KATOL

In 2012, May 22 at approximately 2:30 P.M., a fireball accompanied by detonations was seen and heard by local residents as it streaked over the Akola and Nagpur districts of India, moving in a generally eastward direction. At the same time, the Broadband Seismic Observatory of the Geological Survey of India recorded a 2.1 magnitude seismic event lasting 90 seconds, which was centered 30 kms ENE of Akola. Several meteorite fragments were quickly recovered by residents in and around Katol.

Four fragments were recovered initially by residents at different locations, and these were documented by a team of geoscientists led by Binod Kumar: 1) the largest fragment, weighing 673.5 g, was found at Lakshmi Nagar by Nathoji Ramakrishna Charde; 2) a 74.4 g fragment was found near Khutamba road by Javed Razzak Shaikh after it penetrated the galvanized metal roof of a shed, damaging the concrete floor below; 3) a fragment was found at IUDP Layout by Govinda Muralidhar Mahajan that had penetrated 10 cm into the soil; and 4) a fragment was found at IUDP Layout towards Nagpur road by Pundlik Kashiram Shivarkar. It is now reported that more than 30 fragments have been recovered, having a combined weight of ~13 kg (Ghosh and Murty, 2014).

Extensive analyses of this unique meteorite were conducted at research facilities in both India (Geological Survey of India; Physical Research Laboratory; National Geophysical Research Institute) and America (Center for Meteorite Studies at Arizona State University; Institute of Meteoritics at University of New Mexico), eventually being published in the 2013 Meteoritical Bulletin #102 classified as an L6 chondrite.

An independent classification of Katol was published by Ghosh and Murty (Physical Research Laboratory, India) at the 45th LPSC, #1300 (2014). Here, Katol was classified as a shock-melted L6–7 ordinary chondrite, the first such breccia ever described. Although they report observing no discernable chondrules in the light-gray, recrystallized silicate matrix (primarily composed of olivine and low-Ca pyroxene), they did find rare microchondrules. Minor phases include plagioclase (mostly transformed to maskelynite), troilite, FeN-metal, high-Ca pyroxene, merrillite, and chromite. While specks of FeN-metal and troilite are ubiquitous throughout the meteorite, an ~2 cm-sized, shock-melted, multi-textured troilite–metal nodule was described as a shock-generated fragmental breccia.

The troilite–;metal nodule is composed of a complex intergrowth of most of the same components present in the bulk meteorite, but with the addition of various high-pressure phases including wadsleyite and ringwoodite (Ray et al., 2014). These high-pressure phases correspond to shock pressures of at least 45 GPa (S5) and temperatures in the range of 900–1500°C. In addition, the presence of a complex network of sub-mm to µm-scale shear-stress-induced melt veins with interconnected metal-sulfide melt pockets, as well as silicate grains with planar deformation features, attests to a shock-heating event in which some localized shock pressures approached ~90 GPa (S6+). Based on microtextural evidence such as the quench-texture of the troilite–metal nodule, it was inferred by Ray et al. (2017) that the nodule was formed in a severe impact long after the chondritic host rock had become thermally metamorphosed to type 6–7, and that it was incorporated into the host rock during brecciation processes prior to ejection from the parent body.

A study of seven shocked L chondrites was conducted by Ciocco et al. (2022 #6075) in an effort to determine both the timing of the shock-inducing impacts and the diameters of the impacting parent bodies. Two different shocked L chondrite groups were recognized: (1) a group that does not contain ringwoodite, has higher shock timescales between 11 and 16 seconds, and reflects a collision that occurred 461 (±57) m.y. ago between larger bodies including one that had a diameter of at least 150 km; and (2) a group that contains ringwoodite, has lower shock timescales as low as 0.5 seconds, and reflects a collision that occurred 650 (±160) m.y. ago between smaller bodies measuring ~70 km in diameter. Dating of both groups using U–Pb chronometry gave a common age of 4.481 b.y. after CAIs, which may reflect the time of breakup of the original L chondrite parent body.

In an effort to better define the transition between chondrites and (primitive) achondrites, Tomkins et al. (2020) conducted an integrated study of a broad spectrum of meteorites including Katol. In their investigation of Katol they identified distinct low-Ca pyroxene exsolution lamellae in augite and an interstitial plagioclase, augite, and orthopyroxene network, both of which are features indicative of incipient melting and consistent with a classification of petrologic type 7 in light of improved metamorphism classification criteria (see Systematics Part VI for further details). Tomkins et al. (2020) contend that both decay of short-lived radionuclides like 26Al and severe impact bombardment were occurring at the same time in the early Solar System. Therefore, they propose that the transition from chondrite to (primitive) achondrite should be defined on the basis of the highest temperature attained throughout a sample rather than making a distinction based on whether thermal metamorphism involved radiogenic heating followed by slow cooling on the one hand, and rapid impact-generated melting followed by slow cooling on the other. By adherence to this methodology the classificational terms 'type 7' and 'primitive achondrite' would become inclusive or synonymous terms.

Through measurements of the 60Co and 36Cl abundances, Murty et al. (2014) calculated the pre-atmospheric diameter of the Katol meteoroid to have been 1.7–3.4 m. Based on cosmogenic noble gas studies, they determined the CRE age to be 50 (±5) m.y. New noble gas data was obtained for Katol by Smith et al. (2021), and a younger CRE age of 30.4 (±6.1) m.y. is supported by the results; this is consistent with one of the major exposure age peaks known for L chondrites. The specimen of Katol shown above is a 1.17 g partial slice.