Lower Borrowdale Volcanics: a landscape of low viscosity

Reading Paul Gannon's book I found that the initial volcanoes in the Lake District produced lava with a lower silica content. This meant that the lava had a lower viscosity and was able to flow more freely. The result was a lower landscape of tiered lava flows and rocky knolls. This central Lakeland landscape is shown above and tends to catch the water, becoming peaty. These earlier volcanic rocks are called the Lower Borrowdale Volcanics. I was interested in why the silica content affects the viscosity and this link explains it really well http://sci.sdsu.edu/how_volcanoes_work/Controls.html  I am interested to see that SO4 radicals can polymerise by covalently bonding together. These polymers increase the friction in the lava. The next site gives reasons why you might go from having low silica content to high silica content due to tectonic drift over millions of years. Nearer a plate boundary there will be a higher silica content.  https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3655.html