| 1. |
- Gardiner, Nicholas J., et al.
(författare)
-
The crustal architecture of Myanmar imaged through zircon U-Pb, Lu-Hf and O isotopes : Tectonic and metallogenic implications
- 2018
-
Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X .- 1878-0571. ; 62, s. 27-60
-
Tidskriftsartikel (refereegranskat)abstract
- The Tethys margin in central and eastern Asia is comprised of continental terranesseparated by suture zones, some of which remain cryptic. Determining the crustal architecture, and therefore the geological history, of the Eastern Tethyan margin remains challenging. Sited in the heart of this region, Myanmar is a highly prospective but poorly explored minerals jurisdiction. A better understanding of Myanmar's mineralization can only be realized through a better understanding of its tectonic history, itself reflected in at least four major magmatic belts. The Eastern and the Main Range Provinces are associated with the Late Permian to Early Triassic closure of Palaeo-Tethys. The Mogok–Mandalay–Mergui Belt and Wuntho–Popa Arc are a response to the Eocene closure of Neo-Tethys. However, magmatic ages outside these two orogenic events are also recorded. We present new zirconU-Pb, Lu-Hf and O isotope data from magmatic rocks across Myanmar, which we append to the existing dataset to isotopically characterize Myanmar's magmatic belts. Eastern Province Permian I-type magmatism has evolved εHf (−10.9 to −6.4), whilst Main Range Province Triassic S-type magmatism also records evolved εHf (−13.5 to −8.8). The Mogok-Mandalay-Mergui Belt is here divided into the Tin Province and the Mogok Metamorphic Belt. The Tin Province hosts ca. 77–50 Ma magmatism with evolved εHf (−1.2 to −15.2), and δ18O of 5.6–8.3‰. The Mogok Metamorphic Belt exhibits a more complex magmatic and metamorphic history, and granitoids record Jurassic, Late Cretaceous, and Eocene to Miocene phases of magmatism, all of which exhibit evolved εHf values between −4.6 and −17.6, and δ18O between 6.3 and 9.2‰. From the Tagaung-Myitkyina Belt, we report a magmatic age of 172 Ma and εHf of 18.1 to 10.8. To accommodate the geological evidence, we propose a tectonic model for Myanmar involving a greater Sibumasu – where the documented zircon isotopic variations reflect compositional variations in magmatic source – and invoke the role of a Tengchong Block. The Baoshan Block and Greater Sibumasu were likely assembled on or before the Triassic, a former Andean margin and suture which may lie across the Northern Shan Plateau, and reflected in isotopic differences between the northern and southern parts of the Mogok Metamorphic Belt. This contiguous Sibumasu–Baoshan Block then sutured onto the Indochina margin in the Late Triassic. We propose that a Tengchong Block within Myanmar provides for a southerly termination of the Meso-Tethys suture immediately north of the Mogok area. A discrete Tengchong Block may explain a discontinuous arc of Late Triassic to Jurassic I-type magmatism in central Myanmar, representing an Andean-type margin sited above a subducting Meso-Tethys on the margin of Sibumasu. The Tengchong Block sutured onto Greater Sibumasu before the Late Cretaceous, after which subduction of Neo-Tethys drove the magmatism of the Wuntho-Popa Arc and ultimately that of the Tin Province. The metallogenic character of granite belts in Myanmar reflects the crustal architecture of the region, which is remarkable for its prolific endowment of granite-hosted Sn-W mineralization in two quite distinct granite belts related to sequential Indosinian and Himalayan orogenesis.
|
|
| 2. |
- Fritschle, Tobias, et al.
(författare)
-
Peri-Gondwanan Ordovician arc magmatism in southeastern Ireland and the Isle of Man : Constraints on the timing of Caledonian deformation in Ganderia
- 2018
-
Ingår i: GSA Bulletin. ; 130:11-12
-
Tidskriftsartikel (refereegranskat)abstract
- The timing of and tectonic controls on Ordovician magmatism and deformation within accreted terranes are key elements in reconstructing the generation of the Caledonian-Appalachian orogen. This paper addresses the topic through integrated geochronological, structural, and multi-isotope geochemical investigation of magmatic arc–related peri-Gondwanan rocks of Ganderian affinity in the Leinster-Lakesman terrane in SE Ireland and the Isle of Man.A basaltic andesite from a previously unrecognized volcaniclastic sequence in the Manx Group at Port-e-Vullen on the Isle of Man yielded an age of 472.7 ± 2.8 Ma (secondary ion mass spectrometry [SIMS] zircon U-Pb), and an arc-related rhyolite from the Avoca volcanic sequence in SE Ireland was dated at 463.6 ± 2.6 Ma. Two granitoids from Graiguenamanagh (SE Ireland) yielded ages of 462.0 ± 2.7 Ma (augen gneiss) and 460.5 ± 3.2 Ma (equigranular granite), whereas the Dhoon granite (Isle of Man) was dated at 457.2 ± 1.2 Ma. Each of the granitic rocks from Graiguenamanagh and Dhoon was previously considered to be of Silurian–Devonian age. In addition, two sheets of the Croghan Kinshelagh granite (SE Ireland) yielded indistinguishable ages of 456.9 ± 2.4 Ma and 455.4 ± 2.8 Ma.Multi-isotopic analyses (SIMS zircon oxygen, laser ablation–multi-collector–inductively coupled plasma–mass spectrometry [LA-MC-ICP-MS] zircon Lu-Hf, whole-rock Sm-Nd) on the rocks of the Leinster-Lakesman terrane suggest a significant source contribution from the Ganderian microcontinent, represented by the Early Ordovician metasedimentary Ribband and Manx Groups.Structural relationships at Graiguenamanagh demonstrate a late Middle Ordovician deformation event at ca. 460 Ma. This deformation appears to be equivalent to the widespread D1 event that affected Early Ordovician rocks in SE Ireland and corresponds to the early structures within the East Carlow deformation zone, previously interpreted as an exclusively Devonian structure. Along strike, the early deformation is spatially associated with serpentinite emplacement. The East Carlow deformation zone is interpreted as an intra-Ganderian suture along which separate fragments of a peri-Gondwanan magmatic arc were juxtaposed at ca. 460 Ma. This deformation represents a Caledonian tectonic event that has not been recognized within Ganderia in the Appalachian sector of the orogen.
|
|
| 3. |
- Kusiak, Monika A., et al.
(författare)
-
Peak to post-peak thermal history of the Saglek Block of Labrador : A multiphase and multi-instrumental approach to geochronology
- 2018
-
Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 484, s. 210-223
-
Tidskriftsartikel (refereegranskat)abstract
- The Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8–2.7Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7–3.6Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7Ga, but also reveal high-temperature conditions at ca. 2.6Ga and 2.5Ga. The former is interpreted as the waning stages of the 2.7Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2Ga may represent either cooling associated with the 2.5Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.
|
|
| 4. |
- Leat, Philip T., et al.
(författare)
-
Jurassic high heat production granites associated with the Weddell Sea rift system, Antarctica
- 2018
-
Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 722, s. 249-264
-
Tidskriftsartikel (refereegranskat)abstract
- The distribution of heat flow in Antarctic continental crust is critical to understanding continental tectonics, ice sheet growth and subglacial hydrology. We identify a group of High Heat Production granites, intruded into upper crustal Palaeozoic metasedimentary sequences, which may contribute to locally high heat flow beneath the West Antarctic Ice Sheet. Four of the granite plutons are exposed above ice sheet level at Pagano Nunatak, Pirrit Hills, Nash Hills and Whitmore Mountains. A new UPb zircon age from Pirrit Hills of 178.0±3.5Ma confirms earlier RbSr and UPb dating and that the granites were emplaced approximately coincident with the first stage of Gondwana break-up and the developing Weddell rift, and ~5m.y. after eruption of the Karoo-Ferrar large igneous province. Aerogeophysical data indicate that the plutons are distributed unevenly over 40,000km2 with one intruded into the transtensional Pagano Shear Zone, while the others were emplaced within the more stable Ellsworth-Whitmore mountains continental block. The granites are weakly peraluminous A-types and have Th and U abundances up to 60.7 and 28.6ppm respectively. Measured heat production of the granite samples is 2.96–9.06μW/m3 (mean 5.35W/m3), significantly higher than average upper continental crust and contemporaneous silicic rocks in the Antarctic Peninsula. Heat flow associated with the granite intrusions is predicted to be in the range 70–95mW/m2 depending on the thickness of the high heat production granite layer and the regional heat flow value. Analysis of detrital zircon compositions and ages indicates that the high Th and U abundances are related to enrichment of the lower-mid crust that dates back to 200–299Ma at the time of the formation of the Gondwanide fold belt and its post-orogenic collapse and extension.
|
|
| 5. |
- Riley, Teal R., et al.
(författare)
-
Episodicity within a mid-Cretaceous magmatic flare-up in West Antarctica : U-Pb ages of the Lassiter Coast intrusive suite, Antarctic Peninsula, and correlations along the Gondwana margin
- 2018
-
Ingår i: Geological Society of America Bulletin. - 0016-7606 .- 1943-2674. ; 130:7-8, s. 1177-1196
-
Tidskriftsartikel (refereegranskat)abstract
- Long-lived continental margin arcs are characterized by episodes of large-volume magmatism (or flare-ups) that can persist for ∼30 m.y. before steady-state arc conditions resume. Flare-up events are characterized by the emplacement of large-volume granodiorite-tonalite batholiths and sometimes associated rhyodacitic ignimbrites. One of the major flare-up events of the West Gondwana margin occurred during the mid-Cretaceous and was temporally and spatially associated with widespread deformation and Pacific plate reorganization. New U-Pb geochronology from the Lassiter Coast intrusive suite in the southern Antarctic Peninsula identifies a major magmatic event in the interval 130–102 Ma that was characterized by three distinct peaks in granitoid emplacement at 130–126 Ma, 118–113 Ma, and 108–102 Ma, with clear lulls in between. Mid-Cretaceous magmatism from elsewhere in West Antarctica, Patagonia, and New Zealand also featured marked episodicity during the mid-Cretaceous and recorded remarkable continuity along the West Gondwana margin. The three distinct magmatic events represent second-order episodicity relative to the primary episodicity that occurred on a cordillera scale and is a feature of the North and South American Pacific margin. Flare-up events require the development of a highly fusible, lower-crustal layer resulting from the continued underplating of hydrous mineralogies in the melt-fertile lower crust as a result of long-lived subduction. However, the actual trigger for melting is likely to result from external, potentially tectonic factors, e.g., rifting, plate reorganization, continental breakup, or mantle plumes.
|
|
| 6. |
- Sałacińska, Anna, et al.
(författare)
-
Complexity of the early Archean Uivak Gneiss : Insights from Tigigakyuk Inlet, Saglek Block, Labrador, Canada and possible correlations with south West Greenland
- 2018
-
Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 315, s. 103-119
-
Tidskriftsartikel (refereegranskat)abstract
- The Saglek Block of Labrador comprises Eoarchean to Neoarchean lithologies, metamorphosed at high temperature at ca. 2.7 Ga. Here, we investigate the gneisses of Tigigakyuk Inlet, previously identified as the locality exposing the most ancient rocks in the Saglek Block. New geochronological and geochemical results reveal a multistage history. Precise magmatic emplacement ages of 3.75 to 3.71 Ga refine the age of the Uivak Gneiss. Zircon rims and neoblastic grains with low Th/U record metamorphism at ca. 3.6 and 2.8-2.7 Ga. Magmatism between these tectono-metamorphic events is recorded by the presence of meta-mafic dykes in the gneisses, gabbroic enclaves in ca. 2.7 Ga syn-tectonic granitoids, as well as by a ca. 3.56 Ga age for monzonitic gneiss in which metamorphic zircon is present as xenocrysts. Felsic (TTG) magmatism between ca. 3.75 Ga and 3.71 Ga, as well as metamorphism at both ca. 3.6 Ga and 2.8-2.7 Ga, is also recognised in the Itsaq Gneiss Complex of south West Greenland, and is restricted to the Færingehavn Terrane. Our new data enable a more rigorous correlation between these formerly conjugate parts of the North Atlantic Craton.
|
|
| 7. |
- Turnbull, Rose E., et al.
(författare)
-
Recognition of mid-Paleozoic volcanism in New Zealand
- 2018
-
Ingår i: New Zealand Journal of Geology and Geophysics. - : Taylor & Francis. - 0028-8306 .- 1175-8791. ; 61:4, s. 413-427
-
Tidskriftsartikel (refereegranskat)abstract
- Two felsic volcanic clasts from conglomerates in Fiordland and northwest Nelson provide U–Pb zircon ages of 359 and c. 362 Ma respectively; ages that occur within the interval between voluminous Western Province plutonic S-type magmatism of the Karamea and Ridge suites. Both volcanic clasts have inherited zircon populations, and trace element signatures suggesting derivation from crustal melts. The dacitic clast from the mid-Cretaceous Seek Cove Formation in southwest Fiordland has whole-rock chemistry and an O–Hf–zircon isotopic signature consistent with derivation from the Takaka Terrane. A rhyolite clast from the Pupu Conglomerate in northwest Nelson also has chemistry consistent with derivation from a Takaka Terrane source. We therefore correlate both volcanic clasts to the S-type Ridge Suite. No comparable S-type plutonic source of the same age has been recognised in the northwest Nelson section of the Takaka Terrane. These volcanic clasts represent the oldest recognised episode of S-type Ridge Suite magmatism in the Takaka Terrane.
|
|
| 8. |
- van der Meer, Q H A, et al.
(författare)
-
Magmatic Evolution during the Cretaceous Transition from Subduction to Continental Break-up of the Eastern Gondwana Margin (New Zealand) documented by in-situ Zircon O and €“Hf Isotopes and Bulk-rock Sr and €“Nd Isotopes
- 2018
-
Ingår i: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 59:5, s. 849-880
-
Tidskriftsartikel (refereegranskat)abstract
- Major changes in tectonic style can lead to tapping of highly variable magma sources and potentially result in significant episodes of crustal growth. Here we focus on magmatism associated with a transition from arc magmatism to subsequent over-thickening and eventual orogenic collapse. This transition is associated with cessation of subduction and was followed by continental extension and finally continental break-up as recorded in the Cretaceous magmatic record of Zealandia. Orogenic collapse peaked at 110 Ma and is expressed through core complex formation and the intrusion of I- to evolved I/S-type Rahu Suite plutons that have widely varying chemical compositions but homogeneous whole-rock and zircon isotopic signatures that are intermediate between mantle and local upper crust values. The Rahu Suite is interpreted to be derived from differing degrees of melt extraction from a pre-existing lower crustal source and lacks a demonstrable juvenile component. This lower crustal source was likely formed by magmatic underplating and melt–crust hybridization during preceding arc volcanism (Separation Point and Darran suites), effectively smearing out a pulsed event of crust formation in the zircon record. Therefore, late orogenic I- and I/S-type suites do not have to equate to crustal growth and can be an expression of crustal re-melting. An abrupt change in magma sources in Zealandia occurred after 100 Ma during the onset of progressive crustal extension. A juvenile alkaline component (presumably derived from the lithospheric mantle) is suggested to have been present from >97 Ma. This component became more pronounced with time until the emplacement of granites and trachytes with isotopic signatures overlapping with coeval mafic mantle-derived dikes during bimodal rift-related magmatism. The juvenile alkaline component dictated the composition of the felsic magmas but did not represent a significant crustal growth event due to small total volumes.
|
|
| 9. |
- Bergemann, Christian A., et al.
(författare)
-
Constraining long-term fault activity in the brittle domain through in situ dating of hydrothermal monazite
- 2018
-
Ingår i: Terra Nova. - : Wiley. - 0954-4879. ; 30:6, s. 440-446
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract SIMS Th–Pb dating of hydrothermal fissure-vein monazite-(Ce) has the unique potential to date multiple tectonic events under low-grade metamorphic brittle/ductile conditions over large time frames. Monazites-(Ce) from brittle fault systems in the Eastern Alps allow us to constrain their Cretaceous activity over 20 Ma within single crystals, recording all major tectonic events. Eo-Alpine formation of the fluid-filled fissure-veins occurred 90 Ma ago at 352 ± 19°C and 342 ± 42 MPa. This corresponds to peak conditions during regional metamorphism of the Cretaceous collisional nappe stacking. Several stages of dissolution–reprecipitation/recrystallization record fault activity between 84 and 70 Ma. Corresponding fluid inclusions indicate conditions of 229 ± 10°C and 143 ± 20 MPa. This correlates with the formation of sedimentary basins during post-orogenic extension associated with strike-slip movements. The results strengthen the hypothesis that many large fault systems in the Eastern Alps developed during the Cretaceous orogeny and became reactivated during Neogene Alpine tectonics.
|
|
| 10. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
-
Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
-
Tidskriftsartikel (refereegranskat)abstract
- In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR-related S-isotope systematics, particularly regarding formation of large fractions of S-34-rich pyrite.
|
|
