Granite magmatism

Abstract

Read's two presidential addresses to the Geological Society (1948, 1949) heralded the end of the coherent rearguard action by the 'granitizers' against the 'magmatists'. They were the distillation of his thoughts on the genesis of granite and culminated in his concept of the 'Granite Series'. In this, he identified a continuity from metamorphic through migmatitic rocks to granite. Although he was wrong on granitization, the general idea remains intact and granites are produced by high-temperature metamorphism leading to partial melting. However the role of migmatites is still contentious. Not all granites belong to the granite series as he presented it; this particularly applies to Cordilleran (Andean) type granites. The genesis of this type will be discussed in the context of the earlier, classic work of Nockolds (1940) on the Garabal Hill complex where he demonstrated fractional crystallization was a major process in producing the diversity present and was similar to that seen in volcanic rocks, which had clearly been liquids. He also proposed that the source was basaltic with the implication, strongly supported by modern isotopic studies, that granites of this type are essentially mantle derived. Nockolds contribution was a geochemical confirmation of Bowen's belief in the importance of closed-system fractional crystallization in the differentiation of plutonic rocks. Most authorities today would accept this but would not necessarily follow Bowen in the belief that major granitic batholiths formed by differentiation of basalt or that the system was closed. Recent models of the generation of the two main types of granite are presented, incorporating many of the ideas of Nockolds and Read. The discussion focuses on high-level differentiation, partial melting and intrusion in an extensional regime, high-T/low-P metamorphism associated with the magmatism, and 209-238.

Contrasting Two Facies of Muncung Granite in Lingga Regency Using Major, Trace, and Rare Earth Element Geochemistry

“…Precipitation of plagioclase is also evidenced from Rb/Sr ratio versus SiO 2 plotting. Only B facies has 'J' shaped trend of Rb/Sr ratio which suggests the importance of fractional crystallization process with plagioclase as the major precipitating felsic phase (Atherton, 1993;Cid et al, 2001;Ahmad et al, 2002;Ghani et al, 2013;Ray et al, 2011). The negative correlations of CaO and Al 2 O 3 to SiO 2 are relevant with the fractional crystallization (Sun et al, 2010).…”

Structure of volcano plumbing systems: A review of multi-parametric effects

“…When large enough, these bodies intruded the overlying metasediments, but were soon halted as they became watersaturated. The zone of granite ponds corresponds to the zone of partial melting, segregation and collection (a) in the division of plumbing systems of Atherton (1993), above which there are the transport zone (b) and the emplacement zone (c), where freezing occurs (Fig. 5).…”

“…In the case of low melt content, small batches of magma will be able to rise and will soon stop. In the case of large melt fraction, such as for example in the case of high thermal gradients (80-100°C/km), large magma batches can ascend giving rise to huge plutons, especially if associated with contemporaneous rifting or local extension related to pull-apart structures or releasing bends within transcurrent shear zones and the consequent horizontal regional ductile extension (Atherton, 1993).…”

“…Notwithstanding this, some authors indicate that granitic plutons are mostly thin with aspect ratios (thickness to width) up to 1:15 and a flat shape (e.g. Atherton, 1993). Geophysical and structural studies showed that some plutons are sill-like, low aspect-ratio, tabular bodies (Bridgwater et al, 1974;Lefort, 1981;Cruden, 1998;Petford et al, 2000), whereas magma chambers and plutons are often represented as spherical bodies (e.g.…”

“…In zone -c‖ of Atherton (1993) storage processes occur and most magma is emplaced in the form of plutons. Storage includes a series of mechanisms that can be summarized by two endmembers, although it is reasonable to consider that a spectrum of intermediate possibilities exists.…”