Geochemistry and petrogenesis of Ordovician arc-related mafic volcanic rocks in the Popelogan Inlier, northern New Brunswick

2003 ◽  
Vol 40 (9) ◽  
pp. 1171-1189 ◽  
Author(s):  
Reginald A Wilson
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Volcanic Rocks ◽  
Type I ◽  
Type Ii ◽  
Pyroclastic Rocks ◽  
Middle Ordovician ◽  
Element Abundances ◽  
Bearing Plate ◽  
Ridge Subduction

The Popelogan Inlier consists mainly of mafic volcanic rocks (lapilli tuffs and massive to amygdaloidal, plagioclase-phyric flows) of the Middle Ordovician Goulette Brook Formation. Pyroclastic rocks include high-MgO–Cr–Ni picritic tuffs (type I) containing, in some cases, >20% MgO, and related high-MgO andesitic tuff (type II). High-MgO rocks were generated by 30–40% partial melting of an enriched mantle source; type II is descended from type I mainly by fractionation of olivine. Mafic flows comprise basaltic andesites (type III) with low trace-element abundances and strongly fractionated, trace-element-enriched andesites (type IV). Types III and IV represent ~20 and ~10% partial melts, respectively, of a mantle source similar to that of the pyroclastic rocks, based on similar ratios of high field strength elements (HFSE). Unlike types I and II, petrogenesis of mafic flows involved fractionation of plagioclase and possibly amphibole. Volcanic arc signatures include negative Nb and Ti anomalies in all basalt types, along with low abundances of HFSE. Trace-element abundances are inconsistent with prior depletion in the back arc and require involvement of a mantle plume or subcontinental lithosphere. The highly magnesian composition of the picrites demands high melting temperatures and rapid transit through the crust, both of which suggest extension of the arc-bearing plate. Compositionally similar rocks in the South Pacific are associated with unusual tectono-magmatic settings involving ridge subduction, which may have established the necessary extensional environment. It is proposed that subduction of a plume-influenced ridge segment could explain the chemistry of the Goulette Brook volcanic rocks.

Episodic tourmaline growth and re-equilibration in mica pegmatite from the Bihar Mica Belt, India: major- and trace-element variations under pegmatitic and hydrothermal conditions

2016 ◽  
Vol 154 (1) ◽  
pp. 68-86 ◽  
Author(s):  
PRANJIT HAZARIKA ◽  
DEWASHISH UPADHYAY ◽  
KAMAL LOCHAN PRUSETH
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Major Element ◽  
Element Composition ◽  
Coarse Grained ◽  
Partial Replacement ◽  
Type I ◽  
Type Ii ◽  
Hydrothermal Conditions ◽  
Major Element Composition

AbstractMica pegmatites from the Bihar Mica Belt contain three distinct generations of tourmaline. The major-element composition, substitution vectors and trajectories within each group are different, which indicates that the three types of tourmalines are not a part of one evolutionary series. Rather, the differences in their chemistries as well their mutual microtextural relations, can be best explained by growth of tourmaline from pegmatitic melts followed by episodic re-equilibration during discrete geological events. The euhedral, coarse-grained brown type I tourmaline cores have relatively high Ca, Mg (XMgc. 0.37) and Al with correlated variation in Sr, Sc, Ti, Zr, Y, Cr, Pb and Rare Earth elements (REEs). They are inferred to have crystallized from pegmatitic melts. Monazites included within these tourmalines give chemical ages of 1290−1242 Ma interpreted to date the crystallization of the pegmatitic tourmaline. The bluish type II and greyish type III tourmalines with low Ca and Mg contents (XMg = 0.16−0.27) and high Zn, Sn, Nb, Ta and Na, formed by pseudomorphic partial replacement of the pegmatitic tourmaline via fluid-mediated coupled dissolution–reprecipitation, are ascribed to a hydrothermal origin. The ages obtained from monazites included in these tourmalines indicate two alteration events at c. 1100 Ma and c. 950 Ma. The correlated variation of Ca, Mg and Fe and the trace elements Sr, Sn, Sc, Zn and REE within the tourmalines indicates that the trace-element concentrations of tourmaline are controlled not only by the fluid chemistry but also by coupled substitutions with major-element ions.

The Durkan Complex in the western Makran Accretionary Prism (SE Iran): Evidence for a Late Cretaceous tectonically disrupted oceanic seamount

2020 ◽  
Author(s):  
Edoardo Barbero ◽  
Morteza Delavari ◽  
Asghar Dolati ◽  
Luca Pandolfi ◽  
Emilio Saccani ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Regional Scale ◽  
Volcanic Rocks ◽  
Accretionary Prism ◽  
Structural Domain ◽  
Type I ◽  
Accretionary Wedge ◽  
Type Ii ◽  
Type Iii ◽  
New Findings

<p>The Makran Accretionary Prism (SE of Iran) represents the less known segment of the Alpine-Himalayan orogenic system. It results from the Cretaceous to present-day convergence between the Arabian and Eurasian plates that was accommodated by the northward subduction of the Neotethys Ocean below the southern margin of Eurasia. As a peculiar feature, the Makran is the only segment of the Alpine-Himalayan orogenic system, in which subduction is still active. The North Makran is the innermost structural domain of the accretionary wedge. It consists of distinct complexes and tectonic units representing remnants of the Cretaceous-Paleocene accretionary-subduction phases. Among these, the Durkan Complex consists of several tectonic units, which include deformed Early Cretaceous-Paleocene carbonatic and volcanic successions, as well as rare Carboniferous, Permian and Jurassic slices of platform limestones. The Durkan Complex is commonly interpreted as representing the disrupted sedimentary cover of the passive margin of a micro-continent known in literature as the Bajgan-Durkan Complex. However, its stratigraphic succession, as well as the age and geochemistry of the volcanic rocks are still poorly known. Nevertheless, such data are fundamental for constraining its meaning for the pre-Eocene geodynamic evolution of the Makran Accretionary Prism. For this reason, we present new stratigraphic and petrological data on the westernmost sector of the Durkan Complex.</p><p>Our data show that the Durkan Complex includes distinct tectonic slices showing both slightly metamorphic and non-metamorphic highly-deformed stratigraphic successions. Stratigraphic data allow us to recognize three main types of successions. Type I consists of an alternation of pillow lavas and Albian-Cenomanian pelagic shales and radiolarites. Type II consists of pillow and massive lavas with minor volcaniclastic arenites grading up to an alternation of volcanic and volcaniclastic rocks and Cenomanian pelagic limestones and shales. Local intercalations of mass-transport deposits are common, particularly in the upper part of the sequence. Type III consists of pillow lava flows, volcanic breccia, and volcaniclastic sandstone overlain by an Albian-Cenomanian carbonatic platform. All these successions are stratigraphically overlain by a post-Cenomanian pelagic and hemipelagic sequence. Ages were determined by foraminifera and radiolarian biostratigraphy. The volcanic rocks in the distinct successions show similar geochemical features. They consist of basalt and minor trachybasalt showing alkaline affinity with high Nb/Y ratios (0.62 – 4.4), as well as marked LREE/HREE enrichment. The overall geochemical features of the rocks are comparable with those of alkaline oceanic within-plate basalts and plume-type MORBs.</p><p>In summary, our data show that the rock assemblages of the Durkan Complex represent the remnants of a seamount rather than remnants of continental margin successions, as it was previously described. The distinct successions of the Durkan Complex show tectono-stratigraphic features that can be reconciled to the cap (Type III), the slope (Type II), and the foothill (Type I) of a typical seamount environment. Finally, our new findings and regional-scale comparisons suggest that the Late Cretaceous alkaline magmatic pulse recorded in the Durkan Complex was likely related to mantle plume activity in the Makran sector of the Neotethys.</p>

Geochemistry of two metavolcanic arc suites from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada

1991 ◽  
Vol 28 (9) ◽  
pp. 1429-1443 ◽  
Author(s):  
Luc Harnois ◽  
John M. Moore
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Volcanic Rocks ◽  
Parental Magma ◽  
Major Elements ◽  
Grenville Province ◽  
Element Abundances ◽  
Felsic Rocks

Samples of two subalkaline metavolcanic suites, the Tudor formation (ca. 1.28 Ga) and the overlying Kashwakamak formation, have been analysed for major elements and 27 trace elements (including rare-earth elements). The Tudor formation is tholeiitic and contains mainly basaltic flows, whereas the Kashwakamak formation is calc-alkaline and contains mainly andesitic rocks with minor felsic rocks. The succession has been regionally metamorphosed to upper greenschist – lower amphibolite facies. Trace-element abundances and ratios indicate that rocks of the Tudor and Kashwakamak formations are island-arc type. Geochemical modelling using rare-earth elements, Zr, Ti, and Y indicates that the Tudor volcanic rocks are not derived from a single parental magma through simple fractional crystallization. Equilibrium partial melting of a heterogeneous Proterozoic upper mantle can explain the trace-element abundances and ratios of Tudor formation volcanic rocks. The intermediate to felsic rocks of the Kashwakamak formation appear to have been derived from a separate partial melting event. The data are consistent with an origin of the arc either on oceanic crust or on thinned continental crust, and with accretion of the arc to a continental margin between the time of extrusion of Tudor volcanic rocks and that of Kashwakamak volcanic rocks.

Geochemical constraints on the tectonic setting of the mafic rocks of the Bathurst Camp, Appalachian Orogen

1990 ◽  
Vol 27 (9) ◽  
pp. 1182-1193 ◽  
Author(s):  
A. Dogan Paktunc
Keyword(s):  
Trace Element ◽  
Gulf Of California ◽  
Tectonic Setting ◽  
Source Region ◽  
Ocean Basin ◽  
Mafic Rocks ◽  
Middle Ordovician ◽  
Element Abundances ◽  
Fine Grained ◽  
Back Arc

Abundant mafic rocks comprising basalts and gabbros occur in the Bathurst Camp, a complexly deformed Ordovician terrane in northeastern New Brunswick. The mafic rocks form a consanguineous suite of aphyric lavas, subvolcanic sills, and (or) dikes. Gabbros and basalts have somewhat similar major-element compositions but differ in terms of their trace-element contents. Medium-grained gabbros display tholeiitic compositions, whereas basalts and fine-grained gabbros have alkalic affinities. In general, trace-element abundances indicate an enriched source region for the Bathurst mafic rocks. Trace-element characteristics of the tholeiitic group point to a transitional setting going from back-arc to ocean basin, whereas the alkalic group has geochemical characteristics in common with within-plate basalts. Mixing between magmas of these contrasting settings could explain some of the trace-element characteristics of both groups. The back-arc-basin setting appears to be ensialic and is characterized by the absence of an underlying subducted slab during the formation of the basin. The tectonic reason for rifting in such a case could be the strike separation along a series of en echelon faults similar to those of the Gulf of California. Calc-alkaline characteristics of the upper mantle underlying the basin seem to have been inherited from southeasterly subduction of the proto-Atlantic Ocean in Early to Middle Ordovician times.

The Chengwatana Volcanics, Wisconsin and Minnesota: petrogenesis of the southernmost volcanic rocks exposed in the Midcontinent rift

1997 ◽  
Vol 34 (4) ◽  
pp. 536-548 ◽  
Author(s):  
Karl R. Wirth ◽  
Zachary J. Naiman ◽  
Jeffrey D. Vervoort
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Geothermal Gradient ◽  
Limited Range ◽  
Geochemical Data ◽  
Rift System ◽  
Midcontinent Rift ◽  
Element Abundances ◽  
Isotopic Compositions

The southernmost exposed rocks of the North American Midcontinent rift system (1100 Ma) consist of 3000 m of mafic volcanic flows and minor interflow sediment exposed along the St. Croix River in Minnesota and Wisconsin. The flows are mostly high-Fe tholeiitic basalt with plagioclase phenocrysts and ophitic to subophitic clinopyroxene. Abundant secondary chlorite, epidote, and actinolite indicate the group was metamorphosed to greenschist facies (~350 °C). Low sodium (M4 site) and tetrahedral aluminum (AlIV) contents of actinolite indicate low-pressure metamorphism (0.25 GPa) and imply a geothermal gradient of 45 – 50 °C/km. Low magnesium (Mg# = 0.37–0.58) and Ni contents (36–185 ppm) indicate the basalts have undergone significant fractionation and are not primary mantle melts. Incompatible element abundances are inversely correlated with Mg#, and most samples plot within either high or low trace element groups (e.g., Ti, P, Zr). The basalts are enriched in the light rare earth elements and Th, and are variably depleted in Ta and Nb relative to La and Th. Initial 143Nd/144Nd compositions of the group range from 0.51099 to 0.51122 (initial εNd = −4.5 to +0.1). Most flows have isotopic compositions within a relatively limited range (initial εNd = −2.5 to −1.6), but exhibit variable trace element abundances. Flows with the highest and lowest initial 143Nd/144Nd ratios have isotopic compositions that are inversely correlated with trace element abundances and ratios (e.g., La/Yb, Th/La, Th/Ta). The combined geochemical data suggest that the Chengwatana basalts originated from plume-derived melts and underwent variable fractional crystallization and crustal contamination. These melts may have interacted with lithospheric mantle enriched during Penokean subduction.

Petrogenetic modelling of Quaternary post-collisional volcanism: a case study of central and eastern Anatolia

2004 ◽  
Vol 141 (1) ◽  
pp. 81-98 ◽  
Author(s):  
PINAR ALICI ŞEN ◽  
ABİDİN TEMEL ◽  
ALAIN GOURGAUD
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Lithospheric Mantle ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Central Anatolia ◽  
Eastern Anatolia ◽  
Alkali Basalts ◽  
Alkaline Volcanism ◽  
Trace Elemental

Extensive continental collision-related volcanism occurred in Turkey during Neogene–Quaternary times. In central Anatolia, calc-alkaline to alkaline volcanism began in the Middle–Late Miocene. Here we report trace elemental and isotopic data from Quaternary age samples from central and eastern Anatolia. Most mafic lavas from central Anatolia are basalt and basaltic andesite, with lesser amounts of basaltic trachyandesite and andesite. All magma types exhibit enrichment in LILE (Sr, Rb, Ba and Pb) relative to HFSE (Nb, Ta). Trace element patterns are characteristic of continental margin volcanism with high Ba/Nb and Th/Nb ratios. 87Sr/86Sr and 143Nd/144Nd isotopic ratios of central Anatolian lavas range between 0.704105–0.705619 and 0.512604–0.512849, respectively. The Quaternary alkaline volcanism of eastern Anatolia has been closely linked to the collision between the Arabian and Eurasian plates. Karacadaǧ and Tendürek volcanic rocks are represented by alkali basalts and basaltic trachyandesites, respectively. As expected from their alkaline nature, they contain high abundances of LIL elements, but Tendürek lavas also show depletion in Nb and Ta, indicating the role of crustal contamination in the evolution of these magmas. 87Sr/86Sr and 143Nd/144Nd ratios of the Karacadaǧ and Tendürek lavas range from 0.703512 to 0.704466; 0.512742 to 0.512883 and 0.705743 to 0.705889 and 0.512676, respectively. Petrogenetic modelling has been used to constrain source characteristics for the central and eastern Anatolian volcanic rocks. Trace element ratio plots and REE modelling indicate that the central Anatolian volcanism was generated from a lithospheric mantle source that recorded the previous subduction events between Afro-Arabian and Eurasian plates during Eocene to Miocene times. In contrast, The Karacadaǧ alkaline basaltic volcanism on the Arabian foreland is derived from an OIB-like mantle source with limited crustal contamination. Tendürek volcanism, located on thickened crust, north of the Bitlis thrust zone, derived from the lithospheric mantle via small degrees (1.5 %) of partial melting.

Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine: evidence from trace element and isotope geochemistry

2004 ◽  
Vol 141 (2) ◽  
pp. 125-140 ◽  
Author(s):  
DAVID P. WEST ◽  
RAYMOND A. COISH ◽  
PAUL B. TOMASCAK
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Isotope Geochemistry ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Mafic Magma ◽  
Ocean Basin ◽  
Middle Ordovician ◽  
South Central ◽  
Back Arc

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469±3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (−1.3 to +0.6) and felsic (−4.1 to −3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting.

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