DOCSLIB.ORG

Geology, Petrology and PGE-Cu-Ni Mineralization of the Neoarchean Entwine Lake Intrusion, an Intermediate to Mafic Igneous Intrusion

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Geology, Petrology and PGE-Cu-Ni Mineralization of the NeoArchean Entwine Lake Intrusion, an Intermediate to Mafic Igneous Intrusion J.P. Arnold1, R.S. James1 and G. Beakhouse2 1Department of Earth Sciences and Mineral Exploration Research Centre, Laurentian University, Ontario, Canada. P3E 2R9 2Ontario Geological Survey, MNDM, Willet Green Miller Centre, Ramsay Lake Rd, Sudbury, Ontario, Canada, P3E 6B5 e-mail: [email protected] Introduction Regional Geology The Entwine Lake intrusion (ELI) is an In Ontario, the Superior Province of the east west trending, tadpole-shaped, neo-Archean Canadian Shield is divided into thirteen intrusion located 90 km south of Dryden, Ontario. subprovinces based on recently identified tectonic The ELI is approximately 35 km long with a near boundaries (Thurston et al., 1991). Diagnostic to circular, 10 km diameter western portion and a most subprovinces, including the Wabigoon, are narrow tail extending to the east (Stone, 1999). The granite-greenstone assemblages consisting of pluton has recently attracted attention due to PGE- metavolcanic and subordinate metasedimentary Cu-Ni mineralization located in the northern units interleaved and cut by granite batholiths and portion of the intrusion by Champion Bear late intrusions. The Wabigoon Subprovince, a 3.0- Resources. The presence of PGE mineralization is 2.69 Ga, 900km long and 150km wide, northeast of particular interest as this intrusion has trending granite-greenstone belt, has been divided characteristics similar to that of a suite of mantle- into eastern, central and western regions (Blackburn derived monzodioritic intrusions (termed sanukitoid et al., 1991). The Entwine Lake intrusion occurs by Shirey and Hanson, 1984) that have not adjacent to the western boundary of the central previously been examined for their PGE potential. Wabigoon region (Stone, 2000) (Fig. 1). The This M.Sc. thesis project, conducted under central Wabigoon region contains scattered an Ontario Geological Survey/Laurentian remnants of meso-Archean (3.07-2.90 Ga) felsic University (MERC) collaborative project gneiss and greenstone belts that have been intruded agreement, is designed to map the ELI at a scale of by neo-Archean (2.78-2.70 Ga) felsic batholiths 1:20 000 and further our understanding of the and late stocks (Tomlinson, 1997, 1998). The nature and origin of the pluton and its mineral Entwine Lake intrusion is one of these late stocks, potential. which are often crescentic-shaped intrusions mantled by septa of mafic schist and amphibolite gneiss interpreted to be the remnants of older greenstone belt assemblages (Stone, 2000). 93O 00’ 91O 00’ ’ 0 3 O 9 4 599 622 N Hornblende-pyroxene diorite to granite (Sanukitoid suite) 17 Biotite granite Hornblende tonalite to granite Biotite tonalite and tonalite gneiss Metavolcanic and mafic intrusive rocks Metasedimentary rocks, migmatites and two-mica granite Fault Road 01020 Ki lometres 11 ’ 0 4 O 8 4 Figure 1. Regional geology of the central and western Wabigoon and outlined study area. Entwine Lake Intrusion feldspar megacrystic unit are typically gradational The Entwine Lake Intrusion consists of rather than sharp. Meter-wide dykes of this unit cut four geological units. In chronological order these portions of the marginal amphibolite unit that are: 1) an early, foliated meta-monzonite/ encloses much of the intrusion producing local monzodiorite unit, 2) an amphibole-augite hornfelsic assemblages. diorite/gabbro-gabbronorite suite that has been The K-feldspar megacrystic unit (4) is the intruded by both 3) massive, and 4) K-feldspar youngest unit of the Entwine Lake intrusion. Like megacryst-bearing, pyroxene monzonite/ the other units of the monzonite/ monzodiorite suite monzodiorite. it is unlayered. It occurs as two large zones in the The foliated meta-monzonite/monzodiorite western part of the intrusion where it intrudes older unit is the first major magmatic event of the rock units. The potassium feldspar megacrysts Entwine Lake intrusion. It occupies all of the which are diagnostic of this unit, define a shallow, eastern, tail-like part of the intrusion. Petrographic east-plunging lineation (Stone, 2000), that trends data indicates that the fabric in this unit is ~330o subparallel to the metamorphic foliation in metamorphic which decreases in intensity westward unit 1. The megacrysts are a late oikocrystic phase as it approaches the massive monzonite/ of the K-feldspar megacrystic monzonite so it is monzodiorite unit (3) that forms much of the unlikely that their orientation is due to magmatic western lobe of the intrusion. The average mineral flow. A better explanation is that they formed in a foliation in these rocks strikes at 330o and dips stress field related to a post magmatic steeply to the north; adjacent to the massive metamorphism that has caused variable greenschist monzonite/monzodiorite unit the fabric has a more alteration throughout units (3) and (4). northerly orientation. In the following section, detailed features The amphibole-augite diorite/gabbro- of each of the four units of the intrusion are gabbronorite unit occurs in the northern and presented. southern areas of the western lobe of the intrusion (west of unit (1)) where it forms dominantly 1. Foliated Monzonite/Monzodiorite Unit cpx±opx bearing leucodiorite and leucogabbro- This unit forms the eastern ~20 km tail of the norite sequences respectively. In these areas this intrusion. The pervasive foliation in these rocks is unit has been incorporated as large km size blocks defined by secondary amphibole (actinolite) and and inclusions within the massive monzonite/ biotite replacing primary pyroxene and iron oxide monzodiorite (unit (3)). The presence of weakly respectively. Primary igneous feldspars have been developed magmatic layering suggests these rocks completely recrystallized and form a fine-grained are the remnants of a relatively flat lying basic sill; assemblage of untwinned plagioclase and alkali the steeply dipping orientation of the layering is feldspar; the whole rock normative feldspar evidence that this unit has been rotated, and the composition averages An14Ab56Or30. Magnetite pervasive alteration of its mafic mineralogy is and apatite are present as minor primary phases. evidence of recrystallization accompanying No sulfide phases are present in this unit. These intrusion of the later monzonite /monzodiorite rocks are geochemically indistinguishable from the rocks. Scattered metapyroxenite masses occur in unfoliated monzonite/monzodiorites and potassium the same areas as these rocks and are probably part feldspar megacryst-bearing monzonites that form of this geological unit. The diorite/ gabbro- the main mass of the western part of the intrusion; gabbronorite unit is intruded by dykes of the SiO2 =53-62 wt %, Mg#=0.37-0.41 and K2O=2-5 massive monzonite/monzodiorite unit (3) and wt %. REE trends show 115x chondrite enrichment exhibits hornfelsed assemblages where it is in in LREE’s and 6.5x chondrite in HREE’s. The contact with the K-feldspar megacrystic monzonite. REE patterns mimic the gabbroic suite, but are The massive monzonite/monzodiorite (unit slightly more enriched. (3)) is restricted to the western part of the intrusion where it underlies more than half of the area. 2. Leucodiorite - Leucogabbro Unit Dykes of the younger K-feldspar megacrystic unit PGE-Cu-Ni mineralization occurs only in intrude it. Locally along the western margin of the the rafts and inclusions of gabbro/diorite suite rocks intrusion, this unit develops mylonitic fabrics, and is not observed in any other unit. These rocks which are margin parallel and due to late local have been metamorphosed to the upper greenschist metamorphic events. Alternatively, these rocks are facies. Subdivisions of this unit are based on part of the older foliated monzonite/ monzodiorite normative An compositions. This data indicate that unit of similar composition (unit (1)). In the central leucogabbro (An52-65) forms the southern and area of this unit, contacts with the potassium leucodiorite (An40-50) the northern part of this unit. The PGE mineralized Campbell zone is hosted often with fresh cores, and rims of ubiquitous blue- within the northern leucodiorite. Weak, meter- green amphibole. Petrographic analysis of the scale layering, mafic schlieren and associated potassium feldspars suggests they are a late leucocratic patches are common; the latter two are magmatic phase as they often host inclusions of interpreted to be a result of immiscible felsic and finer-grained plagioclase, apatite, and biotite. mafic liquid phases within the magma. Primary These megacrysts commonly show an alignment at phases are plagioclase feldspar, clinopyroxene and ~330o. Whole rock normative feldspar composit- orthopyroxene, minor opaque phases, apatite and ions average An30Ab50Or20. Chemical character- biotite. The pyroxenes are normally altered to istics of this suite are SiO2=52-62 wt %, Mg#= actinolite, often rimmed by blue-green amphibole. 0.35-0.37 and high K2O concentrations ranging Primary crystallizing sulfide phases include from 2.3-4.7 wt %. REE trends show 120x chalcopyrite, pyrrhotite, minor pentlandite and chondrite enrichment in LREE’s and 8x enrichment sphalerite. Magnetite and minor ilmenite are the in HREE’s. REE patterns are similar to the foliated oxide phases. Secondary pyrite is widespread monzonite to monzodiorite trends. consistent with the metamorphism of the magmatic silicate paragenesis. Geochemically, these rocks Late Granitic Dykes
Recommended publications
  • Some Geologic and Exploration Characteristics of Porphyry Copper Deposits in a Volcanic Environment, Sonora, Mexico

    Some Geologic and Exploration Characteristics of Porphyry Copper Deposits in a Volcanic Environment, Sonora, Mexico

    Some geologic and exploration characteristics of porphyry copper deposits in a volcanic environment, Sonora, Mexico Item Type text; Thesis-Reproduction (electronic); maps Authors Solano Rico, Baltazar, 1946- 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 30/09/2021 03:12:43 Link to Item http://hdl.handle.net/10150/566651 SOME GEOLOGIC AND EXPLORATION CHARACTERISTICS OF PORPHYRY COPPER DEPOSITS IN A VOLCANIC ENVIRONMENT, SONORA, MEXICO by Baltazar Solano Rico A Thesis Submitted to the Faculty of the DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE WITH A MAJOR IN GEOLOGICAL ENGINEERING In the Graduate College THE UNIVERSITY OF ARIZONA 19 7 5 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.
  • The Commingling of Diverse Magma Types in the Fwgstaff Ltlke Igneous Complex

    The Commingling of Diverse Magma Types in the Fwgstaff Ltlke Igneous Complex

    Maine Geological Survey Studies in Maine Geology: Volume 3 1989 The Commingling of Diverse Magma Types in the Fwgstaff Ltlke Igneous Complex Roger L. Nielsen1 Emily S. Landis Vincent M . Ceci Cynthia}. Post01i2 Department ofGeo logy University of Maryland College Park, Maryland 20742 1Present address: College of Oceanography Oregon State University Corvallis, Oregon 97331 2 Present address: Building 222, Room A/21 National Bureau ofStandards Gaithersburg, Maryland 20899 ABSTRACT The Flagstaff Lake Igneous Complex is a member of an array of Acadian plutons which extend from the Katahdin batholith in the northeast to New Hampshire in the southwest. It is characterized by four major rock types: (1) gabbro, (2) granite, (3) garnet tonalite, and (4) trondhjemite. Field, petrographic, and geochemical evidence support the hypothesis that these diverse rocks existed as contemporaneous liquids, and that extensive mixing occurred at the time of emplacement. The dominant mafic mineral pairs in the gabbros are olivine-clinopyroxene, two pyroxenes, and pyroxene­ hornblende. The high Fe, low Ni and Cr contents of most of the gab bro sampled imply that it underwent substantial fractional crystallization prior to and during emplacement. The granitic rocks of the Flagstaff Lake Igneous Complex are heterogeneous, ranging from two-mica granites with equal amounts (-30%) of orthoclase, plagioclase, and quartz, to mafic diorites. These K-feldspar-bearing silicic rocks are exposed over -40% of the areal extent of the complex. Trondhjemite containing biotite, plagioclase, cordierite, and quartz, with minor muscovite and K-feldspar, is located along the margins of the intrusion, particularly in areas where the contact between the gabbro and granite intersects aluminous metapelitic wall rocks.
  • Geologic Section of the Black Range at Kingston, New Mexico

    Geologic Section of the Black Range at Kingston, New Mexico

    BULLETIN 33 Geologic Section of the Black Range at Kingston, New Mexico BY FREDERICK J. KUELLMER Structure and stratigraphy of the Black Range, detailed petrology of igneous rocks, and general guides to ore exploration 1954 STATE BUREAU OF MINES AND MINERAL RESOURCES NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY CAMPUS STATION SOCORRO, NEW MEXICO NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY E. J. Workman, President STATE BUREAU OF MINES AND MINERAL RESOURCES Eugene Callaghan, Director THE REGENTS MEMBERS EX OFFICIO The Honorable Edwin L. Mechem ..............................Governor of New Mexico Tom Wiley ................................................ Superintendent of Public Instruction APPOINTED MEMBERS Robert W. Botts .............................................................................. Albuquerque Holm O. Bursum, Jr ................................................................................ Socorro Thomas M. Cramer ...............................................................................Carlsbad Frank C. DiLuzio .............................................................................Los Alamos A. A. Kemnitz ...........................................................................................Hobbs Contents Page ABSTRACT ......................................................... …………………………………… 1 INTRODUCTION ........................................................................................................3 ACKNOWLEDGMENTS .............................................................................................4
  • Petrogenesis of Slab-Derived Trondhjemite-Tonalite-Dacite/ Adakite Magmas M

    Petrogenesis of Slab-Derived Trondhjemite-Tonalite-Dacite/ Adakite Magmas M

    Transactions of the Royal Society of Edinburgh: Earth Sciences, 87, 205-215, 1996 Petrogenesis of slab-derived trondhjemite-tonalite-dacite/ adakite magmas M. S. Drummond, M. J. Defant and P. K. Kepezhinskas ABSTRACT: The prospect of partial melting of the subducted oceanic crust to produce arc magmatism has been debated for over 30 years. Debate has centred on the physical conditions of slab melting and the lack of a definitive, unambiguous geochemical signature and petrogenetic process. Experimental partial melting data for basalt over a wide range of pressures (1-32 kbar) and temperatures (700-1150=C) have shown that melt compositions are primarily trondhjemite- tonalite-dacite (TTD). High-Al (> 15% A12O3 at the 70% SiO2 level) TTD melts are produced by high-pressure 015 kbar) partial melting of basalt, leaving a restite assemblage of garnet + clinopyroxe'ne ± hornblende. A specific Cenozoic high-Al TTD (adakite) contains lower Y, Yb and Sc and higher Sr, Sr/Y, La'/Yb and.Zr/Sm relative to other TTD types and is interpreted to represent a slab melt under garnet amphibolite to eclogite conditions. High-Al TTD with an adakite-like geochemical character is prevalent in the Archean as the result of a higher geotherm that facilitated slab melting. Cenozoic adakite localities are commonly associated with the subduction of young (<25Ma), hot oceanic crust, which may provide a slab geotherm (*9-10=C km"1) conducive for slab dehydration melting. Viable alternative or supporting tectonic effects that may enhance slab melting include highly oblique convergence and resultant high shear stresses and incipient subduction into a pristine hot mantle wedge.
  • General Disclaimer One Or More of the Following Statements May Affect

    General Disclaimer One Or More of the Following Statements May Affect

    General Disclaimer One or more of the Following Statements may affect this Document This document has been reproduced from the best copy furnished by the organizational source. It is being released in the interest of making available as much information as possible. This document may contain data, which exceeds the sheet parameters. It was furnished in this condition by the organizational source and is the best copy available. This document may contain tone-on-tone or color graphs, charts and/or pictures, which have been reproduced in black and white. This document is paginated as submitted by the original source. Portions of this document are not fully legible due to the historical nature of some of the material. However, it is the best reproduction available from the original submission. Produced by the NASA Center for Aerospace Information (CASI) 4f Final Report X85-1. 4025 THE SOUTH-CENTRAL UNITED STATES MAGNETIC ANOMALY (Ld5- I 25 NASA -Lb-174048) 1tB NtfS-1143d ,oulki- l-GN'1nAA. uN11BU 5'1bfE j MAGNbTIC ANCCALY F11141 neirOLt it? UL l.UU U11A.V tb p HL &O5IlMF AU 1 LSLI. UtiG uaclas G3/43 UOC25 Prepared by Pa'.rick J. Starich Geophysics Section Oepartment of Geosciences Purdue University West Lafayette, IN 47907 for the National Aeronautics & Space Administration Greenbelt, MD 20771 Grant No. NAG-5-231. Original Photo ^*a t from EROS Data may h9 PurC;,,. Sioux Fella Oanter S11 ___ 67198 Principal Investigators William J. Hin7e and Lawrence W. Braile Department of Geosciences Purdue University West Lafayette, IN 47907 June, 1984 _,j THE SOUTH—CENTRAL UNITED STATES MAGNETIC ANOMALY A Thesis Submitted to the Faculty of Purdue University by s ;^ Patrick James Starich In Partial Fulfillment of the Requirements for the Degree i of 'i Master of Science August 1984 rf rA~ > ii ACKNOWLEDGEMENTS I would like to express my admiration and gratif.,ude to Dr.
  • Oregon Geologic Digital Compilation Rules for Lithology Merge Information Entry

    Oregon Geologic Digital Compilation Rules for Lithology Merge Information Entry

    State of Oregon Department of Geology and Mineral Industries Vicki S. McConnell, State Geologist OREGON GEOLOGIC DIGITAL COMPILATION RULES FOR LITHOLOGY MERGE INFORMATION ENTRY G E O L O G Y F A N O D T N M I E N M E T R R A A L P I E N D D U N S O T G R E I R E S O 1937 2006 Revisions: Feburary 2, 2005 January 1, 2006 NOTICE The Oregon Department of Geology and Mineral Industries is publishing this paper because the infor- mation furthers the mission of the Department. To facilitate timely distribution of the information, this report is published as received from the authors and has not been edited to our usual standards. Oregon Department of Geology and Mineral Industries Oregon Geologic Digital Compilation Published in conformance with ORS 516.030 For copies of this publication or other information about Oregon’s geology and natural resources, contact: Nature of the Northwest Information Center 800 NE Oregon Street #5 Portland, Oregon 97232 (971) 673-1555 http://www.naturenw.org Oregon Department of Geology and Mineral Industries - Oregon Geologic Digital Compilation i RULES FOR LITHOLOGY MERGE INFORMATION ENTRY The lithology merge unit contains 5 parts, separated by periods: Major characteristic.Lithology.Layering.Crystals/Grains.Engineering Lithology Merge Unit label (Lith_Mrg_U field in GIS polygon file): major_characteristic.LITHOLOGY.Layering.Crystals/Grains.Engineering major characteristic - lower case, places the unit into a general category .LITHOLOGY - in upper case, generally the compositional/common chemical lithologic name(s)
  • 34. the K-Replacement Origin of the Megacrystal Lower Caribou Creek Granodiorite and the Goat Canyon-Halifax Creeks Quartz Monzo

    34. the K-Replacement Origin of the Megacrystal Lower Caribou Creek Granodiorite and the Goat Canyon-Halifax Creeks Quartz Monzo

    1 ISSN 1526-5757 34. The K-replacement origin of the megacrystal Lower Caribou Creek granodiorite and the Goat Canyon-Halifax Creeks quartz monzonite --- modifications of a former tonalite and diorite stock, British Columbia, Canada Lorence G. Collins email: [email protected] February 8, 1999 Introduction About 25 km south of Nakusp and 1 km east of Burton, British Columbia, Canada, is a stock whose western half is the Lower Caribou Creek megacrystal granodiorite and whose eastern half is the Goat Canyon-Halifax Creeks fine- grained quartz monzonite (Fig. 1); Hyndman, 1968). Biotite-hornblende tonalite and diorite are additional facies that occur along the border of the stock. Zoned plagioclase in all these rocks indicates a shallow intrusion and relatively rapid crystallization. This stock was called to my attention by Donald Hyndman because the K-feldspar megacrysts in the granodiorite appeared to be orthoclase whereas the smaller K-feldspar crystals in the fine-grained quartz monzonite were microcline. Subsequently, he loaned me 19 thin sections from his Ph.D thesis study (Hyndman, 1968), and these sections provided a broad representation of the textural and compositional variations in both rock types. Because he indicated that the two granitic facies were gradational to each other, this stock offered an opportunity to study the field and textural relationships across the transitions between the rocks having the two kinds of K-feldspar. Following his loan of thin sections, I visited the area and obtained 44 additional samples (and thin sections) across transitions between the two rock types. Examinations of field relationships and both his and my thin sections provide the basis for the conclusions presented in this article.
  • Precambrian Geology of the Elk Mountain-Spring Mountain Area

    Precambrian Geology of the Elk Mountain-Spring Mountain Area

    Precambrian Geology of the Elk Mountain - Spring Mountain Area, San Miguel County, New Mexico by Ingrid Klich, Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geology New Mexico Institute of Miningand Technology Socorro, New Mexico February, 1983 i ABSTRACT Precambrian rocks of the Elk Mountain - Spring Mountain area, San Miguel County, New Mexico consist primarily of a bimodal (mafic-felsic) metavolcanic assemblage, plus locally abundant metasedimentary rocks (predominantly of volcanic provenance, plus ironstone, shales, and limestone) , and a complex of intrusives including meta- diabase and gabbro, tonal.f.te , granite , syenite and pegmatites. The metavolcanic suite is largely comprised of subaqueous basalts (with well-preserved pillow-structures), plus lesser amounts of felsic volcanic and volcaniclastic rocks ranging from rhyolites to dacites. The supracrustal succession has been subjected to at least two periodsof tight to isoclinal.folding, accompanied byintense tectonic transposition such that present orientations of 1ithol.ogic units no longer represent their original stratigraphy. Thus, delineation of a stratigraphic section for the supracrustal rocks within the study area is not yet possible. Rocks of the supracrustal succession have been variably metamorphosed to lower amphibolite facies with slight retrograde metamorphism to greenschist facies. Chemical analyses verify the compositional bimodality of the supracrustal assemblage. The mafic rocks are characterizedmainly as subaJ.kaline, low-K tholeiites, ii whereas the felsic rocks appear to be both tholeiitic and calc-al.kaline.Tectonic discrimination diagrams suggest formation of: these rocks at an island arc - destructive plate boundary. The submarine environment, bimodal volcanic suite, and relationship to associated sedimentary rocks are all compatible with deposition ina marginal.
  • Geology and Alteration at Northparkes Mines, NSW, Australia

    Geology and Alteration at Northparkes Mines, NSW, Australia

    The Anatomy of an Alkalic Porphyry Cu-Au System: Geology and Alteration at Northparkes Mines, NSW, Australia Adam Pacey1,2,*, Jamie J. Wilkinson2,1, Jeneta Owens3, Darren Priest3, David R. Cooke4,5 and Ian L. Millar6 1Department of Earth Science and Engineering, Imperial College London, South Kensington, London, SW7 2AZ, United Kingdom 2Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom 3NorthparKes Mines, PO Box 995, ParKes, New South Wales, 2870, Australia 4Centre for Ore Deposit and Earth Sciences (CODES), University of Tasmania, Hobart, Tasmania 7001, Australia 5Transforming the Mining Value Chain (TMVC), an Australia Research Council (ARC) Industrial Transformation Research Hub, University of Tasmania, Hobart, Tasmania 7001, Australia 6NERC Isotope Geosciences Laboratory, Keyworth, Nottingham, NG12 5GG, United Kingdom *Corresponding author: [email protected] Keywords Northparkes, Macquarie Arc, porphyry deposit, propylitic alteration, potassic alteration, hydrothermal alteration, copper, gold Abstract The Late Ordovician-Early Silurian (~455-435 Ma) Northparkes system is a group of silica-saturated, alkalic porphyry deposits and prospects which developed within the Macquarie Island Arc. The system is host to a spectacular and diverse range of rocks and alteration-mineralization textures that facilitate a detailed understanding of its evolution, in particular into the nature and controls of porphyry-related propylitic alteration. The first intrusive phase at Northparkes is a pre- to early-mineralization pluton that underlies all the deposits and varies in composition from a biotite quartz monzonite (BQM) to alkali feldspar granite (AFG). Prior to total crystallization, this pluton was intruded by a more primitive quartz monzonite (QMZ) that marks the onset of a fertile fractionation series.
  • Magma Traps and Driving Pressure: Consequences for Pluton Shape and Emplacement in an Extensional Regime

    Magma Traps and Driving Pressure: Consequences for Pluton Shape and Emplacement in an Extensional Regime

    Missouri University of Science and Technology Scholars' Mine Geosciences and Geological and Petroleum Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works Engineering 01 Sep 1998 Magma Traps and Driving Pressure: Consequences for Pluton Shape and Emplacement in an Extensional Regime John Patrick Hogan Missouri University of Science and Technology, [email protected] Jonathan D. Price M. Charles Gilbert Follow this and additional works at: https://scholarsmine.mst.edu/geosci_geo_peteng_facwork Part of the Geology Commons, and the Petroleum Engineering Commons Recommended Citation J. P. Hogan et al., "Magma Traps and Driving Pressure: Consequences for Pluton Shape and Emplacement in an Extensional Regime," Journal of Structural Geology, vol. 20, no. 9-10, pp. 1155-1168, Elsevier, Sep 1998. The definitive version is available at https://doi.org/10.1016/S0191-8141(98)00063-7 This Article - Journal is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. Journal of Structural Geology, Vol. 20, No. 9/10, pp. 1155 to 1168, 1998 # 1998 Elsevier Science Ltd. All rights reserved PII: S0191-8141(98)00063-7 0191-8141/98/$ - see front matter Magma traps and driving pressure: consequences for pluton shape and emplacement in an extensional regime JOHN P. HOGAN*, JONATHAN D. PRICE and M. CHARLES GILBERT University of Oklahoma, School of Geology and Geophysics, Sarkey's Energy Center, Rm 810, Norman, OK, 73019-0628, U.S.A.
  • RESEARCH a Non–Plate Tectonic

    RESEARCH a Non–Plate Tectonic

    RESEARCH A non–plate tectonic model for the Eoarchean Isua supracrustal belt A. Alexander G. Webb1,*, Thomas Müller2, Jiawei Zuo1, Peter J. Haproff3, and Anthony Ramírez-Salazar2 1DEPARTMENT OF EARTH SCIENCES AND LABORATORY FOR SPACE RESEARCH, UNIVERSITY OF HONG KONG, POKFULAM ROAD, HONG KONG, CHINA 2SCHOOL OF EARTH AND ENVIRONMENT, UNIVERSITY OF LEEDS, MATHS/EARTH AND ENVIRONMENT BUILDING, LEEDS LS2 9JT, UK 3DEPARTMENT OF EARTH AND OCEAN SCIENCES, UNIVERSITY OF NORTH CAROLINA, WILMINGTON, NORTH CAROLINA 28403, USA ABSTRACT The ca. 3.8–3.6-b.y.-old Isua supracrustal belt of SW Greenland is Earth’s only site older than 3.2 Ga that is exclusively interpreted via plate- tectonic theory. The belt is divided into ca. 3.8 Ga and ca. 3.7 Ga halves, and these are interpreted as plate fragments that collided by ca. 3.6 Ga. However, such models are based on idiosyncratic interpretations of field observations and U-Pb zircon data, resulting in intricate, conflicting stratigraphic and structural interpretations. We reanalyzed published geochronological work and associated field constraints previously interpreted to show multiple plate-tectonic events and conducted field-based exploration of metamorphic and structural gra- dients previously interpreted to show heterogeneities recording plate-tectonic processes. Simpler interpretations are viable, i.e., the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ca. 3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. Integrating these findings, we present a new model in which two cycles of volcanic burial and resultant melt- ing and tonalite-trondhjemite-granodiorite (TTG) intrusion produced first the ca.
  • Epidote in Calc-Alkaline Magmas: an Experimental Study of Stability, Phase Relationships, and the Role of Epidote in Magmatic Evolution

    Epidote in Calc-Alkaline Magmas: an Experimental Study of Stability, Phase Relationships, and the Role of Epidote in Magmatic Evolution

    American Mineralogist, Volume 81, pages 462-474, 1996 Epidote in calc-alkaline magmas: An experimental study of stability, phase relationships, and the role of epidote in magmatic evolution MAX W. SCHMIDT1,2 ANDALAN B. THOMPSON3 'Departement Geologie, Universite Blaise Pascal, CNRS-URAIO, 5 rue Kessler, 63038 Clermont-Ferrand, France 2Bayerisches Geoinstitut, Universitat Bayreuth, D-95440 Bayreuth, Germany 3lnstitut flir Mineralogie and Petrographie, Sonneggstrasse 5, Eidgenossische Technische Hochschule, CH-8092 Zurich, Switzerland ABSTRACT Experiments on tonalite and granodiorite were performed at conditions ranging from 2.1 to 18 kbar and 550 to 850°C to establish the magmatic stability field of epidote as a function of P, T, and f02. At water-saturated conditions and f02 buffered by NNO, epidote has a wide magmatic stability field in tonalite. At 13 kbar, this field extends from the wet solidus at 630 to 790 0c. The low-pressure intersection of the magmatic epidote crystallization reaction and the H20-saturated tonalite solidus, and hence the minimum pressure for magmatic epidote, occurs at about 5 kbar. The Clapeyron slopes of epidote melting reactions are moderately positive in P-T space at pressures below the intersection of the epidote melting and the gamet-in reactions at 13 kbar, 790°C. At this intersection, epidote reaches its maximal thermal stability (790°C) in tonalite-H20. In the presence of garnet, that is above 14 kbar, epidote melting reactions have steep negative Clapeyron slopes in P-T space. At P-T conditions near the low-pressure intersection of the epidote melting reaction with the water-saturated solidus, experiments were also performed with f02 buffered by HM.