ZAKŁODZIE


Primitive Enstatite Achondrite or
EL melt rock or E chondrite IMB
(E achondrite, ungrouped in MetBull DB)
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 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, 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). 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 may represent extremely metamorphosed relict chondrules. There are abundant metal flakes, interspersed gas vesicles, and various light and dark inclusions. 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, in addition to silica, feldspar, FeNi-metal, and sulfides. This rock is 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.

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 (4,567.1 m.y.), or an absolute age of ~4,561.7 m.y. (Sugiura and Fujiya, 2008). This age is consistent with other basaltic meteorites which experienced early melting and differentiation from 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 results indicate that Zakłodzie is a relatively recent fall.

Despite the very close similarities in O-isotope compositions bentween Zakłodzie and the ungrouped enstatite achondrite Itqiy, their chemical and mineral compositions, noble gas contents, and terrestrial ages exclude an origin of both meteorites from a common parent body. Likewise, differences between Zakłodzie and enstatite achondrites in some elemental ratios like 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 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 texture 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 may be source-crater paired (Irving and Kuehner, UWS). The specimen of Zakłodzie shown above is a 0.74 g partial slice showing a portion of a metal vein. The photos below show a large mass of Zakłodzie, courtesy of Marcin Cimala.

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