Hugh Rollinson

Bio: Hugh Rollinson is an academic researcher from University of Derby. The author has contributed to research in topics: Granulite & Archean. The author has an hindex of 33, co-authored 82 publications receiving 6190 citations. Previous affiliations of Hugh Rollinson include University of Leeds & University of Leicester.

Using Geochemical Data : Evaluation, Presentation, Interpretation

Abstract: 1. Geochemical Data 2. Selection Methods 3. Controls and Sources of Errors 4. Analysis of Geochemical Data 5. Using Major Element Data 6. Using Trace Elements Data 7. Discriminating Between Tectonic Environments Using Data 8. Using Radiogenic Isotopes and Isotope Data

The geochemistry of mantle chromitites from the northern part of the Oman ophiolite: inferred parental melt compositions

Abstract: Chromitites from a single section through the mantle in the Oman ophiolite are of two different types. Low-cr# chromitites, of MORB affinity are found in the upper part of the section, close to the Moho. High-cr# chromitites, with arc affinities are found deeper in the mantle. Experimental data are used to recover the compositions of the melts parental to the chromitites and show that the low-cr# chromitites were derived from melts with 14.5–15.4 wt% Al2O3, with 0.4 to 0.9 wt% TiO2 and with a maximum possible mg# of 0.76. In contrast the high-cr# chromitites were derived from melts with 11.8–12.9 wt% Al2O3, 0.2–0.35 wt% TiO2 and a maximum melt mg# of 0.785. Comparison with the published compositions of lavas from the Oman ophiolite shows that the low-cr# chromitites may be genetically related to the upper (Lasail, and Alley) pillow lava units and the high-cr# chromitites the boninites of the upper pillow lava Alley Unit. The calculated TiO2–Al2O3 compositions of the parental chromitite magmas indicate that the high-cr# chromitites were derived from high-Ca boninitic melts, produced by melting of depleted mantle peridotite. The low-cr# chromitites were derived from melts which were a mixture of two end-members—one represented by a depleted mantle melt and the other represented by MORB. This mixing probably took place as a result of melt–rock reaction.

Eclogite xenoliths in west African kimberlites as residues from Archaean granitoid crust formation

Abstract: Eclogites are a comparatively rare but petrologically important member of kimberlite xenolith suites. Their broadly basaltic chemistry has led many authors to propose that they represent ancient, subducted ocean crust1,2,3. Recent studies4,5,6, however, have suggested an alternative origin and propose that kimberlitic eclogites are residues from the process of Archaean granitoid crust formation. Geochemical arguments in support of this new model were previously based on the trace-element chemistry of eclogitic minerals. Here I report that the major-element chemistry of eclogite xenoliths also supports a crustal residue model. I examine eclogite xenoliths from kimberlite pipes at Koidu, Sierra Leone, which sample the lithospheric mantle underlying the Archaean (2.8 Gyr) granitoid crust of the West African craton. Geochemical plots of major elements measured in unaltered, whole-rock samples of low-silica eclogite demonstrate that they are complementary to the granitoids of the West African craton and have compositions which indicate that both were derived from a common basaltic parent rock.

A model for Trondhjemite-Tonalite-Dacite Genesis and crustal growth via slab melting: Archean to modern comparisons

Abstract: The petrogenesis of trondhjemite-tonalite-dacite (TTD) involves all major petrologic models in various tectonic settings. A specific subtype of TTD, high-Al type, is the one most commonly associated with Archean gneiss terranes. During the Archean, continental crust formation was operating at an elevated rate relative to the Phanerozoic, and the generation of high-Al TTD played an integral role in its nucleation and growth. High heat flow, rapid convection, and subduction of hotter, smaller plates were unique tectonic elements to the Archean which optimized conditions required for transformation of subducted oceanic crust into sial via partial melting. Anatexis of Archean mid-ocean ridge basalt (MORB) under eclogitic to garnet amphibolitic conditions produced weakly peraluminous to metaluminous high-Al TTD with low heavy rare earth elements (HREE), Y, Nb, K/Rb, and Rb/Sr and high La/Yb and Sr/Y. This study demonstrates that Archean TTD crustal generation processes are also present in selected high-Al Phanerozoic TTD terranes. The Cenozpic high-Al TTD suites are commonly found in tectonic settings which are thought to recreate the elevated Archean thermal gradients, i.e., at sites of young, hot oceanic plate subduction. These relationships imply a petrologic continuity of TTD generation through time. A fertile zone of melting is envisioned at 23–26 kbar (75–85 km) and 700–775°C, where wet partial melting of the subducting slab occurs concurrently with dehydration reactions. At this depth, the converting mantle wedge continuously feeds hot mantle material to the wedge-slab interface, creating strong temperature gradients, intraslab fluid migration, and slab melting. In summary, in modern arc terranes where young ( 30 Ma) oceanic crust is subducted, mantle-derived magmas are dominant, giving rise to basaltandesite-dacite-rhyolite (BADR) fractionation suites. This study introduces the importance of subducted oceanic crustal age on arc petrogenesis.