RE:RE:RE:RE:earlierGC,
For sure the BIF's are 300-500million years later. I forget when exactly. Def. a long time after. Gold ends up in the BIF's sometimes too. See Homestake as prime example.
Start of basalt deposition varies of course but say it's near 2.8Ga.
What caused the basalt? Perhaps a mantle overturn.
Read the LIP research re: sequence 1. Our time is the start.
Sequence 1: The Mount Roe Basalt and Bellary Formation are the lowest and oldest unit and consist of sedimentary rocks of fan-delta, braided fluvial facies, basaltic flows and volcaniclastic rocks, aggregating about 4.5 km in thickness. The lower and upper levels of the Bellary Formation contain massive basaltic flows, hyaloclastite breccias and mafic tuff units.
Was going to dig into more re: LIP's and mantle overturn, but maybe some other time. Instead just leave you with this link.
Late Archean to Early Paleoproterozoic global tectonics, environmental change and the rise of atmospheric oxygen Really, it's all inter-related. Life, Atmosphere & Rocks.
goldencraton wrote: I seem to remember QH mentioning in one of his interviews that the iron formations in the Pilbara were laid down on top of or above our conglomerate targets, making them later in the geological sequence. Also QH theory suggests microbial mats created oxygen which triggered the “Crustal Gold Cycle”. It almost sounds like the mantle turnover may have happened after the gold deposition in the Pilbara. Just my take at this point.
gc
goldencraton wrote: Hi Iskyhigh,
Great posts. I’m just wondering if this fits in with QH’s precipitation theory. Is the mantle turnover part of his equation? Sure sounds to be at the right time in earth’s history. Could this be the “major event” that explains the change in the chemistry of the atmosphere and hydrosphere triggering the ”Crustal Gold Cycle”?
Thanks Isky,
gc
Iskyhigh wrote: while I had it open. my reference for this was from:
https://www.geochron.com.au/wp-content/uploads/2016/11/60.-Nelson-1997.pdf The recognition of major episodes of catastrophic mantle overturn between 2760 and 2670 Ma has important implications for the deposition of the major banded ironformation sequences during the Late Archaean and Early Proterozoic. During these overturn events, the spreading centres within the ocean basins were the main focus of mafic magmatism. It is proposed here that most of the Fe in the Late Archaean to Early Proterozoic banded-iron sequences was derived, by hydrothermal enrichment of seawater in Fe, from extensive ultramafic submarine lava plains erupted during these catastrophic mantle overturn events. The banded iron-formation sequences of the Amazon, So Francisco, Kaapvaal, Karnataka and Pilbara cratons all overlie thick sequences of volcanic rocks that were erupted between c. 2800 and 2680 Ma. Emplacement of these volcanic sequences resulted in slow subsidence of these stable continental platforms until c. 2500 Ma. This subsidence facilitated the deposition, and preservation, of these Late Archaean to Early Proterozoic banded-iron sequences.
Iskyhigh wrote: Supposedly mantle overturn occurred very near to our time period. This is a simulation. See 1:49 for the overturn event.