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

Fig. Geological map of North Central Nicaragua with the catchment of Pantasma depression (Mapa Geologico Minero de la Republica de Nicaragua, INETER, 1995), modified (Ehrenborg 1996; Elming et al. 2001). Inset: location of the Pantasma structure in Central America.

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 e 54Cr value in polymict breccia. Two 40Ar/39Ar plateau ages with a combined weighted mean age of 815  11 ka (2 r; 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.

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