DIACHRONOUS HYPERSOLIDUS DEFORMATION DURING REPEATED MAGMA INJECTION: FIELD OBSERVATIONS FROM THE TILTED WOOLEY CREEK BATHOLITH (WCb)

We present new field and structural observations from the 158-154 m.y.o. (U/Pb TIMS), Wooley Creek batholith, Klamath Mountains, CA. The WCb is tilted to the south and exposes over 15 km of structural relief. The intrusion may be divided into a northern (deeper) gabbroic/diorite/quartz diorite zone, a central, complexly sheeted zone of quartz diorite/tonalite containing abundant mafic magmatic enclaves (MMEs), enclave swarms, and disrupted/deformed mafic dikes, and a southern (shallower) zone of minor gabbro, qtz diorite, tonalite, granodiorite and granite. All foliations are hypersolidus in nature and are defined by laths of plagioclase and amphibole.

Fieldwork in the Cuddihy Basin yields the following observations and interpretations related to the central qtz diorite/tonalite ‘host’ magma. At least seven distinctive intrusive episodes (1: early cognate xenoliths; 2: tonalite/qtz diorite host magma; 3: various coarse-crystalline MMEs; 4: fine-crystalline mafic dikes; 5: net-veined fine- to medium-crystalline mafic dikes; 6: folded amp + bt + pl-phyric dikes; 7: late, leucocratic veins) and three distinctive hypersolidus foliation-forming events occurred in the C.B. The oldest foliation occurs in coarse-crystalline cognate xenoliths of qtz diorite contained within the host magma. Foliations are perpendicular to host foliations and are truncated at the margins of the xenolith. The second set of foliations is N-NE trending and occurs within the host magma. Swarms of mafic enclaves are aligned parallel to this fabric and are cut by late fine-crystalline mafic (gabbroic to qtz dioritic) dikes. These dikes vary in orientation and are boudined and/or folded within the hypersolidus foliation plane of the host. Where these ‘ribbon dikes’ are folded, an axial planar hypersolidus foliation occurs in both the dikes as well as the host, representing the last fabric to have formed.

Presently it is not clear if the fabrics are related to either regional deformation present during emplacement or emplacement related flow. Both are consistent with NS extension and EW shortening. Whether these processes of deformation held constant or varied in strength throughout the time of multiple injections of host magma is still to be determined.