DOCSLIB.ORG

Geologic Investigations Series U.S

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Geologic Investigations Series U.S U.S. DEPARTMENT OF THE INTERIOR GEOLOGIC INVESTIGATIONS SERIES U.S. GEOLOGICAL SURVEY I–2697 Qtl Ta Ktl Ta CORRELATION OF MAP UNITS microcline phenocrysts as much as 10 cm long making up 2 to 10 The pre-Tertiary rocks of the Tower Peak quadrangle fall into two groups: (1) an here has burst its shell of more mafic differentiates and intrudes older granitic and Qng Qtl Qg a c percent of the rock. Quartz typically occurs in 1/2-cm clots. Mafic L-shaped area of older plutonic and metamorphic rocks, 3 to 10 km wide, that metamorphic rocks, and (2) the Half Dome Granodiorite, which is interpreted as an Qal Qng Tvs Qg 70 Tr p SURFICIAL DEPOSITS Qtl 75 c Qtl Ktl Qga mineral content about 10 percent. Asymmetric schlieren locally extends diagonally both northeast and southeast from near the center of the quadran- earlier, more mafic differentiate of the same magmatic pulse as that for the Ta c Kfl Qal Qtl Qls Qng Holocene Ktl Qtl abundant gle; and (2) a younger group of large, probably composite intrusions that cover large Cathedral Peak Granodiorite. Qtl Ta 70 QUATERNARY a Qal c areas in adjacent quadrangles and extend into the Tower Peak quadrangle from the The northern composite intrusion of the younger group includes the Qal c Kfl Granodiorite of Fremont Lake (Cretaceous)—Medium-dark-gray, Qng Tvs Qg Late Qtl Qtl 65 Tr p Qg medium-grained, hornblende-biotite granodiorite. Where horn- east, north, and southwest. granodiorite of Topaz Lake, a rock almost identical in appearance and age to the Qtl Qtl Pleistocene Tr p Qng Qng 70 a Cathedral Peak Granodiorite, but separated from the latter by a 6- to 7-km septum of Ktl Ta Qg VOLCANIC ROCKS blende-rich, contains abundant lenticular or elongate mafic inclu- Qng Qtl Qtl 70 65 OLDER PLUTONIC AND METAMORPHIC ROCKS older rocks. The Topaz Lake pluton is bordered on the south by the granodiorite of c sions, commonly uniformly distributed, but locally in clusters. In the a a a Qal a Qg 60 Ta southwest part of its occurrence in this quadrangle, it is largely The L-shaped remnant of older plutonic and metamorphic rocks that extends Fremont Lake. The Fremont Lake pluton appears to bear the same relationship to the Tvs 55 c 70 75 northeast and southeast from the center of the quadrangle contains ten plutons with granodiorite of Topaz Lake that the Half Dome Granodiorite does to the Cathedral Kfl a Tr p Miocene mafic free, lacking in inclusions, and tending toward granitic com- Tr p contiguous areas of at least 2.5 sq. km and several complexes of dikes and small Peak Granodiorite. Qal Qtl 65 a a TERTIARY position. Map unit is named for exposures near Fremont Lake where c Qal Qng Ta Tvs Tbb irregular masses. These plutons and dikes intruded silicic and mafic metavolcanic The southwestern composite intrusion of the younger group includes four large a it was mapped by Giusso (1981) in the Sonora Pass quadrangle to Qng 35 c 65 a 50 Kfl a Qal 65 rocks and miogeoclinal metasedimentary rocks. Mutual age relations between the plutons in the southwest corner of the Tower Peak quadrangle and in adjacent Tvs 55 Qng Miocene to the north. The unit extends west into the Pinecrest quadrangle where Ktl Qtl Qal 50 65 a a65 Tvs plutonic rocks are incompletely determined, either because some of the rocks are not a 60 a a Oligocene it has been called the granodiorite of Kinney Lakes (Huber, 1983) quadrangles. These plutons show some evidence of being consanguineous, yet other Tbb Qtl a 80 a in geographically contiguous sequences or because the contacts have ambiguous age evidence suggests a significant hiatus in the sequence. The complex includes, from Qtl Tbb Qg Klc Granodiorite of Long Canyon (Cretaceous)—Dark hornblende-biotite Qal aa85 75 Klc mvr PLUTONIC ROCKS criteria. Structures in this remnant are generally steep, trend northwesterly, and are oldest to youngest, the quartz diorite of Mt. Gibson, the granodiorite of Bearup Tr p 70 [Lines and arrows indicate intrusive relations] granodiorite and quartz-diorite with mafic mineral content of about c c a c cut off sharply by the younger plutons. Lineations, foliations, and zones of recrystal- Lake, the granodiorite of Lake Vernon, and the granodiorite of Boundary Lake. A Tvs a c Qg South and 30 percent and with abundant mafic inclusions aa70 80 lization and shearing, all of supposed metamorphic or tectonic origin, are present in swarm of fine-grained diorite dikes cuts the Mt. Gibson and Bearup Lake, but is 75 msm msq southwestern Northern Eastern Qal 70 gb a75 Klc a 80 a Eastern area some plutons and suggest at least one period of dynamic metamorphism during or apparently cut off by the granodiorite of Lake Vernon. This succession of events Tr p 70 a Qtl area area area a apa a a 75 c Qal 80 70 a Qg Tr p Kcp Cathedral Peak Granodiorite (Cretaceous)—Medium- to coarse- after the period of emplacement of these plutons. The metamorphic and early mafic suggests a time break and interval of cooling. However, the granodiorite of Bearup msh 60 a70 80 Kbl Ktl Kcp rocks are described first below, followed by the plutonic rocks of the northeast arm Lake grades in color index from very near that of the Mt. Gibson where it is in Qg mvr c c grained, hornblende-biotite granodiorite that contains conspicuous 70 a70 85 of the "L", and then the rocks of the southeast arm. Klh Qg a 85 Klv Kfl Khd blocky phenocrysts of microcline as much as 10 cm long. The intrusive contact with the Mt. Gibson to very near that of the Lake Vernon where the a Metamorphosed sedimentary rocks appear to be the oldest rocks. They include latter intrudes the Bearup Lake. This suggests a genetic relationship extending a a aa phenocrysts commonly occur in aligned swarms and asymmetric 80 mvb Qal 75 Kbu Klc Kgm Ktl di ap schlieren are locally abundant pure white orthoquartzite, in beds a few meters thick, that display thin partings bear- across the time gap. 80 80 Kmgc a a mvr i Kut Khd Half Dome Granodiorite (Cretaceous)—Medium- to coarse-grained, ing andalusite and biotite and common internal crossbedding. These are interbedded 80 Tvs a Kmgf CRETACEOUS c 80 a DIORITE DIKES Qtl a 85 equigranular hornblende-biotite granodiorite with abundant elongate with thick (10 to 50 m) units of biotite-andalusite-sillimanite(?) schist, coarsely c Kdl 80 Qg c Kpm Kt Kmp Kbp c a a 75 crystalline marble, and fine to coarse beds of pale-green, calc-silicate hornfels. Sets of diorite dikes (not shown on the geologic map) with at least three 65 c a or flattened mafic inclusions. Characterized by euhedral hornblende 80 c 80 a These metasediments are complexly deformed. The southern body around Benson orientations intrude the granite of Avonelle Lake, and at least one set also intrudes a c g Klh Kal ap Kdl prisms as much as 1 cm long, biotite books as much as 1 cm across, Kfl 85 Lake is mainly quartzite, with some thick biotite-andalusite schist bodies near the the quartz diorite of Mt. Gibson and granodiorite of Bearup Lake. These dikes are a a c and conspicuous sphene. Near Tilden Lake it is mafic-poor and has 80 c Klh c msh a top and marble at the base, folded into a large anticline with a horizontal crest and confined to the southwest part of the quadrangle and do not appear to occur in the 80 i Klh large microcline phenocrysts Qal c 80 vertical limbs. The minimum stratigraphic thickness exposed in this body is 750 m. northeastern part of the Avonelle Lake pluton. One set trends due north and is about 75 c 75 ap c CRETACEOUS Kgm Alaskite of Grace Meadow (Cretaceous)—Sugary, medium- to fine- di gb The northern body, around Bigelow and Snow Lakes, contains abundant marble bod- vertical, another set trends northwest and is about vertical, and the third strikes a a msq Qtl c OR OLDER grained, light-pink to white alaskite with rare dark minerals. ies and about equal amounts of quartzite, biotite schist, and calc-silicate hornfels. It roughly east-west and dips 30 to 45 north. The first two sets appear to predate the 80 ° ° a c Contains abundant inclusions of diorite, gabbro, quartzite, biotite Qal METAMORPHIC ROCKS has been folded at least twice, the first time isoclinally. The latest deformation was formation of the Mahan Peak complex and the intrusion of the Mt. Gibson pluton c schist, and marble a a Qng into a flat-topped dome with nearly vertical flanks along the intrusive contacts. because they are found as inclusions in the former. The diorite dikes probably c CRETACEOUS c a Kut 80 c i mvb mvr Granite of Upper Twin Lake (Cretaceous)—Coarse, equigranular, a Small bodies and inclusions of metasedimentary rocks in several of the plutons indi- represent periods of crustal extension, although it is not clear how extension alone 70 di ms msq msm OR OLDER a 60 Qg 85 pink biotite granite. Locally has a very strong vertical lineation, a Qal Kcp cate that this terrane was once more widespread. In the extreme northeast part of the would produce a dike-swarm dipping 30 north. Qng ° 80 45 Kbp msq probably of metamorphic origin 75 Qg quadrangle, metasedimentary rocks, which may be in depositional sequence with the Where the diorite dikes intrude granite, they are bordered by thin, discontinuous 60 g a g Kfl 70 a Kbp Granite of Bond Pass (Cretaceous)—Gray, moderately foliated, a msq 60 g ms msm metavolcanic rocks, include quartzite and stretched conglomerate.
Load more

Recommended publications
  • Geochemistry of Granitic Aplite-Pegmatite Veins and Sills and Their Minerals from the Sabugal Area, Central Portugal
    N. Jb. Miner. Abh. 188/3, 297 – 316 Fast Track Article PublishedStuttgart, Augustonline November2011 2011 Geochemistry of granitic aplite-pegmatite veins and sills and their minerals from the Sabugal area, central Portugal Ana M. R. Neiva, Paulo B. Silva and João M. F. Ramos With 19 fi gures and 12 tables Abstract: Granitic beryl-columbite-phosphate subtype aplite-pegmatite veins and sills from the Sabugal area intruded a biotite > muscovite granite which is related to another two-mica granite. Variation diagrams of major and trace elements of whole rocks δ18 show fractionation trends. REE patterns and O of whole rocks, BaO and P2O5 contents of K-feldspar, anorthite and P2O5 contents of plagioclase, major element and Li contents of muscovite and lithian muscovite support this series. Least squares analysis of ma- jor elements indicate that the biotite > muscovite granite and aplite-pegmatite veins and sills are derived from the earlier two-mica granite magma by fractional crystallization of quartz, plagioclase, K-feldspar, biotite and ilmenite. Modelling of trace elements shows that magmatic fl uxes and fl uids controlled the Rb, Sr and Ba contents of aplite-pegmatites,Paper probably also lithium micas (zin- nwaldite, polylithionite and rare lepidolite), cassiterite, columbite-tantalite, fl uorapatite and triplite. In aplite-pegmatites, lithian muscovite replaces primary muscovite and late lithium micas replace lithian muscovite. Complexely zoned columbite crystals are chemically characterized and attributed to disequilibrium conditions. Relations of granites and aplite-pegmatites and pegmatites from other Portuguese and Spanish areas are compared. The granitic aplite-pegmatites from Sabugal are moderately fractionated and the granitic complex type aplite-pegmatites from Gonçalo are the richest in Li and Sn, derived from a higher degree of frac- tional crystallization and fl uxes and fl uids control the Ba and Rb behaviours and Li, Sn, F and Ta concentrations.
    [Show full text]
  • Decrepitation Characteristics of Igneous
    DECREPITATIONCHARACTERISTICS OF IGNEOUSROCKS F. G. SMITH Unfuersi,tyof Toronto, Toronto, Canada Ansrnect ._lecrepitation during heating of igneous intrusive rocks is complex, but one stage (D2) appears to be due to misfit of solid inclusions. This stage begins at 6rb + g0'-b in simple granite pegmatite and aplite, Z0S * 80" C in ganiie, Z6E + 50" C in granodiorite and quartz norite, and 1010 + 60o C in gabbro and related rocks. The p2-sQS! of pegmatite and aplite in an area of migmatitic gneiss, with no exposed batholiths, starts at a lower temperature than the corresponding stage of decrepitation of the country gneiss. Introd,wction The rationale of decrepitation due to misfit of solid inclusions in minerals, when heated above the temperature of crystallization, was outlined previously (smith, L952a).A stage of decrepitation of several types of garnet was interpreted to be due to solid inclusions, becausethe frequency of decrepitation was found to be directly related to the abundanceof solid inclusions (smith, lg52b). A similar stage of decrepi- tation of high grade metamorphic rocks was found (Smith, lgb8). The measuredtemperatures of the beginning of this stage of decrepitation of metamorphic minerals are internally consistent, and are not at variance with the small amount of synthetic data. As a further test of the rationale. a few rocks representing several igneous rock clans were heated in the decrepitation apparatus. The results can be interpreted in an analogous manner to give the temperature of crystallization of the constituent minerals. These data, which should be considered as only tentative becauseof the small number in each clan tested, are given below, uncor- rected for the effect of pressiure.
    [Show full text]
  • LAB 3: COMMON MINERALS in SEDIMENTARY ROCKS, Part 1
    EESC 2100: Mineralogy LAB 3: COMMON MINERALS IN SEDIMENTARY ROCKS, Part 1 Learning Objectives: Students will be able to identify minerals that occur commonly in sandstones (quartz and feldspars), both in hand-sample and thin-section Students will be able to determine the composition of plagioclase using the Michel-Levy method New Minerals: Quartz, Plagioclase, Microcline, Orthoclase Clastic sedimentary rocks are composed of grains that have been weathered from pre-existing rocks. The chemical weathering processes of hydrolysis, oxidation, and dissolution act on sediments, destroying those minerals that are most reactive, and forming new minerals that are stable at surface conditions: most halides and sulfates will dissolve; pyrite will form hydroxy-oxides such as limonite; unstable silicates will form clays. Minerals that are susceptible to physical weathering (i.e., minerals that are soft or cleavable) will be reduced in size during transport, and so may only be identified under the microscope. Quartz is a common rock-forming mineral, and resistant to both chemical and physical weathering. Accordingly, it is a common constituent of clastic sedimentary rocks. Feldspars are relatively stable in the surface environment, with potassium feldspars being more resistant to chemical weathering than plagioclase. Mafic minerals readily weather to form clays and iron hydroxy- oxides, and so are uncommon in sedimentary rocks. Thus the most important minerals in clastic sedimentary rocks are quartz, potassium feldspar (microcline and orthoclase), plagioclase, clays, and oxides/hydroxy-oxides (hematite, limonite, goethite). Percentages of quartz, feldspar, and clay are used to classify most clastic sedimentary rocks (sandstones, siltstones, claystones). QUARTZ Examine the four hand samples of quartz (Crystal, White, var.
    [Show full text]
  • Mineralogy and Geology of the \Vkgnerite Occurrence Co Santa Fe Mountain, Front Range, Cobrado
    Mineralogy and Geology of the \Vkgnerite Occurrence co Santa Fe Mountain, Front Range, Cobrado GEOLOGICAL SURVEY PROFESSIONAL PAPER 955 Mineralogy and Geology of the Wignerite Occurance on Santa Fe Mountain, Front Range, Colorado By DOUGLAS M. SHERIDAN, SHERMAN P. MARSH, MARY E. MROSE, and RICHARD B. TAYLOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 955 A detailed mineralogic study of wagnerite, a rare phosphate mineral occurring in the report area in Precambrian gneiss; this is the first recorded occurrence of wagnerite in the United States UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976 UNITED STATES DEPARTMENT OF THE INTERIOR THOMAS S. KLEPPE, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Main entry under title: Mineralogy and geology of the wagnerite occurrence on Santa Fe Mountain, Front Range, Colorado. (Geological Survey Professional Paper 955) Includes bibliographical references. 1. Wagnerite Colorado Santa Fe Mountain. 2. Geology Colorado Santa Fe Mountain. I. Sheridan, Douglas M., 1921- II. Series: United States Geological Survey Professional Paper 955. QE391.W3M56 549'.72 76-10335 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, B.C. 20402 Stock Number 024-001-02844-1 CONTENTS Page Metric-English equivalents .............................. Descriptive mineralogy Continued Page Abstract............................................................ 1 Wagnerite............................................... 5 Introduction....................................................
    [Show full text]
  • Structural Geology of the Upper Rock Creek Area, Inyo County, California, and Its Relation to the Regional Structure of the Sierra Nevada
    Structural geology of the upper Rock Creek area, Inyo County, California, and its relation to the regional structure of the Sierra Nevada Item Type text; Dissertation-Reproduction (electronic); maps Authors Trent, D. D. Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 27/09/2021 06:38:23 Link to Item http://hdl.handle.net/10150/565293 STRUCTURAL GEOLOGY OF THE UPPER ROCK CREEK AREA, INYO COUNTY, CALIFORNIA, AND ITS RELATION TO THE REGIONAL STRUCTURE OF THE SIERRA NEVADA by Dee Dexter Trent A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 7 3 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by __________ Dee Dexter Trent______________________ entitled Structural Geology of the Upper Rock Creek Area . Tnvo County, California, and Its Relation to the Regional Structure of the Sierra Nevada ________________ be accepted as fulfilling the dissertation requirement of the degree of ____________Doctor of Philosophy_________ ___________ P). /in /'-/7. 3 Dissertation Director fJ Date After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:* f t M m /q 2 g ££2 3 This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination.
    [Show full text]
  • Petrographic Study of a Quartz Diorite Stock Near Superior, Pinal County, Arizona
    Petrographic study of a quartz diorite stock near Superior, Pinal County, Arizona Item Type text; Thesis-Reproduction (electronic); maps Authors Puckett, James Carl, 1940- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 23/09/2021 23:40:37 Link to Item http://hdl.handle.net/10150/554062 PETROGRAPHIC STUDY OF A QUARTZ DIORITE STOCK NEAR SUPERIOR, PINAL COUNTY, ARIZONA by James Carl Puckett, Jr. A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 7 0 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author.
    [Show full text]
  • Ocean Drilling Program Scientific Results Volume
    Von Herzen, R. P., Robinson, P. T., et al., 1991 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 118 22. PLASTIC DEFORMATION AT AN OCEANIC SPREADING RIDGE: A MICROSTRUCTURAL STUDY OF THE SITE 735 GABBROS (SOUTHWEST INDIAN OCEAN)1 Mathilde Cannat2 ABSTRACT Microstructural analysis suggests that some Site 735 gabbros were deformed in the crystal mush stage, before they had completely crystallized. Later, solid-state deformation began in granulite-facies metamorphic conditions. At this stage, temperature-dependent diffusion processes may have controlled the plastic deformation of these gabbros, and mylonites formed only in intervals containing more than 10% Fe-Ti oxides. Most oxides in these mylonites are interpreted as magmatic in origin. A sharp change of deformation processes occurred as temperature decreased to the stability conditions of amphibolite-facies metamorphic assemblages: dislocation slip in plagioclase may have become the leading plastic flow mechanism. This change of deformation processes coincides with increased availability of hydrothermal water and with a marked decrease of the plagioclase recrystallized grain size. This reduction in recrystallized grain size is thought to result from an increase of the deviatoric stress, and thus from an increase of the yield strength of the gabbros. In amphibolite-facies metamorphic conditions, dynamic recrystallization of plagioclase locally caused strain-softening, leading to the formation of mylonites. Relict porphyroclasts (plagioclase, olivine, and pyroxenes) in these mylonites are fractured and boudinaged. The cracks produced by this brittle failure are filled with green to brown hydrothermal hornblende. INTRODUCTION the Site 735 deformed gabbros. These results are used to interpret the tectonic evolution of these gabbros (Cannat et A total of 500 m of gabbro was drilled at Site 735 during al., this volume).
    [Show full text]
  • University of Nevada, Reno Igneous and Hydrothermal Geology of The
    University of Nevada, Reno Igneous and Hydrothermal Geology of the Central Cherry Creek Range, White Pine County, Nevada A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology by David J. Freedman Dr. Michael W. Ressel, Thesis Advisor May, 2018 THE GRADUATE SCHOOL We recommend that the thesis prepared under our supervision by DAVID JOSEPH FREEDMAN entitled Igneous and Hydrothermal Geology of the Central Cherry Creek Range, White Pine County, Nevada be accepted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Michael W. Ressel, PhD, Advisor John L. Muntean, PhD, Committee Member Douglas P. Boyle, PhD, Graduate School Representative David W. Zeh, PhD, Dean, Graduate School May, 2018 i Abstract The central Cherry Creek Range exposes a nearly intact, 8-km thick crustal section of Precambrian through Eocene rocks in a west-dipping homocline. Similar tilts between Eocene volcanic rocks and underlying Paleozoic carbonates demonstrate that tilting and exhumation largely occurred during post-Eocene extensional faulting, thus allowing for relatively simple paleo-depth determinations of Eocene intrusions and mineral deposits. The study area is cored by the Cherry Creek quartz monzonite pluton (35 km2 exposure; ~132 km2 coincident magnetic anomaly), which was emplaced into Precambrian and Cambrian meta-sedimentary strata between 37.9-36.2 Ma and is exposed along the east side of the range. The pluton and overlying Paleozoic strata are cut by abundant 35.9-35.1 Ma porphyritic silicic dikes. A range of polymetallic mineralization styles are hosted by the intrusive rocks along two deeply-penetrating, high-angle faults and their intersections with favorable Paleozoic units.
    [Show full text]
  • LAYERED PEGMATITE-APLITE Division of Earth Sciences, The
    MINERALOGICAL SOCIETY OF AMERICA, SPECIAL PAPER 1, 1963 INTERNATIONALMINERALOGICALASSOCIATION,PAPERS, THIRD GENERAL MEETING LAYERED PEGMATITE-APLITE INTRUSIVES 1 RICHARD H. JAHNS AND O. FRANK TUTTLE Division of Earth Sciences, The Pennsylvania State University, University Park, Pennsylvania ABSTRACT Intrusive bodies of granitic pegmatite and aplite with simple or complex layering include those representing multiple injections of magma from external sources and those representing single injections of magma followed by segregation dur- ing crystallization. Those of the latter category can be subdivided into four classes, intergradations among which are not uncommon: 1. Bodies of aplite or fine-grained pegmatite with very large phenocrysts, or megacrysts. 2. Aplite bodies with mar- ginal or interior pegmatite masses generally formed in situ. 3. Pegmatite bodies with marginal or interior aplite masses formed in situ or by autoinjection. 4. Highly asymmetric bodies whose upper parts consist mainly or wholly of pegmatite and whose lower parts consist mainly or wholly of aplite. Zonal structure defines a gross layering within many pegmatite bodies, and a layer-like distribution of pegmatite and aplite also is common over a wide range of scales. Some of the aplites are faintly to distinctly flow layered, and others are featured by rhythmic layering in which adjacent thin and regular units differ from each other in composition. None of the observed types of layering is regarded as a result of crystal accumulation. The bulk composition of the layered intrusive bodies falls in the thermal valley of petrogeny's residua system at an average composition corresponding to a parent magma saturated with water at high pressures (e.g.
    [Show full text]
  • Chapter 1 – Introduction – Review of Rocks and Plate Tectonics Practice Exam and Study Guide
    Chapter 1 – Introduction – Review of Rocks and Plate Tectonics Practice Exam and Study Guide To be able to understand the material covered during this course you need to have a basic background in the kinds of rocks making up our planet. This section of the study guide is aimed at helping you gain that background. 1. What are the three major groups of rocks found on planet Earth? Igneous Rocks 2. Which of the following processes is associated with igneous rocks? a. Solid‐state recrystallization b. Weathering and erosion c. Transportation and deposition d. Cooling a silicate liquid to a solid rock e. The accumulation of granitic debris in a moraine 3. If a silicate liquid flows out along the Earth’s surface or seabed, then it is called _______________. 4. If a silicate liquid exists beneath the Earth’s surface or seabed, then it is called _______________. 5. Which of the following terms refer to a body of magma or its solidified equivalent? a. Basalt b. Sandstone c. Gneiss d. Pluton e. Schist 6. If you can see the crystals making up an igneous rock with the naked eye, then the texture is described as a. Pyroclastic b. Phaneritic c. Aphanitic d. Porphyritic e. Aphyric from Perilous Earth: Understanding Processes Behind Natural Disasters, ver. 1.0, June, 2009 by G.H. Girty, Department of Geological Sciences, San Diego State University Page 1 7. In an aphanitic igneous rock can you make out the outlines of individual crystals with the naked eye? Yes or No 8. What type of igneous rock is the most volumetrically important on our planet? Intrusive Igneous Rocks 9.
    [Show full text]
  • Petrology and Major Element Geochemistry of Albite Granite Near Sparta, Oregon Robert Brayton Almy III Western Washington University
    Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Winter 1977 Petrology and Major Element Geochemistry of Albite Granite near Sparta, Oregon Robert Brayton Almy III Western Washington University Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geochemistry Commons, and the Geology Commons Recommended Citation Almy, Robert Brayton III, "Petrology and Major Element Geochemistry of Albite Granite near Sparta, Oregon" (1977). WWU Graduate School Collection. 792. https://cedar.wwu.edu/wwuet/792 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. PETROLOGY AND MAJOR ELEMENT GEOCHEMISTRY OFJ\LBITE GRANITE NEAR SPARTA, OREGON A Thesis ' Presented to The Faculty of Western Washington State College In Partial Fulfillment Of the Requirements for the Degree Master of Science by Robert B. Almy III March, 1977 345c 112 MASTER'S THESIS In presenting this thesis in partial fulfillment of the requirements for a master's degree at Western Washington University, I grant to Western Washington University the non-exclusive royalty-free rightto archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and w/arrant this is rhy original work and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files.
    [Show full text]
  • A More Informative Way to Name Plutonic Rocks— Comment by Frost Et Al
    COMMENTS & REPLY A More Informative Way to Name Plutonic Rocks— Comment by Frost et al. B. Ronald Frost, Carol D. Frost, Dept. of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA; J. Lawford Anderson, Dept. of Earth and Environment, Boston University, Boston, Massachusetts 02215, USA; Calvin G. Barnes, Dept. of Geosciences, Texas Tech University, Lubbock, Texas 79409, USA; and Marjorie Wilson, School of Earth & Environment, Leeds University, Leeds LS2 9JT, UK In a recent paper, Glazner et al. (GSA ≥10% quartz (the most common group) a more precise description of the rock. This Today, Feb. 2019) proposed a major change are described by only 23 names, many of suggestion indicates a confusion of preci- in the terminology of plutonic rocks, which share the same root name. These sion and accuracy. Modes are difficult to whereby a simplified rock name is prefixed names need not be memorized because determine in the field where, as Glazner et with the mode. In this classification, a they are present in the various IUGS dia- al. (2019) observe, the distinction between granite might be named 20,20,50 granite. grams for rock names, a diagram that is alkali feldspar and plagioclase can be sub- Glazner et al. (2019) proposed this classifi- easily pasted into field notebooks. tle. Field estimation of modes is unlikely to cation system for three reasons. First, they The argument of Glazner et al. (2019) be better than ±10%. With this precision, a maintain that rock terminology is too com- that rock names are determined by rock classified as a 25,25,40 granite would plex; they note that at least 157 igneous rock “arbitrary” boundaries is not compelling.
    [Show full text]