(Supplemet S1) Silicon oxide and Potassium + Sodium oxide from the PACManus hydrothermal area

This study presents a systematic analysis and interpretation of autonomous underwater vehicle-based microbathymetry combined with remotely operated vehicle (ROV) video recordings, rock analyses and temperaturemeasurements within the PACManus hydrothermal area located on Pual Ridge in the Bismarck Sea of eastern Manus Basin. The data obtained during research cruise Magellan-06 and So-216 provides a framework for understanding the relationship between the volcanism, tectonismand hydrothermal activity. PACManus is a submarine felsic vocanically-hosted hydrothermal area that hosts multiple vent fields locatedwithin several hundredmeters of one another but with different fluid chemistries, vent temperatures and morphologies. The total area of hydrothermal activity is estimated to be 20,279m**2. Themicrobathymetrymaps combinedwith the ROV video observations allow for precise high-resolution mapping estimates of the areal extents of hydrothermal activity.We find the distribution of hydrothermal fields in the PACManus area is primarily controlled by volcanic features that include lava domes, thick andmassive blocky lava flows, breccias and feeder dykes. Spatial variation in the permeability of local volcanic facies appears to control the distribution of venting within a field.We define a three-stage chronological sequence for the volcanic evolution of the PACManus based on lava flow morphology, sediment cover and lava SiO2 concentration. In Stage-1, sparsely to moderately porphyritic dacite lavas (68-69.8 wt.% SiO2) erupted to form domes or cryptodomes. In Stage-2, aphyric lava with slightly lower SiO2 concentrations (67.2-67.9 wt.% SiO2) formed jumbled and pillowed lava flows. In the most recent phase Stage-3, massive blocky lavaswith 69 to 72.5wt.% SiO2were erupted throughmultiple vents constructing a volcanic ridge identified as the PACManus neovolcanic zone. The transition between these stages may be gradual and related to progressive heating of a silicic magma following a recharge event of hot, mantle-derived melts.

K-Ar age and chemical composition of volcanites from the Sea of Okhotsk

Volcanogenic rocks from the Sea of Okhotsk are divided into seven age complexes: Late Jurassic, Early Cretaceous, Late Cretaceous, Eocene, Late Oligocene, Late Miocene, and Pliocene-Pleistocene. All these complexes are united into two groups - Late Mesozoic and Cenozoic. Each group reflects a certain stage of development of the Sea of Okhotsk region. Late Mesozoic volcanites build the geological basement of the Sea of Okhotsk, and their petrochemical features are similar to those of the volcanic rocks from the Okhotsk-Chukotka Volcanogen. Pliocene-Pleistocene volcanites reflect stages of tectono-magmatic activity; the latter destroyed the continental margin and produced riftogenic troughs. Geochemical features of volcanites from the Sea of Okhotsk indicate influence of the sialic crust on magma formation and testify formation of the Okhotsk Sea Basin on the destructive margin of the Asian continent.

(Table 1) Geochemistry of glass shards at DSDP Site 87-582 and 87-583

In the Leg 87A holes, 45 ash layers were sampled in Recent to upper Pliocene strata. The main volcanogenic deposits came from single eruptions or subcontemporaneous eruptions of cognate volcanoes. Some of them are mixed ashes produced from multiple eruptions and accumulated in reworked sediments. The petrographic and geochemical patterns indicate rhyolitic and dacitic compositions; andesitic glasses are scarce. We infer a magmatic affinity with calc-alkaline sources and a possible origin from the volcanic arc of southwestern Japan. A few samples may originate from the alkaline volcanism of southwestern Japan or the area south of Korea and the Sea of Japan.

(Table 1) K-Ar age determinations on biotite from coarse sand within DSDP Sample 72-516F-76-4,107-115

Qualitative petrographic study of selected clastic horizons within the Eocene section of Hole 516F has revealed the presence of abundant fine-grained lithic fragments, probably volcanic, along with coarser fragments of quartz and feldspar apparently derived from a nearby plutonic terrain. In detail, poor sorting, presence of graded bedding, and an abundance of clay suggest these are turbidite horizons locally derived from a mixed volcanic/plutonic terrain, possibly with some direct contribution from contemporary volcanic ash falls. A progressive increase in plutonic versus volcanic components with time is, however, more consistent with an erosional origin for most of this material. Unusual euhedral dark biotite is abundant in several of the lower clastic horizons; it is most easily interpreted as microphenocrysts weathered in situ out of alkalic volcanic ash. Biotite separated from Sample 516F-76-4,107-115 cm, has been dated by the K-Ar method at about 46 Ma. Alkaline volcanoes active on the Rio Grande Rise in the middle Eocene would be the most probable source of this ash and would be consistent with other evidence for potassic, alkaline volcanism along the Rio Grande Rise and at the Tristan da Cunha hot spot.

(Table 1) Trace element and isotopic data for ODP Hole 145-887D basalts

Age-progressive, linear seamount chains in the northeast Pacific appear to have formed as the Pacific plate passed over a set of stationary hotspots; however, some anomalously young ages and the lack of an "enriched" isotopic signature in basalts from the seamounts do not fit the standard hotspot model. For example, published ages (28-30 Ma) for basalts dredged from the Patton-Murray seamount platform in the Gulf of Alaska are 2-4 m.y. younger than the time when the platform was above the Cobb hotspot. However, the lowermost basalt recovered by ocean drilling on Patton-Murray yielded a 40Ar-39Ar age of 33 Ma. This age exactly coincides with the time when the seamount platform was above the Cobb hotspot, consistent with a stationary, long-lived mantle plume. A 27 Ma alkalic basalt flow recovered 8 m above the 33 Ma basalt is similar in age and composition to the previously dredged basalts, and may be the alkalic capping phase typical of many hotspot volcanoes. A 17 Ma tholeiitic basalt sill recovered 5 m above the 27 Ma basalt was emplaced long after the seamount platform moved away from the hotspot, and may be associated with a period of intraplate extension. Anomalously young phases of volcanism on this and other hotspot seamounts suggest that they can be volcanically rejuvenated by nonhotspot causes, but this rejuvenation does not rule out the hotspot model as an explanation for the initial creation of the seamount platform. The lack of an "enriched" isotopic signature in any of these basalts shows that enriched compositions are not necessary characteristics of plume-related basalts. The isotopic compositions of the lower basalts are slightly more depleted than the 0-9 Ma products of the Cobb hotspot, despite the fact that the hotspot was closer to a spreading ridge at 0-9 Ma. It appears that this hotspot, like several others, has become more enriched with time.

Age model and elemental data of DSDP Holes 48-401 and 80-549

A growing body of geologic evidence suggests that emplacement of the North Atlantic Igneous Province (NAIP) played a major role in global warming during the early Paleogene as well as in the transient Paleocene-Eocene thermal maximum (PETM) event. A ~5 million year record of major and trace element abundances spanning 56 to 51 Ma at Deep Sea Drilling Project Sites 401 and 549 confirms that the majority of NAIP volcanism occurred as subaerial flows. Thus the trace element records provide constraints on the nature and scope of the environmental impact of the NAIP during the late Paleocene-early Eocene interval. Subaerial volcanism would have injected mantle CO2 directly into the atmosphere, resulting in a more immediate increase in atmospheric greenhouse gas abundances than CO2 input through submarine volcanism. The lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the PETM. Any connection between NAIP volcanism and PETM warming had to occur through the atmosphere.

Mineralogy of Hawaiian Arch sediments

The mineralogy of both bulk- and clay-sized (<2 µm) fractions of sediments from Holes 842A and 842B of Ocean Drilling Program Leg 136 was determined by X-ray diffraction. The sediments consist of a combination of terrigenous (quartz, plagioclase, smectite, illite, kaolinite, and chlorite), volcaniclastic (augite, plagioclase, and volcanic glass), and diagenetic minerals (smectite, phillipsite, clinoptilolite, and opal-CT). Although biogenic silica (radiolarians and diatoms) is common in near-seafloor (<10 mbsf) sediments, biogenic calcite is rare. Variations with depth in abundances of the terrigenous minerals reflect temporal changes in the flux of eolian material to the site. Volcanogenic material derived from the Hawaiian Islands is present in lithologic Unit 1 (0-19.9 meters below seafloor) both as discrete layers and as finely disseminated silt- and clay-sized material. Volcanic glass is present only in the upper 10 m of the sediment column. In Unit 2 (19.9-35.7 mbsf), increased smectite and zeolite abundances with depth as well as indurated, zeolite-rich layers are thought to be the alteration products of volcanogenic material. The source of this older (late Oligocene to middle Miocene) volcanogenic detritus may be continental volcanism. Microfabrics imaged using back-scattered electron imaging reflect the effects of compaction and diagenesis on sediment porosity and matrix structure. As porosity decreases during burial, the matrix changes from an open, floc-like fabric, to an interlocking network of clay mineral domains, and finally to a dense intergrowth of clay minerals and zeolites. Despite the substantial changes in sediment microfabric and mineralogy, correlations between physical and acoustic properties and mineralogy are weak or absent. The sediment has maintained high porosity (>70%), and water content appears to dominate the sediment's physical character and acoustic response.

Geochemistry of volcanic rocks from the Hikurangi and Manihiki Plateaus

Here we present the first radiometric age data and a comprehensive geochemical data set (including major and trace element and Sr-Nd-Pb-Hf isotope ratios) for samples from the Hikurangi Plateau basement and seamounts on and adjacent to the plateau obtained during the R/V Sonne 168 cruise, in addition to age and geochemical data from DSDP Site 317 on the Manihiki Plateau. The 40Ar/39Ar age and geochemical data show that the Hikurangi basement lavas (118-96 Ma) have surprisingly similar major and trace element and isotopic characteristics to the Ontong Java Plateau lavas (ca. 120 and 90 Ma), primarily the Kwaimbaita-type composition, whereas the Manihiki DSDP Site 317 lavas (117 Ma) have similar compositions to the Singgalo lavas on the Ontong Java Plateau. Alkalic, incompatible-element-enriched seamount lavas (99-87 Ma and 67 Ma) on the Hikurangi Plateau and adjacent to it (Kiore Seamount), however, were derived from a distinct high time-integrated U/Pb (HIMU)-type mantle source. The seamount lavas are similar in composition to similar-aged alkalic volcanism on New Zealand, indicating a second wide-spread event from a distinct source beginning ca. 20 Ma after the plateau-forming event. Tholeiitic lavas from two Osbourn seamounts on the abyssal plain adjacent to the northeast Hikurangi Plateau margin have extremely depleted incompatible element compositions, but incompatible element characteristics similar to the Hikurangi and Ontong Java Plateau lavas and enriched isotopic compositions intermediate between normal mid-ocean-ridge basalt (N-MORB) and the plateau basement. These younger (~52 Ma) seamounts may have formed through remelting of mafic cumulate rocks associated with the plateau formation. The similarity in age and geochemistry of the Hikurangi, Ontong Java and Manihiki Plateaus suggest derivation from a common mantle source. We propose that the Greater Ontong Java Event, during which ?1% of the Earth's surface was covered with volcanism, resulted from a thermo-chemical superplume/dome that stalled at the transition zone, similar to but larger than the structure imaged presently beneath the South Pacific superswell. The later alkalic volcanism on the Hikurangi Plateau and the Zealandia micro-continent may have been part of a second large-scale volcanic event that may have also triggered the final breakup stage of Gondwana, which resulted in the separation of Zealandia fragments from West Antarctica.

Trace and rare elements and factors at DSDP Hole 71-511

The distribution of paragenetic assemblages of trace and rare elements, as revealed by factor analysis (R-mode, Q-mode), the ratios of elements to Zr and the interpretation of these data in the context of the known mineralogy, lithology, and geology of the region, provide the bases for the outline of the geochemical history of sedimentation in the study area that forms the subject of this chapter. Two stages may be discerned. 1. Late-Middle Jurassic-Early Cretaceous (160-106? Ma). The sediments that accumulated in relatively shallow water (shelf) were predominantly clay, with dispersed sapropelic organic matter, plant fragments, pyrite, admixtures of acid-medium volcanic glass, and epigenetic crystals of gypsum. The bottom water layers of the basin are notably stagnant. The sediments are characterized by higher amounts of V, Zn, Cu, Cr, Rb, and Be associated with organic matter. Lower Cretaceous sediments, separated from those of the Upper Jurassic by a hiatus, accumulated in a deepened and enlarging basin. These Lower Cretaceous deposits are chemically similar to those of the Upper Jurassic, but contain diagenetic concentrations of Zn, Ni, and La. 2. Early-middle Albian (Unit 5)-middle Maestrichtian (1067-66.6Ma). The prevailing regime was that of an open ocean basin that tended to expand and deepen. During the second half of the early-middle Albian, the biogenic components Ba, Sr, and CaCO3 accumulated. By the end of this interval, Ti/Zr values had increased. In conjunction data on mineral composition, they testify to an outburst of basaltoid volcanism related to tectonic activity before an erosional hiatus (late Albian-Cenomanian). At the end of the Cenomanian-Turonian, residual deposits of predominantly clay sediments with relatively high amounts of Ti and Zr and associated rare alkalis (Li, Rb) accumulated. Clay sediments deposited during the Coniacian-Santonian were characterized by higher concentrations of Ti, Zr, Li, and Rb, by diagenetic carbonate phases of Ni, Zn, and La, and by sulphides and Fe-oxides with an admixture of Ni and Co. The latter half of the interval saw the deposition of fine basaltoid volcanoclastic material, diagenetically altered by zeolitization and carbonatization and enriched with Se, Pb, Ti, Sr, Ba, Y, and Yb. Sediments with a similar chemistry accumulated in the Campanian-middle Maestrichtian. Strong current activity preceding a global hiatus at the Mesozoic/Cenozoic boundary is reflected in both lower sedimentation rates and the presence of higher residual concentrations of Ti, Zr, Ba, Sr, and other elements studied in this chapter.