Rollinson H.R. Using Geochemical Data: Evaluation, Presentation, Interpretation

London: Longman, 1993. — 352 p. — ISBN: 0-582-06701-4.The principal emphasis in this book is on ‘whole-rock’ chemistry; the equally large area of mineral chemistry has only been touched upon tangentially. Furthermore, it has not been possible to cover some of the more novel and esoteric techniques currently being applied to geochemical investigations. This text was conceived as a work to be put into the hands of a graduate student embarking upon a geochemical project. As it has evolved, however, it has become apparent that it serves many more purposes. It may, for example, be used as a text in final-year and graduate-student geochemistry courses. It will be useful to the professional geochemist who has worked chiefly in one sub-discipline of the subject and needs to look more broadly at a problem. It will also be of use to the non-geochemist, whether working in academia, industry or a geological survey, who has access to geochemical data and needs to interpret them. This book has, therefore, two main goals. The first is to put into the hands of a non-expert, who needs to make use of geochemical data, a summary of the methods and techniques currently used in geochemistry, and yet a text which will enable the user to obtain something of geological significance from the data. The second goal is to put within one cover the disparate techniques and methodologies currently in use by geochemists. Thus this text may be read at two levels. Firstly, it may be read by a geochemist who wishes to evaluate and interpret the data. Secondly, it may be read by a geologist or geochemist who wants to understand some of the current geochemical jargon and make sense of the geochemical literature. The reader will detect a number of biases in this book which are an inevitable consequence of the author’s geological interests. The first bias is towards examples chosen from the Archaean, which is the principal area of geology in which I have worked and which is evident also from the place of writing. The second bias is towards igneous and metamorphic petrology, which again are my fields of interest, but also the area in which many of the methods described were first applied.Preface
Acknowledgements
Glossary
Abbreviations of mineral names used in the text
Other abbreviations and symbols used in the text
Geochemical dataGeological processes and their geochemical signatures
Processes which control the chemical composition of igneous rocks
Processes which control the chemical composition of sedimentary rocks
Processes which control the chemical composition of metamorphic rocks
Geological controls on geochemical data
Analytical methods in geochemistry
X-ray fluorescence (XRF)
Neutron activation analysis (INAA and RNAA)
Inductively coupled plasma emission spectrometry (ICP)
Atomic absorption spectrophotometry (AAS)
Mass spectrometry
Isotope dilution mass spectrometry (IDMS)
Inductively coupled plasma emission mass spectrometry (ICP-MS)
Spark source mass spectrometry (SSMS)
Electron microprobe analysis
The ion microprobe
Selecting an appropriate analytical technique
Sources of error in geochemical analysis
Contamination
Calibration
Peak overlap
Detecting errors in geochemical data
Analysing geochemical dataAverages
Correlation
The correlation coefficient
The significance of the correlation coefficient (r)
Assumptions in the calculation of the product-moment coefficient of correlation
Spearman rank correlation
Correlation matrices
Correlation coefficient patterns
Regression
Ordinary least squares regression
Reduced major axis regression
Weighted least squares regression
Robust regression
Some problems with traditional approaches to correlation and regression
Ratio correlation
An example of the improper use of ratio correlation – Pearce element ratio diagrams
Application to trace element diagrams
Ratio correlation in isotope geology
The constant sum problem
The consequences of closure
Correlating compositional data
The means of compositional data-sets
Invalid escape routes
Aitchison's solution to the constant sum effect
An example – basalts from Kilauea Iki lava lake, Hawaii
The interpretation of log-ratios
The interpretation of trends on triangular diagrams
Principal component analysis
Discriminant analysis
An example from igneous petrology
Other applications of discriminant analysis
Whither geochemical data analysis?
Using major element dataRock classification
Classifying igneous rocks using oxide-oxide plots
The total alkalis – silica diagram (TAS)
Using TAS with volcanic rocks
A TAS diagram for plutonic rocks
Discrimination between the alkaline and subalkaline rock series using TAS
The K₂O vs SiO₂ diagram for the subdivision of the subalkaline series
Classifying igneous rocks using the norm
Cation norms
Norm calculations and the oxidation state of iron
Basalt classification using the Ne-Di-Ol-Hy-Q diagram of Thompson (1984)
Granite classification using the Ab-An-Or diagram of O'Connor (1965)
The Q'(F')-ANOR diagram of Streckeisen and Le Maitre (1979)
Classifying igneous rocks using cations
The R1-R2 diagram of de la Roche et al. (1980)
The Jensen cation plot (Jensen, 1976)
The chemical classification of sedimentary rocks
Arenite/wacke
Mudrocks
Discussion
Variation diagrams
Recognizing geochemical processes on a major element variation diagram
Fractional crystallization
Assimilation and fractional crystallization
Partial melting
Mixing lines in sedimentary rocks
The identification of former weathering conditions from sedimentary rocks
Mixing in metamorphic rocks
Element mobility
Artificial trends
Selecting a variation diagram
Bivariate plots
Harker diagrams – bivariate plots using SiO₂ along the x-axis
Bivariate plots which use MgO on the x-axis
Bivariate plots using cations
Bivariate plots using the magnesium number
Triangular variation diagrams
The AFM diagram
Problems in the use of the AFM diagram
Interpreting trends on variation diagrams
Extract calculations
Addition-subtraction diagrams
Trends showing an inflection
Scattered trends
A computer-based approach to mixing calculations
Modelling major element processes in igneous rocks
Discussion
Diagrams on which rock chemistry can be plotted together with experimentally determined phase boundaries
The normative albite-orthoclase-quartz diagram – the ‘granite system’
Water-undersaturated equilibria
The presence of anorthite
The silica-undersaturated portion of the normative nepheline-kalsilite-silica diagram – the ‘nepheline syenite system’
Basaltic experimental systems
CMAS diagrams
Projecting rock compositions into CMAS
Interpreting CMAS diagrams
Diagrams based upon the Yoder-Tilley (1962) normative tetrahedron
Projections in the tholeiite basalt tetrahedron Ol-Pl-Di-Q
The normative Ne-Di-Ol-Hy-Q diagram
The low-pressure tholeiitic basalt phase diagram (Cox et al., 1979)
Problems with CIPW normative projections
Experimental systems for calc-alkaline rocks
The olivine-clinopyroxene-silica projection of Grove et al. (1982)
The projections of Baker and Eggler (1983, 1987)
Discussion
Using trace element dataClassification of trace elements according to their geochemical behaviour
Trace element groupings in the periodic table
Trace element behaviour in magmatic systems
Controls on trace element distribution
Partition coefficients
Measuring partition coefficients
Physical controls on the value of partition coefficients in mineral-melt systems
Composition
Temperature
Pressure
Oxygen activity
Crystal chemistry
Water content of the melt
Selecting a partition coefficient
Partition coefficients in basalts and basaltic andesites
Partition coefficients in andesites
Partition coefficients in dacites and rhyolites
Geological controls on the distribution of trace elements
Element mobility
Partial melting
Batch melting
Fractional melting
Crystal fractionation
Equilibrium crystallization
Fractional crystallization/Rayleigh fractionation
In situ crystallization
Contamination
AFC processes
Zone refining
Dynamic models
Dynamic melting
The RTF magma chamber
Sedimentary processes
Rare earth elements (REE)
The chemistry of the REE
Presenting REE data
Difficulties with chondrite normalization
Choosing a set of normalizing values
REE ratio diagrams
NASC normalization for sediments
Rock normalization
Interpreting REE patterns
REE patterns in igneous rocks
REE patterns in sea and river water
REE patterns in sediments
Clastic sediments
Chemical sediments
Normalized multi-element diagrams or incompatible element diagrams (spider diagrams)
Multi-element diagrams for igneous rocks
Primordial (primitive) mantle-normalized spider diagrams
Chondrite-normalized spider diagrams
MORB-normalized spider diagrams
Which spider diagrams do we use?
Interpreting multi-element diagrams for igneous rocks
Multi-element diagrams for sediments
Interpreting multi-element diagrams for sediments
Platinum metal group element (PGE) plots
Presenting PGE data
Chondrite normalization
Primitive mantle normalization
Interpreting PGE patterns
Transition metal plots
Bivariate trace element plots
The selection of trace elements in igneous rocks for plotting on bivariate graphs
Incompatible element plots
Identification of igneous source characteristics from incompatible element plots
Identification of igneous source characteristics from incompatible element ratio-ratio plots
Calculation of partition coefficients from reciprocal concentration trace element plots
Compatible element plots
Bivariate plots in sedimentary rocks
Enrichment-depletion diagrams
Modelling trace element processes in igneous rocks
Vector diagrams
Modelling on multivariate diagrams
Petrogenetic modelling – examples
Partial melting
Crystal fractionation
Crustal contamination and AFC processes
Open system processes
Magma and source mixing
Demonstrating element mobility
Inversion techniques using trace elements
Constraining fractional crystallization using an inversion method
Constraining partial melting using an inversion method
A final comment on geochemical modelling
Discriminating between tectonic environments using geochemical dataDiscriminant analysis
Immobile trace elements
Tectonic environments
Using discrimination diagrams
Discrimination diagrams for rocks of basaltic to andesitic composition
Trace element discrimination diagrams
The Ti-Zr, Ti-Zr-Y and Ti-Zr-Sr diagrams (Pearce and Cann, 1973)
The Ti-Zr-Y diagram
The Ti-Zr diagram
The Ti-Zr-Sr diagram
Discussion
Other discrimination diagrams using Ti-Zr-Y-Nb variations
The Zr/Y-Zr diagram for basalts (Pearce and Norry, 1979)
The Ti/Y-Nb/Y diagram (Pearce, 1982)
The Zr-Nb-Y diagram (Meschede, 1986)
The causes of Ti-Zr-Y-Nb variations in basalts from different tectonic settings
The Th-Hf-Ta diagram of Wood (1980)
The Ti-V diagram of Shervais (1982)
The La-Y-Nb diagram of Cabanis and Lecolle (1989)
Diagrams which preferentially select volcanic-arc basalts
The Cr-Y diagram (Pearce, 1982)
The Cr-Ce/Sr diagram
Distinguishing between different types of volcanic-arc basalt
The K₂O/Yb-Ta/Yb diagram
Diagrams which distinguish between different types of volcanic-arc andesite (Bailey, 1981)
Diagrams which discriminate between the alkali basalt and tholeiitic magma series
The TiO₂-Y/Nb diagram (Floyd and Winchester, 1975)
The P₂O₅-Zr diagram (Floyd and Winchester, 1975)
The TiO₂-Zr/P₂O₅ diagram (Floyd and Winchester, 1975)
The Nb/Y-Zr/P₂O₅ diagram (Floyd and Winchester, 1975)
Discussion
Discrimination diagrams for basalts based upon major elements
The F1-F2-F3 diagrams of J.A. Pearce (1976)
The MgO-FeO-Al₂O₃ diagram of T.H. Pearce et al. (1977)
Discrimination diagrams for basalts based upon minor elements
The TiO₂-K₂O-P₂O₅ diagram of T.H. Pearce et al. (1975)
The MnO-TiO₂-P₂O₅ diagram of Mullen (1983)
The K₂O-H₂O diagram of Muenow et al. (1990)
Discrimination diagrams for basalts based upon clinopyroxene composition
Discrimination diagrams for rocks of granitic composition
Discrimination diagrams for granites based upon Rb-Y-Nb and Rb-Yb-Ta variations (Pearce et al., 1984)
The Nb-Y and Ta-Yb discrimination diagrams
The Rb-(Y + Nb) and Rb-(Yb + Ta) discrimination diagrams
Discrimination diagrams for granites based upon Hf-Rb-Ta variations
A measure of arc maturity for volcanic-arc granites
Discussion
Discrimination diagrams for clastic sediments
Discrimination diagrams for clastic sediments using major elements
The sandstone discriminant function diagram (Bhatia, 1983)
Bivariate plots as sandstone discrimination diagrams (Bhatia, 1983)
The K₂O/Na₂O vs SiO₂ sandstone-mudstone discrimination diagram (Roser and Korsch, 1986)
Provenance signatures of sandstone-mudstone suites using major elements (Roser and Korsch, 1988)
Discrimination diagrams for clastic sediments using trace elements
Greywackes
Spider diagrams as discriminants of tectonic setting for shales (Winchester and Max, 1989)
Provenance studies (Cullers et al., 1988)
Discussion
Tectonic controls on magmatic and sedimentary geochemistry
An expert system for identifying the tectonic environment of ancient volcanic rocks (Pearce, 1987)
Do tectonic discrimination diagrams still have a function?
Using radiogenic isotope dataRadiogenic isotopes in geochronology
Isochron calculations
Pb isotope isochrons
Fitting an isochron
Errorchrons
The geochron
Model ages
T-CHUR model ages
T-depleted mantle (DM) model ages
Assumptions made in the calculation of model ages
Interpreting geochronological data
Blocking temperatures
Concepts of geological age
Cooling age
Crystallization age
Metamorphic age
Crust formation age
Crust residence age
The interpretation of whole-rock ages
The Rb-Sr system
Pb isotopes
The Sm-Nd system
The interpretation of mineral ages
Rb-Sr mineral ages
Argon methods
Sm-Nd mineral ages
U-Pb dating of zircon
The interpretation of model ages
Radiogenic isotopes in petrogenesis
The role of different isotopic systems in identifying reservoirs and processes
Recognizing isotopic reservoirs
Oceanic mantle sources
Depleted mantle (DM)
HEMU mantle
Enriched mantle
PREMA
Bulk Earth (Bulk Silicate Earth – BSE)
The origin of oceanic basalts
Trace elements and mantle end-member compositions
Continental crustal sources
Upper continental crust
Middle continental crust
Lower continental crust
Subcontinental lithosphere
Seawater
The evolution of mantle reservoirs with time – mantle evolution diagrams
The evolution of Sr isotopes with time
The evolution of Nd isotopes with time
The evolution of Pb isotopes with time
The epsilon notation
Calculating epsilon values
Epsilon values calculated for an isochron
Epsilon values for individual rocks at the time of their formation
Epsilon values for individual rocks at the present day
Epsilon values for Sr isotopes
Calculating the uncertainties in epsilon values when they are determined for isochron diagrams
The meaning of epsilon values
The fractionation factor f^Sm/Nd
Epsilon-Nd time plots
Isotope correlation diagrams
Using isotope correlation diagrams and epsilon plots to recognize mixing processes
Mixing between sources
Mixing in a magma chamber
Applications to contamination
Contamination of magmas by the continental crust
Crustal contamination and AFC processes
Contamination with seawater
Isotope vs trace (and major) element plots
Mantle-crust geodynamics
Plumbotectonics
Geodynamics
Using stable isotope dataNotation
Isotope fractionation
Physical and chemical controls on stable isotope fractionation
Using oxygen isotopes
Variations of δ¹⁸O in nature
Oxygen isotope thermometry
Calibration of oxygen isotope thermometers
Tests of isotopic equilibrium
Applications
Low-temperature thermometry
High-temperature thermometry
Oxygen isotope-radiogenic isotope correlation diagrams
Recognizing crust and mantle reservoirs
Recognizing crustal contamination in igneous rocks
Recognizing simple crystal fractionation in igneous rocks
Fingerprinting hydrothermal solutions using oxygen and hydrogen isotopes – water-rock interaction
Hydrogen isotopes
Calculating the isotopic composition of water from mineral compositions
The isotopic composition of natural waters
Meteoric water
Ocean water
Geothermal water
Formation water
Metamorphic water
Magmatic water
Quantifying water/rock ratios
Examples of water-rock interaction
Interaction between igneous intrusions and groundwater
Interaction between ocean-floor basalt and seawater
Water-rock interaction in metamorphic rocks
Water-rock interaction during the formation of hydrothermal ore deposits
Diagenesis of clastic sediments
Using carbon isotopes
The distribution of carbon isotopes in nature
Controls on the fractionation of carbon isotopes
Combined oxygen and carbon isotope studies of carbonates – δ¹⁸O vs δ¹³C plots
Limestone diagenesis
Hydrothermal calcite
The δ¹³C composition of seawater
Biogeochemical evolution
Carbon isotopes in CO₂
CO₂ dissolved in igneous melts
CO₂ in metamorphic fluids
Granulites
The origin of metamorphic graphite
CO₂ in gold-mineralizing fluids
CO₂ fluid-rock interaction
Carbon isotope thermometry
The calcite-graphite δ¹³C thermometer
The CO₂-graphite thermometer
Using sulphur isotopes
The distribution of sulphur isotopes in nature
Controls on the fractionation of sulphur isotopes
Sulphur isotope fractionation in igneous rocks
Sulphur isotope fractionation in sedimentary rocks
The bacterial reduction of sulphate to sulphide
The bacterial oxidation of sulphide to sulphate
The crystallization of sedimentary sulphate from seawater – evaporite formation
The non-bacterial reduction of sulphate to sulphide
Sulphur isotope fractionation in hydrothermal systems
Sulphur isotope fractionation between sulphide and sulphate phases – sulphur isotope thermometry
Using sulphur isotopes in igneous petrogenesis
Outgassing of SO₂
Contamination
Crystal fractionation
Using sulphur isotopes to understand the genesis of hydrothermal ore deposits
Modern hydrothermal mineralization at mid-ocean ridges
Ancient hydrothermal mineralization
High-temperature inorganic reduction of seawater sulphate
Low-temperature organic reduction of sulphate
Low-temperature bacteriological reduction of sulphate
Sulphur of magmatic origin
References
Index