¹Melissa De Andrade Nunes,¹Ricardo I. F. Trindade,¹João Pedro Rodriguez Pinto,²Alvaro P. Crósta,³Gabriel G. Silva,⁴Ludovic Ferrière,¹Camila R. Sales,¹Giovanna M. Tosi
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70155]
¹Institute of Astronomy, Geophysics and Atmospheric Sciences, University of Sao Paulo, Sao Paulo, Brazil
²Institute of Geosciences, University of Campinas, Campinas, Brazil
³Institute of Chemistry, University of Sao Paulo, Sao Paulo, Brazil
⁴Natural History Museum Abu Dhabi, Abu Dhabi, United Arab Emirates
Published by arrangement with John Wiley & Sons

Geraisites are a newly recognized class of tektite from Brazil. They occur as centimeter-sized, elongated to subspherical bodies scattered across surface gravel and shallow subsurface layers within a ~90-km-long strewn field extending between the municipalities of São João do Paraíso and Curral de Dentro, near the border between the states of Minas Gerais and Bahia. This study presents a rock magnetic characterization of geraisites, aimed at understanding their magnetic mineralogy and remanent magnetization. The samples exhibit weak bulk magnetization dominated by a paramagnetic contribution, consistent with typical tektite compositions. In addition, rock magnetic analyses indicate the presence of a ferromagnetic fraction, as evidenced by demagnetization curves and hysteresis behavior. Lowrie–Fuller test and isothermal remanent magnetization decomposition indicate a dominant low-coercivity component consistent with nanoscale magnetite grains in the single-domain to pseudo-single-domain range. In some samples, the remanence behavior suggests overprinting by transient high-field processes, such as lightning-induced remanent magnetization. Furthermore, geraisites show a distinct relationship between magnetic susceptibility and iron content compared to other splash-form tektites, reflecting their relatively enhanced ferromagnetic contribution. Overall, these results provide new insights into the magnetic properties of geraisites and their comparison with other tektite populations.

¹Shivanshu Dwivedi,^1,2Jayanta Kumar Pati,³Wolf Uwe Reimold,¹Anuj Kumar Singh,⁴Gordon Robert John Cooper,¹Dhananjay Mishra,⁵Álvaro Penteado Crósta,¹Kuldeep Prakash
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70162]
¹Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Prayagraj, India
²National Center of Experimental Mineralogy and Petrology, University of Allahabad, Prayagraj, India
³Institute of Geosciences, Universidade de Brasılia, Brasılia, Brazil
⁴School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
⁵Institute of Geosciences, Universidade Estadual de Campinas-UNICAMP, Campinas, Brazil
Published by arrangement with John Wiley & Sons

The Dhala structure in India, one of the oldest and most deeply eroded impact structures known on Earth, exhibits distinct morphological features. Despite decades of investigation, two fundamental attributes of the Dhala structure, its shape (variously described as rectangular, elliptical, to circular) and diameter (2.96 to ~25 km) have remained unresolved. Here, we report extensive new data pertaining to the spatial disposition of different lithounits with pre-, syn- and post-impact fabric data, and the occurrence within target granitoids of overturned fold structures related to the collapse of the central uplift, and provide an updated estimate of the current impact-melt breccia volume of ~2 km3. We propose a firm constraint on the size of the transient crater based on the extent of shock effects within target rocks and drill cores of the crater floor and below. We also provide compelling evidence for the presence of a collapsed structural uplift in the region of the Central Elevated Area (CEA), which is surrounded by a ring of monomict impact breccia exposures. Diagnostic shock deformation features in target granitoid, Giant Quartz Veins (GQVs), and samples from the breccia ring are also reported. Multispectral remote sensing, combined with digital elevation model analysis using sunshading and radial derivative techniques, reveals multiple elliptical to ovoid features around the CEA. These features, along with structural and fabric data, indicate a strong control of pre-impact basement anisotropies on the final crater geometry. We propose a revised diameter of ~10–12 km for the transient cavity and ~25 km for the final structure based on the integrated field and remote sensing data sets. The Dhala structure exhibits a distinctly elliptical morphology, with its major axis oriented in the southwest-northeast direction. The age of the Dhala impact is revised by ~400 Ma, constraining it now to the 1700 to 2100 Ma interval. The revised age constraint is derived from shock-metamorphic features identified within GQVs of approximately 2.1 Ga age, indicating the pre-impact emplacement of these reefs.

¹Gabriele Giuli,^1,2Maria Rita Cicconi,³Angela Trapananti,⁴Sigrid Griet Eeckhout,⁵Giovanni Pratesi,⁶Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70156]
¹Scuola di Scienze e Tecnologie, sez. Geologia, Universita di Camerino, Camerino (MC), Italy
²Department of Materials Science and Engineering – Inst. Glass and Ceramics, Friedrich-Alexander-Universität,Erlangen-N€urnberg, Germany
³Scuola di Scienze e Tecnologie, sez. Fisica, Universita di Camerino, Camerino, Italy
⁴European Synchrotron Radiation Facility (ESRF), Grenoble, France
⁵Dip. Scienze della Terra, Universita di Firenze, Florence, Italy
⁵Department of Lithospheric Research, University of Vienna, Vienna, Austria
Published by arrangement with John Wiley & Sons

Two thin sections of Muong Nong-type tektites from the Australasian tektite strewn field have been analyzed by Fe K-edge X-ray absorption near edge spectroscopy (XANES), using a hundreds-of-micrometers–sized beam suitable for spatially resolved analysis of the Fe oxidation state across distinct regions of the samples. Earlier analyses with an unfocused beam were inconclusive regarding different amounts of oxidized iron in the Muong Nong-type tektites, but did indicate different chemical compositions of the lighter and darker colored layers. Experimental XANES spectra are very similar in shape to those of other tektites. However, small and reproducible changes were found in the pre-edge peak involving the centroid energy: the pre-edge peak of the spectra collected within the dark layers are reproducibly 0.2 eV at higher energy than those of the spectra collected within the light matrix. This difference in energy position is four times the estimated energy reproducibility and, therefore, is significant. By comparison with pre-edge peak data of Fe model compounds, we estimate the Fe3+/(Fe2++Fe3+) ratios in the light matrix and dark layers to be 5% and 15% (±5), respectively. The heterogeneous distribution of the Fe oxidation state in Muong Nong-type tektites, as opposed to the homogeneous Fe oxidation state distribution in splash-form tektites, is consistent with previous hypotheses, based on volatile contents, of Muong Nong-type tektites resulting from melts that experienced lower temperatures compared to those of splash-form tektites.