Volcanic Rocks from Central Italy: An Oxygen Isotopic Microanalytical and Geochemical Study Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultäten der Georg-August-Universität zu Göttingen vorgelegt von Peter Barnekow aus Bremen Göttingen 2000 D 7 Referent: Prof. Dr. J. Hoefs Korreferent: Prof. Dr. S.F. Foley Tag der mündlichen Prüfung: 30. Oktober 2000 Table of Contents Table of Contents ,QWURGXFWLRQ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 1.1 General Charakteristics of the Tertiary to Quarternary Italian Magmatic Rocks .........1 1.2 Magmatic Provinces in Italy.........................................................................................2 1.3 Overview of the Different Genetic Models ..................................................................3 1.4 Investigated Area and Petrogenetic Subdivision ..........................................................6 1.5 Oxygen Isotopes ...........................................................................................................7 6DPSOH'HVFULSWLRQ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 2.1 Sampling.......................................................................................................................9 2.2 Geological and Petrographical Description of the Samples .......................................10 2.2.1 Monti Vulsini – Roman Province Type Rocks...........................................................10 2.2.2 Orciatico and Montecatini Val di Cecina – Lamproites .............................................11 2.2.3 Roccastrada – Rhyolites..............................................................................................12 2.2.4 San Vincenzo – Rhyolites...........................................................................................12 2.2.5 Torre Alfina – Transitional Rocks Between Tuscan and Roman Mantle Melts.........12 2.2.6 Radicofani – Transitional Rocks Between Tuscan and Roman Mantle Melts ...........13 2.2.7 Monte Amiata – Hybrid Rocks Between Mantle and Crustal Melts ..........................13 2.3 Classification of the Investigated Rocks.....................................................................14 $QDO\WLFDO0HWKRGV BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 3.1 Sample Preparation.....................................................................................................17 3.2 Bulk Rock Analysis ....................................................................................................17 3.2.1 X-Ray Fluorescence Analysis (XFA) .........................................................................17 3.2.2 C and S Analysis by Infrared Absorption Spectroscopy.............................................17 3.2.3 H2O Analysis by the Method of Karl Fischer.............................................................17 3.2.4 FeO Analysis...............................................................................................................18 3.2.5 Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) ....................................18 3.3 Analysis of Mineral Chemistry...................................................................................18 3.3.1 Electron Microprobe Analysis (EMPA) .....................................................................18 3.3.2 Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) ..19 3.4 Oxygen Isotope Analysis by UV Laser Ablation System ...........................................19 3.4.1 Introduction.................................................................................................................19 3.4.2 Sample Pretreatment...................................................................................................20 I Table of Contents 3.4.3 Instrumentation ...........................................................................................................22 3.4.4 Conversion of Oxygen to CO2 ....................................................................................23 3.4.5 Direct Measurement of Oxygen Without Conversion ................................................24 3.4.6 Accuracy of the Oxygen Isotope Measurements ........................................................24 3.5 Oxygen Isotope Analyses by CO2 Laser Ablation System .........................................24 3.6 Comparison of the Different Methods for Oxygen Isotope Ratio Measurement........25 5HVXOWVBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 4.1 Mantle Derived Rocks ................................................................................................28 4.1.1 Introduction.................................................................................................................28 4.1.2 Whole Rock Chemistry...............................................................................................29 4.1.3 Mineral Chemistry......................................................................................................33 4.1.3.1 Olivines.......................................................................................................................34 4.1.3.2 Clinopyroxenes ...........................................................................................................36 4.1.3.3 Orthopyroxenes...........................................................................................................42 4.1.3.4 Alkali Feldspars..........................................................................................................43 4.1.3.5 Plagioclases.................................................................................................................43 4.1.3.6 Leucites.......................................................................................................................44 4.1.3.7 Micas...........................................................................................................................44 4.1.3.8 Oxides.........................................................................................................................46 4.1.3.9 Apatites.......................................................................................................................46 4.1.4 Oxygen Isotopes..........................................................................................................47 4.2 Crustal Derived Rocks................................................................................................50 4.2.1 Introduction.................................................................................................................50 4.2.2 Whole Rock Chemistry...............................................................................................50 4.2.3 Mineral Chemistry......................................................................................................52 4.2.3.1 Plagioclases.................................................................................................................52 4.2.3.2 Sanidines.....................................................................................................................53 4.2.3.3 Biotites........................................................................................................................53 4.2.3.4 Cordierites...................................................................................................................54 4.2.3.5 Ilmenites .....................................................................................................................54 4.2.3.6 Apatites.......................................................................................................................54 4.2.4 Oxygen Isotopes..........................................................................................................54 4.3 Hybrid Rocks Between Mantle and Crustal Melts .....................................................57 4.3.1 Introduction.................................................................................................................57 4.3.2 Whole Rock Chemistry...............................................................................................57 4.3.3 Mineral Chemistry......................................................................................................58 II Table of Contents 4.3.3.1 Clinopyroxenes ...........................................................................................................59 4.3.3.2 Orthopyroxenes...........................................................................................................61 4.3.3.3 Plagioclases.................................................................................................................61 4.3.3.4 Sanidines.....................................................................................................................61 4.3.3.5 Micas...........................................................................................................................62 4.3.3.6 Oxides.........................................................................................................................62 4.3.3.7 Apatites.......................................................................................................................62 4.3.4 Oxygen Isotopes..........................................................................................................63 'LVFXVVLRQ BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 5.1 Tectonic Setting..........................................................................................................65