Transcript Rift-Related Intraplate Magmatism – Iapetus Opening: Basalt

Emerging Data on Rodinia Rifting from
Marathon Fold-Thrust Belt, Southern Laurentia
Patricia W. Dickerson, Daniel F. Stockli, Richard E. Hanson & Jonathon M. Roberts
GSA – Vancouver, 2014
Birth and Death of Supercontinents
Southern Laurentia – West Texas
Ouachita-Marathon
thin-skinned fold and
thrust belt
Goetz in Goetz & Dickerson (1985)
Deformed as Pangea was born, Marathon fold-thrust
belt provides new insight into the dying days of Rodinia
Diablo Platform
Ancestral Rockies-style
basement-cored uplift
L–M Ordovician Strata
Bearing Igneous Clasts
(Roberts et al., 2010)
Host strata: Shelf-derived
fossiliferous limestone
conglomerates within off-shelf
deposits, western OuachitaCuyania Basin
Deposits spanning ~28 Ma
(Intl. Subcom. Ord. Strat., 2007)
3 formations to date:
Woods Hollow (Sandbian)
Ft. Peña Formation (Darriwilian)
Marathon Formation (Floian)
Silicified Alkali Basalt Boulder in Limestone Cobble
Conglomerate, Marathon Fm.
Rift-Related Intraplate Magmatism – Rodinia Breakup:
Basalt & Trachyandesite Clasts in Fort Peña Fm Conglomerate
~706 Ma
U/Pb, zircon
(Hanson,
Roberts,
Dickerson,
& Fanning,
2012, 2013)
Basalt, open blue circle
Trachyandesite, blue X
Trachyandesite, polarized light
Geochronology - Marathon & Ft. Peña Basalts
U-Pb, SHRIMP (Fanning, ANU)
Marathon basalt boulder
207Pb/206Pb ages from ~1920 to ~1270 Ma
Younger ages appropriate for Grenvillian basement rocks
Ft. Peña basalt boulder 1 - ~1230 Ma (Grenvillian)
Ft. Peña basalt boulder 2 - ~720 and ~660 Ma (Neoproterozoic)
Boulder Source(s), Marathon Basin?
No known outcrops of
Neoproterozoic to
Eocambrian
lavas in the region
Seismic and borehole
data indicate that
Grenvillian metamorphic rocks form
foundation for the
Marathon Basin
PROTEROZOIC FOUNDATIONS - W. OUACHITA BASIN
(modified from Karlstrom et al., 2004)
New Data from Marathon Fm:
Two Magmatic Pulses during Rodinia Rifting
Tuff boulders in
debris flows of
the Monument
Spring Mbr
(Roberts, 2012)
Bentonitic
layer in
uppermost
Marathon Fm
780-700 Ma – Neoproterozoic volcanism
580-520 Ma – Eocambrian volcanism
U/Pb, LA-ICPMS, zircon (Stockli, UT-Austin)
COEVAL WITH RIFT MAGMATIC EPISODES OF EASTERN LAURENTIA
Felsic Tuff Clasts
Marathon Fm, Monument Spring Mbr
U/Pb, LA-ICPMS - zircon (Stockli, UT-Austin)
207Pb/206Pb
ages: 1300-1100 Ma – Grenvillian basement source
750-700 Ma – Neoproterozoic rift volcanic source
~520 Ma – Eocambrian rift volcanic source
Bentonitic Layer
Uppermost Marathon Fm
U/Pb, LA-ICPMS – zircon (Stockli, UT-Austin)
207Pb/206Pb
ages: 1400-1100 Ma – Grenvillian basement source
780-750 Ma – Neoproterozoic rift volcanic source
580-520 Ma – Eocambrian rift volcanic source
South-Central Laurentia
(modified from Viele, 1989)
M
Devils River Uplift – Prior to analyses of the Marathon (M) clasts,
DRU provided the sole evidence for co-located Neoproterozoic and
Eocambrian magmatism in this span of the margin.
Devils River Uplift
Neoproterozoic & Eocambrian Magmatism
(modified from Nicholas and Rozendal, 1975)
Subsurface, 75 km ESE of Marathon fold-thrust belt exposures
Rb/Sr, whole-rock age determinations on exploration well cores:
711 ± 23 Ma – metarhyolites
524 ± 32 Ma and 529 ± 31 Ma – metavolcanics within metasediments
Forthcoming geochemical analyses to determine tectonic environment
Eastern Laurentia
Two-Stage Rodinia Rifting – Representative Examples
NEWFOUNDLAND (Cawood et al., 2001)
760 – 700 Ma felsic volcanics, dike swarms
570 – 535 Ma bimodal, basalt and rhyolite
ADIRONDACKS (Cawood et al., 2001; Burton and Southworth, 2010)
760 - 680 Ma
felsic rocks of massif
620 - 580 Ma
mafic dikes
CENTRAL & SOUTHERN APPALACHIANS (McCausland et al., 2011)
750 Ma
dominantly felsic
615 – 590 Ma tholeiites to alkaline basalts
APPALACHIANS, BLUE RIDGE (Southworth et al, 2009; Tollo et al. 2012)
760 – 680 Ma felsic volcanics and plutons
565 Ma
dominantly mafic
N. CAROLINA, GRANDFATHER MT. (Burton and Southworth, 2010)
760 – 700 Ma felsic volcanics
600 – 550 Ma basalt and rhyolite
Opening of Iapetus –
Divergence of Laurentia and Gondwana
(PLATES Program, UTIG, 2011)
Two-stage rifting along E
Laurentian margin at ~760 to
~700 Ma and ~570 to ~535 Ma
Intraplate extension/rift geochemical signature for 706 Ma
volcanic boulders in L-M Ordovician strata of Marathon Basin
750 - 700 Ma
New 780 to 520 Ma ages suggest
that S margin experienced coeval
Neoproterozoic-Eocambrian rift
magmatism
Eos – the dawn of Iapetus
A fragmentary record of
Neoproterozoic - Eocambrian volcanism –
possible within-plate extensional magmatism during
rifting of south-central Laurentia