Petrogensis of Diamonds Petrogensis of Diamonds in Ureilitesin Ureilites

(http://www.geocities.com/~dweir/KENNA.HTM)

Topics for TodayTopics for TodayExplanation of composition of a UreiliteLeading Hypothesis on composition of

diamonds.Support for each Hypothesis.Conclusions.

Explanation of Explanation of Composition of UreiliteComposition of Ureilite

Meteorites (25 Samples found)

Composed of…– Olivine ((MgFe)SiO4)– Pyroxene ((XY) Z3O6)– Pigeonite (Ca.25(MgFe)1.75 Si3O6) – Graphite (C)– Lonsdaleite (C)– Diamond (C)– Small Percentage of other

minerals. (Goodrich et al, 2002)

Explanation of Explanation of Composition of UreiliteComposition of Ureilite

Diamonds range anywhere from 1 m to 9 m

Other than diamonds it is the orientation of olivine that exhibits impact impressions

(Goodrich et al, 2002)

Explanation of Explanation of Composition of UreiliteComposition of Ureilite

Grouping of the ureilites is based on a schema created by John Berkely et al, (1980)– I: High in FeO/MgO <80 mol% of Forsterite

(Mg2SiO4)– II: Intermediate in FeO/MgO 80 – 90 mol% of

Forsterite– III: Low FeO/MgO <90 mol% Forsterite

Explanation of Explanation of Composition of UreiliteComposition of Ureilite

What separates them from other meteorites

1. Strongly recrystallized2. Lack minerals created at low temperatures3. Ureilites pyroxenes are represented by

pigeonite. Normally carbonaceous chondrite meteorites contain Orthopyroxene.

(Vdovykin, 1963)

Leading HypothesisLeading Hypothesis Hypothesis #1

– Diamonds resulting in collisions of asteroid bodies. (Vdovykin, 1963)

Hypothesis #2– Composition with in the ureilite parent body. (UPB)

(Berkley et al, 1980) Hypothesis #3

– Shock wave pressures from impact. (Goodrich et al, 2002)

Hypothesis #1Hypothesis #1Diamonds resulting in collisions of asteroid

bodies. (Vdovykin, 1963)– Before falling to Earth asteroids composted of

the UPB would collide and these collisions had enough pressure to create the diamonds exhibited by some ureilites.

Vdovykin Asteroid Vdovykin Asteroid CollisionsCollisions

Support– Small size of diamonds– No craters at impact

position– Presence of elongated

cavities in urelities

Against– Similar circumstances

can be caused by shock wave impacts. (discussed later in our talk)

Hypothesis #2Hypothesis #2Composition with in the ureilite parent

body. (UPB) (Berkley et al, 1980)– Who stated that it was the UPB that created the

diamonds.– He is against the idea that it was the

shockwaves created the diamonds in ureilites.

Berkley UPB and Berkley UPB and DiamondsDiamonds

Classification System– I: High in FeO/MgO <80 mol% of Forsterite– II: Intermediate in FeO/MgO 80 – 90 mol% of

Forsterite– III: Low FeO/MgO <90 mol% Forsterite

(Berkley et al, 1980)

Berkley UPB and Berkley UPB and DiamondsDiamonds

(Based off information from Berkley et al, 1980)

III 10-25 bars 1200 C

I 70-100 bars 1100 C

II 90-110 bars 1230 C

Hypothesis #3Hypothesis #3Shock wave pressures from impact.

(Goodrich et al, 2002)– The commonly accepted idea that it was

shockwave pressures that is created when a meteorite hits the earth that causes the diamonds to be formed.

Goodrich Shockwave Goodrich Shockwave PressurePressure

Slightly in conflict with Vdovykin and his idea of asteroid collisions.

Slightly different he has evidence that supports his ideas with new evidence.

This evidence is that those with out diamonds exhibit low shock levels.

Opposed to those who have diamonds have high shock evidence.

(Goodrich et al, 2002)

Goodrich Shockwave Goodrich Shockwave PressurePressure

This was done through the analysis of of olivine and graphite.– Olives did not have

and undularated extinction

– Shock lamellae in graphite.

(Goodrich et al, 2002)

ConclusionsConclusionsThree Hypothesis

– Asteroid collision model (Vdovykin, 1963)– Composition with in the ureilite parent body.

(UPB) (Berkley et al, 1980)– Shock wave pressures from impact. (Goodrich

et al, 2002)

ConclusionsConclusionsWho’s Correct?

– All could be all could not be, no definitive answer to the question…

– Where do ureilites?

Thank YouThank YouDr. Bernhard Saini-EidukatDr. Allan Ashworth

Thank YouThank You