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U R R E N T P R O J E C T S |
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Kathodolumineszenz-Bilder
von Zirkonen
FOTOS:
BERNHARD SCHULZ
|
 EMP-dating
of monazite in the Austroalpine basement
to the south of the Tauern Window. |
| In
cooperation with F. Finger from Institut für Mineralogie, Salzburg. |
| Isotope
geochemistry of meta-magmatites and pre-Variscan geodynamics in the
Austroalpine basement to the south of the Tauern Window, Eastern Alps. |
| Analytical
techniques: Radiometric dating by Pb-Pb single zircon evaporation;
XRF whole-rock geochemistry, REE geochemistry, Rb-Sr and Sm-Nd whole
rock geochemistry. - Deutsche Forschungsgemeinschaft (Schu 676/8),
in cooperation with Isotopengeochemisches Labor, Institut für Mineralogie,
TU Bergakademie Freiberg/Sachsen and Institut für Geologie und Dynamik
der Lithosphäre, Göttingen). |
| Geological
mapping and presentation of the official geological map of Blatt 178
Hopfgarten in Defereggen (Eastern Tyrol, Austria). |
| XIn
cooperation with S. Siegesmund, Institut für Geologie und Dynamik
der Lithosphäre, Göttingen, and financed through Österreichische Geologische
Bundesanstalt. |
| Oxygen
isotopes in quartz during crystallization and deformation of veins,
Belle-Ile, Southern Brittany. |
| Analytical
techniques: Laser extraction, fluid inclusion microthermometry. -
Deutsche Forschungsgemeinschaft (Schu 676/6), in cooperation with
Institut de Minéralogie Lausanne, Institut für Mineralogie TU Bergakademie
Freiberg/Sachsen and with C. Audren from Géosciences Rennes. |
| P-T-paths
of glaucophane-eclogites and blueschists in Ile de Groix, Southern
Brittany. |
| Analytical
techniques: Microprobe analyses and thermobarometry. - Deutsche Forschungsgemeinschaft
(Schu 676/6), in cooperation with C. Audren from Géosciences Rennes. |
|
P R O J E C T S I N P R E P A R A T I O N |
| Variscan
vs Cadomian geodynamics in the Léon region, Brittany, France. |
| In
cooperation with C. Audren from Géosciences Rennes. |
| Role
of fluid phase during generation, emplacement and deformation of Permian
pegmatites in the Austroalpine basement, Eastern Alps. |
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| A
B S T R A C T S O F R E C E N T P U B L I C A T
I O N |
| Lucks,
H., Schulz, B., Audren, C. & Triboulet, C. (2003): Variscan P-T evolution
of garnet pyroxenites and amphibolites in the Baie d'Audierne metamorphic
series, Southern Brittany (France). - In: Martinez-Catalán, J. R.,
Hatcher, R. D., Arenas, R., & Diaz Garcia, F. (Eds): Variscan Appalachian
dynamics: the building of the Upper Palaeozoic basement; Geological
Society of America Special Paper, (in press). |
| In
the Baie d´Audierne of the South Armorican Domain, an intermediate
metabasic-ultrabasic complex with isolated garnet pyroxenite lenses
is exposed between upper and lower metasedimentary units. Metabasites
in all units show geochemical characteristics similar to MOR-magmatites.
Garnets in pyroxenites are zoned with increasing XMg from cores to
rims and coexist with clinopyroxene (Jd10 to Jd33) and plagioclase
(An17 to An35) of a mineral assemblage M1. Maximal P-T conditions
of the M1 metamorphism range between 800 °C/14 kbar and 950 °C/19
kbar in different garnet pyroxenite lenses. The HP-HT rocks were overprinted
by an assemblage M2 with Ca-amphiboles. One observes brown-green tschermakitic
Ti-hornblende in some cores and core-to-rim zonations from actinolite
to tschermakite. Increasing AlIV and AlVI toward the rims of green
amphiboles signalize increase of P and T from < 500 °C/3 kbar up to
680 °C/9 kbar. In the metabasites of the lower metasedimentary unit,
the Ca-amphiboles display similar zonation trends from actinolite
cores to tschermakite rims, and a similar prograde P-T path up to
630 °C/6 kbar. Amphibolites in the upper metasedimentary unit show
brown-green amphibole, interpreted as magmatic relict. Zonations from
actinolite to magnesio-hornblende surround these cores and recorded
prograde P-T paths up to 550 °C/5 kbar. The HP-HT rocks were welded
with the metasedimentary units at the end of the first decompression
path M1-M2. Subsequently the units underwent new burial and heating
along an amphibolite-facies P-T cycle M2. The present metamorphic
configuration could be the consequence of thrusting at a late stage
of M2. This two-stage metamorphic history predates late-Variscan granite
intrusions and differs from P-T paths of other Armorican high-pressure
units. |
| Schulz,
B., Audren, C. & Triboulet, C. (2002): Oxygen isotope record of fluid-rock-SiO2
interaction during Variscan progressive quartz veining and deformation
in the meta-volcanosediments of Belle-Ile (Southern Brittany). - J.
Struct. Geol. (in press). |
| Belle-Ile
in the South Armorican Domain is composed of Palaeozoic volcano-detrital
sequences with sericite phyllites and porphyroids. Fine-banded and
folded meta-tuffites, microquartzites and graphitic quartzites occur
in the basal part at Plage de Bordardoué. Phengite compositions constrain
that Variscan metamorphism did not exceed 430 °C/4.5 kbar. Four generations
(1 - 4) of cm-thick quartz veins were precipitated during Variscan
progressive deformation and recorded changing fluid compositions.
Values of 26 ‰ d 18OSMOW in vein 1 quartz exceed high d 18OSMOW in
the host rocks. Decrease of quartz d 18OSMOW from margins to centers
can be observed from the syntaxial veins. Younger veins 4 have lower
d 18O. Their inclusions indicate lower salinities and traces of CH4
in the fluid when compared to veins 1. Veins 1 were overprinted by
shearing and fissuring. Subgrain rotation recrystallization occurred
along briquette structures and subgrain boundaries. The initial isotope
values have been preserved. Larger domains with small-grained quartz
can be identified by lower values d 18O. Homogeneous isotopic compositions
are found in hinges of folded veins 2 with grain boundary migration
recrystallization. The small-scale oxygen isotope variations and the
changing fluid compositions point to a locally hosted fluid system
with limited contribution of meteoric water during multiphase deformation
and vein formation. |
| Schulz,
B., Siegesmund, S., Steenken, A., Schönhofer, R & Heinrichs, T. (2001):
Geologie des ostalpinen Kristallins südlich des Tauernfensters zwischen
Virgental und Pustertal. - Z. dt. geol. Ges., 152, 261-307. |
|
Das
ostalpine Kristallin südlich des Tauernfensters war Teil peri-Gondwanas
und wird aus den prä-oberordovizischen Serien des Altkristallins
und der vermutlich altpaläozoischen Phyllit-Einheit des Thurntaler
Komplexes aufgebaut. Hornblende-Plagioklas-Gneise des nördlichen
Altkristallins zeigen geochemische Signaturen von Volcanic-Arc-Basalten.
Die Amphibolite gliedern sich in Gruppen mit N-MORB-, MORB- und
WPB-Charakter. Die vermutlich jüngste Gruppe dieser prä-variskischen
Magmatite bilden oberordovizisch intrudierte Granitoide. Orthogneise
vom Typ Antholz entstanden anatektisch aus krustalen Protolithen
und sind teils stark peralumine synkollisionale S-Typ-Granitoide.
Orthogneise vom Typ Gsies dagegen sind schwach peralumine bis metalumine
hoch-K-haltige Meta-Granodiorite und könnten aus Unterkrustengesteinen
einer älteren Vulkanbogen-Assoziation erschmolzen worden sein. Bei
der variskischen Kollision erfuhren die Altkristallin-Serien eine
amphibolitfazielle Metamorphose, zuerst druckbetont mit Kristallisation
von Granat, Kyanit, Staurolith und dann später Sillimanit und Andalusit.
Mehrphasige Deformation durch nonkoaxiale Scherung mit Bildung von
Futteralfalten und nachfolgender örtlich steilachsiger Verfaltung
begleitete die variskische Metamorphose.Tschermakitische Hornblende
und Oligoklas belegen eine epidot-amphibolitfazielle variskische
Metamorphose von Metabasiten im Thurntaler Komplex. Domänenweise
duktile alpidische Überprägung unter grünschieferfaziellen Bedingungen
ist an teilweise foliierten Pegmatiten wahrscheinlich permischen
Alters im nördlichen Altkristallin erkennbar. Im Oligozän intrudierte
der Rieserferner-Tonalit in eine sich unter sinistraler Scherung
entlang der Defereggen-Antholz-Vals-Linie und ihren Nebenlinien
öffnenden Pull-Apart-Struktur.
The
Austroalpine basement to the south of the Tauern Window was part
of peri-Gondwana and is assembled by the pre-Upper-Ordovician sequences
of the "Altkristallin" and the presumably Early-Palaeozoic phyllitic
Thurntal Complex. Hornblende-plagioclase-gneisses of the northern
Altkristallin display geochemical signatures of volcanic arc basalts.
Amphibolites belong to distinct groups with the character of N-MORB,
MORB and within-plate alkaline basalts. Granitoids of Upper-Ordovician
age, now orthogneisses, are probably the youngest group among these
meta-magmatites. Orthogneisses of type Antholz are highly peraluminous
syncollisional S-type granitoids, which were generated by the partial
anatexis of crustal protoliths. In contrast, orthogneisses of type
Gsies are former peraluminous to metaluminous high-K-granitoids
of which magmatic source could have been the lower crustal rocks
of a volcanic arc association. During the Variscan collision, the
Altkristallin rocks underwent an amphibolite-facies metamorphism,
at first pressure-dominated with crystallization of garnet, staurolite,
kyanite, and later sillimanite and andalusite. Variscan metamorphism
was coeval with polyphase deformation by noncoaxial shear with formation
of sheath folds and later folding around steeply plunging axes.
Crystallization of tschermakitic amphibole with oligoclase in metabasites
gives evidence of an epidote-amphibolite-facies Variscan metamorphism
of the Thurntal Complex. Ductile Alpine overprinting under greenschist-facies
conditions in the northern Altkristallin is indicated by foliated
pegmatites of probably Permian age. In the Oligocene, the Rieserferner
tonalite intruded in a pull-apart structure which was generated
during sinistral shearing along the Defereggen-Antholz-Vals line.
|
| Schulz,
B., Triboulet, C., Audren, C., Gilg, A. & Pfeifer, H.-R. (2001): Two-stage
prograde and retrograde Variscan metamorphism of glaucophane-eclogites,
blueschists and greenschists from Ile de Groix, Brittany. - Intern.
Journ. Earth Sciences (Geol. Rdsch), 90, 871-889. |
| On
Ile de Groix, Variscan metamorphic former tholeiitic and alkaline
basalts occur as glaucophane-eclogites, blueschists and greenschists
in isolated lenses and layers within metapelites. Whole-rock d 18OSMOW
values of the metabasites show limited variations (10.4 - 12.0 ‰)
and no systematic differences among rock types and metamorphic grades.
This provides no argument for large-scale blueschist-to-greenschist
transformation driven by infiltration of externally derived fluids.
Metamorphic mineralogical changes should have been triggered by internal
fluids. Element variations in interlayered blue- and greenschists
can be attributed to magmatic fractionation. Assemblages with garnet,
clinopyroxene and glaucophane of a HP-LT metamorphism M1, and NaCa-amphiboles
(barroisite, magnesio-hornblende, actinolite) of a MP-MT metamorphism
M2 crystallized during deformation D1. Detailed core-rim zonation
profiles display increasing and then decreasing AlIV in glaucophane
of M1. NaCa-amphiboles of M2, mantling glaucophane and crystallized
in porphyroblasts, show first increasing, then decreasing AlIV and
AlVI. Empirically calibrated thermobarometers allowed P-T path reconstructions.
In glaucophane-eclogites of a metamorphic zone I, a prograde evolution
to M1 peak conditions at 400 - 500 °C/10 - 12 kbar was followed by
a retrograde P-T path within the glaucophane stability field. The
subsequent M2 evolution was again prograde up to >600 °C at 8 kbar
and then retrograde. Similarly, in metamorphic zones II and III, prograde
and retrograde paths of M1 and M2 at lower maximal temperatures and
pressures exist. The almost complete metamorphic cycle during M2 signalizes
that the HP-LT rocks escaped from an early erosion by a moderate second
burial event and explains the long-lasting slow uplift with low average
cooling rates. |
| Schulz,
B., Triboulet, C., Audren, C. & Feybesse, J.-L. (2001): P-T paths
from metapelite garnet zonations, and crustal stacking in the Variscan
inverted metamorphic sequence of La Sioule, French Massif Central.
- Z. dt. geol. Ges., 152, 1 - 25. |
| In
the La Sioule region (Northern French Massif Central), a Variscan
inverted metamorphic sequence around the GPF Echassières drilling
site is made up by high-grade gneiss units which overlie amphibolite-facies
micaschists. Metapelite garnets crystallized during formation of foliations
S1 - S1i - S2. In the lithological units, different Mg, Fe, Mn and
Ca evolution trends are observed in growth-zoned garnets. Geothermobarometers
based on cation exchange and net transfer reactions were applied to
local equilibria of garnet, mica, plagioclase, defined by microstructures
and mineral zonation trends. This led to syndeformational P-T paths
for successive stages of mineral growth and foliation development.
Planar and linear mesoscopic structures are partly related to the
prograde metamorphism and the process of crustal contraction. Different
shapes of P-T paths and peak temperatures in the units confirm an
inverted metamorphic sequence. Kinematics of the synmetamorphic structures
suggest a two-stage evolution. In a northern structural domain, top-to-WNW
shearing ceased at medium pressures and peak temperatures. During
further decompression, the units were stacked into an inverted metamorphic
pile. In the southern domain, this nappe pile was modified and overprinted
by top-to-SE thrusting at lower pressures. Large similarities of P-T
paths from the metamorphic sequences of the La Sioule and Haut Allier
regions support a major allochthony of the Upper and Lower Gneiss
Units in the French Massif Central. |
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