TY - JOUR A1 - Berger, Alfons A1 - Bousquet, Romain A1 - Engi, Martin A1 - Janots, Emilie A1 - Rubatto, Daniela A1 - Schmid, Stefan A1 - Wiederkehr, Michael T1 - Transport of heat and mass in a Barrovian belt : what do we know from nature? Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00167037 U6 - https://doi.org/10.1016/j.gca.2009.05.002 SN - 0016-7037 ER - TY - JOUR A1 - Berger, Alfons A1 - Schmid, Stefan M. A1 - Engi, Martin A1 - Bousquet, Romain A1 - Wiederkehr, Michael T1 - Mechanisms of mass and heat transport during Barrovian metamorphism: A discussion based on field evidence from the Central Alps (Switzerland/northern Italy) JF - Tectonics N2 - Tectonic and metamorphic data for the Central Alps (Switzerland/Italy) are used to discuss this classic example of a Barrovian metamorphic terrain, notably the evolution of its thermal structure in space and time. Available P-T-t data indicate variable contributions of advective and conductive heat transport during collision and subsequent cooling and exhumation. Some areas experienced a prolonged period of partial melting while other areas, at the same time, show but moderate heating. The Barrow-type metamorphic field gradient observed in the final orogen is the result of two distinct tectonic processes, with their related advective and conductive heat transport processes. The two tectonic processes are (1) accretion of material within a subduction channel related to decompression and emplacement of high-pressure units in the middle crust and (2) wedging and related nappe formation in the continental lower plate. The second process postdates the first one. Wedging and underthrusting of continental lower plate material produces heat input into lower crustal levels, and this process is responsible for predominantly conductive heat transport in the overlying units. The interacting processes lead to different maximum temperatures at different times, producing the final Barrovian metamorphic field gradient. The south experienced rapid cooling, whereas the north shows moderate cooling rates. This discrepancy principally reflects differences in the temperature distribution in the deeper crust prior to cooling. Differences in the local thermal gradient that prevailed before the cooling also determined the relationships between cooling rate and exhumation rate in the different areas. Citation: Berger, A., S. M. Schmid, M. Engi, R. Bousquet, and M. Wiederkehr (2011), Mechanisms of mass and heat transport during Barrovian metamorphism: A discussion based on field evidence from the Central Alps (Switzerland/northern Italy), Tectonics, 30, TC1007, doi:10.1029/2009TC002622. Y1 - 2011 U6 - https://doi.org/10.1029/2009TC002622 SN - 0278-7407 VL - 30 IS - 2 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Schmitz, Sylvia A1 - Moeller, Andreas A1 - Wilke, Max A1 - Malzer, Wolfgang A1 - Kanngiesser, Birgit A1 - Bousquet, Romain A1 - Berger, Alfons A1 - Schefer, Senecio T1 - Chemical U-Th-Pb dating of monazite by 3D-Micro X-ray fluorescence analysis with synchrotron radiation N2 - A confocal set-up for three-dimensional (3D) micro X-ray fluorescence (micro-XRF) was used at the mySpot beamline at BESSY II, which allows compositional depth profiling for various applications. We present results obtained with a confocal 3D micro-XRF set-up for chemical age dating using the U, Th and Pb concentrations of monazite within rock thin sections. The probing volume was determined to be approximately 21 x 21 x 24 mu m(3) for W-L alpha using an excitation energy of 19 keV. The relative detection limits particularly for Pb are below 10 ppm (for Counting times Y1 - 2009 UR - http://eurjmin.geoscienceworld.org/ U6 - https://doi.org/10.1127/0935-1221/2009/0021-1964 SN - 0935-1221 ER - TY - JOUR A1 - Wiederkehr, Michael A1 - Bousquet, Romain A1 - Ziemann, Martin Andreas A1 - Berger, Alfons A1 - Schmid, Stefan M. T1 - 3-D assessment of peak-metamorphic conditions by Raman spectroscopy of carbonaceous material an example from the margin of the Lepontine dome (Swiss Central Alps) JF - International journal of earth sciences N2 - This study monitors regional changes in the crystallinity of carbonaceous matter (CM) by applying Micro-Raman spectroscopy to a total of 214 metasediment samples (largely so-called Bundnerschiefer) dominantly metamorphosed under blueschist- to amphibolite-facies conditions. They were collected within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across refolded nappe contacts, both along and across strike within the northeastern margin of the Lepontine dome and adjacent areas. Further to the northeast, the isotemperature contours reflect temperatures reached during the Late Eocene subduction-related blueschist-facies event and/or during subsequent near-isothermal decompression; these contours appear folded by younger, large-scale post-nappe-stacking folds. A substantial jump in the recorded maximum temperatures across the tectonic contact between the frontal Adula nappe complex and surrounding metasediments indicates that this contact accommodated differential tectonic movement of the Adula nappe with respect to the enveloping Bundnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene time. KW - HP-metamorphism KW - Barrovian metamorphism KW - Graphitization KW - Metasediments KW - Micro-Raman spectroscopy KW - Central Alps Y1 - 2011 U6 - https://doi.org/10.1007/s00531-010-0622-2 SN - 1437-3254 VL - 100 IS - 5 SP - 1029 EP - 1063 PB - Springer CY - New York ER - TY - JOUR A1 - Wiederkehr, Michael A1 - Sudo, Masafumi A1 - Bousquet, Romain A1 - Berger, Alfons A1 - Schmid, Stefan M. T1 - Alpine orogenic evolution from subduction to collisional thermal overprint : the Ar-40/Ar-39 age constraints from the Valaisan Ocean, central Alps N2 - The investigated HP/LT metasedimentary units of the Valaisan and adjacent European domains occupy a key position in the Alpine belt for understanding the transition from early subduction-related HP/LT metamorphism to collision-related Barrovian overprint and the evolution of mountain belts in general. The timing of high-pressure metamorphism, subsequent retrogression and following Barrow-type overprint was studied by Ar-40/Ar-39 dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry, texture and associated mineral assemblages. Four distinct age populations of white mica record peak pressure conditions (42-40 Ma) and several stages of subsequent retrograde metamorphic evolution (36-25 Ma). Biotite isotopic analyses yield consistent apparent ages that cluster around 18-16 Ma for the Barrow-type thermal overprint. The recorded isotopic data reveal a significant time gap in the order of some 20 Ma between subduction-related HP/LT metamorphism and collision-related Barrovian overprint, supporting the notion of a polymetamorphic evolution associated with a bimodal P-T path. Y1 - 2009 UR - http://www.agu.org/journals/tc/ U6 - https://doi.org/10.1029/2009tc002496 SN - 0278-7407 ER -