1997 Fiscal Year Final Research Report Summary
Study on the tectonic setting of volcanogenic massive sulfide deposits
| Project/Area Number |
07640648
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Petrology/Mineralogy/Science of ore deposit
|
|---|
| Research Institution | Waseda University |
|---|
Principal Investigator |
MARIKO Tadashi School of Education, Earth Sciences, Professor Waseda Univ., 教育学部, 教授 (00063454)
|
|---|
| Project Period (FY) |
1995 – 1997
|
| Keywords | volcanogenic massive sulfide deposit / tectonic setting / back arc basalt / island arc basalt / Sanbagawa Belt / South Fossa Magana / Northern Andes |
|---|
| Research Abstract |
The results of geochemical studies including major and minor element analyzes by XRF and ICP of the volcanic rocks or metamorphic rocks derived from volcanics forming host rocks of some volcanogenic massive sulfide deposits are as follows :
Sanbagawa belt in the Kantou Mountains amd Tenryu River area The sourse rocks of Sanbagawsa basic schist including Mikabu green rocks imvolve the tholeiite, calc-alkali and alkali basalt series. These are formed in a back-arc basin and divided into P-MORB type, N-MORB type, T-MORB type and island-arc type basalts. The Besshi-type massive sulfide deposits in Sanbagawa belt are estimated to be formed by the hydrothermal activity accompanied with these magmatism in the back-arc basin. They appear to occur closely associated with basic schist derived from N-MORB type basalt.
South Fossa Magna The South Fossa Magna had been considered to be a part of Green Tuff region until numbers of geologist represented recently the consensus that it is the collision product to Honshu arc of paleo-Izu arc-back-arc system formed by the subduction of the Pacific plate under the Philippine plate. The present geochemical study of volcanic rocks in the Tanzawa-Koma-Misaka Mountains of the South Fossa Magna clarify that they are composed of the tholeiite and calc-alkali series rocks and formed in the main-arc and back-arc rift. The Takara massive sulfide deposit occurs closely associated with the andesitic rock formed in the main-arc.
El-Roble ore deposit area The green rocks and the syngenetic El-Roble massive sulfide deposit in the Cretaceous accretional zone composing the Western Cordillera of Northern Andes are formed in the oceanic fore arc-arc-back arc system (supra-subduction zone). In the process of spreading and closing of the Colimbia back arc basin, the ore deposit probably formed at the spreading axis when it approaced to the subduction zone and the back arc magma was generated by mixing of T-MORB and island arc magma components.
|
