Using granite to image the thermal state of the source terrane

Zen, E‐an

doi:10.1017/s0263593300007793

Cited by 13 publications

(3 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Consider a source of area of 10 3 -10 4 km 2 beneath which an average of 1 km 3 per km 2 of melt is extracted from 10 km depth of suprasolidus continental crust (e.g. Zen 1992). For a pluton that is 1 km thick, the melting footprint, the region of melt throughput and the pluton area are identical.…”

Section: Fluxesmentioning

confidence: 99%

The mechanism of melt extraction from lower continental crust of orogens

Brown¹

2004

Earth and Environmental Science Transactions of the Royal Socie

View full text Add to dashboard Cite

Melt extraction is a process with a length scale that spans many orders of magnitude. Studies of residual migmatites and granulites suggest that melt has migrated from grain boundaries to networks of leucosome-filled structures to steeply inclined cylindrical or tabular granites inferred to have infilled ascent conduits. For example, in anatectic rocks from southern Brittany, France, during decompression-induced biotite-breakdown melting, melt is inferred to have been expressed from foliation-parallel structures analogous to compaction bands to dilation and shear bands, based on location of residual leucosome, and from this network of structures to ascent conduits, preserved as dykes of granite. The leucosome-filled deformation band network is elongated parallel to a sub-horizontal lineation, suggesting that mesoscale melt flow was focused primarily in the plane of the foliation along the lineation to developing dilatant transverse structures. The leucosome network connects with petrographic continuity to granite in dykes; however, the orientation of dykes discordant to fabric anisotropy suggests that their formation was controlled by stress, which indicates that the process is a fracture phenomenon. Blunt fracture tips and zigzag propagation paths indicate that the dykes represent ductile opening-mode fractures; these are postulated to have formed by coalescence of melt pockets. The structures record a transition from accumulation to draining; quantitative volume fluxes are calculated and presented for the generalised extraction process. The anatectic system may have converged to a critical state at some combination of melt fraction and melt distribution that enabled formation of ductile opening-mode fractures, but fractal distribution of inferred mesoscale melt-filled structures has not been demonstrated; this may reflect the inherent anisotropy and/or residual nature of the drained source. Melt extraction has been modelled as a self-organised critical phenomenon, but the mechanism of extraction is not described and the relationship between these models and the spatial and temporal granularity of lower continental crust is not addressed. Self-organised critical phenomena are driven systems involving ‘avalanches’ with a fractal frequency-size distribution; thus, the distribution of melt batch sizes might be expected to be fractal, but this has not yet been demonstrated in nature.

show abstract

Section: Fluxesmentioning

confidence: 99%

The mechanism of melt extraction from lower continental crust of orogens

Brown¹

2004

Earth and Environmental Science Transactions of the Royal Socie

View full text Add to dashboard Cite

show abstract

“…Taking an arbitrary crustal section of 100 × 100 km with a thickness of 10 km, which can be regarded as a magmatic system during regional metamorphism, we are able to calculate melt volume in any part of the system under consideration. A total melting of a 1 km 3 per 1 km 2 crustal column seems a reasonable value for total melt volume (Zen 1992), which gives tot V = 10 4 km 3 . Now, considering the above relationships we can calculate that 1 m 3 may contain up to 900 leucosomes with volumes between 1 cm 3 and 1 dm 3 at m = 0.97.…”

Section: − =mentioning

confidence: 93%

Fractality in geology: a possible use of fractals in the studies of partial melting processes

Соэсоо¹,

Kalda²,

Bons³

et al. 2004

Proceedings of the Estonian Academy of Sciences. Geology

View full text Add to dashboard Cite

“…As outlined here, the heat source is mantle upwelling, consequent on rifting. In this model, granite is the end product of mantle advection and/or basalt insertion via dykes high in the crust, and subduction or thrust loading are not responsible (see the modelling of the thermal state of the source of the Boulder Batholith, Zen 1992). Perhaps Read was partly right and there is a separation of plutonism and volcanism, particularly of the eRic-alkaline variety, in that many batholithic granites are not directly related to subduction while many volcanic rocks are!…”

Section: Where Are We Going?mentioning

confidence: 99%

Granite magmatism

Atherton

1995

Memoirs

View full text Add to dashboard Cite

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.

show abstract

Using granite to image the thermal state of the source terrane

Cited by 13 publications

References 30 publications

The mechanism of melt extraction from lower continental crust of orogens

The mechanism of melt extraction from lower continental crust of orogens

Fractality in geology: a possible use of fractals in the studies of partial melting processes

Granite magmatism

Contact Info

Product

Resources

About