T136 Reading Igneous Textures

Monday, 23 September 2019
1:30 PM - 5:30 PM
Room 126ABC, North Building

CRITICAL COMPARISON OF TEXTURES OBSERVED IN IMPACT MELT AND VOLCANIC ROCKS

Paper number: T136-4
Program: Technical Sessions
Time: 2:25 PM – 2:40 PM

Authors

Abstract

Impact glasses, melt rocks, and hot breccias are a special class of igneous rocks that are formed (and emplaced) as the result of the vaporization, fusion and ejection of crustal material in response to shock metamorphism by asteroid and comet collisions. They contain a unique range of macroscale and microscale textures indicative of the broad range of thermodynamic and rheological parameters available during their petrogenesis. Taken without context (e.g. an unambiguous impact crater or meteorites), however, individual textures are not unique to impact rocks; some are especially recognizable to igneous petrologists familiar with disequilibrium systems. Yet a number of these textures (e.g. schlieren, ballen quartz, and checkerboard feldspar) often are cited by impact petrologists as diagnostic of an origin by impact processes. Moreover, terrestrial petrologists might see the same textures and compare the latter two to fish-scaled cristobalite and sieve-textured feldspar observed in normal volcanic rocks.

Although there may be substantive differences among similar textures, they often are subtle, not easily quantifiable, and even unconvincing in the absence of context. Impact petrologists undoubtedly over interpret the importance of some textures in their petrogenetic models, whereas our endogenic colleagues equally overlook impact materials in volcanic terrains. There is considerable need for more communication between the two communities in order to better understand these rocks. This is especially as we look forward to sample-return missions from worlds on which impacts are common, often in volcanic crusts. Toward that end we present a compendium of similar textures that occur in endogenous and exogenous igneous rocks and discuss their interpretation.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-338073

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.