ZAKŁODZIE


Meta-E/E7
(previously primitive enstatite achondrite, EL melt rock, or E IMB)
(E achondrite-ung in MetBull 84)
standby for zakłodzie photo
Found September 1998
50° 45' 46" N., 22° 51' 58" E.

Zakłodzie is an 8.68 kg enstatite-rich achondrite that was found beside a dirt road by Mr. Stanislaw Jachymek, a mineral and fossil collector. This extremely weathered meteorite with remnant fusion crust was found about 40 km west of Zamosc, Poland, near the small village of Zakłodzie. Its meteoritic nature was first verified by Dr. Lukasz Karwowski of the Silesian University Geology Department. The initial mineralogical analysis and classification were performed at the Max-Planck-Institut für Chemie (Dr. Frank Wlotzka), the Polish Geological Institute (Dr. Marian Stepniewski), and the Bartoschewitz Meteorite Laboratory (Rainer Bartoschewitz).

Zakłodzie has a fine-grained, granular texture similar to that of several other recrystallized EL chondrites, including Happy Canyon, MIL 090807, and Ilafegh 009 (Boesenberg et al. (2014). It is composed of ~60 vol% orthoenstatite with ~20 vol% Si-bearing FeNi-metal, along with ~10 vol% of both troilite and feldspar. It also contains accessory schreibersite, tridymite, cristobalite, oldhamite, albandite, amphibole, and ubiquitous graphite. Keilite [(Fe,Mg)S], a mineral phase associated with strongly reducing conditions, has been observed in Zakłodzie (Karwowski et al., 2007; Uribe et al., 2017). Sinoite, a silicon nitride associated with crystallization of an impact melt, has been identified as inclusions within the keilite. While there are no visible chondrules, some elongated enstatite grains arranged in an oval configuration might represent extremely metamorphosed relict chondrules. There are abundant metal flakes, interspersed gas vesicles, and various light and dark inclusions present as well. While 0.1–4 mm (rarely as large as 9 mm; Przylibski et al., 2011) spherical graphite nodules containing metal inclusions (and vice versa), are present in the innermost portion of the meteorite, finely dispersed graphite producing a dark coloration occurs in the outer portion. Raman analysis shows that the graphite has a semi-ordered to ordered structure.

Zakłodzie shows similarities to the QUE 94204 pairing group. The bulk composition and petrography of both meteorites, especially the zoned and skeletal feldspar, unequilibrated anorthite contents in the feldspar, and polysynthetically twinned enstatite grains, suggests a possible rapid cooling at some stage. Moreover, the retention of abundant opaque phases, FeNi-metal surrounding enstatite laths, and relict chondrules, are all features consistent with impact melting and rapid cooling. In addition, the mineral keilite is only stable in conditions of rapid cooling of impact melts. All of these features taken together are considered by some investigators (Burbine et al. [2000], Keil [2007], and Keil and Bischoff [2008]) to best represent a classification for Zakłodzie as an E chondrite impact-melt breccia.

This classification is contrary to that proposed by Przylibski et al. (2005), who argue that rapid cooling from an impact-melt is inconsistent with the characteristics of Zakłodzie (e.g., cumulate texture, relict chondrules, triple junctions, slow cooling rate, silica content, and plagioclase enrichment). They believe instead that the features best fit a scenario in which Zakłodzie experienced initial slow cooling during cumulate processes, all the while undergoing fractional crystallization of forsterite sequentially forming protoenstatite ⇒ orthoenstatite ⇒ clinoenstatite, and also silica, feldspar, FeNi-metal, and sulfides. This rock is consistent with the residual material resulting from rapid partial melting of enstatite chondrite material. They propose that Zakłodzie subsequently experienced a rapid cooling phase as it was entrained in a rising magma column, assimilating chondrule-bearing rock as it rose. Following this stage, the low-melting-point components such as feldspar, metal, and sulfides were partially remelted in a subsequent impact event. Given this scenario, Przylibski et al. (2005) favor a classification for Zakłodzie as a primitive enstatite achondrite. In addition, they favor this classification for the enstatite meteorites Happy Canyon, Ilafegh 009, QUE 94204, and Y-8404. A study of Zakłodzie by Krzesińska et al. (2015) revealed micro-textural features and a mineralogy that suggests the source rock experienced a severe shock event. This was followed by burial under an ejecta blanket where recrystallization and annealing occurred.

In an effort to better understand the petrogenesis of Zakłodzie, Krzesińska et al. (2019) conducted petrofabric, textural, and nanostructural analyses of the mineral components. They recognized two lithologies, A and B, which formed under distinct heating and cooling conditions. The nanostructure of enstatite in Zakłodzie indicates the occurrence of impact shock-induced transformation in an already warm source rock, ultimately leading to an increase in temperature above the melting point. These conditions are different from those under which Ilafegh 009 and Happy Canyon were formed, both of which involved crystallization from a melt. Following the shock event on the Zakłodzie parent body, lithology A experienced a localized increase in temperature resulting in a low degree (up to 20%) of equilibrium partial melting and limited melt migration. This was followed by relatively slow cooling from 1000°C to 500°C, with a somewhat higher cooling rate in affect below this point. By contrast, lithology B experienced relatively slow cooling throughout its cooling and annealing period, consistent with a shallow burial. Krzesińska et al. (2019) cited multiple lines of evidence that suggest the parental source rock for Zakłodzie was likely chondritic prior to the shock-heating event. Based on the results of this study, they argue that this meteorite is neither an impact melt nor a primitive achondrite. Such a metamorphic stage transitional between chondrite and achondrite could be satsisfied by a classification of metachondrite.

Zakłodzie has a K–Ar closure age of ~4.50 (+0.02, –0.01) b.y. (Bogard et al., 2010). Other radiometric chronometers reveal that a melting event occurred ~2.1 b.y. ago, possibly reflecting the remelting impact event. The Al–Mg age of Zakłodzie was determined to be 5.4 (±0.4) m.y. after CAIs (4.5671 b.y.), or an absolute age of ~4.5617 b.y. (Sugiura and Fujiya, 2008). This age is consistent with other basaltic meteorites that experienced early melting and differentiation due to radioactive decay of short-lived radionuclides such as 26Al.

The cosmogenic nuclides in Zakłodzie, including 4He, 40Ar, 129Xe, and Q-type noble gases, indicate a CRE age of 55.3 (±5.5) m.y. This high exposure age is also characteristic of the aubrites, which cluster around 50 m.y. Noble gas studies indicate that Zakłodzie is distinct from equilibrated E chondrites. During its terrestrial residence, considered to be >100 years, Zakłodzie experienced very high oxidation of Fe throughout much of its mass. The Fe in the outer crust has progressed to hematite, with an admixture of the loess minerals in which the mass was found; nevertheless, 14C data indicate that Zakłodzie is a relatively recent fall.

Despite the very close similarities in O-isotope compositions between Zakłodzie and the ungrouped enstatite achondrite Itqiy, their respective chemical and mineral compositions, noble gas contents, and terrestrial ages exclude an origin from a common parent body. Likewise, differences between Zakłodzie and enstatite achondrites in some elemental ratios such as Mn/Cr exclude a common origin. The parent body was most likely a member of the enstatite chondrite group of asteroids, and the chemistry is most similar to the EL group (Stepniewski et al., 2000)—the Si concentration in kamacite of 1.5 wt% is more consistent with the EL group (EH: 1.9–3.8 wt%; EL: 0.3–2.1 wt%).

In 2006, the 685 g achondrite NWA 4301 was found in Algeria. Because this meteorite is almost identical to Zakłodzie in petrology and mineral composition, and since the two stones have similar young terrestrial ages of ~300 years, scientists have deduced that these two ungrouped enstatite meteorites could be source-crater paired (Irving and Kuehner, UWS). Micro-computed tomography (µCT) scans performed on samples of both of these meteorites indicate differences in their degree of weathering and in their metal abundances, with NWA 4301 exhibiting more weathering and more abundant and interconnected metal veining (Uribe et al., 2015). Continued comparative studies of both meteorites by Uribe et al. (2015) revealed some textural differences between these two meteorites, and they suggest that NWA 4301 might have experienced slower cooling than Zakłodzie.

The specimen of Zakłodzie shown above is a 0.74 g partial slice showing a portion of a metal vein. The top photos below show a large mass of Zakłodzie presented courtesy of Marcin Cimala. The middle photo is a thumbnail image to a high-resolution photo shown courtesy of Tomek Jakubowski. The bottom photo is an excellent petrographic thin section micrograph of Zakłodzie shown courtesy of Peter Marmet.

standby for zaklodzie photo
standby for zaklodzie photo
Photos courtesy of Marcin Cimala—PolandMET.com

standby for zaklodzie photo
click on image for a magnified view
Photo courtesy of Tomek Jakubowski

standby for lodran photo
click on image for a magnified view
Photo courtesy of Peter Marmet