The Processes of Melt Differentiation in Arc Volcanic Rocks: Insights from OIB-type Arc Magmas in the Central Mexican Volcanic Belt
Susanne M. StraubArturo Gómez‐TuenaGeorg F. ZellmerRamón Espinasa-PereñaFinlay M. StuartYue CaiC. H. LangmuirAna Lillian Martin‐Del PozzoGary T. Mesko
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Andesite petrogenesis is inextricably linked to plate processing at convergent margins. The details of andesite formation, however, remain poorly understood because the signatures of the initial arc mantle melts are often modified in the overlying crust. To distinguish initial mantle from crustal signatures in arc magmas, we studied two compositionally zoned Holocene monogenetic volcanoes, Texcal Flow and Volcan Chichinautzin, in the central Mexican Volcanic Belt (MVB). Texcal Flow and V. Chichinautzin erupt 'ocean island basalt (OIB)-type', high-Nb (17–36 ppm), olivine-phyric basalts to basaltic andesites (49·4–57·3 wt % SiO2; Mg# = 68–50) that show an arc affinity in their major element oxides. At both volcanoes melt SiO2 increases with time. However, systematic changes of melt SiO2 with 87Sr/86Sr and 143Nd/144Nd, the overall low 87Sr/86Sr = 0·70305–0·70453 and high 143Nd/144Nd = 0·51273–0·51299 relative to continental crust, and the high 3He/4He = 7–8 Ra of olivine phenocrysts preclude melt silica enrichment by crustal assimilation and fractional crystallization. Instead, the data require the existence of silicic initial mantle melts. The high Ni abundances of olivines suggest that the silicic melts originate from segregations of 'reaction pyroxenites' that formed in the peridotite mantle wedge following multiple infiltrations of silicic slab components. Sequential melting of zoned silica-deficient to silica-excess pyroxenites can reproduce the time-progressive evolution of melt silica content at Texcal Flow and V. Chichinautzin. As initial melts always have high Mg# > 70 regardless of their SiO2 content, the low-Mg# values of the magmas erupted must reflect loss of moderate amounts (<15%) of olivine and possibly pyroxenes at crustal levels. Fractional crystallization and recharge mixing nearly erase all mantle signatures in the most silicic V. Chichinautzin magmas, so that their origin can only be inferred from their association with the more mafic precursory melts. The pyroxenite model implies that ∼15–18 wt % of the erupted melt mass, and possibly more, is slab-derived. We infer that the elements Fe, Mg, Ca and Ti are principally mantle-derived, whereas significant amounts of the elements Si, K, Na, P and possibly Al may be contributed from slab. As blends of mantle and slab materials, the OIB-type Texcal Flow and V. Chichinautzin magmas provide limited indication of the composition of the sub-arc mantle prior to subduction modification, which is inferred to be similar to primitive mantle, but less enriched than the sources of the intraplate magmas behind the MVB volcanic front.Keywords:
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<p>The Cretaceous Okhotsk-Chukotka volcanic belt (OChVB) is one of the largest provinces of continental marginal magmatism with length more than 3000 km along the Pacific edge of Asia. In the field studies of 2019 and 2020 we sampled 21 sections in the northern part of the OChVB and 3 sections from basement of OChVB. These sections are represented by basalts and andesites; their tuffs, ignibrites and other volcanic rocks are much less common. The age of these volcanics is estimated based on U-Pb and Ar-Ar published data and our new Ar-Ar dates.</p><p>Based on the obtained data, a new paleomagnetic pole for the Chukotka part of the OChVB was calculated. The latitude of this paleomagnetic pole differs from the expected one when compared with that calculated for Chukotka from published data from Besse and Courtillot, 2003; Torsvik et al., 2012. These results are inconsistent with most of the existing geological data. Only a few works admit younger displacements in the southern part of the Verkhoyansk fold belt or in modern diffuse boundary of the Eurasian and North American plates. Moreover, we compare our OChVB pole with results from basaltic complexes from the basement, which has been likely remagnetized when OChVB was formed.</p><p>Acknowledgements: study of cretaceous volcanics is supported by RSF grant &#8470; 19-47-04110 and jurassic by RSF grant &#8470;18-77-10073.</p>
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If both the Mexican Volcanic Belt (MVB) and the Central American Volcanic Arc (CAVA) have been related to the subduction of the Cocos plate beneath the North American and Caribbean plates, respectively, their magmas, and especially the less evolved basic varieties, should show considerable similarities. The conventional multielement normalized diagrams indicate more complex petrogenetic processes for the MVB than the CAVA. Forty-five statistically coherent tectonomagmatic discrimination diagrams were used to infer the tectonic setting of the controversial geological subprovince of the eastern part of the MVB (E-MVB). Basic rocks from the E-MVB indicated a continental rift setting, whereas the intermediate rocks were more consistent with a transitional setting of rift to collision. The acid rocks, presumably having a larger crustal component than the intermediate and basic rocks, showed inconclusive results. The volcanic rock data from the CAVA were used to successfully test these diagrams. The expected arc setting was consistently indicated for the CAVA from basic, intermediate, and acid rocks, confirming the satisfactory functioning of the diagrams. The data for all three types of rocks from the E-MVB and CAVA were then objectively compared for their similarities and differences. Specially designed computer programs were used to efficiently apply discordancy and significance tests at the strict 99% confidence level. Most (43 out of 50) chemical elements and (25 out of 28) log-ratio parameters in basic rocks from the E-MVB and CAVA showed statistically significant differences. For intermediate rocks and, to a lesser extent, for acid rocks, a large number of parameters also showed differences between the E-MVB and CAVA. The differences in the inferred tectonic settings for basic and evolved rocks from the E-MVB are likely related to the different magmatic sources.
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An understanding of hydrological processes on volcanic islands is vital for both resource and hazard management. The hydrological system can modify the volcanic hazard and react to volcanic perturbations. Understanding this interaction is essential for the development of a truly multi-parameter hazard-monitoring dataset. The Caribbean island of Montserrat provides a unique environment to study such interactions, since it has both active volcanic and hydrological systems. We aim to gain a more complete understanding of the fundamental hydrology in active volcanic island arc settings by using TOUGH2 models to explore the natural productive springs on the flanks of the extinct volcanic center, adjacent to the active Soufriere Hills Volcano.
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The Colima Volcanic Complex trends in a nearly N-S direction in western Mexico, and one of its structures, Colima volcano, is the most historically active volcano in the country. Immediately to the N, there is another volcanic center called El Cántaro volcano, whose activity started around 1.7 Ma in its N portion and migrated to the S in various episodes. Volcanic activity migrated further south, from El Cántaro to the Colima Volcanic Complex where the southernmost manifestation, Hijos del Volcán domes, is located on the south slope of Fuego volcano. The above date appears to mark initiation of the rather continuous volcanic activity in the area. It has been noted that these volcanic manifestations lie on, or near the Rivera-Cocos inland plate boundary. Colima’s Fuego volcano is also the closest to the Middle America Trench, among the polygenetic volcanoes in Mexico. We submit that the anomalous location of volcanism in this area originates in an anomalous subduction process of the Rivera and Cocos plates and evoke a tectonic model, proposed elsewhere, to support the idea. Modeling gravimetric and aeromagnetic data we locate the magma chambers of the Fuego (active) and Nevado (extinct) volcanoes within a 65 mGals negative Bouguer anomaly elongated in a nearly N-S direction. The corresponding aeromagnetic map displays a magnetic high over the southern portion of the Fuego volcano edifice. We found two additional, associated structures whose anomalies have not been previously reported, which appear to follow the southward magmatic migration pattern. One of them is a collapse structure with a circular topographic expression, and the southernmost is a low-density intrusion ~1 km below sea level, associated with a moderate topographic bulge at the surface that we interpret as a magma body. Five lines cross the anomalies; gravimetric and magnetic fields are concurrently modeled along them to locate the magmatic bodies. In addition to the 2-D models we perform 3-D gravimetric and magnetic inversions. For each field a 3-D mesh is built under the area occupied by the Colima Volcanic Complex, the volume elements are then assigned density or magnetic susceptibility values and their surface contributions in various points are evaluated. The process is iterated until the difference between the measured and the calculated fields is less than a predetermined value. The results of each inversion adequately and independently define the location of the magmatic chambers although they cannot distinguish between the individual chambers of the Nevado and Fuego volcanoes. 2-D and 3-D results complement each other and consistently show the locations of potential magmatic regions. Our models support a multiple, complex magmatic system that appears to continue to spread southwardly, which can pose additional volcanic risks to an already threatened local population.
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Volcanic structures are diverse and complex with extraordinary feature in Bangduo region in the central sector of Gangdisian volcanic magmatic arc.It is divided into three volcanic eruptive belts based on regional tectonic setting and space-time distributed characteristics of volcanic rocks strata and lithological character and litho facies,as well as eruptive pattern in the research area.Volcanic eruptive belts from Ningguo to Cuomai is divided into two volcanic tectonic depression including Ningguo and Deruo.Volcanic eruptive belts from Ludang to Chazi is divided into three volcanic eruptive subzones along with Konglong-Banglei and Songlalei-Laerge and Kongjumibo-Chazi.62 volcanic apparatuses are established in the research area.This article expatiates basic features of various scale of volcanic structure,summarizes it's regularities of distribution and occurrence and settles steady foundation for geological investigation of volcanic rocks and the deposits in the whole Gangdisian region.
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