The relationship between the rise of the Andean mountain chain and the onset of aridity on its western margin is poorly understood. Canyon incision on both the eastern and western flanks of the chain is interpreted generally as a direct response to increased rock uplift, but may equally have been the result of climate change. Here we record some of the oldest canyon incision on the western Andean margin by tracking the downward migration of the local water table using (U-Th)/He hematite geochronology on vertical drill-core transects. Our data constrain the incision history of the Quebrada de Parca canyon in northern Chile from ca. 16 Ma to the present day. The erosional and topographic response of the Quebrada de Parca river suggests that incision was induced by a switch to a more arid climate in the middle Miocene, which reduced regional precipitation and river discharge. Geomorphic analysis of the modern river suggests that the Central Andes have gained only ∼700 m of elevation since incision began, and had therefore reached at least 50% of their current elevation by middle Miocene time. We thus conclude that the onset of aridity at ca. 16 Ma occurred subsequent to the main Andean uplift.

Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au-Cu mineral provinces, is a good example. The current models defined four deposit types, all connected to a single (1.88-1.75 Ga) magmatic-hydrothermal event. However, long Province history, diverse geodynamic environment, and older ages of Type-1mineralisation weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By scale-integrated analyses, we revise the tectonic-geological context, structural-hydrothermal alterations, and chlorite-white mica geothermobarometer and propose the type-1 as an older, granitoid-hosted orogenic mineralisation, with subsequent overprinting by the magmatic-hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic-gneiss rocks. Phengite, biotite, chlorite-carbonate phyllonites (3.3-6.1 kbar, 300º-420ºC) host fault-fill quartz veins (pyrite-chalcopyrite-magnetite-pyrrhotite-gold-Bi-Ag tellurides). Mg-rich chlorite-phengite is the main alteration footprint for this mineralisation type. A younger magmatic-hydrothermal event in the Juruena magmatic-arc rocks produced Fe-rich chlorite-white mica alteration zones (0.6-4.6 kbar, 120º-380ºC) and disseminated and stockwork-breccia ore (pyrite-chalcopyrite-gold-molybdenite- Ti minerals-allanite) in porphyry-epithermal deposits. Where the younger mineralisation overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite Sn+1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805-1782 Ma) or disseminated in the ca. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralisation. These two events differ in their alteration styles, P-T conditions, and structural, mineralogical, and textural ore styles. The multi-scale approach enlightens the relationships between the various mineralisation events, allowing a new explorational potential within the province.Supplementary material at https://doi.org/10.6084/m9.figshare.c.6056324

Resumo Novos dados geoquímicos para as rochas vulcânicas da Unidade Maria Preta, Greenstone Belt do Rio Itapicuru, revelaram a presença de dois grupos distintos: um de rochas com afinidade adakítica e outro cálcio-alcalina. A suíte adakítica ocorre na porção oeste da Unidade Maria Preta e é caracterizada por altos valores de Sr/Y, Ti/Y N >1 e pelo enriquecimento em elementos de baixo potencial iônico (LFSE) em relação aos de elevado potencial iônico (HFSE) e também pelo moderado fracionamento dos elementos terras raras. A suíte cálcio-alcalina, que aflora na porção leste, apresenta baixas razões Sr/Y, Ti/Y N <1, menor fracionamento de elementos terras raras e anomalias negativas de Eu. Dados de isótopos de Sm-Nd, recalculados para (2170 Ma) forneceram valores de ε Nd de +4,78 a +2,55 para a suíte adakítica e de +1,37 a + 1,90 para a suíte cálcio-alcalina, sugerindo que as duas suítes podem ter sido geradas em contexto de zona de subducção. Os dois grupos vulcânicos não se relacionam por cristalização fracionada e provavelmente foram derivados de fontes distintas (diferentes razões iniciais Nd). A geoquímica das vulcânicas cálcio-alcalinas foi atribuída à fusão da cunha do manto metassomatizado por fluídos liberados a partir de uma crosta oceânica subductada, seguido por fracionamento de plagioclásio no magma. Por outro lado, a geoquímica dos adakítos requer fusão de meta-basaltos hidratados com granada e/ou hornblenda residual. Esta suíte não apresenta indícios de interação significativa com a cunha do manto, como em adakitos atuais, face aos baixos valores de Cr e Ni. A distribuição geográfica das duas suítes sugere subducção de crosta oceânica para oeste, caso sejam da mesma idade.Palavras-chave: Vulcânicas félsicas, Adakitos, Cálcio-alcalinas, Geoquímica, Greenstone belt do Rio Itapicuru. Abstract Characterization of adakitic and calc-alkaline volcanic rocks in the Rio Itapicuru Greenstone Belt, Bahia: Petrogenesis and geodynamic implications. New geochemical data for andesites anddacites of the Maria Preta Unit, Rio Itapicuru Greenstone Belt, revealed two distinct geochemical groups: one of adakitic affinity and another calc-alkaline. The adakitic suite, localized to the west in the unit, is characterized by high values of Sr/Y, Ti/Y N >1; it shows enrichment in LFSE (Low Field Strength Elements) relative to HFSE (High Field Strength Elements) and moderate rare earth elements fractionation. The calc-alkaline suite shows low Sr/Y ratios, lower rare earth elements fractionation and negative Eu anomalies. It also shows high abundances of incompatible elements (Y, Zr, Th) and high Cr and Ni concentrations. The most likely mechanism of formation for the calc-alkaline rocks is partial melting of mantle peridotite hydrated by fluids released from the subducting slab, followed by plagioclase fractionation. The two suites cannot be linked to each other by fractional crystallization and have probably derived from distinct magmas (different initial Nd ratios). The adakite geochemical features require partial melt of hy...