7 Causes and Consequences of Magmatic and Tectonic Tempos in Continental and Oceanic Arcs (Posters)

Monday, 4 April 2016
8:30 AM - 5:30 PM
Ballroom C

STRUCTURE, CONSTRUCTION, AND EMPLACEMENT OF THE NORTHERN PART OF THE CRETACEOUS SONORA PASS INTRUSIVE SUITE, CENTRAL SIERRA NEVADA BATHOLITH, CALIFORNIA

Paper number: 7-6
Program: Theme Sessions
Time: 8:30 AM – 5:30 PM

Authors

Abstract

The >1,000 km2 Sonora Pass intrusive suite (SPIS) is the least understood of the four major, normally zoned Late-Cretaceous suites in the Sierra Nevada batholith. The SPIS contains an outer unit, the equigranular, ̴ 92 Ma Kinney Lakes hornblende-biotite granodiorite and an inner unit, the porphyritic, ̴ 88 Ma Topaz Lake biotite-hornblende granodiorite. This study focused on the structure of the northern margin of the SPIS and its host rocks, and on the contact of the Kinney Lakes granodiorite and Topaz Lake granodiorite. The Kinney Lakes granodiorite was emplaced into a number of Cretaceous plutons, biotite schist, and granitic gneiss. Foliations in the host rocks dip steeply and have an overall NW strike, which is typical of the regional orientation. The only minor deflection of host rock foliation near the margin, and minimal solid-state deformation in the host rocks supports passive emplacement of the Kinney Lakes granodiorite. The abundance of Kinney Lakes sheets within the host rocks and scarcity of xenoliths in the granodiorite implies emplacement via diking and minor stoping. Sharp internal contacts, indicated by changes in color index (13-20) and foliation intensity, and the abundance of mafic enclave swarms and schlieren-rich zones suggest that the Kinney Lakes granodiorite was constructed by multiple magmatic increments. Magmatic foliations are strongest near the contact with the Topaz Lake granodiorite, and are slightly deflected as the contact is approached. This deflection, along with felsic Topaz Lake sheets that intrude the Kinney Lakes granodiorite, are compatible with Topaz Lake emplacement via minor diking and host rock flow. Weak magmatic foliations in the Topaz Lake granodiorite are concordant to its sharp contact with the Kinney Lakes rocks. The sharpness of this contact implies that the Kinney Lakes granodiorite had completely crystallized before Topaz Lake emplacement.

Geological Society of America Abstracts with Programs. Vol. 48, No. 4

doi: 10.1130/abs/2016CD-274444

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