33 research outputs found
Jurassic cooling ages in Paleozoic to early Mesozoic granitoids of northeastern Patagonia : 40Ar/39Ar, 40Kâ40Ar mica and UâPb zircon evidence
University of Buenos Aires (PICTUBACYT X183), CONICET and ANPCYT (PICT20131162) financial support is acknowledged.UâPb SHRIMP zircon crystallization ages and ArâAr and KâAr mica cooling ages for basement rocks of the YaminuĂ© and Nahuel Niyeu areas in northeastern Patagonia are presented. Granitoids that cover the time span from Ordovician to Early Triassic constitute the main outcrops of the western sector of the YaminuĂ© block. The southern YaminuĂ© Metaigneous Complex comprises highly deformed Ordovician and Permian granitoids crosscut by undeformed leucogranite dikes (UâPb SHRIMP zircon age of 254 ± 2 Ma). Mica separates from highly deformed granitoids from the southern sector yielded an ArâAr muscovite age of 182 ± 3 Ma and a KâAr biotite age of 186 ± 2 Ma. Moderately to highly deformed Permian to Early Triassic granitoids made up the northern YaminuĂ© Complex. The Late Permian to Early Triassic (UâPb SHRIMP zircon age of 252 ± 6 Ma) Cabeza de Vaca Granite of the YaminuĂ© block yielded Jurassic mica KâAr cooling ages (198 ± 2, 191 ± 1, and 190 ± 2 Ma). At the boundary between the YaminuĂ© and Nahuel Niyeu blocks, KâAr muscovite ages of 188 ± 3 and 193 ± 5 Ma were calculated for the Flores Granite, whereas the Early Permian Navarrete granodiorite, located in the Nahuel Niyeu block, yielded a KâAr biotite age of 274 ± 4 Ma. The Jurassic thermal history is not regionally uniform. In the supracrustal exposures of the Nahuel Niyeu block, the Early Permian granitoids of its western sector as well as other Permian plutons and Ordovician leucogranites located further east show no evidence of cooling age reset since mica ages suggest cooling in the wake of crystallization of these intrusive rocks. In contrast, deeper crustal levels are inferred for PermianâEarly Triassic granitoids in the YaminuĂ© block since cooling ages for these rocks are of Jurassic age (198â182 Ma). Jurassic resetting is contemporaneous with the massive Lower Jurassic Flores Granite, and the Marifil and Chon Aike volcanic provinces. This intraplate deformational pulse that affected northeastern Patagonia during the Early Jurassic (SinemurianâPliensbachian) was responsible for the partial (re)exhumation of the mid-crustal Paleozoic basement along reactivated discrete NEâSW to ENEâWSW lineaments and the resetting of isotopic systems. These new thermochronological data indicate that Early Permian magmatic rocks of the Nahuel Niyeu block were below 300 °C for ca. 20 Ma prior to the onset of the main magmatic episode of the Late Permian to Triassic igneous and metaigneous rocks of the YaminuĂ© block.PostprintPeer reviewe
New palaeomagnetic results from Late Paleozoic volcanic units along the western Gondwana margin in La Pampa, Argentina
The Gondwana connections of northern Patagonia
A multidisciplinary study (UâPb sensitive high-resolution ion microprobe geochronology, Hf and O isotopes in zircon, Sr and Nd isotopes in whole-rocks, as well as major and trace element geochemistry) has been carried out on granitoid samples from the area west of Valcheta, North Patagonian Massif, Argentina. These confirm the Cambrian age of the Tardugno Granodiorite (528â±â4âMa) and the Late Permian age of granites in the central part of the YaminuĂ© complex (250âMa). Together with petrological and structural information for the area, we consider a previously suggested idea that the Cambrian and Ordovician granites of northeastern Patagonia represent continuation of the Pampean and Famatinian orogenic belts of the Sierras Pampeanas, respectively. Our interpretation does not support the hypothesis that Patagonia was accreted in Late Palaeozoic times as a far-travelled terrane, originating in the Central Transantarctic Mountains, and the arguments for and against this idea are reviewed. A parautochthonous origin is preferred with no major ocean closure between the North Patagonian Massif and the Sierra de la Ventana fold belt.
Supplementary material: UâPb SHRIMP analytical data, geochemical analyses and sample global positioning system locations are available at www.geolsoc.org.uk/SUP18722
Tectonic implications of a paleomagnetic study of the Sarmiento Ophiolitic Complex, southern Chile
A paleomagnetic study was carried out on the Late Jurassic Sarmiento Ophiolitic Complex (SOC) exposed in the Magallanes fold and thrust belt in the southern Patagonian Andes (southern Chile). This complex, mainly consisting of a thick succession of pillow-lavas, sheeted dikes and gabbros, is a seafloor remnant of the Late Jurassic to Early Cretaceous Rocas Verdes basin that developed along the south-western margin of South America. Stepwise thermal and alternating field demagnetization permitted the isolation of a post-folding characteristic remanence, apparently carried by fine grain (SD?) magnetite, both in the pillow-lavas and dikes. The mean ""in situ"" direction for the SOC is Dec: 286.9 degrees, Inc: -58.5 degrees, alpha-95: 6.9 degrees, N: 11 (sites). Rock magnetic properties, petrography and whole-rock K-Ar ages in the same rocks are interpreted as evidence of correlation between remanence acquisition and a greenschist facies metamorphic overprint that must have occurred during latest stages or after closure and tectonic inversion of the basin in the Late Cretaceous. The mean remanence direction is anomalous relative to the expected Late Cretaceous direction from stable South America. Particularly, a declination anomaly over 50 degrees is suggestively similar to paleomagnetically interpreted counter clockwise rotations found in thrust slices of the Jurassic El Quemado Fm. located over 100 km north of the study area in Argentina. Nevertheless, a significant ccw rotation of the whole SOC is difficult to reconcile with geologic evidence and paleogeographic models that suggest a narrow back-arc basin sub-parallel to the continental margin. A rigid-body 30 degrees westward tilting of the SOC block around a horizontal axis trending NNW, is considered a much simpler explanation, being consistent with geologic evidence. This may have occurred as a consequence of inverse reactivation of old normal faults, which limit both the SOC exposures and the Cordillera Sarmiento to the East. The age of tilting is unknown but it must postdate remanence acquisition in the Late Cretaceous. Two major orogenic events of the southern Patagonian Andes, in the Eocene (ca. 42 Ma) and Middle Miocene (ca. 12 Ma), respectively, could have caused the proposed tilting. (C) 2008 Elsevier B.V. All rights reserved
Poisson relation applied to the Navarrete Plutonic Complex, northeast North-Patagonian Massif, Argentina
Se realizĂł un estudio gravimĂ©trico y magnetomĂ©trico en los afloramientos granĂticos del Complejo PlutĂłnico Navarrete, ubicado al noreste del Macizo NorpatagĂłnico. Se analizĂł el grado de correlaciĂłn entre ambos campos potenciales utilizando la relaciĂłn de Poisson. Para ello, 1) se preparĂł un mapa de gradiente vertical de gravedad, que se comparĂł con el mapa de anomalĂas magnĂ©ticas reducidas al polo, 2) se calculĂł la relaciĂłn magnetizaciĂłn - densidad encontrĂĄndose un notorio cambio de polaridad entre ambos campos potenciales. CĂĄlculos complementarios como las soluciones de la señal analĂtica, en una secciĂłn transversal al Complejo PlutĂłnico Navarrete, muestran la existencia de una falla geolĂłgica central que lo divide en dos bloques. La geometrĂa inferida a partir de un modelo gravimĂ©trico, y los cambios de polaridad en ambos lados del Complejo PlutĂłnico Navarrete, indican diferencias de composiciĂłn mineralĂłgica y gĂ©nesis, entre el Complejo PlutĂłnico Navarrete Oriental y el Occidental.
doi: https://doi.org/10.22201/igeof.00167169p.2010.49.4.13
Characterization of the phenotype and definition of the deletion in a new patient with ring chromosome 22
The clinical phenotype of patients with ring chromosome 22 includes mental
retardation with severe language impairment, hypotonia, and dysmorphic facial
features. In recent years an increasing number of patients with microscopic as
well as cryptic terminal deletion involving band 22q13 have been described and
their phenotype shows clinical features overlapping with patients with ring
chromosome 22. Loss of DNA in the 22q13.3 region may lead to a clinically
recognizable syndrome named "22q13.3 deletion syndrome." We report a patient with
a ring chromosome 22 who has hypotonia, profound mental retardation, language
impairment, dysmorphic features, and behavioral disorders. To check if the
critical region responsible for "22q13.3 deletion syndrome" was absent in this
ring, a fluorescent in situ hybridization (FISH) analysis using a probe
corresponding to the ARSA locus was performed. In our patient, only one ARSA
signal could be detected, indicating that the deletion encompassed the critical
22q13.3 region. A more detailed analysis of the deletion extent then was
performed using a panel of fluorescent probes located within 22q13. These
experiments allowed the identification of the breakpoint between CTA-299D3 and
RP5-925J7 probe, located in 22q13.32. Deletion extent could be estimated to be
about 2.5 Mb, and this larger deletion may explain the severity of clinical
features observed in our patient
Risk of genetic and epigenetic alteration in children conceived following ART: Is it time to return to nature whenever possible?
Assisted reproductive technology may influence epigenetic signature as the procedures coincide with the extensive epigenetic modification occurring from fertilization to embryo implantation. However, it is still unclear to what extent ART alters the embryo epigenome. In vivo fertilization occurs in the fallopian tube, where a specific and natural environment enables the embryo's healthy development. During this dynamic period, major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Over the past decade, concerns relating to the raised incidence of epigenetic anomalies and imprinting following ART have been raised by several authors. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period; therefore, unphysiological conditions, including ovarian stimulation, in vitro fertilization, embryo culture, cryopreservation of gametes and embryos, parental lifestyle, and underlying infertility, have the potential to contribute to epigenetic dysregulation independently or collectively. This review critically appraises the evidence relating to the association between ART and genetic and epigenetic modifications that may be transmitted to the offspring
Chromosome missegregation in single human oocytes is related to the age and gene expression profile
The growing trend for women to postpone childbearing has resulted in a dramatic increase in the incidence of aneuploid pregnancies. Despite the importance to human reproductive health, the events precipitating female age-related meiotic errors are poorly understood. To gain new insight into the molecular basis of age-related chromosome missegregation in human oocytes, we combined the transcriptome profiles of twenty single oocytes (derived from females divided into two groups according to age <35 and 6535 years) with their chromosome status obtained by array comparative genomic hybridization (aCGH). Furthermore, we compared the transcription profile of the single oocyte with the surrounding cumulus cells (CCs). RNA-seq data showed differences in gene expression between young and old oocytes. Dysregulated genes play a role in important biological processes such as gene transcription regulation, cytoskeleton organization, pathways related to RNA maturation and translation. The comparison of the transcription profile of the oocyte and the corresponding CCs highlighted the differential expression of genes belonging to the G protein-coupled receptor superfamily. Finally, we detected the loss of a X chromosome in two oocytes derived from women belonging to the 6535 years age group. These aneuploidies may be caused by the detriment of REEP4, an endoplasmic reticulum protein, in women aged 6535 years. Here we gained new insight into the complex regulatory circuit between the oocyte and the surrounding CCs and uncovered a new putative molecular basis of age-related chromosome missegregation in human oocytes