> A lot to discuss here. I have not read Carey's book yet but will
> attempt to obtain it since I am very interested in the topic.
> Does Carey suggest that hot spots are not required to explain any linear
> volcanic chain or just the Hawaiian Islands?
My understanding of Carey is that he does not have much time for the
concept of hot spots. Rather, linearities are an indication of
crustal stress.
> If not at least we can
> see that the Hawaiian Islands appear similar to other Pacific island
> chains that have active islands at the very tip of the most southeastern
> point . More on other hot spots below.
Yes, but other chains do not consistently "tell the same story" as
the Hawaiian chain!
Source: Geology Today, 14(2), March/April 1998, 65, Geodigest.
"Mantle plumes can't explain everything! At first, geoscientists
looked to that obvious explanation when they contemplated the
Cook-Austral chain of volcanic islands in the South Pacific, but it
soon became apparent that it wouldn't fit in the way that it did for
the Emperor-Hawaiian chain and others - i.e. that the islands were
generated in sequence as a moving plate passed over a stationary
plume. Radiometric ages of samples from the Cook-Austra islands are
both older and younger than would be predicted on the basis of a
single plume now located beneath the active Macdonald seamount
(although the theory does seem to work for the southernmost part of
the chain for just the past 6 million years). So what's going on here?
McNutt and others (Nature, v.389, p.479, 1997) have obtained new
radiometric ages that clearly demonstrate that there are three
distinct chains involved, spanning 34 million years, none of which is
plume-generated. Instead, the location of volcanic activity in the
region appears to be controlled by complex stress changes in the
lithosphere. No, mantle plumes can't explain everything."
> Secondly, let me add one more bit of Radiometric correlation.
> Drowned coral reefs (or whatever you believe them to be) are found in a
> successive layer of rings around the Hawaiian Islands. On the
> Islands of Hawaii these reefs have been dated and a strong correlation is
> found between depth and age such that a rate of subsidence (we can
> discuss the evidence that is subsidence later if you wish) can be
> calculated very simply. On the active end of the island this rate
> of subsidence is nearly the same as the measured rate of subsidence using
> tide gauge data over the past 30 years and dating of drowned Hawaiian
> rock paintings.; Interestingly, drowned reefs on the far end
> of the island demonstrate a slightly lower rate of subsidence. This
> makes sense given the loading of new material at the active end of
> the island and thus a faster rate of settling.
understanding of subsidence away from spreading ridges. He does not
discuss the data you allude to - but insofar as there is recent and
current volcanism, he would expect this to have some impact on the
depth of the ocean floor.
> The linear relationship between coral age and depth suggests that
> the rate of subsidence has been the same over a long period of time
> (100kyr). To avoid such a conclusion either the radiometric dates
> must be suspect but then why would a rate determined from radiometric
> dating be the same or even remotely similar to that determined from
> modern tide-gauge data?
Now I'm trying asking myself the question - have we now moved from
Carey's views to the challenge made to YECs? I don't think Carey
would find a problem with what you have pointed out. OTOH YECs would
not find these data readily accommodated in a short time frame and
would seek a reinterpretation. To my knowledge, a convincing
reinterpretation has not been offered.
> It would appear that the speculation that the base of the islands are
> much older is meant for us to think that the Emperor
> Ridge seamounts are simply eroded stumps of much larger mountains and so
> they have simply eroded down into much older rock and the same could
> occur to the active islands eventually.
No, I do not think this is Carey's position. It seems to me that he
postulates the formation of the sphenochasms over millions of years,
with active volcanism ceasing at different times in a sequential
manner along the Emperor and Hawaii ridges.
I had said:
> The least that can be said about this is that there is here an
> alternative model - and I am a great believer in the evaluation of
> multiple models! I wonder how many geoscientists have
> considered Carey's explanation?
Joel's comment:
> I may be way off but the description of Carey's explanation sounds like
> it would fit within the alternative plate tectonic models promoted by
> Meyerhoff and Meyerhoff in the 1970s (American Association of Petroleum
> Geologists Bulletin 56(2):269-336, 1972).
To my knowledge, the Meyerhoff's were not advocates of an expanding
earth. Carey finds common ground with them in their opposition to
PT. He quotes them approvingly:
"India has been part of Asia since the Proterozoic or earlier time.
This is a geologic fact, which nothing can change". (p.161).
I quoted to Joel: Geology Today, 14(3), May/June 1998, 101-103 which
reported on research suggesting the non-fixity of the Hawaiian hot
spot.
> True, it is difficult to establish the absolute fixity of the spots and a
> major deviation would require some new thinking.
We are agreed on this!
> This still does
> not get us out of the correlation between age and distance even in the
> Emperor Seamounts. If we have dramatic movement of the
> hotspot then how are the radiometric dates to be understood?
> ..... I am willing to leave the
> challenge solely on the data of the Hawaiian Ridge.
OK, but the point of my original post was that other explanations of
the data may be possible (such as Carey's). Have we exhausted the
possibilities? YECs need to propose alternative explanations, but
failure to do this does not lead to the conclusion that no other
explanation exists. Your challenge stands - but it is a challenge,
not a conclusion.
> The Geology Today issue is at the binders (it
> seems everything I ever want is!).; I am surprised I missed that one
> in my literature search was researching the subject recently.
Just for information: I posted all the text on this matter in Geology
Today. The meat is in the articles it cites.
Best regards,
David J. Tyler.