Quantifying uplift and denudation of a thermally heterogeneous crust: a detailed multi-thermochronometeric study of central west Britain

Topography is often thought as exclusively linked to mountain ranges formed by plates collision. It is now, however, known that apart from compression, uplift and denudation of rocks may be triggered by rifting, like it happens at elevated passive margins, and away from plate boundaries by both intra-plate stress causing reactivation of older structures, and by epeirogenic movements driven by mantle dynamics and initiating long-wavelength uplift. In the Cenozoic, central west Britain and other parts of the North Atlantic margins experienced multiple episodes of rock uplift and denudation that have been variable both at spatial and temporal scales. The origin of topography in central west Britain is enigmatic, and because of its location, it may be related to any of the processes mentioned above. In this study, three low temperature thermochronometers, the apatite fission track (AFT) and apatite and zircon (U-Th-Sm)/He (AHe and ZHe, respectively) methods were used to establish the rock cooling history from 200◦C to 30◦C. The samples were collected from the intrusive rocks in the high elevation, high relief regions of the Lake District (NW England), southern Scotland and northern Wales. AFT ages from the region are youngest (55–70 Ma) in the Lake District and increase northwards into southern Scotland and southwards in north Wales (>200 Ma). AHe and ZHe ages show no systematic pattern; the former range from 50 to 80 Ma and the latter tend to record the post-emplacement cooling of the intrusions (200–400 Ma). The complex, multi-thermochronometric inverse modelling suggests a ubiquitous, rapid Late Cretaceous/early Palaeogene cooling event that is particularly marked in Lake District and Criffell. The timing and rate of cooling in southern Scotland and in northern Wales is poorly resolved as the amount of cooling was less than 60◦C. The Lake District plutons were at >110◦C prior to the early Palaeogene; cooling due to a combined effect of high heat flow, from the heat producing granite batholith, and the blanketing effect of the overlying low conductivity Late Mesozoic limestones and mudstones. Modelling of the heat transfer suggests that this combination produced an elevated geothermal gradient within the sedimentary rocks (50–70◦C/km) that was about two times higher than at the present day. Inverse modelling of the AFT and AHe data taking the crustal structure into consideration suggests that denudation was the highest, 2.0–2.5 km, in the coastal areas of the Lake District and southern Scotland, gradually decreasing to less than 1 km in the northern Southern Uplands and northern Wales. Both the rift-related uplift and the intra-plate compression poorly correlate with the timing, location and spatial distribution of the early Palaeogene denudation. The pattern of early Palaeogene denudation correlates with the thickness of magmatic underplating, if the changes of mean topography, Late Cretaceous water depth and eroded rock density are taken into consideration. However, the uplift due to underplating alone cannot fully justify the total early Palaeogene denudation. The amount that is not ex- plained by underplating is, however, roughly spatially constant across the study area and can be referred to the transient thermal uplift induced by the mantle plume arrival. No other mechanisms are required to explain the observed pattern of denudation. The onset of denudation across the region is not uniform. Denudation started at 70–75 Ma in the central part of the Lake District whereas the coastal areas the rapid erosion appears to have initiated later (65–60 Ma). This is ~10 Ma earlier than the first vol- canic manifestation of the proto-Iceland plume and favours the hypothesis of the short period of plume incubation below the lithosphere before the volcanism. In most of the localities, the rocks had cooled to temperatures lower than 30◦C by the end of the Palaeogene, suggesting that the total Neogene denudation was, at a maximum, several hundreds of metres. Rapid cooling in the last 3 million years is resolved in some places in southern Scotland, where it could be explained by glacial erosion and post-glacial isostatic uplift.

Corporate governance and cost of capital: evidence from Pakistani listed firms

This thesis investigates the effectiveness of Corporate Governance (CG) reforms in Pakistan. Using a sample of 160 Pakistani firms from 2003 to 2013 and governance data collected manually from the annual reports, this thesis investigates seven closely related and important corporate issues that are related to the compliance of governance rules. Specifically, it aims to : (i) investigate the degree of CG compliance with 2002 Pakistani Code of CG (PCCG); (ii) determine whether the introduction of 2002 PCCG has improved Pakistani CG practices; (iii) investigate the determinants of CG compliance and disclosure for Pakistani listed firms; (iv) test the nexus between CG compliance with the 2002 PCCG and firms’ cost of capital (COC); (v) investigate the impact of different individual CG mechanisms on listed firms COC; (vi) examine how different ownership structures impact on firms’ COC; and (vii) analyse relationship between CG structures and Cost of Equity (COE) as well as Cost of Debt (COD) for Pakistani listed firms. These empirical investigations report some important results. First, the reported findings suggest that Pakistani firms have responded positively to governance disclosure requirements over the eleven year period from 2003 to 2013. The results also show that the introduction of the PCCG in 2002 has improved CG standards by Pakistani listed firms. Second, the reported results related to the determinants of CG compliance demonstrate that significant and positive association between institutional, government and foreign ownership with CG compliance. However, findings relating to the determinants of CG compliance show a negative and significant association between board size and block ownership with CG compliance and disclosure. The study finds no significant relationship between director ownership, audit firm size and the presence of female board members with the constructed Pakistan Corporate Governance Index (PCGI). Third, the investigation on the relationship between CG and COC report a significantly negative nexus between PCGI and firms’ COC. The investigation on the association between ownership structures and COC report a negative and significant nexus between block ownership with firms’ COC. Further, a number of robustness analyses performed in this study suggest that the empirical results reported in this study are generally robust to the alternative CG variables, alternative COC variables and potential endogeneity problems.