“Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer”—reply to the comment of Poli and Schmidt

Conclusions Although only Al^iv appears in our thermometer expression, this in no way infers that we believe tschermakite (or katophorite, kaersutite and other) substitutions to be unimportant. A careful reading of our earlier papers makes it clear that the reverse is true, e.g. Holland and Richardson 1979; Will et al. 1990a, b; Guiraud et al. 1990. Indeed in B and H (p. 211) we state that natural and synthetic amphiboles are dominated by a combination of edenite, pargasite, hornblende and hastingsite substitutions. What we endeavoured to point out was that because of the nature of reaction (1) and the use of mixing-on-sites activity models the extent of Al substitutions on M2 or Na on M4 do not materially influence our expression for K₁ and consequently our thermometer. Certainly any sophisticated activity model for amphibole explicitly should account for all cross-site interactions between M-, Tl- and A-site cations, as alluded to by P and S in reference to Docka et al. (1987), as well as O3-site anions. However, such a day currently is well away and mixing-on-sites, with modifications as outlined above and to be detailed in T.J.B. Holland and J.D. Blundy (in preparation), seems rather promising for the purposes of amphibole thermometry. We do not share the rather negative and pessimistic outlook on activity models and thermobarometry implicit in P and S comments.     

Reply to the comment by J. R. Ali on “Illawarra Reversal: the fingerprint of a superplume that triggered Pangean breakup and the end-Guadalupian (Permian) mass extinction” by Yukio Isozaki

The following four major questions were raised about my recent proposal for the possible link between the end-Guadalupian extinction and a unique geomagnetic event called the Illawarra Reversal (Isozaki, 2009a); 1) timings of extinction, cooling, and the Illawarra Reversal (end of the Kiaman Superchron), 2) geomagnetic intensity during superchrons, 3) ascent rate of mantle plume, and 4) age constraints of LIP volcanism in east Pangea. The latest research results on the Permian biodiversity change, numerical modeling of plume, and single-crystal measurement of geomagnetism support that the timings of extinction and the Illawarra Reversal, high field intensity during the Kiaman superchron, and ascent rate of plume are reasonably explained in accordance with the integrated “plume winter” scenario (Isozaki, 2009b). The onset ages of LIP volcanism need further refinement for identifying the impingement of a plume head.