Compositionally-Diverse Miocene—Recent Rift-Related Magmatism in Northwest Colorado: Partial Melting, and Mixing of Mafic Magmas from 3 Different Asthenospheric and Lithospheric Mantle Sources
Compositionally-Diverse Miocene—Recent Rift-Related Magmatism in Northwest Colorado: Partial Melting, and Mixing of Mafic Magmas from 3 Different Asthenospheric and Lithospheric Mantle Sources
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DOI：
10.1093/petrology/special_volume.1.351
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发表时间：
1988
影响因子：
3.9
通讯作者：
P. Leat;R. Thompson;M. A. Morrison;G. Hendry;A. Dickin
中科院分区：
文献类型：
--
作者：
P. Leat;R. Thompson;M. A. Morrison;G. Hendry;A. Dickin
26-8百万年格兰德河裂谷向科罗拉多西北部的扩展BP伴随着不同的元素和同位素组成的镁铁质岩浆喷发。火山岩在两个中新世时期（24-20和13.4 - 7.5百万年）爆发。BP），并在第四纪（200万年。BP-4000 BP）。三个镁铁质岩浆端员组成被确定，这是没有相互联系的分离结晶或同化地壳。大多数火山岩代表两个或三个这些端元的杂交，虽然这种混合的结构证据通常是缺乏的。第1组端员是玄武岩，来自OIB源软流圈地幔的部分熔融。第3组端员主要为碱性玄武岩，是软流圈部分熔融，洋壳俯冲改造的产物。第1组源地幔代替第3组源地幔作为11.6 -10百万年区域之下的软流层。BP，但第3组岩浆继续喷发到第四纪。软流圈的这种替换比北美板块西缘大洋岩石圈俯冲的停止晚了约1000万年。第2组端员为矿物，其143 Nd/144 Nd和87 Sr/86 Sr比值与古蒙大拿-怀俄明钾质区相当。这些矿岩被认为是亚科罗拉多岩石圈地幔的部分熔融。第2组岩浆在整个24百万年期间可作为混合的端元。BP到现在，但黑云母-斑状minettes喷发仅在此期间。11.6 - 7.5百万年。BP，在科罗拉多西北部的主要裂谷事件期间。
Propagation of the Rio Grande rift into northwest Colorado at 26–8 m.y. BP was accompanied by eruption of mafic magmas with varied elemental and isotopic compositions. The volcanic rocks were erupted during two Miocene episodes (24–20 and 13·4–7·5 m.y. BP), and in the Quaternary (2 m.y. BP–4000 BP). Three mafic magma end-member compositions are identified which were not related to each other by fractional crystallization or assimilation of crust. Most of the volcanic rocks represent hybrids of two or three of these end-members, although textural evidence for such mixing is normally absent. Group 1 end-members are basanites, derived by partial melting of an OIB-source asthenospheric mantle. Group 3 end-members are mainly alkali basalts, derived by partial melting of asthenosphere modified by subduction of oceanic lithosphere. Group 1 source mantle replaced Group 3 source mantle as the asthenosphere underlying the region 11·6–10 m.y. BP, but Group 3 magmas continued to be erupted into the Quaternary. This replacement of asthenosphere post-dated cessation of subduction of oceanic lithosphere at the west margin of the North America plate by about 10 m.y. Group 2 end-members are minettes, with143Nd/144Nd and87Sr/86Sr ratios comparable to those of the Cretaceous-Recent Montana-Wyoming potassic province. These minettes are thought to represent partial melts of sub-Colorado lithospheric mantle. Group 2 magmas were available as end-members for mixing during the entire period 24 m.y. BP to the present, but biotite-phyric minettes were erupted only during the periodc.11·6–7·5 m.y. BP, during the main rifting event in northwest Colorado.