I- and S-type granites in the Lachlan Fold Belt

1992 ◽  
Vol 83 (1-2) ◽  
pp. 1-26 ◽  
Author(s):  
B. W. Chappell ◽  
A. J. R. White
Keyword(s):  
Volcanic Rocks ◽  
Source Rocks ◽  
Fold Belt ◽  
Mafic Rocks ◽  
Isotopic Compositions ◽  
Deep Crust ◽  
Lachlan Fold Belt ◽  
Higher Temperature ◽  
Sedimentary Source ◽  
Host Rocks

ABSTRACTGranites and related volcanic rocks of the Lachlan Fold Belt can be grouped into suites using chemical and petrographic data. The distinctive characteristics of suites reflect source-rock features. The first-order subdivision within the suites is between those derived from igneous and from sedimentary source rocks, the I- and S-types. Differences between the two types of source rocks and their derived granites are due to the sedimentary source material having been previously weathered at the Earth's surface. Chemically, the S-type granites are lower in Na, Ca, Sr and Fe3+/Fe2+, and higher in Cr and Ni. As a consequence, the S-types are always peraluminous and contain Al-rich minerals. A little over 50% of the I-type granites are metaluminous and these more mafic rocks contain hornblende. In the absence of associated mafic rocks, the more felsic and slightly peraluminous I-type granites may be difficult to distinguish from felsic S-type granites. This overlap in composition is to be expected and results from the restricted chemical composition of the lowest temperature felsic melts. The compositions of more mafic I- and S-type granites diverge, as a result of the incorporation of more mafic components from the source, either as restite or a component of higher temperature melt. There is no overlap in composition between the most mafic I- and S-type granites, whose compositions are closest to those of their respective source rocks. Likewise, the enclaves present in the more mafic granites have compositions reflecting those of their host rocks, and probably in most cases, the source rocks.S-type granites have higher δ18O values and more evolved Sr and Nd isotopic compositions, although the radiogenic isotope compositions overlap with I-types. Although the isotopic compositions lie close to a mixing curve, it is thought that the amount of mixing in the source rocks was restricted, and occurred prior to partial melting. I-type granites are thought to have been derived from deep crust formed by underplating and thus are infracrustal, in contrast to the supracrustal S-type source rocks.Crystallisation of feldspars from felsic granite melts leads to distinctive changes in the trace element compositions of more evolved I- and S-type granites. Most notably, P increases in abundance with fractionation of crystals from the more strongly peraluminous S-type felsic melts, while it decreases in abundance in the analogous, but weakly peraluminous, I-type melts.

Some supracrustal (S-type) granites of the Lachlan Fold Belt

1988 ◽  
Vol 79 (2-3) ◽  
pp. 169-181 ◽  
Author(s):  
A. J. R. White ◽  
B. W. Chappell
Keyword(s):  
Volcanic Rocks ◽  
Source Rocks ◽  
Crystal Fractionation ◽  
Metamorphic Rocks ◽  
Contact Aureole ◽  
High Grade ◽  
Fold Belt ◽  
Fertile Window ◽  
Lachlan Fold Belt ◽  
Sedimentary Source

ABSTRACTS-type granites have properties that are a result of their derivation from sedimentary source rocks. Slightly more than half of the granites exposed in the Lachlan Fold Belt of southeastern Australia are of this type. These S-type rocks occur in all environments ranging from an association with migmatites and high grade regional metamorphic rocks, through an occurrence as large batholiths, to those occurring as related volcanic rocks. The association with high grade metamorphic rocks is uncommon. Most of the S-type granites were derived from deeper parts of the crust and emplaced at higher levels; hence their study provides insights into the nature of that deeper crust. Only source rocks that contain enough of the granite-forming elements (Si, Al, Na and K) to provide substantial quantities of melt can produce magmas and there is therefore a fertile window in the composition of these sedimentary rocks corresponding to feldspathic greywacke, from which granite magmas may be formed.In this paper, three contrasting S-type granite suites of the Lachlan Fold Belt are discussed. Firstly, the Cooma Granodiorite occurs within a regional metamorphic complex and is associated with migmatites. It has isotopic and chemical features matching those of the widespread Ordovician sediments that occur in the fold belt. Secondly, the S-type granites of the Bullenbalong Suite are found as voluminous contact-aureole and subvolcanic granites, with volcanic equivalents. These granites are all cordierite-bearing and have low Na2O, CaO and Sr, high Ni, strongly negative εNd and high 87Sr/86Sr, all indicative of S-type character. However, the values of these parameters are not as extreme as for the Cooma Granodiorite. Evidence is discussed to show that these granites were derived from a less mature, unexposed, deeper and older sedimentary source. Other hypotheses such as basalt mixing are discussed and can be ruled out. The Strathbogie Suite granites are more felsic but all are cordierite-bearing and have chemical and other features indicative of an immature sedimentary source. They are closely associated with cordierite-bearing volcanic rocks. The more felsic nature of the suite results in part from crystal fractionation. It is suggested that the magma may have entered this “crystal fractionation” stage of evolution because it was a slightly higher temperature magma produced from an even less mature sediment than the Bullenbalong Suite. The production of these S-type magmas is discussed in terms of vapour-absent melting of metagreywackes involving both muscovite and biotite. The production of a magma in this way is consistent with the low H2O contents and geological setting of S-type granites and volcanic rocks in the Lachlan Fold Belt.

Source rocks of I- and S-type granites in the Lachlan Fold Belt, southeastern Australia

1984 ◽  
Vol 310 (1514) ◽  
pp. 693-707 ◽  
Keyword(s):  
Volcanic Rocks ◽  
Source Rocks ◽  
Low Grade ◽  
Fold Belt ◽  
Southeastern Australia ◽  
Deep Crust ◽  
Lachlan Fold Belt ◽  
Isotopic Evolution ◽  
Crustal Origin ◽  
Source Materials

Granites and related volcanic rocks derived from both igneous and sedimentary source materials (I- and S-types) are widely distributed in the Palaeozoic Lachlan Fold Belt of southeastern Australia. Many of the granites contain material residual from partial melting of the source rocks, or restite, which enables attempts to be made to calculate source rock compositions. A few of the S-type granites are closely related to regional metamorphic rocks and are of relatively local derivation. Most, however, are intrusive into low-grade rocks and came from deeper levels in the crust; and volcanic equivalents are extensively developed. These dominant S-type rocks have chemical and isotopic properties unlike any known locally exposed sediments. For most of the S-types, and perhaps all of them, no mantle-derived component was present in the source. Chemical and isotopic data on the I-type granites suggest a variety of deep crust sources consisting of mantle-derived material showing differing amounts of isotopic evolution, according to the time since extraction from the mantle. These data do not favour a significant sedimentary component in the sources of even the most isotopically evolved I-type rocks. An origin of the I-type source rocks by crustal underplating is favoured, so that these sources were generally infra-crustal, whereas the S-type sources were of supra-crustal origin.

Compositional variation within granite suites of the Lachlan Fold Belt: its causes and implications for the physical state of granite magma

1996 ◽  
Vol 87 (1-2) ◽  
pp. 159-170 ◽  
Author(s):  
B. W. Chappell
Keyword(s):  
Magma Mixing ◽  
Volcanic Rocks ◽  
Fractional Crystallisation ◽  
Source Rocks ◽  
Compositional Variation ◽  
Fold Belt ◽  
Significant Group ◽  
Lachlan Fold Belt ◽  
Compositional Variations ◽  
Felsic Rocks

ABSTRACT:Granites within suites share compositional properties that reflect features of their source rocks. Variation within suites results dominantly from crystal fractionation, either of restite crystals entrained from the source, or by the fractional crystallisation of precipitated crystals. At least in the Lachlan Fold Belt, the processes of magma mixing, assimilation or hydrothermal alteration were insignificant in producing the major compositional variations within suites. Fractional crystallisation produced the complete variation in only one significant group of rocks of that area, the relatively high temperature Boggy Plain Supersuite. Modelling of Sr, Ba and Rb variations in the I-type Glenbog and Moruya suites and the S-type Bullenbalong Suite shows that variation within those suites cannot be the result of fractional crystallisation, but can be readily accounted for by restite fractionation. Direct evidence for the dominance of restite fractionation includes the close chemical equivalence of some plutonic and volcanic rocks, the presence of plagioclase cores that were not derived from a mingled mafic component, and the occurrence of older cores in many zircon crystals. In the Lachlan Fold Belt, granite suites typically evolved through a protracted phase of restite fractionation, with a brief episode of fractional crystallisation sometimes evident in the most felsic rocks. Evolution of the S-type Koetong Suite passed at about 69% SiO2 from a stage dominated by restite separation to one of fractional crystallisation. Other suites exist where felsic rocks evolved in the same way, but the more mafic rocks are absent. In terranes in which tonalitic rocks formed at high temperatures are more common, fractional crystallisation would be a more important process than was the case for the Lachlan Fold Belt.

Origin of infracrustal (I-type) granite magmas

1988 ◽  
Vol 79 (2-3) ◽  
pp. 71-86 ◽  
Author(s):  
B. W. Chappell ◽  
W. E. Stephens
Keyword(s):  
Partial Melting ◽  
Subduction Zones ◽  
Chemical Weathering ◽  
Volcanic Rocks ◽  
Source Rocks ◽  
Fold Belt ◽  
Small Component ◽  
Lachlan Fold Belt ◽  
Fold Belts ◽  
Type Granite

ABSTRACTI-type granites are produced by partial melting of older igneous rocks that are metaluminous and hence have not undergone any significant amount of chemical weathering. In the Lachlan Fold Belt of southeastern Australia and the Caledonian Fold Belt of Britain and Ireland there was a major magmatic event close to 400 Ma ago involving a massive introduction of heat into the crust. In both areas, that Caledonian-age event produced large volumes of I-type granite and related volcanic rocks. Granites of these two areas are not identical in character but they do show many similarities and are markedly different from many of the granites found in Mesozoic and younger fold belts. These younger, dominantly tonalitic, granites have compositions similar to those of the more felsic volcanic rocks forming at the present time above subduction zones. The Palaeozoic granites show little evidence of such a direct relationship to subduction. Within both the Caledonian and Lachlan belts there are some granites with a composition close to the younger tonalites. A particularly interesting case is that of the Tuross Head Tonalite of the Lachlan Fold Belt, which can be shown to have formed from slightly older source rocks by a process that we refer to as remagmatisation which has caused no significant change in composition. Since remagmatisation has reproduced the former source composition in the younger rocks, the wrong inference would result from the use of that composition to deduce the tectonic conditions at the time of formation of the tonalite. Granites, particularly the more mafic ones, will generally have compositions reflecting the compositions of their source rocks, and attempts to use granite compositions to reconstruct the tectonic environment at the time of formation of the granite may be looking instead at an older event. This is probably also the case for some andesites formed at continental margins.Several arguments can be presented in favour of a general model for the production of I-type granite sources by underplating the crust, so that the source rocks are infracrustal. Such sources may contain a component of subducted sediments with the consequence that some of the compositional characteristics of sedimentary rocks may be present in I-type source rocks and in the granites derived from them. The small bodies of mafic granite and gabbro associated with island arc volcanism have an origin that can be related to the partial melting of subducted oceanic crust or of mantle material overlying such slabs and can be referred to as M-type. These rocks have compositions indistinguishable from those of the related volcanic rocks, except for a small component of cumulative material. The tonalitic I-type granites characteristic of the Cordillera are probably derived from such M-type rocks of basaltic to andesitic composition, which had been underplated beneath the crust. Some of the more mafic tonalites of the Caledonian-age fold belts may also have had a similar origin. More commonly, however, the plutonic rocks of the older belts are granodioritic and these probably represent the products of partial melting of older tonalitic I-type source rocks in the deep crust, these having compositions and origins analogous to the tonalites of the Cordillera. In this way, multiple episodes of partial melting, accompanied by fractionation of the magmas, can produce quite felsic rocks from original source rocks in the mantle or mantle wedge. These are essential processes in the evolution of the crust, since the first stages in this process produce new crust and the later magmatic events redistribute this material vertically without the addition of significant amounts of new crust.

18O/16O and D/H studies along a 500 km traverse across the Coast Range batholith and its country rocks, central British Columbia

1976 ◽  
Vol 13 (11) ◽  
pp. 1514-1536 ◽  
Author(s):  
Mordeckai Magaritz ◽  
Hugh P. Taylor Jr.
Keyword(s):  
British Columbia ◽  
Meteoric Water ◽  
Volcanic Rocks ◽  
Coast Range ◽  
Igneous Intrusions ◽  
Higher Temperature ◽  
Zone Ii ◽  
Host Rocks ◽  
Eastern Edge ◽  
Line Zone

Early Tertiary and Mesozoic ground waters in British Columbia were low in δ18O and δD, making it easy to document interactions of meteoric-hydrothermal H2O with the Coast Range plutons. The isotopic data on the igneous rocks can be grouped as follows:[Formula: see text]Zone I represents the gneissic migmatite core of the batholith, west of the quartz-diorite line. Zone II is the granodioritic eastern part of the batholith, and Zone III is a broad zone that includes the Jurassic Topley intrusions and extends from the eastern edge of the batholith to the Pinchi fault zone. Only in Zone I are isotopically 'normal' plutonic rocks found, and even there small amounts of meteoric water were apparently responsible for the late sericitization. All of the rocks in Zones II and III underwent widespread interaction with hot meteoric H2O, including the volcanic and sedimentary country rocks which have δD = −113 to −167 and δ18O = 1.9 to 10.8. Values of δD biotite < −140 are found in essentially all of the low-18O rocks, as well as in those that have 18O-zoned quartz or high Δ18Oqz–feld. Dike rocks have δD similar to their host rocks, but are typically lower in 18O (has the finer grain size facilitated exchange?). The batholithic intrusions apparently created gigantic meteoric-H2O circulation systems, larger than has heretofore been documented. The calculated δD of the H2O is −120 ± 20 assuming T = 500 to 200 °C, indicating that about 45–55 m.y. ago, the meteoric H2O had a uniform δD throughout the area. However, samples from the 140 m.y. old Topley intrusions suggest more D-rich waters, perhaps indicating a warmer climate in the Jurassic. These higher-temperature meteoric-hydrothermal effects are not found east of Pinchi Lake, a terrane that includes the Permian Cache Creek formation and various sediments, volcanic rocks, and blueschists that have δD = −65 to −117 and δ18O = 13.5 to 28.4. This area lacks igneous intrusions, so the meteoric H2O interactions in this area occurred at much lower temperatures than in Zones II and III (≈ 100 °C). Only the finest-grained rocks underwent partial D/H exchange with the meteoric waters responsible for local silicification, serpentinization, and vein carbonate deposition.

Late Ordovician island‐arc volcanic rocks, northern Capertee Zone, Lachlan Fold Belt, New South Wales

2003 ◽  
Vol 50 (3) ◽  
pp. 319-330 ◽  
Author(s):  
P. F. Carr ◽  
C. L. Fergusson ◽  
J. W. Pemberton ◽  
G. P. Colquhoun ◽  
S. I. Murray ◽  
...  
Keyword(s):  
New South ◽  
New South Wales ◽  
Volcanic Rocks ◽  
Late Ordovician ◽  
Island Arc ◽  
Fold Belt ◽  
South Wales ◽  
Lachlan Fold Belt

Age, geochemistry and Sr-Nd-Pb isotopic compositions of alkali volcanic rocks from Mt. Melbourne and the western Ross Sea, Antarctica

2015 ◽  
Vol 19 (4) ◽  
pp. 681-695 ◽  
Author(s):  
Mi Jung Lee ◽  
Jong Ik Lee ◽  
Tae Hoon Kim ◽  
Joohan Lee ◽  
Keisuke Nagao
Keyword(s):  
Ross Sea ◽  
Volcanic Rocks ◽  
Isotopic Compositions ◽  
Western Ross Sea

Petrogenesis of the peralkaline Flowers River Igneous Suite and its significance to the development of the southern Nain Batholith

2021 ◽  
pp. 1-26
Author(s):  
Taylor A. Ducharme ◽  
Christopher R.M. McFarlane ◽  
Deanne van Rooyen ◽  
David Corrigan
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Second Phase ◽  
Discrete Events ◽  
Volcanic Event ◽  
Volcanic Succession ◽  
Intrusive Suite ◽  
Tectonic Boundaries ◽  
Host Rocks ◽  
Nain Plutonic Suite

Abstract The Flowers River Igneous Suite of north-central Labrador comprises several discrete peralkaline granite ring intrusions and their coeval volcanic succession. The Flowers River Granite was emplaced into Mesoproterozoic-age anorthosite–mangerite–charnockite–granite (AMCG) -affinity rocks at the southernmost extent of the Nain Plutonic Suite coastal lineament batholith. New U–Pb zircon geochronology is presented to clarify the timing and relationships among the igneous associations exposed in the region. Fayalite-bearing AMCG granitoids in the region record ages of 1290 ± 3 Ma, whereas the Flowers River Granite yields an age of 1281 ± 3 Ma. Volcanism occurred in three discrete events, two of which coincided with emplacement of the AMCG and Flowers River suites, respectively. Shared geochemical affinities suggest that each generation of volcanic rocks was derived from its coeval intrusive suite. The third volcanic event occurred at 1271 ± 3 Ma, and its products bear a broad geochemical resemblance to the second phase of volcanism. The surrounding AMCG-affinity ferrodiorites and fayalite-bearing granitoids display moderately enriched major- and trace-element signatures relative to equivalent lithologies found elsewhere in the Nain Plutonic Suite. Trace-element compositions also support a relationship between the Flowers River Granite and its AMCG-affinity host rocks, most likely via delayed partial melting of residual parental material in the lower crust. Enrichment manifested only in the southernmost part of the Nain Plutonic Suite as a result of its relative proximity to multiple Palaeoproterozoic tectonic boundaries. Repeated exposure to subduction-derived metasomatic fluids created a persistent region of enrichment in the underlying lithospheric mantle that was tapped during later melt generation, producing multiple successive moderately to strongly enriched magmatic episodes.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

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