A càrrec de Enrique MERINO (Professor Emèrit, Indiana University, Bloomington, EUA)
Organitzat conjuntament CSIC-UB

Data: 18-05-2011
Hora: 12:00
Lloc: Sala de Juntes de la Facultat de Geologia

Descripció: Bastin, Lindgren and others (1931), just from the visual/petrographic properties of replacement, deduced that the preservation of morphological details (or ghosts) and mineral volume characteristic of replacement (a) requires guest growth and host dissolution to proceed simultaneously and at the same volumetric rate as each other (which requires a strong, instantaneous coupling - but which?) and (b) rules out formation by "dissolution-precipitation". These insights were forgotten.

The next improvement didn't come until 57 years later: Maliva and Siever (1988) proposed that the coupling factor required by the equalization of volumetric rates in replacement is the "force of xln," or, more correctly, the xln stress or induced stress. Dewers and Ortoleva (1989) applied Navier-Stokes eqn for momentum conservation to demonstrate that growth in a rigid rock must trigger other mineral reaction(s) such that volume is conserved; they demonstrated theoretically the existence of the replacement phenomenon. Nahon and Merino (1997) demonstrated how the rates are actually forced to become mutually equal by the crystallization stress. Banerjee and Merino (2011) have so modeled the replacement of limestone by kaolinite in the formation of terra rossa, predicting rates of formation similar to paleomagnetic ones.

Meanwhile, Weyl (1959), Garrels (1960, 1965), and Helgeson (GCA 1968, 1969) constructed a new, formidable quantitative geochemistry that viewed everything from weathering to metamorphism as resulting simply from dissolution and precipitation enabled by transport. But they were unaware of the replacement phenomenon and of its kinetic implications. Later geochemists seem to have converted "dissoln and pptn" to "dissoln-pptn," with the added hyphen perhaps implying some imaginary coupling, and continue to think that replacement forms by "dissoln-precipitation", unaware of the blind spot they are in. A multifaceted research program - experimental, theoretical, modeling, petrographic, even neurological - ought to be undertaken at Barcelona to clarify once and for all this misunderstood phenomenon, fundamental for petrology and for geochemical modeling in rocks.