Page 7 - GSATJanuary2020

CPTZ Xenoliths
Group 2 N
N=8
n=96

Group 1
N=6 Farallon plate >0.706 Nevadaplano
n=112 Sr i <0.706
proto- x’ x’
Franciscan Farallon plate Nevadaplano
wedge
Mojave x x
Desert ~40 km/my
~80 km/my
A ca. 155 Ma 500 km B ca. 120 Ma

N=77
Colorado Plateau
Transition Zone Nevadaplano
l
d
N
Franciscan
wedge Shatsky conjugate
Nevadaplano Franciscan
wedge
x’
N=74 x’
0 50 100 150 200 ~100 km/my x POR Farallon plate POR
Age (Ma)
Shatsky conjugatey conjugate x
Figure 2. Non-normalized kernel density estimates
with 10-m.y. bandwidth comparing U-Pb zircon ~150 km/my
ages from Colorado Plateau transition zone (CPTZ; Farallon plate
Chino Valley and Camp Creek localities) xenoliths C ca. 75 Ma D ca. 65 Ma
with pluton ages from the Mojave Desert (Barth et
al., 2008; Wells and Hoisch, 2008; Needy et al.,
2009; Chapman et al., 2018) and the CPTZ (Vikre et JddF
JdF
al., 2014; Tosdal and Wooden, 2015; Chapman et al., plate
platee
Basin and dsin and
2018). N—number of analyzed samples; n—number B Bas i
R R
of analyzed grains. MT Range gange
M M M
M MT
MTJ
MTJJJ
Colorado
Co
C C C C C C C C Cololorado
Co
uan dee Fuca
Juan de Fuca Co Colorado
Plateau
SCB and, with the exception of a small pro- plate Plateau Plateau
plate
Paci c platecii c plate
portion (<10% of analyzed grains) of Latest x’ Pa PORR CV x’
PO
POR
CV
Cretaceous–early Cenozoic grains, are MTJ PO CV CC CC SC
CC
older than Arizona porphyry copper depos- Paci c plate RTJ x (paleo-sub
elf
its (Vikre et al., 2014; Chapman et al., 2018; x Shelf brea
b
Fig. 2). Furthermore, Late Jurassic zircon (paleo-subduction zone)
Shelf break
bducti
populations in group 1 xenoliths overlap bduction zone)
Mojave Desert pluton emplacement ages ~50 km/my ~60 km/my
and are younger than those expected from
Gdl plate
the Early–Middle Jurassic magmatic arc of E ca. 20 Ma Gdl plate F
F Today Tooday
SW Arizona (Fig. 2). These relations lead
us to assert that arclogitic xenoliths are not Orogenic highland Subduction complex Ridge-transformsidge-tran Early Jurassic arc
complex
R R
native to central Arizona and instead repre- LC-SCML fo Core complex (red) and
LC-SCML foundering
sent LC-SCML fragments displaced east- Active magmatism Oceanic lithosphereosphere Subduction schist (black), showing
Subduction
upper plate transport
megathrus
ward from beneath the SCB and reaffixed Ophiolite- oored forearc/ Extending lithosphere megathrust Farallon/Paci c motion
thosphere
fringing arc basin
Thrustrust
beneath the transition zone. Th ~50 km/my relative to xed N. America
We propose the following model for the Figure 3. SW U.S. plate tectonic reconstruction for (A) middle Jurassic, (B) Early Cretaceous, (C) Late
petrologic and tectonic evolution of Colorado Cretaceous, (D) Latest Cretaceous, (E) late Cenozoic, and (F) Recent time (modified after DeCelles,
Plateau transition zone arclogite (Figs. 3 and 2004; Saleeby and Dunne, 2015). Farallon/Pacific plate trajectories from Engebretsen et al. (1985).
Surface outline of lowermost crust and upper subcontinental mantle lithosphere (LC-SCML) foun-
4). In Late Jurassic time, group 1 (i.e., amphi- dering from Levander et al. (2011) and Erdman et al. (2016). Core complex and schist kinematics from
bole-rich arclogite) xenoliths began forming Dickinson (2009) and Chapman (2017), respectively. See text for details. CC—Camp Creek; CV—Chino
Valley; MTJ—Mendocino triple junction; POR—Pelona-Orocopia-Rand schist; RTJ—Rivera triple
as a mafic keel to continental arc magmas junction; SC—San Carlos; Gdl—Guadalupe plate.
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