No description available.

No description available.

No description available.

Previous work on the Strontian complex has been substantiated by the present investigation, and the knowledge of the structures in the rocks of the complex, and in the adjoining Moine schists end gneisses has been considerably augmented. It has been shown that a planar structure occurs throughout two of the three main unite of the complex - the tonalite and the porphyritic granodiorite. A linear structure also occurs in these rocks in a restricted area it the north. These structures largely conform to a simple pattern common to both tonalite and granodiorite. In the northern part of the complex, the granitic veins end the joints both appear to possess distinctive patterns of orientation, which prevail throughout this northern region. These patterns show little similarity to each other, and appear to be largely unrelated to the orientation of the foliation and lineation in the tonalite and granodiorite in this area. The formation of the complex appears to have been attended by considerable shearing and folding in the Moine country rocks which lie within half a mile of the complex. The overall pattern of the structures within the complex and the adjoining areas of country rock, appears to be distinctive, and does not closely resemble the structural pattern within and around other granitic complexes. It is suggested that the two main units of the complex with a common internal structural pattern have been formed by the more or less simultaneous intrusion of two magmas, and that these magmas were probably emplaced by a process which involved forcible intrusion, and may have under the control of forces associated with the Caledonian orogeny.

Widespread base- and precious-metal anomalies, altered porphyry intrusions and oxidized veins occur in a portion of the Sulphur Springs Range, Nevada (adjacent to the Au-producing Carlin Trend). Some of the Eocene-Oligocene intrusions and cogenetic volcanic rocks in the range exhibit evidence of magma mixing and invite comparisons with other mineralized, Eocene mixed magma systems like the Bingham porphyry Cu deposit 300 km farther to the east. The Sulphur Springs igneous suite ranges compositionally through rhyolite, dacite, andesite and basaltic andesite but is less alkaline than the Bingham volcanic suite. However, the alkali content of the Sulphur Springs suite is similar to other Eocene igneous rocks along the Carlin Trend. The unusual geochemical signature of the Bingham igneous suite, enrichment in Cr, Ni, and Ba, is generally not found in the unaltered Sulphur Springs suite, with the exception of a set of altered mafic and intermediate dikes found in the core of the Sulphur Springs Range. The Bingham and Sulphur Springs volcanic suites both show extensive mixing of mafic magma with more silicic magma to create magma with intermediate compositions. The Bingham suite demonstrates mixing mineralogically by the presence of altered olivine and pyroxene in intermediate composition rocks. One of the disequilibrium Sulphur Springs rocks vividly expresses magma mixing as “andesite" - containing plagioclase, biotite, clinopyroxene, orthopyroxene, olivine, and amphibole coexisting with heavily resorbed megacrysts of quartz and K-feldspar. The Sulphur Springs mixed magma also contains abundant late-stage accessory magnetite and resorbed and oxidized garnet. The most likely parental magmas for this rock are a garnet-bearing quartz porphyry and olivine-bearing basaltic andesite which are both present in the range. Questions these data raise include: 1) Was there an unusual tectonic setting during the Eocene of the western United States that promoted both magma mixing and base- and precious-metal mineralization? 2) How vital might mixing processes and mafic magma be in delivering large amounts of S and chalcophile metals from deeper magmas to the shallow crust and eventual ore deposits?

A combined field and laboratory investigation of the primarily volcanic Roskruge range, Pima County, Arizona, produced the following results: The rocks in the area fall into three major and several minor divisions. The major groups are: (1) The pre-Laramide dark-colored andesites and sediments that floor the range. A K-Ar date on one of the andesites produced a number, 108 m. y. , on a whole rock analysis. (2) The brightly colored and widespread Laramide volcanics and an associated hypabyssal pluton at Cocoraque Butte, which gave K-Ar mineral ages in the 74 m. y. to 66 m. y. spread. (3) The mid-Tertiary potassic basaltic andesites found on an eroded plain that is cut into the Laramide volcanics. These dark-colored extrusives were dated at 23 m. y. by whole rock K-Ar. Amongst the minor units in distribution is the petrographically unusual Recortado ash flow, a small 13 m. ye old unit that preserves a vitrophyre just above its base. Also included in the miscellaneous group of units are the post-orogenic true basalts, which appear as dikes and as a flow(?) at Brawley Wash and which gave whole rock K-Ar dates of about 10 m. y. Initial strontium 87/86 ratios indicate that the Laramide and mid-Tertiary rocks (including the Recortado ash flow) have values ranging from . 7056 to .7092, while the Brawley Wash basalt has a true deep-seated basalt ratio of .7038. The combination of radiochemical assay, petrographic and field study, and isotopic data has established good gross correlation with the already known sequence of formations and plutons in the Tucson Mountains.

To understand the complex structure of magmatic plumbing systems beneath volcanoes, one needs to study the different textures shown in the igneous rocks produced by the volcano in question. By doing this, one can get a clue of the processes that resulted in the final rock. One of the most important methods to use for studying rock samples is the Crystal Size Distribution (CSD), which can reveal a great amount of information about the history of the rock and give an insight in the journey of the crystals during their time in the magma. An extinct volcano named Chachahuén, located in Argentina, South America, was chosen for this study. Samples of rock were collected from one of its laccoliths named Cerro Bayo and was identified as hornblende-bearing dacite. The difference in crystal size was very significant in these samples, with both larger and smaller crystals embedded in the same matrix. This is interesting considering the fact that large crystals form by slow cooling of the magma while smaller crystals form as the magma cools rapidly. By studying the CSD and interpreting other textures found in samples of igneous rock, one may interpret different processes which affected the crystals, indicating what the structure of the magma chamber once looked like. / För att kunna förstå den komplexa strukturen hos magmatiska system under vulkaner måste man studera olika texturer som påträffas i de magmatiska bergarter producerade av vulkanen i fråga. Genom att göra detta kan man få en inblick i de processer som resulterade i den slutgiltiga bergarten. En av de viktigaste metoderna att använda sig av för att studera stenprov är kristallstorleksfördelningen (CSD), som kan avslöja en mängd viktig information om bergarten och kristallernas historia under sin färd i magman. En slocknad vulkan vid namn Chachahuén belägen i Argentina, Sydamerika, valdes ut för denna studie. Stenprover samlades från en av dess lakkoliter med namnet Cerro Bayo, och identifierades som hornblände-bärande dacit. Skillnaden i kristallstorleken var mycket markant, med både större och mindre kristaller inbäddade i samma matrix. Detta är intressant med tanke på att stora kristaller bildas under en långsam nedkylning av magma medan mindre kristaller bildas när magma kyls ner snabbt. Genom att studera CSD och tolka andra texturer som finns hos magmatiska stenprover kan man tolka olika processer som har påverkat kristallerna, vilket i sin tur indikerar hur strukturen av magmakammaren en gång såg ut.

名古屋大学年代測定総合研究センターシンポジウム報告