Monogenetic volcanoes have long been regarded as simple in nature, involving single magma batches and uncomplicated evolutions; however, recent detailed research into individual centres is challenging that assumption. Mt Rouse (Kolor) is the volumetrically largest volcano in the monogenetic Newer Volcanics Province of southeast Australia. This study presents new major, trace and Sr–Nd–Pb isotope data for samples selected on the basis of a detailed stratigraphic framework analysis of the volcanic products from Mt Rouse. The volcano is the product of three magma batches geochemically similar to Ocean–Island basalts, featuring increasing LREE enrichment with each magma batch (batches A, B and C) but no evidence of crustal contamination; the Sr–Nd–Pb isotopes define two groupings. Modelling suggests that the magmas were sourced from a zone of partial melting crossing the lithosphere–asthenosphere boundary, with batch A forming a large-volume partial melt in the deep lithosphere (1.7 GPa/55.5 km); and batches B and C from similar areas within the shallow asthenosphere (1.88 GPa/61 km and 1.94 GPa/63 km, respectively). The formation and extraction of these magmas may have been due to high deformation rates in the mantle caused by edge-driven convection and asthenospheric upwelling. The lithosphere–asthenosphere boundary is important with respect to NVP volcanism. An eruption chronology involves sequential eruption of magma batches A, C and B, followed by simultaneous eruption of batches A and B. Mt Rouse is a complex polymagmatic monogenetic volcano that illustrates the complexity of monogenetic volcanism and demonstrates the importance of combining detailed stratigraphic analysis alongside systematic geochemical sampling.

Variation in parental magmas of Mt Rouse, a complex polymagmatic monogenetic volcano in the basaltic intraplate Newer Volcanics Province, southeast Australia

Monogenetic volcanism produces small-volume volcanoes with a wide range of eruptive styles, lithological features and geomorphic architectures They are classified as spatter cones, scoria (or cinder) cones, tuff rings, maars (maar–diatremes) and tuff cones based on the magma/water ratio, dominant eruption styles and their typical surface morphotypes The common interplay between internal, such as the physical–chemical characteristics of magma, and external parameters, such as groundwater flow, substrate characteristics or topography, plays an important role in creating small-volume volcanoes with diverse architectures, which can give the impression of complexity and of similarities to large-volume polygenetic volcanoes In spite of this volcanic facies complexity, we defend the term “monogenetic volcano” and highlight the term’s value, especially to express volcano morphotypes This study defines a monogenetic volcano, a volcanic edifice with a small cumulative volume (typically ≤1 km3) that has been built up by one continuous, or many discontinuous, small eruptions fed from one or multiple magma batches This definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

Monogenetic volcanism: personal views and discussion

Abstract Small-scale volcanic systems are the most widespread type of volcanism on Earth and occur in all of the main tectonic settings. Most commonly, these systems erupt basaltic magmas within a wide compositional range from strongly silica undersaturated to saturated and oversaturated; less commonly, the spectrum includes more siliceous compositions. Small-scale volcanic systems are commonly monogenetic in the sense that they are represented at the Earth's surface by fields of small volcanoes, each the product of a temporally restricted eruption of a compositionally distinct batch of magma, and this is in contrast to polygenetic systems characterized by relatively large edifices built by multiple eruptions over longer periods of time involving magmas with diverse origins. Eruption styles of small-scale volcanoes range from pyroclastic to effusive, and are strongly controlled by the relative influence of the characteristics of the magmatic system and the surface environment.

Source to surface model of monogenetic volcanism: a critical review

Interpreting chemical compositions of small scale basaltic systems: A review

Cenozoic intraplate volcanism is widespread throughout much of eastern Australia, and manifests as both age-progressive volcanic tracks and non-age progressive lava-fields. Various mechanisms have been invoked to explain the origin and distribution of the volcanism, but a broad consensus remains elusive. We use results from seismic tomography to demonstrate a clear link between lithospheric thickness and the occurrence, composition and volume of volcanic outcrop. Furthermore, we find that non age-progressive lava-fields overlie significant cavities in the base of the lithosphere. Based on numerical simulations of mantle flow, we show that these cavities generate vigorous mantle upwellings, which likely promote decompression melting. However, due to the intermittent nature of the lava-field volcanics over the last 50 Ma, it is probable that transient mechanisms also operate to induce or enhance melting. In the case of the Newer Volcanics Province, the passage of a nearby plume appears to be a likely candidate. Our results demonstrate why detailed 3-D variations in lithospheric thickness, plate motion and transient sources of mantle heterogeneity need to be considered when studying the origin of non age-progressive volcanism in continental interiors.

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The mechanisms underpinning Cenozoic intraplate volcanism in eastern Australia: Insights from seismic tomography and geodynamic modeling

Monogenetic volcanism can produce eruptive suites showing considerable complexity in compositional features and pre-eruptive magma evolution. The � 5 ka Mount Gambier Volcanic Complex (MGVC), a monogenetic volcanic centre in SE Australia’s Newer Volcanics Province (NVP), is a good example. It displays a complex stratigraphy of interbedded deposits related to different eruption styles from a multi-vent system. Formation of the MGVC proceeded through simultaneous eruption of two alkali basaltic magma batches: a more alkaline and light rare earth element enriched basanite batch (Mg# 58^62) in the west and a trachybasalt batch (Mg# 58^64) enriched in SiO2 and CaO in the east. Trace element modelling suggests an origin of both magma batches from a single parental melt formed by 4^5% partial melting of a metasomatized lherzolite source in the asthenospheric mantle (2· 2G Pa; � 80 km). At the base of the lithosphere, part of this parental melt interacted with a deep-seated pyroxenite contaminant to form the trachybasaltic suite. Further modification of either magma batch at crustal levels appears to have been negligible. Isotope and trace element signatures are consistent with the inferred asthenospheric magma source; Pb isotopes in particular suggest a source with mixed Indian mid-ocean ridge basalt^Enriched Mantle 2 affinities, the latter perhaps related to metasomatic overprinting. It is argued that Cenozoic NVP volcanism in SE Australia is not necessarily related to a mantle plume but can be explained by other models involving asthenospheric upwelling. Fast magma ascent rates in the lithosphere evidenced by the presence of mantle xenoliths may reflect reactivation of lithospheric structures that provide magma pathways to the surface.

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Polymagmatic Activity at the Monogenetic Mt Gambier Volcanic Complex in the Newer Volcanics Province, SE Australia: New Insights into the Occurrence of Intraplate Volcanic Activity in Australia

Abstract The Newer Volcanics Province of SE Australia is a very large continental basaltic province, with an area of >23 000 km2, a dense rock equivalent volume of <900 km3 and >400 monogenetic volcanoes; it has been active since c. 8 Ma. Lava fields, shields, scoria cones are common, and there are >40 maars and volcanic complexes. Maars occur dominantly in the south where magmas erupted through Tertiary sedimentary aquifers, whereas in the north, over Palaeozoic crust, there are few. Complex interactions of the magma volatile content, magma ascent rates, conduit characteristics and the availability and depth of aquifers caused diverse eruption styles. Volcanoes commonly occur close to major crustal faults, which acted as magma conduits. There is no simple age pattern of volcanism across the province. Volcanism was probably triggered by transtensional decompression in the crust where fault sets intersect, affecting hot, hydrated mantle that had welled up through edge-driven convection where the base of the lithosphere thins abruptly at the edge of the continent. Rock compositions range from picritic to basaltic andesitic. Some volcanoes are polymagmatic. Regional geophysical datasets have clarified the regional characteristics of the province, whereas detailed ground magnetic and gravity surveys resulted in new insights into the subsurface structure of maar-diatremes.

The dynamics of a very large intra-plate continental basaltic volcanic province, the Newer Volcanics Province, SE Australia, and implications for other provinces

The erupted volumes of tephra from maar volcanoes and estimates of their VEI magnitude: Examples from the late Cenozoic Newer Volcanics Province, south-eastern Australia

J. van Otterloo

Papers

Polymagmatic Activity at the Monogenetic Mt Gambier Volcanic Complex in the Newer Volcanics Province, SE Australia: New Insights into the Occurrence of Intraplate Volcanic Activity in Australia

The dynamics of a very large intra-plate continental basaltic volcanic province, the Newer Volcanics Province, SE Australia, and implications for other provinces

The erupted volumes of tephra from maar volcanoes and estimates of their VEI magnitude: Examples from the late Cenozoic Newer Volcanics Province, south-eastern Australia

Complex evolution of volcanic arcs: The lithofacies and palaeogeography of the Cambrian Stavely Arc, Delamerian Fold Belt, Western Victoria