Paleomagnetic test of the Early Tertiary Plate circuit between the Pacific Basin Plates and the Indian Plate

Abstract

The internal consistency of early Tertiary reconstructions of the Pacific, Antarctic, and Indian plates has been tested by combining seafloor spreading data and paleomagnetic data. These tests show that substantial motion has taken place during the Tertiary across a fossil plate boundary located within one of these plates. We consider two alternative models to reconcile the available paleomagnetic and plate tectonic information. In the first model, East and West Antarctica were separate plates, the early Tertiary position of West Antarctica being one in which the Antarctic Peninsula is adjacent to the southwest border of South America. This model is consistent with the paleomagnetic data from Australia and Antarctica. In the second model the northern and southern parts of the Pacific plate have undergone left‐lateral strike slip motion across a fossil plate boundary located northeast of Chatham Rise. This second model is supported by paleomagnetic data from the northern and southern segments of the Pacific plate. The joint assumptions (1) that the hot spots are fixed and (2) that during the early Tertiary the present Pacific plate was two separate plates (the Chatham Rise plate and the north Pacific plate) are consistent with all of the paleomagnetic data and all of the geometrical constraints of early Tertiary plate reconstructions. The joint assumptions (1) that the hot spots are fixed and (2) that the present Antarctic plate was two early Tertiary plates produce unacceptable overlap and are not consistent with Pacific plate paleomagnetic data unless the Chatham Rise has moved independently of adjacent seafloor.