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Journal ArticleDOI

Pargasite at high pressure and temperature

TL;DR: In this paper, the phase stability field, the thermoelastic behavior and the P-induced deformation mechanisms at the atomic scale of pargasite crystals, from the Phlogopite peridotite unit of the Finero mafic-ultramafic complex (Ivrea-Verbano Formation, Italy), have been investigated by a series of in situ experiments.
Abstract: The P–T phase stability field, the thermoelastic behavior and the P-induced deformation mechanisms at the atomic scale of pargasite crystals, from the “phlogopite peridotite unit” of the Finero mafic–ultramafic complex (Ivrea-Verbano Formation, Italy), have been investigated by a series of in situ experiments: (a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron X-ray diffraction with a diamond anvil cell, (b) at high temperature (up to 823 K), by powder synchrotron X-ray diffraction using a hot air blower device, and (c) at simultaneous HP–HT conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil cell (P max = 16.5 GPa, T max = 1200 K). No phase transition has been observed within the P–T range investigated. At ambient T, the refined compressional parameters, calculated by fitting a second-order Birch–Murnaghan Equation of State (BM-EoS), are: V 0 = 915.2(8) A3 and K P0,T0 = 95(2) GPa (β P0,T0 = 0.0121(2) GPa−1) for the unit-cell volume; a 0 = 9.909(4) A and K(a) P0,T0 = 76(2) GPa for the a-axis; b 0 = 18.066(7) A and K(b) P0,T0 = 111(2) GPa for the b-axis; c 0 = 5.299(5) A and K(c) P0,T0 = 122(12) GPa for the c-axis [K(c) P0,T0 ~ K(b) P0,T0 > K(a) P0,T0]. The high-pressure structure refinements (at ambient T) show a moderate contraction of the TO4 double chain and a decrease of its bending in response to the hydrostatic compression, along with a pronounced compressibility of the A- and M(4)-polyhedra [K P0, T0(A) = 38(2) GPa, K P0, T0(M4) = 79(5) GPa] if compared to the M(1)-, M(2)-, M(3)-octahedra [K P0, T0(M1,2,3) ≤ 120 GPa] and to the rigid tetrahedra [K P0, T0(T1,T2) ~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman’s formalism, which gives: V 0 = 909.1(2) A3, α0 = 2.7(2)·10−5 K−1 and α1 = 1.4(6)·10−9 K−2 [with α0(a) = 0.47(6)·10−5 K−1, α0(b) = 1.07(4)·10−5 K−1, and α0(c) = 0.97(7)·10−5 K−1]. The petrological implications for the experimental findings of this study are discussed.

Summary (2 min read)

Introduction

  • Amphiboles are an important supergroup of rock-forming minerals, with an unusually high chemical variability and the ability to crystallize under almost all conditions relevant to the petrogenesis of crustal or upper mantle rocks, as well as subducting slabs (e.g., Robinson et al.
  • In order to better understand the water cycle in the upper and potentially lower mantle, it is essential to determine the stability of all hydrous minerals subducted into the mantle.
  • Comodi et al. (1991) reported the compressibility of tremolite, pargasite and glaucophane on the basis of in-situ single-crystal Xray diffraction experiments with a diamond anvil cell (DAC) up to about 4 GPa.
  • This lack of knowledge prevents a detailed description of the behavior of amphiboles that are stable at HP-HT conditions and consequently it is still difficult to assess their petrological implications.

Structure of pargasite

  • In each chain, there are two distinct TO4 tetrahedra (with two crystallographically independent T(1) and T(2) sites).
  • The TO4 tetrahedra are connected in such a way that an alternation of pseudo-hexagonal rings, delimitated by six TO4 units, occurs (Fig. 1 ).
  • On the basis of single-crystal X-ray diffraction experiments, Papike at al. (1969) observed the preference of Al for the T(1) site.
  • This finding was later confirmed by Welch and Knight (1999) on the basis of a neutron diffraction experiment on a synthetic pargasite.
  • The topological configuration of the double silicate chains of the octahedral sites (with three crystallographically independent positions M(1), M(2) and M(3), i.e., the C sites of the general amphibole formula), of the 8-fold site M(4) (i.e., the B site) and of the A site are shown in Figs. 1 and 2 .

Experimental methods

  • Several crystals of pargasite from the same rock sample of the "phlogopite peridotite unit", Finero mafic-ultramafic complex (Ivrea-Verbano Formation, Italy), were selected on the basis of optical and X-ray diffraction quality.
  • A 250 m thick rhenium gasket was preindented to 50 m and then drilled with a 200 m diameter hole, in which the crystal of pargasite, together with some ruby chips and a gold fragment (~20 μm thick) as pressure standards, were loaded.
  • In-situ HT powder diffraction data of pargasite were collected at the MCX beamline at ELETTRA (Trieste, Italy), using the high-resolution diffractometer available at the station (Rebuffi et al. 2014) .
  • The diffraction patterns were treated by Le Bail full-profile fit (Le Bail et al. 1988 ), using the GSAS package (Larson and Von Dreele 1994) , aimed to obtain the unit-cell parameters only.

Structure refinement protocol

  • All the structure refinements, based on the intensity data of the HP experiment (at room-T), were performed using the software JANA2006 (Petříček et al. 2014) , starting from the structure model of Hawthorne et al. (1996) , in the space group C2/m.
  • The principal statistical parameters of the structure refinements are listed in Table 5 .
  • The relevant bond distances related to the M(4) and A sites are reported in Table 7 .

-Compressional behavior

  • The experimental P-V data have been best fitted using the Birch-Murnaghan Equation of State (BM-EoS), which is based on the assumption that the strain energy of a solid undergoing compression can be expressed as a Taylor series in the finite Eulerian strain.
  • Two different Birch-Murnaghan equations of state, truncated to the second order, have been fitted to the experimental data within the P-ranges 0.0001-6.53 GPa and 7.20-20.14 GPa, respectively.
  • The axial compressibilities were calculated within the range 0.0001-6.53 GPa, using the "linearized" second-order BM-EoS (Angel 2000) , and the least squares fits were performed accounting for uncertainties in P and length (Table 9 ).

Thermal expansion

  • Within the T-range investigated, the volume thermal expansion coefficient αT increases approximately linearly with temperature.
  • T-V fits to different thermal equations were performed.
  • Given the small changes in volume with temperature, the thermal expansion coefficient at high-T can be expressed as: αT [α0 + α1(T-T0)].
  • No evidence for a phase transition was observed within the T-range investigated.

P-T-phase stability

  • During the two P-T ramps, no evidence of phase transition (e.g., no reflections violating the C2/m extinction conditions, which would be indicative of a transformation to P21/m, as observed e.g. in cummingtonite, Yang et al. 1988 ) or de-hydroxilation was observed.
  • The temperature was then progressively decreased down to ambient-T and, after 150 minutes, a data collection at ambient temperature and 9.4(3) GPa was performed: the structure refinement showed that any P-T effect on the structure of pargasite was fully reversible after T release.
  • The most significant changes of the (Si,Al)O4 double chains, in response to the applied pressure, can be described in terms of the O-O-O inter-tetrahedral angle variation (Fig. 1 ).
  • These two angles are related respectively to O5-O6-O7 and O5-O7-O5 by an inverse geometrical relation (i.e., if the first decreases, the second increases) (Table 11 ).

Discussion

  • The principal effect, in response to the hydrostatic compression, is the kinking of the TO4 units of the tetrahedral doublechain, with the closure of the O6-O5-O6 angle and the consequent contraction of the chains along [001] (Fig. 5 , Table 11 ).
  • To the best of their knowledge, the stability field of individual pargasite compositions has not been previously examined at the conditions employed here, but must extend to a wider P-T range than those obtained in previous studies on multiple mineral assemblages.
  • This may have a significant influence on the H2O cycle of the mantle.

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2
Pargasite at high pressure and temperature
38
39
Davide Comboni
1
, Paolo Lotti
1,2*
,
G. Diego Gatta
1,3
, Marco Merlini
1
,
40
Hanns-Peter Liermann
4
and Daniel J. Frost
5
41
42
1
Dipartimento di Scienze della Terra, Università degli Studi di Milano,
43
Via Botticelli 23, I-20133 Milano, Italy
44
2
ELETTRA Sincrotrone Trieste S.c.P.A., Strada Statale 14, km. 163.5, 34149 Basovizza, Trieste,
45
Italy
46
3
CNR Istituto di Cristallografia, Sede di Bari, Via G. Amendola 122/O, Bari, Italy
47
4
Photon Sciences, DESY, Notkestrasse 85, D-22607 Hamburg, Germany
48
5
Bayerisches Geoinstitute, University of Bayreuth, D-95440 Bayreuth, Germany
49
50
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*Corresponding Author: Dr. Paolo Lotti
52
Phone: +39-02-50315598, Fax: +39-02-50315597, e-mail: paolo.lotti@unimi.it
53
54
55
56
Manuscript to be submitted to Physics and Chemistry of Minerals
57
58
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60
61
62
63
64
65
66
67
68

3
Abstract
69
70
The P-T phase stability field, the thermo-elastic behavior and the P-induced compression
71
mechanisms at the atomic scale of pargasite crystals from the “phlogopite peridotite unitof the
72
Finero mafic-ultamafic complex (Ivrea-Verbano Formation, Italy) have been investigated by a
73
series of in-situ experiments: a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron X-
74
ray diffraction with a diamond anvil cell, b) at high temperature (up to 823 K), by powder
75
synchrotron X-ray diffraction using a hot air blower device, and c) at simultaneous HP-HT
76
conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil
77
cell (P
max
= 16.5 GPa, T
max
= 1200 K). No phase transition has been observed within the P-T range
78
investigated. At ambient T, the refined compressional parameters, calculated by fitting a second-
79
order Birch-Murnaghan Equation of State (BM-EoS), are: V
0
= 915.2(8) Å
3
and K
P0,T0
= 95(2) GPa
80
(
P0,T0
= 0.0121(2) GPa
-1
) for the unit cell volume; a
0
= 9.909(4) Å and K(a)
P0,T0
= 76(2) GPa for the
81
a-axis; b
0
= 18.066(7) Å and K(b)
P0,T0
= 111(2) GPa for the b-axis; c
0
= 5.299(5) Å and K(c)
P0,T0
=
82
122(12) GPa for the c-axis [K(c)
P0,T0
~ K(b)
P0,T0
> K(a)
P0,T0
]. The high-pressure structure
83
refinements (at ambient T) show a moderate contraction of the TO
4
double chain and a decrease of
84
its bending in response to the hydrostatic compression, along with a pronounced compressibility of
85
the A- and M(4)-polyhedra [K
P0
,
T0
(A) = 38(2) GPa, K
P0
,
T0
(M4) = 79(5) GPa] if compared to the
86
M(1)-, M(2)-, M(3)-octahedra [K
P0
,
T0
(M1,2,3) 120 GPa] and to the rigid tetrahedra [K
P0
,
T0
(T1,T2)
87
~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman’s
88
formalism, which gives: V
0
= 909.1(2) Å
3
, α
0
= 2.7(2)·10
-5
K
-1
and α
1
= 1.4(6)·10
-9
K
-2
[with α
0
(a) =
89
0.47(6)·10
-5
K
-1
, α
0
(b) = 1.07(4)·10
-5
K
-1
, and α
0
(c) = 0.97(7)·10
-5
K
-1
]. The petrological
90
implications of the experimental findings of this study are discussed.
91
92
Keywords: pargasite, amphibole, high pressure, high temperature, phase stability, synchrotron X-
93
ray diffraction
94
95

4
Introduction
96
97
Amphiboles are an important supergroup of rock-forming minerals, with an unusually high
98
chemical variability and the ability to crystallize under almost all conditions relevant to the
99
petrogenesis of crustal or upper mantle rocks, as well as subducting slabs (e.g., Robinson et al.
100
1982, Green and Wallace 1988, Hawthorne 1981). This chemical diversity originates from their
101
structure, which is able to accommodate almost all the elements of the periodic table (Hawthorne
102
and Oberti 2007). In particular, the occurrence of hydroxyl groups into the structure has proved to
103
be a significant agent in the water cycle within the upper mantle (e.g., Gill 1981). Amphiboles
104
crystallise from basaltic magmas at mid ocean ridges and are eventually dragged into the upper
105
mantle at subduction zones. During subduction, many hydrous minerals become unstable and water
106
is released, migrating into the overlying and much hotter mantle wedge, causing melting and arc
107
volcanism as e.g. described for the case of talc (Bose and Ganguly 1989). In order to better
108
understand the water cycle in the upper and potentially lower mantle, it is essential to determine the
109
stability of all hydrous minerals subducted into the mantle. Because amphiboles are volumetrically
110
the most abundant hydrous minerals in the lithospheric mantle, they play an important role in a
111
number of metasomatic and metamorphic processes (e.g., Wallace and Green 1991; Ionov and
112
Hofmann 1995; Vannucci et al. 1995; Niida and Green 1999; Foley et al. 2002; Ionov et al. 2002).
113
Thus, a series of studies have been devoted to the P-T stability of amphiboles in subducting slabs,
114
and to clarifying their role in transporting hydrogen (e.g., Poli and Schmidt 1995; Schmidt and Poli
115
1998; Stern 2002; Forneris and Holloway 2003; Fumagalli and Poli 2005). Owing to their
116
importance, a number of in-situ high-pressure (HP) and high-temperature (HT) studies have been
117
performed in order to describe the P-T stability fields, the thermo-elastic behavior and the P- or T-
118
induced deformation mechanisms of amphiboles at the atomic scale. Comodi et al. (1991) reported
119
the compressibility of tremolite, pargasite and glaucophane on the basis of in-situ single-crystal X-
120
ray diffraction experiments with a diamond anvil cell (DAC) up to about 4 GPa. The
121

5
compressibility of grunerite was investigated by Zhang et al. (1992) up to 5 GPa (single-crystal X-
122
ray diffraction experiment with a DAC). Yang et al. (1998) reported the compressional behavior
123
and the P-induced C2/m-P2
1
/m phase transition (at about 1.2 GPa) in cummingtonite, by in-situ X-
124
ray and infra-red experiments with a DAC. Later, Boffa Ballaran et al. (2000) investigated the HP
125
transformation behavior of the cummingtonite-grunerite solid solution (single-crystal X-ray
126
diffraction experiments with a DAC). Comodi et al. (2010) reported the compressional behavior of
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two kaersutites up to 8 GPa, highlighting the role of the oxo-component on the elastic behavior of
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amphiboles (single-crystal X-ray diffraction experiments using a DAC). Jenkins et al. (2010)
129
reported the compressibility of glaucophane based on an in-situ X-ray powder diffraction
130
experiment compressed within DAC up to 10 GPa. Zanazzi et al. (2010) investigated the high-
131
pressure behavior of a crystal of protomangano-ferro-antophyllite up to 9 GPa with a DAC. Welch
132
et al. (2011a) described the elastic behavior of a Mg-rich antophyllite and its deformation
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mechanisms at the atomic scale up to 7 GPa, by in-situ single-crystal X-ray diffraction with a DAC.
134
The compressional behavior of gedrite up to 7 GPa was later reported by Nestola et al. (2012)
135
(single-crystal X-ray diffraction experiments with a DAC). More recently, Thompson et al. (2016)
136
investigated the relation between the frequency of O-H bonds stretching modes and the hydrogen
137
bond symmetrization induced by pressure. The elastic parameters obtained by the aforementioned
138
experiments are listed in Table 1. However, as pointed out in Welch et al. (2007), there is a need to
139
extend the compressibility measurement to P higher than 10 GPa, in order to improve the accuracy
140
of the refined isothermal bulk modulus values and their P-derivatives.
141
A series of in-situ experiments have been performed on the low and high thermal behavior
142
of amphiboles, on the basis of several experimental techniques (e.g., Sueno et al. 1978; Cameron et
143
al. 1983; Cámara et al. 2003, 2007; Iezzi et al. 2005a; Jenkins and Corona 2006), reviewed by
144
Welch et al. (2007). Some more recent studies are, e.g., those of Tribaudino et al. (2008), Welch et
145
al. (2008) and Iezzi et al. (2011) on richterite, Welch et al. (2011b) on anthophyllite and Zema et al.
146
(2012) on gedrite.
147

6
Neutron diffraction experiments at low- and room-T aimed to describe the atomic site
148
ordering and the H-bonding scheme in amphiboles have also been performed (e.g., Welch and
149
Knight 1999; Iezzi et al. 2005b; Gatta et al. 2017).
150
To the best of our knowledge, no simultaneous in-situ P-T studies have been conducted on
151
amphiboles. This lack of knowledge prevents a detailed description of the behavior of amphiboles
152
that are stable at HP-HT conditions and consequently it is still difficult to assess their petrological
153
implications.
154
As pointed out by Niida and Green (1999), pargasite is recognized as a ubiquitous hydrous
155
phase in the Earth’s upper mantle. In this light, we have selected crystals of pargasite from the
156
peridotite of the “phlogopite peridotite unit” of the Finero mafic-ultamafic complex (Ivrea-Verbano
157
Formation, Italy) (Cawthorn 1975; Rivalenti et al. 1975, 1984; Coltorti and Siena 1984; Siena and
158
Coltorti 1989), in order to describe: a) the HP elastic behavior of this amphibole (at P > 4 GPa) and
159
its main compression mechanisms at the atomic scale, b) its HT behavior, along with its potential
160
de-hydroxilation phenomenon, and c) its phase stability field at simultaneous HP-HT conditions.
161
162
163
Structure of pargasite
164
165
Pargasite is a Ca-amphibole associated to medium- or high-pressure/high-temperature
166
conditions. On the basis of the general amphibole formula A
0−1
B
2
C
5
T
8
O
22
W
2
(Hawthorne and
167
Oberti 2007), the ideal chemical formula of pargasite can be written as:
168
A
Na
B
Ca
2
C
(Mg
4
Al)
T
(Si
6
Al
2
)O
22
W
(OH)
2
. Its structure, described in the space group C2/m, is
169
characterized by double chains of TO
4
tetrahedra running parallel to [001] (Fig. 1). In each chain,
170
there are two distinct TO
4
tetrahedra (with two crystallographically independent T(1) and T(2)
171
sites). The TO
4
tetrahedra are connected in such a way that an alternation of pseudo-hexagonal
172
rings, delimitated by six TO
4
units, occurs (Fig. 1). On the basis of single-crystal X-ray diffraction
173
experiments, Papike at al. (1969) observed the preference of Al for the T(1) site. This finding was
174

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TL;DR: In this article, the structural and chemical changes of the clay mineral kaolinite were studied at conditions corresponding to a depth of about 75 km in a cold subducting slab (2.7 GPa and 200 C), and in the presence of water, the authors observed the pressure-induced insertion of water into the mineral.
Abstract: Water is the most abundant volatile component in the Earth. It continuously enters the mantle through subduction zones, where it reduces the melting temperature of rocks to generate magmas. The dehydration process in subduction zones, which determines whether water is released from the slab or transported into the deeper mantle, is an essential component of the deep water cycle. Here we use in situ and time-resolved high-pressure/high-temperature synchrotron X-ray diffraction and infrared spectra to characterize the structural and chemical changes of the clay mineral kaolinite. At conditions corresponding to a depth of about 75 km in a cold subducting slab (2.7 GPa and 200 °C), and in the presence of water, we observe the pressure-induced insertion of water into kaolinite. This super-hydrated phase has a unit cell volume that is about 31% larger, a density that is about 8.4% lower than the original kaolinite and, with 29 wt% H2O, the highest water content of any known aluminosilicate mineral in the Earth. As pressure and temperature approach 19 GPa and about 800 °C, we observe the sequential breakdown of super-hydrated kaolinite. The formation and subsequent breakdown of super-hydrated kaolinite in cold slabs subducted below 200 km leads to the release of water that may affect seismicity and help fuel arc volcanism at the surface. A super-hydrated clay mineral may play an important role in the solid Earth’s water cycle, according to laboratory experiments. The mineral kaolinite can carry and release large amounts of water during subduction.

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Cites background or methods or result from "Pargasite at high pressure and temp..."

  • ...More recently, the thermal equation of state of the end-member pargasite has been experimentally determined (Comboni et al. 2017)....

    [...]

  • ...Our thermal expansion value based on LDA (aLDA) is in very good agreement with the recent synchrotron XRD study on pargasite amphibole, which shows 2.7 × 10-5 K-1 at 300 K and 0 GPa (Comboni et al. 2017) (Fig....

    [...]

  • ...We also made independent estimates of g from experimentally determined thermal parameters at 300 K and 0 GPa, i.e., a (Comboni et al. 2017), V and KS (Brown and Abramson 2016), and CP (Dachs et al. 2010)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the effects of temperature, pH, and experiment duration on amphibole alteration were investigated using X-ray diffractometer, field emission scanning electron microscope, electron probe micro analyzer, and transmission electron microscopy.
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References
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TL;DR: An improved calibration curve of the pressure shift of the ruby R1 emission line was obtained under quasi-hydrostatic conditions in the diamond-window, high-pressure cell to 800 kbar.
Abstract: An improved calibration curve of the pressure shift of the ruby R1 emission line was obtained under quasi-hydrostatic conditions in the diamond-window, high-pressure cell to 800 kbar. Argon was the pressure-transmitting medium. Metallic copper, as a standard, was studied in situ by X ray diffraction. The reference pressure was determined by calibration against known equations of state of the copper sample and by previously obtained data on silver.

3,556 citations

Journal ArticleDOI
TL;DR: JANA2006 as discussed by the authors is a widely used program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/ powder diffraction or on electron diffraction.
Abstract: Abstract JANA2006 is a freely available program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/ powder diffraction or on electron diffraction. The system has been developed for 30 years from specialized tool for refinement of modulated structures to a universal program covering standard as well as advanced crystallography. The aim of this article is to describe the basic features of JANA2006 and explain its scope and philosophy. It will also serve as a basis for future publications detailing tools and methods of JANA.

3,545 citations

Book
12 Aug 1981
TL;DR: In this article, the authors define Orogenic Andesite and discuss its properties and properties, including the following: 1.1 Topography, gravity, heat flow, and conductivity.
Abstract: 1 What is "Typical Calcalkaline Andesite"?.- 1.1 Introduction.- 1.2 Definition of Orogenic Andesite.- 1.3 Magma Series Containing Orogenic Andesites.- 1.4 Overview.- 2 The Plate Tectonic Connection.- 2.1 Spatial Distribution of Active Orogenic Andesite Volcanoes.- 2.2 Initiation of Subduction.- 2.3 Cessation of Subduction.- 2.4 Collisions.- 2.5 Reversal of Subduction Polarity.- 2.6 Forearc and Transform Fault Volcanism.- 2.7 Anomalously Wide Volcanic Arcs.- 2.8 Andesites Clearly Not at Convergent Plate Boundaries.- 2.9 Conclusions.- 3 Geophysical Setting of Volcanism at Convergent Plate Boundaries.- 3.1 Topography, Gravity, Heat Flow, and Conductivity.- 3.2 Crustal Thickness, Structure, and Age.- 3.3 Upper Mantle Beneath the Forearc, Volcanic Arc, and Backarc Regions.- 3.4 Dipping Seismic Zones (Benioff-Wadati Zones) and Underthrust Lithosphere.- 3.5 Partial Melting and Magma Ascent Beneath Volcanic Arcs.- 3.6 Magma Chambers Beneath Orogenic Andesite Volcanoes.- 3.7 Conclusions.- 4 Andesite Magmas, Ejecta, Eruptions, and Volcanoes.- 4.1 Characteristics of Andesite Magma.- 4.1.1 Temperature.- 4.1.2 Density.- 4.1.3 Rheology.- 4.1.4 Miscellaneous Properties and Applications.- 4.2 Andesite Rock, Eruption, and Edifice Types.- 4.3 Variations in Magma Composition During and etween Historic Andesite Eruptions.- 4.4 Variations in Rock Composition During Evolution of Stratovolcanoes.- 4.5 Conclusions About Andesite Magma Reservoirs.- 4.6 Stress Fields and Volcano Spacings Within Volcanic Arcs.- 4.7 Relationships Between the Timing of Arc Volcanism and Plate Movements.- 4.8 Magma Eruption Rates at Convergent Plate Boundaries.- 4.9 Relative Proportions of Andesite.- 5 Bulk Chemical Composition of Orogenic Andesites.- 5.1 Rock Analyses: Significance, Averages, and Representative Samples and Suites.- 5.2 Major Elements.- 5.2.1 Silica Contents and Harker Variation Diagrams.- 5.2.2 Alkalies.- 5.2.3 Iron and Magnesium.- 5.2.4 Titanium.- 5.2.5 Aluminum and Calcium.- 5.2.6 Phosphorous.- 5.2.7 CIPW Normative Mineralogy.- 5.3 Volatiles.- 5.3.1 Water.- 5.3.2 Carbon Dioxide.- 5.3.3 Sulfur.- 5.3.4 Halogens.- 5.3.5 Oxygen.- 5.4 Trace Elements.- 5.4.1 The K-Group: Rb, Cs, Ba, and Sr.- 5.4.2 REE Group: Rare Earth Elements Plus Y.- 5.4.3 The Th Group: Th,U, and Pb.- 5.4.4 The Ti Group: Zr, Hf, Nb, and Ta.- 5.4.5 The Compatible Group: Ni, Co, Cr, V, and Sc.- 5.4.6 The Chalcophile Group: Cu, Zn, and Mo.- 5.4.7 Trace Element Systematics.- 5.5 Isotopes.- 5.5.1 Strontium.- 5.5.2 Lead.- 5.5.3 Neodymium.- 5.5.4 Inert Gases.- 5.5.5 U-Disequilibrium.- 5.5.6 Oxygen.- 5.5.7 Synthesis of Isotope Data.- 5.6 Comparison with Andesites Not at Convergent Plate Boundaries.- 5.7 Geochemical Distinctiveness of Volcanism at Convergent Plate Boundaries.- 5.8 Conclusions: Chemical Diversity of Orogenic Andesites.- 6 Mineralogy and Mineral Stabilities.- 6.1 Plagioclase.- 6.2 Pyroxenes.- 6.3 Amphibole.- 6.4 Olivine.- 6.5 Oxides.- 6.6 Garnet.- 6.7 Other Minerals.- 6.8 Inclusions in Orogenic Andesites.- 6.9 Mineral Stabilities in Andesite Magma.- 6.10 Trace Element Equilibria Between Minerals and Melt.- 6.11 Conclusions.- 7 Spatial and Temporal Variations in the Composition of Orogenic Andesites.- 7.1 Variations in Magma Composition Across Volcanic Arcs.- 7.2 Variations in Magma Composition Along Volcanic Arcs.- 7.3 Effects of Plate Convergence Rate on Magma Composition.- 7.4 Relationships Between Compositions of Orogenic Andesites and Adjacent Oceanic Crust.- 7.5 Changes in the Composition of Orogenic Andesites During Earth History.- 8 The Role of Subducted Ocean Crust in the Genesis of Orogenic Andesites.- 8.1 Characteristics of Subducted Ocean Crust Beneath Volcanic Arcs.- 8.2 Circumstantial Evidence of Slab Recycling in Arc Volcanism.- 8.3 Are Orogenic Andesites Primary Melts of Subducted Ocean Floor Basalt? No.- 8.4 The Sediment Solution.- 8.5 IRS Fluids and Maxwell's Demons.- 8.6 Conclusions.- 9 The Role of the Mantle Wedge.- 9.1 Characteristics of the Mantle Wedge.- 9.2 Circumstantial Evidence that Arc Magmas Originate Within the Mantle Wedge.- 9.3 Are Orogenic Andesites Primary Melts of Only the Mantle Wedge? Rarely.- 9.4 Fluid Mixing, Metasomatism, and Demonology in the Mantle Wedge.- 10 The Role of the Crust.- 10.1 Circumstantial Evidence for Crustal Involvement in Orogenic Andesites.- 10.2 Crustal Anatexis.- 10.3 Crustal Assimilation.- 11 The Role of Basalt Differentiation.- 11.1 General Arguments for and Against Differentiation.- 11.2 Roles of Plagioclase, Pyroxenes, and Olivine.- 11.3 Role of Magnetite and the Plagioclase-Orthopyroxene/Olivine-Augite-Magnetite (POAM) Model.- 11.4 Role of Amphibole.- 11.5 Role of Garnet.- 11.6 Role of Accessory Minerals: Apatite, Chromite, Sulfides, Biotite.- 11.7 Role of Magma Mixing.- 11.8 Role of Other Differentiation Mechanisms.- 11.9 Differentiation Processes Leading to Andesites in Anorogenic Environments.- 12 Conclusions.- 12.1 Andesite Genesis by POAM-Fractionation: the Most Frequent Mechanism.- 12.2 Some Outstanding Problems Requiring Clarification.- 12.3 Origin of Tholeiitic Versus Calcalkaline Andesites.- 12.4 Origin of Across-Arc Geochemical Variations.- 12.5 Epilog.- References.

3,040 citations

Journal ArticleDOI
TL;DR: In this paper, the application of the Rietveld refinement technique to synchrotron X-ray data collected from a capillary sample of Al2O3 in Debye-Scherrer geometry is described.
Abstract: The application of the Rietveld refinement technique to synchrotron X-ray data collected from a capillary sample of Al2O3 in Debye–Scherrer geometry is described. The data were obtained at the Cornell High Energy Synchrotron Source (CHESS) with an Si(111) double-crystal monochromator and a Ge(111) crystal analyzer. Fits to a number of well resolved individual peaks demonstrate that the peak shapes are very well described by the pseudo-Voigt function, which is a simple approximation to the convolution of Gaussian and Lorentzian functions. The variation of the Gaussian and Lorentzian half widths, ΓG and ΓL, with Bragg angle can be approximated quite closely by the functions V tan θ and X/cos θ which represent the contributions from instrumental resolution and particle-size broadening respectively. Rietveld refinement based on this model yields generally satisfactory results. The refined values of V and X are consistent with the expected vertical divergence (≃0.1 mrad) and the nominal particle size (≃ 0.3μm). In particular, the use of a capillary specimen virtually eliminates preferred orientation effects, which are highly significant in flat-plate samples of this material.

2,469 citations

Journal ArticleDOI
TL;DR: In this article, the crystal structure of LiSbWO6 was solved from X-ray powder diffraction data and the structure was refined using Rietveld profile refinement principles.

2,325 citations

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Dipartimento di Scienze della Terra, Università degli Studi di Milano, 43 Via Botticelli 23, I-20133 Milan, Italy 44 ELETTRA Sincrotrone Trieste S.P.A., Strada Statale 14, km. 163.5, 34149 Basovizza, Trieste, 45 Italy 46 CNR  Istituto di Cristallografia, Sede di Bari, Via G. Amendola 122/O, Bari this paper