Reply on RC1

Erica Erlanger

doi:10.5194/se-2021-96-ac1

Abstract

Analysis of new detrital apatite fission-track (AFT) ages from modern river sands, published bedrock and detrital AFT ages, and bedrock apatite (U-Th)/He (AHe) ages from the Northern Apennines provide new insights into the spatial and temporal pattern of erosion rates through time across the orogen. The pattern of time-averaged erosion rates derived from AHe ages from the Ligurian side of the orogen illustrates slower erosion rates relative to AFT rates from the Ligurian side and relative to AHe rates from the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side, but decreased through time on the Ligurian side. Using an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of two slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.

Highlights

The Apennine mountains of Italy are an active orogen characterized by contemporaneous extensional and compressional 20 tectonics
Using an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of two slower relative to the Adriatic side, we demonstrate that 15 cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data
We find that the pattern of apatite fission-track (AFT), apatite (U-Th)/He (AHe), and ZHe cooling ages, and the pattern of vitrinite reflectance across the orogen are broadly consistent with the wedge kinematics for an asymmetric orogen that is dominated by frontal accretion and has slower erosion rates on the Ligurian side by a factor of two. 1.1 Structural evolution Development of the Apenninic wedge began at ~30 Ma, due to convergence and southwest-directed subduction of the Adriatic 45 microplate beneath Eurasia

Summary

Introduction

The Apennine mountains of Italy are an active orogen characterized by contemporaneous extensional and compressional 20 tectonics. Lowtemperature bedrock and detrital thermochronology studies have constrained the timing and rates of exhumation at the orogenscale (e.g. Thomson et al, 2010; Malusà and Balestrieri, 2012), and at the regional scale along the extensional retrowedge 25 (Ligurian side) of the orogen (e.g. Fellin et al, 2007) and in the frontal fold-and-thrust belt (Adriatic side) (Balestrieri et al, 1996; Carlini et al, 2013; Zattin et al, 2002). Age-elevation profiles and multiple thermochronometers have revealed spatially variable exhumation across and along strike of the orogen, and temporal variability in exhumation rates.

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