Growing the Paleo- to Mesoproterozoic margin of the SW Amazonia and the transition from an accretionary to a collisional system

Despite a general consensus of a petrogenetic link in Paleo- to Mesoproterozoic times between the Rio Apa Terrane (RAT) and the Ventuari-Tapajós and Rio Negro-Juruena provinces of the SW Amazonian Craton, their connection with the adjoining Paraguá Terrane is still tentative. Here, we test the connection between SW Amazonia, Rio Apa and Paraguá terranes by comparing an extensive dataset of new and published zircon U–Pb–Hf isotopic data. A locally weighted scatterplot smoothing (LOWESS) curve based on a near continuous zircon εHfT time series (∼1400 data) indicates that the Western domain of the RAT, the San Diablo domain (southern Paraguá Terrane), and the Ventuari-Tapajós Province are characterized by a crustal reworking array associated with the recycling of the Amazonian Archean crust. Change-point statistical analysis indicates the time of a switch from this reworking array to an episode of juvenile input into the magmatic sources at 1809–1805 Ma (95 % confidence), giving rise to the juvenile Eastern domain of the RAT, the Paraguá Terrane and the Rio Negro-Juruena Province. This secular zircon εHfT evolution is interpreted to represent a switch from advancing (crustal reworking) to retreating (juvenile input and crustal growth) episodes in the Paleo- to Mesoproterozoic accretionary orogen of SW Amazonia. Similar temporal isotopic patterns are recorded in modern accretionary orogens such as the Andes. This data supports a petrogenetic link between the RAT, the Paraguá Terrane, and the SW Amazonian Craton. We postulate that the Mesoproterozoic Alto Guaporé orogeny (ca. 1470–1430 Ma, accretionary phase) eventually juxtaposed the high-pressure/medium-temperature (amphibolite facies) RAT and the high-temperature (granulite facies) Paraguá Terrane along the SW margin of Amazonia, establishing a paired metamorphic belt during Rodinia assembly. The newly formed RAT-Paraguá-Amazonia connection lasted until at least ca. 1110 Ma based on the expression of the Rincon del Tigre-Huanchaca large igneous province that crosscut the Amazonia-Paraguá and RAT. The timing of fragmentation and drift of the RAT and the Paraguá Terrane from the SW Amazonia is still unknown

Late‐stage calcites in the Permian Capitan Formation and its equivalents, Delaware Basin margin, west Texas and New Mexico: evidence for replacement of precursor evaporites

Comparison of Upper Guadalupian fore‐reef, reef and back‐reef strata from outcrops in the Guadalupe Mountains with equivalent subsurface cores from the northern and eastern margins of the Delaware Basin indicates that extensive evaporite diagenesis has occurred in both areas. In both surface and subsurface sections, the original sediments were extensively dolomitized and most primary and secondary porosity was filled with anhydrite. These evaporites were emplaced by reflux of evaporitic fluids from shelf settings through solution‐enlarged fractures and karstic sink holes into the underlying strata. Outcrop areas today, however, contain no preserved evaporites in reef and fore‐reef sections and only partial remnants of evaporites are retained in back‐reef settings. In their place, these rocks contain minor silica, very large volumes of coarse sparry calcite and some secondary porosity. The replacement minerals locally form pseudomorphs of their evaporite precursors and, less commonly, contain solid anhydrite inclusions. Some silicification, dissolution of anhydrite and conversion of anhydrite to gypsum have occurred in these strata where they are still buried at depths in excess of 1 km; however, no calcite replacements were noted from any subsurface core samples. Subsurface alteration has also led to the widespread, late‐stage development of large‐ and small‐scale dissolution breccias. The restriction of calcite cements to very near‐surface sections, petrographic evidence that the calcites post‐date hydrocarbon emplacement, and the highly variable but generally ‘light’carbon and oxygen isotopic signatures of the spars all indicate that calcite precipitation is a very late diagenetic (telogenetic) phenomenon. Evaporite dissolution and calcitization reactions have only taken place where Permian strata were flushed with meteoric fluids as a consequence of Tertiary uplift, tilting and breaching of regional hydrological seals. A typical sequence of alteration involves initial corrosion of anhydrite, one or more stage