3.4.14 The Ravenswood Granodiorite Complex and Lolworth Igneous Complex
The study area includes the whole of any property provided at least 10 percent of the land lies within the Desert Uplands bioregion. Consequently, some lithologies and landscapes, not normally considered to be part of the Desert Uplands bioregion, have been included. The landscapes formed on granitic and basaltic substrates in the Dalrymple Shire belong, in fact, to the Einasleigh bioregion.
During the Silurian, 400 – 440 million years ago, magma intruded the Palaeozoic sediments deep below the land surface of that time. With slow cooling the Ravenswood Granodiorite Complex was formed. Subsequent uplift and erosion have removed the overburden of sediments and broken through the metamorphic aureole enclosing the granodiorite. The coarse crystalline structure of the granodiorite allowed moisture to penetrate and initiate rapid chemical weathering. Subsequent erosion has lowered the landscape to below that of the Desert Uplands plateau and formed a landscape of rolling rises.
In contrast, the Lolworth Igneous Complex exists as a prominent mountain range. It has been dated at 390 – 400 million years. Since then the massif has been exposed, deeply weathered and eroded. Considering the intrusion cooled while several thousand feet below the land surface, it is hard to imagine the erosive forces and time required to remove such a vast quantity of material and sculpture the present-day landscape. One small area high up among the peaks represents the only residual of a high-level plateau – an ancient land surface, all but gone. Since tectonic uplift, the region has experienced extrusive volcanism and diverse climates ranging from wet tropical to dry arid and glaciation, with the Lolworth Range in a constant state of weathering and erosion. One product of this erosion is the extensive Campaspe Beds, which underlie the Corea (CA) land system and consist mainly of quartz, feldspar and muscovite, and extend from Lolworth Creek in the north to the confluence of the Cape and Campaspe Rivers at the property ‘Nosnillor’, approximately 130 kilometres to the southeast.