Initial Cenozoic Magmatic Activity in East Africa: New Geochemical Constraints on Magma Distribution within the Eocene Continental Flood Basalt Province

2021 ◽  
pp. SP518-2020-262
Author(s):  
R. Alex Steiner ◽  
Tyrone O. Rooney ◽  
Guillaume Girard ◽  
Nick Rogers ◽  
Cynthia Ebinger ◽  
...  
Keyword(s):  
Shear Velocity ◽  
Flood Basalt ◽  
Main Phase ◽  
Large Igneous Province ◽  
Southern Ethiopia ◽  
East African ◽  
Continental Flood Basalt ◽  
Content Type ◽  
Supplementary Material ◽  
African Rift

AbstractThe initial interaction between material rising from the African Large Low Shear Velocity Province and the African lithosphere manifests as the Eocene continental large igneous province (LIP), centered on southern Ethiopia and northern Kenya. Here we present a geographically well-distributed geochemical dataset comprising the flood basalt lavas of the Eocene continental LIP to refine the regional volcano-stratigraphy into three distinct magmatic units: (1) the highly-alkaline small-volume Akobo Basalts (49.4–46.6 Ma), representing the initial phase of flood basalt volcanism derived from the melting of lithospheric-mantle metasomes, (2) the primitive and spatially restricted Amaro Basalts (45.2–39.58 Ma) representing the early main phase of flood basalt volcanism derived from the melting of the upwelling thermochemical anomaly, and (3) the spatially extensive Gamo-Makonnen magmatic unit (38-28 Ma) representing the mature main phase of flood basalt volcanism that has undergone significant processing within the lithosphere resulting in relatively homogeneous compositions. The focused intrusion of these main phase magmas over 10 m.y. preconditioned the African lithosphere for the localization of strain during subsequent episodes of lithospheric stretching. The focusing of strain into the region occupied by this continental LIP may have contributed to the initial extension in SW Ethiopia associated with the East African Rift.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5557626

Geochemical, petrographic, and stratigraphic analyses of the Portage Lake Volcanics of the Keweenawan CFBP: implications for the evolution of Main stage volcanism in Continental Flood Basalt Provinces

2021 ◽  
pp. SP518-2020-221
Author(s):  
W. R. Davis ◽  
M. A. Collins ◽  
T. O. Rooney ◽  
E. L. Brown ◽  
C. A. Stein ◽  
...  
Keyword(s):  
Trace Elements ◽  
Flow Analysis ◽  
Flood Basalt ◽  
Lava Flows ◽  
Rift System ◽  
Main Stage ◽  
Continental Flood Basalt ◽  
Content Type ◽  
Supplementary Material ◽  
Incompatible Trace Elements

AbstractContinental Flood Basalt Provinces (CFBPs) are large igneous features formed by the extrusion of massive amounts of lavas that require significant evolution within the lithosphere. Although sequential lava flows are effective probes of magmatic systems, CFBPs are typically poorly preserved. We focus on lava flows from the well-preserved 1.1 Ga Keweenawan CFBP that erupted within the Midcontinent Rift System. We present a new geochemical, petrographic, and stratigraphic synthesis from the Main stage Portage Lake Volcanics (PLV). Flow-by-flow analysis of the PLV reveals that major element behavior is decoupled from trace element behavior; MgO exhibits limited variability, while compatible and incompatible trace elements deviate from high to low concentrations throughout the sequence. The concentrations of incompatible trace elements slightly decrease from the base of the sequence to the top. We investigate these observations by applying a recharge, evacuation, assimilation, and fractional crystallization model to geochemical and petrographic data. Our modelling demonstrates a magmatic system experiencing increased evacuation rates while fractionation and assimilation rates decrease, indicating an increase in magmatic flux. The outcome of this modelling is a progressively more efficient magma system within the PLV. This study highlights the utility of joint petrographic and geochemical interpretation in constraining CFBP magma evolution.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5424758

Timing of East African Rift development in southern Ethiopia: Implication for mantle plume activity and evolution of topography

Geology ◽  
2008 ◽  
Vol 36 (2) ◽  
pp. 167 ◽  
Author(s):  
Raphaël Pik ◽  
Bernard Marty ◽  
Jean Carignan ◽  
Gezahegn Yirgu ◽  
Teklewold Ayalew
Keyword(s):  
Mantle Plume ◽  
East African Rift ◽  
Southern Ethiopia ◽  
East African ◽  
African Rift

Low-Ti gabbroic pluton in Dali, SW China: new evidence for back-arc lithospheric melting inducing the early-stage magmatism of the Emeishan large igneous province

2021 ◽  
pp. jgs2020-224
Author(s):  
Bei Zhu ◽  
Zhaojie Guo ◽  
Shaonan Zhang ◽  
Ning Ye ◽  
Ziye Lu ◽  
...  
Keyword(s):  
Early Stage ◽  
Large Igneous Province ◽  
Spinel Peridotite ◽  
Heavy Rare Earth Element ◽  
Content Type ◽  
Igneous Province ◽  
Supplementary Material ◽  
Back Arc ◽  
Emeishan Lip ◽  
Yangtze Plate

The latest studies proved contribution of the Emeishan mantle plume (the widely-regarded origin of the Emeishan LIP in the western Yangtze Plate. LIP: large igneous province) to the Palaeo-Tethys subduction. However, whether the Palaeo-Tethys subduction oppositely affected the formation of the Emeishan LIP remains poorly understood. Here, we report geochronological, petrological, geochemical and isotopic studies of a gabbroic intrusion in this LIP, located in Jiangwei, the Dali area. The gabbro has a weighted mean SHRIMP U-Pb age of ∼262 Ma. Key geochemical features include Nb, Ta and Ti depletion; Th, U and Sr enrichment, low light/heavy rare earth element ratios and ∼0.707 87Sr/86Sr(t) and ∼-0.21 εNd(t) values. We conducted pMELTS thermodynamic modeling and batch melting calculations to evaluate the origin and evolution of the gabbro, based on real components of low-Ti picrites and xenolith of the Yangtze lithosphere. The results support 3% melting of a hydrated spinel peridotite source from the Yangtze lithosphere can produce magma equivalent to the gabbro components. Integrating this conclusion with tectonic background of the western Yangtze Plate and volcano-stratigraphic record of the Emeishan LIP, we infer the early-stage magmatism of the Emeishan LIP was triggered by Paleo-Tethys back-arc extension with fluid modification from subductional slab.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5433267

Petrology and Nd-Sr isotopic composition of alkaline lamprophyres from the Early to Late Cretaceous Mundwara alkaline complex, NW India: Evidence of crystal fractionation, accumulation and corrosion in a complex magma chamber plumbing system

2021 ◽  
pp. SP513-2020-175
Author(s):  
Abhinay Sharma ◽  
Samarendra Sahoo ◽  
N. V. Chalapathi Rao ◽  
B. Belyatsky ◽  
P. Dhote ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Crystal Fractionation ◽  
Large Igneous Province ◽  
Olivine Gabbro ◽  
Plumbing System ◽  
Alkaline Complex ◽  
Content Type ◽  
Alkaline Rocks ◽  
Magmatic Plumbing System ◽  
Supplementary Material

AbstractThe Early to Late Cretaceous Mundwara alkaline complex (comprising the Musala, Mer and Toa plugs) displays a broad spectrum of alkaline rocks closely associated in space and time with the Deccan Large Igneous Province (DLIP) in NW India. Petrology and Nd-Sr isotopic data on two youngest and altogether compositionally different lamprophyre dykes of the Mundwara alkaline complex are presented in this paper to understand their petrogenesis and also to constrain the magmatic processes responsible for generation of the rock spectrum in the complex (pyroxenite, picrite ankaramite, carbonatite, shonkinite, olivine gabbro, feldspathoidal and foid-free syenite). The two lamprophyre dykes occurring in the Mer and the Musala hills are referred to as basaltic camptonite I and camptonite II, respectively. The basaltic camptonite-I is highly porphyritic and contains olivine, clinopyroxene and magnetite macrocrysts embedded within the groundmass of microphenocyrsts composed of clinopyroxene, phlogopite, magnetite and feldspar. Whereas camptonite-II, with more or less similar texture, contains amphibole, biotite, magnetite and clinopyroxene within the microphenocrystic groundmass of amphibole, biotite, apatite and feldspar. Pyroxenes are chemically zoned and display corrosion of the cores revealing that they are antecrysts developed during early stages of magma evolution and later on inherited by more evolved magmas. Mineral chemistry and trace element composition of the lamprophyres reveal that fractional crystallisation was a dominant process. Early segregation of olivine + Cr-rich clinopyroxene + Cr-spinel from a primary hydrous alkali basalt within a magmatic plumbing system is inferred which led to the generation of basaltic camptonitic magma (M1) forming the Mer hill lamprophyre. Subsequently, progressive fractionation of pyroxene and Fe-Ti oxides from the basaltic camptonitic (M1) magma generated camptonitic (M2) magma forming the Musala hill lamprophyre. Both lamprophyre dykes on the Sr-Nd isotopic array reflect plume type asthenospheric derivation which largely corresponds to the Réunion plume and other alkaline rocks of the Deccan LIP. Our study brings out a complex sequence of processes such as crystal fractionation, accumulation and corrosion in the magmatic plumbing system involved in the generation of the Mundwara alkaline complex.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5277073

Birth of the East African Rift System: Nucleation of magmatism and strain in the Turkana Depression

Geology ◽  
2019 ◽  
Vol 47 (9) ◽  
pp. 886-890 ◽  
Author(s):  
Samuel C. Boone ◽  
Barry P. Kohn ◽  
Andrew J.W. Gleadow ◽  
Christopher K. Morley ◽  
Christian Seiler ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Critical Role ◽  
East African Rift ◽  
Southern Ethiopia ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
The North ◽  
Basement Rocks ◽  
African Rift

Abstract The Turkana Depression of northern Kenya and southern Ethiopia contains voluminous plume-related basalts that mark the onset of the Paleogene–recent East African Rift System (EARS) at ca. 45 Ma. Thus, the Turkana Depression is crucial to understanding the inception of intracontinental rifting. However, the precise chronology of early rift-basin formation in Turkana is poorly constrained. We present apatite fission-track and (U-Th-Sm)/He thermochronology data from basement rocks from the margins of the north-south–trending Lokichar Basin that constrain the onset of rift-related cooling. Thermal history modeling of these data documents pronounced Eocene to Miocene denudational cooling of the basin-bounding Lokichar fault footwall. These results, along with ∼7 km of Paleogene to middle Miocene syn-rift strata preserved in the Lokichar fault hanging wall, suggest that formation of the Lokichar Basin began as early as ca. 45–40 Ma. Preexisting lithospheric heterogeneities inherited from earlier Mesozoic rifting and Eocene plume magmatism likely facilitated the broadly concurrent nucleation of strain in the Turkana Depression, up to ∼15 m.y. earlier than EARS initiation elsewhere. Late Paleogene extension in the Lokichar Basin and other parts of Turkana significantly predate the Miocene creation of pronounced plume-related topography in East Africa, suggesting that other mechanism(s), such as far-field stresses or mantle basal drag, likely played a critical role during EARS inception.

Rapid changes from arid to humid conditions during the onset of the Paraná-Etendeka Igneous Provinces: Can volcanic gas emissions from Continental Flood Basalts affect the precipitation regime?

2021 ◽  
pp. SP520-2020-176
Author(s):  
V. G. P. Cruz ◽  
E. F. Lima ◽  
L. M. M. Rossetti ◽  
N. G. Pasqualon
Keyword(s):  
Flood Basalt ◽  
Surface Cooling ◽  
Precipitation Regime ◽  
Volcanic Gas ◽  
Flood Basalts ◽  
Content Type ◽  
Continental Flood Basalts ◽  
Igneous Province ◽  
Volcaniclastic Rocks ◽  
Supplementary Material

AbstractDespite the intriguing correlation between Continental Flood Basalts (CFB) provinces and environmental crises, little is known about how the local/regional sedimentary systems and environment respond to flood basalt volcanism. Active sedimentary systems, and their interaction with volcanism, provides an important rock record to understand palaeoenvironments in volcanic settings. The Paraná-Etendeka Igneous Province is a well-known example of a CFB emplaced on a dry desert environment, but evidence has also shown the existence of humid conditions during the volcanic episode. This work describes and interprets non-volcanic sedimentary and volcaniclastic rocks interbedded with Paraná-Etendeka Igneous Province lavas in southernmost Brazil to better understand palaeoenvironmental process and changes during the onset of volcanism. Non-volcanic sedimentary rocks record the existence of ephemeral sheet-like flows and ponds/lakes while volcaniclastic rocks documents hydromagmatic activity, supporting a change to more humid conditions. Stratigraphic constrains indicate that this change started with the onset of volcanism and affected the whole province. We suggest that SO2 degassing from Paraná-Etendeka province may have caused a net global surface cooling resulting in precipitation redistribution and a local increase in rainfall. This hypothesis may help explaining the cooling and increased humidity observed elsewhere to be closely related with the Paraná-Etendeka emplacement.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5505710

Short-lived alkaline magmatism related to Réunion plume in the Deccan large igneous province: inferences from petrology, 40Ar/39Ar geochronology and paleomagnetism of lamprophyre from the Sarnu-Dandali alkaline igneous complex

2021 ◽  
pp. SP513-2021-34
Author(s):  
Ashish Dongre ◽  
P. S. Dhote ◽  
P. Zamarkar ◽  
S. J. Sangode ◽  
G. Belyanin ◽  
...  
Keyword(s):  
Mantle Metasomatism ◽  
Large Igneous Province ◽  
Alkaline Magmatism ◽  
Content Type ◽  
Igneous Province ◽  
Eruption Age ◽  
Supplementary Material ◽  
Reunion Plume ◽  
Alkaline Complexes ◽  
Metasomatized Mantle

AbstractExisting geochronological information on Deccan indicates prolonged (started at 68.5 Ma) alkaline magmatism related to the Réunion mantle plume based on the 40Ar/39Ar ages from Sarnu-Dandali and Mundwara alkaline complexes. We studied in detail an alkaline lamprophyre, from the Sarnu-Dandali complex, rich in groundmass (magmatic) as well as xenocrystic phlogopites and clinopyroxenes. 40Ar/39Ar age determinations of the phlogopites from this lamprophyre, reveal two distinct ages of 65.44±1.5 Ma and 68.17±1Ma. However, paleomagnetic results show a VGP at 32.31 N and 298.52 E concordant with that of the Deccan Super Pole at 65.5 Ma and support the younger eruption age at ca. 65.44±1.5Ma. Analyzed phlogopites lack any signs of retention of excess radiogenic Ar and yield similar inverse isochron ages, which suggests that the older age of ca. 68.17±1Ma belongs to the crystallization of xenocrystic phlogopite during mantle metasomatism. Trace element compositions support derivation of lamprophyre magma from an OIB- type enriched (metasomatized) mantle source with an involvement of phlogopite.This finding suggests that the pre-Deccan ages of ca. 68-69 Ma reported previously, may reflect the timing of metasomatism of the subcratonic lithospheric mantle during the separation of Greater-Seychelles from India at ca. ∼68.5 Ma. The absence of pre-Deccan alkaline rocks therefore indicates the short-duration (occurred between 67-65 Ma) of alkaline as well as small-volume, volatile-rich magmatism directly related to the Réunion (Deccan) plume.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5490881

scholarly journals Deep open storage and shallow closed transport system for a continental flood basalt sequence revealed with Magma Chamber Simulator

2019 ◽  
Vol 174 (11) ◽  
Author(s):  
Jussi S. Heinonen ◽  
Arto V. Luttinen ◽  
Frank J. Spera ◽  
Wendy A. Bohrson
Keyword(s):  
Magma Chamber ◽  
Fractional Crystallization ◽  
Flood Basalt ◽  
Mineral Chemistry ◽  
Major And Trace Elements ◽  
Large Igneous Province ◽  
Continental Flood Basalt ◽  
Crack Network ◽  
Plumbing Systems ◽  
History Of

Abstract The Magma Chamber Simulator (MCS) quantitatively models the phase equilibria, mineral chemistry, major and trace elements, and radiogenic isotopes in a multicomponent–multiphase magma + wallrock + recharge system by minimization or maximization of the appropriate thermodynamic potential for the given process. In this study, we utilize MCS to decipher the differentiation history of a continental flood basalt sequence from the Antarctic portion of the ~ 180 Ma Karoo large igneous province. Typical of many flood basalts, this suite exhibits geochemical evidence (e.g., negative initial εNd) of interaction with crustal materials. We show that isobaric assimilation-fractional crystallization models fail to produce the observed lava compositions. Instead, we propose two main stages of differentiation: (1) the primitive magmas assimilated Archean crust at depths of ~ 10‒30 km (pressures of 300–700 MPa), while crystallizing olivine and orthopyroxene; (2) subsequent fractional crystallization of olivine, clinopyroxene, and plagioclase took place at lower pressures in upper crustal feeder systems without significant additional assimilation. Such a scenario is corroborated with additional thermophysical considerations of magma transport via a crack network. The proposed two-stage model may be widely applicable to flood basalt plumbing systems: assimilation is more probable in magmas pooled in hotter crust at depth where the formation of wallrock partial melts is more likely compared to rapid passage of magma through shallower fractures next to colder wallrock.

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