The Cretaceous Igneous Province of Madagascar: Geochemistry and Petrogenesis of Lavas and Dykes from the Central-Western Sector   总被引：1，自引：0，他引：1  

MELLUSO  L.; MORRA  V.; BROTZU  P.; MAHONEY  J. J. 《Journal of Petrology》2001,42(7):1249-1278

The Cretaceous lava sequence and associated mafic dyke swarmin central–western Madagascar (Mailaka and Bemaraha areas)range in composition from picrite basalts to cordierite–orthopyroxene-bearingrhyodacites (MgO from 14 to 0·6 wt %). Petrographic andchemical data indicate the presence of both tholeiitic and transitionalmagma series, with variable degree of rare earth element enrichment[(La/Nd)_n = 1–1·4 for tholeiites vs (La/Nd)_n =0·65–1 for transitional rocks]. Initial (at 88Ma) ⁸⁷Sr/⁸⁶Sr and  相似文献   

Geochronology and Petrogenesis of the Cretaceous Antampombato-Ambatovy Complex and Associated Dyke Swarm, Madagascar   总被引：1，自引：0，他引：1  

MELLUSO  LEONE; MORRA  VINCENZO; BROTZU  PIETRO; TOMMASINI  SIMONE; RENNA  MARIA ROSARIA; DUNCAN  ROBERT A.; FRANCIOSI  LUIGI; D'AMELIO  FOSCO 《Journal of Petrology》2005,46(10):1963-1996

The Antampombato–Ambatovy complex is the largest intrusionin the central–eastern part of the Cretaceous flood basaltprovince of Madagascar, with an exposed surface area of about80 km². It has an ⁴⁰Ar/³⁹Ar incremental heating age of 89·9± 0·4 Ma and a U–Pb age of 90 ± 2Ma. The outcropping plutonic rocks range from dunite and wehrlite,through clinopyroxenite and gabbro, to sodic syenite. A dykeswarm cross-cutting some of the above lithologies (and the nearbyPrecambrian basement rocks) is formed of picritic basalts, alkalito transitional basalts, benmoreites and rhyolites; some ofthe latter are peralkaline. A few basaltic dykes have cumulateolivine textures, with up to 26 wt % MgO and 1200 ppm Ni, whereasothers have characteristics more akin to those of primitiveliquids (9 wt % MgO; Mg-number 0·61; 500 ppm Cr; 200ppm Ni). These basalts have relatively high TiO₂ (2·2wt %) and total iron (14 wt % as Fe₂O₃), and moderate contentsof Nb (10–11 ppm) and Zr (c. 100 ppm). Initial (at 90Ma) Sr- and Nd-isotope ratios of the clinopyroxenites and basaltdykes are 0·7030–0·7037 and 0·51290–0·51283,respectively. Syenites and peralkaline rhyolites have Sr- andNd-isotope ratios of 0·7037–0·7039 and 0·51271–0·51274,respectively. The data suggest derivation of the parental magmasfrom a time-integrated depleted mantle source, combined withsmall amounts of crustal contamination in the petrogenesis ofthe more evolved magmas. The isotopic compositions of the mafic–ultramaficrocks are most similar to those of the mid-ocean ridge basalt(MORB)-like igneous rocks of eastern Madagascar, and suggestthe existence of an isotopically ‘depleted’ componentin the source of the entire Madagascar province, even thoughthe Antampombato basalts are chemically unlike the lavas anddykes with the same depleted isotopic signature found in westernMadagascar. If this depleted component is plume-related, thissuggests that the plume has a broadly MORB-source mantle composition.The existence of isotopically more enriched magma types in theMadagascan province has several possible petrogenetic explanations,one of which could be the interaction of plume-related meltswith the deep lithospheric mantle beneath the island. KEY WORDS: geochronology; flood basalts; Antampombato–Ambatovy intrusion; Cretaceous; Madagascar  相似文献   

Constraints on the Mantle Sources of the Deccan Traps from the Petrology and Geochemistry of the Basalts of Gujarat State (Western India)   总被引：6，自引：3，他引：3  

MELLUSO  L.; BECCALUVA  L.; BROTZU  P.; GREGNANIN  A.; GUPTA  A. K.; MORBIDELLI  L.; TRAVERSA  G. 《Journal of Petrology》1995,36(5):1393-1432

The late Cretaceous-early Tertiary flood basalts in the Gujaratarea of the northwestern Deccan Traps (Kathiawar peninsula,Pavagadh hills and Rajpipla) exhibit a wide range of compositions,from picrite basalts to rhyolites; moreover, the basaltic rockshave clearly distinct TiO₂ contents at any given degree of differentiationand strongly resemble the low-titanium and hightitanium basaltsfound in most of the Gondwana continental flood basalt (CFB)suites. Four magma groups are petrologically and geochemicallydistinguished: (1) A low-Ti group, characterized by rocks with varying SiO²saturation, and with TiO₂ <1•8 wt%, extremely low incompatibletrace element abundances, low Zr/ (av- 3•8), Ti/ V (av.27), and a very slight large ion lithophile element (LJLE) enrichmentover high field strength elements (HFSE). These rocks sharesome features with the Bushe Formation of the Western Ghatsfarther south, but have distinct geochemical characters, inparticular the strong depletion in most incompatible trace elements. (2) A high-Ti group, characterized by a more K-rich characterthan the low-Ti rocks, and with a strong enrichment in incompatibleelements, similar to average ocean island basalt (OIB), e.g.high TiO₂ (>1•8 wt% in picrites), Nb (>19 p.p.m.)Zr/ (av. 6•5) and Tt/V (av. 47). (3) An intermediate-Ti group, with TiO₂ contents slightly lowerthan the high-Ti rocks at the same degree of evolution, andwith correspondingly lower incompatible trace element contentsand ratios, in particular K₂O, Nb, Ba and Zr/Y (av. 5•2). (4) A potassium-rich group (KT), broadly similar in geochemicalcharacter to the high-Ti group but showing more extreme K, Rband Ba enrichment (av. K₂0/Na₂0l; Ba/Y20). The most primitive low-Ti and high-Ti picrites, when correctedfor low-pressure olivine fractionation, show distinct major(and trace) element geochemistry, in particular for CaO/AI₂O₃,CaO/TiO₂ and Al₂O₃/TiO₂, and moderate but significant variationsin their SiO₂ and Fe₂O_st contents; these characteristics stronglysuggest the involvement of different mantle sources, more depletedfor the low-Ti picrites, and richer in cpxfor the high-Ti picrites,but with broadly the same pressures of equilibration (27–14kbar). This, in turn, suggests a strong lateral heterogeneityin the Gujarat Trap mantle. Low-Ti picrites and related differentiatesin Kathiawar are reported systematically for the first timehere, and suggest the existence of HFSE-depleted mantle in thenorthwestern Deccan Traps, with extension at least to the SeychellesIslands and to the area of the Bushe Formation near Bombay inthe pre-drift position, before the development of the CarlsbergRidge. The absence of correlations between LILE/HFSE ratiosand SiO₂ argues against crustal contamination processes actingon the low-Ti picrites, possibly owing to their probably rapiduprise to the surface. Consequently, the mantle region of thisrock group was probably re-enriched by small amounts of ULE-richmaterials. The substantially higher, trace element enrichmentof the least differentiated high-Ti picrites, relative to thebasalts of the Ambe-noli and Mahableshwar Formations of theWestern Ghats, testifies also to the presence of more incompatibleelement rich, OIB4ike mantle sources in northern and northwesternGujarat. These sources were geochemicaily similar to the present-dayReunion mantle sources. KEY WORDS: Deccan Traps; geochemistry; petrology; picrite basalts; western India ^*Corresponding author, e-mail: mellujo{at}ds.cued.unina.it  相似文献