Bernard Elgey Leake

Nomenclature of amphiboles : additions and revisions to the International Mineralogical Association's amphibole nomenclature

The introduction of a fifth amphibole group, the Na-Ca-Mg-Fe-Mn-Li group, defined by 0.50 < B(Mg,Fe2+,Mn2+,Li) < 1.50 and 0.50 ≤ B(Ca,Na) ≤ 1.50 a.f.p.u. (atoms per formula unit), with members whittakerite and ottoliniite, has been required by recent discoveries of B(LiNa) amphiboles. This, and other new discoveries, such as sodicpedrizite (which, here, is changed slightly, but significantly, from the original idealized formula), necessitate amendments to the IMA 1997 definitions of the Mg-Fe-Mn-Li, calcic, sodic-calcic and sodic groups. The discovery of obertiite and the finding of an incompatibility in the IMA 1997 subdivision of the sodic group, requires further amendments within the sodic group. All these changes, which have IMA approval, are summarized.

Geodynamic significance of early orogenic high-K crustal and mantle melts: example of the Corsica batholith

Early post-collision Variscan magmatism in Corsica, France was characterised by high-K granitic intrusions of Namurian age. They consist of quartz-monzonites, monzogranites and leuco-monzogranites associated with vaugnerite (meladiorites or hornblende–biotite diorites) intrusive stocks and enclaves. The composition of the vaugnerites shows that they originated from slowly cooled syn-magmatically amphibolitized lamprophyric magmas probably derived from enriched mantle melts that were injected into the lower crust and contributed to its extensive anatexis giving the high-K granitic melts. Deep-seated interactions between felsic and mafic magmas were responsible for the common characteristics of both magma suites. The granitoid suite is characterised by: high K and Mg contents; relatively high concentrations of Th, Rb, Sr and Ba; (La/Yb)N from 10 to 20; LREE enrichments (LaN≈100–300); Sri≈0.707; δ18O≈6; eNd≈−3.5 to −2.5. The Mg-rich minerals of the high-K plutonic suite and the vaugnerites constrain emplacement conditions to: 270±100 MPa (Al-in-hornblende geobarometer), 675±25 °C (solidus temperature), logfO2≈−16 and H2O contents in the range 3–4 wt.%. K-rich magmatism of Carboniferous age mostly occurs in two parallel belts in the high grade zones of the Variscan orogen. It is interpreted as resulting from continental crust–mantle interactions under high-pressure conditions (≈1.5 GPa). The chemical evolution of post-collision plutonism is explained in terms of mantle–crust interactions at decreasing depths during post-orogenic extension.

Stoping and the mechanisms of emplacement of the granites in the Western Ring Complex of the Galway granite batholith, western Ireland

The western end of the Galway granite batholith demonstrates the importance of stoping as a granite emplacement process, which is currently controversial, and also of space generation by uplift of the centre of a ring complex. The granite rings are shown (with a coloured 1:25 000 geological map) to be consanguineous, near coeval, and older than the 407–410 Ma late molybdenite mineralisation. A newly-recognised Mace–Ards granite, around and injected by the Aplitic Murvey-type granite of the ring core (both lacking hornblende and titanite), has biotite–muscovite–cordierite orbs and sulphide–granite orbs, showing separation of immiscible hydrous and sulphide fluids from the late magma which, with vugs, indicates a low pressure, near-roof site. The outer ring of the Errisbeg Townland granite (ETG, the main batholith granite with K-feldspar phenocrysts), was emplaced by progressive outward stoping of the country rock metagabbro, as shown by mapping, and by chemical fractionation of feldspars, biotites and bulk rocks, to the marginal, dry, fine-grained aphyric, in part garnetiferous, highly fractionated, siliceous Murvey granite. Stoping ceased when, after previously invading dense metagabbro, the outer ring complex reached the low-density Roundstone granite, which is shown for the first time to be older than the Galway batholith. This arresting of the batholith intrusion shows that stoping was such a significant process that emplacement ceased when stoping became impossible. The inside edge of the ETG grades into the slightly later, intrusive, aphyric Carna granite, which shows inward fractionation to the wet magma of the Mace–Ards granite. The ring complex core was injected by highly fractionated, dry, Aplitic Murvey-type granite, intensely hydrothermally altered by late magmatic water. The radially outward dipping, inclined igneous layering in the ETG shows that the original ETG centre was pushed upwards by the intruded Carna granite and eroded away. The Galway granite and its nearby magmatism matches the low Ba and Sr, high Th and Rb, Scottish Cairngorm Suite and similarly has few appinitic rocks associated with it. Magmatism extended over >45 Myr from ∼425 Ma to 380 Ma. It originated by slab breakoff and consequent rise of the asthenosphere, causing deep crustal melting.

Mechanism of emplacement and crystallisation history of the northern margin and centre of the Galway Granite, western Ireland

The main phase (~400 Ma) emplacement of the central and northern part of the reversely zoned Galway Granite was incremental by progressive northward marginal dyke injection and stoping of the 470–467 Ma Connemara metagabbro-gneiss country rock. The space was provided by the synchronous ESE-opening, along the strike of the country rocks, of extensional fractures generated successively northward by a releasing bend in the sinistrally moving Skird Rocks Fault or an equivalent Galway Bay Fault. This fault is a prolongation of the Antrim–Galway (a splay off the Highland Boundary Fault) and Southern Upland Faults. The ESE-strike of the spalled-off rocks controlled the resultant ESE-elongated shape of the batholith. The magma pulses (~5–30 m in thickness) were progressively more fractionated towards the northern margin so that the coarse Porphyritic (or Megacrystic) Granite (GP; technically granodiorite) in the centre was followed outwards by finer grained, drier and more siliceous granite, until the movements opening the fractures ceased and the magma became too viscous to intrude. ‘Out-of-sequence’ pulses of more basic diorite-granodiorite (including the Mingling–Mixing Zone) and late main phase, more acid, coarse but Aphyric Granite, into the centre of the batholith, complicated the outward fractionation scheme. The outward expansion, caused by the intrusions into the centre, caused a foliation and flattening of cognate xenoliths within the partly crystallised northern marginal granite and in the Mingling–Mixing Zone to the south. Late phase (~380 Ma) central intrusions of the newly-discovered aphyric Shannapheasteen Finegrained Granite (technically granodiorite), the Knock, the Lurgan and the Costello Murvey Granites, all more siliceous and less dense than the GP, were emplaced by pushing up the already solid and jointed GP along marginal faults. This concentration of lighter granites plus compression shown in thrusting, caused overall fault uplift of the Central Block of the Galway batholith so that the originally deepest part of the GP is exposed where there is the most late phase granite. Chemical analyses show the main and late phase magmas, including late dykes, were very similar, with repetition of the same fractionation except that the late phase magmas were drier and more quickly cooled, giving finer grained rocks.

The anhydrous amphibole ungarettiite from the Woods mine, New South Wales, australia

We report ungarettiite from the Woods mine, New South Wales, Australia; this is the second known occurrence. Electron-microprobe and ion-probe analyses show it to be very close to end-member composition, NaNa 2 Mn 2+ 2 Mn 3+ 3 Si 8 O 22 O 2 . We record the first direct determination of H 2 O (