| dc.creator |
Willcox, Alistair |
|
| dc.creator |
Buisman, Iris |
|
| dc.creator |
Sparks, R. S. J. |
|
| dc.creator |
Brown, R. J. |
|
| dc.creator |
Manya, Shukrani |
|
| dc.creator |
Schumacher, J. C. |
|
| dc.creator |
Tuffen, Hugh |
|
| dc.date |
2016-03-04T09:11:16Z |
|
| dc.date |
2016-03-04T09:11:16Z |
|
| dc.date |
2015-06-05 |
|
| dc.date.accessioned |
2018-03-27T08:56:48Z |
|
| dc.date.available |
2018-03-27T08:56:48Z |
|
| dc.identifier |
Willcox, A., Buisman, I., Sparks, R.S.J., Brown, R.J., Manya, S., Schumacher, J.C. and Tuffen, H., 2015. Petrology, geochemistry and low-temperature alteration of lavas and pyroclastic rocks of the kimberlitic Igwisi Hills volcanoes, Tanzania. Chemical Geology, 405, pp.82-101. |
|
| dc.identifier |
10.1016/j.chemgeo.2015.04.012 |
|
| dc.identifier |
http://hdl.handle.net/123456789/592 |
|
| dc.identifier.uri |
http://hdl.handle.net/123456789/3983 |
|
| dc.description |
Geochemical data are presented for the kimberlitic Holocene Igwisi Hills volcanoes (IHV), Tanzania, which preserve extra-crater lavas and pyroclastic rocks. Their young age and exceptional preservation enable investigation of kimberlite magma compositions and alteration pathways of kimberlites. The IHV lavas have a variable matrix assemblage dominated by calcite, olivine and a serpentine-like mineral (termed serpentine-X). Minor primary groundmass phases include apatite, phlogopite, monticellite, perovskite and spinel representing late-stage crystalisation. Secondary phases include hydrogarnet, a mixed-layer chlorite–vermiculite–montmorrilonite, minor brucite and low-temperature oxides and clays such as goethite and jamborite. The matrix of pyroclastic rocks is dominated by calcite with fewer groundmass phases. The parental magmas are inferred to have had ~ 21 wt.% SiO2, ~ 22 wt.% CaO, ~ 23 wt.% MgO and Mg# ~ 70. The IHV are classified as calcite kimberlites. The total volatile concentrations of the primary melt are ~ 14 wt.%, which predominantly consists of CO2 although the H2O content is also high. Whole-rock geochemical analyses indicate minor crustal contamination, low-temperature alteration and weathering. Pervasive serpentinisation in both lavas and pyroclastic rocks results from low-temperature alteration induced by the circulation of meteoric waters during cooling. Serpentine-X is potentially a new mineral and is richer in Al2O3 and FeO and poorer in SiO2 than published analyses of serpentine minerals. These compositions are attributed to a 1:2 mixture of serpentine and hydrotalcite. We propose that serpentine-X has replaced a reactive, late stage residual silicate glass, the existence of which helps explain the presence of vesicular scoria (similar to glassy basaltic pyroclasts) and viscous kimberlite lavas. |
|
| dc.language |
en |
|
| dc.publisher |
Elsevier |
|
| dc.subject |
Extrusive kimberlite |
|
| dc.subject |
Igwisi Hills |
|
| dc.subject |
Serpentine |
|
| dc.subject |
Geochemistry |
|
| dc.subject |
Petrology |
|
| dc.title |
Petrology, geochemistry and low-temperature alteration of lavas and pyroclastic rocks of the kimberlitic Igwisi Hills volcanoes, Tanzania |
|
| dc.type |
Journal Article |
|