Tectonic controls on the distribution of large copper and go(2)

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Guinea; and the juxtaposition of a series of oceanic arcs and final accretion of those to SE Asian crust in the Philippines.

In western Indonesia, subduction has been going on continuously, with the consumption of the Indian plate below thin crust of SE Asia. The oblique vector of this subduction results in the formation of an important dextral shear zone on Sumatra, the Sumatran Fault Zone. No significant porphyry systems are known in western Indonesia. The subducting oceanic plate in this region comprises cold Eocene crust, while the thin lithosphere of SE Asia is also relatively cold. These factors suggest that the subducting oceanic plate never had time to heat up sufficiently to significantly contribute to the melts within the arc and could explain the apparent paucity of economic porphyry systems.

In Eastern Indonesia the tectonic drivers become significantly more varied. In Borneo, earlier southward subduction of the PSCSP was immediately followed by rotation of Borneo and formation of crustal scale structures, providing conditions in which the slab may have been trapped and heated sufficiently to induce partial melting. It is worth noting that the older systems (e.g. Mount Muro) appear to be located along the southeastward extension of faults which accommodated the dextral escape tectonics and lateral ramp architecture related to collision of India with Asia during the Miocene. In northern Sulawesi, the earthquake data support a lower angle of subduction of the CSP compared to the westward subducting MSP between Sulawesi and Halmahera. Devolatilisation of the hot MSP and additional heat from trapped metasomatised mantle wedge, together with shallow subduction of the CSP, would facilitate higher degrees of partial melting of the subducted CSP, resulting in low sulphidation oxidised melts, suitable for the generation of porphyry copper-gold systems in the region.

In Papua New Guinea, the main tectonic driver was the transverse accretion of young oceanic arcs to the Australian Craton. This transverse movement induced extensional jogs which facilitated the emplacement of some of the porphyry systems. In contrast to the IP below western Indonesia, the oceanic crust of the PSP and CP is relatively young and hot, while subduction was very oblique with respect to the Australian craton. These factors would have possibly facilitated the partial melting of the subducting slab and the formation of adakitic melts to form fertile porphyry systems.

The Philippines is the site of various recent subduction zones, and accretion of relatively young oceanic arc fragments. Subduction along the western side of the islands, in the Manila trench, ceased with the docking of the intra-oceanic arc assemblage to the SE Asian margin. This docking triggered the start of subduction to the east, in the current Philippine trench, which is the driving force of active volcanism on the islands now. The cessation and reprisal of subduction, as well as the relatively young nature of the oceanic arcs and crust would favour the melting of subducted oceanic slab to form richly endowed adakitic melts, explaining the fertility of the archipelago. We note that most mineral systems are localised along the sinistral FFZ or associated extensional jogs.

"Smart Science for Exploration and Mining" P. J. Williams et al. (editors)

斑岩型铜矿相关文献

devolatisation and resultant destabilisation and

participation of the upper plate. In contrast, cessation of Preservation is a key issue in identifying features in

subduction results in longer residence times of the older geological terranes. The epithermal and porphyry

subducted lithosphere, allowing it to actively participate systems in SE Asia are young, and form at a relatively

in the formation of melts. This participation will further high level in the crust, in actively emergent landscape

be enhanced if the subducted plate is relatively young systems. Their preservation potential is therefore quite

and hot, or if through the interaction of a new oblique low, and in similar settings in older systems will

subduction system, devolatisation of the new subducting definitely be a limiting factor of any analysis. A review

plate destabilises not only the lower parts of the upper of the global distribution of pre-Cenozoic deposits shows

plate, but also the detached fossil slab, as could be the that most porphyry and epithermal deposits form in

linear belts at once-active (convergent) margins, case for northern Sulawesi. suggesting that collision- or accretion-related

4 Conclusions magmatism are the main first-order ingredients to the

formation of world class orebodies of that type.

Understanding the tectonic events that can trigger The analysis of the distribution of these deposits in

mineralisation is an important factor in assessing the southeast Asia highlights that subduction alone is no

exploration potential of different structures. However, guarantee for the emplacement large porphyry copper-unravelling a detailed tectonic history in poorly gold or epithermal gold deposits, but that these deposits

form at times when tectonic mechanism changes preserved pre-Cenozoic terrains is much more difficult

than in younger terrains. It is our view, however, that dramatically, such as the cessation or start of subduction.

detailed mapping and structural analysis, combined with It is postulated that the main reason behind this is related

targeted geochronology and rock geochemistry in these to the thermodynamic conditions of the subducted

older terrains can help, to some degree, to identify the lithosphere (Mungall, 2000). In ongoing subduction the

potential tectonic triggers that can lead to large mineral participation of this subducting lithosphere is limited to

porphyry and as …… 此处隐藏：4627字，全部文档内容请下载后查看。喜欢就下载吧 ……