Outline

• Gondwanaland South American • Two : Paleozoic History 1. Pampean (545-500 Ma) 1. Santa Rosita Formation th Group Presentation #1, Feb. 4 2005 2. (520-430 Ma)

Jennifer Lougen • Passive Margin Formation Wil Shaffer • Late Orogenic event Paul Agle

Gondwanaland

• Gondwanaland Movie Evolution of : Early Paleozoic • South America, Africa, , , India, Madagascar

• West Gondwanaland: South America, Africa Jennifer Lougen

Prior to

• : deep marine passive margin

• Opening of Puncoviscana and Iapetus

• 530- 534 Ma last passive margin deposition

1 Pampean Orogeny Cont’d • Pacific Margin: passive Æ active • Fold belts in W. Pampea (Puncoviscana) and E. Pampea (Sierra Cordoba) • 530-520 Ma; Short lived (west) • Pampean Mobile Belt: and Eastern Cordillera • Convergent processes between Rio de la Plata, • Peak , Middle , and Cordoba

Rocks of the Pampean Orogeny

• metasediments

• paragneisses and aluminous schists, migmatites and aluminous

• Calc-alkaline granitoids

• Dacites-rhyolites

After Pampean Orogeny

• No orogenic activity Areas where Various Rock Types can be • Passive margin(Meson Group) found

• Little granitoid emplacement 515-490 Ma

• Arc stopped/decreased

2 Santa Rosita Formation Meson Group

• Records passive margin formation • lies above the Meson Group

•Records infill of retro arc basin; • Tide dominated shelf Sea level fall

• Trough and tabular quartzite • depositional history: fluvial, tide- dominated estuarine, and wave • Regionally extensive tidal deposits probably representing dominated shallow marine deposition in a gently dipping shallow marine ramp •Max thickness ~2300m

•5 members: Tilcara, Casa Colorada, Alfarcito, Rupasca, Humacha (bÆt)

Members Cont’d.

Tilcara Member Rupasca -conglomerate, tabular cross -mudstone bedded quartzose ss -thinly interbedded rippled ss -interbedded ss and mudstone -transgressiveÆregressive events (early ) Casa Colorada -greenish gray mudstone -thinly rippled interbedded ss Humacha -hummocky cross stratified ss Alfarcito -hummocky cross stratified ss -interbedded rippled mudstone and ss

Stratigraphy Column for Analogs to Santa Rosita Fm.

• Passive Margin Formation in Proterozoic (Puncoviscana Fm.)

• Followed by orogeny (Antler Orogeny vs. Pampean Orogeny)

• Followed by quiet period (passive margin formation)

3 The BIG picture SA West Coast events • Break up of Super Ordovician-Early • moving along west 495 - 350 mya eventually colliding with it PLATES_3.mpeg Wil Shaffer

Early Ordovician (490-470 mya) Mid Ordovician (470-450 mya) • Famatinian Subduction – Irúyica event • Tectonic subsidence rates increased from 65m/my • Cambrian metaturbidites and plutons overlain by an to 600m/my angular and shallow marine (qrtz. – Change in basin evolution from extension to SS and SH) [Meson Grp.] compression • Sediments derived from the east • Eastern side of basin there was development of silicicalstic rxs – Magmatic arc further west (basaltic-andesitic lavas – Response to loading in the west (peripheral bulge) – Pillow basalts and sills further East • Further East in Cordillera Oriental there is noted eastward • Indicative of extension subduction by trondhjemite plutons • Formation of a back arc basin (eruption of calc-alkaline – Trondhejemite Æ Phaneritic Qtz-Alb rich plag rxs volcanics) • Docking of Precordillera – Controversial topic

Late Ordovician (450-440 mya) Oclóyic Orogeny models • Amalgamation of the exotic Precordilleran during mid-Ordovician • Fold pattern – The “missing” piece of Texas (Ouachita embayment) – East of basins ÆWest verging folds – Three “excepted” hypothesis of docking mechanisms – West of basins Æ East verging folds •1) Precordillera micocontinent was rifted from Laurentia (during Cambrian) and collided with Gondwana • Folding accompanied by peraluminious – Independent of Laurentian granitoids in N. Chilie, E. Puna basin, and •2) Continent-Continent collision producing a continuous Cordillera Oriental (syn-post tectonic) Taconic- Oclóyic orogenic belt. Upon rifting of the Precordillera was Left attached to Gondwana

• 3) Precordillera was at the tip of a distal plateau on a greatly stretched Laurentian that collided with Gondwana and separated from Laurentia.

4 Precordillera Sediments • Southward and westward there is a Ign. Rx clues transition from shallow-marine carbonates to black shales. • Bentonites within mid-Arenig to – Initial flexural subsidence of a Llanvirn Rxs (the aforementioned transition from LS -> Sh) • Shales grade into flysch-like synorogenic – Document proximity to ! clastic wedges (flow direction from East) – Contradict Continent-Continent type – Mudstones - > - > Conglomerates collision • Regionally diachronous unconformity • Plutons in Sierras Pampeanas yield Early-Late Ordovician ages – Migration of peripheral bulge and flexural – Stopped ~445 mya after Precordillera extension down- going Precordillera plate was docked

Clues closer to home

• Ages of synorogenic clastic wedge in Tenn. is older than events further north.

• Tenn. Embayment – 1) flexural subsidence of foreland basin • Upward transition from Mid. Ord. carbonates to

black shales y X B • Shales prograde into turbidites (coarsen upward) A – Flow direction from orogenic terrain in then east

Ouachita Embayment

5 Continent-Continent collision cont. • Contrasting Paleontological data • Contrasting lithological assemblages in synorgenic clastic wedges in Taconic foreland of SE Laurentia and Ocloyic foreland of the

tinent collision Precordillera terrain indicate two separate basins • Bentonite beds in both locales indicate separate dispersal systems • Gondwanan glacial deposits extend from the sub- Andean ranges into Precordillera but are not found in Laurentia - >considerable latitudinal separation by late Ordovician time Continent-Con • **Eliminates possible continuity of Taconic and

3) Ocloyic orogenic belts

Distal plateau cont. • Modern analog-> Malvinas plateau

• Used to explain Paleontological data u

a • Abandons the continuity of strike between Oclóyic e

t and Taconic belts

a l

p • Requires departure of continental crust from

l Ouachita embayment a

st – No post-Taconic extension has been recognized on

i Alabama promontory

D

) – Southward-facing shallow marine carbonate self and

2 equivalent deep-water self facies surround the Ouachita embayment indicating a passive margin from Late Cambrian to Early Mississippian

Late Paleozoic Tectonic Evolution of South America

Paul Agle Precordillera micocontinent Aforementioned data points to this possibility 1)

6 - (440-350 mya) End of Famatinian Orogeny

• Ign. and meta. activity dies down. ¾ Docking of Terrane • Marine deposition westward to N. Chilie ¾ Middle to Late Devonian – Transgress into soil horizon ¾ Followed by ~100my of tectonic • Denudation () during Silurian quiescence • Subsidence rate goes to 18m/my – Subsidence balanced by detrital input from East

Modified from Rapela et al, 1998

Middle Devonian Silurian to early Late Paleogeography Carboniferous ¾Passive Margin ¾Zorritas Formation ¾Overlies unconformity that spans most of Silurian time, indicating massive erosion ¾East- derived onlapping sequence of shallow marine siliciclastics ¾2700m thick ¾Subsidence rates typical of passive margin

From Wicander and Monroe, 2000

Early Carboniferous Late Carboniferous

¾Zorritas Formation is punctuated by an ¾Must have been an erosional unconformity near end of Early out-board source Carboniferous ¾Many invoke a ¾Probably related to tectonic uplift “Pacific Continent” ¾Passive margin clastic turbidites persist to West ¾No evidence of its existence ¾Las Tortolas, El Toco, and Sierra del Tigre Fms ¾More likely a rifted ¾Western Source! fragment of SA

Modified from Bahlburg and Herve, 1997

7 Schematic Cross Section Toco Event (Late Carboniferous)

¾Syn-sedimentary deformation in Las Tortolas and Sierra del Tigre Fms ¾Slumps, folds, and dismembered bedding ¾Fold axes trend -SN ¾Fold vergences towards West ¾Erosional unconformity in Sierra del Tigre Fm ¾Zorritas Fm unaffected

Modified from Bahlburg and Herve, 1997

Late Carboniferous Problems with Model Paleogeography ¾No evidence for rifting of outboard “Pacific” terrane ¾Terrane has not been found ¾May be accreted to Laurentian margin ¾May have been removed by tectonic erosion ¾Strike- slip component carried it N- ward

From Wicander and Monroe, 2000

Latest Carboniferous through Schematic Cross Section Permian ¾ Onset of Eohercynian Orogeny ¾ Subduction of Proto-Pacific plate on W margin ¾ Folded turbidite units intruded by intrusive and extrusive calc- alkaline ¾ Deformed and incorporated into Chanaral mélange (accretionary prism) ¾ Zorritas Fm intruded and overlain by Peine Group (volcanic arc) ¾ Volcanics and -clastic sediments ¾ Regional High Pressure Metamorphism

Modified from Bahlburg and Herve, 1997

8 Late Paleozoic Volcanics Overview

¾ Sierra Limon Verde Complex (309-276Ma) ¾ Passive Margin ¾ Gneiss, Amphibolite, ¾ Rifting of W margin (?) ¾ High-pressure metamorphism ¾ Deposition in basin from E (Zorritas Fm) and W ¾ Bellavista (318Ma) and Albayay (292-217Ma) (Las Tortolas, El Toco, and Sierra del Tigre Fms) ¾ ¾ Toco Event, folding of Western units ¾ Puna (275-248Ma) ¾ Eohyrcynian Orogeny, subduction begins and ¾ Granodiorite basin (?) closes ¾ Peine Group (305-268Ma) ¾ Pangaea is largely assembled ¾ Granitoids ¾ Volcanic arc persists along western margin into Mesozoic

Late Permian South American Paleozoic Paleogeography Suggested Reading • Bahlburg, H., Herve, F., 1997. Geodynamic evolution and tectonostratigraphic of northwestern Argentina and northern Chile: GSA Bulletin v. 109, 869-884. • Rapela, C.W., Pankhurst, R.J., Casquet, C., Baldo, E., Saavedra, J., Galindo, C., 1998. Early evolution of the Proto-Andean margin of South America: Geology v. 26, 707-710. • Thomas, W.A., Astini, R.A., Bayona, G., 2002. Ordovician collision of the Argentine Precordillera with Gondwana, independent of Laurentian Taconic orogeny: Tectonophysics v. 345, 131-152.

From Wicander and Monroe, 2000

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