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Tonalite

Tonalite is an intrusive igneous rock of intermediate composition, characterized by the presence of quartz (typically 20–60% of the felsic minerals), abundant plagioclase feldspar (oligoclase or andesine), and mafic minerals such as hornblende, biotite, or pyroxene, with alkali feldspar comprising less than 10% of the total feldspars.^[1]^[2]^[3] Named after the Tonale Pass in the Adamello massif of the Italian and Austrian Alps, where it was first described, tonalite forms through the slow crystallization of silica-rich magma in plutons deep within the Earth's crust, often associated with subduction zones and convergent plate boundaries.^[2]^[3] Its phaneritic texture results from this gradual cooling, producing a coarse-grained, "salt-and-pepper" appearance due to the contrasting colors of light-colored quartz and plagioclase against darker mafic minerals.^[1]^[3] Tonalite occupies an intermediate position in the QAPF classification diagram for plutonic rocks, bridging diorite (with less quartz) and granodiorite (with more alkali feldspar), and its extrusive equivalent is dacite.^[1] Varieties include trondhjemite (low in mafic minerals) and melatonalite (high in mafic minerals), with accessory minerals like magnetite, apatite, and zircon commonly present.^[1]^[3] Globally, tonalite occurs in batholiths and plutonic complexes within orogenic belts, such as the Sierra Nevada Batholith in California, the Coast Range Batholith in British Columbia, Precambrian formations in Minnesota, and regions in Norway, Greece, and Antarctica.^[1]^[2] Due to its durability, moderate density, and resistance to weathering, it is valued in construction for dimension stone, aggregates, and architectural elements, though it is less common than granite.^[3]

Etymology and Definition

Naming History

The term "tonalite" originates from the Tonale Pass (Passo del Tonale) in the Adamello massif, located in the border region of the Italian and Austrian Alps. German geologist Gerhard vom Rath first applied the name in 1864 to describe a coarse-grained igneous rock he examined from samples collected during his expedition to this area, noting its distinct mineral composition dominated by plagioclase feldspar and quartz.^[4]^[5] In early geological literature, "tonalite" served as a synonym for quartz diorite, reflecting its intermediate silica content and mineral assemblage similar to diorite but with significant quartz. This usage persisted into the early 20th century, as seen in descriptions equating the two rock types based on their plutonic nature and feldspar-plagioclase balance.^[6] The nomenclature evolved in the late 19th century to refine distinctions among granitic rocks, particularly separating tonalite from granodiorite. Austrian geologist A. Cathrein introduced "adamellite" in 1890 for orthoclase-bearing varieties of tonalite from Monte Adamello, which were later recognized as granodiorites due to higher potassium feldspar content; this term is now deprecated and largely reserved for quartz monzonite.^[7] By this period, tonalite became standardized for rocks with sodic plagioclase exceeding potassium feldspar, aiding clearer petrographic classification. In contemporary frameworks like the IUGS QAPF diagram, tonalite is precisely defined by its modal mineralogy.^[8]

Petrographic Characteristics

Tonalite is defined as a phaneritic, intrusive igneous rock of felsic to intermediate composition, characterized by a coarse-grained texture with crystal sizes typically exceeding 3 mm, making individual minerals visible to the naked eye.^[8] According to the International Union of Geological Sciences (IUGS) classification, it occupies QAPF Field 5 on the modal mineralogy diagram, where the sum of quartz (Q), alkali feldspar (A), and plagioclase (P) is recalculated to 100%, with quartz comprising more than 20% and up to 60% of this total.^[8] Plagioclase dominates the feldspar content, making up over 90% of the total feldspar, and is typically oligoclase or andesine with an anorthite content of An₃₀–An₅₀.^[8] The texture of tonalite is generally equigranular, with subhedral to anhedral grains of roughly equal size, though porphyritic varieties occur where larger phenocrysts of plagioclase or quartz are set in a finer groundmass.^[9] Mafic enclaves, often microgranular and irregular in shape, are commonly incorporated within the rock, reflecting magma mingling processes during emplacement.^[10] These enclaves contribute to a heterogeneous appearance but do not alter the overall modal classification. Tonalite is distinguished from quartz diorite primarily by its higher quartz content; while tonalite requires greater than 20% quartz in the QAPF framework, quartz diorite falls into Fields 9* or 10* with 5–20% quartz and a higher proportion of mafic minerals relative to the total volume.^[8] This distinction ensures precise categorization within plutonic rock suites, emphasizing tonalite's more evolved, silica-rich nature.^[8]

Mineralogy

Essential Minerals

Tonalite's essential minerals define its intermediate composition and granitic texture, consisting primarily of plagioclase feldspar, quartz, and mafic silicates, with limited alkali feldspar. According to the International Union of Geological Sciences (IUGS) classification, tonalite occupies QAPF field 5, requiring quartz to comprise at least 20% but no more than 60% of the total quartz + alkali feldspar + plagioclase + feldspathoid volume, while plagioclase must exceed 90% of the combined feldspars, limiting alkali feldspar to less than 10%.^[8] These proportions ensure tonalite's distinction from related rocks like granodiorite, which has more abundant alkali feldspar. The mafic mineral content is typically less than 90% overall, allowing the felsic components to dominate.^[11] Plagioclase feldspar is the most abundant essential mineral in tonalite, usually forming 40-70% of the rock's volume and appearing as white to gray, tabular or lath-shaped crystals.^[12] It is typically sodic, with compositions ranging from oligoclase (An_{10-30}) to andesine (An_{30-50}), contributing to the rock's light coloration and hypidiomorphic granular texture.^[8] These plagioclase grains often exhibit zoning, with more calcic cores and sodic rims, reflecting fractional crystallization processes.^[2] Quartz constitutes 20-50% of tonalite and occurs as anhedral, interlocking grains that fill spaces between feldspars, enhancing the rock's cohesive, phaneritic fabric.^[12] This mineral imparts translucency and hardness, with grains commonly showing undulatory extinction under crossed polars due to deformation.^[2] The mafic minerals, making up 15-25% of the volume, provide tonalite's characteristic speckled or salt-and-pepper appearance through dark green to black crystals that contrast with the lighter felsics.^[13] Hornblende, a calcic amphibole, is the predominant mafic phase, often forming prismatic crystals with pleochroic halos; it is accompanied by biotite mica, which appears as flaky, brown to black plates.^[2] These minerals together account for the rock's moderate color index (10-40% dark minerals).^[12] Alkali feldspar is a minor essential component, present in amounts less than 5-10%, and typically manifests as perthitic intergrowths of orthoclase or microcline with albite, occurring as irregular patches or stringers within plagioclase.^[11] This limited abundance underscores tonalite's sodium-rich, potassic-poor nature compared to granites.^[8]

Accessory and Alteration Minerals

In tonalite, accessory minerals occur in minor amounts and include apatite, zircon, titanite (also known as sphene), and opaque phases such as magnetite and ilmenite. These minerals typically form small, disseminated crystals that do not significantly influence the rock's texture or classification but provide insights into its crystallization history. Apatite and zircon are common inclusions within major silicates, while titanite often appears as wedge-shaped grains associated with mafic components. Opaque minerals contribute to the rock's magnetic properties and may reflect early magmatic oxidation conditions.^[14]^[15] Less common accessory minerals in tonalite include allanite and monazite, which are typically found in specific geochemical environments rich in rare earth elements. Allanite occurs as elongated prisms, often metamict due to radiation damage from thorium and uranium content, and is more prevalent in calc-alkaline tonalites. Monazite, a phosphate mineral, is rarer and appears in accessory quantities in some evolved tonalitic magmas, aiding in geochronological studies. These rare phases highlight variations in magma source and differentiation processes.^[16]^[17] Alteration minerals in tonalite result from hydrothermal activity, weathering, or low-grade metamorphism, modifying the primary assemblage. Sericite, a fine-grained mica, commonly replaces plagioclase through sericitization, leading to a flaky texture in affected zones. Chlorite forms as a secondary phyllosilicate from the alteration of biotite, often imparting a greenish hue to the rock. Epidote develops from hornblende or plagioclase in propylitic alteration settings, appearing as pistacite-rich varieties that fill fractures or rims. These changes reduce the rock's coherence, potentially decreasing durability in engineering applications.^[18]^[19] The presence of alteration minerals can significantly impact tonalite's visual and physical properties. Oxidation of mafic minerals like biotite and hornblende produces iron oxides (such as hematite or limonite), resulting in reddish tones that contrast with the fresh rock's typical gray to dark gray color. This weathering effect enhances susceptibility to further breakdown, influencing the rock's use in construction where altered varieties may exhibit reduced strength.^[20]^[21]

Petrogenesis

Formation Processes

Tonalite primarily forms through partial melting of hydrated basaltic or gabbroic rocks in the lower crust of subduction zone settings, where fluids released from the subducting slab promote dehydration melting at depths of 20–50 km and temperatures of 750–950°C.^[22] This process generates intermediate to felsic magmas with sodic compositions, distinguishing tonalite from more mafic arc rocks.^[23] In these environments, partial melting typically involves 20–30% of the source material, leaving behind an amphibolite or eclogite residue that retains heavy rare earth elements.^[23] Within the calc-alkaline differentiation series characteristic of continental arcs, tonalitic magmas evolve from more mafic parents, such as diorites, through fractional crystallization dominated by amphibole and plagioclase.^[24] This fractionation, which can account for up to 27% crystallization, enriches the residual melt in silica while suppressing iron enrichment typical of tholeiitic series, resulting in the quartz-plagioclase-hornblende assemblage of tonalite.^[24] The early crystallization sequence favors amphibole over pyroxene due to elevated water content in the magma, influencing the overall mineralogy.^[24] These magmas intrude as batholiths or smaller stocks during orogenic events at convergent margins, where tectonic compression facilitates ascent through the crust.^[25] Emplacement occurs via diapiric rise or conduit filling, often interacting with wall rocks to produce hybrid compositions, and the intrusions cool slowly over millions of years as heat dissipates through conduction and hydrothermal circulation.^[26] This prolonged cooling allows for the development of coarse-grained textures and supports the stabilization of the continental crust.^[25] In Archean crust formation, tonalite plays a central role as a component of tonalite-trondhjemite-granodiorite (TTG) suites, generated by partial melting of hydrous mafic rocks, such as metabasalts or gabbroic sources, at depths of 20–50 km or greater in thickened crust or subduction-related settings.^[23] These processes produce low-density, silica-rich melts that form the protocontinental crust between 3.7 and 2.9 Ga, contributing to the dominant grey gneiss terranes.^[25] These processes were particularly effective prior to 2.9 Ga, when simpler melting of metabasalts without extensive fractionation built the foundational sialic crust.^[25]

Geochemical Signatures

Tonalite magmas are defined by a major element composition that places them in the intermediate to felsic range, with SiO₂ contents typically between 63 and 70 wt%. This silica range distinguishes tonalite from more mafic diorites while aligning it closely with dacitic compositions in volcanic equivalents. Na₂O levels are characteristically elevated at 3–5 wt%, reflecting the dominance of sodic plagioclase in the mineral assemblage, whereas K₂O remains low at less than 3 wt%, resulting in a K₂O/Na₂O ratio often below 0.5. Al₂O₃ is notably high, frequently exceeding 16 wt%, which contributes to the peraluminous to metaluminous nature of these rocks and supports the stability of aluminous phases like plagioclase.^[27]^[28]^[29] In contrast to potassic granites, which exhibit higher K₂O/Na₂O ratios greater than 1, tonalite's lower ratio underscores its sodic affinity and derivation from sources with limited potassium enrichment. This distinction is evident in classification schemes where tonalite plots in the low-K calc-alkaline series, avoiding the perpotassic fields occupied by many granitic rocks. The overall major element budget, including moderate CaO (around 4–6 wt%) and MgO (1–3 wt%), further highlights the role of amphibole and plagioclase fractionation in tonalite evolution.^[29]^[27] Trace element patterns in tonalite are marked by enrichment in light rare earth elements (LREE), with La/Yb ratios often exceeding 10, coupled with negative anomalies in Nb and Ta on primitive mantle-normalized spider diagrams. These features are ubiquitous in arc-derived magmas and arise from subduction zone processes involving fluid-mediated addition of incompatible elements from the slab. High field strength elements like Zr and Hf show moderate enrichment, while large ion lithophile elements (LILE) such as Ba and Sr are elevated, reinforcing the subduction imprint.^[30]^[31] Isotopic compositions provide evidence for crustal involvement in tonalite petrogenesis, with elevated ⁸⁷Sr/⁸⁶Sr ratios (often 0.705–0.710) and variable εNd values ranging from -5 to +5 in modern arc settings, indicating mixing between depleted mantle sources and continental crust. These Sr-Nd systematics reflect assimilation or contamination during magma ascent, particularly in continental arcs where older crustal material imparts radiogenic signatures. In oceanic arcs, εNd tends toward positive values closer to +5, while continental settings shift toward negative, highlighting tectonic context.^[32]^[33]

Geological Occurrence

Global Distribution

Tonalite occurrences are widespread globally, spanning all continents and forming a significant component of continental crust from Archean to Cenozoic times.^[3] These rocks are particularly abundant in Phanerozoic orogenic belts associated with convergent margins, where they contribute to large batholithic complexes.^[34] In Phanerozoic settings, tonalite is common in major Cordilleran batholiths, with peak emplacement during the Mesozoic and Cenozoic. The Sierra Nevada Batholith in California, USA, exemplifies this, dominated by tonalite and granodiorite plutons emplaced primarily between 120 and 80 Ma during arc magmatism.^[35] Similarly, in the Andes of South America, tonalite forms key parts of coastal and north Patagonian batholiths, such as the Peruvian Coastal Batholith and the Varvarco Tonalite in the Cordillera del Viento, with ages ranging from Jurassic to Miocene.^[36]^[37] In Europe, the Variscides host post-collisional tonalite intrusions dated to c. 310–290 Ma.^[38] Archean examples are prominent in ancient cratons, often as part of tonalite-trondhjemite-granodiorite (TTG) complexes formed between 3.5 and 2.5 Ga. In the Superior Province of Canada, tonalite suites dominate the Wabigoon and Abitibi subprovinces, with key emplacements around 2.71–2.67 Ga.^[39]^[22] In Minnesota, USA, the Saganaga tonalite (~2.69 Ga) occurs in Precambrian greenstone-granite terranes of the Superior Province.^[40] The Pilbara Craton in Australia preserves TTG tonalites from 3.5 to 2.8 Ga, reflecting early crustal growth in the East Pilbara Granite-Greenstone Terrane.^[41] In Norway, mafic-tonalitic-trondhjemitic gneisses form part of the Precambrian Tromøy Gneiss Complex.^[42] Notable specific localities include the type area at Tonale Pass in the Italian Alps, where tonalite was first described adjacent to the Tonale Line structural feature during the early 19th century.^[2] In the Pyrenees, the Roc de la Calme tor represents a Hercynian-age (ca. 300 Ma) tonalite outcrop within the Mont-Louis-Andorra pluton.^[43] In Greece, tonalites are present in the Hercynian Pieria Granitoid Complex.^[44] Overall, tonalite ages range from Archean (up to 3.5 Ga) to recent Cenozoic events, with the highest volumes in Cordilleran-style orogenic belts.^[34] In Antarctica, the Tonalite Belt of North Victoria Land represents Early Paleozoic arc magmatism.^[45]

Tectonic Associations

Tonalite is predominantly emplaced in continental arcs above subduction zones, where it forms a key component of calc-alkaline batholiths generated at convergent oceanic-continental margins during Proterozoic and Phanerozoic times.^[34] These settings involve mantle-derived mafic magmas interacting with wall rocks in the lower crust, leading to the production of tonalitic melts that constitute 5-10% of the resulting crustal volume.^[34] Tonalites typically appear as minor to prominent members within mafic-to-siliceous sequences in these arc-related batholiths, often intruding and assimilating older continental crust to contribute to crustal growth.^[34] Tonalites are closely associated with volcanic arcs and back-arc basins in subduction environments, where they intrude as plutons within the arc crust, reflecting ongoing tectonic extension and magmatism behind the main volcanic front.^[46] In such regions, tonalitic magmas pool and differentiate in the mid-to-lower crust, sometimes linked to extension in back-arc settings that facilitate magma ascent.^[47] While rare in anorogenic settings, such as intraplate rifting or non-subduction-related extension, tonalites are more commonly observed in collisional orogens, including the Himalayan system, where they form during continental convergence and crustal thickening.^[48]^[49] During emplacement, tonalites are frequently linked to regional metamorphism and deformation, as their formation involves partial melting of metabasaltic rocks in down-buckled greenstone belts or thickened crust under compressional tectonics.^[34] This process often occurs amid intense orogenic deformation, with tonalitic intrusions remobilizing older gneisses and contributing to the structural evolution of the orogen through syn-tectonic crystallization and fabric development.^[34] In collisional contexts like the Himalayas, such associations highlight tonalite's role in accommodating strain during plate convergence.^[49]

Classification and Varieties

Rock Classification Schemes

Tonalite is classified as a plutonic igneous rock within the International Union of Geological Sciences (IUGS) modal scheme using the QAPF diagram, which plots the relative proportions of quartz (Q), alkali feldspar (A), plagioclase (P), and feldspathoids (F) after normalizing to 100% excluding mafic minerals (M < 90%). In this system, tonalite corresponds to field 5, characterized by Q ranging from 20% to 60%, A 0–5%, the balance plagioclase (P ≈ 35–80%), and F = 0%, positioning it intermediate between diorite (fields 10-12, lower Q) and granite (field 1, higher A). This modal approach relies on thin-section point counting or visual estimates for field identification, emphasizing mineral proportions over chemical composition. The Streckheisen classification, adopted by the IUGS in the 1970s, further distinguishes tonalite from granodiorite (field 3-4) based on plagioclase dominance, where tonalite requires plagioclase to exceed 90% of total feldspar (P/(A + P) > 90), reflecting its sodic to intermediate plagioclase (oligoclase to andesine) and minimal alkali feldspar such as orthoclase or microcline. In contrast, granodiorite allows 65-90% plagioclase with more balanced feldspar ratios. This criterion ensures precise nomenclature for felsic-intermediate rocks in orogenic settings. For volcanic equivalents, such as tonalitic andesite or quartz andesite, the chemical total alkali-silica (TAS) diagram is employed when modal data are unavailable due to fine-grained textures, plotting Na₂O + K₂O (wt%) against SiO₂ (wt%). Tonalitic compositions typically fall within the andesite (52-63% SiO₂) to dacite (63-69% SiO₂) fields, with total alkalis around 3-6 wt%, providing a geochemical proxy aligned with QAPF modal classes. Historically, tonalite classification evolved from qualitative field-based descriptions in the 19th century, such as "quartz diorite" by early petrographers like Rath (1864) and Zirkel (1866), to quantitative modal criteria formalized by Streckeisen (1967, 1976) and the IUGS subcommission (1973-1989), which resolved ambiguities in feldspar ratios and discouraged obsolete terms like "adamellite." This shift prioritized reproducible mineralogic analysis, integrating historical usage with modern petrography for global consistency. Tonalite exhibits several distinct varieties defined by variations in mineral composition and color index. Trondhjemite is a leucocratic, sodic variant of tonalite, primarily composed of sodic plagioclase (oligoclase to albite, with An<30), quartz, and minor biotite or hornblende (<10% mafics), but lacking orthoclase or other K-feldspar minerals.^[8] Leucotonalite represents a light-colored, felsic end-member with low mafic content (color index <5) and elevated quartz and plagioclase proportions, often overlapping with trondhjemite in composition.^[50] Tonalite relates closely to other intermediate plutonic rocks within granitic suites, particularly along compositional continua in batholiths. Granodiorite differs by incorporating more alkali feldspar relative to plagioclase, shifting the feldspar balance toward higher K-content while retaining quartz and mafic minerals like biotite and hornblende.^[8] Quartz diorite contains less quartz (typically 5-20%) than tonalite and features more calcic plagioclase (andesine to labradorite), with prominent mafic phases such as hornblende or pyroxene.^[8] Diorite, in contrast, lacks quartz entirely, relying on intermediate plagioclase and abundant mafic minerals for its darker tone and coarser texture.^[8] These relationships are delineated by QAPF modal boundaries, where tonalite occupies field 5.^[8] The volcanic counterpart to tonalite is dacite, an extrusive rock with comparable silica content (63-69%) and mineral assemblage, including plagioclase, quartz, and minor biotite or amphibole in a porphyritic or aphanitic groundmass.^[51] Metamorphosed tonalite yields gneissic variants, such as tonalitic gneiss, where original plutonic textures are overprinted by foliation and banding under high-grade regional metamorphism, preserving the quartz-plagioclase-mica assemblage in layered form.^[25] These gneisses commonly occur in Archaean terranes, exemplifying crustal recycling processes.^[25]

Significance

Economic Uses

Tonalite is valued as a dimension stone in construction due to its durability, coarse-grained texture, and typically light gray color, making it suitable for building facades, ornamental work, and monuments.^[52] In regions like Oregon's Ashland, Jacksonville, and Gold Hill districts, tonalite has been quarried for these purposes, with operations such as the Oregon Granite Company near Jacksonville extracting it for local buildings.^[52] Similarly, in California's Sierra Nevada, tonalite and related granodiorites from quarries in Madera and Fresno counties have been used historically for ornamental building stone and ashlar, contributing to structures during peak production periods from the late 19th to mid-20th centuries.^[53] When crushed, tonalite serves as a robust aggregate in concrete, road bases, and railroad ballast, prized for its high abrasion resistance and strength under load.^[52] In Oregon's Grants Pass district, for instance, weathered tonalite has been particularly employed for road surfacing and track ballast due to its breakdown into suitable gravel-sized particles.^[52] Extraction of tonalite remains minor compared to more abundant igneous rocks like granite, with key sites limited to areas such as the Sierra Nevada batholith in California and the Siskiyou tonalite batholith in Oregon; this scarcity contributes to higher costs and restricted availability for large-scale projects.^[53]^[52]

Role in Earth Sciences

Tonalite plays a pivotal role in the formation of the Archean continental crust as a primary component of tonalite-trondhjemite-granodiorite (TTG) suites, which represent over 70% of the preserved early silicic crust. These rocks formed through partial melting of hydrous, silicified mafic sources, such as tholeiitic basalts or gabbro-norites, at depths of 20–50 km under moderate pressures (1.0–1.8 GPa) and temperatures of 800–950 °C, often with rutile as a residual phase.^[54]^[55] This process facilitated the initial differentiation of the continental crust from mafic precursors, enabling the extraction of felsic melts that built proto-continents and set the stage for long-term crustal stability.^[55] The resulting TTG magmatism, dominant from 3.5 to 2.5 Ga, underscores tonalite's significance in early planetary evolution by promoting andesitic compositions akin to modern arcs.^[54] As an indicator of subduction initiation in the Precambrian, tonalite within TTG suites records the transition to subduction-like regimes around 3 Ga, marking the onset of plate tectonics. High barium (Ba) contents in these rocks, often exceeding 1000 ppm, serve as a geochemical proxy for low geothermal gradients and fluid fluxing typical of subducting slabs, contrasting with hotter, non-subduction settings.^[56] This enrichment, observed in cratons like Baltica and Pilbara by ~3.1–2.8 Ga, suggests regional slab melting of hydrated basalts, with global subduction becoming widespread after 2.7 Ga.^[56] Such signatures imply that tonalite-bearing TTGs reflect episodic subduction events that drove early crustal growth without requiring fully modern plate tectonics.^[56] Tonalite is extensively used in geochronology through U-Pb dating of zircon crystals to delineate the timing and duration of orogenic cycles. Zircons from tonalitic plutons preserve magmatic ages that pinpoint episodes of arc-related magmatism and subsequent metamorphism, as seen in Permian-Triassic tonalites from the Hida Belt, Japan, dated at 302–254 Ma for initial intrusion and 250–240 Ma for thermal overprints.^[57] This method traces multi-stage orogenic evolution, such as Cordilleran arc systems along continental margins, by resolving primary crystallization from recrystallization events.^[57] In Archean contexts, U-Pb ages from tonalite zircons further constrain the tempo of continental assembly during supercontinent cycles.^[57] In modern studies, tonalite acts as a proxy for arc magma evolution and crustal recycling, revealing how felsic magmas incorporate older crustal material in subduction zones. For instance, Late Archean tonalites in the Superior Province exhibit εNd values from –3.1 to +3.3 and δ18O from +7.1 to +8.9‰, indicating partial melting of overthickened amphibolite lower crust with assimilation of 3.2–3.4 Ga gneisses.^[22] These signatures highlight recycling rates exceeding 50% in some arcs, where tonalite formation involves hybrid sources blending mantle-derived melts with supracrustal components, informing models of crustal reworking without direct mantle input.^[22] Such analyses underscore tonalite's value in quantifying long-term crustal mass transfer in active margins.^[22]

References

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[23]
[PDF] Archean Tonalite-Trondhjemite-Granodiorite Suites - Archimer
Archean TTG rocks are dominant in Earth's earliest crust, formed from partial melting of mafic rocks, and are quartz-rich with sodic plagioclase.
[24]
[PDF] Generation of Archaean TTG Gneisses Through Amphibole ...
Geochemical analyses and fractional crystallization modeling show that diorites can evolve to tonalites and trondhjemites through at most 27% fractional.
[25]
Tonalites in crustal evolution | U.S. Geological Survey - USGS.gov
Before about 2.9 Ga ago they were produced largely by simple partial melting of metabasalt to give the dominant part of Archaean grey gneiss terranes.
[26]
Cooling and exhumation of the southern Idaho batholith | Lithosphere
Apr 1, 2017 · Further, constraining the cooling and exhumation of batholiths provides a record of orogenic crust stabilization through time (e.g., DeCelles et ...
[27]
Early Jurassic monzogranite-tonalite ... - GeoScienceWorld
The tonalite samples from the Shihe area display high Na2O/K2O ratios of 2.84–3.57 and are characterized by high Na2O (5.92–6.72 wt%) and. Al2O3 (17.18–19.34 ...
[28]
Multi-pulse cotectic evolution and in-situ fractionation of calc ...
... (63–70 wt.% SiO2; 4–6 wt.% CaO; 1–3 wt.% MgO) at deep-crustal pressures (Castro et al., 2013). These temperatures exceed the maximum values predicted by ...
[29]
Secondary classification (Sr/Y against K2O/Na2O) of high-and low ...
Strongly sodic granites (K2O/Na2O < 0.6) are derived from sources with a broadly 'basaltic' composition, whereas potassic granites (K2O/Na2O > 1.0) are derived ...
[30]
Subduction zone geochemistry - ScienceDirect.com
... enriched in Pb, resulting in negative Nb-Ta anomalies but a positive Pb anomaly in IAB (Figure 2, Figure 6). In addition to the water-soluble elements such ...
[31]
The composition of subduction zone fluids and the origin of the trace ...
Jun 15, 2021 · Assuming 2 wt% of rutile in the eclogite equilibrated with the saline fluid produces a negative Nb Ta anomaly that is larger than in most ...
[32]
O–H–Sr–Nd isotope constraints on the origin of the Famatinian ...
May 4, 2020 · Tonalite and monzogranite of the Eastern Famatinian Domain yielded εNdt values of −4.3 and −3.1 and 87Sr/ 86Srt values of 0.7086 and 0.7056, ...
[33]
An Example from the Enclav - AGU Journals
These two samples yield the highest and lowest εNd(t) values of +2.6 and -2.2, respectively, while other samples have near-chondrite Nd isotopic compositions.<|control11|><|separator|>
[34]
Tonalites in crustal evolution | Philosophical Transactions of the ...
Uniformitarianism thus goes back one-half of the age of the earth. Tonalites compose about 5-10 % of crust generated in Proterozoic and Phanerozoic time at ...
[35]
Thermal evolution of the Sierra Nevada batholith, California, and ...
Apr 1, 2016 · The Sierra Nevada arc contains plutonic material as old as ca. 250 Ma (Saleeby and Dunne, 2015), but was built primarily by high-flux magmatism ...
[36]
The Coastal Batholith and other aspects of Andean magmatism in ...
They also consist predomi- nantly of tonalites and granodiorites with sub- ordinate monzogranites, but there is a lack of geochemical and isotopic information.
[37]
Emplacement conditions and exhumation of the Varvarco Tonalite ...
Mar 14, 2022 · Along the Matancilla and Chacay creeks, the Varvarco Tonalite can be observed in excellent exposures (Figs 2a, 5a, 6a–d), which include the ...
[38]
Variscan granitoids of central Europe: their typology, potential ...
Post-collisional, epizonal I-type granodiorites and tonalites (ca. 310-290 Ma): These plutons can be found throughout the Central European Variscides.
[39]
Recycled oceanic crust as a source for tonalite intrusions in the ...
The tonalite melts mildly modified due to low degree of mixing and ... European Variscides: Northern Vosges (France) and Northern Schwarzwald (Germany).
[40]
Diversification of Archean tonalite-trondhjemite-granodiorite suites ...
Sep 20, 2021 · Tonalite-trondhjemite-granodiorite (TTG) suites are the dominant component of Earth's first continents, but their origins are debated.
[41]
Evidence for Protracted Intracrustal Reworking of Palaeoarchaean ...
Aug 12, 2022 · ~3.5-2.8 Ga granitoids from the Pilbara Craton in Western Australia are one of the most ancient and best-preserved records of early ...
[42]
File:Roc de la Calme.jpg - Wikimedia Commons
Dec 18, 2024 · It is the highest point in the commune. The tor is an outcrop of a granitoid rock known as tonalite, of Hercynian age. The view is towards the ...
[43]
Late Cambrian tonalite-trondhjemite association in the eastern ...
1. The trondhjemite-tonalite association is not only a minor but important component of arc crust in modern subduction zones (Haraguchi et al.
[44]
A bimodal source for the generation of tonalitic to granitic magmas in ...
The Famatinian back-arc was associated with a generalized extension, marine sediment deposition and anatexis in the lower crust, causing differentiation and ...
[45]
Trans‐Hudson Orogen of North America and Himalaya‐Karakoram ...
Jul 18, 2006 · The older suite includes calc-alkaline layered diorite-tonalite ... collisional orogens), effectively bridging (or bracketing) no less ...<|control11|><|separator|>
[46]
Interplay between oceanic subduction and continental collision in ...
Nov 21, 2022 · l Detail at the contact between a syn-collisional dioritic dyke (~48 Ma) and an older tonalite ... collisional orogens. Earth Planet. Sci ...
[47]
[PDF] Plate 1 (pdf) - USGS Publications Warehouse
color index (<5), these rocks are predominantly leucotonalite, although minor amounts of leucogranodiorite and leucogranite are included. Locally contain ...
[48]
6 Igneous Rocks and Silicate Minerals – Mineralogy - OpenGeology
Besides silicates, chromite and other oxide minerals accumulate in mafic complexes. ... mafic minerals and thus a darker color. While all intermediate and mafic ...
[49]
[PDF] The Mineral Resources of Oregon - Cloudfront.net
Tonalite .. ... Building stone . .... . ..... . ... ........ . .. . .. ....... .......... . Limestone ...
[50]
Mineral Resources of California Bulletin 191
This extract covers the following topics: California Stone - Dimension: Granite quarries in the Sierra Nevada Batholith. Sandstone in California. Limestone and ...Missing: Pyrenees | Show results with:Pyrenees
[51]
Archean Tonalite-Trondhjemite-Granodiorite Suites | Elements
Jun 1, 2024 · The TTG suite hence includes rocks whose typical mineral assemblage consists of sodic plagioclase, quartz, and biotite, with minor to absent K- ...
[52]
Archaean continental crust formed from mafic cumulates - Nature
Jan 24, 2024 · Large swaths of juvenile crust with tonalite-trondhjemite-granodiorite (TTG) composition were added to the continental crust from about 3.5 billion years ago.
[53]
Barium content of Archaean continental crust reveals the onset of ...
Nov 2, 2022 · Earth's earliest continental crust is dominated by tonalite–trondhjemite–granodiorite (TTG) suites, making these rocks key to unlocking the ...
[54]
Zircon U–Pb geochronology and Hf isotope geochemistry of ...
The modal composition corresponds to tonalite. (c, d) ... A Mesozoic Andean-type orogenic cycle in southeastern China as recorded by granitoid evolution.