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The timing and causes of the >1.0 km elevation gain of the southern African Plateau since Paleozoic time are widely debated. We report the first apatite and titanite (U-Th)/He thermochronometry data for southern Africa to resolve the unroofing history across a classic portion of the major escarpment that encircles the plateau. The study area encompasses ~1500 m of relief within Archean basement of the Barberton Greenstone Belt region of the eastern Kaapvaal craton. Titanite dates are Neoproterozoic. Apatite dates are Cretaceous, with most results clustering at ca. 100 Ma. Thermal history simulations confirm Mesozoic heating followed by accelerated cooling in mid- to Late Cretaceous time. The lower temperature sensitivity of the apatite (U-Th)/He method relative to previous thermochronometry in southern Africa allows tighter constraints on the Cenozoic thermal history than past work. The data limit Cenozoic temperatures east of the escarpment to [less than or equal to] 35[degrees]C, and appear best explained by temperatures within a few degrees of the modern surface temperature. These results restrict Cenozoic unroofing to less than ~850 m, and permit negligible erosion since the Cretaceous. If substantial uplift of the southern African Plateau occurred in the Cenozoic as advocated by some workers, then it was not responsible for the majority of post-Paleozoic unroofing across the eastern escarpment. Significant Mesozoic unroofing is coincident with large igneous province activity, kimberlite magmatism, and continental rifting within and along the margins of southern Africa, compatible with a phase of plateau elevation gain due to mantle buoyancy sources associated with these events. doi: 10.1130/G30980.1

Cenozoic uplift of the East African Plateau has been associated with fundamental climatic and environmental changes in East Africa and adjacent regions. While this influence is widely accepted, the timing and the magnitude of plateau uplift have remained unclear. This uncertainty stems from the lack of datable, geomorphically meaningful reference horizons that could record surface uplift. Here, we document the existence of significant relief along the East African Plateau prior to rifting, as inferred from modeling the emplacement history of one of the longest terrestrial lava flows, the ~300-km-long Yatta phonolite flow in Kenya. This 13.5 Ma lava flow originated on the present-day eastern Kenya Rift flank, and utilized a riverbed that once routed runoff from the eastern rim of the plateau. Combining an empirical viscosity model with subsequent cooling and using the Yatta lava flow geometry and underlying paleotopography (slope angle), we found that the prerift slope was at least 0.2[degrees], suggesting that the lava flow originated at a minimum elevation of 1400 m. Hence, high paleotopography in the Kenya Rift region must have existed by at least 13.5 Ma. We infer from this that middle Miocene uplift occurred, which coincides with the two-step expansion of grasslands, as well as important radiation and speciation events in tropical Africa. doi: 10.1130/G31022.1

The Early Cretaceous Ontong Java Plateau was emplaced at almost the same time as marine biotic changes that culminated in oceanic anoxic event 1 (OAE1a). A causative link between these events has been suggested, but direct evidence has been lacking until now. New Os isotope measurements across the Lower Aptian 'Selli Level' black shale deposited during OAE1a in central Italy reveal two negative excursions in marine [sup.187]Os/[sup.188]Os ratios within a period of 2 Ma starting above the Barremian-Aptian boundary and ending just above the Selli Levei horizon, suggesting an order-of-magnitude increase in the global flux of unradiogenic Os. The results are consistent with early and major phases of eruption of the Ontong Java Plateau. The latter phase is estimated to have been as short as ~1 Ma and may have induced widespread oceanic stratification that triggered OAE1a.

Eastern Anatolia is the site of lithospheric thinning, plateau uplift, heating, and synconvergent extension. Using numerical geodynamic experiments, we test the hypothesis that these tectonic anomalies are all related and the consequence of delamination of the mantle lithosphere. Our findings indicate that delamination during plate convergence results in ~2-km-high plateau uplift. The removal of mantle lithosphere induces distinct regions of contraction and thickening, as well as extension and thinning of the crust. The latter occurs even within a regime of plate shortening, although it is muted with increasing plate convergence. Detachment of the delaminating slab results in minor surface topographic perturbation, but only above the delamination hinge. The plateau uplift and pattern of surface contraction and/or extension are consistent with a topographic profile at 42[degrees]E and geologically interpreted zone of synconvergent extension at eastern Anatolia. Keywords: Eastern Anatolian plateau, delamination, lithospheric thinning, synconvergent extension.

East-west extension in the Tibetan Plateau is generally assumed to have resulted from gravitational collapse following thickening and uplift. On the basis of this assumption, several studies have dated east-west extensional structures to determine when the plateau attained its current high elevation. However, independent estimates of elevation are needed to determine whether extension occurred before, during, or after the plateau achieved its current elevation. Because the isotopic composition of meteoric water decreases with increasing elevation, significant change in local elevation throughout the Thakkhola graben depositional history should be recorded by change in [Delta][sup.18]O values of fluvial and lacustrine carbonates. The [Delta][sup.18]O values of-16% to -23% of Thakkhola graben carbonates reflect meteoric water values similar to modern values and suggest that the southern Tibetan Plateau attained its current elevation prior to east-west extension. Initiation of Thakkhola graben extension is constrained between 10 and 11 Ma, based on magnetostratigraphy of the older Tetang Formation. The [Delta][sup.13]O values of soil carbonates suggest an age younger than 8 Ma for the base of the Thakkhola Formation. Keywords: Tibetan Plateau, paleoelevation, oxygen isotopes.