Catálogo de publicaciones - revistas

<jats:p>Cretaceous through Eocene plutonic rocks in northeastern Washington, USA, document a 60 m.y. history of crustal thickening and subsequent collapse and extension in response to two terrane-accretion events. Rocks emplaced 113−53 Ma have increasing La/Yb ratios reflecting orogenic plateau development after arrival of the Insular terrane by 100 Ma. Plutons emplaced 52−45 Ma (the Challis episode) document collapse of this plateau and define a SW-younging age progression attributed to breakoff and rollback of the Farallon slab following accretion of the Siletzia terrane at ca. 50 Ma. All of the rocks have chemical traits of arc magmas, likely inherited from their lower-crustal sources, but low B/Be ratios and the lack of evidence for amphibole fractionation indicate the Eocene magmas formed under drier conditions than are typical of active subduction settings. These magmas also originated at greater depth (eclogitic vs. gabbroic source) and were emplaced more shallowly than the earlier ones. All rocks have overlapping Sr-Nd and O isotopic data, indicating significant contributions from older continental crust, and depleted mantle Nd model ages become older toward the east, defining three regions that correspond with previously inferred lower-crustal domains. Farallon slab rollback also drove extension (core complex formation, dike swarms) and crustal uplift, which, along with voluminous magmatism, define the Challis episode. This tectonic model is further supported by seismic tomography, which has identified remnants of a detached slab in the upper mantle beneath the region.</jats:p>

<jats:p>The Mazraeh Cu skarn deposit, NW Iran, is situated at the lithological contact between an Oligo−Miocene granodiorite and Cretaceous limestones. The causative granodiorite has I-type medium- to high-K calc-alkaline composition that formed in a subduction arc setting. Metasomatism generated exoskarn and endoskarn characterized by a temporal and spatial mineral-chemistry zonation with massive garnet and garnet-pyroxene proximal and epidote-amphibole skarn at the distal zones of the exoskarn. Our data reveal a multi-stage evolution of the hydrothermal system. Accordingly, the prograde stage was formed by barren, oxidized, high-temperature and hypersaline magmatic fluids, which suggests that the parental magma was emplaced at low lithostatic pressure conditions (∼1.5 km depth). By contrast, during the retrograde stage the regime changed from lithostatic to hydrostatic conditions, resulting in a significant decrease in pressure and oxygen fugacity, boiling, cooling, and mixing, respectively. Dilution by meteoric fluids led to additional cooling and lower salinity of the ore fluids. Sulfur isotope compositions (δ34S = −2.8‰−1.3‰) of sulfides indicate a unique magmatic source of the sulfur. The δ18Ofluid and δDfluid values of the prograde stage fluid also indicate a magmatic origin, while their gradual depletions from the prograde to retrograde stage imply increased mixing with meteoric water. We propose that the fluid mixing scenario continued over the entire life cycle of the mineral system in an open hydrostatic regime as reflected in the oxygen isotope values. It is suggested that boiling and fluid mixing played a significant role in the formation of this giant Cu skarn deposit.</jats:p>

<jats:p>Elucidating the petrological and geochemical characteristics of continental arc crustal fragments can provide unique insights into the magmatic evolutional path and physicochemical conditions (e.g., P−T−H2O) of continental magmatic arcs. This contribution provides a comprehensive set of petrological, mineralogical, geochronological, and geochemical data for the Neoproterozoic Nanba intrusive complex of the western Yangtze Block, South China, which features well-exposed middle−upper crustal sections of the Neoproterozoic continental magmatic arc, to evaluate their magmatic source and fractionation process. The Neoproterozoic Nanba intrusive complex, composed of cumulate gabbros, hornblende gabbros, gabbro-diorites, diorites, granodiorites, K-feldspar granites, and monzogranites, was emplaced at ca. 796−790 Ma. The different lithologies of the Nanba intrusive complex display relatively homogeneous Sr-Nd-Hf isotopes, which indicates a cogenetic evolutional process. The predominantly depleted isotopic characteristics, together with high values of Ba, Rb/Y, and Ba/La, demonstrate that these rocks mainly originated from a subduction fluid−metasomatized mantle source. Petrological and geochemical characteristics, as well as hornblende thermobarometric data, collectively support that the ca. 796−790 Ma Nanba intrusive complex, following the calc-alkaline trend, was dominated by the wet cogenetic fractionation of hornblende accompanied by plagioclase and accessory minerals beneath the middle−upper crustal levels (2.4−4.7 kbar). The cumulate gabbros represent the residue of accumulated hornblende + plagioclase + Fe-Ti oxides from fractionated basaltic melts. The high-SiO2 K-feldspar granites and monzogranites display complementary trace elements, which represent residual silicic cumulates and extracted interstitial liquids in the shallower crystal mush reservoir, respectively. In combination with previous studies, we propose that the middle−upper crustal sections of the Neoproterozoic continental arc of the western Yangtze Block underwent hornblende-dominated fractionation that was followed by significant crystal-liquid separation, which led to the genesis of high-SiO2 melts at the shallower crustal level. The cogenetic evolution played a significant role in molding the petrological and geochemical diversity of Neoproterozoic igneous rocks and the differentiation process of continental arc crust in the western Yangtze Block.</jats:p>

<jats:p>The property of regional metamorphism at convergent plate margins is substantially related to the change of geothermal gradients, resulting in different types of crustal reworking through metamorphic dehydration and partial melting. The relationship between crustal metamorphism and thermal evolution of collisional orogens can thus be deciphered by investigating the change of metamorphic thermobaric ratios in both space and time. This is illustrated by a combined study of field observation, petrographic observation, whole-rock and mineral major and trace elements, laser ablation−inductively coupled plasma−mass spectrometry zircon and monazite U-Th-Pb isotopes and trace elements, and phase equilibrium modeling of granitic gneisses from the Cona area, southern Tibet, in the Himalayan orogen. The results reveal variations in spatial level, protolith age, petrological composition, and metamorphic pressure−temperature−time path along an N-S transect across the Higher Himalayas. On this basis, three types of granitic gneisses were identified for the Miocene metamorphism. Type I gneiss was formed at 16.2−14.7 Ma under upper amphibolite facies conditions of 720−735 °C and 0.77−0.82 GPa, Type II gneisses were formed at 18.3−14.3 Ma under granulite facies conditions of 765−795 °C and 0.99−1.06 GPa, and Type III gneisses were formed at 21.8−13.0 Ma under high-pressure granulite facies conditions of 850−875 °C and 1.40−1.45 GPa. These rocks underwent anatectic metamorphism at lower to upper crustal depths from 22 to 13 Ma, and their metamorphic thermobaric ratios increase from 586−803 °C/GPa at 22−18 Ma to 878−967 °C/GPa and finally to 1071 °C/GPa at 15−13 Ma. This increase corresponds to a progressive increase in metamorphic geothermal gradients from 16.1−22.0 °C/km to 24.1−26.5 °C/km and finally to 29.4 °C/km. Therefore, the crustal rocks in the Himalayan orogen experienced the three types of regional metamorphism at the three different geothermal gradients in the Miocene. The progressively elevated geothermal gradients are attributed to continental rifting due to asthenospheric upwelling consequential to thinning of the lithospheric mantle in the collisional orogen. This has important implications for the tectonic evolution of collisional orogens in the post-collisional stage.</jats:p>

<jats:p>Exploring the nature of Archean plate tectonics is crucial for understanding the geodynamic evolution of early Earth. While previous studies have focused on (ultra-)mafic metavolcanic and tonalite−trondhjemite−granodiorite (TTG) rocks, the crust-mantle interactions of Archean intermediate magmatism have received much less attention. Mesoarchean (ca. 2936−2855 Ma) dioritic and tonalitic-trondhjemitic magmatism occurred in the Jiaobei terrane, North China Craton. While low-silica (65.67−68.82 wt%) TTG magmatism persisted throughout the entire magmatic period, both the high-silica (69.79−74.54 wt%) TTG and biotite dioritic (MgO of 1.52−2.45 wt%) magmatism were transient (ca. 2922−2901 Ma). They were mainly sourced from metabasaltic crust, though the biotite dioritic and low-silica TTG rocks show variable mantle input. In comparison, the hornblende dioritic magmatism (MgO of 2.07−5.00 wt%) occurred later (ca. 2912−2865 Ma) and was derived from melt-metasomatized mantle sources. Spatially, the magmatism became younger from northeast to southwest. Combined with increasing crustal melting pressures after ca. 2920 Ma and mildly elevated zircon δ18O (up to +6.8‰) of TTG rocks, a Mesoarchean nascent subduction zone is proposed for the Jiaobei terrane that is featured by the recycling of supracrustal basaltic rocks to thickened lower crust (forming high-pressure and high-δ18O TTG) and subsequent melt-related mantle metasomatism (forming relatively high-Mg hornblende dioritic rocks). The recycled supracrustal materials may have lubricated the basal part of the thickened crust and then triggered the opening of a nascent mantle wedge. Further compilation of data from global Archean dioritic and TTG rocks reveals chemical discontinuities at ca. 3.6−3.5 Ga and after ca. 3.0 Ga; these periods are marked by the occurrence of both high-Mg (median MgO &amp;gt;3 wt%) dioritic magmatism and high-(La/Yb)N (median &amp;gt;30) and high-δ18O (median &amp;gt;5.9‰) TTG magmatism. These data, along with independent geological evidence, suggest that the nascent subduction processes may have initiated locally at ca. 3.6−3.5 Ga but globally after ca. 3.0 Ga.</jats:p>

<jats:p>Arc magmatism along convergent plate boundaries has been a major contributor to continental crustal growth. During the late Paleoproterozoic−Mesoproterozoic assembly of the supercontinent Nuna, following arc-backarc-continent collisions, the Makkovik Orogen, along the southern margin of the Archean North Atlantic Craton, experienced a pulse of continental arc magmatism at ca. 1800 Ma. Lithogeochemistry indicates compositions typical of ferroan, alkali to alkali-calcic, A-type granites. The granitic rocks have εNd(t) values varying from −5.3 to +2.0 and model ages [T(DM)] from 2750 to 1880 Ma. The very high εNd(t) and young model ages imply a substantial juvenile mantle component in their formation. Oxygen fugacity (ƒO2) ratios, estimated by the proxy ratio of FeOT/(FeOT + MgO), range from 0.58 to 0.99, indicating the parental magmas formed in both reducing and oxidizing conditions. The granites also preserve an alkali-calcic alteration that together with inferred ƒO2 makes them more prospective for a variety of intrusion-related styles of mineralization including iron-oxide-copper-gold and uranium. Based on the petrology, lithogeochemistry, and isotopic compositions, the ca. 1800 Ma magmatic event is interpreted to have been developed post-collisionally following the docking of the Cape Harrison Arc/micro-continent with the North Atlantic Craton during the assembly of the supercontinent Nuna. This collision was followed by slab rollback (possibly breakoff), extensional collapse, and mantle upwelling resulting in the generation of the abundant ca. 1800 Ma felsic magmatism. The timing of the ca. 1818−1799 Ma plutonism in the Makkovik Orogen is coeval with significant felsic plutonism preserved in the Julianehåb Igneous Complex (Ketilidian Orogen) of southern Greenland.</jats:p>

<jats:p>The geochemistry of granite is largely controlled by physical and chemical parameters that are closely linked to tectonic processes in evolving orogenic belts. Therefore, temporal changes in the geochemical compositions of granites could be used to infer critical shifts in tectonic processes. The Himalayan leucogranites are crustal anatexis products, providing a case to formulate petrogenetic models for granites and test tectonic models. From west to east, in the High Himalaya and the Tethyan Himalaya, two groups of leucogranites are derived from fluid-absent melting (Group A) and fluid-fluxed melting of muscovite (Group B), respectively. In the Cona and Mount Everest areas, Group B granites crystallized at 26−10 Ma, and Group A granites formed at 19−13 Ma. Group B granites have higher CaO, Sr, Ba, Zr, Hf, Th, Sr/Y, Zr/Hf, and Th/U, and lower Rb, Nb, Ta, U, Rb/Sr, and 87Sr/86Sr than those in Group A granites. These geochemical differences highlight the role of deep-origin fluids and the dissolution control of the accessory phases on the geochemical compositions in silicic magma systems. Field and microstructural observations show that E-W extension occurred synchronously with the granite intrusion derived from fluid-fluxed melting. Elevated heat flow accompanying the E-W extension could dehydrate hydrous minerals and release fluids from deep-seated crust (e.g., Lesser Himalayan Sequence). Such fluids could flux and melt the metasedimentary rocks within the High Himalaya and produce Group B granites. Together with literature data, from the Lhasa terrane to the Himalayan belt, E-W extensions in Tibet may have initiated as early as 26 Ma.</jats:p>

<jats:p>We report three sets of newly identified late Mesoproterozoic mafic intrusions in the southwestern Yangtze Block, China. Secondary ion mass spectrometry (SIMS) baddeleyite and zircon U-Pb analyses yield crystallization ages of ca. 1.15 Ga for the Boka dolerites, ca. 1.07 Ga for the Lanniping gabbros, and ca. 1.06 Ga for the Tong’an mafic dikes. These are tholeiitic to alkaline rocks with enriched mid-ocean-ridge basalt (E-MORB)−like trace-element patterns and superchondritic εNd(t) values, indicating a partial melting origin from the asthenospheric mantle. These results, along with existing data, define two episodes of late Mesoproterozoic, rift-related mafic magmatism in the southwestern Yangtze Block: an early phase at 1.17−1.14 Ga and a late phase at 1.07−1.02 Ga. Initiation of the two episodes of extensional events in the southwestern Yangtze Block coincided with high-grade Grenville-aged metamorphism in Hainan Island and possible early collision of Cathaysia with the southwestern Yangtze Block, indicating an impactogen model. Therefore, we interpret the observed two episodes to have resulted from local collision between the southwestern Yangtze Block and the Cathaysia Block (including Hainan Island), which was possibly a part of western Laurentia during the assembly of Rodinia.</jats:p>

<jats:p>The Tibetan Plateau is the highest plateau on Earth. As an ideal place to decipher the intracontinental deformation mechanisms, the Tibetan Plateau has become a focus of Cenozoic geological studies. The surface uplift history of the Tibetan Plateau can help us to better understand continental collision and processes ranging from global cooling to the onset of the Asian monsoon. Although a lot of research has been done over the years, the mechanism and timing of uplift of the Tibetan Plateau, especially the northern part, continue to be debated. To address how the Tibetan Plateau developed, a better understanding of the uplift and deformation history is needed. The Qiman Tagh Range lies on the northeastern margin of the Tibetan Plateau. Knowing what led to the exhumation of the Qiman Tagh Range could help us to constrain the tectonic evolution of the northern boundaries of the Tibetan Plateau. Here, we present new apatite fission-track data and the thermal history for the north Qiman Tagh Range. The thermal history modeling indicates that the Qiman Tagh Range experienced a four-stage cooling history (i.e., at ca. 230 Ma, 130−90 Ma, ca. 35 Ma, and 20/10−0 Ma). The results reveal that the initial exhumation of the Qiman Tagh Range occurred in the Middle Triassic due to the collision between the western Qiangtang and eastern Qiangtang terranes and the northward colliding and collaging of the Kumukuri microcontinent with the south Qiman Tagh Terrane. The rapid exhumation during the Cretaceous resulted from the collisions between the Lhasa and Qiangtang terranes. The Cenozoic exhumation may be related to the far-field stress effect of the India-Asia collision. Based on our new data, together with tectonic studies around the Qaidam Basin, we reconstructed the big Paleo-Qaidam Basin as it was during late Mesozoic and early Cenozoic time. The Mesozoic uplift of the Qiman Tagh Range was not high enough to form topographical isolation, but the rapid uplift of the Qiman Tagh at ca. 35 Ma completely separated the Kumukol Basin to the south from the Qaidam Basin to the north. The Qiman Tagh Range has experienced an acceleration of uplift since the Miocene to present, which formed the current basin-range landform. The study constrains the uplift history of the northern Tibetan Plateau and helps us to better understand its growth mechanism.</jats:p>

<jats:p>Antimony (Sb) is identified as a critical metal in many countries. The source of hydrothermal Sb-bearing deposits is currently debated in two opposing models (magmatic fluids or country rocks). Some Sb-bearing hydrothermal systems host abundant cadmium (Cd). Due to the close association of Cd and Sb in hydrothermal systems and the distinct Cd isotopic signatures between magmatic and sedimentary rocks, Cd isotopes have the potential to trace the metal origin in Sb-bearing deposits. Here, we conducted Cd isotope analyses of sulfide (jamesonite and sphalerite) collected from the Jianzhupo Zn-Sb deposit, SW China. A narrow range of δ114/110Cd relative to NIST SRM 3108 Cd standard was observed in sphalerites (−0.15‰ to +0.18‰; mean = 0.03‰ ± 0.10‰, one standard deviation [1SD]), identical to that of intermediate igneous rocks (−0.20‰ to +0.15‰); in contrast, pure jamesonites show a large range of δ114/110Cd (−0.42‰ to +0.17‰; mean = −0.22‰ ± 0.20‰, 1SD), differing from those of sphalerite. Different Cd isotope signatures between jamesonite and sphalerite are unlikely to have been triggered by sulfide precipitation, vapor-liquid phase separation, diffusion, and different Cd-S bond strengths. Instead, based on a comparison of δ114/110Cd and Zn/Cd ratio of sulfide and potential source rocks, we propose that a mixing of two ore-forming endmembers, derived from igneous and sedimentary rocks, may better explain the sulfide Cd isotopic signatures. This is supported by the well-defined positive correlation between δ114/110Cd and Zn/Cd ratio in sulfides. This study shows a novel application of Cd isotopes for metallogenetic tracing and demonstrates that Sb-bearing hydrothermal systems can incorporate metals from multiple sources.</jats:p>