UNLV Retrospective Theses & Dissertations 1-1-2000 Petrogenetic study of the Porcupine Lake mafic intrusive complex, Trinity terrane, northern California Edward Robert Muller University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Muller, Edward Robert, "Petrogenetic study of the Porcupine Lake mafic intrusive complex, Trinity terrane, northern California" (2000). UNLV Retrospective Theses & Dissertations. 1171. http://dx.doi.org/10.25669/tnq4-ppc2 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. 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Further reproduction prohibited without permission. PETROGENETIC STUDY OF THE PORCUPINE LAKE MAFIC INTRUSIVE COMPLEX. TRINITY TERRANE, NORTHERN CALIFORNIA by Edward R. M uller Bachelor o f Science Sonoma State University 1997 A thesis submitted in partial fulfillment of the requirements for the Master of Science Degree Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas August 2000 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 1401767 UMI UMI Microform 1401767 Copyright 2001 by Bell & Howell Information and Leaming Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Leaming Company 300 North Zeeb Road P.O. Box 1346 Ann Artx)r, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Çi 2000 Edward R. Muller AU Rights Reserved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thesis Approval The Graduate College University of Nevada, Las Vegas April 21, ■ 20 00 The Thesis prepared bv Edward R. Muller Entitled Pecrogenetic Study of the Porcupine Lake Mafic Intrusive Complex, Trinity Terrane, Northern California is approved in partial fulfillment of the requirements for the degree of _______ Master of Science Exaalvmtionaymiation Committee Ciuiir Dean o f the Graduate College ExA/rfniatwn Committee \/em ber Examination CornmitUc Member Graduate College Faculty Representative pR/icir.?5/i-oü U Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Petrogenetic Study of the Porcupine Lake Mafic Intrusive Complex, Trinit) Terrane, Northern California By Edward R. Muller Dr. Rodney V. Metcalf, Examination Committee Chair Professor of Geoscience University of Nevada, Las Vegas The Early Devonian (404 ± 3 Ma) Porcupine Lake mafic intrusive complex of the Trinity terrane consists primarily of ultramafic-mafic plutonic and dike lithologies. The plutonic rock forms steep intrusive contacts with adjacent Ordovician peridotite, and consists of basal layered peridotite, cumulate clinopyroxenite, and isotropic gabbro. East-west trending mafic-to-felsic aphanitic dikes intrude the plutonic rocks, with high dike concentrations (>80%) in the southern portion of the complex. Gabbro and mafic dikes display subduction-related enrichment of light-ion lithophile elements and high degrees of depletion of high-field strength elements (Nb, Ta = 0.1 NMORB). Trace element mixing models indicate gabbro and mafic dikes are derived from a residual mantle source with enrichment by small amounts of slab-derived aqueous fluids and pelagic sediments. Mafic dikes are also enriched by fertile MORB (asthenospheric) mantle. Subduction zone enrichment of a depleted mantle source suggests the Porcupine Lake mafic intrusive complex formed in a forearc tectonic setting. Ill Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT...........................................................................................................................üi LIST OF FIGURES.............................................................................................................. vii ACKNOWLEDEMENTS...................................................................................................viii CHAPTER I INTRODUCTION...........................................................................................I CHAPTER 2 REGIONAL GEOLOGY.............................................................................. 3 The Eastern Klamath Mountains ..................................................................................... 3 Central Metamorphic terrane .....................................................................................3 Yreka terrane ................................................................................................................4 Eastern Klamath terrane ............................................................................................. 5 The Trinity Terrane ........................................................................................................... 6 Neoproterozoic tectonite assemblage ...................................................................... 6 Mantle assemblage ...................................................................................................... 6 Mafic intrusive complexes ......................................................................................... 7 Pillow basalts ............................................................................................................... 8 CHAPTER 3 METHODS.................................................................................................... 12 Mapping and Sample Collection .....................................................................................12 Petrography .........................................................................................................................12 Geochemistry ..................................................................................................................... 13 Greenschist Facies Metamorphism .................................................................................15 CHAPTER 4 FIELD RELATIONSHIPS..........................................................................16 Introduction ........................................................................................................................ 16 Map Units and Rock Lithologies ....................................................................................17 Host Rock Unit: Ordovician Peridotite (Odp) .......................................................17 Intrusive Pyroxenite Unit: Pyroxenite (pxi) ...........................................................17 Gabbroic Pluton Units: ............................................................................................. 18 Layered Peridotite (pdl) ...................................................................................... 18 Clinopyroxenite (px) ............................................................................................19 Gabbro (Dg) ......................................................................................................... 20 Clinopyroxenite/gabbro (px/g) ..........................................................................22 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Late State Dike Units ..................................................................................................22