WHERE DO THEY COME FROM?

Perhaps a better question to ask is: Do we know where they come from?

From page 1 we feel confident our candidates could be meteorites. If this is the case then we must answer no  to the above question. However, we can compare our candidates elemental composition to that of terrestrial basalt and that basalt type which is found on Venus and see which basalt type it most closely matches.

In order to do this we need elemental data from Venus and we also need to have elemental data on our candidate. We also need to understand there are many similar characteristics that these 2 planets share in common. This is why it could be very difficult to recognize a Venusian meteorite.

In our solar system Venus is the planet most similar to Earth in terms of size, mass, and average density, with Earth just slightly greater than Venus in each of these characteristics.(3)

These similar Earth like characteristics are also found in the elemental composition of the rocks that constitute the lithology of Venus. Venera 13 and Venera 14 have determined for the first time ever the elemental composition of the Venusian rocks at the probes' landing site. The chemical composition of the rock at the Venera 13 landing site proved to be similar to the composition of potassium alkaline basalts of the earth's crust, rocks which can be found on oceanic islands and in rift zones. The chemical composition of the rock at the Venera 14 landing site is similar to that of tholeiitic basalts of the oceanic crust of the earth (1).

TABLE 1 (3)   composition of Venusian rocks, % by mass-------composition of unidentified candidates, % by mass

We could see from the pictures on page 1 the meteorite candidates looked like basalt. We now know for sure by the elemental analysis above that they are indeed a type of basalt. If we examine the above data close enough we can see some discrepancies between the Venera13, Venera 14 and Vega 2 landers.

These discrepancies include very high K2O values at the Venera 13 site but practically non-existent at the Vega 2 site. Same can be noted for Na2O values. Also some vast statistical deviations can occur in the individual elements as seen with the MgO data at the Venera 13 site - MgO can range from 5.2 to 17.6, same can be noted with SO3 and others.

It is important to understand the occurrence of these discrepancies and some latitude should be given. Unfortunately, the available data have not yet provided any possibility of confidently determining the mineralological composition of Venus' surface.(3) We do however find some strong similarities between our candidates and Venusian basalt.

                            TABLE 1a (3)

We now know our candidates are basalt, but what type of basalt? Would they match Alkaline basalts or tholeiitic basalts which are the closest representative basalts found on earth that match Venusian basalt?

In order to help us determine this we need to find elemental data on the average composition of basalts and andesites.

Table 8-6 (12)

At first glance it is difficult to peg down what type of basalt the candidates are composed of. The measurement of SiO2 can be critical in identifying a rock and would be a good place to start. We could say the elemental composition of our candidates do match a tholeiitic basalt and/or an alkali basalt. Several of our candidates were tested and SiO2 values were 45.11-- 49.28 -- and 51.53, for an average SiO2 content of 48.64.

But based on U, Th and high K2O values it also resembles an andesite, but not the SiO2 values of andesite. We require a more comprehensive method of distinguishing the candidates lithological rock type.Like what we would find in a petrographic description. An andesite is typically what we would expect to find if our candidates were just pieces of ordinary basalt that we would pick up on field trips.

Suffice it to say, and that which will be shown on another page. We do know that our meteorite candidates resemble alkali basalts from the petrographic description that was performed, but with strange inconsistancies. With this fact in mind we can also see the strong resemblance to Venusian basalt based on the K2O and SiO2 relationship presented in Table 2. In terrestrial basalt as the K2O content increases so does the content of SiO2.

TABLE 2 (3)

Every K2O and SiO2 value from table 8-6 has been plotted in blue. Those plots in blue represent the compositional trends for terrestrial rocks, as a function of the percentage ratio of silica (SiO2) and Alkalis (K2O), and their comparison with measurement data of radioactive elements at the Venera and Vega landing sites (3).

The red plot represents the average K2O - SiO2 ratio of the candidates that were tested  and which typifies the basalt type found at the Venera 13 landing site. You will notice the Andesites from table 8-6 have also been plotted and can also have high K2O values. However as previously mentioned, as K2O increases so does SiO2 in terrestrial basalts. But not in our candidates case.

So far our candidates do match the basalt type which is found on Venus as equally well if not more so than the basalt we find on Earth.

Another chart we can plot is a chart of comparison to meteorites chart. This shows ratios of elements as compared with each other and where Venusian basalt would plot out on the chart and also where average terrestrial basalts from table 8-6 would plot out.

TABLE 2A

Tholeiite, Oceanic Alkali basalts and Cont. Rift Alkali basalts from table 8-6 have been plotted in purple to compare their distribution as ratios to those candidates which were tested, represented by a blue + and their proximity to the red dot which represents the elemental ratios from the Venera 13 landing site. Again we find the samples matching Venusian basalt more closely than terrestrial basalt

If this seems confusing and it can be, it is because Venus and Earth are very similar in their compositional characteristics so we must dig out and examine everything we can find that might distinguish these 2 planets. This is a very good reason why the statement made at the top of page 1 was quoted. This is not an easy assignment or task we are undertaking.

Recent testing of a 61g sample indicates the mineral composition of plagioclase to be AN70. We therefore know with absolute certainty that the samples do not fall within the categorization of Andesitic basalts whose average composition of plagioclase is equal to AN 50 (2), of which is represented in table (8-6) last 3 columns.

This Andesite, as previously mentioned, is the most typical form of basalt you and I pick up on our field trips. Rather, our meteoric candidates can be classified into the upper Labradorite/lower Bytownite field. This evidence will be presented in the petrographic description that was done on our meteorite candidates.

Comparing the sample data from table 1 and table 1a to the data found on table 8-6 we can see a correlation between the samples tested to a Tholeiitic basalt and Alkali basalt. However, there are some inconsistencies if one assumes these samples are terrestrial in origin. The U and Th content does not match any of the Tholeiitic, Oceanic or Cont. rift basalts (table 8-6), but in fact have a closer relationship to those found in Venusian basalts (see table1a).

We can also recognize this same inconsistency when comparing K2O levels (see table1 and table 8-6). The K2O value is an ideal match with Venusian basalt but not that of terrestrial Tholeiitic, Oceanic or Cont. rift basalts. When comparing elements it is mandatory to compare those elements that constitute the bulk composition of the rock. This will help to define the general rock type. Those elements that are usually expressed as % include Si, Al, Ca, Mg, K, Na, Fe and Ti.

As we compare the sample that was tested to those of Venusian basalt (table1) we can see recognizable similarities. If we compare the sample which was  tested with Oceanic and Cont. rift alkali basalts (table 8-6) we also see recognizable similarities other than those previously mentioned (U, Th and K2O).

Have we answered our question on where did these meteorite candidates come from? The answer is no, but we can say the resemblance to the rock type found on Venus is more than coincidental and intriguing enough to continue our pursuit of further testing of our probable meteorite candidates.

OXYGEN ISOTOPES

Another testing method we can use that can help us identify where a meteorite came from  is called an Oxygen isotope analysis. For a new, unknown meteorite type this examination may or may not tell us if we do in fact have a meteorite.

An oxygen isotope analysis was performed to assist in the determination of the samples parentage or host source. A value of d18O(smow)=8.6 and a value of d17O(smow)=4.3 shows the candidates lie on the terrestrial mass fractionation line of .5, which is expressed on the table below as -0-. Or, trying to make it easier to understand, there is a deviation of ~.3 in the isotopic ratios between Earth and Mars, where as Earth, as plotted below is expressed as the mean or standard and expressed as -0-.

TABLE1 (4)

Oxygen isotopic variation of the terrestrial planets. On this modified version of a three isotope plot mass fractionation lines (constant delta 17O) plot as horizontal lines. Terrestrial data not shown as this spans a very large range in s18O but has a similar scatter to lunar and martian data sets (4). This means the isotopic ratios on earth are not a nice tight line as shown above but have some scattering above and below the line.

It has been proposed by science that the Earth, Moon, Venus and possibly Mercury were all created from the same protoplanetary material. In fact, high precision measurements of Lunar rocks (Wiechert et al.) shows that there is no isotopic difference between the Earth and the Moon, confirming these 2 bodies accreted from the same material. There is also a trend between isotopic ratios and distance from the Sun. As distance from the sun increases the variability in oxygen ratios appears to increase. Without further testing it would be unwise and should not be presumed the meteorite candidates are earth based terrestrial rocks based only on the oxygen isotope ratio.

So what did all that just mean? The Oxygen isotope analysis of the candidates have the same isotopic ratio as Earth rocks and Lunar rocks. We know by the elemental analysis these candidates are not Lunar rocks, so could they be terrestrial basalts? We don't know because we don't have the oxygen isotope data for Venusian basalt.

FIELD EVIDENCE

Show me more....but not too much more.

Strewn field goes over the small set of hills in the background

One of many interesting photos. This photo was recorded onto compact disk from a Hi C8 video camcorder I had with me. The main mass was located after several days plotting smaller fragments. After enough samples were found and plotted by GPS it was determined the main mass should be either to the NE or SW.

It was determined to enter the strewn field from the extreme NE following the centerline of the strewn field in the hopes of encountering the main mass. The main mass was located at the NE end, centerline of the strewn field thus establishing the direction of travel. At the time of this photo the main mass had not been touched, it is in situ.

It was not until later while viewing the film footage was a discovery  made. You should take special note of the ring of sediment much like a waterline (top arrow). Notice it is not level or parallel with the ground as is the bottom arrow and what would be expected if this rock had been lying on the ground for 30.7 million years. The age of which was determined by K/Ar  testing of the meteorite candidates ( Rad 40ar 10  -14 mol/g 1.66).

It is believed that the meteorite candidate, for a lack of a better word, thwacked, into the ground to a depth equal to the accumulation ring, and resting there for a period of time, developed the ring of material which accumulated until some mechanical force such as frost heaving brought it back to the surface. A process of perhaps ~ 100 years or less. This time element and theory will become more apparent to us when we discuss the petrographic description of the samples. Picture characteristics: mid November 2003, white areas directly underneath rock is snow.

To get a better picture or understanding of our candidates lifestyle we need to know where they came from. What were, or still are, the environmental characteristics from where they were found. Do you remember how old they are? This is vital and very revealing information and plays a tremendous role in understanding the petrographic description which will be covered on page 3. Lets refresh our memory. The candidates are 30.7 million years old, they lie on a saline lake bed that is seasonally wet in the spring and winter,  dry and hard in the summer months. The high salt concentrations and alkaline base make for a terribly corrosive environment. The leaching of these compounds into the specimens interior are unfortunately, inevitable.

Lake Bonneville as shown in the below map covered a vast expanse of Utah and some portions of Nevada and Idaho for approximately 18,000 years, beginning 32,000 thousand years ago and ending around 14,000 years ago.(14)

This means that if our meteorite candidates have been lying in situ (in place) for 30.7 million years then that would also mean they have been underwater for 18,000 of those years. We should remember this fact when we address the petrographic description on the next page. Why? because the petrographic description will show that there is no evidence for the presence of any secondary hydrous minerals and also vesicles are abundant and most are not filled. What does this mean? This means our meteorite candidates have not been lying on the ground for very long, most especially submerged in a marine environment for 18,000 years, let alone subjected to 30.7 million years of terrestrial weathering on the saline/alkali lake bed.

Harsh conditions are affecting this specimen. Depending upon where the specimens are found in the strewn field also determines the degree of weathering they endure. On the lakebed they may be submerged during wet years and are always in contact with the mixture of salt and alkali. At higher elevations the soil consists more of sand and dirt which is more abrasive than the salt/alkali combination. Here, wind abrasion is probably the bigger factor in the weathering process.

A nice smaller than walnut sized piece

Some additional photos that support a high speed atmospheric entry.

PHOTO A                                                                       PHOTO B

The specimen in the photograph at right (photo B) is actually a fragment that belongs to the specimen on the left (photo A). It fits in the lower left portion of the rock. The small fragment broke off during atmospheric entry and was oriented and shows signs of orientation while the larger specimen  was unstable during its atmospheric journey. These 2 specimens were found approximately 1/8 mile apart.

PHOTO C

The smaller fragment from photo B has now been put in place on its parent body (photo A) resulting in this picture which is referred to as photo C. It is obvious from the blue arrows that the smaller fragment fits very nicely but whose diameter is smaller. The explanation for this phenomena comes from the fact the smaller piece was dislodged from the host during the atmospheric entry and oriented itself, as is evident from the yellow arrows. This resulted in the oriented face of the smaller specimen receiving most if not all of the ablation effects, thus reducing its mating diameter.

In contrast, the ablation effects on the larger specimen were equally distributed over the rocks surface as it tumbled through the air. This is much like a rock wedged in a tire as it is driven down the road. The tire and rock are spinning in unison, but as the forces grow, the rock (or fragment) becomes dislodged no longer spinning with the tire but travels on its own. The effects pictured in photo C cannot be attributed to any terrestrial weathering process.

So far we have seen corroborative evidence in support of the candidates "matching" that basaltic type rock which is found on the surface of Venus as well, if not better than that of terrestrial origins.

Although the difference among the 2 planets (Venus and Earth) and their respective comparative lithologies are small. We may find there is a difference that can be noted and studied.

In the following presentation (page 3) we will examine the meteorite candidates in even greater detail and present the petrographic description in full, including some wonderful pictures of the mineral structure.

Nice accumulation area of material at top * Note * this piece no longer exists - consumed in testing