Thermochronometric evidence of far-field stress transfer in continental collisions

In this dissertation, two low-temperature thermochronometers [fission-track analysis on apatite and (U-Th)/He analyses on zircons] are applied on various tectonostratigraphic units from three collisional settings: (i) the Bitlis-Pütürge Massif (SE Turkey), (ii) the Lesser Caucasus (Georgia, Armenia, Azerbaijan), and (iii) the Strandja Massif (SE Bulgaria and NW Turkey). The aim of the study is to better understand the syn- and post-collisional thermochronological evolution of collisional orogens, thus elucidating the dynamics of stress partitioning and transmission during continental collisions. Another focal point of this study is to constrain better the timing of the Arabia-Eurasia collision in the area of its maximum indentation and clarify the overall evolution of the area. From a general viewpoint, our dataset for the Eurasian foreland north of the Arabia-Eurasia collision (the Bitlis-Pütürge Massif and the Lesser Caucasus region) suggest that the tectonic stresses related to the collision during mid-Miocene time were transmitted efficiently over large distances, focusing preferentially at rheological discontinuities located as far as the Lesser Caucasus and the Eastern Pontides. Since the late Middle Miocene a new tectonic regime is active as the westward translation of Anatolia is accommodating most of the Arabia-Eurasia convergence, thus decoupling the foreland from the orogenic wedge and precluding efficient northward stress transfer. In the Strandja Massif the mechanism of stress transmission was very different. The bulk of the massif has escaped significant Alpine-age deformation, which is recorded only in the northern sector. We argue that in the Strandja orogen the stress mostly bypassed the orogenic prism and focused on the Srednogorie rift basin to the north, rheologically weakened by previous Late Cretaceous back-arc extension

Increased erosion of high-elevation land during late Cenozoic: evidence from detrital thermochronology off-shore Greenland

Mountain regions at high altitudes show deeply incised glacial valleys that coexist with a high-standing low-relief landscape, whose origin is largely debated. Whether the plateaus contributed to sediment production during the late Cenozoic is a currently debated issue in glacial geomorphology and paleoclimatology. In this study, we used detrital apatite fission-track dating of marine sediments to trace provenance and spatial variation in focused erosion over the last 7 million years. The decomposition of age distributions into populations reveals that, moving upwards through the sections, two young populations get younger, while two older populations get progressively older. We interpreted these trends as the effect of glacial erosion on the valley floors and an increased sediment contribution from the high elevations. To test this hypothesis, we compared the measured ages with synthetic age distributions, which represented a change in the elevation of focused erosion. We conclude that the central-eastern Greenland region is the main source of sediments, and in addition to enhanced valley incision, sediments have also been sourced from progressively higher elevations since 7 Ma. The ageing trend provides an unusual case in detrital thermochronology and a strong evidence that intensified Quaternary glaciations amplify the erosional process both in valley bottoms and at high elevations

Topography, structural and exhumation history of the Admiralty Mountains region, northern Victoria Land, Antarctica

International audienceThe Admiralty Mountains region forms the northern termination of the northern Victoria Land, Antarctica. Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the Antarctic plate, where the Admiralty Mountains region forms the northern termination of the western shoulder of the Mesozoic-Cenozoic West Antarctica Rift System. In this study we combine new low-temperature thermochronological data (apatite fission-track and (U-Th-Sm)/He analyses) with structural and topography analysis. The regional pattern of the fission-track ages shows a general tendency to older ages (80-60 Ma) associated with shortened mean track-lengths in the interior, and younger fission-track ages clustering at 38-26 Ma with long mean track-lengths in the coastal region. Differently from other regions of Victoria Land, the younger ages are found as far as 50-70 km inland. Single grain apatite (U-Th-Sm)/He ages cluster at 50-30 Ma with younger ages in the coastal domain. Topography analysis reveals that the Admiralty Mountains has high local relief, with an area close to the coast, 180 km long and 70 km large, having the highest local relief of >2500 m. This coincides with the location of the youngest fission-track ages. The shape of the area with highest local relief matches the shape of a recently detected low velocity zone beneath the northern TAM, indicating that high topography of the Admiralty Mountains region is likely sustained by a mantle thermal anomaly. We used the obtained constraints on the amount of removed crustal section to reconstruct back-eroded profiles and calculate the erosional load in order to test flexural uplift models. We found that our back-eroded profiles are better reproduced by a constant elastic thickness of intermediate values (Te = 20-30 km). This suggests that, beneath the Admiralty Mountains, the elastic properties of the lithosphere are different with respect to other TAM sectors, likely due to a stationary Cenozoic upper mantle thermal anomaly in the region

Unravelling the Structural and Molecular Basis Responsible for the Anti-Biofilm Activity of Zosteric Acid.

The natural compound zosteric acid, or p-(sulfoxy)cinnamic acid (ZA), is proposed as an alternative biocide-free agent suitable for preventive or integrative anti-biofilm approaches. Despite its potential, the lack of information concerning the structural and molecular mechanism of action involved in its anti-biofilm activity has limited efforts to generate more potent anti-biofilm strategies. In this study a 43-member library of small molecules based on ZA scaffold diversity was designed and screened against Escherichia coli to understand the structural requirements necessary for biofilm inhibition at sub-lethal concentrations. Considerations concerning the relationship between structure and anti-biofilm activity revealed that i) the para-sulfoxy ester group is not needed to exploit the anti-biofilm activity of the molecule, it is the cinnamic acid scaffold that is responsible for anti-biofilm performance; ii) the anti-biofilm activity of ZA derivatives depends on the presence of a carboxylate anion and, consequently, on its hydrogen-donating ability; iii) the conjugated aromatic system is instrumental to the anti-biofilm activities of ZA and its analogues. Using a protein pull-down approach, combined with mass spectrometry, the herein-defined active structure of ZA was matrix-immobilized, and was proved to interact with the E. coli NADH:quinone reductase, WrbA, suggesting a possible role of this protein in the biofilm formation process

Synthetic scheme of compounds 23, 24, 33, 34, 35, 38.

<p>Reagents and conditions: i) from <b>1</b> for <b>23</b>, from <b>5</b> for <b>24</b>, from <b>32</b> for <b>33</b>: H₂SO₄, MeOH, reflux, 1 h; ii) from <b>32</b>: Py · SO₃, DMF dry, 120°C, 25 min; iii) CH₃I, anhydrous K₂CO₃, dry DMF, reflux, 1.5 h; iv) 1N NaOH, EtOH.</p

Global anti-biofilm performance of ZA-related compounds and structures with the most significant anti-biofilm performance.

<p>Global anti-biofilm performance value of each ZA-related compound calculated as (sum of cell adhesion codes of all concentrations)-(sum of planktonic growth codes of all concentrations). Values equal to 0 were considered without anti-biofilm performance, below 0 were considered globally able to exert an anti-biofilm activity, and above 0 were considered able to improve biofilm performance. Yellow: no anti-biofilm performance; Light orange: little anti-biofilm performance; Medium orange: moderate anti-biofilm performace; Dark orange: optimal anti-biofilm performance; Light green: little improvement of anti-biofilm performance; Medium green: moderate improvement of anti-biofilm performance; Dark green: optimal improvement of anti-biofilm performance.</p

Synthetic scheme of compounds 36, 37.

<p>Reagents and conditions: i) Lindlar catalyst, H₂, pyridine, MeOH, r.t., 16 h; ii) 1N NaOH, EtOH/THF (1:1), r.t., 12 h.</p

Synthetic scheme of compounds 23, 24, 33, 34, 35, 38.

<p>Reagents and conditions: i) from <b>1</b> for <b>23</b>, from <b>5</b> for <b>24</b>, from <b>32</b> for <b>33</b>: H₂SO₄, MeOH, reflux, 1 h; ii) from <b>32</b>: Py · SO₃, DMF dry, 120°C, 25 min; iii) CH₃I, anhydrous K₂CO₃, dry DMF, reflux, 1.5 h; iv) 1N NaOH, EtOH.</p

Fluorescence analysis of matrix functionalization.

<p>A) Emission spectrum (λ_exc 380 nm) of 5 mM <i>p</i>-ACA in 0.4 M NaHCO₃, 1 M NaCl (pH 8,3). B) Emission spectra (λ_exc 350 nm) of suspensions of <i>p</i>-ACA/matrix (50 μl, drained volume; solid line) and EA/matrix (50 μl, drained volume; dashed line) in 2 mL of 0.4 M NaHCO₃, 1 M NaCl (pH 8,3). A. U., arbitrary units.</p