The nature of the L chondrite parent body's disruption as deduced from high‐pressure phases in the Sixiangkou L6 chondrite

Abstract

The disruption of the L chondrite parent body (LCPB) at ~470 Ma is currently the best‐documented catastrophic celestial impact event, based on the large number of L chondritic materials associated with this event. Uranium‐lead (U‐Pb) dating of apatite and its high‐pressure decomposition product, tuite, in the Sixiangkou L6 chondrite provides a temporal link to this event. The U‐Pb system of phosphates adjacent to shock melt veins was altered to varying degrees and the discordance of the U‐Pb system correlates closely with the extent of apatite decomposition. This suggests that the U‐Pb system of apatite could be substantially disturbed by high‐temperature pulse during shock compression from natural impacts, at least on the scale of mineral grains. Although many L chondrites can be temporally related to the catastrophic LCPB impact event, the shock conditions experienced by each individual meteorite vary. This could be due to the different geologic settings of these meteorites on their parent body. The shock pressure and duration derived from most meteorites may only reflect local shock features rather than the impact conditions, although they could provide lower limits to the impact conditions. The Sixiangkou shock duration (~4 s), estimated from high‐pressure transformation kinetics, provides a lower limit to the high‐pressure pulse of the LCPB disruption impact. Combined with available literature data of L chondrites associated with this impact event, our results suggest that the LCPB suffered a catastrophic collision with a large projectile (with a diameter of at least 18–22 km) at a low impact velocity (5–6 km s−1). This is consistent with astronomical estimates based on the dynamical evolution of L chondritic asteroids.

Petrogenesis and In Situ U‐Pb Geochronology of a Strongly Shocked L‐Melt Rock Northwest Africa 11042

“…The lower intercept U‐Pb age of 465 ± 47 Myr for NWA 11042 recorded the time of a later severe impact event that may be associated with the breakup event of the L‐chondrite parent body at 470 ± 6 Ma (Heck et al, ; Korochantseva et al, ). The timing of the breakup event is also widely recorded in L‐related rocks such as Novato (U‐Pb, 473 ± 38 Myr; Yin et al, ), NWA 7251 (U‐Pb, 574 ± 82 Myr; Y. Li & Hsu, ), Sixiangkou (U‐Pb, 471 ± 110 Myr; S. Li & Hsu, ), and Chico (Rb‐Sr, 467 ± 15 Myr; Fujiwara & Nakamura, ).…”

“…Many heavily shocked L‐chondrites suffered a major impact event around 470 Ma, which is very likely related to the catastrophic disruption event of the L‐chondrite parent body (Bogard et al, ; Haack et al, ; S. Li & Hsu, ; Y. Li & Hsu, ; Swindle et al, ; Yin et al, ). The strong shock effects of NWA 11042 are most likely related to this event, which also reset the U‐Pb isotopic system of apatite in NWA 11042.…”

“…Many heavily shocked L-chondrites suffered a major impact event around 470 Ma, which is very likely related to the catastrophic disruption event of the L-chondrite parent body (Bogard et al, 1995;Haack et al, 1996;S. Li & Hsu, 2018a;Y.…”

Accretion of a large LL parent planetesimal from a recently formed chondrule population

“…The radiogenic 207 Pb/ 206 Pb compositions of OC phosphates permit calculation of Pb-phosphate dates with sub-million-year resolution that precisely record the 10-to 100-Ma cooling histories of OC bodies. Yet, the temperature dependence of diffusive Pb loss from phosphate minerals can leave this system susceptible to perturbation by secondary reheating events from impact-induced shock heating, as observed in the highly shocked L chondrite Sixiangkou (29). Thermal conditions associated with shock stages ≥S5 are predicted to be requisite for Pb-phosphate system partial resetting (18).…”

The Late Ordovician (Sandbian) Glasford structure: A marine‐target impact crater with a possible connection to the Ordovician meteorite event

“…The age question holds particular interest because the early Cincinnatian estimate implies a possible connection to the "Great Ordovician Meteorite Shower," a period of enhanced meteorite influx caused by the breakup of a large asteroid-the L-chondrite parent body (LCPB)-in the main asteroid belt at approximately 470 Ma (Korochantseva et al 2007). The LCPB breakup has been described as "the largest documented breakup event in the asteroid belt during the past 3.5 Gyr" and is thought to be responsible for the disproportionate number of Middle to Late Ordovician impact craters on the Earth (Korochantseva et al 2007;Orm€ o et al 2014;Schmieder et al 2015;Bergstr€ om et al 2018;Li and Hsu 2018).…”