Crustal Magmatic System Evolution

Anatomy, Architecture, and Physico-Chemical Processes

Matteo Masotta, Christoph Beier, Silvio Mollo, Matteo Masotta, Christoph Beier, Silvio Mollo

• Publisher: American Geophysical Union
• Year: 2021
• ISBN:
  9781119564461
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

A comprehensive picture of the architecture of crustal magmatic systems

The composition of igneous rocks–theirminerals, melts, and fluids–revealsthe physical andchemical conditions under which magmasform, evolve, interact, andmovefrom the Earth's mantle through thecrust.Thesemagmadynamicsaffectprocesses on the surface includingcrustalgrowthanderuptive behaviour of volcanoes.

Crustal Magmatic System Evolution: Anatomy, Architecture, and Physico-Chemical Processes usesanalytical, experimental, and numericalapproaches toexplorethe diversityof crustal processes from magma differentiationand assimilationto eruptionatthe surface.

Volume highlights include:

• Physical and chemical parameterization of crustal magmatic systems
• Experimental, theoretical and modelling approachestargeting crustalmagmatic processes
• Timescales ofcrustalmagmatic processes, including storage, recharge, and ascent through volcanic conduits

The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity.?Its publicationsdisseminate scientific knowledge and provide resources for researchers, students, and professionals. Find out more about this book in a Q&A with the Editors.

Part I
Architecture of Crustal Magmatic Systems

1
Geothermobarometry of Mafic and Ultramafic Xenoliths: Examples From Hualalai and Mauna Kea Volcanoes, Hawaii

Luca Ziberna

Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy

ABSTRACT

Xenoliths of plutonic rocks sporadically torn off by erupting magmas are known to carry valuable information about volcano plumbing systems and the lithosphere in which they are emplaced. One of the main steps in the interpretation of such information is to quantify the pressure and temperature conditions at which the xenolith mineral assemblages last equilibrated. This chapter discusses some aspects of geothermobarometry of mafic and ultramafic rocks using the xenolith populations of the Hualalai and Mauna Kea volcanoes, Hawaii, as case studies. Multiple‐reaction geobarometry, recently revisited for olivine + clinopyroxene + plagioclase ± spinel assemblages, provides the most precise pressure estimates (uncertainties as low as 1.0 kbar). An example is shown that integrates these estimates with the calculated seismic velocities of the xenoliths and the available data from seismic tomography. The results make it possible to better constrain some kilometer‐scale horizontal and vertical heterogeneities in the magmatic system beneath Hawaii. Ultramafic xenoliths at Hualalai are the residuals of magma crystallization at 16–21 km depth, below the pre‐Hawaiian oceanic crust. The few available gabbronorites and diorites record instead lower pressures and likely represent conduits or small magma reservoirs crystallized at 0–8 km depth. At Mauna Kea, on the other hand, a significant portion of the xenolith record is composed of olivine‐gabbros, which crystallized almost over the entire crustal thickness (3–18 km). Ultramafic xenoliths are less abundant and might represent the bottom of the same magma reservoirs that crystallized in the deeper portion of the magmatic systems (11–18 km). Some unresolved issues remain in the geothermometry of mafic and ultramafic rocks representing portions of magma reservoirs that cooled and recrystallized under subsolidus conditions. This suggests that further experimental and theoretical work is needed to better constrain the thermodynamics and kinetics of peridotitic and basaltic systems at low (<1000°C) temperatures.

1.1. INTRODUCTION

The geothermobarometry of magmatic rocks is well known to be one of the key tools used to interpret the processes within volcanic systems. This is why much effort has been put in since the first pioneering studies in petrology (e.g., Bowen, 1928; Green & Ringwood, 1967; Tuttle & Bowen, 1958; Wells, 1977) to perform experimental and theoretical work constraining the relationships between the mineralogy and chemistry of magmatic rocks and the temperatures and pressures at which their constituent phases formed. It was clear since then that the complexity of volcanic processes and the compositional variability of the erupted magmas and their lithic fragments make it difficult to develop geothermobarometers that are both accurate and precise for any sample, but considerable progress has been made in the last three decades. Considering only published work on magmatic systems relevant for crustal processes, more than 6,000 phase equilibrium laboratory experiments have been performed so far (based on the LEPR database at http://lepr.ofm‐research.org and additional literature). These experiments led to the development of geothermobarometers and forward thermodynamic simulations (e.g., Ghiorso & Sack, 1995; Gualda et al., 2012; Jennings & Holland, 2015; Masotta et al., 2013; Mollo et al., 2018; Putirka, 2008, 2016; Ziberna et al., 2017) that can now be used to model the differentiation paths of magmas.

The most common inverse‐modeling approach to estimating the pressure (P) and temperature (T) of volcanic systems is geothermobarometry based on mineral‐liquid equilibria (see Putirka, 2008, for an exhaustive discussion). It is usually applied to porphyric lava samples, using whole‐rock chemical analyses (as representative of liquid compositions) in combination with the chemistry of phenocrysts. As a rule, measured partition coefficients [e.g., K_D(Fe‐Mg)^{mineral‐liquid}] is compared to experimental values to demonstrate equilibrium (e.g., Putirka, 2008). For basaltic to andesitic and trachytic rocks, clinopyroxene‐liquid geothermometry and geobarometry proved to be the most precise methods when tested against experimental data, producing model errors as small as 28 °C and 1.4 kbar (Masotta et al., 2013; Neave & Putirka, 2017; Putirka, 2008). The success of such methods lies in the large entropy and volume change of the reactions used as geothermometers and geobarometers, respectively (Putirka, 2008), and in the ubiquity of clinopyroxene in many basaltic systems. Other common methods are plagioclase‐liquid geothermometry (e.g., Lange et al., 2009; Putirka, 2008), amphibole‐liquid geothermometry and geobarometry (Molina et al., 2015; Putirka, 2016), and mineral‐mineral equilibria like two‐pyroxene geothermometers and geobarometers (e.g., Lindsley, 198...

Table of contents

• Cover
• Table of Contents
• Series Page
• Title Page
• Copyright Page
• LIST OF CONTRIBUTORS
• PREFACE
• Part I: Architecture of Crustal Magmatic Systems
• Part II: Experimental and Numerical Constraints on Magmatic Processes
• Part III: Timescales of Magma Dynamics
• Index
• End User License Agreement