[meteorite-list] Tektites from a Ring Arc (part 2)

From: Graham Christensen <voltage_at_meteoritecentral.com>
Date: Sun Mar 27 04:34:51 2005
Message-ID: <00c901c532b0$64b789b0$c3e13b8e_at_megavolt>

5. THE RING ARC AND THE AUSTRALASIAN FIELD

Distribution. The subsequent passage of the ring arc from west to east and
its collapse on the Earth's surface formed the Australasian strewn field of
tektites and microtektites. The Australasian field forms a single unit
distributed in a band of lattitudes north and south of the equator, a
configuration that would be expected from the decay of the ring arc in an
equatorial orbit. The geographic location of the strewn field on Earth's
surface would depend on the inclination of the ring arc to the equator, the
eccentricity of the orbit, and the argument of perigee at the time of entry.
All of these, as well as the apperent west to east deflection on both
hemispheres that arises from Earth's rotation (the Coriolis Effect), are
reflected in the present longitudinal position of the strewn field relative
to the equator.

It is known that the external shapes of tektites in the Australasian strewn
field form a continuous sequence from Australia to Indochina with
aerodynamically shaped smooth flanged buttons in the southeast, decorated
splash forms in the centre, and blocky, layered, Muong Nong types in the
northwest (O'Keefe 1976).

Flanged buttons. This morphology of tektites could be attributed to heating
due to atmospheric resistance as the ring arc passed through the Earth's
atmosphere. The frontal part of the descending arc would have been exposed
to greater atmospheric resistance and heating. Thus the tektites in the
front of the cluster would have undergone aerodynamic ablation and would
have descended to become the flanged butons (australites) in the southeast
end of the field. The extent of ablation found in these tektites is
consistant with velocities on the order of 10 km/s and entrances to the
atmosphere at low angles (O'Keefe 1976). The velocities of near-Earth
satellites are in this range, and a ring arc curcumscribing the globe would
also have possessed corresponding velocities closer to the Earth's
atmosphere. Thus the frontal portion of the cluster of tektites, when
entering the Earth's atmosphere, would have had the required velocities to
form the observed ablation. Also the tektites in front of the descending
cluseter, experiencing more air resistance, would have been accelerated
ahead of the rest of the body. (This phenomenon is the well known "satellite
paradox," where the drag force accelerates, rather than decelerates, a
satellite descending through the Earth's atmosphere.) And, in fact,
aerodynamically ablated tektites are located only in the foremost southeast
end of the field in Australia, where they are found sperated from the main
portion of the strewn field (O'Keefe 1976).

Microtektites. Collisions that occurred in the circumscribing terrestrial
ring system would have resulted in the formation of particles of different
sizes. As the ring particles aggregated into a cluster at perigee, further
collisions would have resulted in the break-up of constituents into much
smaller particles, which constitute the microtektites.

Splash form. Thus in the ring arc, the main mass of the body consisted of
the larger splash-form type of tektites whith microtektites embedded among
them. The splash-form type would have constituted the most common tektite in
the arc, and this type is, in fact, found in abundance in the Australasian
strewn field. The splash-form tektites in the main body of the arc would
have undergone less resistance and heating during entry than the tektites
exposed in front. Thus, these mid-region tektites were not ablated, and some
of the existing splash-forms even show signs of having been plastic only
when arriving at the surface. The shapes of most of the splash-form types,
such as dumbbells and teardrops, could have resulted from rotation and
break-up in the Earth's atmosphere during the descent. These tektites, as
expected, are found next in sequence to the ablated australites towards the
northwest, and are found widely distributed in the Philippines, Java,
Indochina, etc.

Layered. The microtektites that were embedded and moving within the cluster
of tektites could have accumulated sufficient heat to melt during the
atmospheric descent, fusing together to form larger masses. This process
could explain the formation of Muong Nong-type layered tektites. The
chemical inhomogeneity of these tektites, which has been attributed to a
differential mixing of glasses of different composition (Schnetzler 1992),
and the presence of small glass particles (lenticules) confirm that these
tektites are the result of the welding of a large mass of microtektites
(O'Keefe 1976). As expected from the melting/fusion of the abundant supply
of microtektites embedded within the ring cluster, these large masses are
found as melt sheets or puddles in "layered-only" sub fields, and are
located within the main field (Fiske et al. 1999). These are found as
fragmented masses wighing up to several kilograms towards the rear northwest
end of the field, mainly in Thailand, Laos, and Vietnam.

The dispersal of tektites as the cluster descended through the Earth's
atmosphere could explain the recent findings of tektites in Ganzu Province
in northern China and Tibet, which are considered an extension of the main
field. The Tibetan tektites are of special interest since the Tibetan
Plateau could have been in the path of the descending ring arc. If their
presesnce is confirmed, these tektites could represent the tail end of the
ring arc. The microtektites on the outer boundary that were loosely held to
the ring cluster would have been dispersed over a large area during
atmospheric entry, and deep-sea sediment samples have shown a wide
distribution of microtektites in the Indian and Pacific Oceans and the South
China Sea.

Sculptures and homogeneity. Interparticle collisions occuring during the
aggregation of tektites to form a ring cluster can explain existing tektite
thermal/chemical characteristics and sculptures. These collisions would have
resulted in the formation of microtektites in the cluster, and further
collisions could have occurred between tektites and microtektites. The
accumulation of heat caused by these inelastic collisions could have
resulted in the observed melting and homogenizing of the tektites and also
in the loss of water and other volatiles.

The sculptures seen in splash-form tektites, such as pits and meandering
grooves and gouges, could be the result of direct and grazing low-speed
collisions with smaller microtektites during the accretion of a ring arc.
This scenario is in agreement with the view that these sculpters were formed
before the tektites reached the Earth's surface (O'Keefe 1976). Specimens of
embedded tektites, where one has plunged into the other while in plastic
form, could also be the result of low speed collisions and adhesion
occurring during the formation of the cluster. Thus, it is seen that a swarm
of tektites and microtektites, undergoing inelastic collisions during its
formation, would provide the ideal thermal environment required to explain
the melting, refinding, and homogenizing of existing tektites - the "glass
making problem" as mentioned by O'Keefe (1976) - and also a variety of their
sculptures.

6. FORMATION OF THE NORTH AMERICAN, CENTRAL EUROPEAN, AND IVORY COEAST
FIELDS

The common characteristics that exist among the four tektite-strewn fields
indicate that all originated from a single source. All are dated to within
the last 35 million years of Earth's history, and all strewn fields have
splash-forms and microtektites as a common morphology. In petrology they
differ from terrestrial rocks; they are non-crystalline, homogeneous, and
deficient in water and volatiles; and all have a low ferric/ferrous ratio,
similar isotopic properties, and identical corrosion patterns. Analysis of
the chemical composition of the tektites in the strewn fields shows that a
first-order trend exists among the oxides of silica, magnesium, and calium
(silica is negatively correlated) and that the range from one field to
another is less than the range within a field (O'Keefe 1976). Also a linear
trend can be observed in neodymium/strontium values in tektites of all four
strewn fields (Glass et al. 1998). These common characteristics, which
encompass both chemical and physical domains, indicate that tektites in all
four strewn fields belong to a single family and thus originated from a
common source.

The North American, Central European, and Ivory Coast tektites are
chronologically (though not necissarily in chemical composition) linked to
three impact craters, namely Chesapeake Bay for the North American, Ries
Kessl for the Central European, and Bosumtwi for the Ivory Coast. The
distribution of the tektites is asymmetrical in relation to these craters,
and aerodynamically shaped tektites, similar to australites, have not been
found in these three strewn fields. These fields consist mostly of
splash-forms; layered Muong-Nong type tektites are scarce. Only one
georgiate and some layered-type tektites in deep sea cores are found in the
North American field, and a few layered moldavites are known in the Central
European field (O'Keefe 1976; Heinen 1998).

In the North American field, the tektites are distributed south of the
crater and fan out towards the equator. This strewn field covers a wide area
stretching from New Jersey to Barbados. All tektites here are found north of
the equator converging on the crater, and none are found further north of
the crater (Heinen 1998). Based on these observations, it is possible to
model the formation of the North American field in relation to the orbiting
tektite ring cluster at the time of the Chesapeake Bay impact event. The
impactor, moving from southwest to northeast, either collided or
gravitationally interacted with the orbiting ring cluster. The bolide then
entrained the tektites and microtektites from their orbit and dispesed them
in a southerly direction before impacting on the Earth's surface. Since the
ring arc was in an equatorial orbit, the strewn field would extend north of
the equator and converge towards the impact crater.

The distribution of the tektites in the Ivory Coast field in relation to the
Bosumtwi crater also gives credence to this proposition. In this case, the
impactor moved from west to east, passing the ring arc along the equator,
with the resulting tektite field stretching west of the crater in an
equatorial direction; tektites in the existing field have not been found
east of the crater. Microtektites distribution in the Atlantic Ocean also
shows a large strewn field west of the Botsumtwi crater along the equator.

In the Central European field the distribution again is asymmetrical in
relation to the relevant crater; the tektite strewn field is found east of
the crater, and none are found towards the west, indicating that the passage
of the impactor within the gravitational domain of the ring arc was from
southeast to northwest. Unlike the tektites in the other two fields
mentioned here, these tektites are found in close vicinity to the crater,
about 200 km east, and constitute a small strewn field in mass and
distribution (O'Keefe 1976).

These three fields mostly contain splash-form tektites and microtektites,
which are the main components of the proposed ring cluster. In this impacter
scenario, the entrained particles in the ring arc did not undergo natural
decay through the Earth's atmosphere as in the case of the Australasion
tektites. Thus, this model explains the absence of aerodynamically ablated
tektites and also the scarcity of layered tektites in these three strewn
fields. It is to be noted that these passing bolides would have
gravitationally drawn away less than 1% of the total mass of the ring arc.

7. AGES OF TEKTITE STREWN FIELDS AND COSMIC-RAY EXPOSURE

The ages of tektites and microtektites since arrival at the Earth's surface
have been determined by potassiu-argon (K-Ar) and fission-track analysis.
The former yields an age since the tektites were thoroughly outgassed by
heating and the latter gives a time since the latest heating episode. During
the passage of the tektites through the Earth's atmosphere, friction with
atmospheric gas molecules produced strong heating, which would result in a
partial melting and degassing of argon. Evidence of such melting and melt
flow is seen in tekties. Considering the small unit sizes of tektites, both
in mass and diameter, atmospheric heating could produce sufficient heat for
complete degassing of argon and thus reset the K-Ar clock and the fission
tracks. Thus the age-on-earth of tektites and microtektites determined by
these methods is the same as the statigraphic age of the geological
formations on which the tekties are found. As expected, the impact craters
associated with the North American, Central European, and the Ivory Coast
strewn fields also have the same ages of formation as the respective
tektites.

It is known that the primary cosmic-ray signatures seen in meteorites are
absent in tektites (O'Keefe 1976). This observation could be related to the
fact that the orbiting tektite cluster was enveloped within Earth's magnetic
field. The paths followed by primary cosmic rays are strongly influenced by
the Earth's magnetic field. Depending on their mass, speed, direction of
travel, and field strength, they can be deflected or follow spiral
convoluted paths as they descend towards lower altitudes. Thus the Earth's
magnetic field attenuates the energy of incoming particles and also results
in energy-cut-off values that increase towards low lattitudes. The
pedominance of low-energy particles and the minimum cosmic-ray intensity at
the magnetic equator attest to this shielding influence of the Earth's
magnetic field (Friedlander 1989). Thus, it is seen that tektites and
microtektites orbiting along the equator would not have been exposed to
high-energy cosmic rays such as those observed in meteoroids in
interplanetary space. Thus, the primary cosmic-ray encouners in space that
cause nuclear spallation reactions, resulting in radioactive isotopes, or
nuclei fissions yielding fission tracks, are not found in tektites.

CONCLUSION

As described in this paper, the ring arc model provides a framework to
scientifically explain the well-known characteristics of tektites and their
strewn fields. An orbiting ring arc provides explanations for the geographic
distributions, morphology, and sculptures of tektites. Aggregation into a
ring also furnishes the required conditions for volatile loss and
homogenization. The outer ring cluster can act as well as a souce for the
formation of the three fields related to the Australasian. A special feature
of this model is that the terrestrial ring system provides a rationale for
the existance of a unique family of natural glasses during a 35 million year
period of Earth's history.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Graham Christensen
voltage_at_telus.net
http://www.geocities.com/aerolitehunter
msn messenger: majorvoltage_at_hotmail.com
Received on Sun 27 Mar 2005 04:36:03 AM PST