Middle (174–164 Ma) through Late (164–145 Ma) Jurassic Deformational, Magmatic, and Stratigraphic Events in Nevada: Inferred Relations to Far-Field Plate Movements and Mantle Flow

Evidence of Mid- through Late Jurassic uplift, magmatism and/or deformation
of rocks in Nevada and adjacent regions can be correlated with plate tectonic processes.
The contractional Elko orogeny, beginning ca. 169 Ma, that is manifest by
northeasterly to easterly trending fold hinges and related thrust faults, mainly recognized
in ranges of northern Nevada, is attributed to transpression during plate
rotation of Laurasia accommodated by movement along a sinistral strike-slip fault
between ca. 169–148 Ma. Transpression took place along a regional restraining bend
extending east-northeasterly across Oregon from the northern Klamath Mountains
to the border with Idaho. The suture zone, which developed between the margin of
Jurassic continental crust of North America and slightly older crust with oceanic affinities
adjacent to the north is exposed in the Blue Mountains of Oregon. Concurrently,
southeast-directed subduction, induced as North America overrode hundreds
of km of largely oceanic crust, is inferred to have resulted in formation and intrusion
of plutons across central Nevada, between 166–158 Ma. Coeval basins containing
coarse debris intermingled with magmatic units in eastern California and suites of
correlative volcanic units in western Nevada, which together crop out within the Pine
Nut terrane, record extension attributed to transtension. A Late Jurassic orogenic
event, which overprinted the effects of ongoing plate rotation, is manifest by Nevadan
contraction and magmatism between ca. 163–150 Ma. The Nevadan is inferred to
have taken place in response to arrival of a wave-like mass of mantle that (1) induced
subduction at the plate margin and (2) subsequently moved under the continental
lithosphere causing uplift and erosional exhumation that correlates with the development
of Late Jurassic, J3 and J5 ,unconformities. Where subduction was induced at
the plate margin, A-type as well as typical calc-alkaline arc-related granitoids were
emplaced. Contraction and subduction at the plate margin was followed by eastward
flow of the mantle wave that caused uplift of the Morrison basin contemporaneous
with accumulation of Tithonian upper Brushy Basin member between 151–150 Ma.
Resumption of transtension within the plate margin is recorded by dikes as young as
148 Ma.
Key Words: Jurassic, orogenesis, Elko orogeny, transpression, transtension