ANALYSIS AND CORRELATION OF VOLCANIC ASH IN MARINE SEDIMENTS FROM THE PERU MARGIN, OCEAN DRILLING PROGRAM LEG 201: EXPLOSIVE VOLCANIC CYCLES OF THE NORTH-CENTRAL ANDES A Thesis by SHIRLEY DAWN HART Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 2006 Major Subject: Geology ANALYSIS AND CORRELATION OF VOLCANIC ASH IN MARINE SEDIMENTS FROM THE PERU MARGIN, OCEAN DRILLING PROGRAM LEG 201: EXPLOSIVE VOLCANIC CYCLES OF THE NORTH-CENTRAL ANDES A Thesis by SHIRLEY DAWN HART Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved by: Co-Chairs of Committee, D. Jay Miller Renald Guillemette Committee Member, Will Sager Head of Department, Richard Carlson December 2006 Major Subject: Geology iii ABSTRACT Analysis and Correlation of Volcanic Ash in Marine Sediments from the Peru Margin, Ocean Drilling Program Leg 201: Explosive Volcanic Cycles of the North-Central Andes. (December 2006) Shirley Dawn Hart, B.S., Texas A&M University Co-Chairs of Advisory Committee: Dr. D. Jay Miller Dr. Renald Guillemette A detailed investigation of cores from three Peru Margin sites drilled during Ocean Drilling Program (ODP) Leg 201 has been conducted to determine the occurrence of volcanic ash layers and ash accumulations within marine sediments along the Peru shelf. These sites were previously occupied during ODP Leg 112, which suffered from poor and/or disturbed recovery. Advancements in hydraulic piston coring realized since and employed during ODP Leg 201 resulted in better core recovery and less disturbance of sediment throughout the cored intervals. Since marine sediments potentially undergo less erosion and Leg 201 cores benefited from improved recovery, the tephrachronologic record from Leg 201 has yielded a more complete record of explosive activity for North- Central Andean volcanism than previous studies. The improved recovery of Leg 201 cores has enabled the detailed examination of cores from the above sites needed to test the hypothesis that volcanic ash layers and accumulations are more abundant in the study region than previously reported. Due to iv the low recovery of Leg 112 cores, Pouclet et al. (1993) document only six-ash layers, one ash pod, and eight ash-bearing layers (for a total of 14 cm of ash) from the three sites (Sites 684, 680, and 681) that were reoccupied during Leg 201 (Sites 1227, 1228, and 1229 respectively). This study reports a total of 332.0 cm of ash deposited into the study region which is approximately 24 times that previously reported. Explosive eruption cycles for the Andean region have been deduced from the documentation of Leg 201 ash layers. Our record of volcanic cycles indicates that explosive activity was less intense during the Miocene, in which one ash layer (1.3 cm) was deposited, compared to that of the Pliocene and Pleistocene which experienced most of the explosive volcanic activity in which 52 ash layers (total thickness equal to 208.6 cm) and 14 ash layers (total thickness equal to 122.1 cm) were deposited respectively (Fig. 14). These data are consistent with the previous study of Pouclet et al. (1990); however these data indicate that explosive activity during the Pliocene and Pleistocene was more intense than previously reported. v ACKNOWLEDGMENTS This research used samples and/or data provided by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for this research was provided by a grant awarded to D.J. Miller from the United States Science Support Program (USSSP) (http://www.usssp.iodp.org). I am grateful to Ray Guillemette for his time in running the microprobe and detailed discussions about microprobe analysis of volcanic glass samples. vi TABLE OF CONTENTS Page INTRODUCTION............................................................................................................... 1 GEOLOGIC SETTING....................................................................................................... 9 PREVIOUS WORK .......................................................................................................... 13 Marine Studies ...................................................................................................... 13 Land Studies.......................................................................................................... 16 METHODS........................................................................................................................ 21 RESULTS.......................................................................................................................... 25 Ash Layer Description ......................................................................................... 30 Site 1227 Ash Layers ............................................................................... 30 Site 1228 Ash Layers ................................................................................ 32 Site 1229 Ash Layers ................................................................................ 39 Glass Geochemistry of Type 1 Ash Layers........................................................... 40 Whole Rock Geochemical Analysis...................................................................... 47 Major Element Oxides .............................................................................. 47 Rare Earth Elements.................................................................................. 58 Ash Layer Correlations ......................................................................................... 62 Explosive Volcanic Cycles.................................................................................... 63 DISCUSSION AND CONCLUSIONS............................................................................. 69 REFERENCES.................................................................................................................. 75 APPENDIX A ................................................................................................................... 80 APPENDIX B ................................................................................................................... 82 VITA ............................................................................................................................... 84 vii LIST OF TABLES TABLE Page 1 Leg 201 and Leg 112 recovery comparison ...................................................... 4 2 Leg 201 volcanic ash locations reported in the Initial Reports Summary ............................................................................ 7 3 Leg 201 ash layer description.......................................................................... 26 4 Type 2 through Type 4 ash table..................................................................... 33 5 Average glass analyses.................................................................................... 44 6 Whole rock (bulk aliquot) geochemical analyses of Leg 201 Type 1 ash layers ........................................................................ 48 7 Amount of volcanic ash.................................................................................. 73 8 Leg 201 ash sample location .......................................................................... 81 viii LIST OF FIGURES FIGURE Page 1 Site map....................................................................................................... 3 2 An example of the magnetic susceptibility record from Leg 201 Site 1228 ................................................................... 5 3 Prominent features of the Andes ............................................................... 10 4 Prominent ocean and wind currents of South America........................................................................................... 12 5 Representative Type 1 ash......................................................................... 31 6 Stratigraphic sections for Leg 201 sites .................................................... 38 7 TAS and K2O vs. SiO2 plots, glass analyses ............................................. 42 8 TAS and K2O vs. SiO2 plots for average glass values................................................................................................ 43 9 Bivariant plot for major element oxides, average glass values............................................................................................... 46 10 Whole Rock TAS and K2O vs. SiO2 Plots ................................................ 54 11 Whole Rock major element oxide Plots.................................................... 57 12 REE geochemical zones for Leg 201 and the three volcanic zones of the Andes...................................................................... 60 13 Ash layer correlations................................................................................ 64 14 Leg 201 ash layer thickness and number of ash layers plotted per half million year time period.................................. 67 15 Leg 112 sedimentation rate curves............................................................ 83 1 INTRODUCTION Volcanic material commonly occurs in marine sediment as discrete ash-fall-out layers and/or disseminated ash accumulation within sediment deposits. Ash layers are