Passive margin uplifts and their influence on climatic change and weathering patterns of tropical shield regions

Large scale plateau uplift influences long-term atmospheric circulation patterns. Recent speculation on the role of passive margin mountains in initiating late Cenozoic glaciation around the North Atlantic adds to the debate on the connections between tectonics and climate patterns, and calls for broadening the scope of examining causes of climate change to include other existing passive margins. Three examples from the intertropical zone, the Western Ghats of India, the Borborema of northeast Brazil, and the West African Leo uplift are compared. Palaeoenvironmental and fission track constraints on amplitude, timing and wavelength of the shoulder uplift history for the Western Ghats reveal that high elevation margins can act as effective environmental filters, both as physical barriers to atmospheric circulation and as pace-makers for denudation rates, which in turn steer weathering processes towards producing specific soil and vegetation suites. Predicting interaction between climate and rift–flank tectonics is however shown to be model-dependent, in that assumptions on whether uplift is transient or permanent will influence the timescales and effectiveness of any consequent environmental change.