*A Globally Significant Potential Megascale Geopark: The Eastern Australian Mantle Hotspot… DOI: http://dx.doi.org/10.5772/intechopen.97839*

semi-quantitative evaluation method to determine their International, National, State-wide to Regional, or Local significance (**Figure 2**) [1]. This system has been adopted in other countries and in different geological contexts [18–20]. Brocx & Semeniuk also addressed spatial scale in categorising sites of geoheritage value and identified/defined the small, medium, and large scales of reference

### **Figure 2.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

with geoheritage as a component of their nominated values [14–17].

Brocx & Semeniuk developed the Geoheritage Tool-kit [18], a classification system to categorise and assess sites of geoheritage significance (**Figure 1**), and a

*Diagram showing the scope of geoheritage in terms of its conceptual categories, its scales of application, and potential levels of significance (modified from Brocx & Semeniuk 2007, with an emphasis on volcanology).*

in terms of rock types, major geological structures, history of Life (in fossils), and many other features. In detail, Geoheritage resolves down to the identification, categorisation, and preservation of significant Earth geological features, and is recognised as important globally, as reflected in various international and intra-national bodies set up for conservation, with agreements, conventions, and inter-governmental initiatives [1–4]. To date, however, Geoheritage has mostly focused on medium and large-scale features and cliff faces of significant geology and, in some cases, geological phenomena at the crystal scale [5]. Examples of recognised sites of geoheritage significance include columnar basalt, Isle of Staffa, Scotland [6], chevron folds, Millook Haven, England [7], the Silurian and Devonian unconformity at Siccar Point, Scotland [8], the Cretaceous/Tertiary boundary (K/T contact) at Gubbio, Italy [9], Cambrian fossils, Burgess Shale, Canada [10], the Precambrian Ediacara fauna, Rawnsley Quartzite, South Australia [11], and Uluru, a very large inselberg of geological (and cultural) importance in central Australia [12]. Generally, geological features at the sub-global scale, involving 1000s of kilometres, unless partly integrated into large-scale geoparks, are not included as geoheritage sites: examples include entire mountain chains such as The Himalayas and The Andes that formed by tectonic plate collisions, or extensive (subcontinental-scale) sand-dominated deserts (*e.g.*, the Great Sandy Desert of Western Australia), extensive plains/plateaux formed by lava outpourings (*e.g.*, the Deccan Traps [Deccan Plateau], India), island arcs, and extensive inland-located volcanic chains (such as the Cosgrove hotspot track [13] in eastern Australia or, in our terms, the Cosgrove Volcano Chain, the subject of this Chapter). Exceptions to this are the 2300-km-long Great Barrier Reef offshore from eastern Australia, and Shark Bay (150 km x 100 km), both World Heritage Sites and

**348**

**Figure 1.**

*Diagrammatic representation of the levels of significance applicable to volcanic geoheritage features (modified from Brocx & Semeniuk 2007, with an emphasis on vulcanology). A: International; B: National; C: State-wide to regional; and D: Local. Definitions (after Brocx & Semeniuk 2007) are embodied in the diagram. This method of evaluation is semi-quantitative.*

### **Figure 3.**

*Map of eastern Australia showing outcrops of Cainozoic volcanism and their ages, and the general trackway of the Cosgrove volcanic chain (modified from Davies* et al*. [21]).*

**351**

*A Globally Significant Potential Megascale Geopark: The Eastern Australian Mantle Hotspot…*

assigning numerical limits to the scale of reference [1], but did not venture to the megascale involving mountain chains and other the sub-global geological phe-

Sites of geoheritage significance, regardless of their scale, are important to Society in that they preserve a history of the Earth, can be used for research and teaching, provide reference localities, provide a record of the history of scientific enquiry, can function as sites for geotours, and may be linked to Indigenous cultural history and values (Row A, **Figure 1**). The sites of geoheritage significance listed

In this context, the Cosgrove Volcano Chain (some 2000 km long) in eastern Australia (**Figure 3**) is an example of an extensive suite of volcanic rocks that have global geoheritage significance and qualify to be recognised as a globally-important

mega-geopark. To convey this concept, this paper is structured as follows:

1.mantle plumes, and the significance of xenoliths, xenocrysts, and mag-

4.geoheritage significance of the eastern Australian Cosgrove Volcano Chain

5.Discussion and Conclusions: a globally-significant mega-geopark centred on

While the innumerable papers on the eastern Australian volcanic corridor have focused on petrology, geochemistry, mechanisms of emplacement and extrusion, and origin of the magma [22–26], this Chapter definitively focuses on the geoher-

Convection of hot rock within the Earth's mantle has been proposed as the mechanism for the formation of a magmatic plume or mantle plume (acting like a diapir) that results in volcanic hotspots such as those located at Hawaii or Iceland, and for large igneous provinces such as the Deccan Traps [27–29]. Mantle plumes are thought essentially to be areas of hot, upwelling magma, with a hotspot that develops above the plume (this is the Wilson-Morgan hypothesis of hotspots, typified by high heat flow, positive gravity anomaly and alkalic volcanism, resulting in surface expressions of mantle plumes rising by thermal convection [30]). Magma generated by hotspots rises through the more rigid overlying lithosphere and produces active volcanoes and lava flows at the Earth's surface [31–34]. Accompanying, and critical to this process is the fact that, on its ascent, a plume will entrain rock fragments from deep in the Earth's crust (evident as mafic and ultramafic xenoliths) or, when traversing the lithosphere such as sedimentary basins higher in the Earth's crust, entrain Phanerozoic and Proterozoic xenoliths such as sandstone, shale, coal, low-grade metamorphic rock, and granite [21, 30, 32–36]. Where there is melting or partial melting, xenocrysts can be released [30, 37–40]. Also, where there is melting or partial melting of

**2. Mantle plumes, and the significance of xenoliths, xenocrysts, and** 

the lithosphere there is geochemical contamination of magma [37, 38].

*DOI: http://dx.doi.org/10.5772/intechopen.97839*

above [6–12] accord with these principles.

2.the eastern Australian volcanic framework

the Cosgrove Volcano Chain.

itage significance of one volcanic chain [13].

3.the eastern Australian continent geological framework

nomena noted above.

ma mixing

**magma mixing**

*A Globally Significant Potential Megascale Geopark: The Eastern Australian Mantle Hotspot… DOI: http://dx.doi.org/10.5772/intechopen.97839*

assigning numerical limits to the scale of reference [1], but did not venture to the megascale involving mountain chains and other the sub-global geological phenomena noted above.

Sites of geoheritage significance, regardless of their scale, are important to Society in that they preserve a history of the Earth, can be used for research and teaching, provide reference localities, provide a record of the history of scientific enquiry, can function as sites for geotours, and may be linked to Indigenous cultural history and values (Row A, **Figure 1**). The sites of geoheritage significance listed above [6–12] accord with these principles.

In this context, the Cosgrove Volcano Chain (some 2000 km long) in eastern Australia (**Figure 3**) is an example of an extensive suite of volcanic rocks that have global geoheritage significance and qualify to be recognised as a globally-important mega-geopark. To convey this concept, this paper is structured as follows:


While the innumerable papers on the eastern Australian volcanic corridor have focused on petrology, geochemistry, mechanisms of emplacement and extrusion, and origin of the magma [22–26], this Chapter definitively focuses on the geoheritage significance of one volcanic chain [13].
