Geochemistry and volcanology of the Tertiary basalts of the Giant's Causeway area, Northern Ireland

Abstract

The columnar jointed basalts of the Giant's Causeway in Northern Ireland are a localized group of flows, the Causeway Tholeiite Member within the Tertiary Antrim Lava Group. Major and trace element analyses, including rare-earth element (REE) data, are presented which show a range of compositions from hy-normative tholeiites with mid-ocean ridge basalt (MORB) characteristics, to qz-normative examples with SiO 2 > 54% and K 2 O > 1.0%. Within the Causeway tholeiites are three well defined chemical sub-groups which can be correlated stratigraphically across the area. Zr/Nb data suggest a single mantle source for the lavas with the range of composition the result of variable degrees of partial melting of a progressively depleted mantle, followed by fractional crystallization of the magmas at higher crustal levels. Mass balance calculations are used to model the fractionation processes involved. The lavas of the Causeway result from tectonically controlled decompression melting with magma equilibration in ephemeral chambers at high crustal levels followed by eruption as sheet flows. Disruption of the contemporaneous drainage system and the subsequent flooding of hot flow surfaces modified the cooling regime and formed the characteristic multi-tiered flows with colonnade and entablature development.

The genesis of gold mineralisation hosted by orogenic belts: A lead isotope investigation of Irish gold deposits

“…Tertiary igneous complexes relating to the rifting of North America and Eurasia and the opening of the Atlantic Ocean are present in north-east Ireland (Jolley and Bell, 2002;Stevenson and Bennett, 2011). The vast basaltic lavas of Co. Antrim date to this period (Lyle, 1980;Lyle and Preston, 1993), whilst the Mourne granites of Co. Down were also emplaced at this time (McCormick et al, 1993;Stevenson and Bennett, 2011).…”

Brittle tectonism in relation to the Palaeogene evolution of the Thulean/NE Atlantic domain: a study in Ulster

“…The presence of lateritic alteration at the top of the lower basalt series indicates that a significant period of quiescence otcurred before the emplacement of these tholeiites (and also the emplacement of the Tardree rhyolites, see Figure 2), as pointed out by Wilson (1972) and Lyle and Preston (1993). The age of the Antrim lavas is -61 to -58 Ma (Dickin 1988 (Figure 2) inherited from the Caledonian period and reactivated during the Mesozoic and/or Cenozoic (Lyle and Preston 1993). These faults generally strike NE-SW to ENE-WSW, approximately perpendicular to the dykes which cut the Antrim basalts.…”

“…To the north of the Antrim Plateau (Figure 2), tholeiitic lava flows. including the columnar basalts of the Giant's Causeway, are intercalated between the lower and upper series (George 1967;Lyle and Preston 1993). The presence of lateritic alteration at the top of the lower basalt series indicates that a significant period of quiescence otcurred before the emplacement of these tholeiites (and also the emplacement of the Tardree rhyolites, see Figure 2), as pointed out by Wilson (1972) and Lyle and Preston (1993).…”

“…including the columnar basalts of the Giant's Causeway, are intercalated between the lower and upper series (George 1967;Lyle and Preston 1993). The presence of lateritic alteration at the top of the lower basalt series indicates that a significant period of quiescence otcurred before the emplacement of these tholeiites (and also the emplacement of the Tardree rhyolites, see Figure 2), as pointed out by Wilson (1972) and Lyle and Preston (1993). The age of the Antrim lavas is -61 to -58 Ma (Dickin 1988 (Figure 2) inherited from the Caledonian period and reactivated during the Mesozoic and/or Cenozoic (Lyle and Preston 1993).…”

Contemporary stromatolite formation in high intertidal rock pools, Giant's Causeway, Northern Ireland: preliminary observations.

“…The rocky north coast of Northern Ireland comprises Tertiary basalt flows (Lyle, 2002). The cliffs are up to 120m high and are fronted by rock platforms that exceed 100m in width ( Figure 2).…”