Relative motions between oceanic plates of the Pacific Basin

Abstract

Appendix tables are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C., 20009. Document B84‐012; $2.50. Payment must accompany order. Relative motion poles describing the displacement histories between the Pacific plate and once adjacent oceanic plates (Farallon, Kula, Izanagi I, Izanagi II, and Phoenix) were derived for the late Mesozoic and Cenozoic eras. Because fracture zone and magnetic anomaly data are generally available from the Pacific plate but not from adjacent plates, a new method of analysis for onesided data was required. This analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions. The following are the main conclusions drawn from our analysis: (1) For time intervals of the order of 107 years, termed stages, relative motion poles for plate pairs remained nearly fixed. Between stages, shifts in poles were commonly both large and abrupt. Within stages, rates of plate motion were commonly observed to change markedly, indicating that plates changed speed more frequently than they changed direction. (2) The relative motions of all of the plates analyzed changed at about chron M11 (135 Ma), chron 34 (85 Ma), and chron 25 (56 Ma). (3) During the Early Cretaceous there were five oceanic plates in the Pacific basin rather than the four recognized by previous workers. (4) To determine the number of Farallon plates that existed to the east of the Pacific plate during the time interval from chron 34 (85 Ma) to chron 25 (56 Ma), fracture zones and magnetic anomalies that record Pacific‐Farallon spreading from the northern, central, and southern Pacific plate were analyzed separately and collectively. The analysis shows that a single Pacific‐Farallon relative motion pole and a single rate are consistent with all of the data. (5) Spreading rates along the Pacific‐Kula ridge decreased markedly between chrons 32b and 25 (72–56 Ma), probably in response to the arrival of buoyant Kula lithosphere at a subduction zone northwest of the Bering Sea. (6) Soon after chron 25 (56 Ma), a major reorganization is recorded along the Pacific‐Farallon boundary. The Kula‐Farallon boundary is also thought to have changed during this reorganization. (7) Kula‐Pacific anomalies north of anomaly 25 are modeled by assuming continued Kula‐Pacific spreading after chron 25 (56 Ma). (8) Probably by chron 18 (43 Ma), Pacific‐Kula spreading had ceased and the Kula‐Farallon ridge system had evolved into alignment with the Pacific‐Farallon spreading direction. However, the timing of these events is uncertain because Pacific‐Kula data younger than chron 25 (56 Ma) are sparse.

Guadalupe pluton–Mariposa Formation age relationships in the southern Sierran Foothills: Onset of Mesozoic subduction in northern California?

“…Mid-Cretaceous and later head-on convergence involved at least a modest component of Late Cretaceous dextral transpression [Engebretson et al, 1984;Nadin and Saleeby, 2008], followed by Neogene overriding Ma and intra-arc spreading of the medial Klamath terrane assembly, with oceanic crust produced and/or tectonically inserted outboard (Rattlesnake Creek terrane and Jura-Triassic arc belt) and inboard (North Fork terrane), followed by onset of an important component of transpressive underflow, generating a Middle Jurassic calcalkaline belt with orange trend line of volcanic-plutonic arc from compilation by Irwin [2003] and outboard Red Ant blueschists. (c) Transpressive convergence resulting in hot hanging wall generation of high-grade amphibolites, blueschists, and eclogites at $170-150 Ma, landward arc formation, and deposition of the Galice-Mariposa sequence, followed by westward step out of the transpressive plate junction, with sinistral migration of the Klamath salient relative to the alongstrike Sierran arc attending the 150-140 Ma development of cusps in the North and South American apparent polar wander tracks [May and Butler, 1986;Schettino and Scotese, 2005]; continuing transpression created a modestly active volcanic-plutonic arc, fore-arc section, and trench deposits, giving way at $125 -120 Ma [Sager, 2007] to mid and Late Cretaceous nearly orthogonal subduction and production of the massive Sierra Nevada batholith, involving minor dextral transpression.…”

“…[22] In marked contrast, the calcalkaline flare-up of the arc became paroxysmal during mid Cretaceous time, when a major change from southward to northward tangential component of drift of the Pacific-Farallon plate occurred [Engebretson et al, 1984;Sager, 2007]. T. A.…”

Introduction to Leg 145: North Pacific Transect

“…The validity of our Cretaceous paleoceanographic reconstructions is only as good as our knowledge of the drill-site paleolocations. This is more of a problem in the North Pacific than elsewhere, because a major plate boundary reorganization occurred during the Late Cretaceous magnetic quiet zone, and the exact nature of that history and ensuing Late Cretaceous and Paleogene plate motions remain a matter of interpretation as of the summer of 1992 (see Rea and Dixon, 1983;Engebretson et al, 1984;Mammerickx and Sharman, 1988). Seafloor ages at two of the Leg 145 drilling locations may further our understanding of the tectonic history of the North Pacific Ocean.…”

Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian–Emperor bend

“…A possible plate-scale mechanism for changing asthenospheric flow might be a gradual westward speed-up of the Farallon-Pacific spreading rates, possibly starting at ∼50 Myr ago, which was caused by the increasing pull on the Pacific Plate exerted by the subducting slabs in the IBM and Tonga subduction zones 20,26 . This timing corresponds to the part of the Hawaiian-Emperor Seamount Chain where the trend first starts to rotate from nearly due south to east-southeast, just north of Daikakuji and near Kimmei Seamount, marking the time of inception of the HEB ≥ 50 Myr ago and not the most arcuate 47.5 Myr ago part on the bend 5,9 (see also Supplementary Fig.…”

“…It seems reasonable, therefore, to infer from the striking synchronicity between the 53-52 Myr ago tectonic-magmatic event and subduction of the Izanagi-Pacific spreading ridge (∼52-51 Myr ago; refs 11,20), and subduction initiation at the Izu-Bonin-Marianas subduction zone (IBM) and Tonga (∼51.5 Myr ago, as measured by subductionrelated volcanism) 19,[21][22][23] , that they might be causally connected (Fig. 4).…”