REGIONAL ROCKS- half baked?

CPC (Coastal Plutonic Complex) + CGC (Central Gneiss Complex)

The CPC is a convenient (and dated) label for the belt of similar looking granites (plutons, batholiths) from Baja to Alaska along the Pacific Coast. On closer study, it became obvious the West Coast was a patchwork of many terranes (thus likeness was from similar process of accretion rather than origin).

Geologic studies in the previous several decades had been intrigued by our CPC.
1) The Skeena River cuts through and thus gives geologists a cross-section of a metamorphic rock continuum from the mildly changed (low grade) schists (on Digby Island (labeled "1" below; or more technically greenschist) to the completely altered gneiss (labeled "4" below) of the CGC.

Age is a clue

Ecstall Pluton: Cretaceous 98 ma
Quottoon (65) 58 ma
Kasiks Pluton 53 ma
Ponder 60 ma 

 There are two sources of heat to bake rocks: depth and molten intruded rocks (or more technical).
2) And that leads to the geologically puzzling question: how did the CGC get altered so much (facies at Kasiks implies 35 km deep) but then how did they get to the surface so quickly?

3) Plutons (molten granite intruded at depth) also changed the rocks close to them which were either pushed aside (the contour lines at "3", north of the Ecstall pluton) or even (partially liquefied ("Mictic" below). Thus much of Accrete projects locally have dealt with how and why plutons embedded. See granites section.

Continuum implies arbitrary categories

It is refreshing to see even experts disagree. Skeena rocks have been labeled differently by people who studied the area. (Compare the three maps on this page.) So don't feel bad if you're not sure if the rock in hand is gneiss (foliated) or granite; or if the metamorphic is slate, phyllite or schist.
Even "granite" is a mixture so different naming systems have been used over the years.

Let's just call them: granite, schist and gneiss
Note Gneiss east or Prince Rupert and Mi (Mictic) (Gottesfeld)

 Here is Hutchinson (1982) note Gneiss begins Butze Rapids area PR

  

Sources-or this cartoon is too simple for me

Hutchinson 1982: Geology of the Prince Rupert - Skeena Map Area, British Columbia
Library has a copy
Gottesfeld (1983)---More useful for Terrace to Hazelton area--- Library has a copy

Need a refresher on Metamorphic rocks? Here is a good, easy, non-technical 1st year course

If that's too easy, here's a UBC 2nd year course. There is a rock e.g., greenschist look-up feature on this site.

Not challenging enough? Try this meta-index for Metamorphic rocks; the list of on line journals is convenient.

Back to Nature index or to local schist as street art