Southern Arc Research Articles

HIV in pregnant woman and children: Mother-to-child transmission of HIV in the Brazilian land border from 2010 to 2021.

The aim of the present study was to analyze the profile and trends of HIV mother-to-child transmission (MTCT) in the Brazilian land border strip (LBS). This was a quantitative, ecological, and cross-sectional study using secondary data available in the information systems of the Brazilian Ministry of Health. All cases reported in the Notifiable Diseases Information System between 2010 and 2021 were studied. Between 2010 and 2021, 275 children were born infected through MTCT, and 6076 pregnant women were living with HIV in the Brazilian LBS. HIV detection rates in pregnant women increased in all border arcs. The northern arc experienced the highest increase (19.6%), followed by the central arc (11.4%), and the southern arc (6.1%). Despite historically high detection rates, the southern arc exhibited the smallest increase. While MTCT rate decreased by 37.7% in the border area, the central arc showed no statistically significant reduction. In 2021, the average age of pregnant women was 26.2 years, 25.7% had up to 8 years of schooling, and 55.8% identified as non-white. The majority (92.8%) received antenatal care, and 59.7% were diagnosed with HIV before prenatal care. The use of prophylactic antiretroviral therapy during prenatal care occurred in 69.6% of pregnant women, and infant prophylaxis was provided within first 24 h to 43.6% of live births. The results indicate progress in reducing MTCT cases in Brazilian LBS. Disparities in HIV detection rates may be influenced by differences in testing uptake, despite mandatory testing for all babies. It is crucial to continue implementing strategies to reach these women and ensure equitable access to healthcare services for MTCT prevention.

The ancient DNA of the N.E. Mediterranean/Euro-Asian cultures and the position of the Mycenaean Greeks among the first cultures

Alerted by a trio of papers that appear in the journal SCIENCE today (26th August 2022) I present briefly the essential findings with some extension on the hot subject of ancient DNA studies over all the World but mainly the SE Mediterranean and Euro-Asian neighborhood. These three papers summarize the results of a remarkable Ancient DNA project and involving 202 co-authors. These studies draw on published archaeogenetic records and new DNA analysis of 727 individuals who lived during the Copper and Bronze Ages. These people populated the “Southern Arc,” a swath of land connecting Europe to West Asia through Anatolia including coastal Levant. The findings are critically discussed in the wider frame of aDNA results, the migration and mobilities for the past about 8000 years ago and linked with the non-linear evolution processes of ancient cultures. Particular emphasis here is given to the 2016 expedition at the Late Helladic site of Kastrouli near Delphi in Greece, that contribute to these studies.

The ancient DNA of the N.E. Mediterranean/Euro-Asian Cultures and the Position of the Mycenaean Greeks among the first Cultures

Alerted by a trio of papers that appear in the journal SCIENCE today (26th August 2022) I present briefly the essential findings with some extension on the hot subject of ancient DNA studies over all the World but mainly the SE Mediterranean and Euro-Asian neighborhood. These three papers summarize the results of a remarkable Ancient DNA project and involving 202 co-authors. These studies draw on published archaeogenetic records and new DNA analysis of 727 individuals who lived during the Copper and Bronze Ages. These people populated the “Southern Arc,” a swath of land connecting Europe to West Asia through Anatolia including coastal Levant. The findings are critically discussed in the wider frame of aDNA results, the migration and mobilities for the past about 8000 years ago and linked with the non-linear evolution processes of ancient cultures. Particular emphasis here is given to the 2016 expedition at the Late Helladic site of Kastrouli near Delphi in Greece, that contribute to these studies.

The genetic history of the Southern Arc: A bridge between West Asia and Europe.

By sequencing 727 ancient individuals from the Southern Arc (Anatolia and its neighbors in Southeastern Europe and West Asia) over 10,000 years, we contextualize its Chalcolithic period and Bronze Age (about 5000 to 1000 BCE), when extensive gene flow entangled it with the Eurasian steppe. Two streams of migration transmitted Caucasus and Anatolian/Levantine ancestry northward, and the Yamnaya pastoralists, formed on the steppe, then spread southward into the Balkans and across the Caucasus into Armenia, where they left numerous patrilineal descendants. Anatolia was transformed by intra-West Asian gene flow, with negligible impact of the later Yamnaya migrations. This contrasts with all other regions where Indo-European languages were spoken, suggesting that the homeland of the Indo-Anatolian language family was in West Asia, with only secondary dispersals of non-Anatolian Indo-Europeans from the steppe.

The Amami Rift: Clarifying the roles of rifting and volcanism in the central Ryukyu Arc

Arc volcanism in the Ryukyu subduction system shows an along-arc variation characterized by the development of subaerial volcanoes in the northern arc and submarine ones in the southern arc. The central arc is a transitional area in arc volcanism, but its characteristics and tectonic controls remain largely unknown. This paper presents detailed new data on the tectonic and volcanic features of the Amami Calderas in the central Ryukyu Arc based on high-resolution bathymetry and a seismic reflection profile. Ship-based bathymetry reveals that ENE–WSW to E–W trending normal faults form a local rift structure which is ~60 km long, ~10 km wide and ~ 400 m deep. Small volcanic edifices and crater-like depressions are scattered in and around the rift. A number of bubble plumes were detected by shipboard multibeam sonar in the rift. AUV near-bottom mapping confirmed positive temperature anomalies near the bubble plumes, indicative of hydrothermal venting. Our observations demonstrate that the previously named Amami Calderas are not volcanic in origin, but are instead tectonic, and we therefore re-name these features the Amami Rift. The Amami Rift is the northernmost active rift along the central Ryukyu Arc and its unique location provides new insights into the interaction of rifting and arc volcanism. Yokoate-jima Island is a large volcanic edifice close to the Amami Rift whose surrounding seafloor shows no distinctive rift structures and few diffuse lineaments. In contrast, the Amami Rift consists of small scattered volcanic edifices and a prominent focused rift. This sharp volcano-tectonic contrast between Yokoate-jima Island and Amami Rift suggests that focused rifting makes arc volcanism scattered rather than focused in the area, with relatively small volcanic edifices. Another notable feature of the Amami Rift and surrounding area is that volcanic edifices, indicators of hydrothermal activity and bubble plumes are aligned not parallel to the rift, but in the cross-arc direction, indicating the presence of cross-arc volcanism. Cross-arc volcanism has been recently reported in the northern Ryukyu Arc, but this is the first time it has been observed in the central arc. Our observations combined with previous studies suggest a combination of cross-arc volcanism and crustal extension characterizes the spatial distribution of active magmatism in the central Ryukyu Arc.

Skarn fluid sources as indicators of timing of Cordilleran arc emergence and paleogeography in the southwestern United States

Abstract Oxygen isotope ratios of garnet provide well-established means to investigate crustal fluid histories. Traditionally, δ18O values from skarn garnets have been used to track the hydrothermal evolution of an individual skarn body through time. We, however, use garnet from 14 skarns from the Jurassic (ca. 175 to ca. 148 Ma) Cordilleran margin arc (southwestern United States) to provide regional tectonic context to arc magmatism and hydrothermal activity. We document arc-wide garnet δ18O variability of ~19‰ (−8.9‰ to +10.3‰, n = 159), providing a record of contrasting meteoric fluid ingress between northern (Sierra Nevada) and southern (Mojave Desert) arc segments. Strongly negative garnet δ18O values (≤−3‰) are limited to the Mojave Desert arc segment and can only form in the presence of meteoric fluid, requiring shallow formation in subaerial crust. When combined with U-Pb garnet ages, the δ18O data provide a minimum radiometric age of local subaerial arc emergence and temporal constraint on the migration of the Jurassic paleoshoreline in the Mojave Desert section of the arc.

Matïna then Matïgwana, two large islands that have formed over time geologically emerged parts of the southern arc of the eastern Caribbean.

Matïna then Matïgwana, two large islands that have formed over time geologically emerged parts of the southern arc of the eastern Caribbean.

Variability of Shelf Growth Patterns along the Iberian Mediterranean Margin: Sediment Supply and Tectonic Influences

Clinoform depositional features along the Iberian Mediterranean margin are investigated in this study, with the aim of establishing the causes of their varied shapes and other characteristics. We have analyzed the broad-scale margin physiography and seismic stratigraphic patterns based on high-resolution bathymetric data and previously interpreted seismic data. In addition, we have evaluated regional supply conditions and the uplift-subsidence regime of the different shelf sectors. The upper Quaternary record is strongly dominated by shelf-margin regressive wedges affected by the prevailing 100 ka cyclicity. However, the margins exhibit considerable lateral variability, as the result of the balance between the amount of sediment supply and the uplift-subsidence relationship. Three major shelf sectors with distinct morpho-sedimentary features have been defined. The relatively narrow northern shelves (Roses, La Planassa and Barcelona) are supplied by discrete river outlets that collectively constitute a linear source and are mainly affected by tectonic tilting. The wide middle shelves (Ebro Shelf, the Gulf of Valencia, and the Northern Arc) receive the sediment supply from the large Ebro River and other medium rivers. Although the tectonic regime changes laterally (strong subsidence in the north and uplift in the south), shelf growth is maintained by lateral advection of sediments. The southern shelves (the Southern Arc and the northern Alboran Shelf) are very abrupt and narrow because of the uplifting Betic Cordillera, and the torrential fluvial regimes that determine a very efficient sediment by-pass toward the deep basin. Submarine canyons deeply incised in the continental margin constitute a key physiographic feature that may enhance the transport of sediment to the deep sea or individualize shelf sectors with specific sedimentation patterns, as occurs in the Catalan margin.

Across-arc geochemical variation in the Jurassic magmatic zone, Southern Tibet: Implication for continental arc-related porphyry Cu[sbnd]Au mineralization

The Jurassic Gangdese arc hosts the giant Xietongmen (Xiongcun) porphyry CuAu magmatic-hydrothermal centre. In order to understand the tectonomagmatic framework of the arc and its controls on the origin and temporal-spatial distribution of porphyry mineralization we conducted extensive major and trace, and isotopic analysis on a suite of samples collected regionally. Geochemical variations were observed across the Jurassic arc from south to north, controlled by northward subduction of the Neo-Tethyan oceanic plate and overlying Lhasa lithosphere. In the frontal arc (latitude 29°–29.55°N), the magmas had high Ba/La and Ba/Th ratios, high εNd(t) (+3 to +7) values, and their zircons have high εHf(t) (+10 to +18) values, and heterogeneous O isotopic compositions (δ18O=+3.6 to +6.6‰). The low titanium-in-zircon temperature and zircon saturation temperature (both average=~700°C) suggest that a greater flux of dehydration fluids from the subducting slab triggered partial melting of the mantle wedge in the southern arc. High zircon Eu/Eu* and Ce/Nd ratios (>0.4 and >20, respectively) indicate highly oxidized, fertile magmas, from which the Xietongmen porphyry CuAu deposit formed. In contrast, the interior arc (north of latitude 29.55°), close to the ancient Tibetan basement, shows low Ba/La and Ba/Th ratios, low εNd(t) (−0.1 to +2.5) and zircon εHf(t) (+2 to +12) values, and less heterogeneous zircon O isotopic compositions with higher δ18O values. Higher titanium-in-zircon and zircon saturation temperatures (mostly >750°C) suggest that less water was involved during the partial melting of mantle wedge in this region. Low zircon Eu/Eu* and Ce/Nd ratios (mostly <0.4 and <20, respectively) point towards less oxidized magmatic conditions. We conclude that across-arc geochemical and fluid-flux variations controlled the formation and spatial distribution of Jurassic porphyry deposits in the Gangdese belt.

Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada

Ongoing arc magmatism along western North America was preceded by ancestral arc magmatism that began ca. 45 Ma and evolved into modern arc volcanism. The southern ancestral arc segment, active from ca. 30 to 3 Ma, adjoins the northern segment in northern California across a proposed subducted slab tear. The east edge of the Walker Lane approximates the east edge of the southern arc whose products, mostly erupted from stratovolcanoes and lava dome complexes arrayed along the crest of the ancestral arc, extend down the west flank of the Sierra Nevada. Southern arc segment rocks include potassic, calc-alkaline intermediate- to silicic-composition lava flows, lava dome complexes, and associated volcaniclastic deposits. Northern and southern segment rocks are similar to other convergent-margin magmatic arc rocks but are compositionally distinct from each other. Southern segment rocks have lower TiO 2 , FeO*, CaO, and Na 2 O contents and higher K 2 O contents, and exhibit less compositional-temporal variation. Compositional distinctions between the northern and southern segment rocks reflect the composition and thickness of the crust beneath which the associated magma systems were sourced. Northern segment rock compositions are consistent with generation beneath thin, primitive crust, whereas southern segment rocks represent magmas generated and fractionated beneath thicker, more evolved crust. Although rocks in the two arc segments have similar metal abundances, they are metallogenically distinct. Small porphyry copper deposits are characteristic of the northern segment whereas significant epithermal precious metal deposits are most commonly associated with the southern segment. These metallogenic differences are also fundamentally linked to the tectonic settings and crustal regimes within which these two arc segments evolved.

Steady rotation of the Cascade arc

Displacement of the Miocene Cascade volcanic arc (northwestern North America) from the active arc is in the same sense and at nearly the same rate as the present clockwise block motions calculated from GPS velocities in a North American reference frame. Migration of the ancestral arc over the past 16 m.y. can be explained by clockwise rotation of upper-plate blocks at 1.0°/m.y. over a linear melting source moving westward 1–4.5 km/m.y. due to slab rollback. Block motion and slab rollback are in opposite directions in the northern arc, but both are westerly in the southern extensional arc, where rollback may be enhanced by proximity to the edge of the Juan de Fuca slab. Similarities between post–16 Ma arc migration, paleomagnetic rotation, and modern GPS block motions indicate that the secular block motions from decadal GPS can be used to calculate long-term strain rates and earthquake hazards. Northwest-directed Basin and Range extension of 140 km is predicted behind the southern arc since 16 Ma, and 70 km of shortening is predicted in the northern arc. The GPS rotation poles overlie a high-velocity slab of the Siletzia terrane dangling into the mantle beneath Idaho (United States), which may provide an anchor for the rotations.

Geochemical Characteristics and Ore Prediction of the Pb-Zn Polymetallic District in Kanmashan of Lancang County, Yunnan

According to the analysis of geological characteristics and Elemental correlation charac –teristics, Threshold and R-factor analysis leading to the results geochemistry characteristics of Kanmashan Pb-Zn polymetallic deposit which is located in Lancang county of Yunnan province, the deposit is discovered in the southern arc of Chong mountain-lincang-menghai mountain, alonging the contact strip of Lincang granitoid batholith and proterozoic group in LanCang, metallogenic conditions near fracture is relatively ideal, which can be used as a further work area.

Across‐ and along‐arc geochemical variations of lava chemistry in the Sangihe arc: Various fluid and melt slab fluxes in response to slab temperature

The Sangihe arc, northern Indonesia, is an oceanic arc that is the western half of the only active arc–arc collision on Earth. To elucidate magma genesis and slab thermal structure in such a setting, we have obtained new geochemical data for lavas from the entire Sangihe arc. In the southern arc, the volcanic front lavas are enriched in fluid‐mobile elements, while the rear arc lavas are more enriched in melt‐mobile elements. The proportion of sediment versus altered oceanic crust in the slab component is only ∼20% but still larger in Sangihe than other arcs in the western Pacific such as Izu, suggesting more subduction of the thick sediments in the narrowing Molucca Sea. The slab component changes in character across the arc from low‐temperature fluid, through high‐temperature fluid, to partial melt during progressive subduction. The geochemical systematics, the estimated mass fraction of the slab component, and the inferred stability of accessory rutile, zircon, and phengite in the slab are all similar between the southern Sangihe and Izu arcs, indicating that the thermal structure of the slab is not affected by impending collision. In contrast, lavas from the dormant northern Sangihe arc show geochemical characteristics similar to the Quaternary rear arc rather than the Quaternary volcanic front lavas in the southern arc. This may be related to advanced collision in the northern arc that could have slowed the subduction rate and heated the slab in the Pliocene followed by cessation of volcanic activity in the Quaternary.

Geometry and kinematic evolution of a long‐living foreland structure inferred from field data and cross section balancing, the Sainte‐Victoire System, Provence, France

The Sainte‐Victoire System (SVS) is a key area to understand how the shortening is accommodated in outer foreland of the Pyrenean‐Provence orogen between Late Cretaceous and Eocene. Structural data, growth strata and fault slip analysis, and four balanced cross sections are used to decipher the along‐strike geometry, deformational characteristics and kinematics of the SVS. The SVS is divided into two structural domains separated by a regional relay zone: the eastern domain is governed by a N‐vergent thin‐skinned tectonic style above Triassic series and the western domain, by a mixed S‐vergent thick‐ and thin‐skinned tectonic style with tectonic inversion of Late Paleozoic‐Triassic half grabens. Growth strata indicate that the eastern SVS grew during Danian as a result of shortening transfer from the southern Arc Basin. In contrast, the western SVS is an independent structure which has recorded the early stage (∼83 Ma) of shortening and focused continuous deformation during ∼40 Myr. The shallow N‐S shortening is ∼5 km (∼25%) and ∼8 km (∼34%) in the western and eastern SVS, respectively. At a regional scale, the tectonic inversion of the SVS and the Arc Basin recorded a deep shortening of the order of 15–18 km (∼34%). Although the shortening magnitude of the SVS remains small, other structures similar to the SVS were synchronously active across foreland basin, suggesting a significant amount of cumulated shortening. This outer foreland shortening may account for a non‐negligible amount of deformation at the Pyrenean‐Provence orogen scale.

Des tramways contre-nature ? Regards croisés sur les processus de décision des projets de TCSP de l’arc Sud de l’aire métropolitaine lilloise

Cet article porte sur les processus de decision de trois projets de tramway en France : le projet du Syndicat Mixte des Transports Artois-Gohelle compose d’une ligne autour de Lens et d’une ligne autour de Bethune; le Transport Collectif en Site Propre (TCSP) de Douai, appele tramway par le maitre d’ouvrage, mis en service en 2010; et le tramway de Valenciennes dont la premiere ligne a ete ouverte en deux phases en 2006 et 2007. Les trois perimetres des transports urbains (PTU) dans lesquels s’inscrivent ces projets regroupent plus d’un million d’habitants et se positionnent comme l’arc sud de la grande aire metropolitaine lilloise. Cependant, ils cumulent des handicaps qui interrogent sur la capacite a realiser un projet de tramway et sur la pertinence de cette demarche. Dans un contexte economique difficile, comment des regions portant encore les stigmates de plus d’un siecle d’exploitation miniere et organisees sur un profil urbanistique multipolaire ou lineaire peuvent-elles envisager la realisation d’un tramway moderne ? Comment convaincre du choix du mode lorsque les projets sont a la limite des criteres de faisabilite economique et financiere ? Cette contribution se propose de demontrer comment les choix locaux s’accommodent du cadre reglementaire national pour mener a bien des projets de transports avant tout politiques. En outre, elle identifie un double role de l’Etat qui propose des outils incitatifs pour la realisation des tramways dans le cadre de la politique « Grenelle de l’Environnement » et fixe les regles d’evaluation.

An ongoing Austronesian expansion in Island Southeast Asia

The Austronesian expansion into Island Southeast Asia and the Pacific was the last and most far-reaching prehistoric human migration. Austronesian languages replaced indigenous languages over nearly half the globe, yet the absolute number of Austronesian colonists was small. Recently, geneticists have identified large geographic disparities in the relative proportions of Asian ancestry across different genetic systems (NRY, mitochondrial DNA, autosomes and X chromosomes) in Austronesian-speaking societies of Island Southeast Asia and the Pacific. Surprisingly, a substantial genetic discontinuity occurs in the middle of a continuous chain of islands that form the southern arc of the Indonesian archipelago, near the geographic center of the Austronesian world. In the absence of geographic barriers to migration, this genetic boundary and swathe of Austronesian language replacement must have emerged from social behavior. Drawing on decades of comparative ethnological research inspired by F.A.E. van Wouden’s structural model of Austronesian social organization, later codified by Claude Lévi-Strauss as “House societies” (“sociétés à maison”), we propose a two-stage ethnographic model in which the appearance of matrilocal “House societies” during the initial phase of the Austronesian expansion, and the subsequent disappearance of “House societies” in lowland rice-growing regions, accounts for the observed linguistic, genetic and cultural patterns.

Isolated communities of Epsilonproteobacteria in hydrothermal vent fluids of the Mariana Arc seamounts

Low-temperature hydrothermal vent fluids represent access points to diverse microbial communities living in oceanic crust. This study examined the distribution, relative abundance, and diversity of Epsilonproteobacteria in 14 low-temperature vent fluids from five volcanically active seamounts of the Mariana Arc using a 454 tag sequencing approach. Most vent fluids were enriched in cell concentrations compared with background seawater, and quantitative PCR results indicated that all fluids were dominated by bacteria. Operational taxonomic unit-based statistical tools applied to 454 data show that all vents from the northern end of the Mariana Arc grouped together, to the exclusion of southern arc seamounts, which were as distinct from one another as they were from northern seamounts. Statistical analysis also showed a significant relationship between seamount and individual vent groupings, suggesting that community membership may be linked to geographical isolation and not geochemical parameters. However, while there may be large-scale geographic differences, distance is not the distinguishing factor in the microbial community composition. At the local scale, most vents host a distinct population of Epsilonproteobacteria, regardless of seamount location. This suggests that there may be barriers to exchange and dispersal for these vent endemic microorganisms at hydrothermal seamounts of the Mariana Arc.

Symbolic behaviour and the peopling of the southern arc route to Australia

It is now widely accepted that modern humans dispersed from Africa some time after 100 ka, arriving in Australia before 40 ka via a route known as the southern arc. Along this route modern humans would have encountered new and diverse environments but their dispersal into and settlement of new areas was rapid. Language and other symbolic behaviours would have contributed to the flexibility of social and economic strategies required for such rapid dispersal and colonisation. However, there is generally little material evidence in the southern arc for the existence of this symbolic behaviour, except in Australia. We believe that previous assessments of the quantities of such evidence in Australia have underestimated its abundance. The crucial point is that colonisation of the southern arc is itself evidence for the existence of complex information exchange systems, planning depth and symbolic conceptualisation.

Detrital-zircon geochronology of Paleozoic sedimentary rocks in the Hangay–Hentey basin, north-central Mongolia: Implications for the tectonic evolution of the Mongol–Okhotsk Ocean in central Asia

Understanding the development of the Central Asian Orogenic System (CAOS), which is the largest Phanerozoic accretionary orogen in the world, is critical to the determination of continental growth mechanisms and geological history of central Asia. A key to unraveling its geological history is to ascertain the origin and tectonic setting of the large flysch complexes that dominate the CAOS. These complexes have been variably interpreted as deep-marine deposits that were accreted onto a long-evolving arc against large continents to form a mega-accretionary complex or sediments trapped in back-arc to fore-arc basins within oceanic island-arc systems far from continents. To differentiate the above models we conducted U–Pb geochronological analyses of detrital-zircon grains from turbidites in the composite Hangay–Hentey basin of central Mongolia. This basin was divided by a Cenozoic fault system into the western and eastern sub-basins: the Hangay Basin in the west and Hentey basin in the east. This study focuses on the Hentey basin and indicates two groups of samples within this basin: (1) a southern group that were deposited after the earliest Carboniferous (∼ 339 Ma to 354 Ma) and a northern group that were deposited after the Cambrian to Neoproterozoic (∼ 504 Ma to 605 Ma). The samples from the northern part of the basin consistently contain Paleoproterozoic and Archean zircon grains that may have been derived from the Tuva–Mongol massif and/or the Siberian craton. In contrast, samples from the southern part of the basin contain only a minor component of early Paleozoic to Neoproterozoic zircon grains, which were derived from the crystalline basement bounding the Hangay–Hentey basin. Integrating all the age results from this study, we suggest that the Hangay–Hentey basin was developed between an island-arc system with a Neoproterozoic basement in the south and an Andean continental-margin arc in the north. The initiation of the southern arc occurred at or after the early Carboniferous, allowing accumulation of a flysch complex in a long-evolving accretionary complex.

Processes controlling along‐arc isotopic variation of the southern Izu‐Bonin arc

The southern Izu‐Bonin arc is the volcanic representation of Pacific Ocean lithosphere subduction beneath the oceanic crust of the Philippine Sea plate. We present new geochemical data including high‐precision Pb isotopic measurements from the 700 km length of this intraoceanic arc. An aim of this study is to link the along‐arc characteristics with variations in the subducting Pacific crust. Chemical variations have been previously recognized along the northern section of the arc as a southward decrease in 87Sr/86Sr and increase in 206Pb/204Pb. This trend continues into the southern arc as far as 27.5°N. An overall correlation between 87Sr/86Sr and fluid‐mobile element enrichment between 35 and 27.5°N implies a contribution of a slab‐derived fluid, mainly from altered oceanic crust and pelagic sediment. However, the observation that volcanoes plot systematically closer to the Northern Hemisphere Reference Line (NHRL) with increasing 206Pb/204Pb indicates that a component other than pelagic sediment and ocean crust plays a key role toward the south. South of 27.5°N, the along‐arc isotopic trend changes dramatically, with 87Sr/86Sr increasing southward from 27.5°N and the 206Pb/204Pb becoming highly radiogenic (∼19.6). This isotopic signature requires involvement of a component with high 206Pb/204Pb and low Δ8/4. Volcaniclastic sediments originating from HIMU oceanic islands on the subducting Pacific Plate are possible candidates to introduce such a component into the mantle wedge. This is consistent with the sedimentary section of ODP Site 801, located outboard of the Mariana arc which has &gt;40% mass of HIMU volcaniclastics. An aqueous fluid, not melt, has played a major role in the source magma compositions in the 27.5–25°N segment. South of 25°N the isotopic characteristics again change significantly. 143Nd/144Nd decreases down to 0.51280, but the high 206Pb/204Pb and low Δ8/4 signatures are retained. The remarkable Th enrichment associated with low 143Nd/144Nd, Δ8/4, and Δ7/4 suggests that melting a mixture of HIMU volcaniclastics and pelagic sediment is responsible for the geochemical characteristics of this most southerly section.