Petrochemistry, tectonic history, and Sr–Nd systematics of the Liscomb Complex, Meguma Lithotectonic Zone, Nova Scotia

The Liscomb Complex (area ca. 240 km2), located in the Meguma Lithotectonic Zone of the Canadian Appalachians, consists of three main lithological components: high-grade gneisses, mafic plutons, and peraluminous granitoid bodies. Field relations and 40Ar/39Ar dating (369–377 Ma) embracing all three lithological groups show that the complex is post-Acadian. The gneisses occur as a domal uplift and represent a mixed volcano-sedimentary package that is structurally, metamorphically, and chemically distinct from the surrounding low-grade metawackes and metapelites of the Meguma Group. The mafic intrusions (quartz gabbro to quartz diorite) have major and trace element compositions (e.g., Ti–Zr–Y, Nb–Zr–Y, Th/Yb – Ta/Yb, rare earth elements) typical of within-plate or volcanic arc materials. The peraluminous granitoid rocks range from two-mica granodiorites to leucomonzogranites, and are mineralogically and chemically very similar to granitic rocks elsewhere in the Meguma Zone. Neodymium and strontium isotopic analyses show that (i) the gneisses have a wide range of εNd and initial Sr isotopic ratios, with Nd model ages that are generally younger than those of the Meguma Group; (ii) the mafic intrusive rocks represent magmas derived from slightly depleted mantle sources (εNd +3.3 to +1.4), in part modified by crustal contamination (εNd +0.5 to −5.0); and (iii) the granitoid rocks isotopically overlap both the South Mountain Batholith and the intermediate gneisses of the Liscomb Complex. The combined field, petrological, and chemical evidence suggests that underplating by mafic magmas, followed by thermal doming of the gneisses, diapirism through the Meguma Group, anatexis, and multiple intrusion of both mafic and felsic magmas best explain the observed relationships in the Liscomb Complex. This mechanical model may also apply to granite generation throughout the Meguma Zone.

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The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

10.5194/egusphere-egu21-6494 ◽

2021 ◽

Author(s):

Banafsheh Vahdati ◽

Seyed Ahmad Mazaheri

Keyword(s):

Subduction Zones ◽

Tectonic Setting ◽

Crustal Contamination ◽

Oceanic Lithosphere ◽

Late Triassic ◽

Common Belief ◽

Thrust Tectonics ◽

Wide Range ◽

Lree Enrichment ◽

Granitoid Rocks

Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO2: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na2O and K2O show a positive correlation with silica while Al2O3, TiO2, CaO, Fe2O3, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.

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The age of the Ritscherflya Supergroup and Borgmassivet Intrusions, Dronning Maud Land, Antarctica

Antarctic Science ◽

10.1017/s0954102095000125 ◽

1995 ◽

Vol 7 (1) ◽

pp. 87-97 ◽

Cited By ~ 38

Author(s):

A.B. Moyes ◽

J.R. Krynauw ◽

J.M. Barton

Keyword(s):

Mantle Source ◽

Crustal Contamination ◽

Unconsolidated Sediments ◽

Rock Types ◽

Geological Age ◽

Depleted Mantle ◽

Wide Range ◽

Dronning Maud Land ◽

Depositional Age ◽

Nd Model Age

The Ahlmannryggen-Borgmassivet area of western Dronning Maud Land comprises a relatively undeformed, unmetamorphosed sequence of sedimentary-volcanogenic rocks, the Ritscherflya Supergroup, intruded by a suite of continental tholeiites, the Borgmassivet Intrusions. New Rb-Sr and Sm-Nd whole rock data from the Högfonna Formation at Grunehogna indicate a depositional age of ≈1080 Ma, the first reported direct dating of any member of the Ritscherflya Supergroup. These rocks are interpreted as a molasse-type deposit following the Kibaran orogeny at 1200–1100 Ma, and correlation is made with the Umkondo and Koras groups of southern Africa. The Ritscherflya Supergroup is intruded by the Grunehogna and Kullen sills; the ≈1000 Ma Grunehogna sill intruded unconsolidated sediments, causing partial melting of the sediments. Rb-Sr data from the Kullen sill yield an age of 1429 Ma, clearly inconsistent with these data. Combined Sr and Nd data are compatible with crustal contamination of this sill, producing a Rb-Sr pseudo-isochron with no geological age significance. By comparison with other outcrops of the Borgmassivet Intrusions at Robertskollen and Annandagstoppane, it is concluded that contamination and pseudo-isochrons may be responsible for the wide range in reported ages older than 1000 Ma. Thus the intrusive age of the Borgmassivet Intrusions is concluded to be ≈1000 Ma old. Nd model age data indicate that all rock types were ultimately derived from material separated from a depleted mantle source at ≈2200 Ma.

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Archean Boninite-like Rocks of the Northwestern Youanmi Terrane, Yilgarn Craton: Geochemistry and Genesis

Journal of Petrology ◽

10.1093/petrology/egaa002 ◽

2019 ◽

Vol 60 (11) ◽

pp. 2131-2168 ◽

Cited By ~ 4

Author(s):

Jack R Lowrey ◽

Derek A Wyman ◽

Tim J Ivanic ◽

R Hugh Smithies ◽

Roland Maas

Keyword(s):

Trace Element ◽

Crustal Contamination ◽

Mantle Metasomatism ◽

Chemical Compositions ◽

Yilgarn Craton ◽

Fine Grained ◽

Mafic Intrusions ◽

Field Evidence ◽

Isotopic Analyses ◽

Geochemical Analyses

Abstract Rocks with chemical compositions similar to Cenozoic boninites occur in many Archean cratons (boninite-like rocks), but they are rarely well-preserved, well-sampled, or presented within chrono- and chemo-stratigraphic context. This study provides a detailed description of the most extensive and well-preserved Archean boninite-like rocks reported to date. Within the 2820 to 2740 Ma magmatic suites of the northwest Youanmi Terrane, Yilgarn Craton, boninite-like rocks occur as two distinct units. The first boninite-like unit is thinner (several 10 s of m thick), occurs close to the base of the 2820–2800 Ma Norie Group and includes both volcanic flows and subvolcanic intrusions. The second boninite-like unit is thicker (locally several 100 s m), occurs near the base of the 2800–2740 Ma Polelle Group and consists of mainly fine-grained volcanic flows with local cumulate units. On average, major and trace element compositions for Youanmi Terrane boninite-like rocks are marginal between basalt, picrite and boninite and they have asymmetrically concave REE patterns, and Th–, Zr–Hf enrichments, similar to many Phanerozoic low-Si boninite suites, but at generally higher MREE–HREE contents. We report over 300 new whole-rock geochemical analyses, and 16 new Sm–Nd isotopic analyses, and associated petrographic evidence, including representative mineral compositions, which we support with published geochemical analyses and several decades of fieldwork in our study area. Comparison between Archean boninite-like rocks and Cenozoic boninites shows that most Archean examples had less depleted sources. We consider two possible petrogenetic models for the Youanmi Terrain examples: (1) they reflect variably contaminated komatiites, or (2) they reflect melts of metasomatised refractory mantle, analogous to Phanerozoic boninites. Trace element modelling indicates that crustal contamination could potentially produce rocks with boninite-like compositions, but requires an Al-enriched komatiitic parent liquid, for which there is no field evidence in our study area. Initial εNdT values in pre-2800 Ma rocks (εNdT -0·4 to +1·2) are on average slightly higher than those in 2800–2733 Ma examples (εNdT -3·2 to +1·2), compatible with increasing mantle metasomatism involving recycling of ≥ 2950 Ma crust. Integration of trace element and Nd isotopic data demonstrates that significant direct crustal assimilation was restricted to felsic magmas. The Th–Nb and Ba–Th systematics of mafic-intermediate rocks reflect fluid- and sediment-derived processes in the mantle, with boninite-like examples being linked primarily to fluid metasomatism. We compare the well-preserved igneous textures and mineralogy of Youanmi Terrane boninite-like rocks with those of their Phanerozoic counterparts, and based on studies of the latter, suggest that former had similarly hot, H2O-rich parent magmas. The association of boninite-like rocks in the Norie and Polelle Groups with coeval high-Mg andesites, sanukitoids and hydrous mafic intrusions of the Narndee Igneous Complex strongly suggests a metasomatised mantle source and subduction operating in the Yilgarn between 2820 and 2730 Ma.

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The Origins of Strongly Peraluminous Granitoid Rocks

The Canadian Mineralogist ◽

10.3749/canmin.1800075 ◽

2019 ◽

Vol 57 (4) ◽

pp. 529-550 ◽

Cited By ~ 3

Author(s):

D. Barrie Clarke

Keyword(s):

Partial Melting ◽

Bulk Composition ◽

Aqueous Fluid ◽

Granitic Rocks ◽

Peraluminous Granite ◽

Granite Magma ◽

Metasedimentary Rocks ◽

South Mountain Batholith ◽

Peraluminous Granites ◽

Granitoid Rocks

Abstract Strongly peraluminous granites (SPAGs), with 1.20 < A/CNK < 1.30, are relatively rare rocks. They contain significant modal abundances of AFM minerals such as Bt-Ms-Crd-Grt-And-Toz-Tur-Spl-Crn of potentially magmatic, peritectic, restitic, and xenocrystic origin. Determining the origin of a SPAG depends to a large extent on establishing the correct origin of these AFM minerals. Strongly peraluminous granitic rocks can form in eight distinctly different ways: (1) as the melt fraction resulting from dehydration partial melting of peraluminous metasedimentary rocks; (2) as the bulk composition of diatexitic migmatite resulting from extensive partial melting of peraluminous metasedimentary rock; (3) as a diatexite modified by incomplete restite unmixing; (4) by bulk contamination of a less strongly peraluminous granite magma with highly peraluminous metasedimentary rocks; (5) by selective acquisition or concentration of AFM minerals by a less strongly peraluminous granite magma; (6) by fractional crystallization of quartz and feldspar from a less strongly peraluminous granite magma; (7) by removal of alkalies (Ca, Na, K) by release of a suprasolidus aqueous fluid from a less strongly peraluminous granite magma; and (8) by subsolidus hydrothermal alteration of a less strongly peraluminous granite rock. Contamination by pelitic material is the most effective process for creating SPAG plutons. A detailed case study of the South Mountain Batholith shows that its early SPAGs contain high modal abundances of Bt-Crd-Grt, largely of external origin, whereas its later SPAGs contain high modal abundances of Ms-And-Toz, largely the products of fluido-magmatic processes.

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New approaches to crustal evolution studies and the origin of granitic rocks: what can the Lu-Hf and Re-Os isotope systems tell us?

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300006738 ◽

1996 ◽

Vol 87 (1-2) ◽

pp. 339-352 ◽

Cited By ~ 19

Author(s):

Clark M. Johnson ◽

Steven B. Shirey ◽

Karin M. Barovich

Keyword(s):

Continental Crust ◽

Isotope Ratios ◽

Granitic Rocks ◽

Nd Isotope ◽

Volcanic Arcs ◽

Depleted Mantle ◽

Os Isotopes ◽

Isotope System ◽

Os Isotope

ABSTRACT:The Lu-Hf and Re-Os isotope systems have been applied sparsely to elucidate the origin of granites, intracrustal processes and the evolution of the continental crust. The presence or absence of garnet as a residual phase during partial melting will strongly influence Lu/Hf partitioning, making the Lu–Hf isotope system exceptionally sensitive to evaluating the role of garnet during intracrustal differentiation processes. Mid-Proterozoic (1·1–1·5Ga ) ‘anorogenic’ granites from the western U.S.A. appear to have anomalously high εHf values, relative to their εNd values, compared with Precambrian orogenic granites from several continents. The Hf-Nd isotope variations for Precambrian orogenic granites are well explained by melting processes that are ultimately tied to garnet-bearing sources in the mantle or crust. Residual, garnet-bearing lower and middle crust will evolve to anomalously high εHf values over time and may be the most likely source for later ‘anorogenic’ magmas. When crustal and mantle rocks are viewed together in terms of Hf and Nd isotope compositions, a remarkable mass balance is apparent for at least the outer silicate earth where Precambrian orogenic continental crust is the balance to the high-εHf depleted mantle, and enriched lithospheric mantle is the balance to the low-εHf depleted mantle.Although the continental crust has been envisioned to have exceptionally high Re/Os ratios and very radiogenic Os isotope compositions, new data obtained on magnetite mineral separates suggest that some parts of the Precambrian continental crust are relatively Os-rich and non-radiogenic. It remains unclear how continental crust may obtain non-radiogenic Os isotope ratios, and these results have important implications for Re-Os isotope evolution models. In contrast, Phanerozoic batholiths and volcanic arcs that are built on young mafic lower crust may have exceptionally radiogenic Os isotope ratios. These results highlight the unique ability of Os isotopes to identify young mafic crustal components in orogenic magmas that are essentially undetectable using other isotope systems such as O, Sr, Nd and Pb.

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Chemotactic cytokines, obesity and type 2 diabetes:in vivoandin vitroevidence for a possible causal correlation?

Proceedings of The Nutrition Society ◽

10.1017/s0029665109990218 ◽

2009 ◽

Vol 68 (4) ◽

pp. 378-384 ◽

Cited By ~ 41

Author(s):

Henrike Sell ◽

Jürgen Eckel

Keyword(s):

Insulin Resistance ◽

Adipose Tissue ◽

Low Grade ◽

Obese Patients ◽

Tissue Mass ◽

Tissue Biology ◽

Wide Range ◽

Adipose Tissue Mass

A strong causal link between increased adipose tissue mass and insulin resistance in tissues such as liver and skeletal muscle exists in obesity-related disorders such as type 2 diabetes. Increased adipose tissue mass in obese patients and patients with diabetes is associated with altered secretion of adipokines, which also includes chemotactic proteins. Adipose tissue releases a wide range of chemotactic proteins including many chemokines and chemerin, which are interesting targets for adipose tissue biology and for biomedical research in obesity and obesity-related diseases. This class of adipokines may be directly linked to a chronic state of low-grade inflammation and macrophage infiltration in adipose tissue, a concept intensively studied in adipose tissue biology in recent years. The inflammatory state of adipose tissue in obese patients may be the most important factor linking increased adipose tissue mass to insulin resistance. Furthermore, chemoattractant adipokines may play an important role in this situation, as many of these proteins possess biological activity beyond the recruitment of immune cells including effects on adipogenesis and glucose homeostasis in insulin-sensitive tissues. The present review provides a summary of experimental evidence of the role of adipose tissue-derived chemotactic cytokines and their function in insulin resistancein vivoandin vitro.

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Systematic identification of non-coding somatic single nucleotide variants associated with altered transcription and DNA methylation in adult and pediatric cancers

NAR Cancer ◽

10.1093/narcan/zcab001 ◽

2021 ◽

Vol 3 (1) ◽

Author(s):

Fengju Chen ◽

Yiqun Zhang ◽

Chad J Creighton

Keyword(s):

Dna Methylation ◽

Brain Tumor ◽

Low Grade ◽

Single Nucleotide Variants ◽

Multiple Cancer ◽

Single Nucleotide ◽

Altered Expression ◽

Wide Range ◽

Mutational Hotspots ◽

Cancer Types

Abstract Whole-genome sequencing combined with transcriptomics can reveal impactful non-coding single nucleotide variants (SNVs) in cancer. Here, we developed an integrative analytical approach that, as a first step, identifies genes altered in expression or DNA methylation in association with nearby somatic SNVs, in contrast to alternative approaches that first identify mutational hotspots. Using genomic datasets from the Pan-Cancer Analysis of Whole Genomes (PCAWG) consortium and the Children's Brain Tumor Tissue Consortium (CBTTC), we identified hundreds of genes and associated CpG islands for which the nearby presence of a non-coding somatic SNV recurrently associated with altered expression or DNA methylation, respectively. Genomic regions upstream or downstream of genes, gene introns and gene untranslated regions were all involved. The PCAWG adult cancer cohort yielded different significant SNV-expression associations from the CBTTC pediatric brain tumor cohort. The SNV-expression associations involved a wide range of cancer types and histologies, as well as potential gain or loss of transcription factor binding sites. Notable genes with SNV-associated increased expression include TERT, COPS3, POLE2 and HDAC2—involving multiple cancer types—MYC, BCL2, PIM1 and IGLL5—involving lymphomas—and CYHR1—involving pediatric low-grade gliomas. Non-coding somatic SNVs show a major role in shaping the cancer transcriptome, not limited to mutational hotspots.

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An Individualized Approach to Appendectomy in Children Based on Anatomico-Laparoscopic Findings

The American Surgeon ◽

10.1177/000313480707300817 ◽

2007 ◽

Vol 73 (8) ◽

pp. 814-817

Author(s):

Michael W.L. Gauderer

Keyword(s):

Disease Stage ◽

Patient Specific ◽

Low Grade ◽

Open Approach ◽

Overweight Children ◽

Trocar Site ◽

Lower Quadrant ◽

Wide Range ◽

Individualized Approach ◽

Complex Cases

Whether an appendectomy should be performed “open” or laparoscopically is the subject of considerable debate. This study in children was undertaken to test the hypothesis that an individualized approach, based on disease stage, body habitus, and laparoscopic findings should dictate the removal technique. Data on 108 consecutive pediatric appendectomies were prospectively recorded. Except in complex cases, a 5 mm laparoscope was inserted umbilically, the findings were evaluated, and the best removal approach was selected. Depending on the degree of inflammation and mobility, the appendix was fully delivered and resected, either through the initial umbilical trocar site or, more commonly, through a second right lower quadrant (RLQ) trocar site. The second RLQ trocar incision was enlarged for limited or full conversion to an open approach, if needed. In overweight children, three trocars and a stapler were used. Children (63 boys, 45 girls) ranged in age from 3 to 18 years (mean, 11 years). A single umbilical port was used in 16 patients with low-grade appendiceal inflammation. A two trocar, laparoscopically-assisted appendectomy was used in 63 cases. Of these 63, a limited extension of the RLQ trocar incision was necessary in 4 patients and conversion to an open incision was needed in 4 children. The three trocar technique was used 21 times. Twelve of these were cases involving obese patients. A stapler was used 13 times. Four trocars were needed once. Seven patients with complex appendicitis did not undergo laparoscopy. Twenty-nine appendices were perforated, and there were 3 complications: 2 intra-abdominal abscesses and one trocar site wound infection. Because appendiceal disease is a spectrum, and children encompass a wide range of ages and sizes, an individualized approach, based on the anatomical parameters and the clinical and laparoscopic findings, allows for an efficient, patient-specific appendectomy: single trocar for minimally inflamed appendices, two trocars for the most common types, three trocars plus a stapler for overweight children, and an “open” procedure for complex cases.

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Final-Stage Magmatic Record of Paleo-Asian Oceanic Subduction? Insights from Late Permian to Early Triassic Intrusive Rocks in the Yanbian Area, Easternmost Central Asian Orogenic Belt

Minerals ◽

10.3390/min10090799 ◽

2020 ◽

Vol 10 (9) ◽

pp. 799

Author(s):

Chao Zhang ◽

Franz Neubauer ◽

Zheng-Hong Liu ◽

Fang-Hua Cui ◽

Qing-Bin Guan

Keyword(s):

Partial Melting ◽

Granitic Rocks ◽

Early Triassic ◽

Crustal Material ◽

Late Permian ◽

The North ◽

Wide Range ◽

Intrusive Rocks ◽

Subduction Setting ◽

T Values

This paper reports new zircon LA–ICP–MS U–Pb and Hf isotope data, and whole-rock major and trace element data for Late Permian to Early Triassic intrusive rocks in the Yanbian area, NE China. These data provide new insights into the timing of the final subduction of the Paleo-Asian Ocean beneath the North China Craton. The zircon U–Pb age data indicate that a suite of Late Permian to Early Triassic intrusive rocks related to subduction is present within the Yanbian area. The Late Permian intrusive rocks consist of diorites while the Early Triassic granites and hornblende gabbros constitute a geochemically bimodal igneous rock association. Furthermore, the Early Triassic granites show the geochemical characteristics of shoshonitic rocks. All the rocks are characterized by enrichment in LILEs and LREEs, and depletion in HREEs and HFSEs, suggesting they formed in a subduction setting. Zircons from the Early Triassic gabbros have εHf(t) values and TDM2 ages of +7.6 to +10.7 and 735–1022 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of lithospheric mantle material that had been previously modified by subduction-related fluids. The Late Permian diorites have εHf(t) values and TDM2 ages of +0.5 to +9.5 and 853 to 1669 Ma, respectively, while they have high contents of Al2O3, Fe2O3, and low contents of SiO2, Cr, and Ni, indicating Late Permian diorites should derive from the mantle and are influenced by some crustal material. Early Triassic granitic rocks have a wide range of εHf(t) values and TDM2 ages of −4.8 to +9.4 and 852 to 2136 Ma, respectively. Their zircons imply that the Early Triassic granites could be mainly derived from partial melting of the crust, with minor contribution of the crustal material of an ancient crust. The Early Triassic bimodal intrusive rocks in Yanbian area, combined with the regional geologic information; therefore, record a final post-subduction extensional environment due to the break-off of the previously subducted slab.

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