How much oceanic crust in the Southern Pacific?

“Oceanic” magnetic anomalies were “calibrated”, on Iceland, for just the last 4 million years. They extrapolated to 84 Ma (20x!) in the South Atlantic (Heirtzler et al., 1968), where there are 34 magnetic stripes west of the Mid Atlantic ridge. They extend back to 84 Ma and Cretaceous “Quiet Period” crust. This crust, however, is continental, not oceanic, and was not a 37 million year episode when Earth forgot to reverse its magnetic field.

There are 57 magnetic lineaments in the SE Pacific (140 Ma?), never discussed.

During the birth of Plate Tectonics Vine & Mathews (1963) famously related magnetic stripes to geomagnetic reversals. They noted, however, that alternations of ridges of high intensity and valleys of low intensity could result from presence of strongly magnetized material adjacent to weakly magnetized material. This qualification does not appear in subsequent literature.

In their paper Heirtzler et al., (op. cit.) qualified their work, writing: “the possible error in extrapolation cannot be overemphasized; if the Vine & Mathews (1963) theory is in error, the conclusions of this paper do not apply”. Thus, if the Vine & Mathews (op. cit.) qualification, above, is correct, extrapolation in the S Atlantic is incorrect.

What is “oceanic crust”? Karner (2008) described thinning of continental passive margin from 30 – 40 k to10 km, followed by rupture. Extension (100s percent) forms zones 100s km wide with organized magnetic anomalies from serpentinization. Correlatable magnetic anomalies do not unambiguously define “oceanic crust”.

Serpentinization involves reaction of peridotite with water at less than 500^oC. The reaction is exothermic and results in volume increase as much as 45%. Magnetite forms.

Southern Pacific Ocean magnetic striping is symmetric between extended and largely subsided continent Zealandia and South America.

Onshore, thick basinal prisms, elongated parallel to the Andes, have steep western (Liassic deep water shales) and gentle eastern (Upper Triassic shallow water carbonates) boundaries. The basins shallow up to carbonates, red beds and evaporites. The ages correspond to Pangaean breakup.

The asymmetric basins were uplifted from the Pacific via transpression along the N-S, dextral strike-slip plate boundary (Liquiñe Fault).

They came from the Pacific.

Triassic-Jurassic rifting marked initiation of Pangaean breakup along the NW margin of Colombia, also a zone dextral strike-slip faulting (Romeral suture: oceanic rocks to the west, continental rocks to the east). Transpression shortened the Jurassic-late Cretaceous passive margin into metasediments (graphitic schists and black marbles in the western and central Andean Cordillera).

Further northwards the striping pattern becomes complex. The spreading ridge approaches the Americas and evolves into the San Andreas dextral strike-slip fault.

Seismic data record seaward-dipping wedges in the eastern Pacific.

So, in view of all this, how much “oceanic” crust is there in the Southern Pacific?