Geology of Saipan, Mariana Islands; Part 1, General geology

Cloud, Préston; Schmidt, Robert George; Burke, Harold W

doi:10.3133/pp280a

Cited by 59 publications

(44 citation statements)

References 22 publications

(30 reference statements)

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“…Here, lavas erupted in both subaerial and submarine environments are exposed (Cloud et al, 1956;Tracey et al, 1963). Because hypersthene-augite andesites are common in the volcanic sequences on both islands, they probably originated in a volcanic arc environment.…”

Section: Discussionmentioning

confidence: 99%

Petrology of Volcanic Rocks from the Fore-Arc Sites

Meijer¹,

Anthony²,

Reagan³

1982

Initial Reports of the Deep Sea Drilling Project

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Late Eocene and Oligocene submarine lavas recovered along the Mariana arc-trench slope appear to represent an early stage of arc volcanism along the Palau-Kyushu-Mariana trend. At Site 458, 90 km west of the Mariana Trench, the oldest lavas recovered were two pyroxene andesites with chemical and mineralogic characteristics generally associated with the arc tholeiite series. These are overlain by an unusual series of pyroxene (bronzite) andesites with relatively high Mg, Ni, and Cr and very low Ti, Zr, Y, and REE contents. Lavas with similar characteristics from the Bonin Islands have been called boninites. Because the Site 458 samples show a wider range of textures than is commonly attributed to boninites, the term "boninite series" is suggested for the purpose of discussion. These lavas probably derived from wet partial melting of very depleted mantle materials overlying the Palau-Kyushu-Mariana subduction zone. In Hole 459B, 50 km west of the trench, all the lavas recovered have the general chemical characteristics of arc tholeiite series andesites. Petrographically, volcanic cobbles recovered in sedimentary deposits on the lower trench slope at Sites 460 and 461 (Holes 460, 460A, 461, and 461 A) 23 and 11 km, respectively, from the trench axis are similar to Hole 459B lavas. Chemical data for samples from these sites are compatible with this association.All the volcanic rocks recovered show evidence of secondary alteration. Secondary minerals include clays, carbonate, zeolite, cristobalite, quartz, tridymite, celadonite, chlorite/clay, Fe-hydroxides, and other minor phases. In spite of the alteration, primary phases including pyroxenes, Plagioclase, Fe-Ti-oxides, and glass remain unaltered in some samples. This type of alteration is similar to that observed in typical seafloor volcanic sections in the major ocean basins. No evidence of high P, low T metamorphic conditions has been uncovered.The proximity of arc-related volcanic rocks to the trench axis is difficult to explain in terms of current models of subduction complexes. Possible causes include magma generation at shallow depths along the Eocene-Oligocene subduction zone and tectonic erosion of the lower trench slope.

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Section: Discussionmentioning

confidence: 99%

Petrology of Volcanic Rocks from the Fore-Arc Sites

Meijer¹,

Anthony²,

Reagan³

1982

Initial Reports of the Deep Sea Drilling Project

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“…The final event was the intrusion of sills at about 32 Ma, possibly related to the initial rifting of the Palau-Kyushu Ridge . Cloud et al (1956) and Schmidt (1957) mapped Saipan, K-Ar radiometric dating again supplied by boninitic series dacite of the Sankakuyama Formation (41 Ma), followed by the andesitic pyroclastic rocks and lava flows of the late Eocene-Oligocene (35.7+0.5 Ma) Hagman Formation. 5.…”

Section: Oaoga Shima^792mentioning

confidence: 99%

Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction

Pearce¹,

Laan²,

Arculus³

et al. 1992

Proceedings of the Ocean Drilling Program

288

265

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Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component.The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250°C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks e...

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“…The lack of iron enrichment and high Ba and Sr contents in the basalts suggests that they have calc-alkalic affinities (Meijer, 1976;Dixon and Batiza, 1979). The volcanic islands of the southern ridge consist mainly of basalts and basaltic andesites interbedded with and overlain by, predominantly calcareous sediments (Stark, 1963), although more evolved igneous rocks occur, for example, dacite on Saipan (Cloud et al, 1956;Schmidt, 1957;Taylor et al, 1969). These lavas also lack a trend of strong iron enrichment and plot as a hypersthenic series on an AFM diagram (Stark, 1963).…”

Section: Regional and Tectonic Settingmentioning

confidence: 99%

Geochemistry of Igneous Rocks Recovered from a Transect across the Mariana Trough, Arc, Fore-Arc, and Trench, Sites 453 through 461, Deep Sea Drilling Project Leg 60

Wood¹,

Marsh²,

Tarney³

et al. 1982

Initial Reports of the Deep Sea Drilling Project

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Major and trace element analyses are presented for 110 samples from the DSDP Leg 60 basement cores drilled along a transect across the Mariana Trough, arc, fore-arc, and Trench at about 18°N. The igneous rocks forming breccias at Site 453 in the west Mariana Trough include plutonic cumulates and basalts with calc-alkaline affinities. Basalts recovered from Sites 454 and 456 in the Mariana Trough include types with compositions similar to normal MORB and types with calc-alkaline affinities within a single hole. At Site 454 the basalts show a complete compositional transition between normal MORB and calc-alkaline basalts. These basalts may be the result of mixing of the two magma types in small sub-crustal magma reservoirs or assimilation of calc-alkaline, arc-derived vitric tuffs by normal MORB magmas during eruption or intrusion.A basaltic andesite clast in the breccia recovered from Site 457 on the active Mariana arc and samples dredged from a seamount in the Mariana arc are calc-alkaline and similar in composition to the basalts recovered from the Mariana Trough and West Mariana Ridge. Primitive island arc tholeiites were recovered from all four sites (Sites 458-461) drilled on the fore-arc and arc-side wall of the trench. These basalts form a coherent compositional group distinct from the Mariana arc, West Mariana arc, and Mariana Trough calc-alkaline lavas, indicating temporal (and perhaps spatial?) chemical variations in the arc magmas erupted along the transect.Much of the 209 meters of basement cored at Site 458 consists of endiopside-and bronzite-bearing, Mg-rich andesites with compositions related to boninites. These andesites have the very low Ti, Zr, Ti/Zr, P, and rare-earthelement contents characteristic of boninites, although they are slightly light-rare-earth-depleted and have lower MgO, Cr, Ni, and higher CaO and AI2O3 contents than those reported for typical boninites. The large variations in chemistry observed in the lavas recovered from this transect suggest that diverse mantle source compositions and complex petrogenetic process are involved in forming crustal rocks at this intra-oceanic active plate margin.

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Geology of Saipan, Mariana Islands; Part 1, General geology

Abstract: ______________ 1 Introduction _ 2 Basis and scope of the report.._ 2 Acknowledgments. ________!_ 3 General history of the region. 3 Geographic terminology _________

Cited by 59 publications

References 22 publications

Petrology of Volcanic Rocks from the Fore-Arc Sites

Petrology of Volcanic Rocks from the Fore-Arc Sites

Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction

Geochemistry of Igneous Rocks Recovered from a Transect across the Mariana Trough, Arc, Fore-Arc, and Trench, Sites 453 through 461, Deep Sea Drilling Project Leg 60

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