Roca Dorrel

Dorrel Rock ( 75°26′S 111°22′W / 75.433°S 111.367°W / -75.433; -111.367 ) es un nunatak ubicado a 20 km (12 mi) al suroeste de la cima del Monte Murphy , que sobresale del hielo cerca de la cabecera del Glaciar Pope , en la Costa Walgreen , Tierra de Marie Byrd . Fue cartografiado por el Servicio Geológico de los Estados Unidos a partir de estudios y fotografías aéreas de la Armada de los Estados Unidos , 1959–66, y fue nombrado por el Comité Asesor sobre Nombres Antárticos en honor a Leo E. Dorrel, de la Armada de los Estados Unidos, un sanitario del grupo de invierno de la Estación Byrd , 1966. ^{[ 1 ] [ 2 ]}  

Dorrel Rock is an 2 km (1.2 mi) in diameter exposure of gabbro cut by dikes of benmoreite and trachyte. Dorrel Rock is a unique exposure of intrusiveCenozoicigneous rocks within Marie Byrd Land. The gabbro is coarse-grained and composed of labradorite, diopside and ilmenite, with minor titanomagnetite, kaersutite, biotite, and amphibole. The benmoreite dikes consist largely of sodic oligoclase, hastingsite-ferropargasite, scarce magnetite, and minor biotite. The trachyte dike is characterized by large euhedralphenocrysts of potassium feldspar. They are surrounded by microphenocrysts and groundmass composed of hastingsite, minor hedenbergite and magnetite, and trachytoid sanidine.^[3]40Ar/39Ar dating of biotite and amphibole from the gabbro yielded an age of 34.15±0.22 Ma. Since the gabbro cooled as deep as 3 km (1.9 mi) beneath the surface, this age indicates that 3 km (1.9 mi) of the block of Antarctica's crust containing Dorrel Rock has been uplifted and removed by erosion over the past 34 million years in response the formation of the West Antarctic Rift.^[4]