S-type Suite Research Articles

Crustal anatexis in the Aouli-Mibladen granitic complex: A window into the middle crust below the Moroccan Eastern Variscan Meseta

The Moroccan Variscan belt comprises numerous granitoid bodies, which have been isotopically studied, but still lack a detailed petrogenetic model. The Variscan Aouli-Mibladen granitic complex in the Moroccan Eastern Meseta provides an excellent opportunity for studying the petrogenesis and the relationship with adjacent Cambro-Ordovician metasediments. This region exposes mainly M-to I-type metaluminous mafic to granitic bodies as well as migmatites and peraluminous S-type anatectic granites. An exceptional xenoliths and garnets cumulate deposit covers an area of ∼2 km2 located NE of the complex. The S-type suite includes cordierite bearing microgranite dykes and two small two-mica leucogranitic stocks, crosscutting the eastern metamorphic aureole of the complex.Petrological analysis shows that biotite dehydration melting reactions produced anatectic melt and peritectic cordierite and garnet. Garnet shows complex zoning profiles, with typical prograde growth zoning in the core, and resorption and reprecipitation rims. Peritectic cordierite (XFe = 0.37) is associated with restitic biotite (XFe = 0.65), whereas abundant cotectic cordierite (XFe = 0.65) belongs to the granites paragenesis (Bt + Kfs + Pl + Crd + Qtz). Garnet crystals are also frequently mantled by a retrograde cordierite type.Thermodynamic modelling shows that biotite dehydration melting took place under granulitic facies conditions (830–870 °C and 6 kbar), producing a significant amount of peraluminous melts. Their ascent and emplacement led to the S-type suite of the Aouli-Mibladen complex, including the local xenolith-cumulate deposit. We envisage a petrogenetic model during the Variscan orogeny, in which mantle derived mafic magmas stagnated in large reservoirs at 18–20 km depth, causing isobaric heating and partial melting of the surrounding metapelitic protolith. Differentiated M-I-type and S-type magmas were emplaced at higher levels concomitantly, with limited mixing and mingling during their final crystallization, at a depth of 9–10 km leading to contact metamorphism (600 °C, 3 kbar). These findings open a window into the hitherto unknown Moroccan Variscan mid-crust and permit to discuss the nature and age of the underlying basement terranes.

The U-Pb age, geochemistry and tectonic significance of granitoids in the Soursat Complex, Northwest Iran

The Soursat Complex in northwestern of Iran is part of the Sanandaj-Sirjan metamorphic belt. Three granitoid suites are present: Type I- syenogranite and deformed syenogranite; Type II- Turkeh Dare and Pichagchi plutons; and Type III- quartz porphyry. The granites can be assigned to a medium-K calc-alkaline to high-K calc-alkaline series. The Type I granitoids are weakly to strongly peraluminous and belong to a S-type suite, whereas Type II plutons are metaluminous to weakly peraluminous with I-type character. Type III granitoids are weakly peraluminous and can be labelled as a highly fractionated I-type suite. U/Pb zircon dating of the syenogranite and deformed syenogranite from Type I and Type II granitoids by laser inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded ^{238}U/^{206}Pb emplacement ages of ~540 Ma (543±6 Ma and 537±8 Ma) and 59.0±2.7 Ma, respectively. Rare Earth Elements in the Type I granitoids are strongly fractionated with (La/Lu)_N= 32 to 52 and negative Eu anomalies (Eu/Eu*= 0.09-0.72), typical for plagioclase fractionation; the primitive mantle-normalized element patterns are homogeneous with marked negative Ba, Nb, Ta, Sr and Eu anomalies. Based on geochemical data, Type I granitoids are formed in a continent-continent collision, which could be related to Cadomian collision along the northern margin of Gondwana after its final amalgamation. Types II and III granitoids have I-type affinities and show homogeneous and moderately fractionated REE patterns with (La/Lu)_N= 17-34. Primitive mantle-normalized element patterns are homogeneous with marked negative Nb, Ta, Sm and Ti anomalies. The Soursat Complex is shown to contain early- to syn-collisional granitoid magmatism of Ediacaran-Cambrian age and a subsequent group of Palaeocene I-type granitoids that are syn- to post-collisional with respect to the Arabia-Eurasia collision and are interpreted to represent roll-back during the closure of Neotethys, pre-dating the Arabia-Eurasia collision.

U-Pb geochronology of mid-Paleozoic plutonism in western New Zealand: Implications for S-type granite generation and growth of the east Gondwana margin

Research Article| September 01, 2009 U-Pb geochronology of mid-Paleozoic plutonism in western New Zealand: Implications for S-type granite generation and growth of the east Gondwana margin A.J. Tulloch; A.J. Tulloch † 1GNS Science, Private Bag 1930, Dunedin 9054, New Zealand †E-mail: a.tulloch@gns.cri.nz Search for other works by this author on: GSW Google Scholar J. Ramezani; J. Ramezani 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar D.L. Kimbrough; D.L. Kimbrough 3Department of Geological Sciences, San Diego State University, San Diego, California 92182, USA Search for other works by this author on: GSW Google Scholar K. Faure; K. Faure 4GNS Science, P.O. Box 30368, Lower Hutt 5040, New Zealand Search for other works by this author on: GSW Google Scholar A.H. Allibone A.H. Allibone 5Rodinian Pty Ltd., P.O. Box 1970, Queanbeyan, NSW 2620, Australia Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (9-10): 1236–1261. https://doi.org/10.1130/B26272.1 Article history received: 16 Jun 2007 rev-recd: 07 Aug 2008 accepted: 12 Aug 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A.J. Tulloch, J. Ramezani, D.L. Kimbrough, K. Faure, A.H. Allibone; U-Pb geochronology of mid-Paleozoic plutonism in western New Zealand: Implications for S-type granite generation and growth of the east Gondwana margin. GSA Bulletin 2009;; 121 (9-10): 1236–1261. doi: https://doi.org/10.1130/B26272.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract New U-Pb isotope-dilution–thermal ionization mass spectrometry (ID-TIMS) ages (371–305 Ma) for 30 granitic plutons along the New Zealand sector of the East Gondwanan active margin reveal a highly episodic emplacement history and crustal growth pattern. The Late Devonian–late Carboniferous ages also establish specific links with both the mostly older, Lachlan and the mostly younger, New England fold belts of eastern Australia. Dated plutons are representative of two S- and I-type suite pairs, the volumetrically predominant Karamea-Paringa (371–360 Ma) and minor Ridge-Tobin (355–342 Ma) pulses, as well as sporadic Foulwind Suite A-type granites (350–305 Ma). Emplacement of the bulk of the dominant ~3400 km2 Karamea Suite S-type granite-granodiorite plutons within a 2.1 Ma interval is explained by major and intimate intrusion of mantle-derived magma into largely metasedimentary crust during intra-arc extension of previously overthickened crust. Transient emplacement rates were thus of similar magnitude as some young ignimbrite flare-ups and an order of magnitude greater than long-term averages for Mesozoic-Cenozoic cordilleran batholiths of the western Americas. Extension likely was terminated abruptly by resumption of convergence, possibly associated with amalgamation of the Buller and Takaka terranes, between 368 and 355 Ma. Significant crustal growth occurred during generation of the two S-type suites, where mantle basalt contributed mass, and heat for rapid melting, during transient intra- or backarc extensional episodes. In contrast, the I-type suites were dominated by partial melting of meta-igneous crust, and they are relatively small in volume. The Karamea S-type suite shares striking similarities in terms of age, composition, and extensional tectonic setting with S-type granites of the Melbourne terrane of the Lachlan fold belt. Both regions may have formed in a backarc position with respect to the Late Devonian–early Carboniferous subduction zone in the New England fold belt. Foulwind Suite A-type magmatism in New Zealand overlaps in age with the widespread 320–285 Ma A- and I-type magmatism in the northern New England fold belt. The likely continuation of the New England subduction system must have subsequently been removed from outboard of the New Zealand region after 320–285 Ma magmatism, and prior to Triassic accretion of a Permian oceanic arc terrane to the New Zealand margin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemistry of the Bafoussam Pan-African I- and S-type granitoids in western Cameroon

The Bafoussam area in western Cameroon is part of the Central African Orogenic Belt. It is dominated by granitoids which belong to the Pan-African syn- to post-collisional post-650 Ma group. Syenogranites are predominant, but alkali-feldspar granite, monzogranite, quartz-monzonite and quartz-monzodiorite occur as well. Four granitoid suites, biotite granitoids and deformed biotite granitoids with amphibole, megafeldspar granitoids with megacrysts and two-mica granitoids with primary muscovite and igneous garnet are distinguished. The granites can be assigned to high-K calc-alkalic to shoshonitic series. The partly shoshonitic biotite granitoids are metaluminous to weakly peraluminous and can be labelled as a highly fractionated I-type suite. The megafeldspar granitoids are weakly peraluminous with I-type character whereas the two-mica granitoids are weakly to strongly peraluminous and belong to an S-type suite. Emplacement ages at 558–564 Ma for the two-mica granitoids have been dated from monazite by the EMP Th–U–Pb method. The REE in the biotite granitoids are moderately fractionated with (La/Lu) N = 23–38. Enrichment of Nb and Ta varies by one order of magnitude. The megafeldspar granitoids show homogeneous and strongly fractionated REE patterns with (La/Lu) N = 27–42. The primitive mantle-normalized element patterns are homogeneous with marked negative Ba, Nb, Ta, Sr, Eu and Ti anomalies. The two-mica granitoids are characterized by low to moderate total REE contents with strongly fractionated REE expressed by (La/Lu) N ranging from 7 to 59. The negative Nb and Ta anomalies are less significant. Nd and Sr whole-rock isotope data confirm different sources for the granitoid suites. The source of the I-type biotite granitoids was probably a juvenile mantle which has been variably metasomatized. The source of the I-type megafeldspar granitoids is characterized by juvenile mantle and lower crust components. Anatectic melts of the upper continental crust with variable contribution of lower continental crust or mantle melts can explain the heterogeneous isotopic signatures of the S-type two-mica granitoids. It is suggested that the melting of these sources was successively initiated by the rising isotherms during a syn- to post-collisional setting which followed a subduction.

Geochemical and Nd-Pb-O isotope systematics of granites from the Taltson Magmatic Zone, NE Alberta: implications for early Proterozoic tectonics in western Laurentia

The early Proterozoic Taltson Magmatic Zone (TMZ) comprises the southern part of the Taltson-Thelon orogenic belt of northwestern Canada. The TMZ is dominated by 1.96–1.99-Ga I-type and 1.93–1.95-Ga S-type suites of granitoids. Previous workers attributed the formation of the I-type granitoids to subduction of oceanic crust beneath the Churchill craton in an Andean-type setting, and generation of the S-type granitoids to subsequent collision between the Churchill craton and the Buffalo Head Terrane. To test this hypothesis, we carried out a geochemical and isotopic (Nd, Pb and O) study of granitoids and associated metasedimentary rocks and basement gneisses from the southern part of the TMZ. Both I- and S-type suites of granitoids are characterized by relatively high SiO 2 content, with the great majority of samples containing more than 64 wt.% SiO 2. The two suites also have strongly crustal εNd (T) values of −3.8 to −9.8 and an average T DM of 2.8 Ga. The initial Pb isotope composition of the granitoids as determined from leached feldspar mineral separates forms a linear array that is bracketed by the isotopic compositions of basement orthogneisses and metasediments. Similarly, δ 18O values of the granitoids overlap those of the orthogneisses and metasediments. These isotopic data are consistent with derivation of the granitoids from a mixture of metaigneous and metasedimentary source rocks similar to those presently exposed in the TMZ. Importantly, the data suggest that both I- and S-type granitoids of the southern TMZ had an exclusively intra-crustal origin unlike Phanerozoic examples of subduction-related magmatism where a significant mantle contribution is easily recognized. Therefore, we argue that the existing Andean-type model for early TMZ magmatism is not viable. The TMZ granitoids show geochemical and isotopic similarities to the Cordilleran interior granitoids of western North America, which formed in response to crustal thickening in the distant hinterland of a convergent plate margin. We propose that these hinterland granitoids are a more appropriate analogue for TMZ magmatism than are the granitoids of plate margins. The tectonic implication of this proposal is that the Taltson-Thelon orogenic belt does not mark the location of the plate boundary in western Laurentia at 1.9–2.0 Ga. Rather, the tectonic setting of the TMZ at that time may have been more akin to the present-day intra-continental mountain belts of central Asia (e.g. Tian Shan Mountains) where compressional tectonism and crustal thickening are occurring well inboard from a convergent plate margin.

Calculated melt and restite compositions of some Australian granites

ABSTRACTThe thermodynamic relations embodied in the Quasicrystalline Model of Burnham and Nekvasil (1986), as recently extended by the author, have been used to quantitatively assess the feldspar-quartz liquidus relations in two I-type (Jindabyne and Moruya) and two S-type (Bullenbalong and Dalgety) suites of Australian granites, using analytical data provided by B. W. Chappell and co-workers. Among the more notable results obtained from these calculations at a constant pressure of 5·0kbar and = 0·30 (≍2·8 wt% H2O), for purposes of comparison, are that: (1) felsic melts of remarkably uniform, but distinctive composition can be extracted from each suite, leaving solid residues in amounts up to 65 mol%; (2) all melts from both S-type suites have two feldspars plus quartz on their liquidii, whereas both I-type suites have only plagioclase plus quartz on their liquidii; (3) the total solid residue ranges from 27-63% in the Jindabyne suite, from 15–62% in the Moruya suite, from 30–65% in the Bullenbalong suite, and from 27–65% in the Dalgety suite; (4) liquidus temperatures of the S-type Bullenbalong and Dalgety melts are similar (856° and 860°C), reflecting similar feldspar compositions of An53, Or75 and An60, Or77, respectively; (5) liquidus temperatures of the I-type Jindabyne and Moruya melts, however, are distinctly different (950° and 894°C), reflecting correspondingly different plagioclase compositions of An80 and An52; (6) the calculated liquidus plagioclase composition throughout a given suite is very uniform (±1%) and amounts to as much as 46% of the total rock; and (7) these calculated liquidus and residual plagioclase compositions are also the same, within the uncertainty of measurement, as those of the plagioclase crystal-cores determined optically by A. J. R. White. The only plausible explanation for this remarkable consanguinity in plagioclase liquidus, residue, and crystal-core compositions, hence liquidus temperatures, is that the bulk of the residue is restite, in accordance with the model of White and Chappell (1977). This explanation is corroborated by the very systematic variations in the amounts of individual restite minerals with respect to total restite contents. Accordingly, those members of each suite that contain more than 60% total restite probably closely represent the bulk composition of the source rock, which is dioritic or andesitic for the Jindabyne suite, tonalitic or dacitic for the Moruya suite, pelitic metagreywacke for the Bullenbalong suite, and feldspathic metagreywacke for the Dalgety suite. As a corollary, those members with less than 60% restite must have undergone melt-restite segregation (unmixing), probably during ascent and emplacement.