### Abstract

The horizontal (L) and vertical (T) dimensions of broadly tabular,
sub-horizontal intrusions of mafic to felsic composition emplaced into
shallow to mid-crustal levels of continental crust reveal two well-defined
and continuous curves in log L vs. log T space. The data set spans six and
five orders of magnitude in L (1 m to 1000 km) and T (10 cm to 10 km),
respectively. Small tabular sheets and sills (mafic and felsic) define a
straight line with a slope * 0.5 at all horizontal length scales, similar to
the known geometric scaling of mafic dikes, indicating that the L/T ratio of
these intrusions to increases with increasing L (horizontal lengthening
dominates over vertical thickening). Laccoliths, plutons, layered mafic
intrusions and batholiths define an open, continuous S-shaped curve that
bifurcates from the tabular sheets and sills curve at L * 500 m towards
higher T values. For L * 0.5 to 10 km the slope of this curve is * 1.5,
corresponding to laccoliths that are characterized by a decrease in L/T ratio
with increasing L (vertical thickening dominates over horizontal lengthening).
Between L * 10 and 100 km the slope has a mean value * 0.8,
indicating that plutons and layered mafic intrusions have a tendency for
horizontal lengthening over vertical thickening as L increases. Batholiths and very large layered mafic intrusions with L > 100 km lie on a slope
* 0 with a threshold thickness * 10 km. The continuous nature of the
dimensional data over such a wide range of length scales reflects a
spectrum of igneous emplacement processes repeated in space and time.
We discuss how thresholds and transitions in this spectrum, defined by
bifurcations between the curves (e.g., between sill and laccolith emplacement)
and changes in slope, largely reflect depth- and time-dependent
changes in emplacement mechanisms rather than factors such as magma
viscosity, composition and temperature.

Original language | English |
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Title of host publication | Physical Geology of Shallow Magmatic Systems |

Subtitle of host publication | Dykes, Sills and Laccoliths |

Editors | Christoph Breitkreuz, Sergio Rocchi |

Place of Publication | Switzerland |

Publisher | Springer |

Chapter | 2 |

Pages | 11-38 |

Number of pages | 27 |

Edition | 1 |

ISBN (Electronic) | 2364-3285 |

ISBN (Print) | 2364-3277 |

Publication status | Published - 2018 |

### Publication series

Name | Advances in Volcanology: An Official Book Series of the International Association of Volcanology and Chemistry of the Earth’s Interior |
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Publisher | Springer |

ISSN (Print) | 2364-3277 |

ISSN (Electronic) | 2364-3285 |

## Cite this

Cruden, A. R., McCaffrey, K. J. W., & Bunger, A. (2018). Geometric Scaling of Tabular Igneous Intrusions: Implications for Emplacement and Growth. In C. Breitkreuz, & S. Rocchi (Eds.),

*Physical Geology of Shallow Magmatic Systems: Dykes, Sills and Laccoliths*(1 ed., pp. 11-38). (Advances in Volcanology: An Official Book Series of the International Association of Volcanology and Chemistry of the Earth’s Interior). Springer.