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11.
Recent studies on mineralogy, geochronology, fluid inclusion and stable isotope (Pb, Os, S, C, O, Sr) characteristics were reviewed to determine constraints for genetic models of the Chilean manto‐type copper deposits. The Chilean manto‐type deposits are divided into the two geologic categories of the northern areas (Arica–Iquique, Tocopilla–Taltal) and the central areas (Copiapó, La Serena, Santiago). The former is distributed in the coastal range composed of Jurassic andesite‐dominated volcano‐sedimentary piles and younger plutonic intrusions, and yields chalcocite (‐digenite) and bornite as the principal hypogene copper sulfides. The latter is hosted mostly in Lower Cretaceous volcano‐sedimentary sequences, and has chalcopyrite‐rich mineral associations. The fluid inclusion data indicate that the primary copper mineralization was commonly generated in the temperature range 150–360°C under low‐pressure conditions near the boiling curve, mediated with relatively saline brines. Generally, homogeneous Pb and S isotope compositions for primary copper minerals imply direct magma source or leaching of igneous rocks. Pb and Os isotope data published for some deposits, however, suggest that ore‐forming metals were derived mainly from the volcano‐sedimentary host rocks. The noticeably negative isotope ratios of primary sulfide sulfur and hydrothermal calcite carbon of some central area deposits indicate influx of sedimentary rock components, and the high 87Sr/86Sr initial ratios of hydrothermal calcite from the Tocopilla–Taltal area deposits imply contribution of the contemporaneous seawater or marine carbonates. These isotopic constraints imply a formation mechanism in which the Chilean manto‐type copper deposits formed epigenetically in the process of hydrothermal interaction of non‐magmatic surface‐derived brine with the volcano‐sedimentary host rocks, which is inferred to have been induced by a deep‐seated plutonic complex as the possible heat source. 相似文献
12.
Spinel, which constitutes from 0.7% to 3% of lherzolite inclusions, occurs as primary anhedral grains (chrome-rich variety) and as a secondary phase as breakdown products of garnet (alumina-rich variety). Although individual primary spinel grains are chemically homogeneous, spinels are characterized by a wide range of Cr/Al ratios and a relatively narrow range of Mg/Fe″ ratios, even in a single lherzolite sample. The chemical variations of spinels are considered to have the following origin: When garnet lherzolite enters the stability field of the spinel peridotite facies as a consequence of slow upward transport, both orthopyroxenes and clinopyroxenes are recrystallized with loss of jadeite and some Tschermak's component to reach equilibrium. A part of the Tschermak's component reacts with olivine to form pyroxene and spinel. This secondary spinel component is alloted to the primary chromian spinel. However, these reactions did not always reach equilibrium with the major constituent minerals in the lherzolites. 相似文献
13.
The Kanmon Group (Lower Cretaceous) is a non-marine sequence in the Inner Zone of southwest Japan and is divided into the lower Wakino (lacustrine) and the upper Shimonoseki (fluvial) subgroups. Major diagenetic changes in this group are compaction, iron-oxide cementation, calcite cementation and grain replacement, quartz overgrowth and pore-fill cementation, illite authigenesis, chlorite pore-fill cementation and grain replacement, albitization of feldspar, and grain replacement by pyrite. Two subgroups of the Kanmon Group present no significant differences in general diagenetic features, paragenetic sequence, or the degree of diagenetic changes despite differences in depositional environments (lacustrine vs. fluvial) and stratigraphic positions. However, some differences are recognized in the content and chemistry of authigenic minerals caused by different sandstone framework compositions. The content of authigenic clay minerals is higher in sandstones of the Shimonoseki Subgroup containing abundant volcanic rock fragments. In addition, the composition of chlorite, the most abundant authigenic clay mineral in Kanmon sandstones, is Mg-rich in the volcanoclastic Shimonoseki sandstones, compared to an Fe-rich variety in Wakino sandstones. The original sandstone composition played a significant role in pore-water composition and diagenetic reactions.The Wakino sandstones lost most of its porosity by compaction, whereas Shimonoseki sandstones are only compacted in the vicinity of the basin-bounding fault. The weakly compacted Shimonoseki sandstones, instead, were largely cemented by pore-filling calcite during early diagenesis; cementation prevented compaction during further burial. The Kanmon Group sediments were heated to about 300 °C based on illite crystallinity values. 相似文献
14.
Ken-ichiro Hisada Masaaki Sugiyama Katsumi Ueno Punya Charusiri Shoji Arai 《Island Arc》2004,13(1):119-127
Abstract Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north‐west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean‐floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion. 相似文献
15.
Hidetoshi HARA Miyuki KUNII Ken-ichiro HISADA Katsumi UENO Yoshihito KAMATA Punya CHARUSIRI Thasinee CHAROENTITIRAT 《地球学报》2012,33(S1):15-15
The accretionary complex related to the Pa-leo-Tethys subduction was developed along western margin of the Indochina Block in northern Thailand. The provenance, source rock compositions, and sedi-ment supply system of the accretionary complex were reconstructed based on the petrography and geochem-istry of clastic rocks, U-Pb dating of detrital zircons. 相似文献
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17.
Hidetoshi Hara Koji Wakita Katsumi Ueno Yoshihito Kamata Ken-ichiro Hisada Punya Charusiri Thasinee Charoentitirat Pol Chaodumrong 《Gondwana Research》2009,16(2):310
We reconstructed the accretion process related to Paleo-Tethys subduction recorded in northern Thailand, based on mélange and thrust structures, and metamorphic temperatures derived from illite crystallinity data. Mélange formation was characterized by hydrofracturing and cataclastic deformation, with mud injection under semi-lithified conditions followed by shear deformation and pressure solution. Illite crystallinity data suggest metamorphic temperatures below 250 °C during mélange formation. The combined structural and metamorphic data indicate that during mélange formation, the accretionary complex related to Paleo-Tethys subduction developed at shallow levels within an accretionary prism. Asymmetric shear fabrics in mélange indicate top-to-south shear. After correction for rotation associated with collision between the Indian and Eurasian continents, the trend of the Paleo-Tethys subduction zone is estimated to have been N80 °E. We conclude that the Paleo-Tethys was subducted northward beneath the Indochina Block from the Permian to Triassic. 相似文献
18.
This paper describes the pedogenic features of paleosols in the upper Lower Cretaceous Shiohama Formation, the lowest unit of the Shimonoseki Subgroup, in Yoshimi, Yamaguchi Prefecture, southwest Japan. The paleosol profiles in the Shiohama Formation are compound and complex, characterized by the presence of abundant calcrete horizons. An analysis of these profiles reveals that the floodplain upon which the Shiohama Formation was deposited was part of an unstable aggradation system characterized by the intermittent influx of sediments and occasional erosion. Furthermore, the mean annual range of precipitation was less than about 30 mm, suggesting only minor seasonal change between wet and dry conditions during deposition of the Shiohama Formation. The microstructures of the observed calcretes include dense microfabric, floating detrital grains, micronodules, circum-granular cracks, and complex cracks. These features formed by chemical precipitation under dry conditions, with little bioactivity. The calcrete horizons are classified into seven types (I–VII) based on their modes of occurrence. Two processes of carbonate accumulation can be identified based on the size and abundance of nodules: VI–V–III–(II)–I and VI–(V)–IV–II–I. These processes represent the development of calcrete horizons from the early to late stages of calcretization. Type I represents the most highly developed stage of calcretization. Calcretes within the Lower Member sequence of the Shiohama Formation show repetitions of type I and types II and III. Thus, it is interpreted that the frequency of sediment supply to the floodplain changed repeatedly over time. 相似文献
19.
Titanochondrodite and titanoclinohumite derived from the upper mantle in the Buell Park Kimberlite,Arizona, USA 总被引：2，自引：0，他引：2
Ken-ichiro Aoki Kiyoshi Fujino Masaki Akaogi 《Contributions to Mineralogy and Petrology》1976,56(3):243-253
Kimberlite from Buell Park, Arizona, which was intruded into Permian sediments about 30 m.y. ago, is characterized by the hydrous silicates titanochondrodite and titanoclinohumite. Titanochondrodite is the first finding in kimberlites. Optical properties, chemical compositions and cell dimensions of these two minerals are determined.Titanochondrodite and titanoclinohumite are considered to crystallize from kimberlite magma at a depth of about 100 km and at 1,000° C, on the basis of kimberlite mineralogy, petrography and high pressure experimental work. Although there is no direct evidence, the importance of these two minerals in peridotite wedges above sinking lithosphere at the continental margins is also discussed. 相似文献
20.
Titanochondrodite and titanoclinohumite derived from the upper mantle in the Buell Park kimberlite,Arizona, USA 总被引：1，自引：0，他引：1
Ken-ichiro Aoki 《Contributions to Mineralogy and Petrology》1977,61(2):217-218
Titanoclinohumite, titanochondrodite, and associated Na-bearing tremolite occurring as crystal fragments in the Buell Park kimberlite are not likely crystallization products of a kimberlite magma. They more likely formed as phases in hydration assemblages of peridotite at temperatures below 700 ° C and pressures below 18 kbar. The crystals were dispersed in kimberlite as rock fragments were comminuted during transport to the surface. 相似文献