Age and correlation of volcanism in central Livingston Island, South Shetland Islands: K-Ar and geochemical constraints

first_imgVolcanic sequences in central Livingston Island can be divided into two broad groups. The older group consists of basalt-dacite lavas, clastic rocks and associated hypabyssal intrusions. The lavas are lithologically and compositionally similar to other pre-Pliocene, volcanic arc lavas in the South Shetland Islands. The outcrops vary from relatively fresh (at Cape Shirreff, Hannah Point and Siddons Point) to indurated and pervasively altered (at Mount Bowles, Burdick Peak and Hurd Peninsula). Samples from the fresh outcrops yielded Late Cretaceous ages for eruption or intrusion, ranging from 90.2 ± 5.6 Ma at Cape Shirreff, to 73.0 ± 2.3 at Siddons Point. Chemical analyses of the lavas suggest that the sequences at these two outcrops can probably be correlated stratigraphically with the Byers Group and Coppermine Formation, respectively. Two samples from Hannah Point yielded conflicting ages of 87.9 ± 2.6 Ma and 67.5 ± 2.5 Ma from the centre and top of the sequence, respectively. The stratigraphical affinities of the Hannah Point sequence cannot yet be determined unambiguously but it is unlikely to be part of the Byers Group. All of the samples from the altered outcrops (which correspond to the Mount Bowles Formation) yielded Eocene-Oligocene K-Ar ages (44.4 to 35.0 Ma), interpreted as reset ages related to the emplacement and cooling of a nearby Eocene tonalite pluton responsible for much of the alteration, and also dated in this study (43.3 ± 2.8 Ma). A Cretaceous eruptive age (possibly Late Cretaceous) for the altered outcrops is likely but cannot yet be proven. By contrast, the younger group consists of degraded basalt lava flows, tuff cone and tuff ring remnants, which are part of the Inott Point Formation. The lavas are very fresh and Pleistocene or Recent in age (≤ 1 Ma). They are compositionally distinctive and are indistinguishable from supra-subduction alkali basalts preserved elsewhere in Livingston, Greenwich and Penguin islands.last_img read more


City will go ahead with allowing medical marijuana facilities

first_imgAddThis Sharing ButtonsShare to FacebookFacebookShare to TwitterTwitterShare to MoreAddThisAlpena, Mich. — Alpena city council will proceed with allowing medical marijuana sales and facilities within city limits.A vote was taken at Monday night’s city council meeting where four voted in favor and only one against. Earlier this year, city council opposed recreational marijuana facilities and sales within city limits.Prior to Monday’s meeting, city council ordered the zoning and planning commission to look at locations where medical facilities could potentially fit. After last night’s vote, the next steps will be to draft ordinances and zoning rules for facilities. No timetable has been set for when we could see businesses begin to arrive.Catch ‘Minute with the Mayor’ this Thursday to learn more about the next steps in the process and a potential smoking/vaping ban in city parks.AddThis Sharing ButtonsShare to FacebookFacebookShare to TwitterTwitterShare to MoreAddThis Tags: alpena, Alpena City Council, City Council, City Park, Medical Marijuana, Medical Marijuana Facilities, Medical Marijuana SalesContinue ReadingPrevious Photo of the Day for Tuesday, May 21Next Pets of the week May 21, 2019last_img read more