52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)

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THE BULK MINERALOGY AND WATER CONTENTS OF THE CARBONACEOUS CHONDRITEFALLS KOLANG AND TARDA. A. J. King1, H. C. Bates1, P. F. Schofield1 and S. S. Russell1 1Department ofEarth Science, Natural History Museum, London, UK (a.king@nhm.ac.uk).

Introduction: Carbonaceous chondrites offer
crucial insights into the abundance, distribution, andtransport of volatile species in the early solar system.
The low albedo asteroids from which they originate
likely played an important role in the delivery of waterand organic phases to the terrestrial planets [e.g. 1].
However, carbonaceous chondrites are susceptible toweathering processes and their volatile components are
rapidly modified upon entering the Earth’s atmosphere[e.g. 2]. Ideally, they are recovered, curated, andanalyzed as soon as possible after landing. In 2020
there were two large carbonaceous chondrite falls,Kolang and Tarda, providing an opportunity toinvestigate volatiles that have experienced minimal
exposure to the terrestrial environment.
The Kolang meteorite landed in Indonesia on the 1stAugust 2020 and ~2.5 kg of material has beencollected. In the Meteoritical Bulletin interior stones
are described as ranging from dark gray to black incolor and having a brecciated texture with chondrulerich and chondrule-poor lithologies [3]. Chondrules are
partially to fully hydrated and set within a matrix ofphyllosilicates, tochilinite, Fe-sulfides, and carbonates.
The mineralogy and oxygen isotopic composition of
the average Kolang lithology (δ17O ~1.75 ‰, δ18O~8.47 ‰) led to a CM1/2 classification [3].
On the 25th August 2020, the Tarda meteorite wasseen to fall in Morocco, with the first samples
collected the following day. Tarda has a total mass of~4 kg and is a breccia with abundant matrix (~80vol%) in which small chondrules and chondrulefragments are embedded [3]. The matrix consists ofphyllosilicates, magnetite, Fe-sulfides, and carbonates.
There are no calcium- and aluminum-rich inclusions(CAIs) but an igneous achondrite clast has been found.
The δ18O composition of separate fragments of Tarda
have a bimodal distribution overlapping with the CI(δ18O ~17 ‰) and CY (δ18O ~22 ‰) chondrites butwith lower Δ17O values than either group. It isclassified as a C2ung chondrite [3].
Here, we have used position-sensitive-detector Xray diffraction (PSD-XRD) and thermogravimetricanalysis (TGA) to characterize the bulk mineralogy
and water contents of Kolang and Tarda ~4 months
after their fall. We conclude that Kolang is the mostaltered CM chondrite fall recovered to date, and that
Tarda likely formed on a hydrated parent body beyond
the orbit of Jupiter.

Experimental: Approximately 200 mg fusioncrust free chips of Kolang and Tarda were powdered
and homogenized using an agate mortar and pestle.
The powdered meteorites were then loaded into
aluminum sample wells (~50 mg) and analyzed using aPSD-XRD at the Natural History Museum (NHM),London. Following our established procedures,
diffraction patterns were collected for 16 hours for themeteorites and 30 minutes for standards, and mineralabundances were quantified using a profile-stripping
method [4‒6].
After the PSD-XRD measurements, ~12 mg ofeach meteorite powder was analyzed using a TA
Instruments SDT Q600 TGA at the NHM. The powder
was loaded into an alumina crucible and mass loss
recorded as the sample was heated at 10°C/min fromroom temperature to 1000°C under an N 2 flow. Water
contents were determined by assuming that all massloss between 200 ‒ 800°C was due to the dehydrationof -OH/H2O-bearing phases; this is a slightoverestimate as Fe-sulfides, carbonates, and organics
also breakdown in this temperature range [7, 8].
Results & Discussion: Figs. 1 and 2 show thePSD-XRD patterns and TGA curves for Kolang andTarda. Fig. 3 compares their bulk phyllosilicate andwater contents to the CI, CM and CY chondrites.

Fig. 1. PSD-XRD patterns of Kolang and Tarda.

Kolang. Kolang is comprised of phyllosilicates (82vol%), olivine (8 vol%), pyroxene (5 vol%), magnetite(3 vol%), Fe-sulfides (1 vol%) and calcite (1 vol%).
Tochilinite was not detected by PSD-XRD. We concurwith a CM1/2 classification; Kolang has aphyllosilicate fraction (PSF) of 0.86, whichcorresponds to a petrologic sub-type of 1.3 on the scale52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548)

of Howard et al. [5] and 2.2 on the scale of Rubin et al.
[9]. The TGA derived water abundance is ~13 wt%
and while Kolang is a breccia, Fig. 3 confirms that its
bulk mineralogy and water contents are consistent withthe most altered altered CM chondrites [6, 10].
Other highly altered CM chondrites have relatively
low δ18O values (~2 ‒ 6 ‰) [11]. The oxygen isotopic
composition of Kolang’s average lithology plots in themiddle of the CM field and is heavier than all otherCM1/2 and CM1 chondrites (excluding several hot
desert meteorites), although the composition of ourKolang powder is yet to be determined. Models predictheavier oxygen isotopic compositions with increasingalteration by δ18O-rich fluids [e.g. 12]. Previously
analyzed CM1/2 and CM1 chondrites were desert
finds, and their low δ18O values might be explained byterrestrial contamination [11]. Kolang is the mostaqueously altered CM chondrite fall and has
experienced negligible weathering, so further studiesof this meteorite will be important to establish therelationship between alteration and oxygen isotopes onprimitive asteroids.

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We find no compelling evidence for phyllosilicate
dehydration and recrystallisation in Tarda.
The oxygen isotopic composition of Tarda issimilar to that of WIS 91600 (δ18O ~17 ‰), an unusual
heated (~400‒500°C) and magnetite-rich (~9 vol%)CMan chondrite believed to have formed at ~10 AU[15]. However, considering both isotopic andmineralogical characteristics, we suggest that Tarda isa C1/2ung chondrite most closely related to the uniqueC2ung Tagish Lake (δ18O ~18 ‰). The bulk mineralogyof Tagish Lake includes phyllosilicates (71 vol%), FeMg carbonates (12 vol%), olivine (7 vol%), magnetite(5 vol%) and Fe-sulfides (5 vol%) [4]. The Tagish
Lake parent body is estimated to have formed at ~8 ‒13 AU [16]. Tarda is also likely a sample from theouter regions of the solar system, a hypothesis that will
be tested by upcoming infrared (IR) measurements.

Fig. 3. Phyllosilicate and TGA derived water abundances for
Kolang and Tarda compared to CI, unheated and heated(Stages I‒IV) CM, and heated CY chondrites. Data are takenfrom [6, 8, 10, 13, 17, 18].
Fig. 2. TGA mass loss curves for Kolang and Tarda.

Tarda. Tarda consists of phyllosilicates (72 vol%),olivine (10 vol%), magnetite (8 vol%), Fe-sulfides (8vol%) and dolomite (2 vol%), giving a PSF of 0.88 anda petrologic sub-type of 1.3. The PSD-XRD pattern of
Tarda is comparable to the CI chondrites but its TGA
mass loss curve is different [8, 13]; sulphates and Fe(oxy)hydroxides are absent, and the profile of thecurve suggests that the phyllosilicates may belong tothe chlorite-group (e.g. chamosite and clinochlore).
The estimated water abundance is ~13 wt%.
Based on its mineralogy and water contents weagree that Tarda is distinct from the CI chondrites. It
also differs from the CY chondrites, whose heavy
oxygen isotopic compositions have been attributed tothermal metamorphism at temperatures >500°C [14].

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[5] Howard K. T. et al. (2015) GCA, 149, 206‒222. [6]King A. J. et al. (2017) M&PS, 52, 1197‒1215. [7]Garenne A. et al. (2014) GCA, 137, 93‒112. [8] KingA. J. et al. (2015) Earth, Plan. Spa., 67, 198. [9] Rubin
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