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Metasedimentary rocks constitute an

[1] The Late Jurassic to Early Cretaceous Rocas Verdes basin constitutes one of the most poorly understood components of the southernmost Andes. As a result, accurate reconstructions and interpretations of deformation associated with the Andean orogeny and the kinematics of Scotia arc development also remain poorly constrained. In this data brief, we report U-Pb zircon ages from sandstones of the Rocas Verdes basin fill and from a crosscutting pluton in the southernmost Andes of Argentine Tierra del Fuego. Detrital samples contain predominant Early to early Middle Cretaceous (circa 130-105 Ma) U-Pb zircon age populations, with very small or single-grain middle Mesozoic and Proterozoic subpopulations. A very small subpopulation of Late Cretaceous ages in one sample raises the unlikely possibility that parts of the Rocas Verdes basin are younger than perceived. A sample from a crosscutting syenitic pegmatite yields a crystallization age of 74.7 +2.2/À2.0 Ma. The data presented herein encourage further geochronologic evaluation of the Rocas Verdes basin in order to better constrain the depositional ages and provenance of its contents.Components: 9330 words, 4 figures, 1 table.

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[1] Petrographic, mineral-chemistry and subsurface studies reveal that orogenic sedimentation had already begun in the Bengal basin by the early Miocene. Laser 40 Ar/ 39 Ar age determinations were made for detrital muscovite grains (145 total, among 4 samples) from the lower-to-middle Miocene Bhuban Formation. The laser fusion ages range from circa 12 Ma to 516 Ma, and thus suggest derivation from a combination of sources: the Himalayas, Indo-Burman ranges and possibly the Indian shield and Tibetan plateau. Modes of circa 16 Ma, 18 Ma, 26 and 40 Ma in the age distributions of these samples are most consistent with unroofing of the Higher Himalayas since the early Miocene. Detrital micas of such an early age (16 Ma) for the Bhuban Formation are interpreted to indicate that little time elapsed between the isotopic closure of 40 Ar in the muscovite and its ultimate deposition in middle Miocene strata. The detrital ages of circa 16 and 22 Ma in this study, most prominent in the highest stratigraphic levels sampled in this study, are younger than those previously reported in the western Himalayan foreland basins. These younger detrital ages are consistent with rapid middle Miocene unroofing and erosion as has been proposed for crystalline rocks of the eastern Himalayas. The minimum 40 Ar/ 39 Ar ages for muscovite in a particular sample seem proportional to the stratigraphic level sampled, i.e., younger ages tend to occur for samples of higher stratigraphic level. These results support earlier studies indicating that detrital geochronology can be used as an effective tool in evaluating stratigraphic ages.