Teresa Orozco-Esquivel

The area of sierras Las Jarillas-El Potrero in northern Sonora is interpreted as a portion of the lower plate of the Magdalena metamorphic core complex. Rock units that characterize this locality range in age from Jurassic to Eocene. Jurassic units comprise a small area of metasedimentary rocks that is probably correlative with the regional Middle Jurassic La Jojoba metasandstone and, is intruded by the La Cebolla granite of 158.1 ± 1 Ma (U-Pb, zircon). A younger succession consists from base upwards of a lower metasedimentary unit, a metalimestone unit, and an upper metasedimentary unit. The lower and upper units have similar lithologies of metapelites, metasandstones, and metavolcanic rocks for which maximum depositional ages (U-Pb, zircon) of ca. 119 to ca. 112 Ma were obtained. The intermediate unit consists of recrystallized limestone with interbedded metapelite and metasandstone. These three units that probably correlate with nearby unmetamorphosed outcrops of the Bisbee Group are intruded by the two-mica and garnet leucocratic mylonitic granites Las Jarillas, dated (U-Pb, zircon) at 60.1 ± 0.9 Ma (MSWD= 7), and La Yegua, dated at 46.9 ± 0.3 Ma (MSWD= 0.8). At the outcrop scale, Las Jarillas granite is fine-grained and saccaroid, whereas the La Yegua granite is medium- to coarse-grained, with common pegmatitic zones and abundant xenoliths of quartzo-feldspathic schists. Mylonitic foliation in the area predominantly strikes NNW-SSE and dips gently NE and SW, with a NE65°SW trending lineation and average plunge of 16° NE and SW. The mylonitic granites record ductile to brittle-ductile deformation with foliation defined by bands of dynamically recrystallized quartz that envelop feldspar porphyroclasts. The metasedimentary and metavolcanic rocks show continuous and/or spaced cleavage defined by alignments of muscovite, biotite and epidote and subordinate tourmaline, titanite, garnet, hornblende, staurolite, actinolite, zoisite, and opaque minerals. These minerals suggest upper greenschist to lower amphibolite facies metamorphism for the rocks in the area. Mica-fish and S-C foliation kinematic indicators consistently indicate a top-to-the-SW tectonic transport direction. A concentrate of muscovite and quartz from a metasandstone sample yielded a cooling age of 24.14 ± 0.57 Ma (40Ar/39Ar), similar to muscovite ages reported by Wong et al. (2010) for the nearby Magdalena-Madera metamorphic core complex. We consider Sierras Las Jarillas-El Potrero to be part of the Magdalena-Madera complex that was exhumed in the footwall of the regional Magdalena-Tubutama detachment fault, which is inferred to pass directly southwest of the study area. A secondary, west-dipping detachment fault in the study area separates the Jurassic and Lower Cretaceous footwall successions near Cerro Picacho. The identified Jurassic through Eocene units, structural overprint, and new geochronologic results are consistent with large-magnitude late Oligocene-early Miocene extension that has affected the region.

Post-collisional volcanism contains important clues for understanding the processes that prevail in orogenic belts, including those in the mantle and the uplift and collapse of continents. Here we report new geochronological and geochemical data for a suite of post-collisional Miocene to Pleistocene volcanic rocks from northwest Iran. Four groups of volcanic rocks can be distinguished according to their geochemical and isotopic signatures, including: (1) Miocene depleted lavas with high Nd and Hf but low Pb and Sr isotopic ratios, (2) less depleted lavas with quite variable Pb isotopic composition, (3) lavas with non-radiogenic Nd and Hf isotopic values, but highly radiogenic Sr and Pb isotopic composition, and (4) Pleistocene adakitic rocks with depleted isotopic signatures. The isotopic data reveal that the Miocene rocks are derived from asthenospheric and highly heterogeneous sub-continental lithospheric mantle sources. Evidence suggests that the lithospheric mantle contains recycled upper continental material and is isotopically similar to the enriched mantle two (EMII) endmember. Analysis of Sr-Nd-Pb-Hf-O isotopes in both mineral and rock groundmass, in conjunction with energy-constrained assimilation and fractional crystallization (EC-AFC) numerical modeling, demonstrates that the incorporation of continental crust during magma fractionation via AFC had an insignificant impact on the isotopic composition of the Miocene lavas. Moreover, adakites are the youngest rocks and show a geochemical signature consistent with the partial melting of a young and mafic continental lower crust. Both seismological data and geochemical signatures on these Miocene to Pleistocene volcanic rocks indicate the initiation of asthenospheric upwelling and orogen uplift in the Arabia-Eurasia collision zone, which occurred after slab break-off, following the Neotethyan closure.

The Los Cabos Block, at the southern end of Baja California, exposes part of the Late Cretaceous Peninsular Ranges Batholith over 2700 km². In the Los Cabos block, the Los Cabos Batholitic Complex is exposed in two massifs, Sierra La Laguna to the west and Sierra La Trinidad to the east. The two sierras are separated by the ~75 km long, N-S striking, San José del Cabo extensional fault system, and the homonymous basin. Here, we present field observations, new U–Pb and Ar–Ar ages, and thermobarometric determinations to constrain the magmatic history of this composite batholith and the structural relations between Sierra La Laguna and Sierra La Trinidad. Field observations show that the batholith at Sierra La Laguna comprises several granodiorite bodies, felsic sills, and dikes with complex magma mingling and mixing features typical of an upper-middle crustal system within a mush zone of intermediate to silicic composition. U–Pb zircon crystallization ages for La Laguna massif define the main period of plutonism between ~89.9 and 73.9 Ma, with progressively younger ages from west to east. Zircon chemistry and published whole-rock isotopic data point to mantle contributions to arc magmatism with significant crustal thickening with time. Hornblende thermobarometry suggests a wide range interval of crystallization (depth: 12–18 km; temperature: 670–740°C). Sierra La Trinidad has a more felsic and narrow compositional range, with crystallization ages like those from the eastern, younger part of Sierra La Laguna and lower crystallization depth, indicating that it represents the shallower portion of the Los Cabos Batholitic Complex magmatic system. The integration of our study with previous research indicates that Sierra La Trinidad is the hanging wall block of the San José del Cabo fault system, which implies a low angle geometry (18 Ma).

Iodine is a crucial component of thyroid hormones, and several reports have shown that iodine per se is implicated in the physiopathology of other organs. Innovative ion chromatography detection following a four-step temperature ramp microwave digestion in 25-50 mM nitric acid was developed to measure total iodine in biological fluids and tissue samples from female Sprague-Dawley rats supplemented with 0.05% molecular iodine (I2) or 0.05% potassium iodide (I(-)) in drinking water. The reported method allows the measurement of total iodine with a limit of quantification of 13.7 μg L(-1), recoveries of 96.3-100.3%, and intra- and inter-assay variations, of 3.5% and 7.4% respectively. Analysis of biological fluids showed that after 48 hours, iodine-supplemented animals exhibited significantly higher levels of total iodine in both serum and urine compared with those supplemented with iodide. The half-life of iodine in serum and urine measured over the first 48 h showed similar patterns for both the I2 (7.89 and 7.76 hours) and I(-) (8.27 and 8.90 hours) supplements. Differential uptake patterns were observed in tissues after 6 days of supplements, with I(-) preferentially retained by thyroid, lactating mammary gland, and milk, and a slightly but significantly higher capture of I2 in pituitary, ovary, and virgin mammary gland. We developed a rapid, selective, and accurate digestion method to process fluid and tissue samples that permits reproducible measurements of total iodine by ion chromatography; iodine or iodide supplement show a similar serum and urine half-life, but organ-specific uptake depends on the chemical form of the iodine supplement.