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- Fellowship
Diploma of Geology - RMIT (Australia)
- PhD
Monash University (Australia)
- Fellow
of the Mineralogical Society of Great Britain and Ireland
- Fellow
of the Mineralogical Society of America
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- Igneous
Petrogenesis, especially of granitic rocks
- High
grade metamorphism and crustal melting
- Experimental
Petrology
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| My
current research projects all centre around the general theme
of the generation and evolution of granitic magmas in Earth’s
crust. The individual projects address the unifying complex
question of “How do granitic rocks attain their present
compositions, what processes and physical and chemical conditions
govern this, how does the continental crust compositionally
evolve, and what is the meaning of all this for local and global
tectonic processes? |
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1.
Genesis of High-K, Calcalkaline, Granitic Magmas
In orogenic and post-orogenic systems, there are suites of metaluminous,
calcalkaline, granitic rocks with elevated K/Na ratios. It is
generally assumed that their high-K character stems from the
potassic nature of the crustal source rocks that partially melted
to form these magmas. However, in many cases, such rock suites
contain mafic members that also possess this potassic character
and have some isotopic ratios that demand a mantle origin. Recently
published work with Darbyshire (formerly of NIGL, Nottingham,
UK) suggests that metasomatised mantle, hyper-enriched in LILE
and radiogenic Sr, is a significant source component of high-K
melts, and that mixing between these and felsic crustal melts
is a major process in producing metaluminous high-K suites.
There are important implications for the tectonic settings during
formation of the mantle precursors. This work is being extended
now to examine the prevalence of the mantle influence in such
rock suites. |
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2.
Genesis of Adakitic and Sanukitoid magmas
Some Na-rich felsic rocks (modern adakites and Archaean TTG
series) have trace-element characteristics that suggest high-pressure
origins of the magmas. There is an active debate about the tectonic
settings, source rocks and melting processes involved. With
Moyen (St Etienne, France), Petford (Northampton University,
UK) and Coldwell (Macquarie University, Australia) I am investigating
the genesis of these rocks, using a variety of geochemical,
petrographic and experimental techniques.
The peculiar “K-adakitic” rocks of China and the
Tibetan margin have similar geochemical characteristics to the
adakites and TTG rocks but, unlike these, they are relatively
potassic. The possible origins of these are being investigated
using field studies, petrology, geochemistry and experiments,
in association with Xiao and research students at the China
University of Geosciences (Wuhan).
Sanukitoids (potassic and magnesian granitoids) are another
early-Earth phenomenon, the generation of which has probable
important implications for the chemical and physical evolution
of the Archaean lithosphere. Petrological and experimental studies
of these unusual magmas are underway with collaborators Kovalenko
(St Petersburg, Russia) and Moyen (St Etienne). |
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| 3.
Genesis of Archaean Granitoids and Their Roles in Crustal
Evolution
The spectrum of TTG and more potassic granitic rocks that
occur in Archaean cratons is the subject of a number of petrological,
geochemical and experimental investigations with collaborators
Stevens and Moyen (St Etienne, France), and research students.
Uncovering the modes of formation of these magmas is providing
us with important insights into tectonic regimes and processes
that operated in the ancient Earth.
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4.
Mechanisms of Magma Ascent and Emplacement
Theoretical and modelling investigations of the processes involved
in the ascent of felsic magmas, and their emplacement as plutons,
especially in the upper crust, have provided us with some fundamental
constraints on the modes of fluid and magma transport in the
shallow lithosphere. Results of this work provide the springboard
for more detailed investigations into the physics of magma emplacement
and the interactions between successive magma batches, during
pluton construction. Collaborators here are Petford (Northampton),
Ablay (UK Ministry of Defence), Simakin (Chernogolovka, Russia)
and Kisters. |
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5.
The Configurations and Origins of Chemical Structure in Granitic
Plutons
Petrological, geochemical and rock magnetic techniques are being
used to map the internal compositional structure of plutonic
masses and to investigate the mechanisms by which granitic magmas
attain their compositional heterogeneity. Standard models that
invoke differentiation from a single parent magma seem to carry
little validity. Instead, granitic plutons appear to be constructed
by the amalgamation of numerous batches of contrasting magma,
whose composition depends mainly on the entrainment of peritectic
mineral phases (produced in melting reactions) and, in a minority
of cases, on mingling with mafic magmas. In related work we
are beginning to demonstrate that the compositions of both metaluminous
and peraluminous granitic magmas are tightly constrained by
the nature and proortions of peritectic minerals produced in
the melt-forming reactions. Benn (Ottawa, Canada), Helps (formerly
at Kingston University, UK), Petford (Northampton), Stevens
and Moyen (St Etienne) are the main collaborators. We hope to
discover the fundamental controls on the chemical structure
of the majority of granitic magmas. |
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6.
Equilibrium and the Kinetics of Partial Melting in Metasedimentary
Rocks
Much can learned from studying field occurrences of partially
melted metasedimentary rocks. Issues such as the controls on
the distribution of partial melt, their relationship to the
structures in the host rocks and the spatial mineralogical and
textural information are providing us (Kisters, Stevens, Buick)
with insights into the triggers for melting, the mechanisms
of melt segregation and the timing and modes of melt extraction
and magma formation. These field-based studies (e.g., in the
Damara of Namibia and the Limpopo Belt of South Africa) are
underpinned by experimental modelling of the processes involved,
with the aim of determining the effects of physicochemical variables.
The ultimate goal is to understand better the processes that
have led to crustal-scale compositional differentiation. |
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7.
High Pressure Melting Behaviour in Simple, Quartz-saturated,
Silicate-Volatile Systems
To accompany the above studies, it is necessary to investigate
melting in simplified systems, to isolate the effects of compositional
variables on the behaviour of rock systems undergoing anatexis.
The emphasis is on the melting of simple, analogue, rock systems
saturated with SiO2, as models for the behaviour of felsic igneous
rocks and metasediments. This work is in collaboration with
Stevens. |
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| Clemens,
J. D., Birch, W. D. and Dudley R. J. (2011) S-type
ignimbrites with polybaric crystallisation histories: the Tolmie
Igneous Complex, Central Victoria, Australia. Contrib. Mineral.
Petrol., DOI: 10.1007/s00410-011-0652-1. |
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| Coldwell,
B., Petford, N., Clemens, J.D., Barry, T. &
Ablay, G. 2011. Deep crustal melting in the Peruvian Andes:
Felsic magma generation during delamination and uplift. Lithos,
10.1016/j.lithos.2011.02.011. |
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| Clemens,
J. D. & Benn, K. (2010) Anatomy, emplacement and
evolution of a shallow-level, post-tectonic laccolith: the Mt
Disappointment pluton, SE Australia. Journal of the Geological
Society of London, 167: 915-941. |
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| Clemens,
J.D., Belcher, R.W. & Kisters, A.F.M. 2010. The
Heerenveen Batholith, Barberton Mountain Land, South Africa:
Mesoarchaean, Potassic, Felsic Magmas Formed by Melting of an
Ancient Subduction Complex. Journal of Petrology, 51(5), 1099-1120,
10.1093/petrology/egq014. |
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| Clemens,
J.D., Helps, P.A. & Stevens, G. 2010. Chemical
structure in granitic magmas – a signal from the source?
Earth and Environmental Science Transactions of the Royal Society
of Edinburgh, 100(1-2), 159-172, 10.1017/s1755691009016053. |
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| Clemens,
J. D., Darbyshire, D. P. F. & Flinders, J. (2009)
Sources of post-orogenic calcalkaline magmas: the Arrochar and
Garabal Hill-Glen Fyne complexes, Scotland. Lithos 112, 524–542. |
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| Clemens,
J. D. (2009) The message in the bottle: “Melt”
inclusions in migmatitic garnets. Geology 37, 671–672. |
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| Ablay,
G. J., Clemens, J. D. and Petford, N. (2008)
Large-scale mechanics of fracture-mediated felsic magma intrusion
driven by hydraulic inflation and buoyancy pumping, in Thomson,
K. and Petford, N. (eds), Structure and Emplacement of High-Level
Magmatic Systems, Geol. Soc. London Spec. Pub. 302: 3-29. |
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| Xiao,
L., Zhang, H. F., Clemens, J. D., Wang, Q.
W., Kan, Z. Z., Wang, K. M., Ni, P. Z. and Liu, X.M. (2007)
Late Triassic granitoids of the eastern margin of the Tibetan
Plateau: geochronology, petrogenesis and implications for tectonic
evolution. Lithos 96: 436-452. |
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| Xiao,
L. and Clemens, J. D. (2007) Origin of potassic
(C-type) adakite magmas: experimental and field constraints.
Lithos, 95: 399-414. |
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| Watkins,
J. M., Clemens, J. D. and Treloar, P. J. (2007)
Archaean TTGs as sources of younger granitic magmas: melting
of sodic metatonalites at 0.6 – 1.2 GPa. Contrib. Mineral.
Petrol., 154: 91-110. |
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| Clemens,
J. D., Yearron, L. M. and Stevens, G. (2006) Barberton
(South Africa) TTG magmas: Geochemical and experimental constraints
on source-rock petrology, pressure of formation and tectonic
setting. Precambrian Res. 151: 53-78. |
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Kovalenko,
A., Clemens, J. D. and Savatenkov, V. (2005)
Petrogenetic constraints for the genesis of Archaean sanukitoid
suites: geochemistry and isotopic evidence from Karelia, Baltic
Shield. Lithos 79: 147-160. |
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| Clemens,
J. D. (2006) Melting of the continental crust: fluid
regimes, melting reactions and source-rock fertility, in Brown,
M. and Rushmer, T. (eds) Evolution and Differentiation of the
Continental Crust, Cambridge University Press, pp. 397-331. |
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Brown,
M., Pitcher, W. S., Vernon, R. H. and Clemens, J.
D. (2005) Invited comments on Clemens’s ‘Granites
and granitic magmas’. Proc. Geol. Assoc. 116: 17-32. |
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| Clemens,
J. D. (2005) Granites and granitic magmas: strange
phenomena and new perspectives on some old problems. Proc. Geol.
Assoc. 116: 9-16. |
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| Droop,
G. T. R., Clemens, J. D. and Dalrymple, D.
J. (2003) Processes and conditions during contact anatexis,
melt escape and restite formation: the Huntly gabbro complex,
NE Scotland. J. Petrol. 44: 995-1029. |
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| Clemens,
J. D. (2003) S-type granitic magmas – petrogenetic
issues, models and evidence. Earth Sci. Rev. 61: 1-18. |
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| Finger,
F. and Clemens, J. D. (2002) Cadomian lower-crustal
contributions to Variscan granite petrogenesis (South Bohemian
Batholith, Austria): a comment. J. Petrol. 43, 1179-1181. |
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| Clemens,
J.D. & Watkins, J.M. 2001. The fluid regime of
high-temperature metamorphism during granitoid magma genesis.
Contributions to Mineralogy and Petrology, 140, 600-606. |
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| Clemens,
J.D. & Holness, M.B. 2000. Textural evolution and
partial melting of arkose in a contact aureole: a case study
and implications. Electronic Geosciences (now Visual Geosciences),
5, No 4. |
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| Petford,
N. & Clemens, J.D. 2000. Granites are not
diapiric! Geol. Today, September-October, 180-184. |
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| Roberts,
M.P., Pin, C., Clemens, J.D. & Pacquette,
J.L. 2000. Petrogenesis of mafic to felsic plutonic rock associations:
the Calc-alkaline Querigut Complex, French Pyrenees. Journal
of Petrology, 41, 809-844. |
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| Vigneresse,
J.L. & Clemens, J.D. 2000. Granitic magma
ascent and emplacement: neither diapirism nor neutral buoyancy.
Geological Society, London, Special Publications, 174(1), 1-19,
10.1144/gsl.sp.1999.174.01.01. |
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| Current
Postgraduate Students |
| Name |
Risa
Matsumura |
| Degree |
MSc
(Co-supervised with Prof Gary Stevens) |
| Thesis
Title |
The
Petrogenesis of the Nelshoogte Pluton, the Youngest TTG Magma
Body in the Barberton Granite-Greenstone Terrain |
| Current
Status |
In
progress |
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| Graduated
Postgraduate Students |
| Name |
Paul
Helps |
| Degree |
PhD
- Co-supervised with Prof N Petford (Bournemouth University,
UK) |
| Thesis
Title |
Scales
and Origins of Heterogeneities in Granitoid Magmas |
| Current
Status |
Degree
Awarded 2010 |
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| Name |
Beverley
Coldwell
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| Degree |
PhD
- Co-supervised with Prof N. Petford (Bournemouth University,
UK) and Dr P. Murphy (Kingston University, UK) |
| Thesis
Title |
Evolution
of the Peruvian subduction margin at 9°S: evidence from
geochemistry, experimental petrology and melt inclusion studies
on adakite-like ignimbrites |
| Current
Status |
Degree
Awarded 2008 |
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| Name |
Lorraine
M. Yearron
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| Degree |
PhD
- Co-supervised with Prof G. Stevens |
| Thesis
Title |
Archaean
granite petrogenesis and implications for the evolution of the
Barberton Mountain Land, South Africa |
| Current
Status |
Degree
Awarded 2003 |
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| Name |
Jennifer
M. Watkins
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| Degree |
PhD
- Co-supervised with Prof P. Treloar (Kingston University, UK) |
| Thesis
Title |
Crustal
melting processes and the formation of granulites and granites:
a study based on the Lewisian Complex, NW Scotland |
| Current
Status |
Degree
Awarded 2002 |
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| Name |
Stefano
Pugliese
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| Degree |
PhD
- Co-supervised with Prof. N. Petford (then of Kingston University,
UK) |
| Thesis
Title |
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| Current
Status |
Degree
Awarded 1996 |
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| Name |
Helen
Orme
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| Degree |
PhD
- Co-supervised with Prof. N. Petford (then of Kingston University,
UK) |
| Thesis
Title |
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| Current
Status |
Degree
Awarded 1996 |
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| Name |
James
Flinders
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| Degree |
PhD
- Co-supervised with Prof. N. Petford (then of Kingston University,
UK) |
| Thesis
Title |
A
study of the Arrochar-Garabal Hill and Glen Fyne intrusions,
southwest Grampians, Scotland |
| Current
Status |
Degree
Awarded 1996 |
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| Name |
Gary
Stevens
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| Degree |
PhD
- Co-supervised with Dr G. T. R. Droop (Manchester University,
UK) |
| Thesis
Title |
Compositional
controls on partial melting in high-grade metapelites; a petrological
and experimental study |
| Current
Status |
Degree
Awarded 1995 |
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| Name |
David
Dalrymple
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| Degree |
PhD
- Co-supervised with Dr G. T. R. Droop (Manchester University,
UK) |
| Thesis
Title |
Contact
anatexis of Dalradian metapelites from the Huntly-Knock area,
Aberdeenshire, NE Scotland |
| Current
Status |
Degree
Awarded 1995 |
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| Name |
Malcolm
P. Roberts
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| Degree |
PhD |
| Thesis
Title |
Petrogenetic
relationships between diorites, ultramafic rocks, granites and
their enclaves, Quérigut Massif, French Pyrenees |
| Current
Status |
Degree
Awarded 1994 |
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