PaleoMac: A Macintosh™ application for treating paleomagnetic data and making plate reconstructions

Abstract

This brief note provides an overview of a new Macintosh™ application, PaleoMac, (MacOS 8.0 or later, 15Mb RAM required) which permits rapid processing of paleomagnetic data, from the demagnetization data acquired in the laboratory, to the treatment of paleomagnetic poles, plate reconstructions, finite rotation computations on a sphere, and characterization of relative plate motions. Capabilities of PaleoMac include (1) high interactivity between the user and data displayed on screen which provides a fast and easy way to handle, add and remove data or contours, perform computations on subsets of points, change projections, sizes, etc.; (2) performance of all standard principal component analysis and statistical processing on a sphere [Fisher, 1953] etc.); (3) output of high quality plots, compatible with graphic programs such as Adobe Illustrator, and output of numerical results as ASCII files. Beyond its usefulness in treating paleomagnetic data, its ability to handle plate motion computations should be of large interest to the Earth science community.

Late Paleozoic paleogeographic reconstruction of Western Central Asia based upon paleomagnetic data and its geodynamic implications

“…11b) At this time, only a remnant part of the Junggar Ocean was still in subduction in the inner part of the orocline (Windley et al, 2007). The closure of the basin was accommodated by internal deformation of the orocline and by the development of strike slip faults with dextral kinematics in Tian Shan (Laurent-Charvet et al, 2002, 2003Wang et al;2007) and Kazakhstan (Samugyn, 1974) (Fig. 11d) Since Permian or Early Triassic, the Central Asia has experienced successive reactivations due to the agglomeration of Tibetan blocks and the collision India-Eurasia.…”

“…This motion was accommodated by large sinistral and dextral dextral motion in Altai and Tian Shan shear zones, respectively. As evidenced by numerous Ar-Ar dating and kinematic studies (Laurent-Charvet et al, 2002, 2003Wang et al;2007), strike-slip faulting continues in Late Permian, leading to large rotations to achieve the present configuration of Central…”

“…Dextral criteria can be observed along these faults (Laurent-Charvet et al, 2002;2003;Wang et al, 2006Wang et al, , 2007 and Ar-Ar dating yield ages ranging from 290 Ma to 240 Ma for the deformation (Yin and Nie, 1996;Zhou et al, 2001;Laurent-Charvet et al, 2002, 2003. The center of the best fitting small circle intercepting this curved shear zone is around 50°N, 92°E, with a radius of about 880km.…”

“…North-verging folds and top-to-the north kinematic criteria observed in these series argue for a deformation associated with a south-dipping subduction (Wang et al, 2006). Superimposed Permian dextral strike-slip faults affected the accretionary complex and the magmatic arc as well (Laurent-Charvet et al, 2002, 2003Wang et al, 2006). Post-collisional pull-apart basins, with bimodal magmatism (e.g.…”

“…Site-mean directions were computed by spherical statistic (Fisher, 1953). Paleomagnetic softwares written by Cogné (2003) and Enkin (unpublished) were used for the data analysis. Concerning the samples from South Junggar, the fine to medium-grained greywacke of Tashikula formation (P 1t ) and siltstone and sandstone of Wulapo and Jingjingzigou formations (P 2w and P 2j ) show similar magnetic behaviors: a saturation of >95% below 300 mT (Fig.…”