[meteorite-list] Selakopi and Glanggang and the Problem of Meteorite Pairing - Part 2 of 2

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Oct 20 15:31:33 2005
Message-ID: <DIIE.0000002C00003E3D_at_paulinet.de>

Best wishes,

Bernd


BENOIT P.H. et al. (2000) The non-trivial problem
of meteorite pairing (MAPS 35-2, 2000, 393-417):

Abstract

Pairing is the procedure of identifying fragments of a single meteorite fall
(that were separated during atmospheric passage or during terrestrial history)
by establishing the similarity of two or more meteorite fragments. We argue that
pairing is governed by two principles, that only a single mismatch of properties
is required to refute a proposed pairing, and that virtually all pairings bear some
degree of uncertainty. Using data distributions for modern falls, we take a probability
approach to estimate degrees of certainty associated with proposed pairings, emphasiz-
ing the importance of unusual features. For new pairing criteria or new analytical
additions to old criteria, the degree of variation within individual meteorites must
be delineated and the degree of variation within meteorite classes must be quantified.
Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid
space history indicators, and (3) terrestrial history indicators. Included in these cate-
gories are 11 specific criteria, including petrographic textures, mineralogy and mineral
composition, terrestrial age estimates, cosmic-ray exposure ages, and natural thermolumines-
cence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings
suggested in the literature have been subjected to this analysis. Many literature pairings,
especially those involving common meteorite types, bear large uncertainties due to lack of data.

"It turns out that the assigning of different meteorites to the same or to different
falls is a non-trivial problem ... The reason for the ambiguity is that similarities
are not necessarily proof of a common fall... " Schultz et al. (1991).

Introduction

"Pairing" is the procedure of identifying fragments of individual meteorite finds from
observations made during collection, from their macro- or microscopic properties, or
from analytical data. Meteorites fragment during atmospheric passage and during
weathering on Earth. Pairing groups can involve three or more samples, sometimes
as many as hundreds of fragments. Pairing is not a simple exercise but a challenging
endeavor that tests the limits of modern data sets. Here we summarize current ideas
concerning pairing with emphasis on degree of certainty, we review suggested literature
pairings, and we apply a probability approach to literature pairings ...

Pairing is important because it can affect the choice of samples for research, but it is
of fundamental importance in studies that deal with the statistics of classes or types of
meteorites. An example is the debate over if there are changes in the flux of meteorites
to Earth that are reflected in differences between Antarctic meteorites and modern falls.
Other examples include the delineation of ancient and modern strewn fields, studies of
factors affecting meteorite preservation, and comparisons of meteorite find concentrations
 .
Scott (1984a, 1989) summarized accepted pairing procedures and reviewed proposed pairings
of several hundred Antarctic meteorites. Since Scott's work, some pairing procedures have
been enhanced, whereas other procedures are now considered less important. In addition,
several analytical techniques relevant to pairing, such as 14C terrestrial age estimation,
thermolumincscence (TL), and M?ssbauer spectroscopy of weathering products have become
available and several data bases have been enlarged considerably, especially 36Cl terrestrial
ages and cosmogenic noble gas abundances.

The last decade has seen the addition of over 10 000 meteorite specimens to the worldwide
collection, including thousands more firom Antarctica and a growing number from hot deserts,
such as North Africa and the Nullarbor Plain of Australia. The listing of proposed pairings
has thus grown considerably.
Received on Thu 20 Oct 2005 03:31:30 PM PDT