Pantasma: Evidence for a Pleistocene circa 14 km diameter impact crater in Nicaragua

Abstract

The circa 14 km diameter Pantasma circular structure in Oligocene volcanic rocks in Nicaragua is here studied for the first time to understand its origin. Geomorphology, field mapping, and petrographic and geochemical investigations all are consistent with an impact origin for the Pantasma structure. Observations supporting an impact origin include outward‐dipping volcanic flows, the presence of former melt‐bearing polymict breccia, impact glass (with lechatelierite and low H2O, <300 ppm), and also a possible ejecta layer containing Paleozoic rocks which originated from hundreds of meters below the surface. Diagnostic evidence for impact is provided by detection in impact glass of the former presence of reidite in granular zircon as well as coesite, and extraterrestrial ε54Cr value in polymict breccia. Two 40Ar/39Ar plateau ages with a combined weighted mean age of 815 ± 11 ka (2 σ; P = 0.17) were obtained on impact glass. This age is consistent with geomorphological data and erosion modeling, which all suggest a rather young crater. Pantasma is only the fourth exposed crater >10 km found in the Americas south of N30 latitude, and provides further evidence that a significant number of impact craters may remain to be discovered in Central and South America.

Magnetic Properties and Redox State of Impact Glasses: A Review and New Case Studies from Siberia

“…This morphology may be typical of impact melts generated from target bearing large oxide grains, but this generalization needs further investigation. We note that some of the target rocks of these three craters are similar: andesitic to rhyolitic lavas [11,36]. Lavas are the only target rocks for Pantasma and El'gygytgyn while sedimentary target rocks dominate over lavas in Zhamanshin.…”

“…On the other hand, one may find metallic iron spherules due to impactor contamination [48,49]. The present synthesis will build on the two new Siberian impact glasses studied above, previous synthesis [9] as well as magnetic studies on Lappajärvi crater melt rocks [50], Lonar crater glass [51,52], of Mistastin crater melt rocks [53], of Jänisjärvi crater melt rocks [10], of Pantasma crater glass [11], complemented with M RS data from [20]. Data from [12] on irghizites will also be used to complement the database [9].…”

“…Table 3. Synthesis on magnetic properties of non paramagnetic impact glasses, after [9] complemented with data from [10][11][12]20,50,52,53] and this work. Sites are ordered by increasing mean susceptibility, with impact melt sheets at the end.…”

“…Microprobe analyses of South-Ural glass were carried out at IGEM RAS (Moscow, Russia) using JEOL8200. Water content of the South-Ural glass was determined in Grenoble using Fourier transform infra-red (FTIR) transmission microscopy with a VERTEX V70 spectrometer coupled to a Hyperion 3000 infrared microscope (see [11] for further details on the methodology). XAS measurements at the K-edge of Fe were performed at the LISA CRG beamline (BM-08) [22] at the European Synchrotron Radiation Facility (ESRF, Grenoble -France).…”

“…The purpose of the present paper, besides a summary of early studies, is to present a synthesis review of the magnetic properties of impact glasses, updating [9] using recent publications [10][11][12] as well as new results. These include a specific effort on glasses from Siberia (site 7-10 in Figure 1) either associated to a known crater (Popigai and El'gygytgyn) or not (Urengoite and South-Ural glass; [13]).…”