NEOGENE FORELAND UPLIFT HISTORY IN THE FLAT SUBDUCTION REGION, TRANSITION ZONE, AND NORMAL SUBDUCTION REGION, NW ARGENTINA .

Reynolds, James H., ESMNS, Brevard College, Brevard, NC 28712

More than 15 years of chronostratigraphic research by North American and Argentine investigators allow a preliminary, regional uplift history model across the three tectonic domains present in NW Argentina. Magnetostratigraphic and isotopic dates limit uplift ages in the: 1) flat subduction region (FR; 36° 15'S-28°S), 2) Transition Zone (TZ; 28°S-24°S), and 3) northern normal subduction region (NR; 24°S-22°S). The Cretaceous Salta Rift Basin influences most TZ deformation.

Foreland deformation commenced across the region by 16 Ma with uplift of the Puna (NR, TZ) and western Precordillera (FR). Thrusting migrated eastward in the Central Precordillera (FR) by 14 Ma and continued until at least 5 Ma.

Uplift in the northern and central Sierras Pampeanas (TZ, FR) began between 13-12 Ma. No data exist for the eastern or southern ranges. Pampean uplift migrated westward in the FR to the present but eastward in the TZ. TZ uplift from 13-10 Ma created the Cordillera Oriental . The earliest recorded NR Cordillera Oriental uplift is 11.4 Ma.

Subandean Zone deformation began after 9 Ma in the Santa Barbara System (TZ) along primarily west-verging faults and around 8.5 Ma in the Sierras Subandinas (NR) along primarily east-verging faults. Uplift migrated eastward in both areas.

The Salta Rift strongly influenced diachronism of W-E foreland deformation migration. Initial W-E migration began in the FR, followed by the TZ, and finally the NR. W-E migration rates appear to increase northward although uplift in the south is predominantly E-W today.

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