Petrology and structure of high-grade calcsilicates and granites of the Inkerman Shear Zone

Grabovickic, Stephanie (2000) Petrology and structure of high-grade calcsilicates and granites of the Inkerman Shear Zone. Masters (Research) thesis, James Cook University.

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Abstract

The Inkerman Shear Zone represents a characteristic structurally anomalous series of lineaments with a west - southwest trend. Low outcropping ridges of amphibolites, calcsilicates and granitic gneiss that form an older metamorphic unit represent these lineaments. Permo-Carboniferous dykes of various compositions form a dominant structural trend at right angles to these ridges. It is strictly not a shear zone of Permo-Carboniferous age, but represents a high strain zone of amphibolite facies metamorphics and granitoids (Inkerman Metamorphics).

The metamorphic rocks have undergone different metasomabc changes including the skarn development within the lithologies of the study area. Amphibolite found in the area generally is strongly foliated hornblende-plagioclase-quartz rock with accessory magnetite and titanite. Various calcsilicate rocks are common and are usually medium to coarse grained. In composition they vary from wollastonite-garnet rocks to various layered gneisses composed of gamet, clinopyroxene, hornblende, plagioclase and quartz.

The most common foliation fabric that can be found in the Inkerman Metamorphics has been named S₂. This fabric has developed during the second deformation event D₂ that was marked by intrusion of abundant granitic veins. A large body of monzogranite found in the southern part of the study area have a weak steeply dipping S₂ or S₄ foliation. Therefore, the granitoids of the study area are intruded pre D₄ or altematively intruded late in D₂.

The peak metamorphic conditions were obtained at 4.5 kbar, at temperatures up to 650°C and at low XC0₂ conditions. Inclusions in garnet porphyroblasts in Ink2 indicate several growth stages, with S₂ developed in the matrix only, so the earlier metamorphic growth stages occurred under static conditions. This was calculated using a pressure determined from Hornblende on a granodioritevein and a phase diagram calculated using "Thermocalc" for assemblages in sample Ink2.

Because of local meatasomatism, many granitic veins contain clinopyroxene and anorthite rich plagioclase, up to An₉₀, it is postulated that the metasomatic conditions resulted in the conversion of granitic veins to endoskarn. This metasomatic process involved addition of Ca and probable removal of alkalies (Na and K). Consequently, most of the endoskarn veins are composed of Ca rich plagioclase and with very little or no K-feldspar. These pegmatitic veins are probably late D₂ to post D₂. Small pods of andradite-rich garnet formed earlier were boudinaged during D₂.

Ages of the deforrnation events related to the formation of the Inkerrnan Metamorphics are uncertain. Correla.tives may be found in metamorphic rocks of Argentine and Running River Metamorphics and are likely to be Proterozoic to Lower Palaeozoic. The peak metamorphisrn of the Harvey's Range rocks was syn-D₃ Foliation S₃ (Edison, 1995.) that corresponds to this event is of similar orientation to S₂ foliation found in the Inkerrnan Metarnorphics.

Item ID: 28253
Item Type: Thesis (Masters (Research))
Keywords: geology; Inkerman; Stokes Range; metasomatic process; metamorphics
Date Deposited: 08 Aug 2013 06:54
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 80%
84 MINERAL RESOURCES (excl. Energy Resources) > 8499 Other Mineral Resources (excl. Energy Resources) > 849999 Mineral Resources (excl. Energy Resources) not elsewhere classified @ 20%
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