Major and trace element compositions of melt particles and associated phases from the Yaxcopoil-1 drill core, Chicxulub impact structure, Mexico

Abstract

Abstract-Melt particles found at various depths in impactites from the Yaxcopoil-1 borehole into the Chicxulub impact structure (Yucatán) have been analyzed for their major and trace element abundances. A total of 176 electron microprobe and 45 LA-ICP-MS analyses from eight different melt particles were investigated. The main purpose of this work was to constrain the compositions of precursor materials and secondary alteration characteristics of these melt particles. Individual melt particles are highly heterogeneous, which makes compositional categorization extremely difficult. Melt particles from the uppermost part of the impactite sequence are Ca-and Na-depleted and show negative Ce anomalies, which is likely a result of seawater interaction. Various compositional groupings of melt particles are determined with ternary and binary element ratio plots involving major and trace elements. This helps distinguish the degree of alteration versus primary heterogeneity of melt phases. Comparison of the trace element ratios Sc/Zr, Y/Zr, Ba/Zr, Ba/Rb, and Sr/Rb with compositions of known target rocks provides some constraints on protolith compositions; however, the melt compositions analyzed exceed the known compositional diversity of possible target rocks. Normalized REE patterns are unique for each melt particle, likely reflecting precursor mineral or rock compositions. The various discrimination techniques indicate that the highly variable compositions are the products of melting of individual minerals or of mixtures of several minerals. Small, angular shards that are particularly abundant in units 2 and 3 represent rapidly quenched melts, whereas larger particles (>0.5 mm) that contain microlites and have fluidal, schlieric textures cooled over a protracted period. Angular, shard-like particles with microlites in unit 5 likely crystallized below the glass transition temperature or underwent fragmentation during or after deposition.

A Rhaetian40Ar/39Ar age for the Rochechouart impact structure (France) and implications for the latest Triassic sedimentary record

“…The same idiomorphic K‐secondary feldspars as in the Videix gneiss, are widely represented in Rochechouart impactites such as in vesicles of impact melt rocks (e.g., near Babaudus, Valette, and La Chauffie in the central part of the Rochechouart impact structure), and in the Chassenon suevite. Similar observations have been reported from some other impact structures on Earth, e.g., Chicxulub (Mexico; Tuchscherer et al. 2006) and Kärdla (Estonia; Versh et al.…”

Petrographic investigation of melt and matrix relationships in Chicxulub crater Yaxcopoil-1 brecciated melt rock and melt rock-bearing suevite (846–885m, units 4 and 5)

“…The sedimentary rocks at the Yax-1 site can contribute Mg to the fluids from the breakdown and decomposition of the carbonate-rich components in the upper units. The presence of shock-induced, recrystallized carbonate particles, including dolomite have been reported in Yucatán 6, Yaxcopoil-1, and UNAM-7 drill core samples, and Chicxulub ejecta by many authors (Jones et al, 2000;Claeys et al, 2003;Dressler et al, 2004;Hecht et al, 2004;Pope et al, 2005;Tuchscherer et al, 2006;Salge, 2007;Yancey and Guillemette, 2008;Schulte et al, 2009Schulte et al, , 2010. This may mean there is actually a substantial dolomitic component in the ejecta given the dolomite-rich Cretaceous target.…”

Reconstruction of the Chicxulub ejecta plume from its deposits in drill core Yaxcopoil-1

“…Different rates of quenching are indicated by variable amounts of plagioclase phenocrysts that increase with depth. Phenocryst/groundmass ratios are ~10%-20% at 800 m, 20%-40% at 815 m, 40%-60% at 824 m, 60%-80% at 830 m, and >80% at 840-860 m. Such a quenching trend in Yax-1 was noted by Hecht et al (2004), Tuchscherer et al (2004aTuchscherer et al ( , 2006, and Wittmann et al (2006).…”