular plots, are compared to establish a relation between petrochemistry and tectonic position with respect to the rift, and to determine temporal changes in volcanicity. No consistent systematic chemical variations across the rift were found, except locally. The only observed chemical change along the rift axis is the southward increase in TiO2-index of rift basalts. Three volcanic districts (Mt. Taylor-Mesa Chivato, Sierra Blanca and Trans-Pecos Texas) differ significantly from the others, in higher total alkali (especially Na2O), total iron oxide, and TiO2 and lower SiO2. These differences do not appear to be related to the Rio Grande rift. The strongly alkalic composition of the Mt. Taylor-Mesa Chivato field (Pliocene-Pleistocene) may arise from its location on the Jemez lineament, which may penetrate to greater depths in the mantle. The considerably older (Oligocene) Sierra Blanca and Trans-Pecos Texas districts, on the other hand, form the eastern­ most of a series of parallel magmatic belts in northern Mexico and Texas, which may have been associated with a broad, eastward-dipping subduction zone during the middle Tertiary. The absence of a distinct petrochemical "signature" for the Rio Grande rift lavas implies that the physico­ chemical environment of melting has remained the same throughout the region. Although the Rio Grande rift is a well-defined geophysical entity, it belongs to a broader zone of crustal extension in the Basin and Range province. The rift has been localized in part by structural "inheritance", and in part by its position as the eastern boundary between the Colorado Plateau and Southern Rockies. Transverse structures, such as the Jemez lineament, have also played an important role in localizing contemporaneous volcanism of highly variable and differentiated compositions, often strongly alkalic.

PRELIMINARY STUDY OF THE METAMORPHOSED YANLINGGUAN FORMATION OF TAISHAN GROUP OF XINTAI, SHANDONG, CHINA

The Yanlingguan Formation of lhe Arehean Taishan Group of Xintai, Shandong province. China, mostly metamorphosed to amphibolite fades of the low-to moderate-pressure series and with a metarnorphic age of about 2,500 Ma, was originally a dominantly basic volcano-sedimentary series 1,000-1,400 m thick, containing subordinate basic intrusions and ultrabasic rocks, with the lowermost part influenced by migmatization. It is sub-divided into two sub-formations, each constituting a major eruption-sedimentational cycle and containing two to four minor ones, showing an up-ward succession of lower tuff or lava (plagioclase-amphibolite), main lava and upper tuffaceous sandy rocks (hornblende-leptitic rocks] often with intercalations of semipelitic types (Moine-type biotite-granulite). The basic lava usually corresponds to the high-ferromagnesian and especially high-ferreous type of the tholeiitic basalt. Judging from petrochemical data, the eruption could have taken place for part of the volcano-sedimentational period in a transitional belt between the island arc area and deep marine basin. All other geological characteristics, however, reveal that the rocks were accumulated mostly in water masses under conditions of crustal unstability. ln fact, part of them were formed in subaqueous and subaerial and even, lagoon environments.

Petrology and petrogenesis of the Trinity peridotite, An upper mantle diapir in the eastern Klamath Mountains, northern California

The Trinity peridotite is an enormous ultramafic massif situated in the eastern Klamath Mountains of northern California and composed of a diverse assemblage of ultramafic rocks including dunite, harzburgite, plagioclase lherzolite and clinopyroxene‐rich lithologies. These rocks preserve an excellent record of a complex mantle history involving plastic deformation, partial melting, recrystallization and reaction with transient silicate melts in a large peridotite mass as it ascended through the upper mantle. Structural data are utilized to determine the relative ages of events that affected the peridotite, and petrochemical data are utilized to place constraints on the pressures and temperatures at which the events occurred. The Trinity peridotite is inferred to have ascended through the upper mantle from an initial depth of not less than 30 km, based on evidence for replacement of spinel by plagioclase. Ariegite bands and dikes formed, and isoclinal folding occurred while the peridotite was in the spinel lherzolite stability field (P > 10 kbar). The peridotite passed its solidus and partially melted at a pressure of ≤10 kbar, producing a basaltic melt with tholeiitic affinities. Plagioclase lherzolite formed where partial melt was trapped and minerals reequilibrated during subsequent low pressure cooling of the peridotite. Clinopyroxene‐rich dikes were emplaced after the peridotite had passed into the plagioclase lherzolite field (P < 10 kbar). Plastic deformation, recorded by penetrative foliation and lineation, occurred continuously during the diapiric rise of the Trinity body. The emplacement of undeformed gabbro marks the arrival of the Trinity at the base of the crust. Large, tabular dunite bodies, clinopyroxene‐rich dikes and ariegite dikes mark channels through which melts passed and reacted with the peridotite en route to the surface. The interiors of the dunite bodies and the dikes are interpreted to have formed as crystal cumulates from the transient melts. The margins of the dunite bodies and depleted zones around some clinopyroxene‐rich dikes formed as a ‘restite’ by assimilation of pyroxene and plagioclase from the peridotite wall rocks by the transient melts. The melts are hypothesized to have formed by partial melting of peridotite at a great depth (e.g., 45–60 km) and to have penetrated the Trinity peridotite at shallower depths (<30 km) where they were not in equilibrium with pyroxene or plagioclase. Structural and stratigraphic data suggest that these events occurred near an oceanic volcanic highland in a setting analogous to a modern island arc or back‐arc basin.

The Loch Doon granite: an example of granite petrogenesis in the British Caledonides

The Loch Doon igneous complex lies to the N of the Solway–Shannon Iapetus Ocean suture line through the British Isles, but in a region lacking the Proterozoic continental basement which is known to exist further N. It comprises a genetically related magma suite ranging from hypersthene diorite margins through quartz monzonite to granite at the centre. Petrochemical data, studies of xenolith and autolith densities and field radiometric mapping indicate that the suite lacks sharp internal boundaries but is gradational and based on a monzodiorite parental magma which evolved through a two-stage crystal fractionation process. The early crystallization of dioritic margins was dominated by pyroxene-plagioclase precipitation and these minerals were joined later by biotite as acidic residual liquids developed. Biotite formation and fractionation at the expense of pyroxenes is related to contamination of the magma by water from the roof zone. Partial assimilation of roof material, particularly in the form of xenoliths, and mixing between cumulates and residual liquids are also recognized but are of relatively minor importance. These petrochemical, geophysical and isotopic studies of the Southern Uplands granites indicate the generation of parental magmas by the partial fusion of metabasaltic lower crust or crustal underplate as a late event in the evolution of the Iapetus Ocean.

Early Silurian volcanic rocks at Arisaig, Nova Scotia

Petrochemical data for the Early Llandovery subaerial volcanic rocks at Arisaig, Antigonish Highlands, Nova Scotia, show that they are a bimodal suite of altered rhyolites and basalts of tholeiitic affinity with some alkaline tendencies extruded in a nonorogenic extensional environment within a continental plate. These data do not support the island arc origin frequently inferred for these rocks but are consistent with recent petrological data from the Silurian – Lower Devonian Coastal Volcanic Belt in southern Maine, which may be a strike continuation of the Arisaig volcanics. The close spatial and temporal association of basalts and rhyolites is attributed to anatexis of the crust upon contact with the rising basaltic magma.

Classification of metahyperbasites and metabasites on the basis of petrochemical data (Southwest Pamir)

Classification of metahyperbasites and metabasites on the basis of petrochemical data (Southwest Pamir)

Geochemistry of volcanic rocks from the Tetagouche Group, Bathurst, New Brunswick, Canada: Discussion

A recent paper by Whitehead and Goodfellow (1978) presented much needed petrochemical data on volcanic rocks of the Ordovician Tetagouche Group in northern New Brunswick. Although analytical results were not tabulated, numerous plots of major and trace elements confirm an earlier suggestion by Davies et al. (1973) that the Tetagouche volcanic rocks are essentially bimodal, and that andesites are rare or absent. The mafic rocks are subdivided into three distinct groups, group A being either tholeiitic or calc-alkaline basalts, groups B and C being alkaline basalts. The dacitic to rhyolitic rocks belong to the calc-alkaline clan. The following model for the evolution of the Tetagouche Group is proposed in their paper: 1. An ocean-floor sequence of basalts formed as a result of the opening of the Proto-Atlantic. Tholeiitic basalts (group A) generated at a ridge are overlain by alkaline basalts (group B) believed to have been deposited in an off-axis environment. 2. During the Ordovician Period subduction started. Tholeiitic and calc-alkaline mafic and intermediate rocks expected to be extruded at the early stages of a developing island arc have not been recognized. They are thought to have been either subducted subsequently to their formation or uplifted and eroded; or they may underlie Carboniferous rocks in the southeast. 3. During continued evolution of the island arc calc-alkaline dacitic to rhyolitic pyroclastic rocks and lavas were deposited directly on the ocean floor (groups A and B). This discussion is not about the petrochemical classifications presented, but intends to show some of the problems arising from geological models established on the basis of petrochemical models without considering existing geological constraints. Although all workers familiar with the Bathurst district would agree that the whole stratigraphic and structural story of the Tetagouche Group has not been told yet, the published literature leaves considerably less room for modeling than the authors have taken. The model ignored the fact that the volcanic rocks of the Tetagouche Group are underlain by a quartz-rich sedimentary sequence (Smith 1957; Poole 1967; Helmstaedt 1971, 1973; Fyffe 1976), which is mainly of Early Ordovician age. Whereever the contact with the overlying volcanic rocks can be observed, the volcanic rocks are acidic, and basic volcanic rocks follow higher in the sequence (Helmstaedt 1971, 1973; Luff 1977). In the northeastern part of the district, where basic volcanic rocks predominate, the stratigraphic relationships to surrounding sedimentary rocks are not always clear. However, the basic volcanic rocks of sample areas 2 and 3 (Whitehead and Goodfellow 1978) are structurally continuous (Skinner 1974), and in area 3 contain interlayered limestones with fossils (Helmstaedt 1971 ; Skinner 1974) younger than those of the lower sedimentary sequence (Fyffe 1976). The basic volcanic rocks near the city of Bathurst (sample area 4) are either similar in age to those in areas 2 and 3 (Skinner 1974), or even younger, as suggested recently by Pajari et al. (1977). Is the model of Whitehead and Goodfellow (1978) compatible with this information? 1. The ocean-floor sequence (group A) in area 2, inferred to be related to the rifting of the ProtoAtlantic and therefore presumably of preOrdovician age, postdates Lower Ordovician metasediments as well as much of the acidic volcanic rocks making up the major volume of the Tetagouche Group. If the group A volcanic rocks represent an environment of rifting, this must be related to a later episode, perhaps back-arc spreading, as the main arc had been established already. So far, no Lower Ordovician ophiolites have been recognized in the Tetagouche Group; however, they are thought to exist in the Elmtree-Fournier inlier north of the Rocky Brook Millstream fault (Pajari et al. 1977). C an . J . E ar th S ci . D ow nl oa de d fr om w w w .n rc re se ar ch pr es s. co m b y Q ue en s U ni ve rs ity o n 05 /0 2/ 14

Monzonitic plutons, California, and a model for generation of alkali-rich, near silica-saturated magmas

Petrochemical data suggest that early Mesozoic alkali-rich monzonite plutons in California were generated by partial melting of a garnet-bearing, virtually feldspar-free source which was rich (compared to abyssal basalt or sub-oceanic mantle peridotites) in LIL elements. These monzonites are characterized by high Na2O+K2O (near 10 wt% total) and Sr (1000 to 2000 ppm), moderate SiO2 (53 to 63 wt%), steep negatively sloping REE patterns (from >100 to <10 × chondritic abundance), and moderate initial 87Sr/86Sr ratios (0.705 to 0.707). Most are very slightly oversaturated in silica, but one pluton includes both oversaturated and undersaturated units.

The tertiary dike swarms of the Kangerdlugssuaq area, East Greenland

Detailed field studies supplemented by petrographic and petrochemical data of dikes in the Kangerdlugssuaq area lead to the recognition of six distinct generations, which may be correlated with the major structural and magmatic events in this part of the North Atlantic Province. In order of decreasing age these swarms are: 1. A broad coastparallel dike swarm of high Fe and Ti tholeiitic basalts, identified as feeders for the plateau basalts of East Greenland and intruded prior to coastal flexuring. 2. A radial tholeiitic dike swarm with MORB affinities, related both in chemistry and chronology to the major gabbroic plutons (including Skaergard) and penecontemporaneous with the coastparallel flexure of East Greenland. 3. A coastparallel alkaline dike swarm, most intense some 20 km inland, composed of picritic to hawaiitic rock types and intruded subsequent to flexuring. 4. Peralkaline rhyolites found in the immediate neighbourhood of the nordmarkitic syenites and clearly related to the major period of salic plutonism. 5. A radial strongly alkaline swarm, including several types of alkaline olivine basalts and trachybasalts differentiating to oversaturated trachytes. 6. Simultaneous with the last, a coastparallel dike swarm composed of transitional basalts differentiating to rhyolitic rock types.

Revised age for Midway volcano, Hawaiian volcanic chain

New conventional K-Ar, 40Ar/ 39Ar, and petrochemical data on alkalic basalt pebbles from the basalt conglomerate overlying tholeiitic flows in the Midway drill hole show that Midway evolved past the tholeiitic shield-building stage and erupted lavas of the alkalic suite 27.0 ± 0.6m.y. ago. The data also show that previously published conventional K-Ar ages on altered samples of tholeiite are too young by about 9 m.y. These results remove a significant anomaly in the age-distance relationships of the Hawaiian chain and obviate the need for large changes in either the rate of rotation of the Pacific plate about the Hawaiian pole or the motion of the plate relative to the Hawaiian hot spot since the time of formation of the Hawaiian-Emperor bend. All of the age data along the Hawaiian chain are now reasonably consistent with an average rate of volcanic propagation of 8.0 cm/yr and with 0.83°/m.y. of angular rotation about the Hawaiian pole.

Solid rocks of the floor of the central part of the Sea of Okhotsk

We present petrographic and petrochemical data on the solid rocks of the floor of the central part of the Sea of Okhotsk, samples of which were obtained by dredging during the 53rd cruise of the research vessel Vityaz' (1971) and the 13th cruise of the research vessel Dmitriy Mendeleyev (1971). Most of the outcrops of the acoustic basement are of magmatic rocks: quartz diorites, granodiorites, gabbro-noritcs, plagiorhyolites, dacites, basalts, and andesites. Greenschists appearing with them are supposedly torn-off fragments from an older basement. The volcanic rocks belong mainly to the typical calc-alkaline series. The intrusive rocks may be assigned to the plagiogranite-granodiorite association. The absolute age of most of the magmatic rocks is 85-95 m.y. (Late Cretaceous). On the whole, we may assume that the solid rocks from the floor of the Sea of Okhotsk form an island-arc complex and record the position of the Late Cretaceous volcanic arc. In this light, the existance of a sunken crystalline massif...

Keybam—a system of interactive computer programs for use with the petros petrochemical data bank

KEYBAM is a system of interactive FORTRAN IV programs for accessing and operating on major-element whole-rock chemical analyses stored in data bank PETROS. KEYBAM's capabilities include subfile creation based on user-supplied criteria, normative calculations and rock classification, graphical displays including histograms, X—Y plots, triangular plots, and various statistical analyses based on the SPSS System. We have attempted to design KEYBAM so that it is machine independent and can be used for research and teaching in petrology at most modern computer installations.

Age of the Hawaiian-Emperor bend

40Ar/ 39Ar age data on alkalic and tholeiitic basalts from Diakakuji and Kinmei Seamounts in the vicinity of the Hawaiian-Emperor bend indicate that these volcanoes are about 41 and 39 m.y. old, respectively. Combined with previously published age data on Yuryaku and Ko¯ko Seamounts, the new data indicate that the best age for the bend is 42.0 ± 1.4 m.y. Petrochemical data indicate that the volcanic rocks recovered from bend seamounts are indistinguishable from Hawaiian volcanic rocks, strengthening the hypothesis that the Hawaiian-Emperor bend is part of the Hawaiian volcanic chain. 40Ar/ 39Ar total fusion ages on altered whole-rock basalt samples are consistent with feldspar ages and with 40Ar/ 39Ar incremental heating data and appear to reflect the crystallization ages of the samples even though conventional K-Ar ages are significantly younger. The cause of this effect is not known but it may be due to low-temperature loss of 39Ar from nonretentive montmorillonite clays that have also lost 40Ar.

Syn-orogenic igneous alkaline rocks of eastern Ontario and northern Norway

Igneous alkaline rocks were emplaced during the Grenville orogeny in eastern Ontario and during the Caledonian orogeny in west Finnmark, northern Norway. Extensive nephelinization of country rocks accompanied this event in each locality, but this paper focuses on the parent igneous magmas. The apparent differentiation sequence is discussed for each region utilizing all available petrochemical data including nine new major and trace element analyses, and ten new trace element analyses for rocks with previously published major element analyses. The magmas of both areas are miaskitic in mineralogy and chemistry. Each suite has certain coherent chemical characteristics suggesting a common genetic mode for all the rocks of the region but anomalies between lithological groups and between rocks of different localities suggest that independent evolution of magmas took place at a number of localities.

A Discussion on volcanism and the structure of the Earth - Proposals concerning the variation of volcanic products and processes within the oceanic environment

An attempt is made to fit available petrochemical data on oceanic volcanic rocks into the structural model for the ocean basins presented by the plate tectonic theory. It is suggested that there are three major volcanic regimes: (i) the low-potassic olivine tholeiite association of the axial zones of the oceanic ridges where magmatic liquids are generated at low pressures high in the mantle, (ii) the alkalic (Na &gt; K) associations along linear fractures where liquids generated at greater depth gain easy egress to the surface, (iii) those alkalic associations, rich in incompatible elements, of island groups, remote from fracture zones, where magmas created at depth proceed slowly to the surface and in consequence suffer intense fractionation. There are certain discrepancies in this pattern, notably that there is no apparent relation between rate of sea-floor spreading and degree of over-saturation of the axial zone basalts and that certain areas, such as Iceland, are characterized by excess volcanism. Explanation of these anomalies is sought by examining an oceanic area in an early stage of development—the Red Sea. It is tentatively suggested that the initial split of a contiguous continent might be brought about by the linking of profound fractures, caused by domal uplift related to rising isolated lithothermal systems, and that the present anomalies in oceanic volcanism may reflect the variation in rate of thermal convection within the original isolated lithothermal plumes.

Petrography and petrochemistry of the basalt sequences around mahape, Mumbra and Kalyan, Maharashtra, India

The volcanic sequences in three vertical sections (starting from m.s.l.) of the Deccan trap flows around Mahape, Mumbra and Kalyan have been demarcated into zones, mainly based on the megascopic texture and the degree of abundance of vesicles and amygdules. Petrographic, mineralogical and modal study of twelve samples indicate that the basalts are tholeiitic and are characterised by lateral inhomogeneities. Petrochemical data are suggestive of limited differentiation, a hyperferric iron enrichment, a Hawaiian trend and an affinity to alkalic and high-alumina basalt.

Magma types of volcanic rocks and crustal history in the Japanese pre-Cenozoic geosynclines

Magma types and temporal variations of the volcanic rocks erupted in the Japanese pre-Cenozoic geosynclines are examined using the petrochemical data of almost 550 new analyses. It is assumed that the alteration of these rocks was isochemical in nature. The characteristic rock type is basalt, but some variations of rock type are observed in certain areas: 1. (1) In western Japan, the parental magmas of Permian age are mostly inferred to be alkali basalt series and high-alkali tholeiite rock series. The rocks of low-alkali tholeiite are few if any. High-alumina basalts are observed in limited localities. 2. (2) The rocks of the Mikabu metamorphic belt, probably products of Permian submarine volcanism, lack any appreciable high-alumina basalt. These petrochemical features support the conclusion that the geosynclinal basalt from western Japan is much closer to the oceanic basalt than are the Japanese Cenozoic volcanics (Sugisaki et al., 1970). 3. (3) The changes of rock characteristics in the southern Kitakami area with time show that the magma has progressively changed since the Devonian from alkali basalt, high-alkali tholeiite and low alkali tholeiite, through high-alumina basalt and high-alkali tholeiite rock series finally to low-alkali tholeiite rock series. The several magma types show significant differences in both major and minor elements: 1. (1) the Japanese Paleozoic geosynclinal tholeiite is the petrochemical equivalent of the abyssal tholeiite of the Mid-Atlantic Ridge and East Pacific Rise, which was studied by several authors: Engel et al. (1965), Gast (1968), Hart (1969), and Miyashiro et al. (1970). 2. (2) the geosynclinal tholeiite was differentiated in a manner similar to that of the abyssal tholeiite. The weathering effect of sea-water was not significant in the geosynclinal basalts, implying that the volcanic rocks were confined under thick sediments soon after the eruption. These lithologic changes in the Japanese pre-Cenozoic geosynclines may record: 1. (1) the genesis of the geosynclines. 2. (2) the variations in crustal thicknesses in the early stage of the geosynclines; and (3) the crustal evolution (continental and oceanic) of the Japanese Islands.

Petrological study of the Neogene basalts from the western part of Hokkaido

Etai-dake basalt complex, first named by Satoh (1961), forms a large lava platform (5×7km), situating the eastern flnak of Shokanbetsu volcano, in western Hokkaido. It consists of olivine bearing basalt and basaltic andesite lava flows of Pliocene age (Table 1). Satoh (1961) published the description of the basalts from geological and petrological view points, but no petrochemical data were presented. The basalts are rich in olivine but poor in plaigoclase phenocrysts, and contain little hypersthene. Sometimes xenoliths of the basement rocks are included. In thin section, most of plagioclase phenocrysts have dusty inclusions in their inner zone, suggesting some events in crystallization process. Chemical analyses of seven representative rocks (Table 3) indicate that the basalts have a little alkalic character and are slightly undersaturated or oversaturated in silica. And the basalts have a intermediate position between alkali olivine basalt and calc-alkaline andesite, in the silica-alkalis diagram (Figure 2).