Geochemistry of Cretaceous subduction initiation related cumulate gabbros in a forearc setting from Chaldoran ophiolite, NW Iran

2020 ◽  
Author(s):  
Mahleqa Rezaei ◽  
Mohssen Moazzen ◽  
Tian-Nan Yang
Keyword(s):  
Source Region ◽  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Nw Iran ◽  
Subduction Initiation ◽  
Rock Types ◽  
Original Magma ◽  
Ree Patterns ◽  
Ree Pattern ◽  
Cretaceous Subduction

<p>The Neo-Tethys-related Chaldoran ophiolite in NW Iran and at the Turkish border is a part of the larger Khoy ophiolite. Cumulate and isotropic gabbro along with serpentinized peridotite, pillow basalt, pelagic limestone, rare radiolarites, and volcano-sedimentary units are the main rock types in the area. The gabbros occur as lenses with ultramafic rocks, or as relatively large exposures with fault contact with ultramafic rocks. In this study, we provide new whole-rock geochemistry, mineral chemistry and zircon U/Pb age for the cumulate gabbros from the Chaldoran area. Gabbros have tholeiitic composition and are highly depleted. Chondrite normalized rare earth elements (REE) pattern for gabbros are comparative with REE patterns for N-MORB, but overall with more depleted features. The N-MORB normalized multi-elements pattern shows high depletion in HREE and HFSE and enrichment in some LREE and LILEs. Negative anomaly for some HFSE relative to N-MORB, along with enrichment in LILE for the samples indicates the source region as subduction influenced mantle. The cumulated gabbro whole rock and Clinopyroxenes geochemistry indicate an intra-oceanic forearc setting for the studied samples. They also have many similarities to boninite in mineral and whole rock geochemistry. U-Pb zircon dating of the gabbro samples indicates 95.3-114.1 Ma ages for the generation of the gabbros parent magma. The original magma was related to the later stages of the forearc setting in the subduction initiation (SI) stage. This ‘SI’ related Albian-Cenomanian the Chaldoran depleted gabbro likely are the continuation of Taurus SI related late Cretaceous ophiolite complexes in Turkey.</p>

scholarly journals Structure and Petrology of the Red Hill Complex, Nelson

2021 ◽  
Author(s):  
◽  
Richard Irving Walcott
Keyword(s):  
Bulk Composition ◽  
Mineral Chemistry ◽  
Parent Material ◽  
Preferred Orientation ◽  
Ultramafic Rocks ◽  
Rock Types ◽  
Basal Zone ◽  
Upper Paleozoic ◽  
Two Generations ◽  
Thick Lens

<p>The Red Hill Complex is an essentially concordant ultramafic body enclosed in Upper Paleozoic flysch facies sediments which include Pelorus Group (oldest), Lee River Group and Maitai Group. The Pelorus Group contains rare submarine lavas and is largely derived from spilitic volcanics. The Lee River Group consists of spilitic pillow lavas, volcanic breccias and spilitic basalts and dolerites. The Maitai Group consists of limestone, sandstone and argillite; an extensive conglomerate lens in the argillites is largely composed of andesitic pebbles. The Red Hill Complex is a 12,000 ft. thick lens and is part of a sheet of peridotites which may extend 40 miles northward to Dun Mountain. The Complex is divided into a 3000 ft thick Basal Zone of massive harzburgite and a 9000 ft thick Upper Zone of layered harzburgite and dunite with minor variants, feldspathic-peridotite, eucrite, lherzolite, wehrlite and pyroxenite. The bulk composition of both zones is approximately the same but the Upper Zone contains about 0.2 per cent feldspar not present in the Basal Zone. There is no significant regional change in mineral chemistry throughout the Complex and the average composition is about; olivine Fo91, 70 per cent; orthopyroxene, En88, 22 per cent; clinopyroxene, 5 per cent; feldspar An96, less than 0.2 per cent; spinel 2 per cent. Layering and foliation are common in the top of the Upper Zone. Layering is of at least two generations of which at least one is of metamorphic origin. Metamorphic layering was formed by metasomatic replacement probably along subhorizontal shear planes during intrusion of the ultramafic sheet. Pyroxene pegmatites formed after flow ceased. The diversity of rock types in the top of the Upper Zone is considered by the writer to have been caused by metamorphic differentiation of parent material the same composition as the Basal Zone. The preferred orientation of olivine in lineated, foliated, laminated and layered rocks has the same pattern suggesting a close genetic relationship between those structures. Evidence strongly supports a tectonic origin for the preferred orientation. Rocks in the Upper Zone are xenomorphic-granular in texture and those in the Basal Zone are typically protoclastic. Xenomorphic-granular textures are derived in part from protoclastic by post-deformational recrystallization. The ultramafic rocks are cut by a number of dykes composed of hornblende-labradorite, hypersthene-augite-bytownite assemblages or minor variants of these. The dykes were intruded shortly after emplacement of the ultramafic rocks. The Red Hill Complex is considered to have been emplaced as a sheet at shallow depths which intruded superficial deposits on the ocean floor and was later overlain by volcanics</p>

scholarly journals Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil)

2001 ◽  
Vol 73 (1) ◽  
pp. 71-98 ◽  
Author(s):  
GIANBOSCO TRAVERSA ◽  
CELSO B. GOMES ◽  
PIERO BROTZU ◽  
NICOLETTA BURAGLINI ◽  
LUCIO MORBIDELLI ◽  
...  
Keyword(s):  
Complex Network ◽  
Parental Magma ◽  
Mineral Chemistry ◽  
Central Core ◽  
Chemical Data ◽  
Carbonate Minerals ◽  
Silicate Minerals ◽  
Rock Types ◽  
Ree Patterns ◽  
Petrographic Study

The Araxá complex (16 km²) comprises carbonatites forming a central core and a complex network of concentric and radial dykes as well as small veins; additionally, it includes mica-rich rocks, phoscorites and lamprophyres. Fenites also occur and are represented by Proterozoic quartzites and schists of the Araxá Group. The petrographic study of 130 borehole samples indicates that the complex is basically made up by two rock-types, carbonatites and mica-rich rocks, and subordinately by a third unit of hybrid composition. Carbonatites range chemically in composition, the most abundant type being magnesiocarbonatites. Dolomite and calcite correspond to the chief constituents, but other carbonate phases, including the Ce-group RE minerals, are also recognized. Phosphates and oxides are widespread accessories whereas silicate minerals consist of olivine, clinopyroxene, mica and amphibole. Mica-rich rocks are represented by abundant glimmeritic rocks and scarce cumulitic phlogopite-, olivine- and diopside-bearing pyroxenites. Hybrid rocks mainly contain phlogopite and tetraferriphlogopite as cumulus and intercumulus phases, respectively; carbonate minerals may also be found. Chemical data indicate that the carbonatites are strongly enriched in REE and have lower contents of Nb, Zr, V, Cr, Ni and Rb compared to the mica-rich rocks. The higher K, Nb and Zr contents of the latter rocks are believed to be related to metasomatic processes (glimmeritization) of the pyroxenites. Similar REE patterns for carbonatites and mica-rich rocks seem to suggest that they are related to a single parental magma, possibly of ijolitic composition. Steep LREE/HREE fractionation and high sigmaREE content of some carbonatite samples would be explained by hydrothermal and supergenic processes.

scholarly journals Structure and Petrology of the Red Hill Complex, Nelson

2021 ◽  
Author(s):  
◽  
Richard Irving Walcott
Keyword(s):  
Bulk Composition ◽  
Mineral Chemistry ◽  
Parent Material ◽  
Preferred Orientation ◽  
Ultramafic Rocks ◽  
Rock Types ◽  
Basal Zone ◽  
Upper Paleozoic ◽  
Two Generations ◽  
Thick Lens

<p>The Red Hill Complex is an essentially concordant ultramafic body enclosed in Upper Paleozoic flysch facies sediments which include Pelorus Group (oldest), Lee River Group and Maitai Group. The Pelorus Group contains rare submarine lavas and is largely derived from spilitic volcanics. The Lee River Group consists of spilitic pillow lavas, volcanic breccias and spilitic basalts and dolerites. The Maitai Group consists of limestone, sandstone and argillite; an extensive conglomerate lens in the argillites is largely composed of andesitic pebbles. The Red Hill Complex is a 12,000 ft. thick lens and is part of a sheet of peridotites which may extend 40 miles northward to Dun Mountain. The Complex is divided into a 3000 ft thick Basal Zone of massive harzburgite and a 9000 ft thick Upper Zone of layered harzburgite and dunite with minor variants, feldspathic-peridotite, eucrite, lherzolite, wehrlite and pyroxenite. The bulk composition of both zones is approximately the same but the Upper Zone contains about 0.2 per cent feldspar not present in the Basal Zone. There is no significant regional change in mineral chemistry throughout the Complex and the average composition is about; olivine Fo91, 70 per cent; orthopyroxene, En88, 22 per cent; clinopyroxene, 5 per cent; feldspar An96, less than 0.2 per cent; spinel 2 per cent. Layering and foliation are common in the top of the Upper Zone. Layering is of at least two generations of which at least one is of metamorphic origin. Metamorphic layering was formed by metasomatic replacement probably along subhorizontal shear planes during intrusion of the ultramafic sheet. Pyroxene pegmatites formed after flow ceased. The diversity of rock types in the top of the Upper Zone is considered by the writer to have been caused by metamorphic differentiation of parent material the same composition as the Basal Zone. The preferred orientation of olivine in lineated, foliated, laminated and layered rocks has the same pattern suggesting a close genetic relationship between those structures. Evidence strongly supports a tectonic origin for the preferred orientation. Rocks in the Upper Zone are xenomorphic-granular in texture and those in the Basal Zone are typically protoclastic. Xenomorphic-granular textures are derived in part from protoclastic by post-deformational recrystallization. The ultramafic rocks are cut by a number of dykes composed of hornblende-labradorite, hypersthene-augite-bytownite assemblages or minor variants of these. The dykes were intruded shortly after emplacement of the ultramafic rocks. The Red Hill Complex is considered to have been emplaced as a sheet at shallow depths which intruded superficial deposits on the ocean floor and was later overlain by volcanics</p>

Petrological and geochemical characterization of the arc-related Suru–Thasgam ophiolitic slice along the Indus Suture Zone, Ladakh Himalaya

2021 ◽  
pp. 1-20
Author(s):  
I.M. Bhat ◽  
T. Ahmad ◽  
D.V. Subba Rao ◽  
N.V. Chalapathi Rao
Keyword(s):  
Suture Zone ◽  
Secondary Mineral ◽  
High Field Strength ◽  
Geochemical Characterization ◽  
Rock Types ◽  
Ladakh Himalaya ◽  
Magnesian Olivine ◽  
Textural Relationship ◽  
Ree Patterns

Abstract The Ladakh Himalayan ophiolites preserve remnants of the eastern part of the Neo-Tethyan Ocean, in the form of Dras, Suru Valley, Shergol, Spongtang and Nidar ophiolitic sequences. In Kohistan region of Pakistan, Muslim Bagh, Zhob and Bela ophiolites are considered to be equivalents of Ladakh ophiolites. In western Ladakh, the Suru–Thasgam ophiolitic slice is highly dismembered and consists of peridotites, pyroxenites and gabbros, emplaced as imbricate blocks thrust over the Mesozoic Dras arc complex along the Indus Suture Zone. The Thasgam peridotites are partially serpentinized with relict olivine, orthopyroxene and minor clinopyroxene, as well as serpentine and iron oxide as secondary mineral assemblage. The pyroxenites are dominated by clinopyroxene followed by orthopyroxene with subordinate olivine and spinel. Gabbros are composed of plagioclase and pyroxene (mostly replaced by amphiboles), describing an ophitic to sub-ophitic textural relationship. Geochemically, the studied rock types show sub-alkaline tholeiitic characteristics. The peridotites display nearly flat chondrite-normalized rare earth element (REE) patterns ((La/Yb)N = 0.6–1.5), while fractionated patterns were observed for pyroxenites and gabbros. Multi-element spidergrams for peridotites, pyroxenites and gabbros display subduction-related geochemical characteristics such as enriched large-ion lithophile element (LILE) and depleted high-field-strength element (HFSE) concentrations. In peridotites and pyroxenites, highly magnesian olivine (Fo88.5-89.3 and Fo87.8-89.9, respectively) and clinopyroxene (Mg no. of 93–98 and 90–97, respectively) indicate supra-subduction zone (SSZ) tectonic affinity. Our study suggests that the peridotites epitomize the refractory nature of their protoliths and were later evolved in a subduction environment. Pyroxenites and gabbros appear to be related to the base of the modern intra-oceanic island-arc tholeiitic sequence.

The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

2019 ◽  
Vol 60 (10) ◽  
pp. 1991-2024 ◽  
Author(s):  
M G Kopylova ◽  
E Tso ◽  
F Ma ◽  
J Liu ◽  
D G Pearson
Keyword(s):  
North Atlantic ◽  
Thermal State ◽  
Mineral Chemistry ◽  
Mantle Metasomatism ◽  
Labrador Sea ◽  
The North ◽  
Rock Types ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as &lt;1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as &lt;1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

scholarly journals Mineral chemistry of magnetite and fluid inclusions studies in the Kuh-Baba iron deposit, south of Hashtroud, NW Iran

2019 ◽  
Vol 27 (4) ◽  
pp. 755-766
Author(s):  
Majid Hafez Darbani ◽  
◽  
Ali Abedini ◽  
Farhang Aliyari ◽  
AliAsghar Calagari ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Mineral Chemistry ◽  
Iron Deposit ◽  
Nw Iran

Geochemistry of Late Proterozoic amphibolites and ultramafic rocks, southeastern Canadian Cordillera

1988 ◽  
Vol 25 (8) ◽  
pp. 1323-1337 ◽  
Author(s):  
James H. Sevigny
Keyword(s):  
Partial Melting ◽  
Major And Trace Elements ◽  
Ultramafic Rocks ◽  
Canadian Cordillera ◽  
Elemental Abundances ◽  
Late Proterozoic ◽  
Group I ◽  
Heterogeneous Mantle ◽  
High Degree ◽  
Ree Patterns

Late Proterozoic amphibolites and ultramafic rocks from the southeastern Canadian Cordillera have been analysed for major and trace elements in order to determine the nature and origin of the protoliths. Geologic relations indicate that these rocks were produced during an episode of continental rifting in the Precambrian. Based on rare-earth-element (REE) patterns, immobile-incompatible-element ratios, and characteristic elemental abundances, amphibolites are subdivided into alkaline and tholeiitic metabasalts. Alkaline basalts are recognized by their steep REE patterns, high Zr/Y, high TiO2 and P2O5 abundances, and low Y/Nb and Ti/Zr. Tholeiitic basalts are subdivided into three groups: (I) high-Mg#, high-field-strength-element (HFSE)-depleted, light-REE (LREE)-enriched tholeiites with flat heavy REE (HREE) patterns; (II) LREE-enriched tholeiites depleted in HREE; and (III) low-Mg# tholeiites with flat REE patterns. Ultramafic rocks occur as boudins of partially recrystallized Cr-spinel-bearing harzburgite or therzolite, enriched in LREE (Ce/Sm = 1.7–1.9), HFSE, CaO, Al2O3, and TiO2 relative to depleted mantle.Geochemical data suggest that the basalts were derived from a heterogeneous mantle source that underwent different degrees of partial melting with variable amounts of subsequent crystal fractionation of the melts. High Mg#, high Cr and Ni abundances, low HFSE abundances, and high olivine saturation temperatures suggest that group I tholeiites are primary mantle melts produced by a relatively high degree of partial melting of a LREE-enriched, HFSE-depleted source. Group II and III basalts have undergone moderate olivine and pryoxene and limited plagioclase fractionation. Mass-balance calculations suggest that the ultramafic rocks represent a crustally contaminated primary-mantle-derived melt.Les éléments majeurs et traces des amphibolites et des ultramafites, d'âge protérozoïque tardif, du sud-est de la Cordillère canadienne ont été analysés dans le but de déterminer la nature et l'origine des protolithes. Les relations géologiques indiquent que ces roches se sont formées durant un épisode de rifting continental dans le Précambrien. Les diagrammes des terres rares, les rapports des éléments immobiles et incompatibles et les compositions chimiques caractéristiques ont permis de subdiviser les amphibolites en métabasaltes tholéiitiques et alcalins. Les basaltes alcalins sont reconnus par les courbes abruptes dans les diagrammes des terres rares, les rapports Zr/Y élevés et les fortes teneurs en TiO2 et P2O5 et les rapports Y/Nb et Ti/Zr faibles. Les basaltes tholéiitiques sont subdivisés en trois groupes : (I) avec Mg# élevé, appauvrissement en éléments de force de champ élevée, tholéiites enrichies en terres rares légères avec courbe horizontale des terres rares lourdes; (II) tholéiites enrichies en terres rares légères et appauvries en terres rares lourdes; et (III) tholéiites avec Mg# faible et avec courbe horizontale des variations des terres rares. Les ultramafites se présentent en boudins formés d'harzburgite incluant un spinelle chromifère partiellement recristallisé ou de therzolite qui sont enrichies en terres rares légères (Ce/Sm = 1,7–1,9), en éléments à force de champ élevée, en CaO, Al2O3 et TiO2, comparativement à un manteau appauvri.

scholarly journals Building Arc Crust: Plutonic to Volcanic Connections in an Extensional Oceanic Arc, the Southern Alisitos Arc, Baja California

2019 ◽  
Vol 60 (6) ◽  
pp. 1195-1228 ◽  
Author(s):  
Rebecca A Morris ◽  
Susan M DeBari ◽  
Cathy Busby ◽  
Sarah Medynski ◽  
Brian R Jicha
Keyword(s):  
Reference Model ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Mineral Chemistry ◽  
Major And Trace Elements ◽  
Low Velocity ◽  
Fractionation Process ◽  
Process Step ◽  
Rock Types ◽  
Plutonic Rocks

Abstract The ∼50 km long Rosario segment of the Cretaceous Alisitos oceanic arc terrane provides undeformed three-dimensional exposures of the upper 7 km of an oceanic extensional arc, where crustal generation processes are recorded in both the volcanic and underlying plutonic rocks. These exceptional exposures allow for the study of the physical and chemical links between the rock units and help constrain the differentiation processes active during the growth and evolution of arc crust. This study focuses on the southern third of the Rosario segment, previously referred to as the southern volcano-bounded basin, and its plutonic underpinnings. Upper crustal rocks in the Rosario segment consist of a 3–5 km thick volcanic–volcaniclastic section with hypabyssal intrusions. Plutons intrude these units at various levels along-strike, but at each intrusive contact the transition is complete over a distance of <150 m, where stoped volcanic blocks are present. There is striking compositional overlap in whole-rock and mineral chemistry between the plutonic and volcanic units, suggesting a comagmatic source. Whole-rock geochemistry shows coherent trends in major and trace elements in mafic to intermediate compositions, but less coherent trends above 63 wt % SiO2. Units are predominantly low-K with flat rare earth element patterns, and show large ion lithophile element enrichment and high field strength element depletion. Initial Nd and Pb isotope ratios overlap for all units and imply no cratonic continental involvement. This agrees with low Sr/Y ratios of all rock types, indicative of thin, immature oceanic arc crust. Modeling results show that closed-system fractional crystallization drove crustal differentiation from mafic to intermediate compositions, but open-system processes likely occurred to produce some of the felsic compositions. Differentiation occurred in a two-step fractionation process. Step 1, from basaltic andesite to andesite, fractionated an anhydrous gabbroic cumulate (∼40% crystallization). Step 2, from andesite to rhyolite, fractionated a hydrous amphibole cumulate (∼65% crystallization, total), which is similar to what fluid dynamical models suggest for production of rhyolite (between 50–70% crystallization). Our results can be used as a reference model for differentiation processes relating to the growth of the middle and upper crust within active extensional arc systems. The Rosario segment plutonic rocks may be analogous to the low-velocity zone (Vp = 6·0–6·5 km s–1) imaged within the extensional Izu–Bonin arc. The chemistry of the plutonic and volcanic rocks is most similar to those of volcanic rocks in the Izu–Bonin active rift.

Whole-rock and mineral chemistry of cumulates from the Kızıldağ (Hatay) ophiolite (Turkey): clues for multiple magma generation during crustal accretion in the southern Neotethyan ocean

2005 ◽  
Vol 69 (1) ◽  
pp. 53-76 ◽  
Author(s):  
U. Bağci ◽  
O. Parlak ◽  
V. Höck
Keyword(s):  
Tectonic Setting ◽  
Mineral Chemistry ◽  
Chromian Spinel ◽  
Olivine Gabbro ◽  
Crustal Accretion ◽  
Magma Generation ◽  
The North ◽  
Rock Types ◽  
Suprasubduction Zone ◽  
Ocean Ridge

AbstractThe late Cretaceous Kızıldağ ophiolite forms one of the best exposures of oceanic lithospheric remnants of southern Neotethys to the north of the Arabian promontory in Turkey. The ultramafic to mafic cumulate rocks, displaying variable thickness (ranging from 165 to 700 m), are ductiley deformed, possibly in response to syn-magmatic extension during sea-floor spreading and characterized by wehrlite, olivine gabbro, olivine gabbronorite and gabbro. The gabbroic cumulates have an intrusive contact with the wehrlitic cumulates in some places. The crystallization order of the cumulus and intercumulus phases is olivine (Fo86–77)± chromian spinel, clinopyroxene (Mg#92–76), plagio-clase(An95–83), orthopyroxene(Mg#87–79). The olivine, clinopyroxene, orthopyroxene and plagioclase in ultramafic and mafic cumulate rocks seem to have similar compositional range. This suggests that these rocks cannot represent a simple crystal line of descent. Instead the overlapping ranges in mineral compositions in different rock types suggest multiple magma generation during crustal accretion for the Kızıldağ ophiolite. The presence of high Mg# of olivine, clinopyroxene, orthopyroxene, and the absence of Ca-rich plagioclase as an early fractionating phase co-precipitating with forsteritic olivine, suggest that the Kızıldağ plutonic suite is not likely to have originated in a mid-ocean ridge environment. Instead the whole-rock and mineral chemistry of the cumulates indicates their derivation from an island arc tholeiitic (IAT) magma. All the evidence indicates that the Kızıldağ ophiolite formed along a slow-spreading centre in a fore-arc region of a suprasubduction zone tectonic setting.

The role of magma injection and crystal sorting in the formation of early gabbros at the Coldwell Complex, Ontario, Canada

2019 ◽  
Vol 56 (7) ◽  
pp. 715-737 ◽  
Author(s):  
Yong-hua Cao ◽  
David J. Good ◽  
Robert L. Linnen ◽  
Iain M. Samson
Keyword(s):  
Major Element ◽  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Chemical Compositions ◽  
Olivine Gabbro ◽  
Additional Observation ◽  
Midcontinent Rift ◽  
Layered Series ◽  
Incompatible Elements

The Layered Series of the Midcontinent Rift related Coldwell Complex comprises thick sections of gabbro, without any known associated ultramafic rocks. It represents a major early intrusive unit of the Coldwell Complex and consists of thick accumulations of olivine gabbro and oxide augite melatroctolite. This study combines petrography, mineral chemistry, and lithogeochemistry to constrain the magma composition and petrogenesis of the Layered Series. The presence of cumulus orthoclase together with the observation that the Layered Series rocks plot in the alkaline field on a total alkali–silica diagram indicate that the Layered Series magma has an alkaline parentage. The stratigraphy of the Layered Series cannot be fully correlated between different areas using lithogeochemistry and mineral chemistry. This together with observed normal and reverse trends for mineral chemical compositions in different areas suggest that the processes related to magma emplacement and crystallization were different in different locations. The whole-rock concentrations of incompatible elements and the compositions of major minerals of the olivine gabbro and oxide augite melatroctolite units are chemically similar. However, major element lithogeochemistry is variable, dominantly due to differences in the abundances of olivine, clinopyroxene, plagioclase, and magnetite. An additional observation is that olivine and clinopyroxene are not in chemical equilibrium. Together, these observations are interpreted to reflect a combination of multiple injections of magma and crystal sorting in an open system.

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