As massif type anorthosites are in fact characteristic of Proterozoic time, not Archaean, and the Archaean anorthosites are quite different. So I am not sure whether Archean anorthosites can indicate the unusually high Archean geothermal gradient. In addition, what is the detailed difference between the equivalents in Archean and Proterozoic? Thank you.
Dear Houxiang
In order to understanding the relationship between anorthosite and high geothermal gradient during Archean, you can see links below:
https://books.google.de/books?id=Tr7rCAAAQBAJ&pg=PA306&lpg=PA306&dq=Archean+geothermal+gradient+anorthosite&source=bl&ots=58YGnC1d77&sig=BoSph7FbzzTJkvcIXeJMRyRp9gY&hl=en&sa=X&ved=0ahUKEwjx5aLDoMrKAhWJNz4KHTcOB3AQ6AEIIjAB#v=onepage&q=Archean%20geothermal%20gradient%20anorthosite&f=false
https://books.google.de/books?id=lO7fBAAAQBAJ&pg=PA253&lpg=PA253&dq=Archean+geothermal+gradient+anorthosite&source=bl&ots=gipUmmqffi&sig=FlzoeHSPqg_BEopyOAhzyUr29MQ&hl=en&sa=X&ved=0ahUKEwjx5aLDoMrKAhWJNz4KHTcOB3AQ6AEIKjAE#v=onepage&q=Archean%20geothermal%20gradient%20anorthosite&f=false
https://books.google.de/books?id=Nl73ymr7cgIC&pg=PA373&lpg=PA373&dq=Archean+geothermal+gradient+anorthosite&source=bl&ots=Qli5LWmfsv&sig=MMu3mMq5X6OSfYxR8jBqw9qN0GE&hl=en&sa=X&ved=0ahUKEwjx5aLDoMrKAhWJNz4KHTcOB3AQ6AEINTAG#v=onepage&q=Archean%20geothermal%20gradient%20anorthosite&f=false
https://books.google.de/books?id=QQhxCQAAQBAJ&pg=PA241&lpg=PA241&dq=Archean+geothermal+gradient+anorthosite&source=bl&ots=B_cghxY2-X&sig=cetAWsFdoPyJYrK_xo_UeVx8m74&hl=en&sa=X&ved=0ahUKEwjx5aLDoMrKAhWJNz4KHTcOB3AQ6AEIOzAI#v=onepage&q=Archean%20geothermal%20gradient%20anorthosite&f=false
Regards
Massih
Archean volcanic sequences is used as evidence that geothermal gradients were present as in the case of the Kapuskasing belt of Ontario.
Geologist from India also measured the geothermal gradient in southern granulite terrain in India. This Is archean in age
Hi Houxiang,
Have you given any consideration to the idea that the Proterozoic lower continental crustal thermal regime was actually more energetic than that of the mid-late Archean?
While it is almost certain that global radiogenic heat production, secular heat loss and mantle potential temperature during the Archean were all higher than during the Proterozoic, it does not necessarily follow that heat flux and geothermal gradients across continental lithospheric nuclei were significantly higher during the mid-late Archean. Evidence for a ‘near-normal’ Archean continental thermal structure (similar to today's) comes from the p-t relations of mid-late Archean granulites, the radionuclide-depleted nature of co-eval Archean SCLM xenoliths, p-t relations of inclusions in Archean SCLM-derived diamonds, and some (but not all) numerical thermal modelling studies.
Furthermore, it has been argued that thermal blanketing during the Proterozoic caused by continental crustal amalgamation into supercontinents may have locally increased underlying mantle temperatures, raising lower crustal geotherms and leading to increased anorogenic melting, including the generation of the massif-type anorthosites so characteristic of the Proterozoic.
A good starting point to understand the differences between anorthosites of differing ages and geological settings is Lewis Ashwal’s "The temporality of anorthosites." in The Canadian Mineralogist 48.4 (2010) pages 711-728 (available on Researchgate).
Regards
Graham
Dear all,
Genuine thanks for all the helpful answers! I have got some useful information from the papers you provided. Thank you.