VOLCANISM AND EVOLUTION OF THE AFRICAN LITHOSPHERE

By KAREN MARTINEZ

CONTENTS 1 LATE MESOZOIC TO QUATERNARY INTRAPLATE MAGMATISM AND ITS RELATION TO THE NEOPROTEROZOIC LITHOSPHERE IN NE AFRICA—NEW DATA FROM LOWER-CRUSTAL AND MANTLE XENOLITHS FROM THE BAYUDA VOLCANIC FIELD, SUDAN 2 HOLOCENE OPENING DIRECTIONS ALONG THE AXES OF THE RED SEA (AFAR) AND MAIN ETHIOPIAN RIFTS: AN OVERVIEW 3 THE UPPER-MANTLE LOW-VELOCITY ANOMALY BENEATH ETHIOPIA, KENYA, AND TANZANIA: CONSTRAINTS ON THE ORIGIN OF THE AFRICAN SUPERSWELL IN EASTERN AFRICA AND PLATE VERSUS PLUME MODELS OF MANTLE DYNAMICS 4 THE ETHIOPIA AFAR GEOSCIENTIFIC LITHOSPHERIC EXPERIMENT (EAGLE): PROBING THE TRANSITION FROM CONTINENTAL RIFTING TO INCIPIENT SEAFLOOR SPREADING 5 PERIDOTITE XENOLITHS FROM ETHIOPIA: INFERENCES ABOUT MANTLE PROCESSES FROM PLUME TO RIFT SETTINGS 6 EVOLUTION OF THE LITHOSPHERIC MANTLE BENEATH THE EAST AFRICAN RIFT IN TANZANIA AND ITS POTENTIAL SIGNATURES IN RIFT MAGMAS 7 PETROLOGY AND GEOCHEMISTRY OF ALKALINE LAVA SERIES, KILIMANJARO, TANZANIA: NEW CONSTRAINTS ON PETROGENETIC PROCESSES 8 TRACE-ELEMENT DISTRIBUTION BETWEEN COEXISTING AQUEOUS FUMAROLE CONDENSATES AND NATROCARBONATITE LAVAS AT OLDOINYO LENGAI VOLCANO, TANZANIA 9 CAMEROON LINE ALKALINE MAGMATISM (CENTRAL AFRICA): A REAPPRAISAL 10 MINERALOGICAL AND GEOCHEMICAL FINGERPRINTS OF MANTLE METASOMATISM BENEATH NYOS VOLCANO (CAMEROON VOLCANIC LINE) 11 DOLOMITIC VOLCANISM IN ZAMBIA: CR AND K SIGNATURES AND COMPARISONS WITH OTHER DOLOMITIC MELTS FROM THE MANTLE 12 POST-PALEOZOIC MAGMATISM IN ANGOLA AND NAMIBIA: A REVIEW 13 IS THE AFRICAN CRATONIC LITHOSPHERE WET OR DRY? 14 NEW 40AR-39AR AGES AND PETROGENESIS OF THE MASSIF D’AMBRE VOLCANO, NORTHERN MADAGASCAR 15 METASOMATISM VERSUS HOST MAGMA INFILTRATION: A CASE STUDY OF SAL MANTLE XENOLITHS, CAPE VERDE ARCHIPELAGO 16 MAGMATIC EVIDENCE FOR AFRICAN MANTLE PROPAGATION INTO THE SOUTHERN TYRRHENIAN BACKARC REGION LATE MESOZOIC TO QUATERNARY INTRAPLATE MAGMATISM AND ITS RELATION TO THE NEOPROTEROZOIC LITHOSPHERE IN NE AFRICA— NEW DATA FROM LOWER-CRUSTAL AND MANTLE XENOLITHS FROM THE BAYUDA VOLCANIC ? ELD, SUDAN ABSTRACT A VARIETY OF XENOLITHS FROM THE LOWER CRUST TO MANTLE TRANSITION OCCUR IN QUA- TERNARY MA? C INTRAPLATE LAVAS OF THE BAYUDA VOLCANIC ? ELD OF NORTHERN SUDAN THE LOWER-CRUST XENOLITHS INCLUDE PLAGIOCLASE- AND GARNET-BEARING MA? C GRANULITE ULTRA- MA? C GARNET-BEARING PYROXENITE, WEBSTERITE, HORNBLENDITE, AND DISTINCT PERIDOTITE XENOLITHS ARE FROM THE UPPER LITHOSPHERIC MANTLE SR, ND, AND PB ISOTOPE SIGNATURES DISTINGUISH BETWEEN ULTRAMA? C AND GRANULITE XENOLITHS THE LATTER SHOW A STRONG COM- POSITIONAL AF? NITY TO JUVENILE NEOPROTEROZOIC CRUST THE PB ISOTOPE COMPOSITION OF THE ULTRAMA? C XENOLITHS RESEMBLES THE DISTINCT HIGH-µ SIGNATURE (206PB/204PB >195) OF THEIR HOST BASANITE THESE XENOLITHS MAY REPRESENT CUMULATES OF LATE MESOZOIC TO QUATERNARY MA? C INTRAPLATE MAGMATISM THE FELSIC UPPER CRUST IN A SCHEMATIC LITHOSPHERIC PRO? LE OF THE BAYUDA AREA INCLUDES PREDOMINANTLY GRANITOIDS, MIGMA- TITES, AND METASEDIMENTARY ROCKS THAT REPRESENT REWORKED OLD CRATONIC OR JUVENILE NEOPROTEROZOIC ROCKS THE DEEP LOWER CRUST IS REPRESENTED BY MA? C GRANULITE, LIKELY CUMULATE ROCKS FROM NEOPROTEROZOIC JUVENILE MAGMATISM THE CRUST-MANTLE TRANSI- TION IS CHARACTERIZED BY ULTRAMA? C CUMULATE ROCKS POSSIBLY FROM THE LATE MESOZOIC TO QUATERNARY MAGMATISM THE PERIDOTITES OF THE SAME XENOLITH SUITES REPRESENT TYPICAL LITHOSPHERIC MANTLE WITH VARIABLE DEGREES OF DEPLETION BY MELT EXTRACTION MEDITERRANEAN SEA ARABIAN PLATE CA 38 - 155 MA SUDAN RED SEA NILE EGYPT AFAR YEMEN 30° 20° 10°N 40° 30°E 0 KM 500 KM BAYUDA BAYUDA CA 1 - 4 MA CA 1 - 4 MA BAYUDA CA 1 - 4 MA REWORKED CRATON CA 20 - 80 MA CA 20 - 80 MA CA 03 - 38 MA CA 03 - 38 MA CA 20 - 80 MA CA 03 - 38 MA JUVENILE JUVENILE CRUST CRUST JUVENILE CRUST CA 33 MA CA 33 MA CA 33 MA A B ETHIOPIAN-YEMENITE ETHIOPIAN-YEMENITE FLOOD BASALTS FLOOD BASALTS ETHIOPIAN-YEMENITE FLOOD BASALTS FIGURE 1 (A) DISTRIBUTION AND AGES OF INTRAPLATE MAGMATISM IN NE AFRICA AND OCCURRENCES OF INTRAPLATE VOLCANISM ON THE WESTERN ARABIAN PLATE AND THE ETHIOPIAN-YEMENITE “AFAR” ? OOD BASALT PROVINCE (COMPILED FROM SCHANDELMEIER AND REYNOLDS, 1997; BERTRAND ET AL, 2003; SHAW ET AL, 2003) THE NEOPROTEROZOIC BASEMENT IS SUBDIVIDED BY THE THICK GRAY LINE INTO MAINLY REWORKED PALEOPROTEROZOIC CRATON (WEST) AND MAINLY NEOPROTEROZOIC JUVENILE CRUST (EAST; EG, KÜSTER AND LIÉGEOIS, 2001; ABDELSALAM ET AL, 2002) (B) ENLARGED MAP FROM THE BAYUDA MAIN VOLCANIC ? ELD SAMPLE LOCATIONS OF THE LOWER CRUST XENOLITHS ARE INDICATED (TABLE 1) BLANK AREAS ARE THIN COVER OF SEDIMENTARY ROCKS OR METAMORPHIC-MAGMATIC BASEMENT VOLCANISM AND EVOLUTION OF THE AFRICAN LITHOSPHERE