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	<title>thin-section Archives - Geology North</title>
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		<title>The Hawsen Burn</title>
		<link>https://www.geologynorth.uk/the-hawsen-burn/</link>
		
		<dc:creator><![CDATA[Stephen]]></dc:creator>
		<pubDate>Mon, 20 Apr 2015 19:13:53 +0000</pubDate>
				<category><![CDATA[Uncategorised]]></category>
		<category><![CDATA[andesite]]></category>
		<category><![CDATA[Dunmoor Hill]]></category>
		<category><![CDATA[epidote]]></category>
		<category><![CDATA[evolved granite]]></category>
		<category><![CDATA[fine-grained granophyric]]></category>
		<category><![CDATA[Hawsen Burn]]></category>
		<category><![CDATA[Hedgehope Hill]]></category>
		<category><![CDATA[hornfels]]></category>
		<category><![CDATA[hydrothermal alteration]]></category>
		<category><![CDATA[ring dyke]]></category>
		<category><![CDATA[Standrop Burn]]></category>
		<category><![CDATA[The Cheviot]]></category>
		<category><![CDATA[thin-section]]></category>
		<guid isPermaLink="false">http://www.geologynorth.uk/?p=20826</guid>

					<description><![CDATA[<p>We find plenty of fine-grained granophyric rock but we are not convinced that it really is of the same type as the &#8216;Evolved&#8217; rock from the summit and north slopes of the Cheviot. Subsequent thin section analysis suggests that it and samples from the Standrop Burn are rather different from the &#8216;Evolved&#8217; type. However, the &#8230; <a href="https://www.geologynorth.uk/the-hawsen-burn/" class="more-link">Continue reading <span class="screen-reader-text">The Hawsen Burn</span> <span class="meta-nav">&#8594;</span></a></p>
<p>The post <a href="https://www.geologynorth.uk/the-hawsen-burn/">The Hawsen Burn</a> appeared first on <a href="https://www.geologynorth.uk">Geology North</a>.</p>
]]></description>
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<p>We find plenty of fine-grained granophyric rock but we are not convinced that it really is of the same type as the &lsquo;Evolved&rsquo; rock from the summit and north slopes of the Cheviot. Subsequent thin section analysis suggests that it and samples from the Standrop Burn are rather different from the &lsquo;Evolved&rsquo; type. However, the Hawsen Burn samples do share the high quartz and low plagioclase content of the &lsquo;Evolved&rsquo; rock of the Upper Cheviot area. At any rate, we now feel that there is insufficient evidence to argue that the fine-grained granophyric rocks are all part of a common ring dyke system. They are quite likely to be separate intrusions, some of them representing very late magmatic activity.<br />
We locate a medium-grained but rather altered, pink porphyritic variety at NT 94299 23027 which seems to correspond with varieties found on Dunmoor and Hedgehope Hills.<br />
There is plenty of evidence of altered andesite, hornfelsed by contact with the pluton as we would expect here as the Hawsen Burn runs along the boundary between the two in some places.</p>
<p>Altered yellowish andesite at NT 94504 23011 is stated in some guides to contain massive epidote but there was none in the samples that we thinned.</p>
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<p>The post <a href="https://www.geologynorth.uk/the-hawsen-burn/">The Hawsen Burn</a> appeared first on <a href="https://www.geologynorth.uk">Geology North</a>.</p>
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		<title>Dunmoor Hill</title>
		<link>https://www.geologynorth.uk/dunmoor-hill/</link>
		
		<dc:creator><![CDATA[Stephen]]></dc:creator>
		<pubDate>Sat, 03 May 2014 22:15:28 +0000</pubDate>
				<category><![CDATA[Uncategorised]]></category>
		<category><![CDATA[Al-Hafdh]]></category>
		<category><![CDATA[andesite]]></category>
		<category><![CDATA[aplite]]></category>
		<category><![CDATA[boundaries]]></category>
		<category><![CDATA[chilled margin]]></category>
		<category><![CDATA[classification]]></category>
		<category><![CDATA[Cunyon Crags]]></category>
		<category><![CDATA[Dunmoor Hill]]></category>
		<category><![CDATA[felsic content]]></category>
		<category><![CDATA[granophyric]]></category>
		<category><![CDATA[hornfels]]></category>
		<category><![CDATA[intrusion sequence]]></category>
		<category><![CDATA[mafic content]]></category>
		<category><![CDATA[medium-grained porphyritic]]></category>
		<category><![CDATA[ring dyke]]></category>
		<category><![CDATA[thin-section]]></category>
		<category><![CDATA[vein]]></category>
		<guid isPermaLink="false">http://www.geologynorth.uk/?p=16875</guid>

					<description><![CDATA[<p>We go to Dunmoor Hill in search of Al-Hafdh’s hitherto elusive chilled margins. Dunmoor Hill is a particularly good site as exposure, unlike in many areas of the Cheviot hills, is plentiful. We are finding Al-Hafdh’s thesis on the Cheviot pluton immensely stimulating. It has provided clear direction to our own research, although we are &#8230; <a href="https://www.geologynorth.uk/dunmoor-hill/" class="more-link">Continue reading <span class="screen-reader-text">Dunmoor Hill</span> <span class="meta-nav">&#8594;</span></a></p>
<p>The post <a href="https://www.geologynorth.uk/dunmoor-hill/">Dunmoor Hill</a> appeared first on <a href="https://www.geologynorth.uk">Geology North</a>.</p>
]]></description>
										<content:encoded><![CDATA[<p>We go to Dunmoor Hill in search of Al-Hafdh’s hitherto elusive chilled margins. Dunmoor Hill is a particularly good site as exposure, unlike in many areas of the Cheviot hills, is plentiful. We are finding Al-Hafdh’s thesis on the Cheviot pluton immensely stimulating. It has provided clear direction to our own research, although we are beginning to doubt his proposal that the Cheviot pluton consisted of a series of ring dykes.<br />
The area below Cunyon Crags has plenty of small outcrops where we find a bewildering mixture of felsic and mafic fine-grained material. At first, we think that the mafic rock is altered andesite. However, thin sections show very well-developed granophyric texture in the felsic rock which imply late intrusion into already established plutonic bodies. The mafic rock has a very high biotite/opaque iron oxide content, and appears to be restite.<br />
Subsequently, we are able to trace the junction between the pink rock (Al-Hafdh’s Dunmoor type) and the more mafic Marginal rocks right across the south slope of Dunmoor Hill. The junction doesn&#8217;t show a clear cut boundary but it does present frequent inter-penetration of the two types. The implication is that neither type was fully consolidated when the intrusion took place.<br />
We are still unable to find any chilled margins to confirm an intrusion sequence. Finer rocks always turn out to be aplite veins or small dykes.</p>
<p>The post <a href="https://www.geologynorth.uk/dunmoor-hill/">Dunmoor Hill</a> appeared first on <a href="https://www.geologynorth.uk">Geology North</a>.</p>
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