Stratigraphy and petrology of the lower part of the Mulcahy Gabbro, northwestern Ontario: origin of reverse and normal fractionation trends and implications for tectonic setting of late Archean mafic magmatism

1991 ◽  
Vol 28 (11) ◽  
pp. 1753-1768 ◽  
Author(s):  
Richard H. Sutcliffe ◽  
Alan R. Smith ◽  
Alan D. Edgar
Keyword(s):  
Marginal Zone ◽  
Tectonic Setting ◽  
Basaltic Magma ◽  
Spatial Association ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Density Currents ◽  
Lower Zone ◽  
Calc Alkaline ◽  
Mineral Compositions

The Mulcahy Gabbro (2.73 Ga) is an exceptionally well-preserved tholeiitic layered intrusion located in the Wabigoon Subprovince of the Superior Province. The intrusion has a 900 m thick marginal zone of weakly layered gabbronoritic cumulate rocks characterized by a trend of upward Mg-enrichment. The overlying 1100 m thick lower zone consists of well-layered cumulate rocks that display a prominent trend of upward Fe-enrichment. The order of appearance of cumulus minerals in the lower zone is orthopyroxene + plagioclase, augite, apatite, pigeonite, Fe-rich olivine, magnetite.The upward increase in the XMg in marginal-zone cumulus low-Ca pyroxene and augite from 0.44 to 0.72 and 0.57 to 0.79, respectively, is primarily attributed to the injection of successively less fractionated batches of magma into the chamber, rather than to the effect of trapped liquid on cumulus mineral compositions. In the lower zone, crystal fractionation control results in an upward decrease in XMg in low-Ca pyroxene and augite from 0.72 to 0.32 and 0.79 to 0.45, respectively. The change from weakly developed layering in the marginal zone to the well-layered lower zone may represent the transition from a regime of cooling through the chamber floor to one of cooling predominantly through the chamber roof and walls. Rhythmic layering on a scale of centimetres to metres in the lower zone is largely attributed to magmatic density currents. Sulphur saturation occurs near the marginal zone – lower zone transition from reverse to normal fractionation and is attributed to mixing of the older fractionated magma with an injection of buoyant younger primitive magma.Based on cumulus mineral compositions, the most primitive parental magma for the lower zone is determined to have had an Mg# equal to or less than 0.46 and weak enrichment of light rare-earth elements ((Ce/Yb)N = 1.4). The cumulates are derived from a hydrous, high-Al2O3 basaltic magma with a moderately high silica activity. These constraints and the close temporal and spatial association with calc-alkaline granitoid rocks suggest that the Mulcahy Gabbro is a cumulate assemblage from a high-Al tholeiite magma and is part of a late Archean calc-alkaline, arc-related plutonic complex.

Prolonged magma emplacement as a mechanism for the origin of the marginal reversal of the Fongen–Hyllingen layered intrusion, Norway

2012 ◽  
Vol 149 (5) ◽  
pp. 909-926 ◽  
Author(s):  
VERA EGOROVA ◽  
RAIS LATYPOV
Keyword(s):  
Open System ◽  
Marginal Zone ◽  
Basaltic Magma ◽  
Layered Intrusion ◽  
General Mechanism ◽  
Layered Series ◽  
Primitive Magma ◽  
Mineral Compositions ◽  
Olivine Gabbronorites ◽  
Layered Sequence

AbstractThe ~100 m thick marginal zone of the Fongen–Hyllingen Intrusion (FHI) consists of non-layered, highly iron-enriched ferrodiorites that are overlain by a ~ 6 km thick layered sequence of gabbroic to dioritic rocks of the Layered Series. From the base upwards the marginal zone becomes more primitive as exemplified by a significant increase in whole-rock MgO, Mg-number and normative An. The reverse trends are also evident from an upward increase in An-content of plagioclase (from ~ 30 to ~ 43 at.%) and Mg-number of amphibole (from ~ 9 to ~ 23 at.%) and clinopyroxene (from ~ 23 to ~ 33 at.%). The marginal zone is abruptly terminated at the contact with the overlying Layered Series as is evident from a step-like increase in Mg-number of mafic minerals and An-content of plagioclase, as well as a sharp increase in whole-rock MgO and Mg-number in overlying olivine gabbronorites of the Layered Series. Based on these features the marginal zone of the FHI can be interpreted as an aborted marginal reversal. Reverse trends in whole-rock and mineral compositions, as well as a sharp break in these parameters are indicative of its formation in an open system with the involvement of the prolonged emplacement of magma that became increasingly more primitive. Such development of the marginal reversal was interrupted by the emplacement of a major influx of more primitive magma that produced the Layered Series. The open system evolution of a basaltic magma chamber may represent a general mechanism for the origin of marginal reversals in mafic sills and layered intrusions.

A Grenville-age layered intrusion in the subsurface of west Texas: petrology, petrography, and possible tectonic setting

1995 ◽  
Vol 32 (12) ◽  
pp. 2159-2166 ◽  
Author(s):  
Hulusi Kargi ◽  
Calvin G. Barnes
Keyword(s):  
Tectonic Setting ◽  
Basaltic Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Magma Source ◽  
Rock Types ◽  
Hornblende Gabbro ◽  
Tectonic Environment ◽  
Extensional Tectonic ◽  
General Order

The Nellie intrusion is a thick (more than 4420 m) mafic to ultramafic layered intrusion with a radiometric age of ~1163 Ma. Rock types change abruptly with stratigraphic height and include norite, pyroxenite, gabbronorite, hornblende gabbro, gabbro, anorthosite, harzburgite, and lherzolite. Norite is most abundant, but gabbro and hornblende gabbro are locally abundant. Rare olivine-rich layers are also present. The general order of crystallization was olivine, orthopyroxene, plagioclase + clinopyroxene, and hornblende. Mg#'s, expressed as 100 Mg/(Mg + Fe), range from 76.3 to 85.8 for olivine, 56.7 to 84.9 for orthopyroxene, 62.5 to 90.3 for clinopyroxene, and 52.4 to 82.8 for amphibole. Mg#'s vary with height and display abrupt reversals, which indicate open-system addition of new mafic magma. Eleven cyclic units were identified on the basis of evidence for injection of basaltic magma; these can be grouped into three megacyclic units. The abundance of orthopyroxene, and mineral compositional evidence for Fe enrichment within cyclic units, indicates that parental magmas were subalkaline and tholeiitic. Plagioclase in equilibrium with olivine ranges from An65 to An46, which precludes an arc-related magma source. Although the intrusion is approximately coeval with Keweenawan magmatism and with emplacement of diabasic dikes in western North America, it is dissimilar in detail to both suites of rocks. Nevertheless, its composition and geophysical setting are consistent with emplacement in an extensional tectonic environment.

Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

2016 ◽  
Vol 155 (1) ◽  
pp. 109-118 ◽  
Author(s):  
C. ISHWAR-KUMAR ◽  
V.J. RAJESH ◽  
B.F. WINDLEY ◽  
T. RAZAKAMANANA ◽  
T. ITAYA ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Tectonic Setting ◽  
Basaltic Magma ◽  
Parental Magma ◽  
Tholeiitic Basalt ◽  
Ultramafic Complex ◽  
Layered Gabbro ◽  
Arc Setting ◽  
Melt Composition ◽  
High Degree

AbstractThe Ranomena ultramafic complex in NE Madagascar consists of layered gabbro, harzburgite, orthopyroxenite, clinopyroxenite, garnet websterite and chromitite-layered peridotite. This study of the Ranomena chromite chemistry aims to better understand the petrogenesis and palaeotectonic environment of the complex. The chromite from the Ranomena chromitite is unzoned/weakly zoned and has a Cr# (Cr/(Cr + Al)) of 0.59–0.69, a Mg# (Mg/(Fe + Mg)) of 0.37–0.44, and low Al2O3(15–23 wt %) suggesting derivation from a supra-subduction zone arc setting. Calculation of parental melt composition suggests that the parental magma composition of the Ranomena chromitite was similar to that of a primitive tholeiitic basalt formed at a high degree of mantle melting, suggesting the parental melt composition was equivalent to that of an island-arc tholeiite (IAT). The parental magma of the Ranomena chromite had a FeO/MgO ratio of 0.9 to 1.8, suggesting arc derivation. The parental magma was Al- and Fe-rich, similar to a tholeiitic basaltic magma. The composition of orthopyroxene from the chromitite indicates a crystallization temperature range of 1250–1300°C at 1.0 GPa. The chemistry of the chromite in the Ranomena chromitite further suggests that the complex formed in a supra-subduction zone arc tectonic setting.

scholarly journals Chemical Evolution of Calc-alkaline Magmas during the Ascent through Continental Crust: Constraints from Methana, Aegean Arc

2020 ◽  
Vol 61 (3) ◽  
Author(s):  
Milena V Schoenhofen ◽  
Karsten M Haase ◽  
Christoph Beier ◽  
Dominic Woelki ◽  
Marcel Regelous
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Basaltic Magma ◽  
High Water ◽  
Calc Alkaline ◽  
Mafic Enclaves ◽  
Aegean Arc ◽  
Mineral Compositions

Abstract Quaternary calc-alkaline andesitic to dacitic lavas effusively erupted on top of about 30 km thick accreted continental crust at Methana peninsula in the western Aegean arc. We present new data of major and trace element concentrations as well as of Sr–Nd–Pb isotope ratios along with mineral compositions of Methana lavas and their mafic enclaves. The enclaves imply a parental basaltic magma and fractional crystallization processes with relatively little crustal assimilation in the deep part of the Methana magma system. The composition of amphibole in some mafic enclaves and lavas indicates deeper crystallization at ∼25 km depth close to the Moho compared with the evolved lavas that formed at <15 km depth. The presence of amphibole and low Ca contents in olivine suggest high water contents of ∼4 wt% in the primitive magmas at Methana. The compositions of andesitic and dacitic lavas reflect fractional crystallization, assimilation of sedimentary material, and magma mixing in the upper 15 km of the crust. The Methana magmas have fO2 of FMQ + 1 to FMQ + 2 (where FMQ is the fayalite–magnetite–quartz buffer) at temperatures of 1200 to 750 °C and the fO2 does not vary systematically from mafic to felsic compositions, suggesting that the mantle wedge was oxidized by sediment subduction. Amphibole is an important fractionating phase in the more evolved Methana magmas and causes significant changes in incompatible element ratios. Although xenocrysts and mineral compositions indicate magma mixing, the major and trace element variation implies only limited mixing between dacitic and basaltic melts.

Mineral chemistry, petrogenesis, and tectonic setting of the Wateranga layered intrusion, southeast Queensland, Australia

2005 ◽  
Vol 42 (11) ◽  
pp. 1967-1985 ◽  
Author(s):  
Reddy VR Talusani ◽  
Warwick J Sivell ◽  
Paul M Ashley
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Mineral Chemistry ◽  
Geochemical Data ◽  
Magma Source ◽  
Olivine Gabbro ◽  
Layered Mafic Intrusion ◽  
Southeast Queensland

The Wateranga layered mafic intrusion (28 km2 in area, > 500 m thick) is a tholeiitic, undeformed, unmetamorphosed, Permo-Triassic layered gabbroic pluton intruded into the late Carboniferous Goodnight beds of the Goodnight Block in southeast Queensland. The intrusion mainly consists of gabbro and norite, associated with subordinate amounts of troctolite, anorthosite, and orthopyroxenite, and rare picrite. Olivine gabbro is the dominant rock type of the intrusion. Fractionation followed a tholeiitic trend with iron enrichment in the liquid. Petrographic, mineral chemical, and whole-rock geochemical data have been used to divide the intrusion into Lower, Middle, and Upper zones, which are interpreted as reflecting magma chamber replenishment. The observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data. The common differentiation indices, such as An content of plagioclase, Mg#s of olivine, clinopyroxene, orthopyroxene and whole-rocks, and the whole-rock concentrations of various incompatible trace elements (Zr, Y, Nb, La Ba, Rb, Sr, and Nd), all vary widely with stratigraphic depth and display abrupt shifts at the zone boundaries, indicating open system addition of new mafic magma. Temperatures estimated from two-pyroxene geothermometer vary from 1057 to 927 °C. During the course of crystallization, pressure probably was > 2 and < 4 kbar (1 kbar = 100 MPa). The variation trend of anorthite content of plagioclase versus the forsterite content of olivine precludes an arc-related magma source. The composition and geological setting of the intrusion are consistent with emplacement in a post-subduction extensional tectonic environment.

Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

2021 ◽  
Vol 57 ◽  
pp. 239-273
Author(s):  
Allan Ludman ◽  
Christopher McFarlane ◽  
Amber T.H. Whittaker
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
East Central ◽  
Arc Volcanism ◽  
Middle Ordovician ◽  
Volcanic Suite ◽  
Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

scholarly journals Geochemical Classification and Geotectonic Setting of Granitic Gneisses from Southeastern Margin of Western Nigeria Basement

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Mohammed Olatoye Adepoju ◽  
Yinusa Ayodele Asiwaju-Bello
Keyword(s):  
Inductively Coupled Plasma ◽  
Tectonic Setting ◽  
Calc Alkaline ◽  
Granitic Gneiss ◽  
Basement Complex ◽  
Southwestern Nigeria ◽  
Inductively Coupled ◽  
Continental Arc ◽  
Southeastern Margin ◽  
Geochemical Classification

Chemical whole-rock major oxides and some trace element analyses were done on granitic gneiss rocks located on the southeastern margin of western Nigeria Basement Complex, exposed in parts of Dagbala-Atte District, southwestern Nigeria. This was meant to classify the rocks and to understand the tectonic setting in order to evaluate their crustal evolution. The chemical analyses were done using inductively-coupled plasma mass spectrometer. From the results obtained, these rocks classified into calc-alkaline to shoshonite series with metaluminous to peraluminous varieties, they are I-type granitoids of feroan composition. The granitic gneisses formed from metamorphism of granite and granodiorite. Tectonically, most of the rock samples plotted in the field of island arc, continental arc and continental-collisional granitoids, which indicated that the protolith granite and granodiorite are orogenic and are arc related inferring arc tectonic setting.

Neoproterozoic Amdo and Jiayuqiao microblocks in the Tibetan Plateau: Implications for Rodinia reconstruction

2020 ◽  
Author(s):  
Yiming Liu ◽  
Yuhua Wang ◽  
Sanzhong Li ◽  
M. Santosh ◽  
Runhua Guo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
South China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
South China Craton ◽  
Neoproterozoic Magmatism ◽  
T Values

The Tibetan Plateau is composed of several microblocks, the tectonic affinity and paleogeographic correlations of which remain enigmatic. We investigated the Amdo and Jiayuqiao microblocks in central Tibet Plateau with a view to understand their tectonic setting and paleogeographic position within the Neoproterozoic supercontinent Rodinia. We present zircon U-Pb and Lu-Hf isotope, and whole-rock geochemical data on Neoproterozoic granitic gneisses from these microblocks. Zircon grains from the Jiayuqiao granitic gneiss yielded an age of 857 ± 9 Ma with variable εHf(t) values (−8.9 to 4.0). The Amdo granitic gneisses yielded ages of 893 ± 5 Ma, 807 ± 5 Ma, and 767 ± 11 Ma, with εHf(t) values in the range of −4.9 to 3.5. Geochemically, the granitoids belong to high-K calc-alkaline series, with the protolith derived from partial melting of ancient crustal components. The ascending parental magma of the Amdo granitoids experienced significant mantle contamination as compared to the less contaminated magmas that generated the Jiayuqiao intrusions. In contrast to the Lhasa, Himalaya, South China, and Tarim blocks, we suggest that the Amdo and Jiayuqiao microblocks probably formed a unified block during the Neoproterozoic and were located adjacent to the southwestern part of South China craton. The Neoproterozoic magmatism was probably associated with the subduction of the peripheral ocean under the South China craton and the delamination of lithospheric mantle beneath the Jiangnan orogen.

scholarly journals Discovery of two new super-eruptions from the Yellowstone hotspot track (USA): Is the Yellowstone hotspot waning?

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 934-938
Author(s):  
Thomas R. Knott ◽  
Michael J. Branney ◽  
Marc K. Reichow ◽  
David R. Finn ◽  
Simon Tapster ◽  
...  
Keyword(s):  
The United States ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Robust Approach ◽  
Large Igneous Provinces ◽  
Yellowstone Hotspot ◽  
Trace Element Chemistry ◽  
Igneous Provinces ◽  
Mineral Compositions ◽  
Size Estimates

Abstract Super-eruptions are amongst the most extreme events to affect Earth’s surface, but too few examples are known to assess their global role in crustal processes and environmental impact. We demonstrate a robust approach to recognize them at one of the best-preserved intraplate large igneous provinces, leading to the discovery of two new super-eruptions. Each generated huge and unusually hot pyroclastic density currents that sterilized extensive tracts of Idaho and Nevada in the United States. The ca. 8.99 Ma McMullen Creek eruption was magnitude 8.6, larger than the last two major eruptions at Yellowstone (Wyoming). Its volume exceeds 1700 km3, covering ≥12,000 km2. The ca. 8.72 Ma Grey’s Landing eruption was even larger, at magnitude of 8.8 and volume of ≥2800 km3. It covers ≥23,000 km2 and is the largest and hottest documented eruption from the Yellowstone hotspot. The discoveries show the effectiveness of distinguishing and tracing vast deposit sheets by combining trace-element chemistry and mineral compositions with field and paleomagnetic characterization. This approach should lead to more discoveries and size estimates, here and at other provinces. It has increased the number of known super-eruptions from the Yellowstone hotspot, shows that the temporal framework of the magmatic province needs revision, and suggests that the hotspot may be waning.

scholarly journals Widespread Permian granite magmatism in Lower Austroalpine units: significance for Permian rifting in the Eastern Alps

2020 ◽  
Vol 113 (1) ◽  
Author(s):  
Sihua Yuan ◽  
Franz Neubauer ◽  
Yongjiang Liu ◽  
Johann Genser ◽  
Boran Liu ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Eastern Alps ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Three Samples ◽  
High K ◽  
Icp Ms ◽  
Granite Magmatism ◽  
Austroalpine Unit ◽  
Granite Suite

Abstract The Grobgneis complex, located in the eastern Austroalpine unit of the Eastern Alps, exposes large volumes of pre-Alpine porphyric metagranites, sometimes associated with small gabbroic bodies. To better understand tectonic setting of the metagranites, we carried out detailed geochronological and geochemical investigations on the major part of the porphyric metagranites. LA–ICP–MS zircon U–Pb dating of three metagranites sampled from the Grobgneis complex provides the first reliable evidence for large volumes of Permian plutonism within the pre-Alpine basement of the Lower Austroalpine units. Concordant zircons from three samples yield ages at 272.2 ± 1.2 Ma, 268.6 ± 2.3 Ma and 267.6 ± 2.9 Ma interpreted to date the emplacement of the granite suite. In combination with published ages for other Permian Alpine magmatic bodies, the new U–Pb ages provide evidence of a temporally restricted period of plutonism (“Grobgneis”) in the Raabalpen basement Complex during the Middle Permian. Comparing the investigated basement with that of the West Carpathian basement, we argue that widespread Permian granite magmatism occurred in the Lower Austroalpine units. They belong to the high-K calc-alkaline to shoshonitic S-type series on the base of geochemical data. Zircon Hf isotopic compositions of the Grobgneis metagranites show εHf(t) values of − 4.37 to − 0.6, with TDM2 model ages of 1.31–1.55 Ga, indicating that their protoliths were derived by the recycling of older continental crust. We suggest that the Permian granitic and gabbroic rocks are considered as rifted-related rocks in the Lower Austroalpine units and are contemporaneous with cover sediments.

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