late neoproterozoic-early cambrian schists have been occurred in southwest of zanjan city from the soltanieh belt. the soltanieh belt in northwest of iran is uplifted basement of precambrian-paleozoic in main central iran zone and includes outcrops of precambrian, paleozoic and mesozoic formations. late neoproterozoic-early cambrian schists, the oldest stratigraphy unit in the region, consist o...

Ž . We investigate seismic layering i.e., discontinuities, regions of anomalous velocity gradients, and anisotropy and its Ž . lateral variability in the upper mantle by comparing seismic models from three tectonic regions: old ;100 Ma Pacific Ž . plate, younger ;40 Ma Philippine Sea plate, and Precambrian western Australia. These models were constructed by combining two data sets: ScS-reflecti...

Uranium-lead data indicate that the high-pressure granulitic and charnockitic nuclei within the medium-grade metamorphic complex of the Peruvian coastal area must be related to an orogenic event 2 x 10(9) years ago. As in western Africa and Brazil, this old granulitic basement is reworked by Late Precambrian orogeny. Its presence along the Peru-Chile Trench must be taken into account in interpr...

Solar evolution implies, for contemporary albedos and atmospheric composition, global mean temperatures below the freezing point of seawater less than 2.3 aeons ago, contrary to geologic and paleontological evidence. Ammonia mixing ratios of the order of a few parts per million in the middle Precambrian atmosphere resolve this and other problems. Possible temperature evolutionary tracks for Ear...

Southern Indian states are endowed with rich gem mineral wealth. High potential region for the occurrence of gem deposits appear to be the Precambrian region in the Eastern Ghats. Gemstones which are of mineral origin are found largely in metamorphic terrain. Salem district which is primarily enclosed by high grade metamorphic rocks is the study area. This study addresses field investigation an...