METAMORPHIC AND IGNEOUS ROCKS OF THE MERRIMAC AREA, PLUMAS NATIONAL FOREST, CALIFORNIA

摘要

The pre-granitic rocks of an area in the northern Sierra Nevada consist of metamorphosed sedimentary and volcanic series ranging in age from Carboniferous to Jurassic. Synkinematic ultrabasic intrusives, now serpentines, cut these rocks concordantly and discordantly. Magmatic series ranging from basalt to dacite and soda-rhyolite occur together with the normal basalt-rhyolite series among the meta-volcanics. The younger intrusives (Sierra Nevada series), ranging from gabbros to granodiorites and granites, show great chemical similarity to the meta-volcanic series. Furthermore, soda-rich members are common among the pre-granitic intrusives and younger dike rocks. The pre-granitic rocks were folded and metamorphosed to green schist and epidote-amphibolite facies prior to emplacement of granodiorite and granite batholiths. The later contact metamorphism affected the areas next to the contacts of the batholitic intrusions, causing crystallization of such minerals as garnet, diopside, epidote, and andalusite. The plutonic rocks obtained the space needed partly by pushing the country rocks aside and partly by stoping and assimilation.