Publications by authors named "Zhengbin Deng"

4 Publications

  • Page 1 of 1

The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record.

Proc Natl Acad Sci U S A 2020 12 16;117(49):30973-30979. Epub 2020 Nov 16.

Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, 1350 Copenhagen, Denmark;

Combining U-Pb ages with Lu-Hf data in zircon provides insights into the magmatic history of rocky planets. The Northwest Africa (NWA) 7034/7533 meteorites are samples of the southern highlands of Mars containing zircon with ages as old as 4476.3 ± 0.9 Ma, interpreted to reflect reworking of the primordial Martian crust by impacts. We extracted a statistically significant zircon population ( = 57) from NWA 7533 that defines a temporal record spanning 4.2 Gyr. Ancient zircons record ages from 4485.5 ± 2.2 Ma to 4331.0 ± 1.4 Ma, defining a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma. We interpret these to represent intense bombardment episodes at the planet's surface, possibly triggered by the early migration of gas giant planets. The unradiogenic initial Hf-isotope composition of these zircons establishes that Mars's igneous activity prior to ∼4.3 Ga was limited to impact-related reworking of a chemically enriched, primordial crust. A group of younger detrital zircons record ages from 1548.0 ± 8.8 Ma to 299.5 ± 0.6 Ma. The only plausible sources for these grains are the temporally associated Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir, indicating that Mars has been in a stagnant-lid tectonic regime for most of its history. Our results imply that zircon is ubiquitous on the Martian surface, providing a faithful record of the planet's magmatic history.
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http://dx.doi.org/10.1073/pnas.2016326117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7733809PMC
December 2020

Early oxidation of the martian crust triggered by impacts.

Sci Adv 2020 Oct 30;6(44). Epub 2020 Oct 30.

Université de Paris, Institut de physique du globe de Paris, CNRS, 75005 Paris, France.

Despite the abundant geomorphological evidence for surface liquid water on Mars during the Noachian epoch (>3.7 billion years ago), attaining a warm climate to sustain liquid water on Mars at the period of the faint young Sun is a long-standing question. Here, we show that melts of ancient mafic clasts from a martian regolith meteorite, NWA 7533, experienced substantial Fe-Ti oxide fractionation. This implies early, impact-induced, oxidation events that increased by five to six orders of magnitude the oxygen fugacity of impact melts from remelting of the crust. Oxygen isotopic compositions of sequentially crystallized phases from the clasts show that progressive oxidation was due to interaction with an O-rich water reservoir. Such an early oxidation of the crust by impacts in the presence of water may have supplied greenhouse gas H that caused an increase in surface temperature in a CO-thick atmosphere.
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http://dx.doi.org/10.1126/sciadv.abc4941DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7608801PMC
October 2020

High-precision in situ silicon isotopic analyses by multi-collector secondary ion mass spectrometry in olivine and low-calcium pyroxene.

Rapid Commun Mass Spectrom 2019 Oct;33(20):1589-1597

Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA.

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http://dx.doi.org/10.1002/rcm.8508DOI Listing
October 2019

Titanium isotopes as a tracer for the plume or island arc affinity of felsic rocks.

Proc Natl Acad Sci U S A 2019 01 3;116(4):1132-1135. Epub 2019 Jan 3.

Institut de Physique du Globe de Paris, Université Paris Diderot, Université Sorbonne Paris Cité, CNRS UMR 7154, 75005 Paris, France.

Indirect evidence for the presence of a felsic continental crust, such as the elevated Ti/Ti ratios in Archean shales, has been used to argue for ongoing subduction at that time and therefore plate tectonics. However, rocks of intermediate to felsic compositions can be produced in both plume and island arc settings. The fact that Ti behaves differently during magma differentiation in these two geological settings might result in contrasting isotopic signatures. Here, we demonstrate that, at a given SiO content, evolved plume rocks (tholeiitic) are more isotopically fractionated in Ti than differentiated island arc rocks (mainly calc-alkaline). We also show that the erosion of crustal rocks from whether plumes (mafic in average) or island arcs (intermediate in average) can all produce sediments having quite constant Ti/Ti ratios being 0.1-0.3 per mille heavier than that of the mantle. This suggests that Ti isotopes are not a direct tracer for the SiO contents of crustal rocks. Ti isotopes in crustal sediments are still a potential proxy to identify the geodynamical settings for the formation of the crust but only if combined with additional SiO information.
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http://dx.doi.org/10.1073/pnas.1809164116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6347677PMC
January 2019