The Chuacús Metamorphic Complex, central Guatemala : geochronological and geochemical constraints on its Paleozoic - Mesozoic evolution

The Chuacús Metamorphic Complex is located in Central Guatemala, between the Polochic and Motagua fault zones. It is made up of complexly intercalated, mafic and felsic high-grade gneisses, amphibolites, pelitic and quartzofeldsphatic metasediments and subordinate marbles. Mafic dikes and lenses metamorphosed to amphibolite and eclogite facies are tholeiitic and similar to mid-ocean ridge basalts. In contrast, metamorphosed intrusives (gabbro, diorite and granite) are calc-alkaline and have the geochemical signature of arc magmas. Laser Ablation Inductively Coupled Plasma Mass Spectrometry U-Pb zircon geochronology allows the recognition of three episodes of metamorphism. The first eclogite facies metamorphism (M1) is bracketed between Ordovician magmatism in the northern Chuacús Metamorphic Complex and the neighboring Rabinal granitic suite; the second corresponds to an Upper Triassic period of arc magmatism and migmatization (M2); the third high-grade metamorphic event (M3) occurred during the Late Cretaceous. The tectonic evolution of the Chuacús Metamorphic Complex began during the Early Paleozoic as a basin in the Rheic Ocean that received detrital material from the Maya Block, Acatlán and southeastern México. The Chuacús Metamorphic Complex evolved to an active margin that subducted to HP conditions during the Mid- Late Paleozoic, and then was exhumed and involved in two tectonothermal events during the Upper Triassic and Late Cretaceous. The Chuacús Metamorphic Complex was accreted to the southern Maya Block during the Late Cretaceous, as a result of the convergent tectonics between the latter and either the Greater Antillean arc or the Chortís Block

Crustal recycling by subduction erosion in the central Mexican Volcanic Belt

Recycling of upper plate crust in subduction zones, or ‘subduction erosion’, is a major mechanism of crustal destruction at convergent margins. However, assessing the impact of eroded crust on arc magmas is difficult owing to the compositional similarity between the eroded crust, trench sediment and arc crustal basement that may all contribute to arc magma formation. Here we compare Sr–Nd–Pb–Hf and trace element data of crustal input material to Sr–Nd–Pb–Hf–He–O isotope chemistry of a well-characterized series of olivine-phyric, high-Mg# basalts to dacites in the central Mexican Volcanic Belt (MVB). Basaltic to andesitic magmas crystallize high-Ni olivines that have high mantle-like 3He/4He = 7–8 Ra and high crustal δ18Omelt = +6.3–8.5‰ implying their host magmas to be near-primary melts from a mantle infiltrated by slab-derived crustal components. Remarkably, their Hf–Nd isotope and Nd/Hf trace element systematics rule out the trench sediment as the recycled crust end member, and imply that the coastal and offshore granodiorites are the dominant recycled crust component. Sr–Nd–Pb–Hf isotope modeling shows that the granodiorites control the highly to moderately incompatible elements in the calc-alkaline arc magmas, together with lesser additions of Pb- and Sr-rich fluids from subducted mid-oceanic ridge basalt (MORB)-type altered oceanic crust (AOC). Nd–Hf mass balance suggests that the granodiorite exceeds the flux of the trench sediment by at least 9–10 times, corresponding to a flux of ⩾79–88 km3/km/Myr into the subduction zone. At an estimated thickness of 1500–1700 m, the granodiorite may buoyantly rise as bulk ‘slab diapirs’ into the mantle melt region and impose its trace element signature (e.g., Th/La, Nb/Ta) on the prevalent calc-alkaline arc magmas. Deep slab melting and local recycling of other slab components such as oceanic seamounts further diversify the MVB magmas by producing rare, strongly fractionated high-La magmas and a minor population of high-Nb magmas, respectively. Overall, the central MVB magmas inherit their striking geochemical diversity principally from the slab, thus emphasizing the importance of continental crust recycling in modern solid Earth relative to its new formation in modern subduction zones

Perturbation of the Dimer Interface of Triosephosphate Isomerase and its Effect on Trypanosoma cruzi

Most of the enzymes of parasites have their counterpart in the host. Throughout evolution, the three-dimensional architecture of enzymes and their catalytic sites are highly conserved. Thus, identifying molecules that act exclusively on the active sites of the enzymes from parasites is a difficult task. However, it is documented that the majority of enzymes consist of various subunits, and that conservation in the interface of the subunits is lower than in the catalytic site. Indeed, we found that there are significant differences in the interface between the two subunits of triosephosphate isomerase from Homo sapiens and Trypanosoma cruzi (TcTIM), which causes Chagas disease in the American continent. In the search for agents that specifically inhibit TcTIM, we found that 2,2′-dithioaniline (DTDA) is far more effective in inactivating TcTIM than the human enzyme, and that its detrimental effect is due to perturbation of the dimer interface. Remarkably, DTDA prevented the growth of Escherichia coli cells that had TcTIM instead of their own TIM and killed T. cruzi epimastigotes in culture. Thus, this study highlights a new approach base of targeting molecular interfaces of dimers

A Ribosomal Misincorporation of Lys for Arg in Human Triosephosphate Isomerase Expressed in Escherichia coli Gives Rise to Two Protein Populations

We previously observed that human homodimeric triosephosphate isomerase (HsTIM) expressed in Escherichia coli and purified to apparent homogeneity exhibits two significantly different thermal transitions. A detailed exploration of the phenomenon showed that the preparations contain two proteins; one has the expected theoretical mass, while the mass of the other is 28 Da lower. The two proteins were separated by size exclusion chromatography in 3 M urea. Both proteins correspond to HsTIM as shown by Tandem Mass Spectrometry (LC/ESI-MS/MS). The two proteins were present in nearly equimolar amounts under certain growth conditions. They were catalytically active, but differed in molecular mass, thermostability, susceptibility to urea and proteinase K. An analysis of the nucleotides in the human TIM gene revealed the presence of six codons that are not commonly used in E. coli. We examined if they were related to the formation of the two proteins. We found that expression of the enzyme in a strain that contains extra copies of genes that encode for tRNAs that frequently limit translation of heterologous proteins (Arg, Ile, Leu), as well as silent mutations of two consecutive rare Arg codons (positions 98 and 99), led to the exclusive production of the more stable protein. Further analysis by LC/ESI-MS/MS showed that the 28 Da mass difference is due to the substitution of a Lys for an Arg residue at position 99. Overall, our work shows that two proteins with different biochemical and biophysical properties that coexist in the same cell environment are translated from the same nucleotide sequence frame

The role of subducted sediments in the formation of intermediate mantle-derived magmas from the Northern Colombian Andes

Unraveling the sources and processes that produce intermediate continental arc volcanoes is still a challenge for geoscientists. To address this problem, here we use comprehensive geochemical and isotopic data from Nevado del Santa Isabel and Cerro Machín volcanoes in the North Volcanic Province of Colombia, and from oceanic sediments sampled outboard the Colombian continental margin. Volcanoes along this province have been influenced by the subduction of a compositionally contrasting sedimentary column constituted by a carbonate-rich pelagic layer overlain by a clay-and-apatite-rich hemipelagic unit. The studied volcanoes exhibit the high Mg# (~60) and calc-alkaline affinities that are typical of continental arcs but display unusually high and contrasting Th(U)/La, Nb/Ta and Dy/Yb ratios and isotopic compositions. We argue that the geochemical variations within and among these volcanoes are not controlled by differentiation or crustal contamination of a parental basaltic magma but formed by melting of different kinds of subducted sedimentary materials detached from the slab as buoyantly rising diapirs at various depths. This model accounts for the reworking of refractory carbonates into arc magmatism and suggests that the geochemical diversity of the North Volcanic Province is mainly controlled by the nature of the subduction inputs and their exhumation pathways within the mantle wedge. © 201

El terreno Cuicateco: ¿cuenca oceánica con influencia de subducción del Cretácico Superior en el sur de México? Nuevos datos estructurales, geoquímicos y geocronológico

The southestern portion of the Cuicateco terrane, between Matías Romero and Juchitán, Oaxaca, is made up by a low metamorphic grade vulcanosedimentary sequence that shows at least three deformation events, D1: isoclinal-recumbent F1 folding of the S0 surfaces with northeastern verging and development of a S1 axial plane cleavage with southwestern dipping. Parallel to S1 surfaces can be observed the development of hornblende, epidote, chlorite, muscovite and quartz. Such structures are related to a post-Maastrichtian left transcurrent deformational event. D2: Paleocene(?) event characterized by thrust faulting with displacement direction to north-northeast, such as the Vista Hermosa mesostructure fault, and the development of the S2 cleavage without associated recrystallization. D3: Miocenic event, defi ned by normal and lateral faulting. Chemical composition of the amphibolitic rocks of the Cuicateco terrane resembles that of tholeiitic basalts (SiO2 45�50%), with a depletion in LREE and fl at HREE patterns. Trace elements show a pattern depleted in the highly incompatible elements with respect to the less incompatible elements, and negative anomalies of Nb and Th. A contribution of subduction-related magmas is also shown by the Ta/Yb vs. Th/Yb relationships. U-Pb dating by LA-MC-ICPMS on zircons belonging to the amphibolite yielded a Maastrichtian age (65.7 ± 1.2 Ma) that is interpreted as the crystallization age of the basaltic protolith. U-Pb analyses on detrital zircons of a vulcanoclastic phyllite suggest a maximum depositional Maastrichtian age (~78 Ma) with signifi cant peaks at 113 Ma, 542 Ma, 1198 Ma, 1662 Ma, 2791 and 3062 Ma. Zircons from a sandstone belonging to the Todos Santos Formation indicate a maximum depositional age of the Middle-Upper Triassic (228 Ma), with important peaks at 571 Ma, 1026 Ma, 1530 Ma, 1978 Ma and 2909 Ma. Petrological, structural and geochronological data suggest the development of a mafi c volcanism and sedimentation in an ocean basin and close relationships with a subduction process during the Late Cretaceous. This volcanic-sedimentary sequence was deformed by two events: a transpressive to compressive deformation, during the Latest Cretaceous � Paleocene, and a later, Miocenic normal-lateral faulting, which can be associated to the Polochic-Motagua faulting tectonic systemLa porción suroriental del terreno Cuicateco, entre Matías Romero y Juchitán, Oaxaca, está compuesta por una secuencia vulcanosedimentaria de bajo grado metamórfi co que presenta por lo menos tres eventos de deformación, D1: plegamiento recumbente a isoclinal F1 de la superfi cie de estratifi cación S0, con una vergencia general hacia el noreste y desarrollo de una esquistosidad de plano axial S1 con echado hacia el suroeste. Paralelo a las superfi cies S1 se observa el desarrollo de hornblenda, epidota, clorita, moscovita y cuarzo. Este deformación está relacionada a un evento transcurrente con cinemática sinestral de edad post-maastrichtiana. D2: evento paleocénico? caracterizado por cabalgaduras con dirección de desplazamiento al norte-noreste, como la falla Vista Hermosa, y el desarrollo de la superfi cie de esquistosidad S2 sin una aparente recristalización asociada. D3: evento miocénico defi nido por fallamiento de tipo normal y lateral. La composición química de las rocas anfi bolíticas del terreno Cuicateco es de basalto toleítico (SiO2 de 45 a 50%), con empobrecimientos relativos en tierras raras ligeras y patrones casi planos de tierras raras pesadas. Los elementos en traza muestran un patrón empobrecido en elementos más incompatibles con respecto a los menos incompatuble y anomalías negativas de Th y Nb en algunas muestras. Una componente de magmas relacionados con subducción es también evidente por su relación Ta/Yb vs. Th/Yb. Los fechamientos de U-Pb por LA-MC-ICPMS en zircones de una anfi bolita arrojaron una edad de 65.7 ± 1.2 Ma (Maastrichtiano) interpretada como la edad de cristalización del protolito basáltico. De igual manera, los zircones detríticos de una fi lita vulcanoclástica indican una edad máxima de depósito maastrichtiana (78 Ma) con picos signifi cativos en 113 Ma, 542 Ma, 1198 Ma, 1662 Ma, 2791 y 3062 Ma. Los zircones de una arenisca de la Formación Todos Santos arrojaron una edad máxima del depósito posterior al Triásico Medio - Superior (228 Ma) con picos importantes en 571 Ma, 1026 Ma, 1530 Ma, 1978 Ma y 2909 Ma. Los resultados petrológicos, estructurales y geocronométricos sugieren el desarrollo de un vulcanismo básico en un ambiente de cuenca oceánica con infl uencia de subducción durante el Cretácico Superior que sufrió los efectos de dos deformaciones, una transpresiva y otra compresiva, durante el Cretácico Superior¿Paleoceno, seguido por un fallamiento normal y lateral miocénico que se asocia a la dinámica del sistema de fallas Polochic-Motagua

Mesozoic geologic evolution of the Xolapa migmatitic complex north of Acapulco, southern Mexico: implications for paleogeographic reconstructions

The Xolapa Complex in the Acapulco-Tierra Colorada area, southern Mexico, is made up of orthogneisses and paragneisses, both affected by a variable degrees of migmatization. These rocks are intruded by several episodes of Jurassic-Oligocene, calc-alkaline granitic magmatism. Three phases of ductile deformation affected the gneisses and migmatites. D1 produced an amphibolite-facies metamorphic banding (M1) and a penetrative S1 foliation, axial planar to isoclinal, recumbent F1 folds with axes parallel to a NE to NW, gently plunging, L1 stretching lineation. D2 consists of a S2 foliation defined by hornblende, biotite and garnet, synchronous with M2 migmatization that generated leucosomes, which are generally parallel to S1. D3 is made up of asymmetric, chevron F3 folds that deform the composite S1/S2 foliation during greenschist to lower amphibolite metamorphism (M3). U-Pb SHRIMP (Sensitive High-Resolution Ion Micropobe) geochronology carried out on zircon separated from two orthogneisses yielded an Early Jurassic magmatic event (178.7 ± 1.1 Ma) and the age of migmatization (133.6 ± 0.9 Ma). Two episodes of Pb loss were also recognized, the first at 129.2 ± 0.4 Ma, and the second during the earliest Paleocene (61.4 ± 1.5 Ma); they are probably associated with two episodes of magmatism. The Early Jurassic magmatic arc may be correlated with a magmatic arc in the eastern Guerrero terrane. The Early Cretaceous migmatization is inferred to have resulted from shortening, possibly due to the accretion of an exotic block, such as the Chortís block along whose northern margin contemporaneous, high-pressure metamorphism has been recorded.El Complejo Xolapa es el terreno metamórfico más extenso en el sur de México. En el segmento que va de Acapulco a Tierra Colorada está constituido por ortogneises y paragneises, afectados por un grado variable de migmatización. El basamento del Complejo Xolapa está también afectado por diversos episodios de magmatismo granítico de afinidad geoquímica calcialcalina y edades que van del Jurásico al Oligoceno. Tres fases de deformación dúctil afectan los gneises y migmatitas. Un bandeamiento metamórfico se desarrolla durante D1, y está asociado con una foliación penetrativa S1, en facies de anfibolita, que actúa como plano axial de pliegues de recumbentes a isoclinales F1. Una lineación de estiramiento L1 está presente en toda el área de estudio, con buzamiento tanto al NE como NW. La orientación de las estructuras D1 controla el emplazamiento de los lentes de leucosoma D2, generados durante el proceso de migmatización. Afuera de los dominios leucosomáticos, la foliación S2 está caracterizada por la asociación hornblenda + biotita + granate. Pliegues asimétricos de tipo chevron relacionados a la fase F3 deforman la foliación compuesta S1/S2, en condiciones de facies de esquistos verdes hasta anfibolita. La geocronología de U-Pb por SHRIMP (microsonda iónica de alta resolución) realizada en zircones separados de dos muestras de ortogneises permitió reconocer un evento magmático jurásico temprano (178.7 ± 1.1 Ma), así como la edad de migmatización en esta porción del complejo de Xolapa calculada en 133.6 ± 0.9 Ma. Dos episodios de pérdida de Pb se pueden reconocer en algunos de los zircones de las muestras fechadas. El primero es posterior al pico de migmatización (129.2 ± 0.4 Ma), y el segundo ocurrió durante el Paleoceno temprano (61.4 ± 1.5 Ma), y probablemente ambos son un efecto térmico asociado a dos de los episodios magmáticos posteriores. Estos datos sugieren que un arco magmático del Jurásico temprano habría constituido el basamento del Complejo Xolapa; se sugiere que este mismo arco corresponda a la porción este del terreno Guerrero, en donde algunas edades magmáticas similares han sido reportadas. La migmatización ocurrió durante el Cretácico temprano como consecuencia del acortamiento producido por la accreción de un bloque exótico. El bloque de Chortís es un candidato posible para tal colisión, ya que registra un evento metamórfico de alta presión contemporáneo con el evento de migmatización en el Complejo Xolapa