---

High Pressure Petrology

Dr. Adrian P. Jones (last updated 10/10/2000)
email: adrian.jones@ucl.ac.uk
telephone: 0207 679 2415

High Pressure Petrology And Mantle Melts at UCL

Page jumps [news, diamond, carbonatite, magma, impact melts, volcano,pictures, links]

***NEWS***

EUROCARB

We* are delighted to announce new ESF funded 3-year Network, "Eurocarb" to study the role of mantle carbon in the Earth's total carbon cycle.
(*together with Frances Wall, NHM: New website in prep, watch this space or try this link http://www.eurocarb.ucl.ac.uk/eurocarb.html)

---

---

Diamond research

- synthetic diamond analogues to natural systems. Our results in carbonate-graphite systems produces low temperature nucleation and growth above 8 GPa .

Recent collaborative programmes with the Russian Academy of Sciences, Moscow, and the National Institute for Reseach in Inorganic Materials, Tsukuba, Japan.

Carbonatites

- The August 2000 special issue of Mineralogical Magazine was devoted to recently discovered carbonatites in Italy (Jones A P (2000) Carbonatite Thematic Set, Mineralogical Magazine 64, 581-582; and pages thereafter) with emphasis on their volcanic nature and rare exhumation of mantle- derived xenoliths. Amongst the papers previously presented at the tenth UK carbonatite workshop (hosted at UCL in 1999) is an intriguing paper by Bailey and Collier (op cit, 675-682) which casts doubt on most popular models for carbonatite gensis, including mantle plumes.

Magma/melt rheology

Carbonate Impact Melts

We have recently interpreted distinctive feathery-textured carbonate in the upper part of the Chicxulub suevite breccia as quenched carbonate melts (Jones et al, 1998);

(click images for enlargement)
these distinctive fragments make up to ~10 vol% of the breccia. Carbonate clasts and spherules occurring in the ejecta-rich basal part of the coarse clastic sequence which marks the K/T boundary all around the Gulf of Mexico, may represent distal quenched droplets of carbonate liquids. In seeking to explain this widespread carbonate impact melting phenomenon, we have re-examined the available experimental evidence. The important decarbonation reaction for calcite CaCO3 = CaO + CO2 is inhibited by very small pressures up to temperatures >2000K. We conclude that massive decarbonation by direct shock pressure is unlikely without attainment of temperatures >~4000K. Therefore, decarbonation generally can only occur during post-shock cooling for carbonates at low pressure (~< 10 bars). We assume that post-shock cooling is quasi-thermodynamic, and provide a general P-T model for carbonate spanning 11 orders of magnitude in pressure (atmosphere to core). Subtle differences in sample preconditioning can probably explain the wildly divergent experimental shock data. A major planetary implication for the formation of the Earth's early atmosphere is that impacts on limestone would be less likely to have contributed substantial CO2 than has previously been assumed. Lastly, we note that carbonate melts at high pressures serve as excellent catalysts for diamond growth, and may have contributed to the widespread formation of some impact diamond.

Reference: Jones AP, Claeys P, and Heuschkel S (2000) Impact melting of carbonates from the Chicxulub impact crater. In (Gilmour I and Koeberl C eds) Impacts and the early Earth, Springer, Lecture notes in the Earth Sciences, 91, 343-361.

Volcano petrology

ESF IMPACT Programme: Svalbard 2001 Icey impacts

A workshop of the ESF programme IMPACT (Response of the Earth Sysytem to Impact Processes) to be held in Spitzbergen next year will have a special session on icey impacts which I am co-organising.

(Svalbard link)



Pictures

Links

• UKvolcano
• European Science Foundation
  Svalbard meeting
• synchrotron

Back to top of HPP page