The Altered Zone unexcelled in the Colorado Plateau for showing the effects of hot water or hydrothermal alteration of igneous rocks and the development of clays in the weathering process associated with the late phases of igneous activity.
22.
Although igneous activity in the Southern California region was ongoing throughout the Mesozoic Era, the peak of the plutonism in the southern Sierra Nevada region was in the Late Cretaceous, about 100 to 80 million years ago.
23.
.. . that "'Jodhpur Group-Malani Igneous Suite Contact "', a National Geological Monument at the Mehrangarh Fort in Jodhpur, India, represents the last phase of igneous activity of Precambrian age?
24.
Major igneous activity, of Early Cretaceous and Palaeogene times, is also likely to have produced fluid circulation patterns and some additional fluid transport channels along the flanks of volcanic centres, through associated dyke systems and compaction-associated faults above the volcanic centres.
25.
Such exceptional flow rates and the implied associated volumes of water released could not be sourced by precipitation but rather demand the release of water from some long-term store, probably a subsurface aquifer sealed by ice and subsequently breached by meteorite impact or igneous activity.
