10 August 2017 – Seminar
When: 16:00 on Thursday, 10th August 2017
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)
Speaker: Prof. Balz Kamber (Department of Geology, Trinity College Dublin)
Title: Why Archaean cratons differ from younger continental lithosphere.
Abstract:
The most outstanding features of Archaean cratons are their extraordinary thickness and enduring longevity. Seismically, Archaean cratonic fragments are sharply-bounded deep roots of buoyant cold lithospheric mantle, clearly distinguishable from non-cratonic lithosphere. The age of diamond inclusions and the Os-isotope composition of deep cratonic xenoliths support a model of coeval formation of the crustal and residual mantle portions.
Archaean and post-Archaean crust also differ, not in bulk composition, but in crustal architecture. Key drivers of crustal rearrangment were the radioactive heat-producers U, Th and K. In the early Earth, high radioactive heat production led to self-organisation into evolved, potassic upper and refractory lower crust. The lag time between crust formation and re-organisation was much shorter than today. An additional factor contributing to cratonic restruc-turing was the emplacement of dense supracrustal rocks in ensialic greenstone belts, leading to gravitational inversion. The dome and keel architecture of Archaean cratons was thus driven by crustal radioactive heat and high temperature mantle melting, yielding dense, low viscosity lavas piling up at surface.
A pleasing complementary observation from cratonic mantle roots is that refractory mantle nodules also suggest very high degrees of melting and extraction. Thus, the most logical conclusion seems that the komatiite mantle source was up to 500ºC hotter than modern astheno¬sphere. With higher degree and depth of melting, a thicker and severely depleted bouyant cratonic residue was formed, perfectly equipped to preserve the Archaean crustal record.
However, there are significant inconsistencies in this otherwise convincing line of reasoning. They include: Archaean crust is not especially thick, the dunites expected after very high degree melting are rare, many cratonic harzburgites are much richer in orthopyroxene than predicted [1], and cratonic harzburgites often contain garnet. Finding a solution to these issues has important ramifications for secular evolution of the continents and thermal evolution of the mantle. In this presentation, I will contrast the various proposed solutions, including purging of surprisingly carbonated ancient mantle [e.g. 2], onset of plate tectonics, a Neoarchaean superplume event and collapse of Hadean cumulate barriers.
[1] Boyd (1989) EPSL 89, 15-26
[2] Herzberg (2016) J. Petrol. 57, 2271-2288
Leave a Comment
Last Updated: 23rd May 2018 by Anna
2017-8-10 – Seminar by Prof. Balz Kamber (TCD)
10 August 2017 – Seminar
When: 16:00 on Thursday, 10th August 2017
Where: DIAS, Geophysics Section, 5 Merrion Square, Dublin 2, (library)
Speaker: Prof. Balz Kamber (Department of Geology, Trinity College Dublin)
Title: Why Archaean cratons differ from younger continental lithosphere.
Abstract:
The most outstanding features of Archaean cratons are their extraordinary thickness and enduring longevity. Seismically, Archaean cratonic fragments are sharply-bounded deep roots of buoyant cold lithospheric mantle, clearly distinguishable from non-cratonic lithosphere. The age of diamond inclusions and the Os-isotope composition of deep cratonic xenoliths support a model of coeval formation of the crustal and residual mantle portions.
Archaean and post-Archaean crust also differ, not in bulk composition, but in crustal architecture. Key drivers of crustal rearrangment were the radioactive heat-producers U, Th and K. In the early Earth, high radioactive heat production led to self-organisation into evolved, potassic upper and refractory lower crust. The lag time between crust formation and re-organisation was much shorter than today. An additional factor contributing to cratonic restruc-turing was the emplacement of dense supracrustal rocks in ensialic greenstone belts, leading to gravitational inversion. The dome and keel architecture of Archaean cratons was thus driven by crustal radioactive heat and high temperature mantle melting, yielding dense, low viscosity lavas piling up at surface.
A pleasing complementary observation from cratonic mantle roots is that refractory mantle nodules also suggest very high degrees of melting and extraction. Thus, the most logical conclusion seems that the komatiite mantle source was up to 500ºC hotter than modern astheno¬sphere. With higher degree and depth of melting, a thicker and severely depleted bouyant cratonic residue was formed, perfectly equipped to preserve the Archaean crustal record.
However, there are significant inconsistencies in this otherwise convincing line of reasoning. They include: Archaean crust is not especially thick, the dunites expected after very high degree melting are rare, many cratonic harzburgites are much richer in orthopyroxene than predicted [1], and cratonic harzburgites often contain garnet. Finding a solution to these issues has important ramifications for secular evolution of the continents and thermal evolution of the mantle. In this presentation, I will contrast the various proposed solutions, including purging of surprisingly carbonated ancient mantle [e.g. 2], onset of plate tectonics, a Neoarchaean superplume event and collapse of Hadean cumulate barriers.
[1] Boyd (1989) EPSL 89, 15-26
[2] Herzberg (2016) J. Petrol. 57, 2271-2288
Category: Geophysics Section News & Events, News
This work was to help towards the preservation of the Irish Language, to maintain it's continuity with the past, and was to become a resource for teachers to check pronunciation #DIASdiscovers #Irish #Irishlanguage #CelticStudies #Gaelic
The researchers used the International Phonetic Alphabet, slightly modified to represent vowels and consonants of living speech. At that time there were concerns over the deterioration of the Irish language due to the "overpowering influence of English"
Date: 02 June 1943 Paper: The Irish Press Synopsis: In 1943, a phonetic investigation led by Brian Ó Cuív, Risteárd B. Breathnach and Tomás de Bhaldraithe of DIAS would begin the first systematic scientific recording of the varied sounds of modern Gaelic speech.
Happy Birthday! twitter.com/thecelticist/s…
The papers were 1) Affine Field Theory: conservation identitites and relation to Weyl and Eddington 2)The Union of the three fundamental fields (Gravitation, Menson, Electromagnetism) Which went on to secure worldwide acclaim. #DIASdiscovers
Date: 01 December 1943 Paper: The Irish Press Headline: Two Papers by Dr. Schroedinger Synopsis: 1943 was a busy year for Schroedinger. Not only did he deliver the "What is Life?" Lectures in @tcddublin in February in November he delivered two papers in the @RIAdawson (1/2)
Available to buy on the DIAS bookshop: books.dias.ie/index.php?main… (5/5) #DIASdiscovers #celtic #studies #twopatricks
He spoke on "Palladius and Patrick". Palladius was the first bishop of the Christians of Ireland. (2/5)
He was known by his first name Patricius, which in later times would lead to confusion as he was succeeded by another apostle of the same name (Saint Patrick or Patricius in Latin). (3/5)
"In the lives of St. Patrick, the two saints are invariably fused into one", said Prof. O'Rahilly in his lecture. The lecture was a condensation from O’Rahilly’s book “The two Patricks: a lecture on the history of Christianity in fifth-century Ireland”. (4/5)
Date: 21st March 1942 Paper: The Irish Press Headline: Palladius and Patrick | School Of Celtic Studies Lecture Synopsis: The first public lecture under the auspices of the School of Celtic Studies was delivered in Trinity College by Professor T. F. O'Rahilly in 1942. (1/5)
As part of our ongoing participation in the @HistFest we decided to take a look into the Irish Newspaper Archives and see where DIAS made it into print over the last 80 years. There were so many articles, the hardest part was selecting what we would post. We hope you enjoy!
@AReillyFailte @CultureNight @VisitDublin Thanks Antoinette! Glad you enjoyed 😊
Big thank you to @MartinaPQuinn of @helloalicepr for moderating the discussion, and of course to our panel @NeasaMcG @CormacORafferty and @laoneill111
@CormacORafferty "to cut yourself off from fundamental research means you could miss out on some of the biggest ideas"
@laoneill "it's our job as researchers to keep reminding governments how important basic research is" "For Dev basic research being carried out in Ireland was a badge of pride"
@NeasaMcG Schrödinger's work in causality was not well received by the religious authorities at the time At the same time DIAS did have Catholic priests working on research projects in the early days, so there was not the conflict you might think between science and religion