10 research outputs found
New stratigraphic, geochronological, and structural data from the southern Guanajuato Mining District, MĂ©xico: implications for the caldera hypothesis
<div><p></p><p>The Cenozoic stratigraphy of the southern Guanajuato Mining District (GMD) was established 40 years ago. The existence of a caldera structure that produced the Cenozoic volcanic cover was postulated and the world-class silver ore deposit of the Oligocene age has been closely related to magmatism. In this context, we present a new geological map of the southern GMD, UâPb and ArâAr ages of the volcanic units, and structural data for the Cenozoic faults. Our results document that the volcanic centre was active between ca. 33.5 Ma and ca. 31.3 Ma, coeval with NWâSE normal faulting. We propose that the Bufa, Calderones, and Cedro formations are stratigraphic units directly related to the volcanic centre. Although the younger ChichĂndaro Rhyolite scarcely crops out within the study area, it appears to be more extensive outside of the study area, forming part of the rhyolitic volcanism of the Mesa Central of Mexico. In the study area, the ChichĂndaro Rhyolite buries major faults, demonstrating that it was emplaced after the peak of faulting. The two main structures are the El Cubo and Veta Madre grabens; also there are several faulted and brecciated zones where silverâgold mineralization was emplaced. The extension direction changed from NE to NW producing normal faulting, reactivating older structures and allowing dike intrusion. The extensional phase continued to be active throughout the Oligocene. The age of the volcanic event and a new KâAr age of the Veta Madre vein of 29.8 ± 0.8 Ma (KâAr in adularia) indicate that the hydrothermal event began immediately after the emplacement of the Cedro Formation. The emplacement of the ChichĂndaro Rhyolite allowed hydrothermal activity to be active for two million years or more.</p></div
Simultaneous quantification of four antiretroviral drugs in breast milk samples from HIV-positive women by an ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method
<div><p>The primary strategy to avoid mother-to-child transmission of human immunodeficiency virus (HIV) through breastfeeding is administration of highly active antiretroviral therapy (HAART) to HIV-positive pregnant women. Because significant changes in the pharmacokinetics of antiretroviral (ARV) drugs occur during pregnancy, quantifying HAART and the viral load in breast milk in this population is essential. Here, we developed an analytical assay for the simultaneous quantification of four ARV drugs in breast milk using ultra-performance liquid chromatography coupled to tandem mass spectrometry. We validated this method following Mexican and international guidelines. ARV drugs. We extracted the ARV drugs from 200 ÎŒL samples of breast milk and detected these drugs in a triple quadrupole mass spectrometer with positive electrospray ionization. The validated concentration ranges (ng/mL) for zidovudine, lamivudine, lopinavir, and ritonavir were 12.5â750, 50â2500, 100â5000 and 5 to 250, respectively. Additionally, the absolute recovery percentages (and matrix effects) were 91.4 (8.39), 88.78 (28.75), 91.38 (11.77) and 89.78 (12.37), respectively. We determined that ARV drugs are stable for 24 h at 8°C and 24°C for 15 days at â80°C. This methodology had the capacity for simultaneous detection; separation; and accurate, precise quantification of ARV drugs in human breast milk samples according to Mexican standard laws and United States Food and Drug Administration guidelines.</p></div
Correlation between nominal concentration <i>vs</i> measured concentration (ng/mL) for intra-day (n = 3) and inter-day (n = 3) validation of each ARV.
<p>Correlation between nominal concentration <i>vs</i> measured concentration (ng/mL) for intra-day (n = 3) and inter-day (n = 3) validation of each ARV.</p
Transition ions and optimal conditions to obtain relative abundance of product ions.
<p>Transition ions and optimal conditions to obtain relative abundance of product ions.</p
Accuracy and precision for the quantification of antiretroviral in breast milk.
<p>Accuracy and precision for the quantification of antiretroviral in breast milk.</p
Chromatographic conditions: Mobile phase gradient program.
<p>Chromatographic conditions: Mobile phase gradient program.</p
Representative ion chromatograms of separation and retention time (minutes) of each ARV drug and IS: 0.29, 0.62, 1.61, 1.71 and 2.11 for LMV, ZDV, RTV, LPV, and SMV, respectively, corresponding only to LQC (ng/mL) of each ARV.
<p>Total run time was 2.5 minutes, with an ACQUITY UPLC BEH C 18 column, formic acid and ACN gradient as mobile phase.</p
Short-term stability of antiretroviral drugs in processed samples.
<p>Short-term stability of antiretroviral drugs in processed samples.</p
Nominal concentrations of each calibration curve and quality control standards in breast milk samples.
<p>Nominal concentrations of each calibration curve and quality control standards in breast milk samples.</p
The North American-Caribbean Plate boundary in Mexico-Guatemala-Honduras
<p>New structural, geochronological, and petrological data highlight which crustal sections of the North AmericanâCaribbean Plate
boundary in Guatemala and Honduras accommodated the large-scale sinistral offset. We develop the chronological and kinematic
framework for these interactions and test for Palaeozoic to Recent geological correlations among the Maya Block, the ChortĂs
Block, and the terranes of southern Mexico and the northern Caribbean. Our principal findings relate to how the North AmericanâCaribbean
Plate boundary partitioned deformation; whereas the southern Maya Block and the southern ChortĂs Block record the Late CretaceousâEarly
Cenozoic collision and eastward sinistral translation of the Greater Antilles arc, the northern ChortĂs Block preserves evidence
for northward stepping of the plate boundary with the translation of this block to its present position since the Late Eocene.
Collision and translation are recorded in the ophiolite and subductionâaccretion complex (North El Tambor complex), the continental
margin (Rabinal and ChuacĂșs complexes), and the Laramide foreland foldâthrust belt of the Maya Block as well as the overriding
Greater Antilles arc complex. The Las Ovejas complex of the northern ChortĂs Block contains a significant part of the history
of the eastward migration of the ChortĂs Block; it constitutes the southern part of the arc that facilitated the breakaway
of the ChortĂs Block from the Xolapa complex of southern Mexico. While the Late Cretaceous collision is spectacularly sinistral
transpressional, the EoceneâRecent translation of the ChortĂs Block is by sinistral wrenching with transtensional and transpressional
episodes. Our reconstruction of the Late MesozoicâCenozoic evolution of the North AmericanâCaribbean Plate boundary identified
Proterozoic to Mesozoic connections among the southern Maya Block, the ChortĂs Block, and the terranes of southern Mexico:
(i) in the EarlyâMiddle Palaeozoic, the AcatlĂĄn complex of the southern Mexican Mixteca terrane, the Rabinal complex of the
southern Maya Block, the ChuacĂșs complex, and the ChortĂs Block were part of the TaconicâAcadian orogen along the northern
margin of South America; (ii) after final amalgamation of Pangaea, an arc developed along its western margin, causing magmatism
and regional amphiboliteâfacies metamorphism in southern Mexico, the Maya Block (including Rabinal complex), the ChuacĂșs complex
and the ChortĂs Block. The separation of North and South America also rifted the ChortĂs Block from southern Mexico. Rifting
ultimately resulted in the formation of the Late JurassicâEarly Cretaceous oceanic crust of the South El Tambor complex; rifting
and spreading terminated before the Hauterivian (<em>c</em>. 135 Ma). Remnants of the southwestern Mexican Guerrero complex, which also rifted from southern Mexico, remain in the ChortĂs
Block (Sanarate complex); these complexes share Jurassic metamorphism. The South El Tambor subductionâaccretion complex was
emplaced onto the ChortĂs Block probably in the late Early Cretaceous and the ChortĂs Block collided with southern Mexico.
Related arc magmatism and high-<em>T</em>/low-<em>P</em> metamorphism (TaxcoâViejoâXolapa arc) of the Mixteca terrane spans all of southern Mexico. The ChortĂs Block shows continuous
Early CretaceousâRecent arc magmatism.
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