**6. Discussion and conclusions: a globally significant mega-geopark centred on the Cosgrove volcano chain**

As reiterated above, Australia, having finally split from Antarctica some 33 million years ago, has been migrating northwards towards the Eurasian plate progressively passing on its eastern side over a mantle hotspot (magma plume) which intersected various, variable lithologic packages such as Phanerozoic sedimentary basins, fold belts and metamorphic terranes, and Precambrian rocks. With xenolith plucking, enclave plucking, and xenocryst incorporation, there had been compositional evolution of the magma plume. The volcanic chain, the individual volcanoes, and the lava fields that are spread latitudinally along 2000 km of eastern Australia present a globally-significant volcanic system that provides insights into Earth magma and crust interactions, into the variability of xenoliths and xenocrysts, into magma evolution dependent on setting, and into the story of the Earth. The Cosgrove Volcano Chain stands as an example of a globally-unique example of these processes and a potential megascale geopark.

In summary, this Chapter has described the significance of a magma plume pulsing though a heterogeneous continental crust, with lithospheric heterogeneity giving rise to a mix in magma composition and a mix of xenoliths/xenocrysts. The movement of the Australian plate to northward gives clues (as a window) to subcontinental lithology via the enclosed xenoliths and xenocrysts and the influence of the thickness of crust as to whether there is volcanic expression of the magma plume at the Earth's surface [13]. And while they have been noted in previous studies and their occurrence is important, xenoliths and xenocrysts have not been a detailed focus of many studies, yet they are important as they provide clues to the sub-crustal influences and processes at the base of a magma plume. The phenomena of magma mixing, nature of xenoliths and xenocrysts, the influence of lithospheric lithologies in generating xenolith/xenocryst types and on magma contamination, and the relationship of volcanic expression to crust thickness are applicable to other volcanic trackways here in eastern Australia and elsewhere globally.

Also, it is worth pointing out that a similarly large volcanic field has been recognised for its geoheritage values in Harrat Khaybar, Kingdom of Saudi Arabia [60, 61] which has local and global implications for geo-education, research, and reference site for global volcanism.

On a final note, we emphasise that we consider the Cosgrove Volcano Chain to be a megascale geological feature of global geoheritage significance and should be considered as a potential megascale geopark. In effect, it would be the volcanic equivalent of the latitudinally extensive Great Barrier Reef which is accepted as a World Heritage Site.

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

in perpetuity.

breccias;

tary basins;

regimes.

as follows:

climates with its attendant influence on erosion and weathering styles and transformation of volcanic rock and tephra to climate-specific landforms and climate specific soils. This variability in volcanic expression, in a north-to-south gradient influences content of xenoliths and xenocrysts and magma composition, as well as volcanic landscape types, and in climate-influenced weathering styles changing progressively over 33 million years – it thus provides a globally-unique natural laboratory as a window into Earth processes, and a teaching and research resource

The key elements of the Cosgrove Volcano Chain of geoheritage significance are

1.first example of a long, continent-length volcanic chain [13];

3.volcanic magma composition linked to lithosphere heterogeneity;

5.magma evolution at a volcano, *e.g.*, from basalt lava to rhyolitic lava;

9.volcanic expression at different scales linked to magma composition;

10.northwards volcano drift passes through different climates and weathering

To further the disciplines of geoheritage and geoconservation, Brocx & Semeniuk provided a Geoheritage Tool-kit to systematically compile an inventory of the full diversity at various scales of geological and geomorphological features in a given area, assess their levels of significance, and address whether geoheritage features are treated in isolation or as inter-related suites that should be conserved as an ensemble. Utilising the Geoheritage Tool-kit, many of the features listed 1–10 above individually would be evaluated as internationally to nationally significant, but specifically (1), (2), (3), and (8) are globally significant features of this volcanic chain. However, the cross-continent assemblage of volcanic features of the Cosgrove Volcano Chain should not be viewed as isolated separate geological phenomena spread across the north-to-south length of Australia but, from a geoheritage perspective, should be viewed as a single, integrated ensemble recording 1. a gradient of magma types, 2. the effect of a variable thickness of lithosphere, 3. the variety of volcanic landform expression, 4. the rock types intersected by the ascending plume, and 5. the changes in styles of erosion and weathering as the volcanoes passed through the various climate zones. However, while the Cosgrove Volcanic Chain is suggested as a global-significant mega-park, there is much planning, valorisation, community involvement, and government support required to

6.magma and volcanic evolution, *e.g.*, magma flows varying to ash beds and

8.volcanic xenolith/xenocryst linked to lithosphere heterogeneity and sedimen-

2.volcanic activity linked to lithosphere thickness;

4.variability of magma along the volcanic chain;

7.volcanic eruption style linked to magma composition;

achieve this (matters that are beyond the scope of this Chapter).

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*
