Biogeography of Argylia D. Don (Bignoniaceae): Diversification, Andean Uplift and Niche Conservatism

Andean uplift and the concomitant formation of the Diagonal Arid of South America is expected to have promoted species diversification through range expansions into this novel environment. We evaluate the evolution of Argylia, a genus belonging to the Bignoniaceae family whose oldest fossil record dates back to 49.4 Ma. Today, Argylia is distributed along the Andean Cordillera, from 15°S to 38.5°S and from sea level up to 4,000 m.a.s.l. We ask whether Argylia’s current distribution is a result of a range expansion along the Andes Cordillera (biological corridor) modulated by climatic niche conservatism, considering the timing of Andean uplift (30 Ma – 5 Ma). To answer this question, we reconstructed the phylogenetic relationships of Argylia species, estimated divergence times, estimated the realized climatic niche of the genus, reconstructed the ancestral climatic niche, evaluated its evolution, and finally, performed an ancestral range reconstruction. We found strong evidence for climatic niche conservatism for moisture variables, and an absence of niche conservatism for most of the temperature variables considered. Exceptions were temperature seasonality and winter temperature. Results imply that Argylia had the capacity to adapt to extreme temperature conditions associated with the Andean uplift and the new climatic corridor produced by uplift. Ancestral range reconstruction for the genus showed that Argylia first diversified in a region where subtropical conditions were already established, and that later episodes of diversification were coeval with the of Andean uplift. We detected a second climatic corridor along the coastal range of Chile-Peru, the coastal lomas, which allowed a northward range expansion of Argylia into the hyperarid Atacama Desert. Dating suggests the current distribution and diversity of Argylia would have been reached during the Late Neogene and Pleistocene.

A new species of Maraenobiotus Mrázek, 1893 (Copepoda: Harpacticoida: Canthocamptidae) from Colombian Andean mosses, with an identification key for the American species

Maraenobiotus wellsi sp. nov. (Canthocamptidae) is described based on material collected in mosses in the “páramo” region of the Andean Cordillera of Colombia. The new species is closely related to M. australis Apostolov, 2001 from Tierra de Fuego in Argentina, but can be distiguished by the shape of the caudal rami, the insertion point of its terminal seta IV, and the chaetotaxy of distal segments of legs 3 and 4. We discuss morphological differences with other congeners inhabiting South America (Peru), i.e. M. naticochensis Delachaux, 1917, M. fontinalis Harding, 1955 and M. fontinaloides Löffler, 1960. Major distinguishing features were observed in the chaetotaxy of legs 2 and 3, the morphology and size of the caudal rami, and the ornamentation of the anal operculum. We also discuss morphological characters that distinguish the new species from those living exclusively in mosses, such as M. cuspidatus Štěrba, 1968 and M. canadensis Flössner, 1992, and those reported from mosses and other habitats i.e.. M. vejdovskyi Mrázek, 1893, M. brucei brucei (Richard, 1898), M. zschokkei Kreis, 1920, M. brucei himalayensis Chappuis, 1928b, M. truncatus (Gurney, 1932), M. insignipes elgonensis Chappuis, 1936, M. insignipes nepalensis Löffler, 1968 and M. kinabaluensis Löffler, 1973. A distribution map of American species and an identification key for females are provided.

Episodic construction of the early Andean Cordillera unravelled by zircon petrochronology

The subduction of oceanic plates beneath continental lithosphere is responsible for continental growth and recycling of oceanic crust, promoting the formation of Cordilleran arcs. However, the processes that control the evolution of these Cordilleran orogenic belts, particularly during their early stages of formation, have not been fully investigated. Here we use a multi-proxy geochemical approach, based on zircon petrochronology and whole-rock analyses, to assess the early evolution of the Andes, one of the most remarkable continental arcs in the world. Our results show that magmatism in the early Andean Cordillera occurred over a period of ~120 million years with six distinct plutonic episodes between 215 and 94 Ma. Each episode is the result of a complex interplay between mantle, crust, slab and sediment contributions that can be traced using zircon chemistry. Overall, the magmatism evolved in response to changes in the tectonic configuration, from transtensional/extensional conditions (215–145 Ma) to a transtensional regime (138–94 Ma). We conclude that an external (tectonic) forcing model with mantle-derived inputs is responsible for the episodic plutonism in this extensional continental arc. This study highlights the use of zircon petrochronology in assessing the multimillion-year crustal scale evolution of Cordilleran arcs.

Role of Basement Structural Inheritance and Strike-Slip Fault Dynamics in the Formation of the Pataz Gold Vein System, Eastern Andean Cordillera, Northern Peru

New regional- to vein-scale geologic mapping and structural analysis of the Carboniferous Pataz gold vein system (~10 Moz Au) reveal critical insights into the structural control on gold mineralization along the Eastern Andean Cordillera of northern Peru. The Pataz basement comprises continental volcanic arc and marginal to marine sedimentary rocks, which experienced intensive D2 deformation associated with Late Famatinian northeast to southwest compressive fold-and-thrust belt development. The D2 event produced an E-NE–dipping structural grain, including (1) tilted and F2 folded S1 foliations, (2) local F2 axial planar S2 foliations, and (3) subparallel D2 thrust faults. Intrusions, constituting the ca. 342 to 332 Ma (Mississippian) Pataz batholith, were emplaced along strike of the prominent Río Marañón fault and inherited the D2 basement structures, as evident in the orientation of suprasolidus magmatic flow zones and intrusive contacts within the batholith. Progressive horst-and-graben development affecting the volcanic carapace of the Pataz batholith records late syn- to postmagmatic uplift and transition into a NW-SE–extensional regime. We show that the E-NE–dipping, batholith-hosted gold vein system formed through synchronous activation of two geometric fault-fill vein types, following (1) the moderately E-NE–dipping D2 basement-inherited competency contrasts within the batholith and (2) shallow NE-dipping Andersonian footwall thrusts, during NE-directed shortening (D3a). Both geometric vein types display an early paragenetic stage (I) of quartz-pyrite, progressing texturally from hydraulic breccia into crack-seal laminated shear veins. A second (II), undeformed quartz-pyrite-sphalerite-galena paragenetic stage is observed to fill previously established dilational sites adjacent to newly formed D3b normal faults, which likely formed during regional NW-SE–extensional horst-graben development. Kinematics and relative timing indicate that, upon batholith solidification, D3a transpressional dextral strike-slip ruptures along the Río Marañón fault superimposed a lower-order Riedel-type fault system. Fluid-assisted fault activation preferentially impinged on the D2 basement-inherited competency contrasts within the batholith. Subsequent transition into a transtensional regime led to the D3b normal faulting, providing a feeder system for stage II fluid influx. The tectonic switch may be explained either by increasing tensile strain accommodation upon progressive strike-slip movement within a regional dilational jog or by larger-scale crustal relaxation of the late Gondwana margin upon final Pangea assembly. Our new structural model for the Pataz vein system evolution highlights the importance of basement structural inheritance in controlling the localization of gold mineralization along polycyclic supercontinent margins. We provide valuable insights for exploration targeting of complex vein arrays within rheologically heterogeneous host rocks.

The Glacial Geomorphology of central-Patagonia (44 – 46°S): glacier dynamics within and beyond the austral Andes

<p>The former Patagonian Ice Sheet (PIS, 38 – 56°S) was one of the largest ice masses to develop in the Southern Hemisphere. Its formation was uniquely influenced by the Southern Westerly Winds (SWWs) colliding with the Andean Cordillera, generating a marked West-East precipitation gradient. Variability in the strength and position of the SWWs is thought to have played a significant role in ice sheet dynamics. In particular, understanding of the timing of palaeo-glacier fluctuations is required to elucidate the role of these regional climate drivers on ice retreat. However, in order to fully understand the structure and pace of deglacial ice fluctuations, detailed glacial geomorphological reconstructions must be completed.</p><p>During deglaciation, as the PIS retreated from local Last Glacial Maxima positions, large proglacial lakes formed east of the austral Andes, ice-dammed by the Andean Cordillera. In central-Patagonia (44 – 46°S) during the final stages of deglaciation, these ice-dammed lakes drained to the west, through the Andean Cordillera, opening new drainage corridors towards the Pacific Ocean. As a result, the floors of these valleys are now exposed subaerially, preserving a complex suite of glacial and glaciolacustrine landform assemblages. Moreover, as most of the region is now ice-free, excluding smaller mountain ice caps such as Queulat (44.4°S, ~2000 m a.s.l) more recent Holocene geomorphology has also been exposed. These landforms possess the potential to yield new insights into the style and manner of regional ice retreat, during the transition from large terrestrial ice-lobes, to smaller mountain glaciers and ice caps.</p><p>We mapped seven terrestrial palaeo-ice lobes of the PIS: the Río Pico (~44.2°S), Río Cisnes (~44.6°S), Lago Plata-Fontana (~44.8°S), Río El Toqui (~45°S), Lago Coyt/Río Ñirehuao (~45.3°S), Simpson/Paso Coyhaique (~45.5°S) and Balmaceda (~46°S) lobes. Mapping was then extended west, into the Andean Cordillera. Landforms were mapped using ESRI™ DigitalGlobe World (1-2 m) and Sentinel-2 (10 m) imagery, verified with field surveys. These new data build on previous work in the area. To date, over 60,000 ice-marginal, ice-contact, subglacial, glaciolacustrine and glaciofluvial landforms have been mapped across a ~70,000km<sup>2</sup> area of the Andean Cordillera and adjacent valleys. When combined with robust geochronological reconstructions, these data possess the potential to inform on the role of the SWWs, versus local topography, and ice-marginal processes in regulating the structure and rate of regional deglaciation.</p>

Upper Cretaceous intrusives in the Coastal Cordillera near Valdivia: forearc magmatism related to the passage of a triple junction?

Upper Cretaceous intrusives of limited extent crop out in the Coastal Cordillera near of Valdivia (39º48’ S), 100 km west of the main topographic divide of the Andean Cordillera. Given that plutonic rocks of the same age crop out at the same latitudes in the high Andes the coastal intrusives emplaced in a forearc position in the upper plate of a subduction setting. They correspond to hypabyssal intrusives displaying mainly porphyritic texture and lithological variations with microtonalites (minor), porphyritic microgranodiorites (main) and microgranites. They intrude the Upper Paleozoic-Triassic accretionary complex of the Bahia Mansa Metamorphic Complex. These intrusives, that comprise the Chaihuín Pluton and minor stocks of porphyritic felsic rocks, have calc-alkaline affinities with metaluminous and peraluminous character. They are geochemically similar to the contemporaneous main arc-related plutonic rocks of the Gualletué Plutonic Group. The microgranitoids and dacitic rocks from Los Boldos, the low and Loncoche are peculiar because they show an apparently adakitic affinity in Sr/Y and LaN/YbN discriminant diagrams; nevertheless Sr contents of these rocks (

Vochysia tepuiandina (Vochysiaceae), a new species from the sub Andean Cordillera forests

Vochysia tepuiandina is here described and illustrated. It occurs in southern Ecuador and northern Peru, and is associated with the disjunct “Andean Tepuis” forests found within the Andean piedmont and of the Amazonian forests. This species is placed in the Vochysia section Ciliantha subsection Ferrugineae. It is compared with the similar species V. angustifolia and V. sprucei.

Una especie nueva de Furcraea (Agavaceae) de Colombia

As a result of recent studies of South American Agavaceae, a new species of Furcraea is described. This species is endemic of a small area of the Andean Cordillera Oriental of Colombia and it belongs to Furcraea sect. Furcraea. The uses and popular names are documented for the new species. Based on IUCN criteria, the new species is categorized as “critically endangered” (CR). Thus, a total of five species of Furcraea are currently known in Colombia, F. abisaii Giraldo-Cañas, F. acaulis (Kunth) B. Ullrich, F. cabuya Trelease, F. foetida (L.) Haworth, and F. selloana K. Koch. A key for the Colombian species is included. The new species is more similar to F. hexapetala (Jacq.) Urb. and F. selloana K. Koch, and therefore, their features are given.