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The Cambrian to Cretaceous Tuhua Intrusives, New Zealand, preserve an igneous record of Phanerozoic subduction and crustal growth at the margin of Gondwana. Within the Tuhua Intrusives, the coeval gabbroic and trondhjemitic intrusions of the c. 261–243 Ma Longwood Suite stand out as being isotopically more primitive and chemically distinct from all other New Zealand plutonic suites. We present new U-Pb crystallization ages, trace element analyses and Sr-Nd isotope compositions of the Longwood Suite. U-Pb SHRIMP zircon ages of 258.5 ± 2.5 Ma, 256.0 ± 1.8 Ma, 247.8 ± 2.7 Ma and 243.2 ± 2.4 Ma obtained from plutons on Ruapuke Island, and a dike at Bluff, affirm the restricted time range and expand the known areal extent of the Longwood Suite. Longwood Suite granitoids are I-type and sodic (K/Na < 0.4), with distinctive low Rb and Nb/Ta, flat rare earth element patterns (La/Yb < 10), unradiogenic Sr/Sr (0.7029 to 0.7032) and radiogenic eNd (+6.3 to +8.2), compared to the nearby, calc-alkaline, Late Triassic Darran Suite I-type plutons of the Tuhua Intrusives. Stable Nd isotope ratios of Longwood Suite samples are highly variable (δNd = 233 ppm) compared to global plutonic rocks (δNd = 44 ppm) and reflect the removal of phosphate minerals. Collectively, these geochemical characteristics are consistent with generation of the granitoids by shallow (garnet-absent) melting of an amphibolitic residue, from which we infer relatively thin lithosphere. The Longwood Suite has a maximum areal addition rate of 43 km/Ma, substantially less than the subsequent plutonic suites when the magmatic arc was fully established. We suggest a petrotectonic model whereby Gondwana continental margin crust was tectonically underplated by Permian intra-oceanic island arc crust and mantle lithosphere, which subsequently melted to generate the isotopically primitive gabbro and trondhjemite plutons of the Longwood Suite.

The Ellsworth belt is one of several fault-bounded blocks exposed along the southeastern coast of Maine that formed within Ganderia. New ID-TIMS U–Pb geochronological data integrated with field relationships provide additional insights into the timing of magmatism and deformation in the Ellsworth belt. The deformed Lamoine Granite was selected for U–Pb zircon analysis to: (i) establish the protolith age; (ii) provide direct temporal constraints on regional low-grade metamorphism and deformation; and (iii) elucidate relationships between the Ellsworth belt and coeval rocks elsewhere in the Appalachian orogen. The Lamoine Granite was emplaced within the Ellsworth Schist at 492 ± 1.7 Ma; this is the first unequivocal evidence for a Furongian magmatic event in the Ellsworth belt. The schistosity in the Lamoine Granite is parallel to the main fabric of the host Ellsworth Schist and provides a maximum estimate for timing of the regional metamorphic overprint. Widespread deformation in the Ellsworth belt where kinematic indicators indicate a top-to-northwest sense of shear is attributed to thrusting during which progressive horizontal shortening, caused crustal thickening and peak greenschist facies metamorphism. The Cambrian U–Pb age permits correlation of the Lamoine Granite with the Cameron Road Granite in the Annidale belt of New Brunswick where subduction-related magmas intruded the Penobscot arc–back-arc and were subsequently deformed during the Penobscot Orogeny.

The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated TZr 6 wt.%). Zircon analyses by LA-ICP-MS and SHRIMP yielded a concordia age of 2 119±10 Ma for the porphyritic facies and an upper intercept age of 2 111±15 Ma for the equigranular facies. The whole-rock Sm-Nd TDM ages vary from 2.4 to 2.8 Ga with eNd(2.1) values between −0.7 and −5.3, indicating crustal derivation from distinct and/or heterogeneous protoliths. Field observations indicate that the Gentio metagranitoid was formed through different pulses of magma. Individual batches were subject to little or even no fractionation process after its emplacement. Although the Gentio metagranitoid crosscuts metamafic and metaultramafic rocks akin to an oceanic arc setting, this pluton is likely originated by partial melting of a more evolved quartz-feldspathic crustal igneous rock in a post-collisional environment, after the accretion of the arcs from the Mineiro belt and rocks of the Mantiqueira Complex.

Whole-rock major- and trace-element data are presented on a sample collection from the >3 Ga Amikoq Layered Complex (ALC), and hosting amphibolites within the Mesoarchean Akia terrane, SW Greenland. The lithologies range from leuconorite to melanorite/feldspathic orthopyroxenite, orthopyroxenite to harzburgite through to dunite, and tholeiitic basaltic–picritic mafic host rocks. The Amikoq Layered Complex samples are primitive (Mg#: 65–89) with elevated Ni and Cr contents. However, the absence of troctolitic lithologies and the presence of two orthopyroxene compositional trends, suggests that the successions might not be comagmatic. On the basis of trace-element cumulate models, relatively low Ni contents and minor negative Sr-Eu anomalies in some high-Ti ultramafic rocks, it is not possible to exclude a petrogenesis related to a melt similar to that of the mafic host-rocks. Ultramafic samples with U-shaped trace-element distribution patterns are petrogenetically related to the noritic sequences, either through cumulus mineral accumulation or melt-rock reactions. Assimilation-fractional-crystallisation modelling of melanorites nevertheless require the parental melt to have been contaminated/mixed with a component of island-arc-like tholeiite affinity. A boninite-like parental melt might have been derived from the subcontinental lithospheric mantle of the Akia terrane, or alternatively via assimilation of an ultramafic parental melt with island-arc-like tholeiite. Given the complex geological evolution and high-grade metamorphic overprint of the Amikoq Layered Complex, we are unable to differentiate between the two models.

The Famatinian is a segment of the Ordovician Terra Australis accretionary orogen that stretched along the SW Margin of Gondwana from Australia to Colombia. The present knowledge of this orogenic segment still is incomplete. We present geochemistry and U–Pb SHRIMP zircon geochronology of igneous and metamorphic rocks from the Central Famatinian Domain, one of the several domains recognized by Rapela et al. (Earth Sci Rev 187: 259–285. https://doi.org/10.1016/j.earscirev.2018.10.006) that includes the northern Sierras Pampeanas and the southern Puna of North West Argentina. Six samples of igneous rocks (peraluminous granitoids, mafic and felsic rocks, volcanic/subvolcanic rocks) and six samples of associated meta-sedimentary rocks, all from the Puna were dated and chemically analysed. The results indicate that the Central Famatinian Domain is in turn a composite domain that includes a Cordilleran-type magmatic arc (ca. 470 Ma) and a yuxtaposed fault-bounded older terrain formed in an extensional setting at the very start of the Famatinian orogeny, between 480 and 485 Ma, i.e., shortly after the SW Gondwana margin switched from passive to active. This short period of extension with related sedimentation, volcanism and mainly granitoid plutonism has not been previously recognised. It occurred before the Cordilleran-type magmatic arc -that resulted from a magmatic flare-up between ca. 473 and 468 Ma-, set up coincident with a contractional phase. The evidence confirms that accretionary orogeny results from tectonic switching (pull–push orogeny) and that the extensional and contractional phases are of relatively short duration.

The Gurupi Belt, in north-northeastern Brazil, is a mobile belt developed in the south-southwestern margin of the Sao Luis cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover. Field, petrographic, geochemical, geochronological, and Nd isotopic information (new and published) constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed. The Rhyacian was the main period of magmatic activity, which can be grouped into two main stages. (1) ~2185–2130 ​Ma: pre-collisional, juvenile, calc-alkaline magnesian and calcic ferroan granitoid suites, and minor calc-alkaline and tholeiitic mafic plutonism (now amphibolites), formed in intra-oceanic to transitional/continental arcs; and intra- or back-arc volcano-sedimentary basin. (2) ~2125–2070 ​Ma: syn- (two-mica granites) to late-collisional (potassic to shoshonitic granites and quartz-syenite) plutonic suites produced after crustal thickening and melting, with localized migmatization, that intruded during the compressive D1 deformational phase and concomitantly with greenschist to amphibolite metamorphism. There is a zonation of the Rhyacian episodes, with intra-oceanic stages occurring to the northeast, and the continental arc and collisional phases occurring to the southwest, indicating the presence of an active continental margin to the southwest, and subduction from NE to SW (present-day configuration). This magmatic framework is a continuation to the south of what is described for the Sao Luis cratonic fragment to the north, and the orogenic scenario is identical to what is observed for the same period in the West African Craton (Eburnean/Birrimian orogen), which additionally supports previous geological correlations. In the Neoproterozoic, a few magmatic occurrences are recognized. An extensional event allowed the intrusion of an anorogenic, nepheline syenite at ca. 730 Ma, which was followed by the intrusion of a crustal, calc-alkaline microtonalite, of uncertain tectonic setting, at 624 ​Ma. Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 ​Ma. This metamorphic event is probably related to crustal thickening, which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 ​Ma. The absence of oceanic and arc-related assemblages, along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic–Early Cambrian evolution of the Gurupi Belt, with rifting and posterior closure of the basin, without oceanization. Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly, respectively, but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events, but, instead, as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time.

The Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive m...

International audience; In this work, we present the results of a petrographic and geochemical study that involves seven Cenozoic plutons located in a NS trending belt in western Patagonia, south of the present Chile Triple-Junction and to the east of the present magmatic arc. Four plutons were studied in the northern end, and three in the southern part of the belt. The petrographic and geochemical characteristics (major and trace element contents, eNdt, 87Sr/86Sr initial ratios), of these plutons are different enough to propose a further classification for them: Only the Monte Balmaceda intrusive complex in the southern end of the belt is alkaline (sensu stricto). The Río de Las Nieves and San Lorenzo plutons in the northern area, and the Torres del Paine intrusive complex, in the southern area have “intra-plate transitional” calc-alkaline affinity. Paso de Las Llaves and Cerro Negro del Ghío plutons in the northern area, and Cerro Donoso pluton in the southern area show “arc transitional” calc-alkaline character. The “transitional” character, together with the pluton’s location, and their regional geological context, can be explained by a Mio-Pliocene eastward arc migration coeval with the beginning of the Chile Rise subduction. A slab flattening hypothesis is favoured to explain the arc-migration, which together with the different length and time of arrival of the Chile Rise segments to the subduction zone, contributed to the heterogeneous geochemistry of the studied plutons.

We present a new dataset of zircon U–Pb ages that document igneous activity in the SW Japan arc during middle Miocene time and discuss its relationship with the opening of the Japan Sea, Philippine Sea plate migration, and subduction of the young hot lithosphere of the Shikoku Basin. Precursory magmatism, characterized by dike and stock intrusions, startedc. 15.6 Ma in both Kyushu and the Kii Peninsula. Most plutonism occurred between 15.5 and 13.5 Ma in an area 600 km long and 150 km wide. No along-arc trend was recognized in the U–Pb ages of igneous activity near the trench. Our data indicate that all near-trench middle Miocene igneous activity occurred immediately after the opening of the Japan Sea ceased, i.e. after 16 Ma, implying that melt extraction and the emplacement of granites in the near-trench region had some influence on the back-arc opening. Our data also imply that the trench–trench–trench-type triple junction between the Japan arc and the Izu–Bonin–Mariana arc must have reached the east side of the Kii Peninsula by 15.6 Ma. The wide distribution of contemporaneous magmatic activity along the arc requires a trench-parallel heat source, such as the subduction of a trench-parallel ridge or a young and highly segmented ridge–fracture zone system in addition to the hot wedge mantle condition related to the opening of Japan Sea.

U-Pb baddeleyite ages for key mafic dykes of the Amazonian Craton reveal four significant intraplate episodes that allow connections with global igneous activity through time and supercontinent cycles. The oldest dykes (Carajas-Rio Maria region) are diabases with ages of 1880.2 ± 1.5 Ma and 1884.6 ± 1.6 Ma, respectively, corresponding with the Tucuma swarm which crops out to the west and is age-equivalent. The magmatic activity has a genetic link with the ca. 1.88 Ga Uatuma Silicic Large Igneous Province (SLIP), characterized by felsic plutonic-volcanic rocks. There is an age correlation with LIP events (ca. 1880 Ma) in the Superior, Slave, Indian and other cratons. This magmatism could be derived from significant perturbations of the upper mantle during the partial assembly of Columbia. Gabbronorite of the Rio Perdido Suite (Rio Apa Terrane) crystallized at 1110.7 ± 1.4 Ma, and is identical to that of the Rincon del Tigre-Huanchaca LIP event of the Amazonian Craton. This event was synchronous with the initiation of Keweenawan magmatism of central Laurentia (Midcontinent Rift) and also with coeval units in the Kalahari, Congo and India cratons. The two youngest U-Pb dates (535 and 200 Ma) occur in the Carajas region. Diabase of the Paraupebas swarm yields an age of 535.1 ± 1.1 Ma, which may be correlative with the giant Piranhas swarm located ca. 900 km apart to the west. The Paraupebas swarm is correlative with post-collisional plutonism within the Araguaia marginal belt. Therefore, the Cambrian dykes may reflect reactivation of cooled lithosphere, due to crustal extension/transtension active along the craton’s margin during assembly of West Gondwana. This magmatism is also contemporaneous with the 539–530 Ma Wichita LIP of southern Laurentia. The youngest studied Carajas region dyke was emplaced at ca. 200 Ma, corresponding with 40 Ar/ 39 Ar ages for the Periquito dykes west of Carajas and with most K-Ar ages of the giant Cassipore swarm, located north of the study area. The newly dated ca. 200 Ma dyke fits well into the known, brief span of ages for the CAMP Large Igneous Province event, around the present central and northern Atlantic Ocean.

Las Canas Plutonic Complex (LCPC) is a small representative of the Famatinian Ordovician plutonism (470.4 ± 8.1 Ma) located in the northeastern sector of Sierra Grande de San Luis, Argentina. The LCPC was emplaced into a metasedimentary sequence, which reached their metamorphic climax under high-temperature/low-pressure conditions (∼680 ± 37 °C and 550 ± 120 MPa). The bodies of the LCPC are zoned by rocks of different compositions that represent ultrabasic, basic, intermediate and acidic trends (hornblendites, gabbros, tonalites, and granodiorites). Their petrological, mineralogical and geochemical characteristics indicate that multiple processes formed them, mainly crystal fractionation of magnesian, calc-alkaline and metaluminous magmas (typical of arc), but also different assimilation degrees of crustal melts from the fusion of metawackes involving AFC processes. Fieldwork (structural and petrological data), the geochemical characteristics of rocks [eg. Low Sr/Y and (Gd/Yb)C-N], and thermobarometric results, indicate a relatively shallow fractionalization for the LCPC, which is in line with a pre-collisional arc stage linked to an extensive retro-arc setting for the Famatinian orogeny in Sierra de San Luis.

Under oblique convergence, the intraoceanic subduction zones tend to have a tectonically-escaped accretionary prism, incorporates exotic materials from different sources and oceanic crust fragments. The western part of the Allaqi-Heiani suture (AHS) is the type locality for a significant accretionary prism extends for ⁓ 200 km; this prism is mainly metavolcanic, and metasedimentary rocks have interwoven serpentinite, marble blocks and intruded with different phases of plutonism. Geologic studies of the western part of the AHS have suggested the allochthonous origin for this complex, and terrane accretion happened earlier than ⁓ 700 Ma and subsequently thrusted over Gabgaba terrane to the south. Magnetic data was applied to follow the deep-seated structures and the connectivity between ophiolite belts in the AHS. Magnetic data unravelled the presence of a deep-seated strike-slip faults aligned along N–S and NNE trends underneath the northern belt, and this fault zone was erased at the surface by a major zone of the post-accretionary left-lateral strike-slip faults. In the southern part, E-W and WNW-ESE faults are dominant at the edge of the autochthon Gabgaba terrane. At greater depths, thrusts related to the emplacement of the northern belt disappeared, while those to the south aligned with the suture zone becomes significant. In conclusion, there are two ophiolite belts are located in the western part of the AHS; the southern belt is extended along the edge of the Gabgaba terrane to the south and the Eastern Desert (ED) to the north. This south belt is the western extension of a major arc-arc suture zone that extends to the east into the Arabian shield. The northern ophiolite belt was emplaced onto the southern part of the ED ⁓ 70 km away from the arc-arc to the south.

The Vinjamuru Domain is an important crustal segment in the Nellore schist belt (NSB) and the tectono-metamorphic evolution of the belt provides insights into Proterozoic orogenesis in southeastern India, and is also relevant to an Indo-Antarctic correlation in the Late Paleoproterozoic and Middle Mesoproterozoic. Garnet-staurolite-kyanite bearing metapelites in this domain exhibit three metamorphic stages, e.g. M1S, M2S and M3S in the Saidapuram–Sangam area (sector-S) and M1N, M2N and M3N in the Vinjamuru–Malakonda area (sector-N). In both sectors, the metapelites exhibit shallow foliation (S2) axial planar to recumbent folds (F2) of an earlier schistosity (S1), and overprinted by gently-plunging upright F3 folds, with axial planar fabric (S3) trending north in sector-S, and NNE in sector-N. Syn-D3S garnet + staurolite + kyanite + muscovite + biotite + quartz + ilmenite ± plagioclase and garnet (late-D2N to early-D3N) + kyanite + muscovite + biotite + quartz + ilmenite + plagioclase ± staurolite assemblages characterize the peak metamorphic episodes in the sector-S (M3S, P = 8.8–9.2 kbar, T = 630–650 °C) and sector-N (M3N, P = 6.5–7.5 kbar, T = 620–640 °C) respectively. The peak P–T conditions in the metapelites (M3S/M3N) are broadly contemporaneous with the steep-dipping S3S in sector-S and shallow-dipping S2N in sector-N. Total-Pb monazite dating in the chemically distinct monazite domains yields age populations at 1.65–1.55 Ga, 1.50–1.40 Ga, 1.38–1.25 Ga and 0.84–0.76 Ga. The oldest age population (1.65–1.55 Ga) possibly corresponds to large-scale reworking of the pre-existing crust in the Vinjamuru domain. Subsequently, the domain experienced prograde metamorphism (M1S/M1N–M2S/M2N) between 1.50 and 1.40 Ga, which may be attributed to a mid-crustal shortening within the NSB. The 1.38–1.25 Ga ages correspond to upper amphibolite facies metamorphism (M3S/M3N) and coincides with widespread felsic plutonism in the NSB. The Neoproterozoic ages (0.84–0.76 Ga) arguably represent an alteration event that affected the NSB during Rodinia supercontinent breakup. The Mesoproterozoic metamorphism and the long-lived orogenic events (1.65–0.76 Ga) in the Vinjamuru domain are similar to those recorded in the basement rocks of East Antarctica, suggesting a possible tectonic linkage along accretionary margins.

The well-characterized Sierra Nevada magmatic arc offers an unparalleled opportunity to improve our understanding of continental arc magmatism, but present bedrock exposure provides an incomplete record that is dominated by Cretaceous plutons, making it challenging to decipher details of older magmatism and the dynamic interplay between plutonism and volcanism. Moreover, the forearc detrital record includes abundant zircon formed during apparent magmatic lulls, suggesting that understanding the long-term history of arc magmatism requires integrating plutonic, volcanic, and detrital records. We present trace-element geochemistry of detrital zircon grains from the Great Valley forearc basin to survey Sierra Nevadan arc magmatism through Mesozoic time. We analyzed 257 previously dated detrital zircon grains from seven sandstone samples of volcanogenic, arkosic, and mixed compositions deposited ca. 145–80 Ma along the length of the forearc basin. Detrital zircon trace-element geochemistry is largely consistent with continental arc derivation and shows similar geochemical ranges between samples, regardless of location along strike of the forearc basin, depositional age, or sandstone composition. Comparison of zircon trace-element data from the forearc, arc, and retroarc regions revealed geochemical asymmetry across the arc that was persistent through time and demonstrated that forearc and retroarc basins sampled different parts of the arc and therefore recorded different magmatic histories. In addition, we identified a minor group of Jurassic detrital zircon grains with oceanic geochemical signatures that may have provenance in the Coast Range ophiolite. Taken together, these results suggest that the forearc detrital zircon data set reveals information different from that gleaned from the arc itself and that zircon compositions can help to identify and differentiate geochemically distinct parts of continental arc systems. Our results highlight the importance of integrating multiple proxies to fully document arc magmatism, demonstrating that detrital zircon geochemical data can enhance understanding of a well-characterized arc, and these data may prove an effective means by which to survey an arc that is inaccessible and therefore poorly characterized.

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO2 = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO2 = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045–0.707959, εNd(t) = −3.23 to +3.80, and the Nd model ages (TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.705513 to 0.707275 and εNd(t) from −1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite. Keywords: Urumieh–Dokhtar magmatic belt, Granitoid rocks, Subduction, Zircon U–Pb ages, Radiogenic isotopes, Central Iran

The western Indian volcanic rifted margin, and its large-scale tectonic feature called the Panvel flexure, formed at 62.5 Ma during the late stages of Deccan Traps flood volcanism. We present a geological account of late-stage (≤ 62.5 Ma) Deccan volcanism and plutonism in the relatively poorly studied Thane–Vasai region in the Panvel flexure zone. The study area shows west-dipping basaltic sequences up to hundreds of meters thick, overlain by pyroclastic deposits of various types. The volcanic units are intruded by gabbro plutons, and all these units are in turn intruded by dykes of varied compositions (including tholeiitic basalt, lamprophyre, and granophyre). There are also early tholeiitic dykes, some of which may be feeders to the basaltic sequence. We focus on the gabbro intrusions and provide extensive petrographic and mineral chemical data on them. The gabbros are tholeiitic, and of considerable interest in commonly containing interstitial silicic melts (granophyre or silicic glass). One of the intrusions, the Chena pluton, shows clear outcrop transitions from gabbro, and gabbro with interstitial granophyre, to transitional gabbro-granophyre, and then to a distinct upper zone of granophyre and microgranite. Granophyre is common in mafic intrusions in continental flood basalt provinces of the world (e.g., the Palisades Sill and the Skaergaard Intrusion), where its genesis is ascribed to mechanisms such as fractional crystallisation, liquid immiscibility, or crustal melting, typically based on geochemical data. The Chena gabbro outcrops are valuable in providing direct evidence for a fractional crystallisation origin of the granophyres (and silicic glasses) found in the Thane–Vasai gabbro intrusions, with which the mineral chemical compositions are also consistent.

Shallow high-silica granites provide a window into processes that may precede many styles of rhyolitic volcanic eruptions., Rhyolitic melt that fuels explosive eruptions often originates in the upper crust via extraction from crystal-rich sources, implying an evolutionary link between volcanism and residual plutonism. However, the time scales over which these systems evolve are mainly understood through erupted deposits, limiting confirmation of this connection. Exhumed plutons that preserve a record of high-silica melt segregation provide a critical subvolcanic perspective on rhyolite generation, permitting comparison between time scales of long-term assembly and transient melt extraction events. Here, U-Pb zircon petrochronology and 40Ar/39Ar thermochronology constrain silicic melt segregation and residual cumulate formation in a ~7 to 6 Ma, shallow (3 to 7 km depth) Andean pluton. Thermo-petrological simulations linked to a zircon saturation model map spatiotemporal melt flux distributions. Our findings suggest that ~50 km3 of rhyolitic melt was extracted in ~130 ka, transient pluton assembly that indicates the thermal viability of advanced magma differentiation in the upper crust.

The southern part of the West African Craton includes the Baoule-Mossi Domain, the world’s premier Paleoproterozoic gold province (~10,000 metric ton gold endowment). Structural, metamorphic, and geochronological data suggest gold mineralisation occurred during three episodes that span much of the Eoeburnean and Eburnean orogenic cycles. Eoeburnean orogenic and rare skarn-hosted gold deposits formed between ca. 2200 and 2135 Ma during repeated episodes of volcanism, plutonism, and shortening, which thickened the Paleoproterozoic crust. Early Eburnean orogenic and placer gold deposits formed between ca. 2110 and 2095 Ma during inversion, metamorphism, and subsequent oblique shortening of intra-orogenic basins filled after ca. 2135 Ma. This episode of mineralisation terminated when the Baoule-Mossi Domain docked with the Archean Kenema-Man Domain at ca. 2095 Ma. Late Eburnean orogenic and less common intrusion-related gold deposits formed between ca. 2095 and 2060 Ma during strike-slip to oblique-slip tectonics, post-collisional high-K plutonism and crustal reworking across the western and southern Baoule-Mossi Domain. Eoeburnean gold deposits include ca. 10 % of the gold endowment of the Baoule-Mossi Domain, whereas the Early Eburnean and Late Eburnean deposits include ca. 50–70% and 20–40%, respectively. Here, we highlight the favourable confluence of accretion-collision tectonics, involving juvenile crust formation as well as protracted magmatic, metamorphic, and deformation histories that resulted in diachronous gold events spread over at least 100 myr throughout the Baoule-Mossi Domain.

Role of arc(s) formation in the development of the Neoproterozoic Arabian–Nubian Shield (ANS) is very important, particularly from the geotectonic perspective. For almost two decades, several models have been suggested for the ANS evolution in which the theory of plate tectonics is accredited and the old geosynclinal theory is abandoned. In this respect, the models include (1) infrastructural model, (2) Turkic-type orogenic model, (3) hot-spot model and (4) arc accretion model. In this chapter, basics of arc assembly/arc accretion are presented aiming to understand the evolution of the ANS in a reasonable way. Ages of arc collisions are discussed with an emphasis on the mechanism and structure(s) of the arc collision stage. Owing to their intimate relationship with the formation of arc systems, their distribution, age, field characteristics (including rock associations), geochemistry and petrogenetic models are given. The chapter sheds light on the role of arc formation when the so-called core or gneissic complexes are developed, particularly in the Egyptian Eastern Desert (e.g. at Hafafit, Beitan, Khud’a, El-Shelul and Sibai). Such complexes are widely accepted in recent works to represent syn-arc collision massive plutonic injections along thrusts. This took place during the arc collisions opposing an old concept that considers them as pre-Pan-African windows to the old continent (i.e. infrastructural unit). A synopsis on the terranes including gneissic rocks is given, which deals with the metamorphic complexes in the Sinai Peninsula, in addition to some notes for the aerial distribution and age of accretions in the Neoproterozoic shield of Saudi Arabia.

Low-pressure metamorphic assemblages are very common in many orogenic belts. Characteristically, they are related to the thermal metamorphism caused by post-orogenic rift-related plutonism. However, it has proven correct that magmatic activity at any stage of the orogen can provide the required temperature to initiate and drive the metamorphism. The Arabian–Nubian Shield (ANS), the northern part of the Neoproterozoic East African Orogen (EAO), is characterized by widespread exposures of the pelites-dominated metasedimentary terranes originated in different tectonic settings. Low-pressure metamorphic belts constitute important components, controversial in places, of some of these terranes. The current chapter documents the field characterization of four multiply deformed and metamorphosed low-pressure/medium- to high-temperature metamorphic belts located in the Eastern Desert and Midyan terranes in the extreme north-eastern tip of the ANS.

NJG thanks Australian Research Council grant FL160100168 for financial support. The northern part of the North Atlantic Craton (NAC) in southern West Greenland comprises a large tract of exposed Meso-Neoarchaean continental crust, divided into the ca 3300–2900 Ma Akia and ca 2900–2500 Ma Tuno terranes. We combine aeromagnetic, stream sediment geochemical, new litho-chemical and zircon geochronological data with previously published data to re-evaluate the crustal architecture and evolution of the Akia terrane and its boundary towards the Tuno terrane. The previously recognised, but overlooked, Alanngua complex, situated between the Akia and Tuno terranes is bounded by aeromagnetic lineaments interpreted as Neoarchaean shear zones and has a distinct spectrum of Neoarchaean magmatic and metamorphic zircon ages that are rare in the Akia terrane. The Alanngua complex comprises components derived from both the Akia and Tuno terranes and is interpreted as a tectonic melange created during the Neoarchaean assembly of the NAC. Within the Akia terrane, the chemistry of orthogneiss samples indicate that a large percentage is too mafic to classify as TTG s.s., implying that not only partial melting of mafic crust, but also some yet unaddressed mantle involvement is necessary in their formation. Previous models for the generation of the ca. 3015–2990 Ma quartz-dioritic Finnefjeld and Taserssuaq complexes conflict with their geochemical variation. The complexes are spatially associated with strong aeromagnetic responses that are interpreted to reflect a large gabbro-diorite intrusion, and we propose that the protoliths of the Finnefjeld and Taserssuaq complexes are genetically linked to such intrusion. Formed at same time are carbonatite, high-Mg gabbro and tonalite-trondhjemite, and we propose that this wide spectrum of rocks could have formed by lithospheric and crustal melting in response to asthenospheric upwelling possibly in an extensional setting. Periods of extensive magmatism in the Akia terrane were previously recognised at ca. 3220-3180 Ma and 3070-2970 Ma. We now subdivide the latter period into three episodes: juvenile basaltic-andesitic volcanism at 3070–3050 Ma; tonalitic and dioritic plutonism at 3050–3020 Ma, and gabbroic-dioritic plus tonalitic-trondhjemitic plutonism at 3020–2985 Ma. This last episode was immediately followed by crustal reworking during collision at 2980–2950 Ma. Publisher PDF

I am pleased to learn that James Forbes’ notes from Jameson's lecture course survive at the University of St Andrews and thank John Gordon for bringing their existence to general notice. Cunningham (1990) provides a good summary and the timing of Forbes’ attendance is particularly useful. As a student in the 1827–28 session, …

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, withTDM2model 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.

The Vale do Cura&ccedil, &aacute, and Riacho do Pontal copper districts are located within the northern part of the Archaean S&atilde, o Francisco Craton and represent two pulses of mineralization. The copper districts have been identified as Iron-Oxide-Copper-Gold (IOCG) classes of deposits. An older metallogenic event associated with the Cara&iacute, ba copper deposit, which is located in the Vale do Cura&ccedil, district, is related to Palaeoproterozoic (ca. 2 to 2.2 Ga) hydrothermal processes. A younger Neoproterozoic (ca. 750 to 570 Ma) episode of volcanism and associated plutonism is represented by the Riacho do Pontal mineral district. Seismic tomography data from across east-central Brazil show that the multiage Caraj&aacute, s province and Vale do Cura&ccedil, and Riacho do Pontal copper districts sit along either side of a prominent NW-trending upper lithospheric high-velocity zone. The edges of the high-velocity zone point to long-lived subparallel transcrustal structures that have been the focus of multiple reactivations and copper mineralization events. Regional gravity and magnetic maps show that the Vale do Cura&ccedil, copper district extends over an area greater than 110 km by 22 km. The magnetic and gravity values show significant variations correlated with this area. The district includes high gravity values associated with the Cara&iacute, ba copper mine (&gt, &minus, 35 mGal), which has a greater density (3.13 g/cm&sup3, ) than the nonmineralized host rock density (2.98 g/cm&sup3, ). The gravity anomaly signature over the Riacho do Pontal copper district is characterized by a 40-km long NW&ndash, SE trending Bouguer gravity low. The Ria4 occurrences of the Riacho do Pontal copper district are situated in these regional low-gravity domains. Data from regional airborne magnetic and ground gravity surveys were inverted to obtain a 3D magnetic susceptibility and density model, respectively, for the known districts. The results show that the Cara&iacute, ba deposit is characterized by a both dense and magnetic source showing structural control by thrust shear zones. The 2D and 3D geological models show two main NNW prospective trends. Trends I and II have a sigmoidal shear shape and are positioned in the contact zone between domains with high magnetic susceptibility (SI &gt, 0.005) and density &gt, 0 g/cm&sup3, ). Trend I is 40 km &times, 10 km in size and hosts the Cara&iacute, ba, Surubim, and Vermelho copper mines and other minor deposits. The results obtained from the 3D magnetic inversion model for the region of the Riacho do Pontal district show weak magnetic anomaly highs extending along a NW&ndash, SE magnetic gradient trend. The gradient is related to mapped shear zones that overprint older and deeper NE&ndash, SW features of the S&atilde, o Francisco cratonic root. The area includes high gravity values associated with the Cara&iacute, ba copper deposit, which has a greater density (3.13 g/cm&sup3, ) than the nonmineralized host rock density (2.4 g/cm&sup3, ).

The Batié granitic massif in western Cameroon is NE–SW elongated, follows the regional foliation, and is parallel to the Kekem–Fotouni shear zone, which is the southwestern extension of the Tcholliré–Banyo Fault (TBF). This massif comprises two petrographic units: biotite granite and amphibole granite. Major, trace, REE, Sr–Nd isotopic, and new U–Pb data are used to constrain their nature and origin. The results indicate that they are high-K alkali-calcic with shoshonite affinity. The amphibole granite is metaluminous, whereas biotite granite is weakly peraluminous. Both granites are high-temperature I-type granites and crystallized under oxidizing conditions. Initial (87Sr/86Sr)620 Ma ratios (0.7062–0.7080) and εNd620 Ma (−12.6 to −8.9) indicate that the parental magmas were produced by partial melting of thick Paleoproterozoic crust and were mixed with felsic magma from the upper continental crust. Their Nd TDM typically varies from 1.68 to 1.96 Ga. The massif was mostly emplaced between 630 and 547 Ma during the transitional period between the crustal thickening (630–610 Ma) and the development of the shear zones, which began with sinistral movements (610–580 Ma) and continued with dextral movements (585–540 Ma). Plutonism continued during the dextral movements. The Batié granite is geochemically and isotopically similar to other post-collisional pan-African granitic massifs located along the TBF.

Hyper-solidus fabrics of the early Permian Brocken granite pluton, exposed over an area of c. 160 km² and elongated in NNE–SSW direction, were determined by measuring the anisotropy of magnetic susceptibility (AMS). The Brocken granite pluton consists of five petrographically distinguishable and mappable granitic varieties characterized by a generally paramagnetic behavior with primary biotite, partly altered to chlorite, and secondary tourmaline as the major carrier of the susceptibility. Whereas biotite modal content isolines roughly follow petrographic trends, the tourmaline modal contents do not, hence implying secondary, post-emplacement processes that controlled tourmaline distribution. A few samples with primary and secondary magnetite show ferrimagnetic behavior and are co-axial with the paramagnetic fabrics. The generally low magnetic anisotropies in all granitic varieties are a distinct and challenging feature for determining magmatic flow directions. AMS data indicate the predominance of sub-horizontal fabrics outlining an NNE–SSW trending dome axis interpreted to have resulted from granite sheets stacked syn-magmatically in a high crustal level building up a laccolithic pluton. AMS fabrics together with age data and geophysical indications suggest that the emplacement and distribution of the Brocken granite pluton is structurally controlled by NNE–SSW striking deep fault structures, and only weakly influenced by WNW/NW-trending structures. Late Carboniferous-to-early Permian plutonism in the Harz Mountains evolved in an E–W directed extensional regime, and was accompanied by volcanic activity and development of NW- and NE-trending sedimentary basins.

The Ga’erqiong-Galale ore district in the Bangong-Nujiang metallogenic belt hosts two large skarn Cu-Au deposits, associated with voluminous Late Cretaceous volcanism and plutonism. In this study, we present new zircon U-Pb age and Hf isotopic data, whole-rock geochemical and Sr-Nd-Pb isotopic data to constrain the geodynamic mechanisms of Late Cretaceous magmatism and metallogenesis within the Ga’erqiong-Galale ore district. The intrusive rocks in the district include diorite, quartz diorite, granodiorite, granite, and dioritic porphyrite. Zircon U-Pb analyses suggest those rocks mainly emplaced at early Late Cretaceous (84–95 Ma), which coincide with the ore-forming age of Ga’erqiong and Galale deposits (87 and 88 Ma, respectively). Geochemically, the granodiorite and dioritic porphyrite are metaluminous with depletion of Nb, Ta, and Ti and characterized by high MgO (2.68–4.16 wt%), Mg # (55–87), Sr (414–616 ppm), Sr/Y (30–56), Cr (22.5–105.0 ppm), and Ni (26.6–59.7 ppm), low Y (10.6–14.0 ppm), and heavy rare earth elements (HREE), showing geochemical signatures of high Mg# adakitic rocks. Four dioritic porphyrite and three granodiorite samples exhibit homologous Sr-Nd-Pb isotope compositions and have positive whole rock eNd(t) values of +1.1 to +3.0, (87Sr/86Sr)i values of 0.7045–0.7048, (206Pb/204Pb)t ratios of 18.42–18.73, (207Pb/204Pb)t ratios of 15.58–15.63, and (208Pb/204Pb)t ratios of 38.54–38.88. Besides, 116 analyses from the Ga’erqiong-Galale adakitic rocks give positive zircon eHf(t) values (+4.3 to +12.1). The geochemical and isotopic data indicate that the early Late Cretaceous high Mg# adakitic rocks in the Ga’erqiong-Galale ore district originated from the delaminated juvenile lower mafic crust that has been modified by the previously subduction. Partial melting of previously subduction modified, delaminated juvenile lower crust not only formed the hydrous adakitic melts in highly oxidation state, but also provided the ore metals (e.g., Cu, Au, Mo) for the subsequent mineralization. Such melts reacted with surrounding mantle peridotite to elevate the contents of metallic elements again. Then the melts experienced varying degrees of fractional crystallization process in the shallow magma chamber to form the dioritic and granodioritic magmas. Those magmas emplaced into the limestone of Duo’ai and Jiega Formation to form the Ga’erqiong and Galale skarn Cu-Au deposits, respectively. Field observation, together with geochronological and geochemical data, indicate that the early Late Cretaceous mineralization events in the northern and central Lhasa subterranes took place in a transition tectonic setting from collisional orogeny to extension and the input of subduction modified juvenile crust play an important role in the Late Cretaceous ore-forming events.

We present field and petrographical characteristics, zircon U–Pb ages, Nd isotopes, and major and trace element data for the magmatic epidote-bearing granitic plutons in the Bellur–Nagamangala–Pandavpura corridor, and address successive reworking and cratonization events in the western Dharwar Craton (WDC). U–Pb zircon ages reveal three stages of plutonism including: (i) sparse 3.2 Ga granodiorite plutons intruding the TTG (tonalite–trondhjemite–granodiorite) basement away from the western boundary of the Nagamangala greenstone belt; (ii) 3.0 Ga monzogranite to quartz monzonite plutons adjoining the Nagamangala greenstone belt; and (iii) 2.6 Ga monzogranite plutons in the Pandavpura region. Elemental data of the 3.2 Ga granodiorite indicate their origin through the melting of mafic protoliths without any significant residual garnet. Moderate to poorly fractionated REE patterns of 3.0 Ga plutons with negative Eu anomalies and Nd isotope data with eNd(T) = 3.0 Ga ranging from −1.7 to +0.5 indicate the involvement of a major crustal source with minor mantle input. Melts derived from those two components interacted through mixing and mingling processes. Poorly fractionated REE patterns with negative Eu anomalies of 2.6 Ga plutons suggest plagioclase in residue. The presence of magmatic epidote in all of the plutons points to their rapid emplacement and crystallization at about 5 kbars. The 3.2 Ga intrusions could correspond to reworking associated with a major juvenile crust-forming episode, whilst 3.0 Ga potassic granites correspond to cratonization linked to melting of the deep crust. The 2.6 Ga Pandavpura granite could represent lower-crustal melting and final cratonization, as 2.5 Ga plutons are absent in the WDC.

Robert Jameson is generally remembered for championing Neptunist geology (originated by Abraham Werner) during its early nineteenth-century competition with the rival Plutonist theory (initiated by James Hutton). Hutton9s ideas prevailed and Jameson9s intellectual transition to Plutonism is documented in the surviving notes taken by students who attended his lectures at Edinburgh University: one early record is from 1809, a second record is from c. 1820 and four sets of notes are from the early 1830s. Of the latter four, two have not been previously considered from a geological perspective and prove to be the most revelatory of Jameson9s conversion; notes compiled by the Royal Navy surgeon Robert McCormick are particularly comprehensive. Although Jameson attempted to maintain the essentials of Werner9s theory for its well-ordered stratigraphy, he progressively adopted a Plutonist approach to more contentious issues such as the origin of granite, veining and mountain building. Jameson used Edinburgh9s Salisbury Crags sill for field demonstrations and the students’ notes illustrate his changing views in terms of the origins of this classic geological feature. Of the students whose lecture notes survive, it is only McCormick for whom Jameson appears to have been a lasting geological influence.

In paleogeographic reconstructions of the Columbia and Rodinia Supercontinents, the position of the Greater India landmass is ambiguous. This, coupled with a limited understanding of the tectonic evolution of the mobile belts along which the mosaic of crustal domains in India accreted, impedes precise correlation among the dispersed crustal fragments in supercontinent reconstructions. Using structural, metamorphic phase equilibria, chronological and geochemical investigations, this study aims to reconstruct the tectonic evolution of the Chottanagpur Gneiss Complex (CGC) as a distinct crustal block at the eastern end of the Greater Indian Proterozoic Fold Belt (GIPFOB) along which the North India Block (NIB) and the South India Block (SIB) accreted. The study focuses on two issues, e.g. dating the Early Neoproterozoic (0.92 Ga) accretion of the CGC with the NIB contemporaneous with the assembly of Rodinia, and documenting the widespread (>24,000 km2) plutonism of 1.5–1.4 Ga weakly peraluminous, calc-alkalic to alkali-calcic and ferroan A-type granitoids (± garnet) devoid of mafic microgrannular enclaves and coeval mafic emplacements in the crustal block. These dominantly within-plate granitoids arguably formed by asthenospheric upwelling induced partial melting of garnet-bearing anatectic quartzofeldspathic gneisses that dominate the Early Mesoproterozoic basement of the block. The major and trace element chemistry of the granitoids is similar to the 1.35–1.45 Ga A-type granitoids in Laurentia/Amazonia emplaced contemporaneous with the 1.5–1.3 Ga breakup of the Columbia Supercontinent. This study suggests the Chottanagpur Gneiss Complex occured as a fragmented crustal block following the breakup of the Columbia Supercontinent; the crustal block was subsequently integrated within India during the Early Neoproterozoic oblique accretion between the NIB and SIB contemporaneous with the Rodinia Supercontinent assembly.

Structural data collected in the Carajas Province region led to a new interpretation of the southeastern Amazonian Craton geotectonic evolution. The purpose of this article is to present a new evolutionary proposal for the region. A detailed analysis of the several extensional-compressional cycles that overprinted each other from the Archean to the Neoproterozoic-Cambrian is presented. At about 2.87–2.83 Ga, collisional processes led to the formation of a stable crustal substrate that supported the installation of an extensional basin at 2.76–2.70 Ga and the deposition of the Itacaiunas Supergroup shallow marine volcanosedimentary sequences, together with contemporary bimodal plutonism. Paleoproterozoic arc magmatism in the Bacaja Domain was followed by collision with the Carajas Province between 2.09 and 2.06 Ga, resulting in expressive tectonic thickening and low to high grade regional metamorphism, and in the deposition of the Aguas Claras Formation. A second Paleoproterozoic orogenic event affected the Carajas Province, which resulted in oblique tectonism and regional counterclockwise rotation of previous associations, followed by late to post-orogenic sedimentation and 1.88 Ga anorogenic alkaline A-type magmatism. The eastern Carajas Province margin was extensionally reactivated during the Neoproterozoic, in a rifting event, followed by tectonic inversion during the Ediacaran/Cambrian.

Trace elements in igneous zircon crystals are variable within single crystals or amongst populations of crystals and are particularly sensitive to changes in melt composition. In this study, we present zircon trace element data from both volcanic and plutonic rocks of the Yandangshan caldera complex from SEChina. The erupted rhyolitic rocks are interpreted to represent the most differentiated magma, whereas the intruded porphyritic quartz syenites are thought to be representative of the residual crystal mush. The zircon crystals of both lithologies are subdivided into two types based on their internal structures: type A with a distinct oscillatory growth zoning and type B crystals are bright in cathodoluminescence (CL-bright). Type B zircon occurs as rims of type A zircon or as individual grains. Compared to type A, type B zircons commonly show lower Hf, U, Th and Y concentrations and higher Ti and Zr/Hf and Eu/Eu* ratios. The zircon trace element compositions of the volcanic samples generally overlap those of the intracaldera porphyritic quartz syenite and mafic microgranular enclaves that contain both type A and type B zircons. Despite a general overlap, zircon grains from the volcanic rocks show relatively higher Hf contents and Y/Dy ratios, lower Ti contents and Th/U ratios and larger negative Eu anomalies than the plutonic samples. We suggest that the inter- and intragrain compositional variability of zircon crystals can be used to track the evolution of magmatic systems. We show that in our case, the volcanic and plutonic rocks crystallized continuously during the magmatic evolution in a common magma system and that the magmas of these rocks may be linked by fractional crystallization. Furthermore, the type B zircon grains are inferred to have crystalized in relatively hot and less evolved magma indicating a magma recharge event. Consequently, the geochemical variability of igneous zircon crystals can be used to infer on the magmatic evolution of single volcanic system which may also be applicable in other geodynamic environments.

The lithologic diversity and protracted geologic history of the Minnesota River Valley (MRV) gneiss terrane at the southern margin of the Archean Superior Province provide key perspectives on the growth and modification of this craton. Innovations in geochronology, specifically the application of the chemical abrasion technique to remove Pb-loss domains in zircon, and the tandem use of in situ geochemistry and precise isotope dilution age analysis for establishing the petrologic context of radioisotopic ages, are yielding new insights into these old rocks. First, U-Pb geochronology on a variety of plutonic to mesoscale intrusive rocks from the Morton and Montevideo blocks of the MRV provide precise constraints on the Neoarchean (2603–2584 Ma) Sacred Heart orogeny, which sutured the Mesoarchean gneisses of the MRV to the southern margin of the Superior craton in an episode of contractional deformation, high-grade metamorphism, and voluminous plutonism. Second, we report the first radioisotopic age constraints on the St. Leo and Taunton belts of greenstone and supracrustal rocks within the Yellow Medicine shear zone, an inferred lithosphere-scale structure juxtaposed between the Morton and Montevideo gneisses. Titanite from a metadiorite intrusion into the St. Leo belt yields igneous (∼2539 Ma) and metamorphic (∼2510 Ma) ages, confirming the Archean provenance of the host greenstones and revealing a latest Neoarchean episode of magmatism and deformation focused along and within the shear zone. Third, a new ∼1781 Ma U-Pb zircon age for one of a number of small granitic plugs in the southern Montevideo block confirms its correlation to the more voluminous East-Central Minnesota Batholith and its origin in the Yavapai orogeny. Again later magmatism was focused along the Yellow Medicine shear zone suggesting the lithosphere-scale significance of that structure. This more resolved history for the Neoarchean to Proterozoic evolution of the southern Superior craton provides new opportunities to test Archean craton correlations and reconstructions, including links to the Wyoming and Slave cratons.

This paper presents petrographic and U-Pb LA-ICP-MS isotopic data of a single peraluminous intrusion (alkali-feldspar granite of Airekan) with partial gneissic foliation on the north western margin of the Yazd Block in the west of the Central-East Iranian Microcontinent (CEIM) to discuss the evolution of this terrain. This intrusion typically suggests a continental collision orogenesis along the northern frontier of Gondwana in the CEIM. The U-Pb dating of zircons indicates that Airekan granite has a distinctive inherited magmatic component at ∼518.2 ± 4.9 Ma but zircons with 892, 679, 614 and 554 Ma ages. These zircons were likely to be ultimately sourced from neighboring Neoproterozoic – Cambrian leucogranite terrains, similar to the other localities in the northern margin of Gondwana, along the Alpine-Himalayan belt from Europe, Turkey, NE Iran, CEIM, Pakistan, India to southern Tibet. The zircons and overgrowths around the inherited components with igneous morphology indicate a plutonism at Lower Ordovician (∼483 ± 2.9 Ma). Petrographic features and morphology of zircon crystals indicate that partial resetting of the U-Pb system in zircons have occurred at ∼382.6 ± 3.2 Ma in Devonian, during the Paleo-Tethys evolutions in Khur region (Anarak-Jandaq terrane) in the southern active margin of Laurasia.

Meta-pelitic rocks with interlayers of meta-psammites within the inner thermal aureole of the Alvand plutonic complex (Sanandaj-Sirjan Zone (SaSZ), western Iran) underwent partial melting; generati...

The Sveconorwegian orogeny is a more than 250 Myr-long multiphase orogenic event that contributed to the amalgamation of Fennoscandia into Rodinia at the end of the Mesoproterozoic. We propose a new lithospheric-scale tectonic model for the pre- to early Sveconorwegian orogenic evolution between 1280 and 1080 Ma. This evolution is recorded in southern Norway by two c. 25 km wide belts of up to granulite-facies rocks, the Bamble and Kongsberg Lithotectonic Units, and a c. 80 km belt in the Telemarkia Lithotectonic Unit, which contains lower-grade rocks and evidence of widespread plutonism. New zircon U–Pb geochronological data from 54 samples confirm magmatic activity between 1575 and 1485 Ma, and 1210 and 1140 Ma. The new data constrain peak amphibolite to granulite-facies metamorphism in Bamble and Kongsberg to between 1145 and 1130 Ma. New geological mapping shows that the Kongsberg Lithotectonic Unit is characterized by a regional, N–S trending highly transposed lithological banding reflecting E–W orthogonal shortening as expressed by tight to isoclinal folds, and a penetrative subvertical foliation bearing a steep peak-metamorphic lineation. Telemarkia is instead characterized by crustal extension-related bimodal magmatism and intermontane basin sedimentation between 1280 and 1080 Ma. Paired and in part coeval extension and compression are interpreted as reflecting asthenospheric upwelling, orogenic plateau development and delamination of the sub-continental lithospheric mantle beneath Telemarkia, followed by foundering (dripping-off) of the lithospheric mantle slab under the Kongsberg and Bamble Lithotectonic Units. This model stresses the pull effect of a foundering mantle slab in an actively shortening orogen to facilitate highly localised compression and granulite-facies metamorphism in the crust. It accounts for the well-known, first-order geological characteristics of the orogen and does not require the accretion of exotic terranes to explain the early-Sveconorwegian orogenic evolution.

Antarctica contains continental fragments of Australian, Indian and African affinities, and is one of the key elements in the reconstruction of Nuna, Rodinia and Gondwana. The Bunger Hills region in East Antarctica is widely interpreted as a remnant of the Mesoproterozoic Albany–Fraser Orogen, which formed during collision between the West Australian and Mawson cratons and is linked with the assembly of Rodinia. Previous studies have suggested that several generations of mafic dyke suites are present at Bunger Hills but an understanding of their origin and tectonic context is limited by the lack of precise age constraints. New in situ SHRIMP U-Pb zircon and baddeleyite dates of, respectively, 1134 ± 9 Ma and 1131 ± 16 Ma confirm an earlier Rb-Sr whole-rock age estimate of ca. 1140 Ma for emplacement of a major mafic dyke suite in the area. Existing and new geochemical data suggest that the source of the dyke involved an EMORB-like source reservoir that was contaminated by a lower crust-like component. The new age constraint indicates that the dykes post-date the last known phase of plutonism at Bunger Hills by ca. 20 million years and were emplaced at the end of Stage 2 of the Albany-Fraser Orogeny. In current models, post-orogenic uplift and progressive tectonic thinning of the lithosphere were associated with melting and reworking of lower and middle crust that produced abundant plutonic rocks at Bunger Hills. A major episode of mafic dyke emplacement following uplift, cooling, and plutonic activity with increasing mantle input, suggests that the dykes mark the end of a prolonged interval of thermal weakening of the lithosphere that may have been associated with continued mafic underplating during orogenic collapse. If the undated olivine gabbro dykes with similar trend, geochemistry and petrology at Windmill Islands are coeval with the ca. 1134 Ma dyke at Bunger Hills, this would suggest the presence of a major dyke swarm at least 400 km in extent. In such case, the dykes could have been emplaced laterally from a much more distant mantle source, possibly a plume, and interacted with the locally heterogeneous and variably metasomatised lithosphere.

This study investigates the diversity, origin and tectonic significance of the Ourilândia do Norte Mesoarchean granitoids, emplaced near Rio Maria-Carajas domains boundary, southeastern Amazonian Craton (Brazil). In this area, previous works has identified sanukitoids (∼2.87 Ga), (quartz) diorites of BADR affinity and undifferentiated leucogranites, with charnockites cross-cutting the other granitoids. New geological mapping data allowed to differentiate three new groups of granitoids: (i) biotite monzogranites (BMzG); (ii) epidote-biotite granodiorites (EBGd); and (iii) porphyritic granitoids (pGrt). Thus, this paper aims to define their classification, nature, formation processes and deformation aspects, and discuss the relations between plutonism and deformation for the Ourilandia do Norte granitoids. The petrographic data showed that each one of these groups can be subdivided into two facies. The BMzG is differentiated into equigranular (eBMzG) and heterogranular (hBMzG) and the EBGd into heterogranular (hEBGd) and sparsely porphyritic (spTEBGd). These granitoids constitute two batholiths separated by a rock strip of sanukitoid and BADR affinities. Both are largely dominated by BMzG rocks, with less abundant EBGd lenses. The pGrt is individualized in porphyritic granodiorites (pBHGd) and trondhjemites (pEBTd), which occur as smaller bodies. Structurally, the central portions these plutons represent lower strain domains, while their borders are marked by large-scale shear zones, where occur submagmatic and mylonitic fabrics of ENE-WSW main direction and subvertical dip, respectively. The meso- and microstructural data indicate that the rocks studied are syn-to late-tectonic and were affected by high temperature deformation (>500 °C) and low differential stress, in a sinistral transpression regime, indicating that both fabrics are related to the a same deformational event. Geochemically, except the pEBTd facies that has sodic affinity, the Ourilândia do Norte granitoids can be grouped into two suites: (i) Fe-K suite formed by BMzG and spTEBGd; and (ii) Mg-K suite composed of sanukitoids (including hEBGd and pBHGd) and (quartz) diorites of BADR affinity. The origin of the eBMzG is attributed to anatexis of a 2.92–2.98 Ga old TTG crust. The hEBGd has sanukitoid affinity and was produced by intense fractionation of hornblende ± clinopyroxene from the Rio Maria Granodiorite. The granitoids of spTEBGd, hBMzG, pBHGd and pEBTd facies show mingling evidence between contrasting magmas, indicating that their origins require interaction between metassomatized mantle- and crustal derived magmas. Geochemical data and modeling were used to identify their different formation processes: (i) spTEBGd is enriched in HFSE (Ti, Zr and Y) and LILE (Ba and Sr) and it was interpreted as product of the partial melting of an enriched mantle source, with participation of crustal liquids; (ii) hBMzG is generated by the interaction between spTEBGd (60%) and eBMzG (40%) magmas; (iii) pBHGd by hybridization between sanukitoid (80%) and eBMzG (20%); and (iv) pEBTd by mixture between trondhjemitic (70-80%) and BARD-affinity (20-30%) liquids. Therefore, at ∼2.87–2.86 Ga a significant crustal growth and reworking occurred in the final stages of stabilization of the first geotectonic cycle of Carajas province, where all the Ourilândia do Norte Mesoarchean granitoids were emplacement during the second stage of a tectono-magmatic two-stage (subduction-collision) model: (i) first stage (2.98–2.92 Ga) - low-angle subduction with emplacement of slab-melt and mantle wedge metasomatism; (ii) second stage (∼2.87–2.86 Ga) - collisional environment, where shear zones conditioned the rise and emplacement of the Ourilândia do Norte magmas.

Late Carboniferous to Early Permian is a critical period for the final amalgamation of the Central Asian Orogenic Belt (CAOB). However, as most of the accreted terranes of the CAOB are unclear in tectonic nature and origin, the timing and processes of their mutual amalgamation have been poorly constrained. To understand assembly of the West Junggar Terrane with the Yili Block, a suite of the late Paleozoic magmatic rocks, including ignimbrite, rhyolite and granite, in northwestern Chinese Tianshan Belt were studied for their petrogenesis and tectonic implications. Our new results of secondary ion mass spectrometry (SIMS) zircon U-Pb dating reveal two separate magmatic episodes, ca. 300 Ma volcanism (ignimbrite and rhyolite) and ca. 288 Ma plutonsim (biotite granite). Geochemically, for the ca. 300 Ma volcanism, the ignimbrites have low SiO2 (65.8–71.5 wt.%) and Mg# (6–13) values, and exhibit arc affinity with significantly enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) such as Nb, Ta and Ti. The whole-rock eNd(t) and zircon eHf(t) values range from +6.9 to +7.0 and +9.9 to +14.1 respectively, indicating a juvenile basaltic lower crustal origin. Rhyolites have slightly high SiO2 (72.7–74.0 wt.%) and K2O (3.86–4.53 wt.%) contents, high zircon δ18O (11.67–13.23‰) values, and low whole-rock eNd(t) (+2.9 to +3.8) and zircon eHf(t) (+2.8 to +10.0) values, which may suggest sediment involvements during magma generation. In contrast, for the ca. 288 Ma plutonism, the biotite granites have obviously higher SiO2 (74.7–75.5 wt.%) contents and whole-rock eNd(t) (+7.7 to +8.8), zircon eHf(t) (+9.8 to +12.7), and lower zircon δ18O (5.99–6.84‰) values, than those of the ca. 300 Ma volcanic rocks, which are consistent with signatures of juvenile magma source. According to our estimates of zircon saturation temperatures, together with their contrasting genesis, we attribute the formation of ca. 300 Ma high temperature (815–938 °C) volcanism to oceanic slab break-off during assembly of the West Junggar Terrane with the Yili Block, and relate the generation of ca. 288 Ma low temperature (723–735 °C) plutonism to subsequent strike-slipping of North Tianshan Fault that facilitated introduction of water-fluxes triggering hydrous partial melting of juvenile lower crust. The sequential magmatic episodes in the northwestern Chinese Tianshan Belt may provide a crucial clue to a tectonic transition from plate convergence to intra-plate adjustment during the formation of the Kazakhstan Orocline in the late Paleozoic.

The western Himalaya of Pakistan forms a classic fold and thrust belt with a foreland defined by the Salt Range thrust, Main Boundary thrust, and Panjal-Khairabad thrust, and a hinterland that stretches northward from the Panjal-Khairabad thrust across the Peshawar Basin, through the mountains of Swat and Hazara, to the Main Mantle thrust (MMT), which is the westward extension of the Indus suture zone. The MMT separates the Indian plate from the Kohistan island arc complex, which forms the southern margin of the amalgamated Asian tectonic plate. Rocks in the hinterland underwent deformation and regional metamorphism in early Cenozoic as a result of the collision between India and Kohistan along the MMT. The purpose of this contribution is to review the stratigraphy, structure, and thermal evolution of the western Himalayan hinterland region in order to clarify our present knowledge and to address inconsistencies regarding geologic history. The goal is to create a comprehensive understanding and working model of the hinterland region. We do this by synthesizing and evaluating all published isotopic age data from the region, and by placing each age into the stratigraphic and structural framework of a geologic map created during more than 1.5 years of traverse and reconnaissance field mapping over a 12-year period. We add 17 new isotopic ages that have bearing on the stratigraphic, intrusive, and metamorphic history. Stratigraphy is described as pre-. syn-, and post-rift, dependent on its age relative to a strong Carboniferous-Triassic rifting event that featured plutonism, normal faulting, deposition, the erosional removal of Paleozoic rocks from northern areas of the hinterland, and potentially multiple periods of Panjal Trap volcanism extending to the Late Triassic. We show that stratigraphy can be traced continuously across the hinterland region without disruption across Cenozoic faults except in the MMT zone where there are four separate areas of Indus melange and three adjacent thrust slices of Indian plate rock, one of which is newly recognized. We provide evidence that all of the melange and Indian plate thrust slices were emplaced at about the same time prior to peak Cenozoic metamorphism in underlying hinterland rocks, and prior to 50 Ma. We find no evidence for thrusting since that time. Geologic and isotopic evidence suggests that the Kohistan arc and underlying thrust slices were emplaced in a southwestward direction and that the arc was in place against hinterland rocks prior to ca. 48.1 Ma. Hinterland rocks had reached peak metamorphism and were cooling by ca. 50 Ma except in the Loe Sar and Kotah domes where cooling was delayed until ca. 39 Ma. The Kohistan arc underwent eastward translation post-45.8 Ma during folding and erosional exhumation of hinterland rocks. The Indus syntaxis is a long-lived anticlinal structure that it is currently active. Pre-Cenozoic history includes plutonism in the Paleoproterozoic, Neoproterozoic, Early and Middle Ordovician, and Permian, and possible tectonism in Late Cretaceous-Early Paleocene. There are indications of pre-Cenozoic regional metamorphism within metasedimentary rock, but they are masked by Cenozoic metamorphism such that their extent, if any, is unknown.

Magmatic activity is an integral component of orogenic processes, from arc magmatism during convergence to post-collisional crustal melting. Southern Iberia exposes a Late Paleozoic suture zone within Pangea and where a crustal fragment of Laurussia (South Portuguese Zone) is juxtaposed with parautochthonous Gondwana (Ossa Morena Zone). Fault-bounded oceanic metasedimentary rocks, melanges and ophiolite complexes characterize the suture zone and are intruded by plutonic rocks and mafic dykes. The generation and emplacement of these intrusive rocks and their relationship to development of the suture zone and the orogen are undetermined. Field evidence combined with U/Pb (zircon) geochronology reveals three main phases of plutonism, a pre-collisional unfoliated gabbroic phase emplaced at ca 354 Ma, crosscut by a syn-tectonic ca 345 Ma foliated granodiorite phase followed by a ca 335 Ma granitic phase. Geochemical analyses (major, trace, rare earth elements) indicate that the gabbro exhibits a calc-alkaline arc signature whereas the granodiorite and granite are typical of post-collisional slab break-off. Taken together, these data demonstrate a protracted development of the orogen and support a complex late stage evolution broadly similar to the tectonics of the modern eastern Mediterranean. In this scenario, the highly oblique closure of a small tract of oceanic lithosphere postdates the main collision event resulting in escape of parautochthonous and allochthonous terranes toward the re-entrant.

We present regional variations of whole-rock Sr/Y and (La/Yb)N ratios of magmatic rocks along the Cenozoic Urumieh-Dokhtar and Alborz magmatic belts, Iran. Both the magmatic belts are located at the north of the main Zagros Neo-Tethyan suture. The Urumieh-Dokhtar magmatic belt (UDMB), which trends NW-SE for 1000 km across Iran, was characterized by the intensive volcanism and plutonism, and defined the magmatic front (MF) of the Zagros orogenic belt. The Alborz magmatic belt (AMB) is situated to the north, and characterized by less intense magmatic activity. The Alborz magmatic belt was formed behind it in the rear-arc (RA) domain. A striking feature of the both magmatic belts is the transition from normal calc-alkaline arc magmatism during the Eocene–Oligocene to adakite-like calc-alkaline magmatism during the Middle to Late Miocene–Pliocene. The late-Cenozoic magmatism of the UDMB and AMB shows higher Sr/Y and (La/Yb)N. However, it should be noted that crustal thickening event is intensive in the UDMB than AMB during Late Cenozoic. Using the composition of the Lale-Zar zircons from the SE UDMB we determined the oxygen fugacity (fO2) during zircon crystallization to be between FMQ (fayalite–magnetite–quartz buffer) -0.69 to +2.41, whereas those of the Hashroud-Teckmdash-Gormolla zircons from NW AMB range from −1.22 to +5.99. The fO2 estimates suggest relatively more oxidized conditions for the Late Cenozoic igneous rocks of the AMB. Compiled data from the UDMB and AMB intrusions show an increase in average zircon crystallization temperatures with decreasing age. These outcomes have been interpreted in terms of variation of the crustal thickness, from 30 to 35 km during Eocene-Oligocene to 40–55 km during the middle-late Miocene. We propose the increase in crustal thickness is associated with the collision between the Arabian plate and Iran and subsequent convergence during the middle-late Miocene.

The Kamarbon Jurassic alkaline basic intrusion crops out in Central Alborz, north Iran, along the northern margin of the Alpine-Himalayan belt. The intrusion includes foid gabbros at the margins and foid monzodiorites towards the center. The foid monzodiorites are considered as the evolved melts after the fractional crystallization mostly of olivine and clinopyroxene from a foid gabbro parental magma. Based on mass balance calculation the evolution of the Kamarbon alkaline gabbro could be explained by 19.2% fractionation of clinopyroxene, 13.8% of olivine, 3% of plagioclase and 1.0% Ti-Magnetite, with 63% of residual liquid. REE inversion modeling indicates that the Kamarbon intrusion magma was generated by low degrees (

The Aracuai orogen is the Brazilian counterpart of the Aracuai-West Congo orogenic system (AWCO), a component of the Ediacaran-Cambrian orogenic network formed during the amalgamation of West Gondwana. The northwestern portion of the Aracuai orogen is dominated by a succession of metasedimentary rocks made up of Meso- to Neoproterozoic rift, passive margin and syn-orogenic sequences, locally intruded by post-collisional granites. These sequences are involved in three distinct tectonic units, which from west to east are: the southern Espinhaco fold-thrust system (SE-thrust system), the normal-sense Chapada Acaua shear zone (CASZ) and the Salinas synclinorium. Three deformation phases were documented in the region. The first two phases (D1 and D2) are characterized by contractional structures and represent the collisional development stage of the orogen. The third phase (D3) is extensional and currently viewed as a manifestation of orogenic collapse of the system. The distribution of the metamorphic mineral assemblages in the region characterizes two metamorphic domains. The M-Domain I on the west, encompassing the SE-thrust system and the CASZ, is marked by a syn-collisional (syn-D1) Barrovian-type metamorphism with P–T conditions increasing eastwards and reaching ~8.5 kbar at ~650°C between 575 and 565 Ma. The M-Domain II comprises the Salinas synclinorium in the hangingwall of the CASZ, and besides the greenschist facies syn-collisional metamorphism, records mainly a Buchan-type metamorphic event, which took place under 3–5.5 kbar and up to 640°C at c. 530 Ma. The northwestern Aracuai orogen exhibits, thus, a paired metamorphic pattern, in which the Barrovian and Buchan-type metamorphic domains are juxtaposed by a normal-sense shear zone. Lithospheric thinning during the extensional collapse of the orogen promoted ascent of the geotherms and melt generation. A large volume of granites was emplaced in the high grade and anatectic core of the orogen during this stage, and heat advected from these intrusions caused the development of Buchan facies series over a relatively large area. Renewed granite plutonism, hydrothermal activities followed by progressive cooling affected the system between 530 and 490 Ma.