Age derminations of rocks from the Read Mountains, Antarctica

The Shackleton Range can be divided into three major units: (1) The East Antarctic Craton and its sedimentary cover (Read Group and Watts Needle Formation), (2) the allochthonous Mount Wegener Nappe (Mount Wegener Formation, Stephenson Bastion Formation, and Wyeth Heights Formation), and (3) the northern belt (basement: Pioneer and Stratton Groups, sedimentary cover: Haskard Highlands Formation (allochthonous?), and Blaiklock Glacier Group). The northern units are thrust over the southern ones. The thrusting is related to the Ross Orogeny. The Mount Wegener Nappe, which appears to be a homogeneous tectonic unit, consists of a Precambrian basement (Stephenson Bastion Formation, Wyeth Heights Formation?) and a Cambrian cover (Mount Wegener Formation). Some questions are still open for discussion: the position of the Haskard Highlands Formation (trilobite shales) may be erratic or represent a tectonic sliver, the relation of the former Turnpike Bluff Group, the origin of the crystalline basement west of Stephenson Bastion and others.

(Table) Argon isotope ratios and argon ages of rocks obtained from the Chernorud zone, western Baikal area

Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to upper crustal levels. The process is subdivided into four discrete stages, which corresponded to metamorphism to the granulite facies (500-490 Ma), metamorphism to the amphibolite facies (470-460 Ma), metamorphism to at least the epidote-amphibolite facies (440-430 Ma), and postmetamorphic events (410-400 Ma). The earliest two stages likely corresponded to the tectonic stacking of the backarc basin in response to the collision of the Siberian continent with the Eravninskaya island arc or the Barguzin microcontinent, a process that ended with the extensive generation of synmetamorphic granites. During the third and fourth stages, the granulites of the Chernorud nappe were successively exposed during intense tectonic motions along large deformation zones (Primorskii fault, collision lineament, and Orso Complex). The comparison of the histories of active thermal events for Early Caledonian folded structures in the Central Asian Foldbelt indicates that active thermal events of equal duration are reconstructed for the following five widely spiced accretion-collision structures: the Chernorud granulite zone in the Ol'khon territory, the Slyudyanka crystalline complex in the southwestern Baikal area, the western Sangilen territory in southeastern Tuva, Derbinskii terrane in the Eastern Sayan, and the Bayankhongor ophiolite zone in central Mongolia. The dates obtained by various isotopic techniques are generally consistent with the four discrete stages identified in the Chernorud nappe, whereas the dates corresponding to the island-arc evolutionary stage were obtained only for the western Sangilen and Bayankhongor ophiolite zone.

Chemical composition of rocks and minerals from DSDP holes

The book summarizes materials obtained by Soviet scientists during participation in legs of D/S Glomar Challenger and in post-cruise studies. Results on stratigraphy and lithology of the sedimentary cover, petrography and geochemistry of magmatic rocks of the oceanic crust are discussed in the book. A modern analysis of the geophysical structure of the oceanic crust and of the tectonic structure of the ocean floor is given.