Early Cenozoic Denudation of Central West Britain in Response to Transient and Permanent Uplift Above a Mantle Plume

Abstract

Upwelling mantle plumes beneath continental crust are predicted to produce difficult to quantify, modest uplift and denudation. The contribution of permanent and transient components to the uplift is also difficult to distinguish. A pulse of denudation in Britain in the Early Paleogene has been linked, although with some controversy, with the arrival of the proto‐Iceland mantle plume. In this contribution we show that combining apatite and zircon (U‐Th‐Sm)/He and apatite fission track analyses from central west Britain with numerical modeling clearly identifies a pulse of early Cenozoic denudation. The data indicate that rock uplift and denudation were centered on the northern East Irish Sea Basin and 1.0–2.4 km of rocks were removed during the latest Cretaceous‐early Paleogene. Uplift and erosion appears to have started a few million years before the earliest magmatism in the region. The regional denudation pattern mirrors the distribution of low‐density magmatic rocks that has been imaged in the deep crust. However, the injection of the underplating melt is not enough to account for the total denudation. An additional regional uplift of at least 300 m is required, which is consistent with a transient thermal effect from the hot mantle plume. The rapid exhumation event ceased by ~40 Ma and the data do not require significant Neogene exhumation.

Observational estimates of dynamic topography through space and time

“…Prominent erosional surfaces are limited in spatial extent, and determining their absolute ages can be challenging. In the absence of these large-scale features, local constraints on the timing and magnitude of denudation (the amount of overburden stripped off) are still very valuable for inferring changes in dynamic topography, as erosion is isostatically related to the amplitude of tectonic or dynamic uplift (England & Molnar, 1990;Brodie & White, 1994;Japsen et al, 2006;Luszczak et al, 2018). In order to extract quantitative estimates of denudation, the last few decades have seen a proliferation of geochronologic techniques that exploit radioactive decay, either induced by bombardment of atoms by cosmogenic radiation or from spontaneous alpha, beta, and fission decay of radionuclides.…”

“…Application of such analyses to the problem of landscape denudation can bracket the timing of the onset of incision, peneplanation episodes, burial by sedimentary deposition, or active tectonic processes, all of which may be associated with regional epeirogenic uplift (e.g. Japsen et al, 2006;Stanley et al, 2015;Luszczak et al, 2018;Wildman et al, 2016). Landscape evolution models indicate that the maximum magnitudes of denudation associated with dynamic topographic motions should be on the order of 2-3 km (e.g.…”

Observational Estimates of Dynamic Topography Through Space and Time

“…Prominent erosional surfaces are limited in spatial extent, and determining their absolute ages can be challenging. In the absence of these large-scale features, local constraints on the timing and magnitude of denudation (the amount of overburden stripped off) are still valuable for inferring changes in dynamic topography, as erosion is isostatically related to the amplitude of tectonic or dynamic uplift (England & Molnar, 1990;Brodie & White, 1994;Japsen et al, 2006;Luszczak et al, 2018;Jess et al, 2018). In order to extract quantitative estimates of denudation, the last few decades have seen a proliferation of geochronologic techniques that exploit radioactive decay, either induced by bombardment of atoms by cosmogenic radiation or from spontaneous alpha, beta, and fission decay of radionuclides.…”

“…Application of such analyses to the problem of landscape denudation can bracket the timing of the onset of incision, peneplanation episodes, burial by sedimentary deposition, or active tectonic processes, all of which may be associated with regional epeirogenic uplift (e.g. Japsen et al, 2006;Stanley et al, 2015;Luszczak et al, 2018;Wildman et al, 2016;Guillaume et al, 2013). Landscape evolution models indicate that the maximum magnitudes of denudation associated with dynamic topographic motions should be on the order of 2-3 km (e.g.…”