Sunday, 19 January 2025

The Altar Stone Source - the essential points

The research paper provides key evidence indicating that the Stonehenge Altar Stone likely originated from a Laurentian rock source. Here's a breakdown of the significant points:

Mineral Composition and Age

The researchers analyzed three types of mineral grains found in the Altar Stone fragments:

1. Detrital zircon: Largely composed of Mesoproterozoic and Archaean sources (very old, ranging from about 1 to 3.5 billion years) [1][3].

2. Rutile and apatite: Dominated by a mid-Ordovician source (approximately 460 million years old) [1][3].

Laurentian Origin

The ages of these grains strongly suggest derivation from a Laurentian crystalline source region [1][3]. Laurentia refers to the ancient continental craton that formed the core of North America and Greenland[2]. This is significant because:

- The presence of very old zircon grains (Mesoproterozoic and Archaean) matches igneous events in Laurentia [2].

- These events did not occur in other terranes like Gondwana, Ganderia, Meguma, or East Avalonia, which now form most of England and Wales[2].

Grampian Overprint

The mid-Ordovician ages (around 460 million years ago) of the rutile and apatite grains indicate that the Laurentian source region was overprinted by Grampian magmatism [1][3]. This refers to a phase of the Caledonian orogeny, a major mountain-building event that affected what is now Scotland.

Similarity to Orcadian Basin

Detrital age comparisons with sedimentary rocks throughout Britain and Ireland revealed a remarkable similarity between the Altar Stone and the Old Red Sandstone of the Orcadian Basin in northeast Scotland [1][3]. This basin includes parts of northeastern Scotland, Orkney, and Shetland [2].

This evidence collectively points to a Scottish origin for the Altar Stone, specifically from an area north of the Iapetus Suture, where rocks with Laurentian characteristics are found [2]. 

But not Orkney 

However, a follow-up study published in September 2024 in the Journal of Archaeological Science: Reports specifically examined megaliths from Orkney and concluded that the Altar Stone was not sourced from Mainland Orkney. This research used portable X-rays to analyze stones at the Stones of Stenness and the Ring of Brodgar, comparing their composition to that of the Altar Stone [4].

.

Citations:

[1] https://www.nature.com/articles/s41586-024-07652-1

[2] https://www.megalithic.co.uk/article.php?sid=2146415628

[3] https://research.aber.ac.uk/en/publications/a-scottish-provenance-for-the-altar-stone-of-stonehenge

[4] https://doi.org/10.1016/j.jasrep.2024.104738

No comments:

Post a Comment

Comments welcome on fresh posts - you just need a Google account to do so.