Natural processes driven by heat flow can be understood using quantitative reconstruction of the thermal history of accessory and common minerals that were formed or modified in these processes. Thermochronology assumes that isotopes are lost from minerals by thermally-activated volume diffusion, and forms the basis of many studies of the thermal evolution of the crust. However, some studies challenge this assumption and suggest that the mechanisms controlling isotope transport in minerals over geological time-scales are dominated by aqueous fluid flow within mineral pathways. Here, we test these contrasting hypotheses by inverse modelling apatite uranium–lead (U–Pb) dates to produce theoretical t–T solutions assuming Pb was lost by volume diffusion. These solutions are compared with independent geological constraints and intra-grain apatite U–Pb dates, which demonstrate that volume diffusion governed the displacement of Pb. This confirmation, combined with an inverse-modeling procedure that permits reheating and cooling paths to be distinguished between ∼375 and 570 °C, provides geologists with a unique tool for investigating the high-temperature thermal evolution of accessory minerals using the U–Pb method

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66The term 'Budleighensis' river was first proposed to account for the deposition of thick, regionally-67 significant, fine to medium-grained, red-bed sandstone-dominated facies of Triassic (Olenekian - 68Anisian) age across south, central and north-east England (Wills 1970;Audley-Charles 1970). 69Interpreted to flow from south to north, and with deposits apparently related to this system 97The sandstones targeted in this study form a regionally important aquifer and a proven reservoir 98 for hydrocarbons in a number of sedimentary basins in the area, including the Wessex and East 99Irish Sea basins (McKie et al. 2007;Meadows and Beach 1993). Provenance analysis of the 100 drainage system supplying these sands is important because its scale is relatively poorly 101 constrained (<200 km or >500 km?) and it is uncertain as to how far it extends northward, 119In petrographic terms, the nature of these sandstones poses some additional questions. It is 128The Pb-in-K-feldspar provenance tool is particularly applicable to addressing some of the above 149One of the major advantages of the Pb K-feldspar provenance tool is that, in contrast to 150 provenance approaches that utilise signals in robust grains (e.g. U-Pb zircon), it provides a 151 means of assessing first-cycle sand-grain provenance. Furthermore, where it occurs as a 152 significant framework component (~20% modal abundance), K-feldspar must presumably be 153 more representative of the source area than relatively minor components such as zircon which 154 typically make up << 1% of the mode. In these circumstances, K-feldspar can be a proxy for the 155 source of a large portion of the detrital quartz as there is a reasonable probability both minerals 156 are derived from the same source/s. As fresh detrital K-feldspar is unlikely to survive more than 157 one sedimentary cycle, these grains can be tracked back directly to their basement source, 158allowing the scale and geometry of the drainage system to be constrained. These types of 159 insights can improve prediction of reservoir sandstone distribution and quality in the subsurface. 160Importantly, there is much published Pb data from potential basement source areas in the North 161Atlantic Region with which detrital data can be compared. In this study, additional basement data 162 were collected to provide further constraints on possible sources. 164This study is specifically focussed on Middle Triassic sandstones. Although there are 195Backscatter electron and cathodoluminescence imaging: 196After initial petrographic assessment, sections of ~300μm thickness were prepared from which K- 212Two different collector configurations were used during analysis. An ion counter collector 213 configuration was implemented at MUN, allowing Pb analysis from ~30 μm laser ablation pits, 214 which is only slightly larger than spot sizes used to collect Pb isotopic data using secondary ion 219Repeat analyses of the same grains replicated the initial data within error (Table 1). 7 221The analytical technique is d...