Shape and intrusion history of the Late Caledonian Newry Igneous Complex, Northern Ireland

The Tellus high-resolution airborne magnetic and radiometric maps define previously unmapped zones within the Newry Igneous Complex, County Down. High-precision uranium–lead zircon dating of nine rock samples from different parts of the complex provides a robust set of age constraints (c.414–407 Ma), which confirm that the different plutons of the complex young towards the south-west. Combined, these new data allow an innovative model of intrusion to be developed, with intrusion beginning in the north-east and progressing towards the south-west

Orta Anadolu’da eş zamanlı geç Kretase kalkalken ve alkalen magmatizma (Türkiye): Petrojenezde oksijen izotop kısıtlamaları

Orta Anadolu Kristalen Kompleksi içerisinde yeralan farklı türdeki kayaç tipleri geç Kretase magmatizması ile üretilmiştir. Bu kayaçlar üç farklı birime ayırt edilmiştir: (i) kalkalkalen, (ii) yarıalkalen/geçişli, ve (iii) alkalen. Kalkalkalen kayaçlar genelde metalüminüs (I-tip) olup, bileşimleri monzodiyoritden granite kadar değişir. Yarıalkalen/geçişli kayaçlar da metalüminüs (I-tip) olup, bileşimleri monzonitden granite kadar değişir. Alkalen kayaçlar genelde peralkalen (A-tip) olup, bileşimleri feldispatoyidli monzosiyenitden granite kadar değişir. Kompleksdeki tüm kaya oksijen izotop verileri 6.5‰ ve 14.8‰ arasında önemli oranlardaki ?18O değerlerine sahiptir. İlksel 87Sr/86Sr-143Nd/144Nd oranları, ve her iki oran-?18O diyagramları göstermektedir ki intrüzif kayaçlar dalma-batma ile değişikliğe uğramış mantodan türemiş ve ayrıca fraksiyonal kristalleşme ve kabuksal kirlenme geçirmiştir. Kompleks de farklı magmatizmaların başlangıcı için uygun mekanizmalar ya termal sınır tabakasının delaminasyonu ya da dalmakta olan levhanın (kırılıp?) yok edilmesidir (slab breakoff).A wide variety of rock types were produced by the latest Cretaceous magmatism in the Central Anatolian Crystalline Complex. These rocks can be divided into three distinct units: (i) calc-alkaline, (ii) subalkaline/transitional, and (iii) alkaline. The calc-alkaline rocks are mainly metaluminous (I-type) ranging from monzodiorite to granite. The subalkaline/transitional rocks are also metaluminous (I-type) ranging from monzonite to granite. The alkaline rocks are mainly peralkaline (A-type), ranging from feldspathoid-bearing monzosyenite to granite. Whole-rock oxygen isotope data from the complex have a considerable range of δ18O values between 6.5‰ and 14.8‰. Initial 87Sr/86Sr versus 143Nd/144Nd ratios, and both ratios versus δ18O values diagrams show that the intrusive rocks are derived from a subduction-modified mantle and also have experienced fractional crystallisation coupled with crustal assimilation. Delamination of a thermal boundary layer, and/or slab breakoff is the likely mechanisms for the initiation of the diverse magmatism in the complex

Zonation and structure of the Late Caledonian Newry Igneous Complex, Northern Ireland from Tellus geophysical datasets [abstract]

The Late Caledonian Newry Igneous Complex was intruded into the Southern Uplands-Down-Longford Terrane just after final closure of Iapetus (c. 425 Ma). Work to date has shown it to be composed of three overlapping, I-type, granodioritic plutons and an intermediate-ultramafic body. The intrusions are aligned and young from NE-SW. Petrographical and geochemical studies have shown the NE and SW plutons to be normally zoned (more basic at margins) and the central pluton reversely zoned, however to date no mapped internal division of the plutons has been published. Interpretation of high resolution geophysical imagery, from the Geological Survey of Northern Ireland Tellus project, has allowed internal zonation and structures not previously described for the complex to be mapped. Ternary radiometric data show the central pluton and the south-western part of the NE pluton to be relatively rich in potassium, compared to the north-eastern area of the NE pluton which is thorium elevated. Occurring within this thorium elevated zone is the intermediate-ultramafic body and a similar mass in the vicinity of Kilcoo near Lough Island Reavy, which show a mixed potassium/thorium signal. Magnetic data reveal striking magnetite enriched rings inside the central and NE plutons, and also define the intermediateultramafic bodies. There are also two circular, parallel structures visible on the magnetic image. The inner defines the outer edge of the magnetic ring of the NE pluton, while the other, outer structure cuts the country rock and north-eastern part of NE pluton. Associated with this structure are outlying granodiorite masses such as that mapped at Ballynafern ~ 6 km NNE of Rathfriland

Laccolithic, as opposed to cauldron subsidence, emplacement of the Eastern Mourne pluton, N. Ireland: evidence from anisotropy of magnetic susceptibility

<p>The structural evolution and emplacement of the Eastern Mourne pluton was investigated using anisotropy of magnetic susceptibility (AMS) measurements (carried out on 112 oriented block samples) and structural data from the host rocks. From these new data cauldron subsidence, as the emplacement mechanism, is disputed and evidence for an alternative, laccolithic style model involving inflation is presented. This includes deflection and uplift of host-rock bedding close to contacts and the magnetic fabric pattern, which has a gentle dome geometry, even close to contacts. The magnetic lineations usually plunge down-dip near the external margins but otherwise have a general SSW–NNE trend that diverges northward. This suggests a northward-directed inflow direction. The model for the emplacement of the Eastern Mourne pluton is a laterally fed laccolith, emplaced south to north. The eastern margin is interpreted as a faulted contact facilitating the inflation of an asymmetrical ‘breached’ laccolith. </p

A Palaeocene intracanyon-style lava emplaced during the early shield-building stage of the Cuillin Volcano, Isle of Skye, NW Scotland

The twin summits of Preshal More and Preshal Beg, near Talisker, Isle of Skye, comprise the erosional remnants of a thick (at least 120 m) compound olivine tholeiite lava, or flow field, that ponded in palaeo-valleys within the Palaeocene lava field of west-central Skye. This unique flow field constitutes the Talisker Formation and is the youngest preserved extrusive unit of the Skye Lava Field. The lava inundated a complex of palaeo-valleys incised into the higher stratigraphical levels of the existing lava field, and remnants of the original sedimentary fill of these valleys still exist, the Preshal Beg Conglomerate Formation. The lava displays spectacularly well-developed two-tier (colonnade-entablature) columnar joint sets that formed as a consequence of slow, uninterrupted cooling through its base and sidewalls, aided by groundwater circulation and water ingress (from displaced drainage) directed into the lava's interior by master-joint systems. Intrusive phenomena developed at both the base and the top of the lava and there is evidence for the existence of subsurface feeder tubes. The tholeiitic composition of the Talisker Formation lava contrasts with the transitional, mildly alkaline characteristics of the remainder of the (older) lavas of Skye Lava Field. In broad terms, the Talisker Formation lava is compositionally very similar to the suite of cone-sheets emplaced into the oldest of the four intrusive centres that comprise the Skye Central Complex – the Cuillin Intrusive Centre – together with a high proportion of the Skye regional dyke swarm. The stratigraphical position, field relationships and compositional characteristics of the lava indicate that it was erupted and emplaced as an intracanyon-style flow field during the early shield-building stage in the growth of the (tholeiitic) Cuillin Volcano, which post-dates the main Skye ‘plateau’ Lava Field. Although the remnant outcrops are detached from their likely source area through erosion, this tholeiitic lava provides the first direct evidence linking the central complexes of the British Palaeogene Igneous Province and their eruptive products