Teneurs en eau et compositions isotopiques de H, O et Li des minéraux des granulites de la croûte continentale inférieure de l'Est de la Chine, Water content and H-O-Li isotopes in lower crustal granulite minerals

Xiaozhi Yang

Description

Sous la direction de Etienne Deloule, Qunke Xia
Thèse soutenue le 03 juillet 2008: University of Science and Technologie of China, INPL
Pour la première fois, une étude par spectroscopie infrarouge à transformée de Fourrier et par microsonde ionique des minéraux majeurs de la croûte inférieure et des péridotites mantelliques a été entreprise afin de mieux caractériser les mécanismes d’incorporation et les teneurs en eau de ces minéraux nominalement anhydres, et de déterminer leurs compostions isotopiques en H, O, et Li pour retracer les échanges latéraux et horizontaux de l’eau dans la lithosphère continentale profonde. Les résultats montrent que: (1) Les minéraux nominalement anhydres, comme les pyroxènes et plagioclase, dans les granulites de la croûte inférieure contiennent de l’eau en trace essentiellement sous forme hydroxyles et accessoirement sous forme moléculaire, avec des concentrations (exprimées en poids H2O) allant de 200 à 2330 ppm pour les clinopyroxènes, de 60 à 1875 ppm pour les orthopyroxènes, de 65 à 900 ppm pour les plagioclases. Les teneurs calculées pour chaque roche totale d’après sa composition minéralogique et la teneur en eau des minéraux varient de 155 à 1100 ppm. (2) Les teneurs en H2O des minéraux majeurs et en roche totale de la croûte continentale inférieure sont manifestement plus élevées que celles du manteau lithosphérique sous-jacent, suggérant des variations verticales de la quantité d’H2O dans la lithosphère continentale profonde. Un tel contraste peut affecter de façon notable le comportement rhéologique de la lithosphère continentale. (3) Les rapports isotopiques de l’oxygène des pyroxènes étudiés, et probablement les roches totales, exprimés en [delta]18OSMOW , vont de ~ 4,5 à 12,5‰. Ceci indique la contribution de matériaux recyclés de la croûte continentale durant la pétrogenèse des échantillons ayant un TM18O élevé. (4) Les minéraux de la granulites sont caractérisés par des valeurs de élevées TMD, avec des valeurs de -80~-10‰ exprimées en [delta]DSMOW; les minéraux sont le plus souvent en équilibre les uns avec les autres lorsque l’on considère leurs compositions isotopiques moyennes. (5) Les compositions isotopiques du Lithium mesurée dans les minéraux de nos échantillons de granulites, exprimées en [delta]7Li par rapport à Lsvec, varient de -13 à +4.7 ‰. Ces valeurs sont donc pour la plus part inférieures à celles mesurées sur les MORB (2 – 6‰). La dispersion des valeurs reflètent l’hétérogénéité de la source des granulites, et les valeurs bassent resultent probablement de la perte par diffusion de Li pendant la mise en place des liquides silicatées provenant du manteau dans la croûte inférieure. (6) La grande hétérogénéité des teneurs en eau et en Lithium, et des compositions isotopiques de H-O-Li indique l’absence de circulation de fluide pervasive au travers de la croûte inférieure, qui aurait pour effet de supprimer les hétérogénéités à petite échelle et de les diminuer fortement à grande échelle
-Granulite
-Chine de l’Est
-Teneur en eau
-REE
-Isotope de H
-O et Li
-FTIR
-IMS
-Croûte continentale inférieure
-Manteau lithosphérique
-Péridotite
For the first time, systematic investigations of water content and H-O-Li isotopic compositions of minerals in lower crustal granulites, as well as water content of minerals in mantle peridotites, from eastern China have been carried out by Fourier transform infrared spectrometer and ion microprobe. The results show that: (1) Nominally anhydrous minerals, such as pyroxenes and plagioclase, in the lower crust generally contain trace amounts of structural water, with their content (H2O by wt.) varying from 200 to 2330 ppm for clinopyroxene, 60 to 1875 ppm for orthopyroxene, 65 to 900 ppm for plagioclase and 155 to 1100 ppm for the estimated bulk compositions. (2) Water contents of minerals in lower crustal granulites from eastern China, and their bulk values, are significantly higher than those in the underlying upper mantle, implying vertical heterogeneities of water distribution in the deep continental lithosphere; the contrast in water content even affect the rheological strength of the lithosphere. (3) The O-isotopic compositions of pyroxenes in the lower crustal granulites from eastern China are highly variable between different localities (~ 4.5 to 12.5‰, expressed in [delta]18OSMOW values), indicating variable influences from recycled crustal materials on their protoliths. (4) The H-isotopic compositions of granulite minerals from eastern China, are mostly in the range of -80 to -10‰ expressed in [delta]DSMOW values, and these minerals are usually in equilibrium with their [delta]D values. The relatively high [delta]D of granulite minerals may be related with degassing loss of H during the genesis of granulites. (5) The Li-isotopic compositions of granulite minerals from eastern China are usually in the range of -13 to 4.7‰, mostly lower than those of MORB (2-6‰). They reflect the source heterogeneity and are probably results of high-T Li diffusion during the intrusion of their original melts into the preexisting lower crust. (6) The large dispersion of Li and water contents and of H-O-Li isotopic results indicate the absence of any pervasive fluids in the lower crust
-Granulite
-Peridotite
-Eastern China
-Water contents
-REE
-H
-O
-Li isotopes
-FTIR
-IMS
-Continental lower crust
-Upper Mantle
Source: http://www.theses.fr/2008INPL028N/document

Sujets

• Teneur en eau
• Sahnish
• IMS
• Péridotite

Informations

• Publié par: Thesee
• Nombre de lectures: 36
• Langue: English
• Poids de l'ouvrage: 6 Mo

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and Technology of China Polytechnique de Lorraine

Water content and H-O-Li isotopes
in lower crustal granulite minerals

Thesis by
Xiao-Zhi YANG

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY from USTC and DOCTOR from INPL
June, 2008

Committee Members
ZHANG Hongfu IGG/CAS Beijing reviewer for INPL
INGRIN Jannick, LMTG-OMP Toulous reviewer for INPL
REISBERG Laurie CRPG-CNRS Nancy
ZHENG Yongfei USTC Hefei
XU Yigang KLIGG/CAS Guangzhou
ZHENG Jiangping FES/CUG Wuhan
LI Shuguang USTC Hefei

XIA QunKe USTC Hefei PhD director
DELOULE Etienne CRPG-CNRS PhD Director



















© 2008
Xiao-Zhi Yang
All Rights Reserved
2






It was a long time before man came to understand that
any true theory of the earth must rest upon evidence fur-
nished by the globe itself, and that no such theory could
properly be framed until a large body of evidence had been
gathered together.


----Sir Archibald Geike, 1905
Acknowledgements
First and foremost, I would like to thank Qunke Xia and Etienne Deloule,
my thesis advisors and trusted friends, not only for their excellent supervising
and full supports on my Ph.D academic work but also for their always care on
my living both at USTC and CRPG during the past several years. This thesis
could not have been accomplished in this form without the scientific freedom
they allowed me throughout the work.
I cannot fully express my gratitude to Shun Karato, Roberta Rudnick, David
Kohlstedt, Hans Keppler, Kent Condie, Jannick Ingrin, George Rossman, John
Valley, Eric Rybacki, Sylvie Demouchy, Cin-Ty Lee and Catherine McCammon
for many fruitful discussions. I especially thank Shun for his always kindly
guidance, encouragement and suggestions, which arose my further interest
into the field of mineral physics, and Roberta for her careful opinions on many
questions, which help me go deep into a lot of issues. I also thank Roland
Stalder, Horst Marschall, Roland Burgmann, Attila Demeny, Luigi Dallai, Jochen
Hoefs, Juan Carlos Afonso, Anne Peslier, Peter Kelemen, Jennifer Wenner, Terry
Plank, John D. Clemens, John Tarney, Eugen Libowitzky, Thomas J. Shankland,
Ikuo Katayama, Elizabeth Johnson, Friedemann Freund, Qicheng Fan, Yongfei
Zheng, Xiaolong Huang, Yigang Xu, Xiachen Zhi, Yongsheng Liu and Peifen Xu
for their suggestions and discussions on many subjects, both on geochemistry
and geophysics, although many of them were not included in this thesis.
I appreciate Denis Mangin, Claire Rollion-Bard and Michael Champenois for
their invaluable help, assistance and teaching on ion microprobe, and Caroline
Guilmette on H extraction and isotopic analysis by H-manometry and Isotopic
Ratios Mass Spectrometry (IRMS). Without their help, I could not finish the
instrumental analyses and this thesis on time. I thank Romain Mathieu,
Anne-Sophie Bouvier, Céline Martin, Johanna Marin, Clément Yonta Ngouné,
Maxence Paul, Magali Pujol and Lei Zheng, my fellow graduate students, and
ivLaurent Tisssandier, a postdoc worker, and Aurelie Didot, the secretary, who
helped me so much for my living and studying at CRPG.
I encountered many excellent teachers and received wonderful education
for my undergraduate and graduate studies at USTC. Thanks to all of them for
preparing me a good background on many disciplines, upon which I could go
further and deeper into this thesis and enjoy the research. A debt of gratitude
to my classmates and many friends at both Hefei and Nancy, who helped me a
lot to go through this thesis, especially when I got into hard work and sometimes
fell into a blue mode with my research. I thank the Programme Sino-Français de
Recherches Avancées (PRA) program for providing me the financial support for
my survival at CRPG. I also thank Bernard Marty for driving me to Cologne and
and Marc Chaussidon for arranging me a car to Nancy in the 2007 Goldschmidt
Conference and CRPG for providing me the financial support.
I thank David Bell for providing me the KBH-2 opx samples, Qicheng Fan,
Yigang Xu, Jianping Zheng and Xiachen Zhi for some granulite and peridotite
samples. Many thanks also go to Florence Atig for translating the abstract into
French.
Last, but never least, I would like to thank my parents ---- from whom the
support and encouragement enables me the education in China for about 20
years. On a more personal level, I thank Li, my girlfriend, whose love and
eternally optimistic perspective on life provided me the encouragement and
patience I needed in order to go through this work.
vAbstract
Systematic Fourier transform infrared spectrometer (FTIR) and ion microp-
robe (SIMS) investigations of common lower crustal minerals (pyroxenes and
plagioclase: from Hannuoba, Nushan and Daoxian of eastern China), as well as
mantle peridotite minerals (pyroxenes and olivine: from Hannuoba and Nushan),
were undertaken to better understand the composition of structurally bound
H-species within these nominally anhydrous minerals, the possible lateral and
vertical variations of H O in the deep continental lithosphere (lower crust and 2
upper mantle), and the H-, O-, and Li- isotopes and REE compositions of the
coexisting minerals within the continental lower crust. This is the first time to
document the water content and H-O-Li isotopes of the main minerals in the
continental lower crust.
The nominally anhydrous minerals, such as pyroxenes and plagioclase, in
the lower crustal granulites generally contain trace amounts of water in the
form of structurally bound hydroxyl and less molecular H O, with their contents 2
(H O by wt.) varying from 200 to 2330 ppm for clinopyroxene, 60 to 1875 ppm 2
for orthopyroxene, 65 to 900 ppm for plagioclase and 155 to 1100 ppm for the
estimated bulk compositions. The average bulk content is about 450 ppm, and
18therefore the lower crust is estimated to contain ~ 4.26 × 10 kg H O in the 2
nominally anhydrous minerals. A significant contrast in water content is ob-
served between Precambrian and Phanerozoic continental deep crust, implying
a more hydrous ancient lower crust relative to the modern one.
H O contents of the main continental lower crustal minerals, and their bulk 2
concentrations, are obviously higher than those in the underlying lithospheric
mantle, despite their large lateral variations, suggesting vertical variations of
H O content in the deep continental lithosphere (lower crust vs. upper mantle). 2
Such water contrast may be related with the petrogenesis of these rocks (e.g.
partial melting and/or fractional crystallization), and can strongly affect the
virheological behavior of the deep continental lithosphere below the North China
Craton, which probably results in different lithospheric structures and proc-
esses between different tectonic zones beneath this craton, e.g. lithospheric
thinning vs. thickening.
The O-isotopic ratios of studied pyroxenes, and probably the bulk samples,
range from ~4.5 to 12.5‰, higher than or nearly comparable to that of normal
18mantle (5.7±0.5‰) depending on the sample localities. Inter-grain δ O
variations up to 2-3‰ can be observed for the same mineral even in <1 cm
scale in some samples, in contrast to their nearly uniform intra-grain distribu-
tion, implying heterogeneities between different grains. Consistency between
O-isotopic and cation exchange temperatures suggests the preservation of
peak-metamorphic compositions.
The lower crustal granulite minerals from the North China Craton are
characterized by relatively high δD values compared to the normal mantle, e.g.
-80~-10‰ for the former vs. -90~-60‰ for the latter. Intra-grain variations of
δD on some grains were probably caused by diffusion-induced processes
shortly before or during their entrainments or exhumation, however, the
minerals were usually in equilibrium with each other with respect to their
average H isotopic compositions, indicating weak influences from such dif-
fusion processes. The relatively heavier D/H ratios o