DOCSLIB.ORG

The Hydrous Phase Equilibria (To 3 Kbar) of an Andesite and Basaltic Andesite from Western Mexico: Constraints on Water Content and Conditions of Phenocryst Growth

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Hydrous Phase Equilibria (To 3 Kbar) of an Andesite and Basaltic Andesite from Western Mexico: Constraints on Water Content and Conditions of Phenocryst Growth Contrib Mineral Petrol (1998) 130: 304±319 Ó Springer-Verlag 1998 Gordon Moore á I.S.E. Carmichael The hydrous phase equilibria (to 3 kbar) of an andesite and basaltic andesite from western Mexico: constraints on water content and conditions of phenocryst growth Received: 10 December 1996 / Accepted: 21 August 1997 Abstract We have conducted high pressure (to 3 kbar), ents containing greater than 6 wt% water. Indeed and- water saturated melting experiments on an andesite (62 esitic magmas could be related to a basaltic andesite wt% SiO2) and a basaltic andesite (55 wt% SiO2) from parent by hornblende-plagioclase fractionation under western Mexico. A close comparison between the ex- the same hydrous conditions. perimental phase assemblages and their compositions, and the phenocryst assemblages of the lavas, is found in water saturated liquids, suggesting that the CO2 content Introduction was minimal in the ¯uid phase. Thus the historic lavas from Volcan Colima (with phenocrysts of orthopyrox- Andesite lavas from the western Mexican volcanic belt ene, augite, plagioclase, and hornblende) were stored at contain a variety of phenocrysts ranging from only a temperature between 950±975 °C, at a pressure be- hornblende, to the most common, plagioclase-horn- tween 700±1500 bars, and with a water content of 3.0± blende-2 pyroxene-titanomagnetite assemblages. This 5.0 wt%. A hornblende andesite (spessartite) from diversity of phenocryst suites, despite similarity in bulk Mascota, of nearly identical composition but with only composition, indicates dierent conditions of magma amphibole phenocrysts, had a similar temperature but storage and phenocryst growth prior to eruption, and it equilibrated at a minimum of 2000 bars pressure with a is to quantify these conditions that this paper is con- dissolved water content of at least 5.5 wt% in the liquid. cerned. Similarly, basaltic-andesite lavas have an array Experiments on the basaltic andesite show that the most of phenocryst assemblages, typically without plagio- common natural phenocryst assemblages (olivine, clase, but their higher temperatures relative to andesites augite, plagioclase) could have precipitated at make hornblende phenocrysts rare among these lavas. temperatures from 1000±1150 °C, in liquids with a wide While we have known for some time the role that range of dissolved water content ( 2.0±6.0 wt%) and a water plays in the generation of continental subduction- corresponding pressure range. A lava of the same bulk related magmatism relative to that in island arc settings composition with phenocrysts of hornblende, olivine, (Osborn 1959; Ewart 1982; Merzbacher and Eggler plagioclase, and augite is restricted to temperatures be- 1984), the majority of hydrous phase equilibria studies low 1000 °C and pressures below 2500 bars, corre- on subduction-related lavas (e.g., andesites and basaltic sponding to <5.5 wt% water in the residual liquid. andesites) have focused on the high pressure assem- Although there is some evidence for mixing in the blages of these rocks (e.g., Baker and Eggler 1987; andesites (sporadic olivine phenocrysts), the broad Eggler and Burnham 1973; Eggler 1972; Holloway and theme of the history of both lava types is that the phe- Burnham 1972) in order to test hypotheses of possible nocryst assemblages for both the andesitic magmas and mantle sources (Osborn 1959; Green and Ringwood basaltic andesitic magmas are generated from degassing 1968). Fewer studies have been conducted concerning and reequilibration on ascent of initially hydrous par- the upper crustal conditions (1±3 kilobars) at which most subduction-zone magmas appear to reside prior to eruption (Luhr 1990; Rutherford and Devine 1988; G. Moore (&)1 á I.S.E. Carmichael Department of Geology and Geophysics, Rutherford et al. 1985; Merzbacher and Eggler 1984; University of California, Berkeley, CA 94720, USA Sisson and Grove 1993a, b). Small amounts of water Present address: dissolved in these magmas at crustal conditions can have 1Department of Geology, signi®cant eects on their phase assemblages, conse- Arizona State University, TEmpe, AZ 85287-14-4, USA quently in¯uencing evolution of melt composition. For Editorial responsibility: T.L. Grove example, water contents greater than 2 wt% in basaltic 305 melts lowers the crystallization temperature and pro- volcanic belt, and to quantify the water contents in the portion of plagioclase, and changes its equilibrium residual liquids required by their phenocryst assem- composition, while at the same time stabilizing olivine blages. (Sisson and Grove 1993a); as water changes the com- For this experimental study, we have chosen two position of the residual liquid, so will it change the representative calc-alkaline lavas from western Mexico: fractionation path taken by the magma. a basaltic andesite and an andesite (Mas-22 and Mas-12 Due to the unique tectonic environment of the west- respectively; Table 1; described in Carmichael et al., ern Mexican volcanic belt (WMVB), the in¯uence of 1996). Lavas with similar compositions are found water on subduction-related magmatism is extensively throughout the entire Mexican volcanic belt (Fig. 1) and displayed. In addition to unusual hydrous, alkaline lava in continental volcanic arcs worldwide (Hasenaka and types (minettes, absarokites) not normally associated Carmichael 1987; Gill 1981). Lange and Carmichael with subduction (Carmichael et al. 1996; Wallace and (1990) noted the distinctive lack of plagioclase in basaltic Carmichael 1992; Wallace et al. 1992), calc-alkaline la- andesites (52±55 wt% SiO2) and the presence of Mg-rich vas of nearly identical composition have widely dierent (Fo70±90) olivine both as phenocrysts and in the phenocryst assemblages. We have used this phenocryst groundmass in many lavas from the San Sebastian area diversity to constrain experimentally the storage condi- (Fig. 2), and Carmichael et al. (1996) described a horn- tions prior to eruption of magmas from the Mexican blende lamprophyre of similar composition from the Table 1 Wet chemical analyses of whole rock compositions and Composition Spessartite Colima Hornblende Basaltic modal percent of phenocrysts in (Mas-12) andesite lamprophyre andesite lavas. Wet chemical analyses (Col-7) (Mas-405) (Mas-22) for Mas-12, 22, 405 from Car- michael et al. (1996); Col-7 SiO2 62.64 61.61 55.25 55.25 from Luhr and Carmichael TiO2 0.63 0.60 0.83 0.74 (1980). Modal data for Col-7 Al2O3 17.25 17.82 17.32 17.41 from Luhr and Carmichael Fe2O3 2.01 2.10 4.04 1.96 (1980), Mas-22, 12, 405 from FeO 2.01 2.96 2.06 4.22 Carmichael et al. (1996) MgO 2.65 2.54 5.59 6.68 CaO 5.64 5.70 7.09 7.28 Na2O 4.05 4.77 4.21 3.97 K2O 1.61 1.43 2.06 1.18 P2O5 0.24 0.20 0.23 0.27 H2O+ 0.80 0.10 0.49 0.61 Total 99.53 99.73 99.28 99.57 Plagioclase 2.4 22.2 0.1 6.5 Orthopyroxene ± 2.9 ± ± Augite ± 1.8 1.6 2.6 Olivine ± tr 1.1 6.5 Hornblende 3.8 1.5 5.6 ± Groundmass 76.0 61.3 84.5 72.0 Fig. 1 General map of Mexico showing the oceanic plates, spreading centers, and the Middle American trench. Box is area of western Mexico shown in Fig. 2. Lined area is the Sierra Madre Occidental ash¯ow province; shaded area labeled MVB is the Mexican Volcanic belt 306 Fig. 2 Geologic map of the Jalisco Block, western Me- xico, showing the major tec- tonic features. (WMVB the western Mexican volcanic belt, MGVF the Michoacan- Guanajuato volcanic ®eld). The numbers 1 and 2 res- pectively are the locations of Volcan Colima and the Mascota-San Sebastian vol- canic ®eld discussed in the text Mascota region with phenocrysts of hornblende, olivine, was found to be within 0.1 log units of the expected value of the augite and minor plagioclase. These assemblages con- oxygen fugacity (Huebner and Sato 1970). Temperature was mea- sured using a ``type S'', Pt-PtRh10 thermocouple that also served as trast with the postulated low-water assemblages (or- one of the leads for the zirconia oxygen sensor. The thermocouple thopyroxene plus plagioclase) of the basaltic andesites was calibrated against the melting point of gold, and was found to from the Michoacan-Guanajuato volcanic ®eld (MGVF be within 5° of the accepted value (1064 °C). in Fig. 2) in the central Mexican volcanic belt (Hasenaka The experimental sample consisted of a paste of polyvinyl al- and Carmichael 1987). Distinctive phenocryst assem- cohol (PVA) and rock powder placed on a Pt loop, which was subsequently hung from a Pt wire cage and suspended in the fur- blages in andesites are also thought to be related to nace using a thin Pt quench wire. Quenching was accomplished by preeruptive water contents. For example, the selected melting the quench wire and dropping the sample cage into a cup of andesite sample (62 wt% SiO2) was erupted as a distilled water placed at the bottom of the furnace. At no time did spessartite (a confusing name, but a variety of lamp- the samples leave the gas stream. All runs used Pt loops that were presaturated with iron to minimize iron loss. This was achieved by rophyre) with only phenocrysts of hornblende (Table 1), running the loop with sample for 24 hours at the oxygen fugacity near the town of Mascota (Fig. 2); in contrast, a nearly and temperature of interest, quenching it and dissolving the glass compositionally identical lava occurs as a lava ¯ow at o the loop by placing it in HF overnight. Fresh rock powder was Volcan Colima (Fig. 2), with phenocrysts of plagioclase, then placed on the ``iron saturated'' loop, and run at the same conditions. The quenched products were then analyzed on the augite, orthopyroxene, and hornblende (Table 1) (Luhr electron microprobe and the results are given in Table 2.
Load more

Recommended publications
  • Hydrogeologic Applications for Historical Records and Images from Rock Samples Collected at the Nevada National Security Site An
    A. 1,461 ft 1,600 ft 2,004.5 ft Lithology interpreted by Richard G. Warren, Comprehensive Volcanic Petrographics, LLC 2,204 ft Figure 3. Representation of rock column derived from lithologic records (A) compared with core samples and thin sections thin-section images (B–E) from the UE-19p borehole. B. Adularia (AA) – Orthoclase (a K-spar polymorph typical of granite), that has formed under hydrothermal rather than magmatic conditions. Image from 2,204 ft at 30 degrees polarization. Acmite (AC) – A Na- and Fe3-rich pyroxene typically found as a Allanite (AL) – An epidote-group mineral containing high contents groundmass phase within devitrified peralkaline rock. Image from of rare-earth elements, found in alkali-calcic volcanic rocks. Image 2,004.5 ft at 90 degrees polarization. from 1,600 ft at 30 degrees polarization. C. Biotite (BT) – A hydrated mafic mineral typical of evolved volcanic rocks. Generally lacking in peralkaline units. Image from 1,461 ft at 90 degrees polarization. Glass (GL) – Typically Ca- and Fe-poor, compositionally at the “granite eutectic” within rhyolitic rocks such as those dominant within the Southwestern Nevada Volcanic Field (SWNVF). Unpolarized image from 1,461 ft. Clinopyroxene (CX) – A Ca-rich pyroxene and anhydrous mafic mineral found in a wide variety of volcanic rocks. Image from 1,461 ft at 30 degrees polarization. D. K-feldspar (KF) – A felsic phenocryst ubiquitous as sanidine within the SWNVF, except absent within the wahmonie Formation. Image from 2,004.5 ft at 30 degrees polarization. Lithic (LI) – A rock fragment incorporated into tuff during eruption, Perrierite/Chevkinite (PE) – A pseudobrookite-group mineral usually from the vent.
    [Show full text]
  • Mineralogy and Petrology of the Santo Tomas-Black Mountain Basalt Field, Potrillo Volcanics, South-Central New Mexico
    JERRY M. HOFFER Department of Geological Sciences, The University of Texas at El Paso, El Paso, Texas 79900 Mineralogy and Petrology of the Santo Tomas-Black Mountain Basalt Field, Potrillo Volcanics, South-Central New Mexico ABSTRACT called the Santo Tomas-Black Mountain basalt field (Hoffer, 1969c). The Santo Tomas-Black Mountain basalts The Santo Tomas-Black Mountain basalt were erupted during the Quaternary from field includes four major centers, each with four centers. Six lava flows are present at one or more cones and associated flows Black Mountain, three at Santo Tomas, and (Hoffer, 1969a). From north to south, the one each at Little Black Mountain and San four volcanic centers are Santo Tomas, San Miguel. The basalts are grouped into three Miguel, Little Black Mountain, and Black major types of phenocryst mineralogy: (l) Mountain. The largest volume of lava has plagioclase abundant, (2) olivine abundant, been extruded from the Black Mountain and and (3) both olivine and plagioclase abundant. Santo Tomas centers where six and three All three types are alkali-olivine basalts, individual flows, respectively, have been showing high alkali-silica ratios and total mapped (Hoffer, 1969a). Each of the two alkali content increasing with silica. intervening centers, Little Black Mountain Seven periods of basaltic extrusion among and San Miguel, shows only a single flow. the centers have been established on the No flow from a given center coalesces with basis of field evidence, phenocryst mineralogy, those from neighboring centers, but all ap- and pyroxene-olivine ratios. K-Ar dates show pear to be closely related in time (Kottlowski, the basalts to be less than 0.3 X 106 m.y.
    [Show full text]
  • Compositional Zoning of the Bishop Tuff
    JOURNAL OF PETROLOGY VOLUME 48 NUMBER 5 PAGES 951^999 2007 doi:10.1093/petrology/egm007 Compositional Zoning of the Bishop Tuff WES HILDRETH1* AND COLIN J. N. WILSON2 1US GEOLOGICAL SURVEY, MS-910, MENLO PARK, CA 94025, USA 2SCHOOL OF GEOGRAPHY, GEOLOGY AND ENVIRONMENTAL SCIENCE, UNIVERSITY OF AUCKLAND, PB 92019 AUCKLAND MAIL CENTRE, AUCKLAND 1142, NEW ZEALAND Downloaded from https://academic.oup.com/petrology/article/48/5/951/1472295 by guest on 29 September 2021 RECEIVED JANUARY 7, 2006; ACCEPTED FEBRUARY 13, 2007 ADVANCE ACCESS PUBLICATION MARCH 29, 2007 Compositional data for 4400 pumice clasts, organized according to and the roofward decline in liquidus temperature of the zoned melt, eruptive sequence, crystal content, and texture, provide new perspec- prevented significant crystallization against the roof, consistent with tives on eruption and pre-eruptive evolution of the4600 km3 of zoned dominance of crystal-poor magma early in the eruption and lack of rhyolitic magma ejected as the BishopTuff during formation of Long any roof-rind fragments among the Bishop ejecta, before or after onset Valley caldera. Proportions and compositions of different pumice of caldera collapse. A model of secular incremental zoning is types are given for each ignimbrite package and for the intercalated advanced wherein numerous batches of crystal-poor melt were plinian pumice-fall layers that erupted synchronously. Although released from a mush zone (many kilometers thick) that floored the withdrawal of the zoned magma was less systematic than previously accumulating rhyolitic melt-rich body. Each batch rose to its own realized, the overall sequence displays trends toward greater propor- appropriate level in the melt-buoyancy gradient, which was self- tions of less evolved pumice, more crystals (0Á5^24 wt %), and sustaining against wholesale convective re-homogenization, while higher FeTi-oxide temperatures (714^8188C).
    [Show full text]
  • GEOLOGIC MAP of the MOUNT ADAMS VOLCANIC FIELD, CASCADE RANGE of SOUTHERN WASHINGTON by Wes Hildreth and Judy Fierstein
    U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP 1-2460 U.S. GEOLOGICAL SURVEY GEOLOGIC MAP OF THE MOUNT ADAMS VOLCANIC FIELD, CASCADE RANGE OF SOUTHERN WASHINGTON By Wes Hildreth and Judy Fierstein When I climbed Mount Adams {17-18 August 1945] about 1950 m (6400') most of the landscape is mantled I think I found the answer to the question of why men by dense forests and huckleberry thickets. Ten radial stake everything to reach these peaks, yet obtain no glaciers and the summit icecap today cover only about visible reward for their exhaustion... Man's greatest 2.5 percent (16 km2) of the cone, but in latest Pleis­ experience-the one that brings supreme exultation­ tocene time (25-11 ka) as much as 80 percent of Mount is spiritual, not physical. It is the catching of some Adams was under ice. The volcano is drained radially vision of the universe and translating it into a poem by numerous tributaries of the Klickitat, White Salmon, or work of art ... Lewis, and Cis pus Rivers (figs. 1, 2), all of which ulti­ William 0. Douglas mately flow into the Columbia. Most of Mount Adams and a vast area west of it are Of Men and Mountains administered by the U.S. Forest Service, which has long had the dual charge of protecting the Wilderness Area and of providing a network of logging roads almost INTRODUCTION everywhere else. The northeast quadrant of the moun­ One of the dominating peaks of the Pacific North­ tain, however, lies within a part of the Yakima Indian west, Mount Adams, stands astride the Cascade crest, Reservation that is open solely to enrolled members of towering 3 km above the surrounding valleys.
    [Show full text]
  • Flow Differentiation, Phenocryst Alignment, and Compositional Trends Within a Dolerite Dike at Rockport, Massachusetts
    Flow differentiation, phenocryst alignment, and compositional trends within a dolerite dike at Rockport, Massachusetts MARTIN E. ROI3S Department of Earth Sciences, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115 ABSTRACT Systematic variations in the volume per- cent, size, and orientation of plagioclase phe- nocrysts up to 12.0 cm long occur across a 5.6-m-thick porphyritic, alkaline dolerite dike in Rockport, Massachusetts. Field measure- ments indicate that phenocryst concentra- tions increase froim nearly zero at the dike margin to 46.0 vol. % at its center. Average phenocryst size increases inward from 4.1 x 2.2 mm at the dike margin to 19.2 * 7.9 mm at the center. The increase in size and abun- dance of phenocrysts toward the center of the dike is interpreted as resulting from flow differentiation. The magma-flow direction is assumed to have been upward and parallel to the dike margins (N7°W strike, 88°E dip). The strikes and dips of all elongate phenocrysts (viewed in cross section) within one traverse across the dike were measured and compared to the dike attitude to determine the degree of flow alignment across I he dike. Average pheno- cryst strike deviations from dike strike in- crease inward 21.8° from the dike margin to Figure 1. Map showing location of the porphyritic dolerite dike exposed as en echelon its midpoint. Phenocryst dip-angle deviations segments (B, C, and D) along the shoreline of Rockport, Massachusetts. Locality B is the from dike dip increase inward by 18.8°. This Headlands segment, subject of this investigation.
    [Show full text]
  • Geology Along the Taylor Highway Alaska
    Geology Along the Taylor Highway Alaska By HELEN L. FOSTER and TERRY E. C. KEITH GEOLOGICAL SURVEY BULLETIN 128 1 A log describing the geology across the Yukon-Tanana Upland, Alaska UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Ubrary of Congress catalog-card No. 71-602340 For sale by the Superintendent of Documents, U.S. Government Prlntln~ Office Washln~ton. D.C. 20402 IV CONTENTS Pal:e FIGURE 13. A typical entrenched meander of South Fork of Fortymile lliver_______________________________________________ 20 14. Abandoned gold dredge_________________________________ 21 15. Plunging anticline______________________________________ 22 16. Mining on Wade CreeL________________________________ 23 17. A large meander of the Fortymile lliver___________________ 25 18. Vertical marble bed___ __ _______________ ___ _ ___ 26 19. Taylor Highway bridge across Fortymile lliver_____________ 27 20. Intricately folded marble and quartzite____________________ 28 21. Woli Mountain________________________________________ 30 22. Steep cliffs of columnar basaIL___________________________ 31 23. Ultramafic rock along the canyon of American Creek_______ 32 24. Eagle and the Yukon lliver- ____________________________ 34 TABLE Page TABLE 1. Approximate sequence and age of geologic events in the country along the Taylor Highway_____________________ 4 GLOSSARY Actinolite. A green mineral which commonly occurs in needlelike crystals. AmygdaloidaI. An adjective that describes a volcanic rock in which many small gas cavities have been filled by secondary minerals. Amygdule. A small gas cavity in a volcanic rock that has been filled with a secondary mineral such as quartz or calcite. Augen gneiss. In the Fortymile area, a gneiss which has light-gray or pink feldspar crystals that are much larger than the other crystals in the rock.
    [Show full text]
  • The Plumbing Systems and Parental Magma Compositions Of
    THE PLUMBING SYSTEMS AND PARENTAL MAGMA COMPOSITIONS OF SHIELD VOLCANOES IN THE CENTRAL OREGON HIGH CASCADES AS INFERRED FROM MELT INCLUSION DATA by STANLEY PAUL MORDENSKY II A THESIS Presented to the Department of Geological Sciences and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Master of Science September 2012 THESIS APPROVAL PAGE Student: Stanley Paul Mordensky II Title: The Plumbing Systems and Parental Magma Compositions of Shield Volcanoes in the Central Oregon High Cascades as Inferred from Melt Inclusion Data This thesis has been accepted and approved in partial fulfillment of the requirements for the Master of Science degree in the Department of Geological Sciences by: Dr. Paul Wallace Chair Dr. Ilya Bindeman Member Dr. Katharine Cashman Member Dr. Dana Johnston Member and Kimberly Andrews Espy Vice President for Research & Innovation/Dean of the Graduate School Original approval signatures are on file with the University of Oregon Graduate School. Degree awarded September 2012 ii © 2012 Stanley Paul Mordensky II iii THESIS ABSTRACT Stanley Paul Mordensky II Master of Science Department of Geological Sciences September 2012 Title: The Plumbing Systems and Parental Magma Compositions of Shield Volcanoes in the Central Oregon High Cascades as Inferred from Melt Inclusion Data Long-lived and short-lived volcanic vents often form in close proximity to one another. However, the processes that distinguish between these volcano types remain unknown. Here, I investigate the differences of long-lived (shield volcano) and short- lived (cinder cone) magmatic systems using two approaches. In the first, I use melt inclusion volatile contents for shield volcanoes and compare them to published data for cinder cones to investigate how shallow magma storage conditions differ between the two vent types in the Oregon Cascades.
    [Show full text]
  • Description of Map Units
    GEOLOGIC MAP OF THE LATIR VOLCANIC FIELD AND ADJACENT AREAS, NORTHERN NEW MEXICO By Peter W. Lipman and John C. Reed, Jr. 1989 DESCRIPTION OF MAP UNITS [Ages for Tertiary igneous rocks are based on potassium-argon (K-Ar) and fission-track (F-T) determinations by H. H. Mehnert and C. W. Naeser (Lipman and others, 1986), except where otherwise noted. Dates on Proterozoic igneous rocks are uranium-lead (U-Pb) determinations on zircon by S. A. Bowring (Bowring and others, 1984, and oral commun., 1985). Volcanic and plutonic rock names are in accord with the IUGS classification system, except that a few volcanic names (such as quartz latite) are used as defined by Lipman (1975) following historic regional usage. The Tertiary igneous rocks, other than the peralkaline rhyolites associated with the Questa caldera, constitute a high-K subalkaline suite similar to those of other Tertiary volcanic fields in the southern Rocky Mountains, but the modifiers called for by some classification schemes have been dropped for brevity: thus, a unit is called andesite, rather than alkali andesite or high-K andesite. Because many units were mapped on the basis of compositional affinities, map symbols were selected to emphasize composition more than geographic identifier: thus, all andesite symbols start with Ta; all quartz latites with Tq, and so forth.] SURFICIAL DEPOSITS ds Mine dumps (Holocene)—In and adjacent to the inactive open pit operation of Union Molycorp. Consist of angular blocks and finer debris, mainly from the Sulphur Gulch pluton Qal Alluvium (Holocene)—Silt, sand, gravel, and peaty material in valley bottoms.
    [Show full text]
  • Plagioclase-Mantled K-Feldspar in the Carboniferous Porphyritic Microgranite Of… 53
    Plagioclase-mantled K-feldspar in the Carboniferous porphyritic microgranite of… 53 PLAGIOCLASE-MANTLED K-FELDSPAR IN THE CARBONIFEROUS PORPHYRITIC MICROGRANITE OF ALTENBERG-FRAUENSTEIN, EASTERN ERZGEBIRGE / KRUVSNÉ HORY AXEL MÜLLER AND REIMAR SELTMANN MÜLLER, AXEL and SELTMANN, REIMAR 2002. Plagioclase-mantled K- feldspar in the Carboniferous porphyritic microgranite of Altenberg-Frauenstein, Eastern Erzgebirge/Kruvsné Hory. Bulletin of the Geological Society of Finland 74, Parts 1–2, 53–78. The Upper Carboniferous porphyritic microgranite of Altenberg-Frauenstein, formerly known as Granitporphyr (Dalmer 1896) and here abbreviated as GP, forms a 36 km long and up to 18 km wide complex of ring dykes related to the Teplice-Altenberg caldera in the German–Czech border region of the Eastern Erzgebirge/Kruvsné Hory. The microgranites are characterized by the occurrence of plagioclase-mantled K-feldspar phenocrysts. The microgranite varieties rep- resent two main stages of intrusion evolved from acid (GP I) to intermediate rocks (GP II) within the intrusion. The most acid rock (GP Icum) occurs as en- claves in GP I and GP II and is interpreted as a cumulate of K-feldspar and quartz phenocrysts. The porphyritic microgranites show field, textural and geochemi- cal evidence suggesting that some of them have formed as a result of interac- tion between felsic and mafic magmas. Mixing features are abundant in the por- phyritic quartz-feldspar-hornblende microgranite (GP II) interpreted as a hybrid rock. They are less discrete in the early phase (GP I) and not obvious in the acid enclaves (GP Icum). This trend seems to reflect a continuous deflation of the magma chamber from the top to the bottom.
    [Show full text]
  • Glossary of Geological Terms
    GLOSSARY OF GEOLOGICAL TERMS These terms relate to prospecting and exploration, to the regional geology of Newfoundland and Labrador, and to some of the geological environments and mineral occurrences preserved in the province. Some common rocks, textures and structural terms are also defined. You may come across some of these terms when reading company assessment files, government reports or papers from journals. Underlined words in definitions are explained elsewhere in the glossary. New material will be added as needed - check back often. - A - A-HORIZON SOIL: the uppermost layer of soil also referred to as topsoil. This is the layer of mineral soil with the most organic matter accumulation and soil life. This layer is not usually selected in soil surveys. ADIT: an opening that is driven horizontally (into the side of a mountain or hill) to access a mineral deposit. AIRBORNE SURVEY: a geophysical survey done from the air by systematically crossing an area or mineral property using aircraft outfitted with a variety of sensitive instruments designed to measure variations in the earth=s magnetic, gravitational, electro-magnetic fields, and/or the radiation (Radiometric Surveys) emitted by rocks at or near the surface. These surveys detect anomalies. AIRBORNE MAGNETIC (or AEROMAG) SURVEYS: regional or local magnetic surveys that measures deviations in the earth=s magnetic field and carried out by flying a magnetometer along flight lines on a pre-determined grid pattern. The lower the aircraft and the closer the flight lines, the more sensitive is the survey and the more detail in the resultant maps. Aeromag maps produced from these surveys are important exploration tools and have played a major role in many major discoveries (e.g., the Olympic Dam deposit in Australia).
    [Show full text]
  • Mineral Analysis in Rocks Using XRD and Petrography
    ICOSITER 2018 Proceeding Journal of Science and Applicative Technology Mineral analysis in rocks using XRD and Petrography Muhamad Ragil Setiawan1, Mochamad Iqbal2, Rahmat Nawi Siregar1 1 Physics Department, Institut Teknologi Sumatera, Lampung Selatan, Lampung. 2 Geological Engineering Department, Institut Teknologi Sumatera, Lampung Selatan, Lampung. Abstract. Rock formation in a region is influenced by many factors such as tectonic and volcanic systems of the area. Both activities will affect the microstructure of the rock. This study analyzes mineral composition in three different rocks. We display the digital image that obtained from XRD and petrography. Rock samples were taken from some formations around Lampung. The analysis was performed on three different rocks: granite, andesite, and schist using XRD and petrography. The granite-R1 sample shows the result of mineral content present in the rock that is quartz, alkali feldspar, plagioclase, biotite. The andesite-R2 sample consists of plagioclase, orthopyroxene, biotite, and volcanic glass. The Schist-R3 sample consist of quartz, muscovite, calcite. 1. Introduction The characteristics of rocks has been investigated with various methods[1],[2],[3] in micro structure as well as macro structure which can describe the physical properties of rocks[4],[5]. The physical properties such as resistivity can be used as a tool in identifying the reservoir of groundwater. Moreover, the information about permeability, porosity and mineral of rocks will provide the properties of rocks. One of the most important tool to find the properties of rocks is by applying the electromagnetic wave in describing the subsurface condition. The electromagnetic wave can be generated in some frequencies by using the active or passive method.
    [Show full text]
  • Andesite Conference Guidebook
    ANDESITE CONFERENCE GUIDEBOOK I NTERNATI 0 NAL UPPER MANTLE PROJECT Sci enti fi c Report 16-S Published by: State of Oregon, Department of Geology and Mineral Industries, as Bulletin 62 International UPPER MANTLE COMMITTEE Prof. V. V. BELOUSSOV, Chairman (Moscow) Dr. Luis R. A. CAPURRO (Buenos Aires) Prof. A. E. RINGWOOD (Canberra) Dr. J. M. HARRISON (Ottawa) Prof. S. K. RUNCORN (Newcastle-upon-Tyne) Prot. Leon KNOPOFF, Secretary-General (Los Angeles) Dr. Klyoo \,VADATI (Tokyo) ANDESITE CONFERENCE July 1 to 6, 1968 Eugene and Bend, Oregon U. S. A. Sponsored by: University of Oregon Center for Volcanology A. R. McBirney, Director International Upper Mantle Committee Prof. Hisashi Kuno, Chairman Working Group on Petrology and Volcanism State of Oregon Department of Geology and Mineral Industries H. M. Dole, State Geologist Financial assistance for the Andesite Conference was provided by the International Union of Geodesy and Geophysics and by the International Union of Geological Sciences. The Upper Mantle Project is an international program of research on the solid earth sponsored by the International Counci I of Scientific Unions; the program is coordinated by the International Upper Mantle Committee, an IUGG committee set up jointly by the International Union of Geodesy and Geophysics and the International Union of Geological Sciences, with rules providing for the active participation of all interested ICSU Unions and Committees. Cover Picture: Andesite Thin Section Cover design is a microdrawing of the hypersthene-augite andesite at the highest peak of Mount jefferson. The rock is typical of the andesites of the Oregon Cascades in both its petrographic features and chemical composition.
    [Show full text]