In this paper, we merge more than 200 new apatite and zircon (U-Th)/He analyses and 21 apatite fission-track analyses from 71 new samples with previous published thermochronologic data using the same systems to understand the growth and large-scale kinematics of the central Andes between 21°S and 28°S. In general, minimum dates decrease and the total range of dates increases from west to east across the range. Large variations in thermochronometer dates on the east side reflect high spatial gradients in depth of recent erosional exhumation. Almost nowhere in this part of the Andes has Cenozoic erosion exceeded ~6–8 km, and in many places in the eastern half of the range, erosion has not exceeded 2–3 km, despite these regions now being 5–6 km above sea level. This means that west of the rapidly deforming and eroding eastern range front, uplift and erosion are largely decoupled as a result of meager precipitation, relatively low relief, internal drainage, and volcanic burial. We interpret the west-to-east pattern of decreasing minimum dates across the range as recording the time-transgressive eastward migration of a focused zone of deformation, erosion, and convergence between the South American plate and the eastern edge of the Andean orogenic plateau. At this scale, the thermochronologic data do not suggest major changes in rates of plateau propagation or shortening/convergence with time. We use the thermochronometer date-distance trend and a simple kinematic model to infer a rate of eastward propagation of deformation and plateau growth of 6–10 km/m.y. This plateau propagation model balances horizontal convergence, erosion, and crustal thickening and predicts rates of shortening and convergence between the Andes block and South American plate that are consistent with geologic and geodetic observations.

We synthesize geologic observations with new isotopic evidence for the timing and magnitude of uplift for the central Andes between 22°S and 26°S since the Paleocene. To estimate paleoelevations, we used the stable isotopic composition of carbonates and volcanic glass, combined with another paleoelevation indicator for the central Andes: the distribution of evaporites. Paleoelevation reconstruction using clumped isotope paleothermometry failed due to resetting during burial. The Andes at this latitude rose and broadened eastward in three stages during the Cenozoic. The first, in what is broadly termed the “Incaic” orogeny, ended by the late Eocene, when magmatism and deformation had elevated to ≥4 km the bulk (~50%) of what is now the western and central Andes. The second stage witnessed the gradual building of the easternmost Puna and Eastern Cordillera, starting with deformation as early as 38 Ma, to >3 km by no later than 15 Ma. The proximal portions of the Paleogene foreland basin system were incorporated into the orogenic edifice, and basins internal to the orogen were enclosed and isolated from easterly moisture sources, promoting the precipitation of evaporites. In the third orogenic stage during the Pliocene–Pleistocene, Andean deformation accelerated and stepped eastward to form the modern Subandes, accounting for the final ~15%–20% of the current cross section of the Andes. About 0.5 km of elevation was added unevenly to the Western Cordillera and Puna from 10 to 2 Ma by voluminous volcanism. The two largest episodes of uplift and eastward propagation of the orogenic front and of the foreland flexural wave, ca. 50 (?)–40 Ma and <5 Ma, overlap with or immediately postdate periods of very rapid plate convergence, high flux magmatism in the magmatic arc, and crustal thickening. Uplift does not correlate with a hypothesized mantle lithospheric foundering event in the early Oligocene. Development of hyperaridity in the Atacama Desert by the mid-Miocene postdates the two-step elevation gain to >3 km of most (~75%) of the Andes. Hence, the record suggests that hyperarid climate was a consequence, not major cause, of uplift through trench sediment starvation.

Mapping and description of the Hadar and Busidima Formations in the northern Awash valley, Ethiopia, have been greatly aided by the use of tephrostratigraphy and tephra correlation in the Dikika, Gona, Hadar, and Ledi-Geraru paleoanthropological project areas. The Hadar Formation contains at least nine dated tuffs, many of which have been correlated across the northern Awash project areas, and all of which are easily distinguished from each other on the basis of major-element chemistry. The overlying Busidima Formation contains at least 35 distinct tuffs, many of which are firmly or approximately dated. Because of their discontinuous and compositionally similar nature, many of the Busidima Formation tuffs are not correlated across the northern Awash project areas. Trace-element compositional data or detailed stratigraphic information may be necessary for correlation or relative placement of many of the Busidima Formation tuffs. Differences in the frequency, chemistry, and extent of Hadar and Busidima Formation tuffs preserved in the northern Awash valley may ultimately be related to the tectonic evolution of the region throughout the Pliocene-Pleistocene, as well as to basin-scale geological processes. Despite a number of known issues in tephra correlation, the composite tephrostratigraphy assembled for the northern Awash valley demonstrates the effectiveness of this technique, which has played a key role in ongoing efforts to document the geological history of this unique and important region.