Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering the following questions: Is the flow strong enough to initiate sediment transport, is the flow strong enough to sustain sediment transport once initiated, and how much sediment is transported by the flow in the saturated state (i.e., what is the transport capacity)? In the geomorphological and related literature, the widespread consensus has been that the initiation, cessation, and capacity of fluvial transport, and the initiation of aeolian transport, are controlled by fluid entrainment of bed sediment caused by flow forces overcoming local resisting forces, whereas aeolian transport cessation and capacity are controlled by impact entrainment caused by the impacts of transported particles with the bed. Here the physics of sediment transport initiation, cessation, and capacity is reviewed with emphasis on recent consensus-challenging developments in sediment transport experiments, two-phase flow modeling, and the incorporation of granular physics' concepts. Highlighted are the similarities between dense granular flows and sediment transport, such as a superslow granular motion known as creeping (which occurs for arbitrarily weak driving flows) and system-spanning force networks that resist bed sediment entrainment; the roles of the magnitude and duration of turbulent fluctuation events in fluid entrainment; the traditionally overlooked role of particle-bed impacts in triggering entrainment events in fluvial transport; and the common physical underpinning of transport thresholds across aeolian and fluvial environments. This sheds a new light on the well-known Shields diagram, where measurements of fluid entrainment thresholds could actually correspond to entrainment-independent cessation thresholds.
The contiguous Cerro Verde and Santa Rosa porphyry copper deposits are hosted by Paleogene granitoid rocks and Precambrian gneiss, and spatially associated with 61 ± 1 Ma (U-Pb zircon: Mukasa, 1986) dacitic porphyry stocks. The age of hydrothermal activity is constrained by laser-induced incremental-heating 40Ar-39Ar sericite (muscovite-2M1) dates of 61.8 ± 0.7 (2 σ ) and 62.0 ± 1.1 Ma for Cerro Verde, and 62.2 ± 2.9 Ma for Santa Rosa, representing the terminal event in the Arequipa segment of the Coastal batholith.
The deposits crop out on the Santa Rosa erosional pediment, which itself is incised into the older La Caldera surface. Two populations, of ages 36.1 to 38.8 Ma and 24.4 to 28.0 Ma, are identified by multiple analyses of a sample from Cerro Verde comprising alunite partially replaced by natroalunite, demonstrating that supergene activity had commenced by the latest Eocene, during the Incaic orogeny, thereafter continuing through the Oligocene. In the Santa Rosa deposit, deep (ca. 300–350 m) leaching in the late Oligocene is recorded by ca. 26 Ma natroalunite that is inferred to have formed beneath the La Caldera surface. At the top of the Cerro Verde pit (2738 m bench), veins of alunite (ca. 23 Ma) and natroalunite (ca. 21 Ma) in a hematitic leached zone are truncated by the Santa Rosa surface, which is inferred to have developed after 21 Ma. Decreasing ages of alunite-group minerals with increasing depth in the Cerro Verde pit (e.g., ca. 12 Ma at the 2648 m level, and 4.9–6.7 Ma at the 2618 m level) are evidence for deepening of the supergene profile through the Miocene beneath this pediment. Jarosite dates (0.7–1.3 Ma) record the persistence of minor supergene activity into the Pleistocene.
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