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1.
The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations.  相似文献   
2.
Alternating chert–clastic sequences juxtaposed with limestone blocks, which are units typical of accretionary complexes, constitute the Buruanga peninsula. New lithostratigraphic units are proposed in this study: the Unidos Formation (Jurassic chert sequence), the Saboncogon Formation (Jurassic siliceous mudstone–terrigenous mudstone and quartz‐rich sandstone), the Gibon Formation (Jurassic(?) bedded pelagic limestone), the Libertad Metamorphics (Jurassic–Cretaceous slate, phyllite, and schist) and the Buruanga Formation (Pliocene–Pleistocene reefal limestone). The first three sedimentary sequences in the Buruanga peninsula show close affinity with the ocean plate stratigraphy of the North Palawan terrane in Busuanga Island: Lower–Middle Jurassic chert sequences overlain by Middle–Upper Jurassic clastics, juxtaposed with pelagic limestone. Moreover, the JR5–JR6 (Callovian to Oxfordian) siliceous mudstone of the Saboncogon Formation in the Buruanga peninsula correlates with the JR5–JR6 siliceous mudstone of the Guinlo Formation in the Middle Busuanga Belt. These findings suggest that the Buruanga peninsula may be part of the North Palawan terrane. The rocks of the Buruanga peninsula completely differ from the Middle Miocene basaltic to andesitic pyroclastic and lava flow deposits with reefal limestone and arkosic sandstone of the Antique Range. Thus, the previously suggested boundary between the Palawan microcontinental block and the Philippine Mobile Belt in the central Philippines, which is the suture zone between the Buruanga peninsula and the Antique Range, is confirmed. This boundary is similarly considered as the collision zone between them.  相似文献   
3.
Abstract Analysis of the 12 samples taken from two horizons (the pre-1991 Mount Pinatubo eruption and the post-1991 Mount Pinatubo eruption layers) of the six deep water cores that were collected along the Eastern South China Sea shows that the absolute abundance of Recent benthic foraminifera (total assemblage) in the post-eruption layer is much lower compared to the pre-eruption layer. The post-eruption layer also shows lower diversity with relative high abundance of Quinqueloculina spp., which probably form part of the recolonization fauna. These observations suggest that environmental stability plays a vital role in the distribution of foraminifera in the eastern margin of the South China Sea. The disturbance created by the immense amount of pyroclastic materials that originated from the 1991 eruption of Mount Pinatubo has resulted in the dilution and, eventually, the decimation of most of the benthic foraminifera. The species that were able to survive might have taken advantage of the small amounts of available nutrient supply. These might also be the species that were able to adapt quickly to the changes in the environmental conditions.  相似文献   
4.
Tin‐polymetallic base metal deposits of Miocene age in the Eastern Cordillera in Bolivia were studied by ICP/MS and EPMA for major and minor elements, paying an attention to indium concentration of the ore deposits. The highest indium content and 1000 In/Zn ratio of individual ore deposits are 5,740 ppm and 22.2 for the Potosi deposits, 2,730 ppm and 7.4 for Bolivar deposit, 2,510 ppm and 17.5 for Siete Suyos–Animas deposits, and 1,290 ppm and 3.3 for San Vicente deposit. The same content and ratio of composite samples of the studied deposits are up to 292 ppm and 4.0 for Potosi deposits, 3,080 ppm and 11.3 for Huari Huari deposit, 100 ppm and 0.3 for Tuntoco deposit, 152 ppm and 1.8 for Porco deposit, 103 ppm and 59.2 for Animas deposit, and 1,160 ppm and 3.7 for Pirquitas deposit. Those of zinc concentrates are as follows: 1,080 ppm and 2.1 at San Lorenzo; 584 ppm and 1.7 at Bolivar; 499 ppm and 1.23 at Porco; 449 ppm and 1.21 at Reserva, and 213 ppm and 0.61 at Colquiri deposit. Indium occurs mostly in dark colored sphalerite and that of the Potosi deposit was found to have one of the highest concentrations, containing up to 1.27 wt% In. Petrukite was discovered in the Potosi deposit, and indium minerals are expected to occur in the Huari Huari deposit and others with the high 1000 In/Zn ratios. The indium contents of the zinc concentrates and composite samples were applied to the produced and remaining ores, then the total amounts of indium in the Bolivian tin‐polymetallic base metal deposits are speculated to be more than 12,000 tons In, which is bigger than that of South China (11,000 tons) and the Japanese Islands (9,000 tons). Sphalerites of the Potosi deposit have one of the highest ranges of indium, similarly to those of the San Vicente deposit. Both the San Vicente and Potosi deposits are rich in silver, implying significance of both silver‐polymetallic and tin‐polymetallic environments for the concentration of trace amounts of indium.  相似文献   
5.
A number of geological studies have already been conducted on the Zambales Ophiolite Complex (ZOC), a north-south trending complete ophiolite sequence exposed in the western portion of Central Luzon, Philippines. Previous works recognized the ZOC as being made up of two blocks, the Acoje and the Coto, acting as an arc-back arc pair sometime during the Eocene.  相似文献   
6.
Sapphirine occurs with humite-group minerals and forsteritein Precambrian amphibole-facies rocks at Kuhi-lal, SW PamirMountains, Tajikistan, a locality also for talc+kyanite magnesiohornblendewhiteschist. Most of these sapphirine-bearing rocks are graphiticand sulfidic (pyrite and pyrrhotite) and contain enstatite,clinohumite or chondrodite, spinel, rutile, gedrite, and phlogopite.A phlogopite schist has the assemblage with XFe = Fe/(Fe+Mg)increasing as follows: chlorite (0-003)<phlogopite (0.004–0.005)sapphirine (0.004–0.006) enstatite (0-006)forsterite (0-006–0-007)<spinel (0-014). This assemblage includes the incompatiblepair sapphirine+forsterite, but there is no textural evidencefor reaction. In one rock with clinohumite, XFe increases asfollows: clinohumite (0-002) <sapphirine (0-003) <enstatite(0-004–0-006) <spinel (0-010). Ion microprobe and wet-chemicalanalyses give 0-57–0-73 wt.% F in phlogopite and 0-27wt.% F in chlorite in the phlogopite schist; 0-04, 1.5–1.9,and 4.4 wt.% F in forsterite, clinohumite, and chondrodite,respectively; and 0-0-09 wt.% BeO and 0-05–0-21 wt.% B2O3in sapphirine. Stabilization of sapphirine+clinohumite or sapphirine+chondroditeinstead of sapphirine+phlogopite is possible at high F contentsin K-poor rocks, but minor element contents appear to be toolow to stabilize sapphirine as an additional phase with forsterite+enstatite+spinel.Although sapphirine+forsterite is metastable relative to spinel+enstatitein experiments conducted at aH2O=1 in the MgO-Al2O3-SiO2-H2Osystem, it might be stabilized at aH2O0.5, P4 kbar, T650–700C.Textures in the Kuhi-lal whiteschists suggest a polymetamorphicevolution in which the rocks were originally metamorphosed atT650C, P 7 kbar, conditions under which sapphirine+clinohumiteand sapphirine+chondrodite are inferred to have formed, andsubsequently affected by a later event at lower P, similar T,and lower aH2O. The latter conditions were favorable for sapphirine+forsteriteto form in a rock originally containing chlorite+forsterite+spinel+enstatite.  相似文献   
7.
Northwestern Ilocos Norte in Luzon, Philippines, exposes cherts, peridotite and a variety of metamorphic rocks including chlorite schist, quartzo‐feldspathic schist, muscovite schist and actinolite schist. These rocks are incorporated within a tectonic mélange, the Dos Hermanos Mélange, which is thrust onto the turbidite succession of the Eocene Bangui Formation and capped by the Upper Miocene Pasuquin Limestone. The radiolarian assemblages constrain the stratigraphic range of the cherts to the uppermost Jurassic to Lower Cretaceous. Stratigraphically important species include Eucyrtidiellum pyramis (Aita), Hiscocapsa acuta (Hull), Protunuma japonicus (Matsuoka & Yao), Archeodictyomitra montisserei (Squinabol), Hiscocapsa asseni (Tan), Cryptamphorella conara (Foreman) and Pseudodictyomitra carpatica (Lozyniak). The radiolarian biostratigraphic data provide evidence for the existence of a Mesozoic basinal source from which the cherts and associated rocks were derived. Crucial to determining the origin of these rocks is their distribution and resemblance with known mélange outcrops in Central Philippines. The mélange in the northwestern Ilocos region bears similarities in terms of age and composition with those noted in the western part of the Central Philippines, particularly in the islands of Romblon, Mindoro and Panay. The existence of tectonic mélanges in the Central Philippines has been attributed to the Early to Middle Miocene arc–continent collision. This event involved the Philippine Mobile Belt and the Palawan Microcontinental Block, a terrane that drifted from the southeastern margin of mainland Asia following the opening of the South China Sea. Such arc–continent collision event could also well explain the existence of a tectonic mélange in northwestern Luzon.  相似文献   
8.
New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age.Radiometric dating of its plutonic and volcanichypabyssal rocks yielded middle Eocene ages.On the other hand,the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge-island arc affiliated Coto block of the ophiolite complex,together with isotopic age datings of its dikes and mafic cumulate rocks,also yielded Eocene ages.This offers the possibility that the Zambales Ophiolite Complex could have:(1)evolved from a Mesozoic arc(Acoje block)that split to form a Cenozoic back-arc basin(Coto block),(2)through faulting,structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or(3)through the interplay of slab rollback,slab break-off and,at a later time,collision with a microcontinent fragment,caused the formation of an island arc-related ophiolite block(Acoje)that migrated trench-ward resulting into the generation of a back-arc basin(Coto block)with a limited subduction signature.This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation.  相似文献   
9.
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10.
The collision of the Palawan microcontinental block with the Philippine mobile belt had significantly influenced the geological evolution of the Philippines. Multiple collisions involving several fragments, through space and time, resulted into the collage of terranes of varying origin exposed in this part of central Philippines. Cusping of the overriding plate, volcanic arc gap, ophiolite emplacement, incipient back-arc rifting, island rotation and tilting, raised coastal terraces, metamorphism, intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision. A late Early Miocene to early Middle Miocene age (20–16 Ma) is proposed for the major collision between the Palawan indenter and the Philippine mobile belt. The collision boundary is located from the northern part of Mindoro through the central mountain range swinging east of Sibuyan Island in the Romblon Island Group and finally threading along the Buruanga Peninsula and eastern side of the Antique Ophiolite Complex before exiting and connecting with the Negros Trench. The collision, through accretion and crustal thickening, has contributed to the crustal growth of the Philippine archipelago.  相似文献   
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