PLACA: a white box for plate reconstruction and best-fit pole determination ?
PLACA was developed as a general purpose computer program for the earth scientist that has to manipulate the rigid plate tectonics theory, from the representation of plate reconstructions to the determination of best-fit poles using magnetic anomalies, fracture zones or volcanic alignments. In the forward mode PLACA has the features of most available demonstration software plus the ability of simulating mid-oceanic ridges (MOR) as dynamic segments that move with a fraction of the relative motion between two plates. The movement can be illustrated by the generation of flow lines, plate trajectories and/or pseudo-magnetic anomalies on the ocean floor. The evolution of simple triple junctions of the RRR type can also be studied. In the modifying mode, best-fit poles can be computed either visually or by a systematic search routine. Five methods are available to evaluate the residuals between predicted and observed reconstructed points. Once the best-fit pole is obtained, several statistical tests can be done to evaluate the confidence on the fit. Surprisingly, the use of high-resolution geophysical data that are now available in the oceanic domain doesnt always imply that the reconstruction poles are better constrained, as shown by an application example. Other examples presented document a discussion on the precision of plate reconstructions and suggest a few words of caution for the general user of PLACA.
precision tectonophysics plate-tectonics fortran confidence region