I AM CONFUSED

                                              Karin Sigloch

                      and westward subsuction

Okay, so this blog mainly is addressed to Nick Zentner and his following (collectively known as Zentnerds and ranging in age from Patrick, age eight, to myself, some 80 years older).  I have just finished watching Nick’s interview with Karin Sigloch – twice – and I have some questions.

Dr. Sigloch indisputably is an ornament to geotectonics; that is not in question.  I understand her tool – seismic tomography – in a rudimentary sort of way, although I have a difficult time with her illustrations.  Probably my eyesight is to blame.  However, here is part of what I think she is saying:

1)    One can use seismic tomography to locate subducted slabs in the mantle.

2)    It is feasible to use the current location of these slabs as evidence of the former location of the trench that created them, and these subducted slabs can be regarded as fixed, thereby providing a frame of absolute – as opposed to relative motion.

3)    Given the above, it follows that the Insular Superterrane remained stationary from Mesozoic time, while the North American plate moved engulf it in a process we call accretion.

4)      The Insular Superterrane was in large part created by westward subduction

Have I got that right?

So, now to my questions:

1)    In view of the fact that the so called “California Triade” clearly requires eastward subduction, was there an oceanic plate caught between North America and Wrangellia that was eliminated by subduction in both – opposite - directions?  

2)    Were these two anti-parallel subduction zones active at the same time?

3)    Does Wrangellia show evidence of a similar “triade”, but facing the other way?  This might be expected to produce two distinct igneous belts.  I seem to recall that in British Columbia there is a second igneous province, called the Cassiar belt inboard of and roughly parallel tothe Coast Plutonic Complex – but I think the chronology won’t work.

4)    Are the rocks that compose “Baja B.C.” part of the accreted block.  In particular, did the Mt. Stuart batholith originate as part North America proper, or was it part of an exotic terrane?

As you can plainly see, I no longer am “cutting edge” where Cordilleran tectonics is concerned – if ever I was.  I hope that future Nick lectures will help me catch up!