RECYCLING OF DETRITAL ZIRCONS FROM JURASSIC EOLIANITES OF THE COLORADO PLATEAU INTO QUARZOSE CRETACE

1
Cintura Data (Sample KBCR) Concordia Plots,
Combined Histogram and Age-Probability Plot,
Sandstone Petrofacies (Red Dot)
Geologic Context of Cintura Sample KBCR (Red
Dots) in Border Rift Belt and Bisbee
Basin (after Dickinson and Lawton, 2001 Sed Geol
14475-504)
RECYCLING OF DETRITAL ZIRCONS FROM JURASSIC
EOLIANITES OF THE COLORADO PLATEAU INTO QUARZOSE
CRETACEOUS SANDSTONE OF THE BISBEE BASIN IN
SOUTHEASTERN ARIZONA William R. Dickinson and
George E. Gehrels (University of Arizona) Timothy
F. Lawton (New Mexico State University) Sandstones
in the Jurassic-Cretaceous Bisbee basin of the
AZSonoraNM border region include multiple
petrofacies (a) arkosic from internal basement
tiltblocks within the Border rift belt, (b)
lithic (volcaniclastic) from the Alisitos arc
southwest of the basin, (c) subquartzose from
sedimentary cover of the rift shoulder north of
the basin, and (d) quartzose inferred to reflect
reworking of Jurassic eolian sand from the
Mogollon highlands of the rift shoulder along the
southern rim of the Colorado Plateau (Dickinson
and Lawton, 2001). Confirmation that sand was
recycled into the Bisbee basin from plateau
eolianites is provided by U-Pb ages of detrital
zircons (n100 with lt10 age uncertainty and lt20
discordance from LA-ICP-MS analysis using a beam
diameter of 35 microns) in a sample (KBCR) of
quartzose sandstone (Qm91-F6-Lt3) in the Lower
Cretaceous (Albian) Cintura Formation of the
Bisbee Group at Rucker Canyon in the Chiricahua
Mountains (SE AZ). Analysis of plateau Jurassic
eolianite provenance has shown that gt295 Ma
zircon grains were derived from deflation of
floodplains lying north and northeast of the
Colorado Plateau near the termini of
transcontinental drainages heading in the
Appalachian province, and include age populations
unrepresented by bedrock in SW Laurentia.
Comparative K-S statistics indicate that
populations of gt295 Ma zircon grains in KBCR
(n84 grains) and 10 plateau eolianites (n887
grains) are statistically indistinguishable
(P-value 0.8), and further that populations of
all gt115 Ma grains in KBCR (n98 grains) and four
Middle to Upper Jurassic eolianites (n365
grains) of the eastern Colorado Plateau north of
the Mogollon highlands are also statistically
indistinguishable (P-value 0.9). The zircon
grains gt115 Ma but lt295 Ma were derived
ultimately from the Permian-Triassic East Mexico
and Mesozoic Cordilleran magmatic arcs south of
the Bisbee basin, but were apparently recycled
into the basin from eastern plateau Jurassic
eolianites exposed to the north. Zircon grains of
distant ultimate provenance in Jurassic
eolianites were recycled into Upper Jurassic and
Cretaceous strata of the Colorado Plateau as well
as into the Bisbee basin. Two post-Jurassic
grains (111-108 Ma) in KBCR represent more
juvenile arc contributions compatible with Albian
(112-100 Ma) deposition.
Comparative Detrital Zircon (DZ) Age
Populations (see column at right for P values
from K-S analyses) note close match for all
eolianite and McCoy pre-285 Ma grains, and tight
match for pre-112 Ma eastern plateau eolianite
grains
Distribution of Bisbee Basin Petrofacies (Dickinso
n and Lawton, 2001 Sed Geol 14475-504)
Regional Geotectonic Setting of Bisbee Basin in
Border Rift Belt
Comparative P-values from K-S (Kolmogorov-Smirnoff
) Analysis (for Pgt0.05, cannot be 95 confident
that two grain populations were not sampled
randomly from the same parent population where
P1.0 would imply statistical identity) P0.756
for gt285 Ma grains (n84) in Cintura KBCR vs gt285
Ma grains (n890) in ten samples of Colorado
Plateau Jurassic eolianites (Aztec, Bluff,
Entrada, Navajo, Nugget, Page, Wingate) see
probability plot at top left P0.898 for gt112 Ma
grains (n98) in Cintura KBCR vs gt112 Ma grains
(n365) in four samples of Middle to Upper
Jurassic eolianites (Entrada and Bluff
Sandstones) of eastern Colorado Plateau see
probability plot and cumulative curve middle left
P0.826 for gt285 Ma grains (n84) in Cintura KBCR
vs gt285 Ma grains (n54) in two samples (MC7,
MC9) of quartzose basal sandstone member of McCoy
Mountains Formation see probability plot at
bottom left
METHODOLOGY sample collection and preparation 1)
20-25 kg of fresh sandstone collected from
outcrop as chips lt5 cm diameter 2) sample crushed
and pulverized using laboratory jaw crusher and
rolling mill 3) disaggregated sample placered
using Wilfley table and sieved for lt350 µm 4)
grains of high specific gravity separated with
heavy liquid (methylene iodide) 5)
ferromagnetic-paramagnetic grains rejected using
a Frantz magnetic separator 6) epoxy mount (1
strip) of gt90 zircon fraction sanded down to 20
µm depth data collection and reduction 1) U-Pb
ages from laser-ablation inductively-coupled
plasma mass spectrometry 2) Excimer laser
ablation at wavelength of 193 mm with spot
diameter of 35 µm 3) every fifth data point Sri
Lanka standard zircon of known age for
calibration 4) data corrected for U/Pb and Pb/Pb
fractionation and for common lead 204Pb 5) ages
calculated from 206Pb/238U (lt1 Ga grains) and
206Pb/207Pb (gt1Ga grains) 6) ages with gt20
discordance or gt10 uncertainty omitted (100 ages
retained) data presentation and analysis 1)
concordia plot for graphical evaluation of age
concordance of individual grains 2) histogram of
best estimates of individual grain ages falling
into 50 Ma age bins 3) age-probability plot
(age-distribution curve) from probability-density
function 4) cumulative age-probability curve
(from 0 to 100) for array of grain ages 5)
P-value from K-S statistics (Pgt0.05indistinguisha
ble at 95 confidence level) 6) comparisons of
Cintura zircon age populations with Colorado
Plateau Jurassic eolianites and with lower McCoy
Mountains Formation of Mojave Desert key
uranium-lead systematics 1) let asterisk ()
denote radiogenic lead and italics denote ratios
for common lead 2) measured isotopic ratios
206Pb/238U, 206Pb/207Pb, 206Pb/204Pb 3) ratio
206Pb/238U 206Pb/238U 1 (206Pb/204Pb)/(206Pb
/204Pb) 4) ratio 207Pb/235U (206Pb/238U) x
(207Pb/206Pb) x 137.88 (from 238U/235U
137.88 at current stage of Earth history with
207Pb/206Pb derived from 207Pb/206Pb by common
lead correction analogous to point 3) 5) use
206Pb/207Pb (instead of 207Pb/235U) with
206Pb/238U to control concordia (can measure Pb
isotopes more accurately than 235U of which there
is so little) 6) analytical age uncertainties
tabulated at 1s (highly variable for different
grains)
Regional Stratigraphy of Border Rift Belt
Distribution of Bisbee Group in Bisbee Core and
Flank Basins
Summary of Cintura Provenance Relations (see
subregional map above where asterisk denotes
Cintura sample site in Rucker Canyon) 1. Age
populations of the dominant gt285 Ma detrital
zircons (ultimate derivation from eastern and
central North America) in the Cintura Formation
and in Jurassic eolianites of the Colorado
Plateau are compatible with recycling of
quartzose sand into the Bisbee basin from
eolianites exposed in Late Jurassic and Early
Cretaceous time along the Mogollon Highlands rift
shoulder of the Bisbee basin. 2. Age populations
of all gt112 Ma detrital zircons in the Cintura
Formation of the Bisbee Group and in Middle to
Upper Jurassic eolianites of the eastern Colorado
Plateau (Entrada Sandstone and Bluff Sandstone)
are compatible with recycling of both
far-travelled (eastern-central North American)
and western North American (arc-derived) grains
from eastern plateau eolianites into which
far-travelled and arc-derived grains were
pre-mixed before initiation of the Bisbee
basin. 3. Eastern plateau eolianites were exposed
along the Mogollon Highlands directly north of
the quartzose petrofacies tract of the Bisbee
basin, whereas direct delivery of arc-derived
grains to the quartzose petrofacies tract from
arc terranes lying to the west and southwest was
precluded by intervening lithic (volcaniclastic)
and arkosic petrofacies tracts within the Bisbee
basin. 4. The dominant gt285 Ma age population of
detrital zircons in the quartzose petrofacies of
the basal sandstone member of the McCoy Mountains
Formation deposited at the distal northwest
extremity of the Border rift belt are compatible
with recycling of detrital zircons from western
plateau eolianites exposed to the north (in
parallel with recycling of sand from eastern
plateau eolianites into the coeval Bisbee Group
farther east).
Outcrop photographs (left across road, right
close up) of sample KBCR sandstone ledge (steep
dip to right or east) in Cintura Formation of
Bisbee Group at Rucker Canyon in the southern
Chiricahua Mountains of southeastern Arizona
Stratigraphy of Bisbee Basin (topcore basin in
AZ-NM bottom flank basin in Sonora)