Role In Crustal Evolution Research Articles

Mechanism of Paleoarchean continental crust formation as archived in granitoids from the northern part of Singhbhum Craton, eastern India

Abstract Many Paleoarchean cratons display a gradual change from early sodic tonalite–trondhjemite–granodiorite magmatism to late K-rich granitoid magmatism; the geodynamic significance of this change is debatable though. This contribution presents field, geochemical and zircon U–Pb age and Hf isotope results of four different 3.32–3.25 Ga granitoid bodies from the northern part of Singhbhum Craton to investigate their petrogenesis and role in crustal evolution. The granitoids range in composition from tonalites to trondhjemites, derived from intracrustal melting at low- to medium-pressure conditions. The source was mainly low-K mafic rock. The granitoids show intrasuite fractional crystallization. These sodic granitoids represent the last stage of granitoid magmatism in the Singhbhum Craton which formed contemporaneously with K-rich granitoids occurring in other parts of the craton. This fact suggests that, contrary to the popular notion (of only potassic granitoids), both sodic and potassic granitoids could form at the terminal phase of cratonization, implying reworking of heterogeneous (mafic to tonalite) crust. A combination of evidence from geochemical data, secular change in granitoid composition, structural pattern and rock association of the Singhbhum Craton reflects that recurring mantle plume-related mafic–ultramafic magma emplacement in an oceanic plateau setting and attendant crustal melting can explain the Paleoarchean crustal evolution pattern.

Detrital zircon ages and Hf isotopic compositions of metasedimentary rocks in the Wuqia area of Southwest Tianshan, NW China: implications for the early Paleozoic tectonic evolution of the Tianshan orogenic belt

ABSTRACTThe Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of −22.0 to +11.3 and two-stage model ages (TDM2) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (−15.0 to −0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.

Early Neoarchaean A-type granitic magmatism by crustal reworking in Singhbhum craton: Evidence from Pala Lahara area, Orissa

Several volumetrically minor \(\sim \)2.8 Ga anorogenic granites and rhyolites occur along the marginal part of the Singhbhum craton whose origin and role in crustal evolution are poorly constrained. This contribution presents petrographic, geochemical, zircon U–Pb and trace element, and mineral chemical data on such granites exposed in the Pala Lahara area to understand their petrogenesis and tectonic setting. The Pala Lahara granites are calc-alkaline, high-silica rocks and define a zircon U–Pb age of 2.79 Ga. These granites are ferroan, weakly metaluminous, depleted in Al, Ca and Mg and rich in LILE and HFSE. They are classified as A2-type granites with high Y/Nb ratios. Geochemical characteristics (high \(\hbox {SiO}_{2}\) and \(\hbox {K}_{2}\hbox {O}\), very low MgO, Mg#, Cr, Ni and V, negative Eu anomaly, flat HREE and low Sr/Y) and comparison with melts reported by published experimental studies suggest an origin through high-temperature, shallow crustal melting of tonalitic/granodioritic source similar to the \(\sim \)3.3 Ga Singhbhum Granite. Intrusion of the Pala Lahara granites was coeval with prominent mafic magmatism in the Singhbhum craton (e.g., the Dhanjori mafic volcanic rocks and NNE–SSW trending mafic dyke swarm). It is suggested that the \(\sim \)2.8 Ga A-type granites in the Singhbhum craton mark a significant crustal reworking event attendant to mantle-derived mafic magmatism in an extensional tectonic setting.

Age and geochemistry of the intrusive rocks from the Shaquanzi-Hongyuan Pb–Zn mineral district: Implications for the Late Carboniferous tectonic setting and Pb–Zn mineralization in the Eastern Tianshan, NW China

The Central Tianshan Terrane (CTT) in the Eastern Tianshan (Xinjiang, NW China) is an important Pb–Zn metallogenic belt and played a pivotal role in crustal evolution and collisional tectonics of the southern Central Asian Orogenic Belt. The Shaquanzi gabbro and Hongyuan granodiorite are located in the northern margin of the CTT and associated with Pb–Zn mineralization. Zircon U–Pb dating yielded weighted mean ages of 307.2±1.5Ma and 301.2±1.5Ma for the Shaquanzi gabbro and the Hongyuan granodiorite, respectively. These rocks are medium-K calc-alkaline series and enriched in large ion lithophile elements (LILEs; e.g., K, Rb, Ba) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), displaying typical arc affinities.The Shaquanzi gabbro shows low Nb/Ta (11.0–14.2), a high Mg# range (56–59), positive zircon εHf(t) (+3.30−+7.26) and whole rock εNd(t) (+0.70−+1.38) values, and low ISr ratios (0.704858–0.705137), which indicate that the protolith was probably derived from the sub-continental lithospheric mantle that had been metasomatized by subduction-related fluids. The Hongyuan granodiorite contains hornblende but lack of Al-rich minerals and has low ISr ratios (0.704769–0.706211<0.707), suggesting an I-type origin. Moreover, the Hongyuan granodiorite has positive εHf(t) (+1.12−+5.57) and εNd(t) (+0.38−+1.86) values, with high Mg# (52), variable Nb/Ta ratios (12.6–12.9), low contents of Ni, Cr and Co and Pb isotopes (206Pb/204Pb=17.461–18.299, 207Pb/204Pb=15.541–15.581, 208Pb/204Pb=37.456–38.129), suggesting the Hongyuan granodiorite was generated by partial melting of juvenile crust sources mixed with some mantle-derived materials.Combined published works with our new geochronological, geological, geochemical and isotopic data, we propose that the CTT may have evolved from a continental arc to a syn-collisional setting during the period of ca. 307–301Ma. The continuing southward subduction of the Junggar oceanic slab beneath the CTT in the Late Carboniferous resulted in extensive arc-related volcanic rocks emplacement that had indirect links to the Pb–Zn mineralization (e.g., reworked/upgraded).

Generation and evolution of Palaeoarchaean continental crust in the central part of the Singhbhum craton, eastern India

Palaeoarchaean granitoids are exposed over wide area in the Singhbhum craton whose origin and role in crustal evolution are not well constrained. This study presents whole-rock and mineral chemical data coupled with zircon U-Pb dating and Hf isotope results on such granitoids from the central part of the craton to understand their petrogenesis, tectonic setting and role in continental crustal evolution. The first phase of granitoid magmatism in this area is represented by a 3.47Ga Na-rich, gneissic tonalite belonging to the Archaean TTG (tonalite-trondhjemite-granodiorite) suite. This rock is characterized by high-HREE (heavy rare earth elements), negative Eu anomaly, low Sr/Y ratio and positive zircon Hf isotope signature (εHft=+2.1 to +4.8). It is interpreted to be formed by shallow melting of a juvenile mafic source. At 3.35Ga a silicic, ferroan porphyritic biotite granite formed. It shows variable K/Na, low Y and high Sr/Y, moderately fractionated HREE and positive zircon εHft (+1.8 to +4.0), and is explained as a product of high-temperature melting of a heterogeneous, juvenile source consisting of tonalites and mafic rocks at lower crustal depth. The final phase of granitoid magmatism is marked by a 3.30Ga non-porphyritic ferroan, silica-rich biotite granite. Geochemical characteristics like moderately high K, moderately fractionated HREE, low Ca and Sr/Y, and zircon εHft (+0.8 to +3.7) suggest that the granite was formed by high-pressure melting of a tonalite-dominated source with short crustal residence. All the three granitoid phases display low Mg, Ni and Cr contents and magnesium number (Mg#) precluding direct involvement of mantle in their origin. Rather, crustal reworking caused by episodic plume-related mafic-ultramafic magma underplating and intraplating in an oceanic plateau setting is suggested as the possible mechanism for formation of the granitoids. Successive crustal reworking events involved progressively greater amount of previously formed felsic crust generating more evolved, K-rich granitoids. It appears to be a globally important process which led to effective crustal differentiation and maturing of the cratons during Palaeoarchaean.

Zircon U–Pb chronology and Hf isotope of the Xingxingxia granodiorite from the Central Tianshan zone (NW China): Implications for the tectonic evolution of the southern Altaids

The Central Tianshan zone is located between the Turpan–Hami and Tarim blocks and played a pivotal role in crustal evolution and collisional tectonics of the southern Altaids (or the Central Asian orogenic belt). The Xingxingxia granodiorite in the eastern Central Tianshan is an Early Paleozoic (424.9 ± 5.8 Ma) intrusion. Petrography, geochemistry and Sr–Nd–Hf isotopes suggest that the Xingxingxia granodiorite was genetically related to a volcanic arc, emplaced above a subduction zone. Thus, the Central Tianshan zone was a magmatic arc above an early Paleozoic subduction zone of the Paleoasian ocean. We present LA-ICP-MS zircon U–Pb dating and Hf isotope determinations of Precambrian zircon grains trapped in the Xingxingxia granodiorite. Three populations of inherited zircons indicate that Neoproterozoic (809 ± 41 Ma; ε Hf(t) = 0.10–5.73), Mesoproterozoic (~ 1400 Ma; ε Hf(t) 8.71–10.05) and Paleoproterozoic (~ 1750 Ma; ε Hf(t) 0.11 and 4.80) tectonomagmatic events in the Central Tianshan zone, which are comparable with those in the Tarim block. Combined with a series of similar geological characteristics between these two blocks, it is suggested that the Central Tianshan zone might have been originally a part of the Tarim block, and was separated from it during the Early Paleozoic time due to pull-apart caused by southward subduction of the Northern Tianshan ocean, a branch of the Paleoasian ocean.

Sedimentation and crustal recycling along an active oblique-rift margin: Salton Trough and northern Gulf of California

Transtensional basins embedded in the San Andreas fault system of Southern California (United States) and northwestern Mexico are fi lled with sediment derived from the Colorado River, which drains a large area of the western U.S. interior. The sediment is rapidly buried, heated, and mingled with intrusions in the deep basins to form a new generation of recycled crust along the active plate boundary. Using a range of values for total basin depth, relative volume of mantle-derived intrusions, and composition of early rift deposits, the volume of Colorado River‐derived sediment in the basins is bracketed between 2.2 and 3.4 ◊ 10 5 km 3 , similar to the volume of rock that likely was eroded from the Colorado River catchment over the past 5‐6 m.y. The volumetric rate of crustal growth by sedimentation is ~80‐130 km 3 /m.y./km, comparable to growth rates in subductionrelated island arcs and slow seafl oor spreading centers. Sedimentary and basinal processes thus play a major role in crustal evolution and recycling in this setting, and may be important at other rifted margins where a large river system is captured following tectonic collapse of a prerift orogenic highland.

A pseudo adakite derived from partial melting of tonalitic to granodioritic crust, Kyushu, southwest Japan arc

Cretaceous peraluminous granitic intrusions occur in Kyushu in the southwest Japan arc as batholiths or stocks accompanied by metaluminous tonalite to granodiorite. The peraluminous intrusions are classed as adakitic based on Sr/Y–Y (ppm) relationships, but they contain abundant K-feldspar, a phase not common in typical adakites. To consider their significance in the arc system, we investigated the Tsutsugatake stock as representative of the intrusions exposed in central Kyushu. The Tsutsugatake rocks are mainly garnet-bearing two-mica leuco-granitoids. Their Sr/Y ratios and rare earth element concentrations are appropriate for adakite, but K 2O/Na 2O ratios (0.53–1.43), and Al 2O 3 (13.7–15.0 wt.%), MgO (0.20–0.55 wt.%), Sr (207–462 ppm), Cr (≤ 12 ppm), and Ni (≤ 8 ppm) contents differ from those of typical adakite. Geochemical modeling shows that the petrogenesis of the Tsutsugatake stock can be explained by partial melting of arc-type tonalite or adakitic granodiorite under middle to lower crustal conditions, leaving amphibole and plagioclase as residual phases. The differences between the Tsutsugatake stock and classical adakites lie in their source rocks and melting conditions. The Tsutsugatake source was not basaltic, and the melting pressure was insufficient to stabilize garnet. The Tsutsugatake rocks are here designated “pseudo adakites”. Such “pseudo adakites” may be found in both modern and ancient arcs, and would play an important role in crustal evolution as a member of the recycled constituent.

40Ar– 39Ar dating of detrital muscovite in provenance investigations: a case study from the Adelaide Rift Complex, South Australia

Detrital zircon ages are commonly used to investigate sediment provenance and supply routes. Here, we explore the advantages of employing multiple, complimentary techniques via a case study of the Neoproterozoic and Cambrian of the Adelaide Rift Complex, South Australia. Detrital muscovite Ar–Ar ages are presented from stratigraphic units, or equivalents, that have previously been the subject of U–Pb detrital zircon dating, and, in some cases, whole-rock Sm–Nd isotope studies. The zircon age ranges and whole-rock Sm–Nd isotope data suggest that early Neoproterozoic sediments from near the base of the Adelaide Rift Complex comprise a mixture of detritus derived from the adjacent Gawler Craton (Palaeoproterozoic to earliest Mesoproterozoic) and overlying Gairdner flood basalts. In contrast, detrital muscovites from this level have a broad scatter of Mesoproterozoic infrared (IR) laser total fusion Ar–Ar ages, while UV laser traverses indicate that the age spread reflects partial resetting by multiple heating events, rather than a mixture of sources. Younger Neoproterozoic sediments document replacement of the Gawler Craton by the more distant Musgrave and/or Albany–Fraser Orogens as the main provenance. The Cambrian Kanmantoo Group marks an abrupt change in depositional style and a new sediment source. The Kanmantoo Group have older Nd model ages than underlying strata, yet are dominated by near to deposition-aged (∼500–650 Ma) detrital zircons and muscovites, suggesting rapid cooling and exhumation of a tectonically active provenance region. Although this source remains uncertain, evidence points towards the distant Pan-African orogenic belts. Deposition in the Adelaide Rift Complex was terminated in the late Early Cambrian by the Delamerian Orogeny, and the results of previous detrital mineral dating studies from the Lachlan Fold Belt to the east are consistent with at least partial derivation of these sediments from reworked upper Adelaide Rift Complex (Kanmantoo Group), rather than a continuation of sediment supply from the Kanmantoo Group sediment source. More broadly, the data suggest a close link between basin formation and orogen exhumation, and we also speculate that mantle plumes have played a significant role in crustal evolution at this Palaeo-Pacific margin of Gondwanaland, challenging the notion that subduction zones are the principle sites of crustal growth and sediment provenance.