A clearer view of crustal evolution: U-Pb, Sm-Nd, and Lu-Hf isotope systematics in five detrital minerals unravel the tectonothermal history of northern China

Much of the global picture of crustal evolution has been constructed using zircon. While this has revealed a rich and complex history, this view is necessarily incomplete because of the lithology-specific affinity of zircon and the high temperatures needed to reset the U-Pb and Lu-Hf systems inherent within it. Here we use a five mineral, multi-isotope system approach to compare the record of crustal evolution recorded by zircon versus the picture provided by monazite, titanite, apatite, and rutile from the Yong-Ding and Luan rivers, northern China. These other minerals sample more diverse lithologies and temperature-pressure conditions that reflect additional tectonothermal events to those recorded solely by zircon. Zircon from both studied rivers predominantly reflects magmatic features, yielding age peaks at 2.6–2.3, 2.0–1.8, and 0.38–0.13 Ga, corresponding to the major magmatic events in their catchments. However, the detrital zircon record from both catchments fails to record and detail several important tectonothermal events. Specifically, the detrital monazite U-Pb ages cluster into two Paleoproterozoic peaks of ca. 1.95 and 1.85 Ga, while detrital apatite and rutile ages document unimodal and protracted U-Pb age peaks at 1.9–1.6 Ga. The different U-Pb closure temperatures of monazite, apatite, and rutile likely record two metamorphic events and the subsequent cooling history—key details that are absent from or obscured in the zircon record. The Phanerozoic mineral U-Th-Pb ages correspond to multiple magmatic events between 0.40 and 0.24 Ga and subsequent 0.24–0.20 Ga metamorphism. The 0.60–0.25 Ga rutile U-Pb ages along with 0.33–0.24 Ga U-Pb ages in some zircon grains with radiogenic Hf isotope compositions from the Luan River do not match the geological records in the North China Craton, but instead reflect the protracted subduction-accretionary history of the Central Asian Orogenic Belt. In addition to their U-Th-Pb ages, Nd model ages of monazite, titanite, and apatite, plus zircon Hf model ages provide additional constraints on regional crustal evolution. The Nd model age information is blurred by the fact that the relationship between the Sm/Nd of these minerals and their former host rocks is not precisely known. Taken at face value, the monazite Nd model ages have two Neoarchean peaks at 2.9–2.7 and ca. 2.5 Ga, that may correspond to two crustal growth episodes, while the titanite Nd model ages with predominant peaks at 2.2–1.8 and 1.5–1.3 Ga broadly correspond with those derived from the whole-rock analyses of the wide spread Phanerozoic granitoids, and hence record extensive crustal reworking. In contrast, the zircon Hf model ages are strongly skewed to a 2.9–2.7 Ga period and fail to record the post-Archean evolution of this region. These data highlight the power of integrating the U-Th-Pb age and Lu-Hf/Sm-Nd isotope compositions of multiple detrital minerals, with a broad range in geochemical behavior and closure temperatures, to gain a more complete understanding of tectonothermal history and crustal evolution than zircon alone.

Mesoarchean silicic volcanics of the Kursk block, Voronezh crystalline massif: composition, age and correlation with the Ukrainian shield

Rhyolites and basite rocks are present in the Archaean greenstone belts of the Kursk Domain (KD) of the East Sarmatia. The rhyolite age is 3122 ± 9 Ma (zircons, SIMS). A positive εNd (3122) = + 0.9 for rhyolites and their Sm-Nd model age ТNd (DM) = 3300 Ma as well as the age of the inherited zircon (3250 Ma) testifies to the participation of the more ancient crust component in the formation of rhyolite magmas. In geochemistry, rhyolites are very close to the TTG of the KD with an age 2.96-3.03 Ga. In the Middle Dnieper granite - greenstone area there are rhyolites and dacites with an age of 3.12 Ga with εNd (T) = + 0.6 - (+1.2) and very close geochemical characteristics. Thus, the hypothesis of a common geological history of the eastern part of Ukrainian Shield and KD in Mesoarchean is confirmed.

Paleoproterozoic age of carbonates and trondhjemites of the central azov group: Sr-isotope chemostratigraphy and U-Pb geochronology

The Sr-isotope composition of the Central Azov Group carbonates (0.70322-0.70352) and Nd model age of silicate sediments (2.34-2.31 Ga) has been reported. The U-Pb age of trondhjemite (2052+5 Ma) cutting the carbonates has been determined. According to the obtained data, the marine sedimentary cover of the Azov block making up the Early Precambrian Sarmatia Continent emplaced in the Early Paleoproterozoic at 2.23-2.34 Ga.

Sources and source areas of the Upper Paleozoic metasedimentary rocks of the Dzhagda terrane of the Mongol-Okhotsk fold belt: the results of Sm-Nd isotope geochemical studies

The article presents the results of Sm-Nd isotope geochemical studies of the Upper Paleozoic metasedimentary rocks of the Dzheskogon, Nektera and Bochagor suites of the Dzhagda terrane. These rocks are characterized by slightly varying values of the Nd model age tNd(DM)=1.5–1.0 Gyr, which gives evidence that the main sources of protoliths were the rocks of the Mesoproterozoic Nd model age (in average). This Nd model age is similar to the ages of the metaterrigenous rocks of the Teply Klyuch, Garmakan and Alga suites of the Tukuringra terrane of the Mongol-Okhotsk Belt. The results obtained in our studies suggest that the sedimentary rocks of the Dzhagda and Tukuringra terranes developed from the material that was mainly sourced from the Amur superterrane (from the south in modern coordinates). A supply of the material from the southern margin of the North Asian craton (from the north in modern coordinates) was either absent or minimal.

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

The relationship between the Dalradian Supergroup and the Highland Border Complex in Scotland has remained contentious for over a century. In western Ireland, the contact between the Dalradian Supergroup and the Clew Bay Complex (a correlative of the Highland Border Complex) is superbly exposed on the island of Achill Beg on the North Mayo coast. The unfossiliferous South Achill Beg succession has been traditionally assigned to the Clew Bay Complex, and this interpretation is supported by a combination of Sm–Nd model age data, heavy mineral analysis and lithostratigraphic correlation. TDM ages range from 1.99–2.66 Ga (mean=2.28 Ga, n=6). Detailed structural mapping shows that both the Dalradian and the Clew Bay Complex share the same structural history. A D1 high strain event is common to both units, and is associated with the development of tectonic slides. The D2 event is responsible for the formation of crustal-scale nappes. In both units, beds are consistently downward facing on the S2 foliation. Later dextral shearing (D3) resulted in the tilting of the originally recumbent, S-facing D2 nappes into this downward-facing orientation. Rb–Sr and 40Ar–39Ar radiometric dating of muscovite confirms that both units were deformed contemporaneously as the S2 nappe fabric in each is dated at c. 460 Ma. This Middle Ordovician age for deformation of the Clew Bay Complex is highly significant, not least because published microfossil data suggest a Silurian age.

Chapter 4 The Loch Maree Group

The supracrustal rocks of the Loch Maree Group (LMG) consist of a variety of metasedimentary rocks interbanded with amphibolites considered to be of volcanic origin. The metasedimentary rocks fall into two distinct categories: a) schistose semipelites, which form the main part of the outcrop; and b) narrow bands of different rock types, including siliceous, carbonate-bearing and graphitic rocks, occurring in close association with the metavolcanic amphibolites. Both the compositional banding and the dominant foliation throughout the LMG outcrop are steeply dipping and trend uniformly NW-SE.The sequence of lithotectonic rock units from SW to NE (structurally upwards) is shown in the cross-section (Fig. 4.1) and briefly described in Table 4.1. The original names of the lithotectonic units (Park 1964) are retained for convenience. The depositional age of the LMG is presumed to be around 2.0 Ga, based on a Sm-Nd model age (O'Nions et al. 1983) and detrital zircon dates (Whitehouse et al. 1991 a, 2001) (see below).Semipelites form several distinct NW-trending belts separated by amphibolite sheets. The most prominent belt comprises the Flowerdale schist unit (see map) which occupies a broad belt about 700 m in width, extending in a northwesterly direction across the Gairloch district, but ending north of the mapped area, where the two amphibolites from either side converge, 3.5 km north of the Gairloch-Poolewe road. This belt is offset in the centre of the area by the Flowerdale fault, and has a total exposed length of about 15 km. Southwest of this belt is the