Glass bombs - part 2 of 3

[Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>]

WOLF VON ENGELHARDT (1967) Chemical composition of Ries glass bombs (GCA
67-8, 1967, pp. 1677-1689, excerpts):

Abstract

Thirty-two chemical analyses of glass bombs, taken from various suevite
localities within and outside the Ries crater, Germany are presented.
Two main glass types, (I: non-recrystallized, III: highly
recrystallized), and one intermediate (II: slightly recrystallized) can
be distingished. All glass bombs originate from the same melt. The
textural differences between the types I, II, and III are due to locally
different cooling rates of the suevite. The melt was formed in the
impact crater by shock melting of a limited mass of magmatic or
metamorphic rocks of uniform granititic composition. Minor chemical
differences between the glasses are mainly caused by later oxidation and
leaching processes which were controlled by the degree of
recrystallization. Some textural features are discussed by which
products of incomplete shock melting (like the Ries glasses can be
distinguished from rocks formed by differential anatexis or magmatic
dissolution.

1. Introduction

H.H. Nininger (1954) described small glassy, porous bombs, found in the
rubble at the rim of the Arizona Meteor Crater. He realized that they
were distinctly different from the volcanic cinders which are scattered
over the surrounding plains and concluded that they were formed as
products of rock fusion by the meteoritic impact. He called these bodies
"impactite slags." The term "impactite" was introduced by Barnes (1940)
for designating glasses "formed by the impact of meteorites fusing the
surface rocks and splashing them outwards into droplets which solidify"
(e.g. the glasses from the Henbury and Wabar crater, Spncer and Hey,
1933). Glass bombs, similar to those described by Nininger, but of
larger size, are to be found in the Ries crater,Germany. They are in the
form of irregular lumps or flat bodies of a characteristic shape (Flädle
or Fladen = pancake, see Hörz, 1965) and occur in the suevite, together
with crystalline rock fragments in different stages of shock
metamorphism (Shoemaker and Chao, I961; Stöffler, 1966; Von Engelhardt
and Stöffler, 1967). The internal texture (vesicles, flow fines) and the
forms of the bombs indicate that they were hurled through the air at a
high speed, in the form of liquid molten masses. They acquired their
outer shapes during this flight, and behaved like solids when they were
embedded in the suevite. It was stated in a previous paper (Von
Engelhardt and Hörz, 1965), on the basis of four old and four new
analyses, that glasses * from different localities in the Ries basin
have a very similar chemical composition. This can now be confirmed by
thirty-two analyses which are presented in Tables 2-6. Only larger bombs
(>50 cm^3) were investigated.
*For lack of an appropriate name, the term "glass" will be used for the
present in a rather broad sense: Ries "glasses" are not true glasses,
because they contain in a glassy matrix mineral fragments and variable
amounts of  recrystallization products, ranging from 0% to nearly 100%.




----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------

---

Follow-Ups:

• Re: Glass bombs - part 2 of 3
• From: almitt <almitt@kconline.com>

---

• Prev by Date: Glass bombs - part 1 of 3
• Next by Date: Glass bombs - part 3 of 3
• Prev by thread: Hap McSween´s revised book
• Next by thread: Re: Glass bombs - part 2 of 3
• Index(es):
  • Date
  • Thread