CONTRIBUTIONS OF ROBERT H. DOTT JR. TO UNDERSTANDING OF THE SOUTHERN ANDES AND THE SCOTIA ARC

Bob Dott was drawn to Gondwana geology by George Woolard at the University of Wisconsin who persuaded him to become involved in Antarctic research during the IGY in the late 1950’s. He initiated a project to compare the geology of the southernmost Andes and the Antarctic Peninsula. Bob and his graduate students worked on the sedimentary history of the Andean foredeep, the Magallanes Basin, and conducted pioneering geochronologic studies both north and south of Drake Passage. Meantime Bob himself became fascinated by the isolation of the mountainous island of South Georgia, located 2000 km east of Tierra del Fuego in an oceanic setting, but clearly of continental character. In the early 1970’s Bob, structural geologist Ian Dalziel and two graduate students sailed to the island with British Antarctic Survey Director Sir Vivian Fuchs.

It is now clear that the Magallanes Basin formed by flexural downwarp resulting from the inversion of an Early Cretaceous back-arc basin. The geochronometry by Bob’s group hinted at the now accepted mid-Cretaceous age of the first Andean compressive event that resulted in back-arc basin inversion and initiation of the foredeep. The mapping on South Georgia, and particularly the sedimentary provenance work of Bob Dott and Bob Winn, firmly established that this microcontinent was originally the southeasternmost extension of the Andean cordillera. Subsequent studies both in the southernmost Andes and on South Georgia have enhanced our knowledge, however, the basic tectonic and sedimentologic framework was established as a result of the studies Bob Dott initiated.

Bob’s involvement in southern South America led to him to further another of his passions, the development of geologic thought. In 2007 he joined Dalziel in leading a Bicentennial Field Excursion for The Geological Society of London: In Darwin’s Footsteps: The Geology of Tierra del Fuego. Research for this trip led him to take the lead in writing a paper with Dalziel on “Darwin the geologist in southern South America”. It was published in 2016 and fittingly, for someone devoted to field geology, had Darwin’s geologic map of southern South America at its heart. Comparison of his 19^thcentury observations and conclusions with modern work reveal him as an astute geologist whose many new observations far outstripped the theory of his time.