Mid‐Cretaceous paleomagnetic results from Marie Byrd Land, West Antarctica: A test of post‐100 Ma relative motion between East and West Antarctica

Abstract

As part of the tripartite, United States ‐ United Kingdom ‐ New Zealand, 1990–1991 South Pacific Rim International Tectonics Expedition, oriented samples were collected for paleomagnetic analysis from mid‐Cretaceous (circa 100 Ma) intrusive rocks at sampling localities across 350 km of the Ruppert and Hobbs Coast area of Marie Byrd Land, West Antarctica. Paleomagnetic results are presented along with several lines of evidence, including a positive tilt test based on the attitude of circa 117 Ma volcanic rocks that the circa 100 Ma rocks intrude, which argue that these results are a representative estimate of the mid‐Cretaceous magnetic field in Marie Byrd Land (MBL). The new circa 100 Ma mean south pole (224.1°E/75.7°S, A95 = 3.8°, N = 19 site means) is concordant with other West Antarctic results of similar age implying that at least Marie Byrd Land, Thurston Island and the Antarctic Peninsula have not experienced any paleomagnetically resolvable relative motion since the mid‐Cretaceous. However, the poles from these Pacific‐bordering blocks of West Antarctica are significantly offset from a synthetic apparent polar wander path that was produced for the East Antarctic craton, implying relative movement between East Antarctica and Pacific West Antarctica since about 100 Ma. Though the paleomagnetic estimate for east‐west Antarctic relative motion may be reconciled with geologic estimates for extension in the Ross Sea at the extremes of the error envelope, the best paleomagnetic estimate of relative motion suggests a larger amount of total extension between East and West Antarctica (MBL) than previously suspected. Both estimates call for several hundreds of kilometers of post‐100 Ma displacement between East Antarctica and the Pacific‐bordering blocks of West Antarctica.

Are the Pacific and Indo–Atlantic hotspots fixed? Testing the plate circuit through Antarctica

“…[15,33,34] DiVenere et al [15] produced an improved 100 Ma paleomagnetic pole for MBL, sampling many of the same units as a prior study by Grindley and Oliver [36] as well as a number of new units, and avoiding some structural complications that may have affected the previous results. Comparison of these new paleomagnetic results from MBL and an independently constructed non-Pacific global synthetic APW path for East Antarctica [15] reveals that there has been significant motion of the Pacific-bordering blocks of West Antarctica, and particularly MBL, with respect to East Antarctica since about 100 Ma.…”

“…We choose to solve for the post-64.7 Ma offset of Suiko Seamount vs. the predicted 64.7 Ma hotspot position because Suiko Seamount is the oldest dated edifice in the Hawaiian-Emperor chain for which there is a seafloor spreading model [8] constrained by fracture zone trends and magnetic anomalies on both sides of the ridge to link the Pacific with Antarctica. The best-fit Euler pole is determined from the intersection of the perpendicular bisector to the ¾100 Ma paleomagnetic poles for East Antarctica and MBL [15] and the perpendicular bisector to the position of Suiko Seamount with respect to MBL at 64.7 Ma and the predicted hotspot position at 64.7 Ma (Fig. 4).…”

“…65 Ma) discrepancy in the predicted hotspot positions. DiVenere et al [15] also argued against large errors in published Cretaceous seafloor spreading data because paleomagnetic poles transferred to Antarctica from North America, Africa, India, and Australia were evenly distributed forming a generally smooth synthetic apparent polar wander (APW) path. Cande et al [8] presented newly acquired seafloor spreading data linking Antarctica with the Pacific plate.…”

“…To address this issue, we compare paleomagnetic poles from the Pacific plate with non-Pacific mean poles of Besse and Courtillot [18] and DiVenere et al [15] We also note that the Late Cretaceous paleomagnetic pole from the Chatham Islands off New Zealand (NZ 75), which was based on paleomagnetic laboratory analysis of 84 samples collected from 29 sites in volcanic rocks [19], lies comfortably with the other Pacific poles of similar age. The Chatham Island pole falls within the estimated error ellipses of both the 76 Ma skewness-based (Pac 76v) and seamount-based (Pac 76s) poles and is therefore not statistically distinct from these.…”

“…Paleomagnetic poles have also been derived from the skewness of marine magnetic anomalies on the Pacific plate [20,[24][25][26][27]. [18] global, non-Pacific, synthetic APW path transferred to Antarctica [15] and to the Pacific using Cande et al [8]; NZ 75, [19] ca. 75 Ma result from Chatham Islands, south Pacific; Pac 32 through Pac 76v are Pacific anomaly skewness poles; Pac 32, [20]; Pac 57, [26]; Pac 65, [24]; Pac 73, [25]; Pac 76v, [27]; Pac 76s, [23] Pacific seamount-based pole; Pac 81, co-latitude circle from Detroit Seamount [47].…”