University of Birmingham Zonation of the Newry Igneous Complex, Northern Ireland, based on geochemical and geophysical data

: The Late Caledonian Newry Igneous Complex (NIC), Northern Ireland, comprises three largely granodioritic plutons, together with an intermediate-ultramafic body at its northeastern end. New whole-rock geochemical data, petrological classifications and published data, including recent Tellus aeromagnetic and radiometric results, have been used to establish 15 distinct zones across the four bodies of the NIC. These become broadly younger to the southwest of the complex and toward the centres of individual plutons. In places, zones are defined by both current compositional data (geochemistry and petrology) and Tellus results. This is particularly clear at the eastern edge of the NIC, where a thorium-elevated airborne radiometric signature occurs alongside distinct concentrations of various elements from geochemistry. However, in the northeastern-most pluton of the NIC a prominent ring-shaped aeromagnetic anomaly occurs independent of any observed surface compositional variation, and thus the zones in this area are defined by aeromagnetic data only. The origins of this and other aeromagnetic anomalies are as yet undetermined, although in places these closely correspond to facies at the surface. The derived zonation for the NIC supports incremental emplacement of the complex as separate, distinct magma pulses. Each pulse is thought to have originated from the same fractionally crystallising source that periodically underwent mixing with more basic magma. We suggest that the NIC was emplaced as a of distinct magma which by the Pitcher, Stevenson, Evidence for this incremental emplacement is provided by the abrupt changes in geochemical, aeromagnetic and radiometric signatures between the various zones. geochemical, petrological and recent geophysical

Unlike aeromagnetic results, these data relate to composition of only the uppermost several centimetres of the ground. Hence, the radiometric signature of an area will often yield concentrations of the three elements within the local topsoil, although these concentrations usually correspond to the composition of the underlying bedrock (e.g., Cook et al., 1996;Martelet et al., 2006).
Here we provide new whole rock geochemical and petrological data on the Newry Igneous Complex (NIC). This is examined alongside existing petrological, geochemical, aeromagnetic, radiometric and geochronological data (Reynolds, 1934;1936;1943;Meighan and Neeson, 1979;Neeson, 1984;Cooper et al., in press) to provide a new detailed zonation for the NIC. This new zonation pattern will require a reexamination of the emplacement of the NIC. We outline possible emplacement implications and suggest relevant hypotheses.

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Composition
Previous petrological work shows that the NIC becomes generally more silicic to the southwest ( Fig. 1) (Reynolds, 1943;Meighan and Neeson, 1979;Neeson, 1984). Individual plutons also display broad internal zoning. The Rathfriland pluton shows normal zoning, ranging in composition from an exterior composed of hornblende granodiorite to an interior composed of biotite granodiorite (Meighan and Neeson, 1979;Neeson, 1984) (Fig. 1).
Normal zoning of the Cloghoge pluton is defined by a relatively abrupt change between an outer hornblende granodiorite and an inner (off-centre) felsic granodiorite (Neeson, 1984). In contrast, the Newry pluton shows reverse zoning, expressed by the occurrence of an outer biotite granodiorite and an inner hornblende granodiorite (Neeson, 1984) (Fig. 1).

Seeconnell Complex
The Seeconnell Complex represents a compositionally distinct body at the northeastern margin of the Rathfriland pluton (Reynolds, 1934;Meighan and Neeson, 1979) (Fig. 1). It is known to be cross cut by the main part of the Rathfriland pluton (Neeson, 1984), and U-Pb geochronology shows that it is the oldest part of the NIC (Cooper et al., in press) (Fig. 2).
The Seeconnell Complex contains a large and variable set of internal facies, consisting of two monzonites, diorite, meladiorite and biotite pyroxenite (Reynolds, 1934(Reynolds, , 1936Meighan and Neeson, 1979;Neeson, 1984). The distribution of these facies within the Seeconnell Complex is intricate and has not been mapped as part of the current study.

Intermediate bodies
A small area in the north of the main Rathfriland pluton exhibits similar monzonitic and dioritic compositions to the Seeconnell Complex (Reynolds, 1934;Neeson, 1984) (Fig. 1).

This has been divided into three intermediate bodies in the vicinity of Rough Hill and
Legananny Mountain (Neeson, 1984) (Fig. 1). The compositional similarity of these bodies to the Seeconnell Complex is thought to reflect similar ages of intrusion (Neeson, 1984).
Thus, together with the Seeconnell Complex, the bodies most likely predate other parts of the NIC.
Another intermediate body occurs in the vicinity of Kilcoo in the southern part of the Rathfriland pluton (Meighan and Neeson, 1979;Neeson, 1984) (Fig. 1). However, this is defined as a quartz diorite and, as such is significantly more felsic than the northern intermediate bodies and the Seeconnell Complex (Neeson, 1984). In fact, Neeson (1984) suggests that this quartz diorite relates more closely to the main part of the Rathfriland pluton than to any of the other more mafic bodies.

Porphyritic granodiorite
A distinct porphyritic granodiorite containing hornblende and biotite phenocrysts occurs within the Newry pluton (Reynolds, 1943;Neeson, 1984). This facies is thought to crop out as a narrow ring, separating the outer biotite granodiorite and inner hornblende granodiorite in this pluton (Neeson, 1984) (Fig. 1), although previous mapping has been based on limited exposure.

Geophysical data
The Tellus Project is an ongoing, comprehensive and multi-award winning geological mapping project of Northern Ireland, managed by the British Geological Survey (BGS), the Geological Survey of Northern Ireland (GSNI) and the Geological Survey of Ireland (GSI) (Leslie et al., 2013). Part of the initial phase of this project, taking place in 2005/2006, was the Tellus Regional Airborne Geophysical Survey of Northern Ireland, arranged in partnership between the BGS and the Geological Survey of Finland.Aeromagnetic and radiometric data for the NIC from this survey were interpreted by Anderson (2015) and Cooper et al. (in press). Cooper et al. (in press) use these results to divide the NIC into a number of geophysical zones, although prior to the current study these have not been correlated with specific lithologic units.

Aeromagnetic data
Aeromagnetic data reveals a number of distinct positive aeromagnetic anomalies within the NIC, including two ring-shaped anomalies within the Rathfriland and Newry plutons respectively ( Fig. 2A). The aeromagnetic ring within the Newry pluton corresponds, in part, to outcrop of the porphyritic granodiorite, whereas the aeromagnetic ring within the Rathfriland pluton lacks a corresponding surface facies ( Fig Less prominent areas of negative aeromagnetic signature are also present throughout much of the Rathfriland and Newry plutons, as well as over a large area occupied by Palaeozoic sediments to the northeast of the NIC ( Fig. 2A).

Radiometric data
Ternary radiometric data indicate an area of thorium enrichment at the eastern rim of the Rathfriland pluton (Fig. 2B). This signature spans the entire eastern rim of the pluton, apart from the Seeconnell Complex, which displays a more mixed radiometric signature (Fig. 2B).
The remaining (western) Rathfriland pluton and entire Newry pluton display a potassiumelevated radiometric signature (Fig. 2B). This signature does not appear to show fluctuations relating to any of the three distinct previously defined facies of the Newry pluton (Fig. 1).

Geochronology
Cooper et al. (in press) report nine U-Pb zircon ages for the NIC, which range from ca. 414 to 407 Ma (with errors of 0.18 to 0.58 Myr at 2) (Fig. 2). The dates confirm that the NIC A C C E P T E D M A N U S C R I P T

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6 was intruded sequentially from northeast to southwest, with the Seeconnell Complex representing the oldest part. These dates also show that the Rathfriland and Newry plutons become younger towards their respective centres (Fig. 2). Overall geochronology suggests that there were large hiatusus in emplacement not only between plutons, but also within plutons.

Large scale mapping
The pluton margins illustrated in Fig However, this mapping is reveals a different location of the Newry-Cloghoge pluton boundary to Neeson's (1984) study of the NIC (Fig. 1). Therefore, the location of this boundary is investigated and confirmed in the current study (see discussion).

Methods
For this study 133 samples were collected from across the NIC (see Appendix 1 for sampling locations), which were analysed geochemically and petrologically. Data obtained are used alongside existing compositional and geophysical data (Neeson, 1984;GSNI, 1997; in press) on the NIC to constrain a new detailed zonation for the complex.

Geochemistry
Samples were reduced to approximately fist-sized blocks by removing weathered surfaces and sub-samples for petrological characterisation (see below). All samples were then delivered to the British Geological Survey (BGS) in Keyworth, Unitied Kingdom to undergo whole rock geochemical analysis. Samples were crushed and milled before analysis through lithium borate fused bead XRFS (0.9 g split) and sodium peroxide fusion ICP-MS (0.2 g split). Loss on ignition was determined gravimetrically (1 g split). Full details of geochemical analysis are provided in Appendix 2.

Petrological classifications
Whereas all samples are geochemically analysed, fifty two samples are additionally used to provide petrological classifications. These were selected from particular areas of the NIC in order to better constrain surface composition where existing data was lacking or variable.
Petrological classifications were made simply by visual estimation of approximate modal proportions of minerals within each sample and determining a relevant descriptive rock name (e.g., hornblende biotite granodiorite).

The Rathfriland pluton
The geochemistry of the ultramafic-intermediate Seeconnell Complex is variable (see Appendix 3), due to the range of lithologies previously mapped (Reynolds, 1934;Meighan and Neeson, 1979;Neeson, 1984). However, the mean concentrations of various elements confirm that this is the most basic part of the NIC (Area 1 in Table 1 and Fig. 3). Within the Seeconnell Complex, mean concentrations of the radiometric elements potassium (K 2 0) and uranium (U) are relatively high (3.98 wt% and 3.5 ppm respectively) and thorium (Th) is moderate (12.4 ppm) in relation to other parts of the NIC (Fig. 4). This is consistent with the interpretation of the Seeconnell Complex as a zone of 'mixed' radiometric signature from airborne data reported by Cooper et al. (in press).
Mean major element concentrations become generally more silicic towards the centre of the Rathfriland pluton ( Fig. 3, Fig. 5). Excluding the Seeconnell Complex, the most significant shift in geochemical concentration within the Rathfriland pluton occurs between the area of airborne Th elevation in the eastern part of the pluton (Areas 2 -3 in Table 1 and  Table 1 and Fig. 3).
Current results confirm that the area of airborne Th elevation also corresponds to geochemical Th elevation (mean concentration of 19.2 ppm - Fig. 4). Geochemistry additionally reveals low SiO 2 and high Fe 2 O 3(t) in this area relative to the inner and southwestern parts of the pluton (Fig. 5). These results support the compositional distinction of the eastern Rathfriland pluton rim indicated by the airborne radiometric data of Cooper et al. (in press) and suggest that the area is more basic than the inner and southwest parts of the pluton.
Current geochemistry also reveals significant variation within the eastern Rathfriland pluton rim (Areas 2 -3 in Table 1 and Fig. 3). This is shown in Fig. 5   Petrological classification shows that the quartz diorites in the eastern Rathfriland pluton (Area 3 in Fig. 3) correspond closely to the positive aeromagnetic signature in this area (Fig.   6). The location of these quartz diorites is also consistent with mapping of the pluton by Neeson (1984) (Fig 1 and Fig. 6).
Within the inner part of the Rathfriland pluton (Areas 4 -6 in Table 1 and Fig. 3) there is comparatively little geochemical change, in terms of both mean concentrations (Table 1 and   Fig. 3) and mapped concentrations (Fig. 5). Hence the prominent shift in aeromagnetic signature corresponding to the positively aeromagnetic ring does not appear to reflect a change in composition.

The Newry pluton
The Newry pluton is less compositionally complex than the Rathfriland pluton, with much of the variation being determined by the presence of a distinctive porphyritic granodiorite facies (Fig. 1). Geochemical and petrological results broadly confirm the reverse zoning of the Newry pluton (Areas 7 and 8 in Table 1  where these are mapped by Neeson (1984) (Fig. 6). Altogether these results broadly support the former division of the Newry pluton into an outer biotite granodiorite, a porphyritic granodiorite ring and inner hornblende granodiorite (Neeson, 1984), although significant compositional variation is also apparent throughout ( Fig. 5 and Fig. 6). Cooper et al. (in press) show that the mapping of the porphyritic granodiorite by Neeson (1984) correlates with a prominent positive aeromagnetic ring. However, in the eastern part of this pluton the shape of the aeromagnetic ring is inconsistent with Neeson's mapping of the porphyritic granodiorite (Fig. 6). Since exposure is poor in this area, aeromagnetic data is considered to outweigh former mapping in determining the general trend of the facies.
This study further elucidates the relationship between the porphyritic granodiorite and the positive aeromagnetic ring in the Newry pluton. Petrological results show that the inner part of the aeromagnetic ring generally corresponds to porphyritic granodiorite, whereas the outer part of this ring generally corresponds to non-porphyritic facies (Fig. 6). Hence the aeromagnetic signature of the porphyritic granodiorite is outward-shifted, rather than precisely matching the outcrop distribution of the facies. This may be due to subsurface penetration of aeromagnetic data (Schetselaar et al., 2000), which would result in an outwardshifted signature if the porphyritic granodiorite is outward-dipping (Fig. 7). This interpretation is consistent with the outward-dipping fabrics within the pluton as shown in vertically-dipping (Fig. 1). Hence, in this area it is likely that the porphyritic granodiorite unit is near-vertical in orientation. Within Fig. 6, the porphyritic granodiorite is remapped according to these new data and interpretations.

The Cloghoge pluton
Geochemistry confirms the broad separation of the Cloghoge pluton into a silica-poor outer part and a silicic off-centre core inferred by Neeson (1984). This is apparent from mean SiO 2 concentrations of the outer and core parts of the pluton, represented in Table 1  A new area of highly variable geochemisty is also reported here (labelled 'area of variable geochemical concentrations' in Fig. 5). This variation corresponds to the occurrence of a number of steeply orientated sheets of mixed composition. Petrological data shows that these sheets consist of granite, felsic granodiorite, hornblende granodiorite, mafic granodiorite, porphyritic diorite and dolerite (Fig. 6). Some of the rock types resemble those observed within other parts of the Cloghoge pluton, as well as the adjacent Newry pluton. In particular, the granite and mafic granodiorite are similar to the felsic granodiorite and hornblende granodiorite within the Cloghoge pluton, whilst the porphyritic diorite displays a textural resemblance to the porphyritic granodiorite of the Newry pluton (Fig. 6). The sheets display variable contact relationships, which include straightforward cross cutting, mixing and mingling. However, the implied age relationships between the units are inconsistent, suggesting that all were intruded penecontemporaneously.
Mean concentrations of the three radiometric elements, K 2 O and Th and U, within the Cloghoge pluton are notably higher (3.89 wt%, 12.6 ppm and 3.0 ppm, respectively) than they are in other parts of the NIC (Fig. 4). These results are consistent with the interpretation of the Cloghoge pluton as an area of 'mixed' K 2 O/Th enrichment (Cooper et al., in press), and further suggest that U is also elevated in this area.

Zonation of the NIC
Based on current and previous studies a total of 15 zones are inferred within the NIC (Fig.   7). These are interpreted to have been sequentially emplaced and are named Zones A-O to

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10 denote this. U-Pb ages from Cooper et al. (in press) are used to suggest that the zones range in age from ca. 414 to 407 Ma.

The Rathfriland pluton
The Seeconnell Complex is distinguished within the NIC by its unqiue intermediateultramafic composition, as well as its strong positive aeromagnetic anomaly and mixed Kand Th-elevated airborne radiometric signature. . Since geochronological data shows that the Seeconnell Complex is the oldest part of the NIC (414.02 ± 0.18 Ma), this area is defined as Zone A (Fig. 8).
The crescent-shaped area of Th-enriched radiometric signature ( Fig. 2B and Fig. 4) and relatively basic geochemistry ( Fig. 3 and Fig. 5) in the eastern part of the Rathfriland pluton is subdivided into Zones B -F on the basis of its internal geochemical variations (Fig. 8). Zone B represents the intermediate bodies close to the Seeconnell Complex (Fig. 8). This is due to the compositional similarity between these bodies and the Seeconnell Complex, which indicates a close relationship between the areas (Reynolds, 1934;Neeson, 1984). The extent of this zone is mapped according to the work of Neeson (1984).
All other parts of the eastern Rathfriland pluton are more felsic than Zones A and B, yet are significantly more basic than the inner pluton. Zone C represents the area of relatively basic geochemistry in the vicinity of Zones A and B (Fig. 8). The hornblende granodiorite in this area exhibits more basic geochemistry than any of the other granodiorites within the NIC.
Hence, this facies is termed basic granodiorite and is thought to reflect evolution of the intermediate magma supplying Zones A and B. Compositionally, Zone C is distinguished from another basic granodiorite (Zone Fsee below) through its higher Fe 2 O 3(t) concentrations.
The area defined as Zone D is significantly more silicic than Zone C (Fig. 8). Zone D also exhibits the next oldest U-Pb age (413.44 ± 0.37 Ma) after the Seeconnell Complex (Zones B and C are currently undated) and consists of hornblende granodiorite. Therefore, Zone D may represent further evolution of the magma supplying Zones A to C.
Zone E is defined as the quartz diorite in the south of the Rathfriland pluton. This is more basic than the Zone D granodiorite, although its geochronological age (412.53 ± 0.33 Ma) clearly suggests that it is the younger of the two facies (Fig. 8). Hence, straightforward evolution of a single source by fractional crystallisation does not account for the variation between these zones, and mixing of more basic magma is thought to have produced the Zone E composition. The quartz diorite (Zone E) is also distinguished by a prominent positive aeromagnetic anomaly ( Fig. 2A). Together with Neeson's (1984) mapping, this anomaly is used to determine the extent of Zone E.

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11 Zone E is surrounded by another area of granodiorite displaying relatively basic geochemistry (Fig.8). Xenoliths of quartz diorite have been observed within this adjacent basic granodiorite (Neeson, 1984), which is thus suggested to be younger than Zone E. The area is defined as Zone F and is referred to as a second basic granodiorite (Fig. 8), which may represent evolution of the magma supplying Zone E. Zone F is distinguished from the other basic granodiorite (Zone C) by its lower Fe 2 O 3(t) concentrations.
The inner (including the southwestern), younger (ca. 412 to 411 Ma), more silicic parts of the Rathfriland pluton (Zones G -I) show comparatively little geochemical variation (Fig. 8).
Thus, the entire area is thought to consist of biotite granodiorite, showing little or no inward change in composition. This is consistent with the interpretation by Neeson (1984) that the Rathfriland pluton broadly consists of an outer hornblende granodiorite and inner biotite granodiorite, although the current study suggests that the boundary between these facies is abrupt.
Due to the consistent geochemistry of the inner Rathfriland pluton, the zonal divisions here are made according to aeromagnetic data. Zone G represents the area outside of the Rathfriland pluton positive aeromagnetic ring, Zone H represents the positive aeromagnetic ring itself, and Zone I represents the area inside of this anomaly (Fig. 8). Fabrics in the inner part of the pluton are steep to vertical (Fig. 1), hence aeromagnetic signature is thought to closely reflect surface extent of facies. Radiometric dates for Zones G, H and I (411.94 ± 0.34, 412.09 ± 0.36 and 411.09 ± 0.18 Ma, respectively) broadly suggest that this part of the pluton becomes younger towards the centre.

The Newry pluton
Geochemistry is consistent with Neeson's (1984) divisions of the Newry pluton, showing that the this pluton becomes more basic towards its centre ( Fig. 5A and Fig. 5B). Since cross cutting relationships and U-Pb geochronology demonstrate that the Newry pluton is slightly younger than the Rathfriland pluton (Neeson, 1984;GSNI, 1997), the three main divisions within the Newry pluton are defined as Zones J, K and L (Fig. 8).
The outermost biotite granodiorite represents Zone J (Fig. 8), as it has the older of the two U-Pb ages obtained from the pluton (411.00 ± 0.58 Ma). Althiugh the adjacent porphyritic (hornblende -biotite) granodiorite ring is undated, it has been observed to crosscut the outer biotite granodiorite (Neeson, 1984); hence, the porphyritic granodiorite represents Zone K (Fig. 8).
The original location of the porphyritic granodiorite (Zone K) inferred by Neeson (1984) has been modified in this study through consideration of aeromagnetic data as discussed previously. The relationship of the porphyritic granodiorite to the positive aeromagnetic ring allows for more accurate mapping of the Newry pluton than has previously been possible ( Fig. 8). As a result the porphyritic granodiorite in the east of the pluton is now shown to be less marginal than it is suggested to be by Neeson (1984) (compare Fig. 1 and Fig. 8). The inner hornblende granodiorite generated the younger of the two U-Pb ages obtained from the Newry pluton (410.29 ± 0.20 Ma) and is, therefore, designated Zone L.

The Cloghoge pluton
The single U-Pb age from the Cloghoge pluton (407.23 ± 0.35 Ma) and the cross cutting relationship between this and the adjacent Newry pluton (Neeson, 1984) shows that the Cloghoge pluton is the youngest part of the NIC. Consequently, the zones within the Cloghoge pluton are defined as M, N and O (Fig. 8). The notably basic geochemistry (low SiO 2 )of the outerCloghoge pluton and the silicic geochemistry of its off-centre core (Fig. 5) is consistent with the broad division of this pluton into an outer (albeit relatively basic) hornblende granodiorite and a felsic granodiorite core (Reynolds, 1943;Neeson, 1984).
Part of the outer Cloghoge pluton as mapped by the GSNI (1997) is now thought to represent the outer Newry pluton (Fig. 8). This area (labelled 'anomalously silicic area' in Fig. 5) exhibits high SiO 2 and low Fe 2 O 3(t) concentrations that are similar to those observed within the Newry pluton. Furthermore, the area was originally mapped as part of the Newry pluton by Neeson (1984). .
The previously unrecognised area of steeply-orientated sheets in the northeast of the Cloghoge pluton is defined as Zone M (Fig. 8). This area is thought to predate other parts of the Cloghoge pluton due its marginal location. Of the sheets in the area, those consisting of porphyritic diorite show similarity to the Newry pluton porphyritic granodiorite (Zone K), while those consisting of mafic granodiorite and granitic sheets show similarity to the remaining outer part and core area of the Cloghoge pluton respectively. Hence it is possible that the sheeted margin of the Cloghoge pluton (Zone M) represents magmas that also supplied other parts of the NIC.
The outer hornblende granodiorite of the Cloghoge pluton is defined as Zone N (Fig. 8).
Although this area is undated, it is tentatively assumed to be older than the pluton core due to the general inward younging relationships observed across the NIC. Finally, the off-centre felsic granodiorite core of the Cloghoge pluton is defined as Zone O (Fig. 8). U-Pb geochronology yields a significantly younger age for this area (407.23 ± 0.35 Ma). The time gap between this and the next youngest age (for Zone L of the Newry pluton) is consistent with Zone O being the youngest part of the NIC.

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We suggest that the NIC was emplaced as a series of distinct magma pulses, which are represented by the inferred zones (Richey, 1928;Pitcher, 1997;Stevenson, 2007;Farina et al., 2012). Evidence for this incremental emplacement is provided by the abrupt changes in geochemical, aeromagnetic and radiometric signatures between the various zones.
Understanding the mechanism through which these pulses were emplaced, and the siting of the NIC as a whole, will require further structural study of the complex and its host rocks.

Parental magma
Geochemical results show that zones within the NIC become broadly more silicic with younging, possibly reflecting evolution of the parental magma. However, exceptions are observed between Zone D (hornblende granodiorite) and Zone E (quartz diorite) of the Rathfriland pluton, between Zone J (biotite granodiorite/) and Zones K/L (porphyritic granodiorite/hornblende granodiorite) of the Newry pluton, and between the Zone L (hornblende granodiorite) and Zone N (more basic hornblende granodiorite) of the adjacent Newry and Cloghoge pluton (Fig. 8). We suggest that these compositional patterns were produced by variations in the parental magma, with fractional crystallisation causing evolution towards more silicic compositions, and with mixing of more basic magmas causing interruptions in this trend.

The reliability of Tellus data in determining zonation
Aeromagnetic data for the NIC (see Fig. 2A) corresponds in places to changes in facies at the surface. This is apparent from the prominent positive aeromagnetic anomalies located at the Seeconnell Complex, the quartz diorite in the Rathfriland pluton and the porphyritic granodiorite in the Newry pluton ( Figs. 2A). However, the correlation between aeromagnetic signature and composition in other parts of the NIC is inconsistent (Fig. 5). This is clearest from the positive aeromagnetic ring within the Rathfriland pluton, which shows no obvious relationship to geochemistry ( fig. 5). Hence, the origin of aeromagnetic anomalies within the NIC is not always clear.
The aeromagnetic anomalies that are linked to facies at the surface do not consistently correlate with these facies in terms of boundary locations. This occurs for the anomalies corresponding to the quartz diorite in the Rathfriland pluton and the porphyritic granodiorite in the Newry pluton (Fig. 6). Schetselaar et al., (2000) suggest that such inconsistencies between aeromagnetic and surface data reflect aeromagnetic detection of facies at depth. This is thought to be the case for the porphyritic granodiorite, which shows an outward-shifted aeromagnetic signature in the east of the Newry pluton (Fig. 7).

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14 Airborne radiometric data for the NIC (Fig. 2B) corresponds to surface zonation more precisely. For example, radiometric Th elevation in the eastern NIC can be correlated to distinct geochemical concentrations of various elements (Fig. 2B, Fig. 4 and Fig. 5). The Seeconnell Complex also corresponds to an area of K elevation (Figs. 2B and Fig. 4). The only apparent inconsistency between radiometric data and surface composition occurs to the east of the Rathfriland pluton, where an elevated Th signature characteristic of the pluton itself is observed for the host rocks, which are predominantly greywackes (Fig. 2B). Cooper et al. (in press) suggest that glacial transport of rock material from the Rathfriland pluton occurs in this area and likely accounts for the anomaly.

Conclusions
The following four main conclusions are drawn from this study: 1. The NIC can be divided into 15 distinct zones (Fig. 8). These are largely defined compositionally by current geochemistry results. Zones are also distinguished by Tellus aeromagnetic and radiometric data. Aeromagnetic data is particularly key to distinguishing zones within the central Rathfriland pluton, within which no compositional variation has been observed. A thorium-elevated radiometric signature additionally helps to distinguish the more basic eastern part of the Rathfriland pluton.
Zones are concentric within the three plutons, excluding the eastern part of the Rathfriland pluton, where several zones are distributed within the more basic crescent-shaped rim, and within the Cloghoge pluton, which exhibits a significantly off-centre core and a single sheeted margin. Zones show a general evolution from intermediate (with associated ultramafic) to felsic throughout the NIC, although there are exceptions where this evolutionary trend is reversed.
2. The 15 derived zones are likely to have been emplaced incrementally via at least this number of distinct magma pulses. However, the mechanism of emplacement of these pulses and the siting of the NIC remains poorly understood and will require further structural study.
3. The general evolutionary trend shown within the NIC is consistent with a magma supply that has undergone substantial fractional crystallisation (see Meighan and Neeson, 1979), together with occasional mixing of more basic magma.
4. Aeromagnetic and radiometric data broadly resolve much of the zonation of the NIC.
However, the boundaries of some aeromagnetic zones are inconsistent with surface exposure of the corresponding facies, and are interpreted to reflect dipping facies margins. Radiometric data is thought to represent surface composition more reliably, although the southwestern boundary of the Rathfriland pluton is not accurately A C C E P T E D M A N U S C R I P T

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15 resolved, due to glacial transport of material from the NIC. Therefore, there would be a number of caveats associated with exclusive use of aeromagnetic and radiometric data to constrain zonation. As has been previously suggested (e.g., Schetselaar et. al., 2000), it is clear that field work and sampling is also required to obtain accurate interpretations of zonations within large igneous plutonic bodies.   Neeson (1984) likely represents the outer Newry pluton (i.e., peripheral to the porphyritic granodiorite). Due to this ambiguity samples from this area are not included in calculation of mean geochemical concentrations Fig. 1: Geology and internal structure of the NIC based on former work (Reynolds, 1934;Neeson, 1984;GSNI, 1997). Surrounding host rocks and other nearby intrusions are also shown.  Table 1) are determined, superimposed on recent Tellus aeromagnetic data published by Cooper et al. (in press). Representative concentrations of SiO 2 and Fe 2 O 2(t) (wt %) are provided as annotations. Areas of the NIC are labelled 1-10, which correspond to the following: 1: Seeconnell Complex; 2: Thorium-elevated Rathfriland pluton rim, excluding quartz diorite; 3: Quartz diorite; 4: Area inside of thorium-elevated Rathfriland pluton rim and outside of Rathfriland pluton positive aeromagnetic ring; 5: Rathfriland pluton positive aeromagnetic ring; 6: Centre of Rathfriland pluton; 7: Outer Newry pluton; 8: Inner Newry pluton; 9: Outer Cloghoge pluton; 10: Off-centre Cloghoge pluton core. Fig. 4: Comparison between recent Tellus radiometric data published by Cooper et al. (2016) and mean concentrations of radiometric elements (K 2 O, Th, U) from current data. Mean concentrations are calculated for the Seeconnell Complex, the thoriumelevated Rathfriland pluton rim, the inner Rathfriland pluton, the Newry pluton and the Cloghoge pluton. Pie charts show normalised concentrations of K 2 O, Th, U from current data (red = K 2 O, green = Th, blue = U).  Cooper et al. (in press). Concentrations of each element are represented by points that are shaded on a greyscale ranging from white (0 on the scale) to black (100 on the scale). Key compositional changes occur within moderately silicic granodiorites (rather than between samples at the extremes of the concentration range), thus the shading range applied to sample points is set in order to emphasise variation in these. This is achieved by displaying any concentration value that is at or below the 5 th percentile in the total concentration range for each element as a white point (i.e., a greyscale value of 0). Any concentration value that is at or above the 95 th percentile in the total concentration range for each element is in turn displayed as a black point (i.e., a greyscale value of 100). Thus the effect of any anomalously low or high concentrations in obscuring variation within the more common rocks of the complex is removed. Further adjustment is also made in order to emphasise concentrations within the 25 th -75 th percentile range. Firstly, concentrations that are between the 5 th and 25 th percentile in the total range are set a greyscale value of 0 to 25 according to the following equation: Greyscale Value = ((Sample concentration -5 th Percentile concentration)/(25 th Percentile concentration -5 th Percentile concentration)) x 25. Concentrations that are between the 75 th and 95 th percentile in the total range are set a greyscale value of 75 to 100 according to the following equation: Greyscale Value = 100 -(((95 th Percentile concentration -Sample concentration)/(95 th Percentile concentration -75 th Percentile concentration)) x 25). Thirdly, concentrations that are between the 25 th and 75 th percentile in the total range are set a greyscale value of 25 to 75 according to the following equation: Greyscale Value = 25 + (((Sample concentration -25 th Percentile concentration)/(75 th Percentile concentration -25 th Percentile concentration)) x 50). Therefore, changes in composition within the 'middle range' granodioritic samples within the complex are observed more easily than they would be if shading of points was entirely proportional to concentration. Fig 6: Petrological classifications for three parts of the NIC (the Quartz Diorite of the Rathfriland pluton, the Newry pluton and the eastern Cloghoge pluton margin). Shading of symbols represents the relative evolution of samples (shown in key). Fig. 7: Schematic NE-SW cross section of the Newry pluton, accounting for the observed aeromagnetic signature. Fig. 8: Derived zonation of the NIC, shown in relation to recent U-Pb dates of Cooper et al. (in press). Table 1: Representative geochemical concentrations for Areas 1 -10 of the NIC (labelled in Fig. 3). Refer to Appendix 1A/1B for sampling locations and Appendix 3A/3B for geochemical concentrations of individual samples within each area. Mean concentrations are calculated using data from all samples, apart from those close to the ambiguous porphyritic granodiorite boundary (Samples N20A -N24 in Appendix 3A/3B).