Marc Jolivet

Most of the hydrothermal uranium (U) deposits from the European Hercynian belt (EHB) are spatially associated with Carboniferous peraluminous leucogranites. In the southern part of the Armorican Massif (French part of the EHB), the Guérande peraluminous leucogranite was emplaced in an extensional deformation zone at ca. 310 Ma and is spatially associated with several U deposits and occurrences. The apical zone of the intrusion is structurally located below the Pen Ar Ran U deposit, a perigranitic vein-type deposit where mineralization occurs at the contact between black shales and Ordovician acid metavolcanics. In the Métairie-Neuve intragranitic deposit, uranium oxide-quartz veins crosscut the granite and a metasedimentary enclave.
Airborne radiometric data and published trace element analyses on the Guérande leucogranite
suggest significant uranium leaching at the apical zone of the intrusion. The primary U enrichment in
the apical zone of the granite likely occurred during both fractional crystallization and the interaction
with magmatic fluids. The low Th/U values (< 2) measured on the Guérande leucogranite likely
favored the crystallization of magmatic uranium oxides. The oxygen isotope compositions of the
Guérande leucogranite (δ18Owhole rock = 9.7 – 11.6 ‰ for deformed samples and δ18Owhole rock = 12.2 - 13.6 ‰ for other samples) indicate that the deformed facies of the apical zone underwent subsolidus
alteration at depth with oxidizing meteoric fluids. Fluid inclusion analyses on a quartz comb
from a uranium oxide-quartz vein of the Pen Ar Ran deposit show evidence of low-salinity fluids (1-6
wt.% NaCl eq.), in good agreement with the contribution of meteoric fluids. Fluid trapping
temperatures in the range of 250-350°C suggest an elevated geothermal gradient, probably related
to regional extension and the occurrence of magmatic activity in the environment close to the
deposit at the time of its formation. U-Pb dating on uranium oxides from the Pen Ar Ran and
Métairie-Neuve deposits reveal three different mineralizing events. The first event at 296.6 ± 2.6 Ma
(Pen Ar Ran) is sub-synchronous with hydrothermal circulations and the emplacement of late
leucogranitic dykes in the Guérande leucogranite. The two last mineralizing events occur at 286.6 ±
1.0 Ma (Métairie-Neuve) and 274.6 ± 0.9 Ma (Pen Ar Ran), respectively. Backscattered uranium oxide
imaging combined with major elements and REE geochemistry suggest similar conditions of
mineralization during the two Pen Ar Ran mineralizing events at ca. 300 Ma and ca. 275 Ma, arguing
for different hydrothermal circulation phases in the granite and deposits. Apatite fission track dating
reveals that the Guérande granite was still at depth and above 120°C when these mineralizing events
occurred, in agreement with the results obtained on fluid inclusions at Pen Ar Ran.
Based on this comprehensive data set, we propose that the Guérande leucogranite is the main
source for uranium in the Pen Ar Ran and Métairie-Neuve deposits. Sub-solidus alteration via
surface-derived low-salinity oxidizing fluids likely promoted uranium leaching from magmatic
uranium oxides within the leucogranite. The leached out uranium may then have been precipitated in the reducing environment represented by the surrounding black shales or graphitic quartzites. As
similar mineralizing events occurred subsequently until ca. 275 Ma, meteoric oxidizing fluids likely
percolated during the time when the Guérande leucogranite was still at depth. The age of the U
mineralizing events in the Guérande region (300 – 275 Ma) are consistent with those obtained on
other U deposits in the EHB and could suggest a similar mineralization condition, with long-term
upper to middle crustal infiltration of meteoric fluids likely to have mobilized U from fertile
peraluminous leucogranites during the Late Carboniferous to Permian crustal extension events.

Authigenic 10 Be/ 9 Be dating method was applied to lacustrine, deltaic and alluvial sequences of the northern Dan-ube Basin (Pannonian Basin System), to bridge the insufficiency of geochronological data for the Late Miocene to Pliocene period. The measurements of 51 samples (both lacustrine and floodplain), ranging from 11.6 to 0.95 Ma are consistent with the existing magnetostratigraphic and biostratigraphic data standing mainly on the evolution degree of endemic mollusk fauna, mammals and dinocysts. This agreement confirms our assumption that the incoming beryllium fluxes remained constant over the studied time period and thus that the two initial 10 Be/ 9 Be ratios determined in actual Holocene/Late Pleistocene sediments (lacustrine and floodplain) are valid for these environments. The obtained ages indicate gradual progradation of the deltaic depositional systems across the Danube Basin with a clear time-transgressional character, replacing basin floor and shelfal environments. Deltaic sedimentation occurred firstly in the north at foothills of the Western Carpathians from 11.0 Ma, and changed to the alluvial environment after 10.5 Ma. At the same time (~10.5 Ma), the paleo-Danube deltaic system draining the Eastern Alps entered the study area from the Vienna Basin situated on the West. Later, the deltaic systems were merged in the central part of the basin and reached its southeastern margin at ~9.4 Ma. Regression of the Lake Pannon from the southernmost part of the study area is evidenced after 8.7 Ma. Alluvial deposition of meandering rivers lasting until 6.0–5.0 Ma followed and was interrupted by the early Pliocene basin inversion. Sedimentation of braided streams took place during the late Pliocene and Pleistocene, reflecting uplift of mountains surrounding the basin margins. This study documents the powerful potential of the authigenic 10 Be/ 9 Be dating method and its reliability in a basin with complicated tectonic and sedimentary history. It demonstrates that this method can effectively be applied to lacustrine and floodplain deposits and to samples from outcrops as well as boreholes.

The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia
convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation
in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd
system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower – Middle
Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without
major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface
that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present
summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement
produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift
phase probably started at 5±3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in
Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan
front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly
higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the
massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries.

This paper reports isotopic, major and minor element geochemistry of igneous and metamorphic rocks from the Kokoxili and Yushu regions of central and eastern Tibet. The first region lies along the Kunlun suture, which separates the Bayan Har-Songpan Ganze (Songpan) terrane from the Tarim and Qaidam blocks. Two Kokoxili granitoids yield U-Pb zircon dates of 217 +/- 10 and 207

Received 13 November 2006; revised 21 May 2007; accepted 6 June 2007; published 28 September 2007. [1] In this work we combined apatite fission track and biotite/K-feldspar 40Ar/39Ar ages with tectonic data in the west central part of the Axial Zone of the Pyrenees. We discuss ...

The concentrations of atmospheric cosmogenic 10Be normalized to the solubilized fraction of its stable isotope 9Be have been measured in the authigenic phase leached from silicated continental sediments deposited since the upper Miocene in the northern Chad Basin. This method is validated by the systematic congruence with the biochronological estimations based on the fossil mammal evolutive degree of faunal assemblages.

Multi-system geochronology was used to unravel the long and complex thermal history of the Song Chay range (Northern Vietnam), a high-grade granitic and metamorphic dome in the vicinity of the Cenozoic, Ailao Shan–Red River fault zone. It was considered to be Proterozoic South China basement, but its geological history was basically unknown. Scattered field observations suggest three episodes of high-temperature

Apatite fission track analysis (AFTA) data are used to bring new light on the long-term and recent history of the Baikal rift region (Siberia). We describe the evolution of the topography along a NW-SE profile from the Siberian platform to the Barguzin range across the Baikal-southern Patom range and the northern termination of Lake Baikal. Our results show that the

ABSTRACT New U-Pb monazite, zircon, and xenotime ages date the Late Carboniferous crystallization of the anatectic Vialais granite in the Montagne Noire Axial Zone and the hightemperature deformation and metamorphism of the augen gneiss (Ordovician granite protolith) from which the granite was likely derived. The U-Pb monazite ages obtained from the augen gneiss (308±3 Ma), late kinematic Vialais granite (303±4 Ma), and post-kinematic leucogranite (298±2 Ma), bracket the high-temperature deformation and metamorphism at ~ 310-300 Ma, clearly postdating regional contraction and nappe emplacement (&amp;gt; 320 Ma). The planar-linear and locally linear fabrics in the augen gneiss outline a regional-scale double dome structure (Caroux and Espinouse sub-domes) containing smaller (km-scale) upright folds. Compared to the Caroux sub-dome, the larger, migmatitic Espinouse sub-dome contains abundant leucosome, leucogranite bodies and late-kinematic intrusions (Vialais granite). The Vialais granite displays a weak magmatic foliation that defines the main layering of the Espinouse migmatite. Ellipsoidal quartz-sillimanite nodules concentrated above the roof of the granite recorded an increment of strain (vertical shortening, E-NE elongation) during granite emplacement and crystallization, consistent with the extension event that exhumed the domes. These new geochronological and structural data suggest that the Montagne Noire double dome formed in a pull-apart structure within a dextral strike-slip system. Upright folding in the sub-domes has been traditionally assigned to a regional contraction event; alternatively, we propose that local contraction is associated with the convergence of low-viscosity crust beneath the upper crust pull-apart. Dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low-viscosity orogenic crust converging and rising to fill the gap created by upper crust extension. This interpretation solves the long-standing problem of apparent coeval contraction and extension in the Montagne Noire double dome and establishes migmatite dome emplacement in strike-slip corridors as a style of late Variscan tectonics.

The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay,