Cosmogenic nuclide surface-exposure dating reveals that glaciers in southern South America (46°S) advanced at ca. 8.5 and 6.2 ka, likely as a result of a northward migration of the Southern Westerlies that caused an increase in precipitation and/or a decrease in temperature at this latitude. The older advance precedes the currently accepted initiation of Holocene glacial activity in southern South America by ~3000 yr. Both of these advances are temporally synchronous with Holocene climate oscillations that occurred in Greenland and the rest of the world. If there are causal links between these events, then rapid climate changes appear to be either externally forced (e.g., solar variability) or are rapidly propagated around the globe (e.g., atmospheric processes).

Evidence of Early Holocene Glacial Advances in Southern South America from Cosmogenic Surface Exposure Dating

The geochemical stability, in terms of potential mobility and derived ecological and human health risks of potentially toxic elements (PTEs), of diverse fresh and old porphyry Cu-mine tailings from Chile was assessed through an integrated methodology comprising four interrelated investigation levels: (1) chemical composition and contamination degree of tailings by PTEs, (2) mineralogical characterization by X-ray diffraction and quantitative automated mineralogy analysis by scanning electron microscopy (QEMSCAN®), (3) partitioning and potential mobility of PTEs within the tailings by a sequential extraction procedure (SEP) and leaching tests, and (4) ecological risk assessment (ERA) and human health risk assessment (HHRA). According to pollution indices, Cu, As, Pb, and Mo are most concerning PTEs present in the tailings. SEP shows that major portion of the PTEs are strongly fixed as residual fraction, and thus are poorly mobilizable and bioavailable. Among the PTEs, Cu, As, and Mo were identified as the PTEs most prone to mobilization. Leaching tests show that a low fraction of PTEs is water-leachable. Seawater enhances Mn and As leaching, while process water increases the leaching of Cu, Mn, and Mo. Phosphate particularly promotes leaching of As and Cu, whereas it does not mobilize or even immobilize Pb in the tailings. ERA suggests that mainly old tailings pose a very high potential risk for ecological receptors (PERI = 663–3356), mostly due to Cu and As. HHRA indicates that the old tailings pose higher potential non-carcinogenic and carcinogenic health risks, while the risk decreases in the order ingestion > dermal > inhalation for both children and adults. Non carcinogenic and carcinogenic HHRA points to As as the main PTE of concern via ingestion pathway in the tailings. Overall, the results revealed that particularly old tailings, containing mixed slag-tailings, pose considerable risks to the environment and human health due to potential PTEs mobilization and this aspect requires scrutiny for proper tailings management, including storage, sealing, and eventual tailings reprocessing and/or site rehabilitation after closure.

Geochemical stability of potentially toxic elements in porphyry copper-mine tailings from Chile as linked to ecological and human health risks assessment

The Fucino 250–170 ka tephra record: New insights on peri-Tyrrhenian explosive volcanism, central mediterranean tephrochronology, and timing of the MIS 8-6 climate variability

The Alpi Apuane (northern Apennines) represent a key area for understanding the processes related to the Apennines building and geodynamic evolution of the central Mediterranean, but the timing of tectono-metamorphic events is still debated. White mica from cover rocks of the Massa and Apuane units was investigated by the 40Ar-39Ar in situ and step-heating techniques. Samples recorded several episodes of deformation developed under low-grade conditions and resulting in a D1 composite schistosity followed by a variably developed D2 retrograde crenulation. In the Massa Unit, D2 crenulation was accompanied by replacement of muscovite-phengite by paragonite, whereas the composition of phengite from the Apuane Unit does not vary noticeably, irrespective of whether phengite is aligned along D1 or D2 schistosities. Both units exhibit a significant intrasample scatter of in situ ages and variably discordant age spectra from step-heating data, due to partial reequilibration of white mica along a deformation path lasting ≥10 Ma, with dates approaching the time of younger events as retrogression becomes more pervasive. The onset of deformation has a minimum age of ∼20 Ma, as documented by 40Ar-39Ar data for the composite D1 foliation in the Massa Unit. D2 deformation shows a common temporal evolution at the scale of the region and is recorded for at least ∼2.5 Ma, starting not after ∼12.5 Ma and ending at ∼10.5 Ma. Results highlight the importance of a detailed microscale characterization and of a careful preselection of samples, as compositionally different domains a few millimeters apart may yield different results because of compositionally driven strain partitioning. 

Dating Low‐Grade Deformation: Role of Lithology and Strain Partitioning on Ar Isotope Records in the Alpi Apuane of Northern Apennines (Italy)

Large wood (LW, log at least 1 m-long and 0.1 m in diameter) in river channels has great relevance in fluvial environments. Historically, the most used approach to estimate the volume of LW has been through field surveys, measuring all the pieces of wood, both as single elements and those forming accumulation. Lately, the use of aerial photographs and data obtained from remote sensors has increased in the study of the amount, distribution, and dynamics of LW. The growing development of unmanned aerial vehicle (UAV) technology allows for acquisition of high-resolution data. By applying the structure from motion approach, it is possible to reconstruct the 3D geometry through the acquisition of point clouds and then generate high-resolution digital elevation models of the same area. In this short communication, the aim was to improve a recently developed procedure using aerial photo and geographic information software to analyze LW wood stored in wood jams (WJ), shortening the entire process. Digital measurement was simplified using only AgiSoft Metashape® software, greatly speeding up the entire process. The proposed improvement is more than five times faster in terms of measuring LW stored in jams.

/pdf/a-faster-approach-to-quantify-large-wood-using-uavs-2l00pusj.pdf

A Faster Approach to Quantify Large Wood Using UAVs

http://manuscript.elsevier.com/S000925412200047X/pdf/S000925412200047X.pdf

Optimizing 40Ar/39Ar analyses using an Isotopx NGX-600 mass spectrometer

Intercalibration of the servicio nacional de geología y minería (sernageomin), chile and wiscar 40 ar/ 39 ar laboratories for quaternary dating

The Saglek-Hebron Complex (northern Labrador, Canada) is a polymetamorphic terrane preserving felsic crustal rocks as old as 3.87 Ga. Crustal rocks of this age are rare and offer opportunities to interrogate how Earth's earliest continent forming processes may have differed from the modern plate tectonic regime. Oxygen isotope ratios (δ18O) in primary crystalline zircon are strongly affected by the incorporation of supracrustal materials during magmatism and can provide useful information about the character of early crustal reworking events. While zircon δ18O signatures >+6.4 ‰ indicate the incorporation of supracrustal material into the source of crustal anatexis, questions remain regarding the volumetric scale, sources, and processes by which supracrustal and magmatic mixing occurred during the Archean. Here, we present 271 zircon in-situ oxygen isotope analyses for a suite of seven Saglek-Hebron granitoids emplaced between 3.87 and 2.79 Ga in age, significantly expanding the temporal and lithologic diversity of the magmatic SHC zircon δ18O record. Collected from carefully characterized grain domains, primary zircon δ18O values range from 5.0 to 8.4 ‰ and include some of the highest igneous Archean zircon oxygen isotope ratios recorded to date. Leveraging an integrated workflow for identifying preserved zircon geochemistry, and correlating our new data with previous information from zircon Hf and whole-rock 142Nd/144Nd isotopes, we identify three periods of contribution from high-δ18O supracrustal material to crustal melts during reworking events in the SHC at 3.63, 3.33, and 2.79 Ga. Our work points towards repeated episodes of interaction between a maturing surface environment and magmatism from 3.6 Ga onwards at this locality. 

Mechanisms for generating elevated zircon δ18O in Archean crust: Insights from the Saglek-Hebron Complex, Canada

Early and variable contributions from supracrustal rocks in archean magmas from the saglek block (labrador, canada)

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