MESOZOIC SYSTEMS ALONG THE PACIFIC 



269 



and Jurassic rocks continued southward into southern California, but is 

 much obscured there by Tertiary lavas and late Cenozoic faulting. See 

 Kg. 17.9. 



Central and Northern California 



At the north end, in the Taylorsville region, the Paleozoic rocks are 

 thrust eastward over the Jurassic, overturning them toward the east, just 

 the opposite of the thrusting along the Mother Lode on the west flank 

 jof the Sierra Nevada. It will be recalled that the Late ( ? ) Jurassic thrust- 

 ''ing in western Nevada was both toward die east and west and locally 

 (probably southward and northward. In the Grass Valley area of the 

 northern Sierra Nevada, Johnston (1940) finds the rocks to have been 

 compressed into northwest-trending isoclinal folds. The metamorphism 

 swas of the feeblest kind. The Mariposa was compacted and cemented, 

 land some of the andesitic rocks acquired schistocity; but the chemical 

 sand physical changes were much less severe than those imposed upon 

 the Calaveras formation in late Paleozoic orogeny. 



Regarding the post-Mariposa plutons, Knopf (1929) says that in the 

 'Mother Lode belt the oldest of these rocks there are peridotites which, 

 •soon after intrusion, were transformed into serpentines. Smaller masses 

 ■of gabbro and hornblendite were then intruded into the peridotite, to 

 iwhich they seem to have a predilection. The peridotite, gabbro, and horn- 

 blende appear to represent the "basic prelude" to tremendous intrusions 

 jof granodiorite that form the bulk of the present Sierra Nevada. 



The granodiorite is uniform in texture and composition, and contains 

 Jbasic clots which are very common in the high Sierra. Quartz diorite 

 porphyry is intrusive into the Mother Lode belt south of Placerville. It 

 [grades into the granodiorite and has exerted no perceptible contact meta- 

 morphism. Knopf believes that the granodiorite ascended to a high level 

 "in the earth's crust in the gold belt area. Dikes and small intrusive masses 

 ?lof a white rock composed almost entirely of albite complete the intrusive 

 licycle. Allied varieties of the granodiorite are quartz-monzonite, granite, 

 'and alaskite. The Mariposa is affected by contact metamorphism as much 

 as a mile away from the granodiorite contact. 



In the northern Sierra Nevada, Johnston (1940) finds essentially the 



CALIF. I NEV 



NARROW I 



VOLCANIC CALIFORNIA TROUGH 



ARCHIPELAGO i 



ASUNCION GR 



WAIN 6ATH0LITHIC INTRUSIONS 

 (NEVADAN OROGENY) AND OEPOSITION DVRINt 

 AL61AN AND CENOMANlAN TIME 



POST-KIMMERIOGIAN FOLD1NO AND THRUSTING 

 DEPOSITION FROM LATE JURASSIC IT1THON1AN) 

 THROUGH LATE EARLT CRETACEOUS 

 (APTIAN) IN NEW WESTERN TROUGH 



I 

 i 

 i 



I 



6ATH0LITHIC INTRUSIONS IN TlTHONlAN 



DEPOSITION THROUGH EARLT LATE JURASSIC 

 (KIHMERIDGIAN) WITH DISTURBANCE IN 

 EARLY JURASSIC 



OEPOSITION THROUGH TRIASSIC WITH 

 DISTURBANCE 8ETWEEN MIDDLE AND 

 UPPER TRIASSIC 



Fig. 17.9. Evolution of the Sierra Nevada through Mesozoic time. C is Calaveras formation of 

 late Mississippian (?) age; F is Franciscan group; K, Knoxville formation; P, Pashenta formation; 

 and H, Horsetown formation. 



same batholitic cycle as Knopf does to the south in the Mother Lode, 

 namely, an intrusive succession of ultrabasic rocks, gabbro, diabase, 

 granodiorite, granite, and aplite. Granodiorite was intruded in tremendous 

 batholithic masses that now form the backbone of the high Sierra. On the 

 western slope, smaller masses of granodiorite are satellitic to the main 

 mass. The earlier formations were shoved aside and possibly in part as- 

 similated, and contact metamorphic zones were developed in the sedi- 

 mentary rocks. From the last emanations of the granitic intrusions were 

 formed die gold quartz veins of the Sierra Nevada. 



In the southern part of the Sierra Nevada, Mayo ( 1941 ) in reviewing 

 the work of others and himself, finds that hornblende gabbro and horn- 

 blende diorite were forerunners to the main granitic intrusions. These 



