Heat flow increase following the rise of mantle isotherms and crustal thinning

Heat flow measurements in the western United States define a zone of high heat flow which coincides with the Basin and Range Province where extension has taken place recently. In this region, the average reduced heat flow is approx 30 mW sq. meters higher than in stable continental provinces; locally (e.g., Battle Mountain High), the heat flow anomaly can be more than 100 mW/sq meters above average. Estimates of the amount of extension range between 30% and 100% for the past 30 Ma. In the Colorado Plateau, which has been uplifted without major tectonic deformation, the heat flow is only slightly above average. Analytical calculations show that an abrupt change in heat flow at the base of the lithosphere 30 Ma ago would not affect the surface significantly. Uplift would proceed at a slow rate. A thermal perturbation at the base of a 40 km thick crust, however, would reach the surface faster and, after 30 Ma, the increase in surface heat flow would be about 75% of the amplitude of the heat flow anomaly. The number of volcanic rocks in the Basin and Range suggests that magma intrusions may provide an effective heat transfer mechanism. It can be show that if the source of the intrusions is at the base of the lithosphere, the response time will be much longer than 30 Ma, and most ot the heat transferred from the asthenosphere will be absorbed in the lithosphere

A methodology for the capture and analysis of hybrid data: a case study of program debugging

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Reworking subducted sediments in arc magmas and the isotopic diversity of the continental crust: The case of the Ordovician Famatinian crustal section, Argentina

International audienceSince the onset of plate tectonics, continents have evolved through a balance between crustal growth, reworking, and recycling at convergent plate margins. The term "reworking" involves the re-insertion of crustal material into pre-existing crustal volumes, while crustal growth and recycling respectively represent gains from and losses to the mantle. Reworking that occurs in the mantle wedge ("source" contamination from slab material) or within the upper plate ("path" contamination), will have contrasting effects on crustal evolution. However, due to limited access to deep crustal and mantle rocks, quantifying source vs. path contamination remains challenging. Based on the 4-dimensional record of the fossil (Ordovician) Famatinian continental arc (Argentina), we demonstrate that source contamination plays a dominant role in imprinting mafic to granitic rocks with crustal oxygen-hafnium (O-Hf) isotopic compositions. We argue that source contamination at convergent plate margins significantly increased the diversity of O-Hf isotopic signatures of continents over geologic time. Our interpretation implies that crustal evolution models attributing this isotopic diversity dominantly to intra-crustal reworking may be over-simplistic and may underestimate continental growth in the last 2.5 billion years

A Middle Paleozoic shear zone in the Sierra de Valle Fértil, Argentina: Records of a continent-arc collision in the Famatinian margin of Gondwana

Geological, petrological and structural observations were obtained along a 30-km-long traverse across a segment of the Valle Fértil shear zone, central-western Argentina. On a regional scale, the shear zone appears as numerous discontinues belts over 25 km in width and is approximately 140 km in length, extended on the western section of the Sierras Valle Fértil – La Huerta mountain range. The steeply dipping shear zone with a vertical mylonitic lineation is composed of amphibolite facies ribbon mylonites and amphibolite to greenschist facies ultramylonites derived from Early Ordovician plutonic and metasedimentary parent rocks. Locally, syn-kinematic retrogression of mylonites formed greenschist facies phyllonites. During the later stages of deformation, unstrained parent rocks, mylonites, ultramylonites and phyllonites were affected by pervasive cataclasis under low greenschist facies conditions associated with localized faulting. One new 40Ar/39Ar age on biotite and published 40Ar/39Ar ages on amphibole in the shear zone yield an average cooling rate of 6.2 °C/Ma for a time period that crosses the Silurian–Devonian boundary. Since in metasedimentary rocks the youngest zircon's rims dated at 465 Ma marks the beginning of cooling, nearly continuous uplift of rocks within the shear zone occurred over a minimum time span of 55 Ma. During the period of active deformation, dip-slip movement can explain uplift of several kilometers of the Early Ordovician arc crust. The Valle Fértil shear zone, which was formed near above the inferred suture zone between the Famatinian arc and Cuyania microcontinent, is a major structural boundary nucleated within the Early Ordovician crust. The simplest geodynamic model to explain the evolution of the Valle Fértil shear zone involves the collision of the composite Cuyania/Precodillera microcontinent against the Famatinian arc.Fil: Cristofolini, Eber Ariel. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Otamendi, Juan Enrique. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Walker, B. A.. University of Washington; Estados UnidosFil: Tibaldi, Alina María. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Armas, María Paula. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bergantz, G. W.. University of Washington; Estados UnidosFil: Martino, Roberto Donato. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Comparative petrogenetic investigation of Composite Kaçkar Batholith granitoids in Eastern Pontide magmatic arc—Northern Turkey

The Pontides are an east-west trending orogenic belt which is subdivided into west, middle and eastern sectors according to their different tectonostratigraphy. The Eastern Pontides are represented by west-east-trending tectonic zones resulted from a common Mesozoic-Tertiary history, comprises dominantly of magmatic rocks. The magmatic belt in the Eastern Pontides includes a large batholith, termed the Composite Kackar Batholith (CKB) in which there are various granitic facies. The emplacement of CKB occurred in pulses between the Early Cretaceous and Eocene period during the development of the eastern Pontide magmatic arc and following collisional events. The members of the CKB are Dereli-Sebinkarahisar (Giresun) in the west, southern Arakli (Trabzon) in the middle and Kackar Mountain and its surrounding area (Rize) in the east. The plutons ranging from syenite through monzonite to granite are typically medium-high K calc-alkaline rarely tholeiitic and metaluminous I-type. The studied members of the CKB intrudes into the Late Cretaceous arc volcanics and are determined to be Late Cretaceous-Eocene (75.7 +/- 1.55; 41.2 +/- 0.89) in K-Ar age. The tectono-magmatic setting of the granitoids has been interpreted as an arc-related granitic suite, a post-collisional granitic suite and a post-orogenic granitic suite. Some plutons including mafic magmatic enclaves (MME) and K-feldspar megacrystals suggest magma mixing/mingling. HFS and LIL element geochemistry of the granitic intrusions also suggest that fractional crystallization, magma mixing/mingling and crustal contamination played an important role in the evolution of the CKB. All the data mentioned above show that the granitoids in the three different regions may have been derived from an arc, developed in response to the northward subduction of the northern branch of neo-Tethyan oceanic crust beneath the Eurasian plate in Late Cretaceous and a collision between the Pontide arc and the Anatolide-Tauride platform in Paleocene