Renal function in IgA nephropathy with established renal failure

This article discusses the feasibility of fitting a straight line to the reciprocal serum creatinine (1/SCr) values obtained from 32 patients with IgA mesangial nephropathy and established renal insufficiency. Three models were tested for fit: linear, logarithmic and quadratic. The decline of renal function, once renal failure has been established, is neither constant nor regular in all patients with this fairly well-diagnosed glomerular disease. Therefore we cannot rely on simple mathematical models to compare sequences of serum creatinine values or to forecast decline in renal function in patients with IgA nephropathy

U-Th/He and fission track dating in north-eastern Corsica (France): extensional versus erosional exhumation.

During the Late Oligocene-to-Miocene, the Alpine Units of north-eastern Corsica experienced a rapid exhumation related to the extensional collapse coeval with the anticlockwise rotation of Corsica and the formation of the Proven\ue7al-Ligurian basin (Jolivet et al., 1998). During the same period of time, shallow-water basins formed in eastern Corsica where alluvial sediments interfingered with marine deposits and recorded the time of exposure to erosion of the Alpine Units and the growth of relief (Orszag-Sperber and Pilot, 1976). New apatite (U-Th)/He and fission-track ages from Corsica record cooling rates as high as 30-40\ub0C/Myr during Early-Middle Miocene when this region is affected by a relatively high geothermal gradient, and possibly by topographic thermal perturbations. Cooling rates are commonly less than 7.5\ub0C/Myr from Middle Miocene to Present when the growth of relief is detected by fluvial adjustments as indicated by the variations in the source areas of alluvial deposits of Late Miocene age. To analyze the roles of extensional exhumation versus topographic thermal perturbations and erosion, a simple one-dimensional model based on age-elevation-distance profiles has been applied to two case studies: namely the St. Florent basin, and the Tenda massif. The Early-to-Middle Miocene St. Florent basin is bordered by ductile-to-brittle extensional shear zones dissecting the Alpine units. The thermochronometric data from the Alpine units along a transect across the base and the shoulder of the basin are analyzed through an age-elevation-distance profile. The model derived from this profile shows that under low-temperature conditions the fault bordering the St. Florent basin produced a vertical throw of 3-4 km, and therefore supports the major role of extensional exhumation versus that of topographic thermal perturbations and erosion. The Tenda massif is the most prominent relief of north-eastern Corsica with elevations up to 1535 m: to the east it is bordered by a low-angle extensional ductile shear zone, and to the west by a high-angle extensional fault. Rounded pebbles from the Tenda massif are included in the sediments of the St. Florent basin indicating that this massif has been exposed to erosion since Middle Miocene, at least. Apatite fission track and U-Th/He data from this massif show an inverse relation with relief, and this relation can be interpreted as either deriving from a thermal topographic perturbations followed by a decrease of relief due to erosion, or to extensional faulting. These two end-member hypothesis are investigated through an age-elevation-distance profile, and this suggests that the present relief of the Tenda massif could be the remnant of a much more elevated paleorelief, and also that extensional faulting under low-temperature conditions might have played a significant role in the surface uplift of this massif

Relief evolution in northern Corsica (western Mediterranean): Constraints on uplift and erosion on long-term and short-term timescales.

The long-term erosional evolution of relief is revealed by low-temperature thermochronometric data, whereas geomorphic features give constraints on the short-term evolution. We discuss the topographic evolution of northeastern Corsica by fission track and (U-Th)/He dating of apatite, the provenance of Neogene alluvial sediments, an analysis of uplifted strath terraces, and the shape of river profiles. Cooling ages indicate high cooling rates of up to 40C/Myr during the early-middle Miocene, when this region was affected by extensional tectonics. Cooling rates are less than 7.5C/Myr from the middle Miocene to the present, when topographic perturbations are detected by variations in the source areas of middle-to-late Miocene alluvial sediments and by the presence of large-scale irregularities along modern river longitudinal profiles. We suggest that the contrast of slow long-term erosion rates and the high local relief in the present Corsican landscape require that the landscape be in a transient state in response to a recent tectonic event

Exhumation of the Northern Apennines core: new thermochronological data from the Alpi Apuane

The metamorphic core of the Northern Apennines is exposed in the Alpi Apuane which form a topographic high located to the west of the axial zone of the range. The metamorphic rocks of the Alpi Apuane are bordered by a tectonic contact which separates a footwall affected by maximum P and T conditions ranging between 0.6-0.8 Gpa and 420-500\ub0C (Massa unit) and 0.4-0.6 Gpa and 350-420\ub0C (Apuane unit), from a hangingwall of unmetamorphosed Macigno sandstone. The metamorphic rocks of the Alpi Apuane have long been interpreted as an example of tectonic exhumation formed during active convergence in the Apennines. Here we report 53 new zircon and apatite (U-Th)/He (ZHe and AHe, respectively) ages on rocks from the Alpi Apuane and the Macigno sandstones to provide a much more detailed understanding of when the Apuane fault was active and how much section was cut out. The ZHe and AHe systems provide cooling ages corresponding to closure temperatures of 180\ub0C and 70\ub0C, respectively. ZHe ages in the crystalline core of the Alpi Apuane are all reset and vary around an average of 5.7 Ma (std deviation 1.2 Ma). In the hangingwall, the Macigno sandstones have ZHe ages which vary between 47.1 and 9.3 Ma, indicating partial resetting. This result indicates that the hangingwall saw a temperature no greater than 160-190 \ub0C, followed by cooling around 9 Ma. AHe ages in the Alpi Apuane and in the Macigno sandstone show no differences and vary around a mean of 4.9 Ma (std deviation 1.2 Ma). Our data clearly constrain different exhumation paths for the Alpi Apuane and the Macigno sandtones between 180\ub0C and 70\ub0C, whereas their paths are similar from 70\ub0C to the surface. The different thermal histories from 180\ub0C to 70\ub0C suggest that between 6 and 4 Ma, 4\ub11 km have been removed along the contact between the Macigno sandstones and the Alpi Apuane. The amount of crustal section removed has been determined assuming a geothermal gradient of 25\ub1\ub0C/km, and a cooling age of 8\ub11 Ma at 110\ub0C for the Macigno sandstones. The geometry of the major Apuane boundary and the different exhumation times suggest that extension under brittle conditions played a major role in the exhumation of the metamorphic core of the Apennines

Thermochronologic evidence for the exhumational history of the Alpi Apuane metamorphic core complex, northern Apennines, Italy

The Apennine Range is a young convergent orogen that formed over a retreating subduction zone. The Alpi Apuane massif in the northern Apennines exposes synorogenic metamorphic rocks, and provides information about exhumation processes associated with accretion and retreat. (U-Th)/He and fission-track ages on zircon and apatite are used to resolve exhumational histories for the Apuane metamorphic rocks and the structurally overlying, very low grade Macigno Formation. Stratigraphic, metamorphic, and thermochronologic data indicate that the Apuane rocks were structurally buried to 15–30 km and 400C at about 20 Ma. Exhumation to 240C and 9 km depth (below sea level) occurred at 10–13 Ma. By 5 Ma the Apuane rocks were exhumed to 70C and 2 km. The Macigno and associated Tuscan nappe were also structurally buried and the Macigno reached its maximum depth of 7 km at 15 to 20 Ma. Stratigraphic evidence indicates that the Apennine wedge was submarine at this time. Thus we infer that initial exhumation of the Apuane was coeval with tectonic thickening higher in the wedge, as indicated by synchronous structural burial of the Tuscan nappe. From 6 to 4 Ma, thinning at shallow depth is indicated by continued differential exhumation between the Apuane and the Tuscan nappe at high rates. After 4 Ma, differential exhumation ceased and the Apuane and the Tuscan nappe were exhumed at similar rates (0.8 km/Ma), which we attribute to erosion of the Apennines, following their emergence above sea level

Pliocene onset of rapid exhumation in Taiwan during arc-continent collision: new insights from detrital thermochronometry

The Coastal Range in eastern Taiwan contains the remnants of the Pliocene–Pleistocene retro-foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio-Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission-track, zircon (U–Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission-track grain ages in 2–4-Myr-old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc–continent collision. Sediments younger than 2-Myr-old yield Pliocene zircon fission-track grain ages and suggest that exhumation, transport and deposition occurred within 0.4–1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro- and retro-foredeep basins and a change in the wedge kinematics from internal shortening to underplating