Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment

Details Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43c1701a&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P43C-1701

Mathematics

Probability

[1040] Geochemistry / Radiogenic Isotope Geochemistry, [1115] Geochronology / Radioisotope Geochronology, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering

Scientific paper

The Late Heavy Bombardment (LHB) is a hypothesized spike in the flux of bolides that impacted the surface of the moon, and by inference the Earth from 3.8 to 4.0 Ga. Evidence for the LHB comes largely from K-Ar ages of Apollo-era lunar samples interpreted to be ejecta formed during meteorite impacts. Few localities on Earth preserve even a scant terrestrial rock record prior to >4 Ga, which limits the search for terrestrial evidence of the LHB. Perhaps the best accessible record can be found in Hadean detrital zircons from the Jack Hills region of Western Australia, which may provide such evidence in the form of epitaxial rims grown during heating events that might have recorded a thermal signature of impacts. Their preserved isotopic signatures can be used to infer temperature histories that may provide insight into the environmental source conditions during the LHB-era. Specifically, are overgrowths formed under such anomalously high temperatures that we are compelled to infer their growth in response to impact heating during the LHB? This potentially can be resolved by comparing crystallization temperatures of LHB-era zircons to temperature spectra of terrestrial Hadean and impact-formed zircons. Terrestrial Hadean zircons yield apparent crystallization temperatures of 680±25oC whereas impact melt zircons yield higher average temperatures of ca. 780oC. We developed a SIMS method simultaneously combining the empirical Ti-in-zircon thermometry with U-Th-Pb. By depth profiling in this manner, we can obtain continuous depth vs. age and temperature data and thus identify temperatures of sub-μm overgrowths that grew epitaxially on detrital cores. Of the eight Hadean zircons Ti-U-Th-Pb depth profiled in this study, four had rims of LHB-era age. A 2D probability density function of age vs. temperature for the depth profiles shows a bimodal temperature distribution, with generally higher crystallization temperatures for ~3.8-4.0 Ga (i.e., LHB-era) zircon rims (ca.~760-870oC) and lower growth temperatures (ca.~630-750oC) for older zircon domains (i.e., ages >4.0 Ga). Thus we confirm the feasibility of using coupled depth profiling in this role and suggest that the high LHB-era formation temperatures likely reflect impact-related heating.

Affiliated with

Also associated with

No associations

Rating

Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ti-U-Th-Pb Depth Profiles of Hadean Zircons: Implications for the Late Heavy Bombardment will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-872334