Distal tephrochronology relies on the synchronous dispersal and deposition of volcanic ash or tephra (i.e. < 2mm) from explosive volcanic eruptions (Plinian/sub-Plinian). Tephrochronology correlates tephra layers to proximal source volcanic eruptions, where proximal age is well constrained, allowing tephra layers to be used as robust age markers. Tephras layers are recorded in a variety of distal environmental archives, thus tephrochronology provides an independent time framework for interpreting palaeoenvironmental proxies in marine and lacustrine cores. Tephrochronology is dependant on precise correlations of distal glass geochemistries with proximal source volcanics. Proximal volcanic deposits have been subject to detailed sampling and glass analyses revealing spatial and temporal changes III magmatic compositions during individual eruptions. Geochemical 'fingerprints' have been determined for Italian explosive proximal deposits using electron probe micro analysis (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Presented are detailed volcanic glass major, minor and trace element compositions for proximal deposits outcropping on the Aeolian Islands, Mount Etna and Ischia. These proximal glass compositions are used to test proximal-distal correlations, . linking visible and crypto-tephra layers from marine (Tyrrbenian, Ionian and Adriatic \ Seas) and lacustrine (Lago Grande di Monticchio, Italy) cores to their volcanic source. Combined major, minor and trace element charcterisation of proximal and distal glasses has valdiated the provenance and age of numerous distal tephra layers. Precise tephra correlations have allowed for the exchange of tephrochronological information over wide geogrpahical distances (up to 800 km). Correlations based solely on major element analyses can be erroneous due to repeated chemistries produced at many of the volcanic centres investigated. Trace element concentrations enable the identification of additional diagnostic features nessesary for distinguishing tephras produced from a single volcanic centre. However, in some instances volcanic systems repeatedly produce glass geochemistries that are indistinguishable at a multi-element level demonstrating the importance of good strati graphic control distally when assigning procvenance. Some tephras identified in the Tyrrhenian Sea (Marsili basin) have no currently identified proximal counterparts. This research demonstrates that proximal stratigraphies are not always fully representative of event stratigraphies due to resurgent activity and in the case of volcanic islands flank collapse and limited on-land deposits.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:588304 |
| Date | January 2012 |
| Creators | Albert, Paul Graham |
| Publisher | Royal Holloway, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0101 seconds