AGE, PETROGENESIS AND TECTONIC IMPLICATIONS OF THE LATE PERMIAN PERALUMINOUS AND METALUMINOUS MAGMATIC ROCKS IN THE MIDDLE GOBI VOLCANOPLUTONIC BELT, MONGOLIA

The Mongol–Okhotsk Belt, the youngest segment of the Central Asian Orogenic Belt, formed by the evolution and closure of the Mongol–Okhotsk Ocean. The oceanic closure formed two volcanoplutonic belts: Selenge Belt in the north and Middle Gobi Belt in the south (in present day coordinates). However, the origin and tectonic evolution of the Mongol–Okhotsk Belt in general, the origin and formation age of the Middle Gobi Belt in particular, remain enigmatic. To better understand the history of the magmatic activity in the Middle Gobi Belt, we conducted geochemical, U–Pb geochronological, zircon Hf, whole-rock Nd isotopic analyses of volcanic and plutonic rocks of the Mandalgovi suite, the major component of the Middle Gobi Belt. Our results show that the Mandalgovi suite consists of (i) 265 ± 2 Ma biotite-granite; (ii) 250 ± 3 Ma hornblende-granitoids; (iii) their volcanic equivalents of both: and (iv) gabbro-diorites. The geochemical compositions indicate that their precursor magmas were derived from crustal source. The protoliths of the biotite and hornblende-granitoids were metagraywacke and metabasalt, respectively. They are characterized by positive whole-rock εNd(t) and zircon εHf(t) values, indicating the molten protoliths were juvenile crust. The biotite-granites formed by remelting of fore-arc sediments by ridge subduction and later hornblende-granites were emplaced at an intra-oceanic arc by the subduction of the Mongol–Okhotsk Ocean. We conclude that the magmatic rocks of the Middle Gobi formed in an active continental margin and/or intra-oceanic arc setting.

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Geochronology, geochemistry and tectonic implications of early Carboniferous plutons in the southwestern Alxa Block

Geological Magazine ◽

10.1017/s0016756821000984 ◽

2021 ◽

pp. 1-17

Author(s):

Zeng-Zhen Wang ◽

Xuan-Hua Chen ◽

Zhao-Gang Shao ◽

Bing Li ◽

Hong-Xu Chen ◽

...

Keyword(s):

Alkali Feldspar ◽

Early Carboniferous ◽

Sedimentary Deposits ◽

The North ◽

Magmatic Rocks ◽

Central Asian ◽

Continental Arc ◽

Isotopic Analyses ◽

Western Segment ◽

Extensional Setting

Abstract The southeastern Central Asian Orogenic Belt (CAOB) records the assembly process between several micro-continental blocks and the North China Craton (NCC), with the consumption of the Paleo-Asian Ocean (PAO), but whether the S-wards subduction of the PAO beneath the northern NCC was ongoing during Carboniferous–Permian time is still being debated. A key issue to resolve this controversy is whether the Carboniferous magmatism in the northern NCC was continental arc magmatism. The Alxa Block is the western segment of the northern NCC and contiguous to the southeastern CAOB, and their Carboniferous–Permian magmatism could have occurred in similar tectonic settings. In this contribution, new zircon U–Pb ages, elemental geochemistry and Sr–Nd isotopic analyses are presented for three early Carboniferous granitic plutons in the southwestern Alxa Block. Two newly identified aluminous A-type granites, an alkali-feldspar granite (331.6 ± 1.6 Ma) and a monzogranite (331.8 ± 1.7 Ma), exhibit juvenile and radiogenic Sr–Nd isotopic features, respectively. Although a granodiorite (326.2 ± 6.6 Ma) is characterized by high Sr/Y ratios (97.4–139.9), which is generally treated as an adikitic feature, this sample has highly radiogenic Sr–Nd isotopes and displays significantly higher K2O/Na2O ratios than typical adakites. These three granites were probably derived from the partial melting of Precambrian continental crustal sources heated by upwelling asthenosphere in lithospheric extensional setting. Regionally, both the Alxa Block and the southeastern CAOB are characterized by the formation of early Carboniferous extension-related magmatic rocks but lack coeval sedimentary deposits, suggesting a uniform lithospheric extensional setting rather than a simple continental arc.

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A Triassic-Jurassic westward scissor-like subduction history of the Mudanjiang Ocean and amalgamation of the Jiamusi Block in NE China: Constraints from whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes of the Zhangguangcai Range granitoids

10.5194/egusphere-egu2020-606 ◽

2020 ◽

Author(s):

Maohui Ge ◽

Jinjiang Zhang ◽

Long Li ◽

Kai Liu

Keyword(s):

Pacific Ocean ◽

Tectonic Evolution ◽

Eurasian Plate ◽

Ne China ◽

Volcanic Arc ◽

The North ◽

Tectonic Transition ◽

Magmatic Rocks ◽

Central Asian ◽

History Of

NE China recorded the key tectonic evolution history of the Eurasian Plate from the Paleozoic-Mesozoic collisional formation of the Central Asian Orogenic Belt to the Mesozoic subduction of the Paleo-Pacific Ocean. To better understand this tectonic transition, it is crucial to constrain the time and pattern of the initial subduc- tion of the Paleo-Pacific Ocean. Recently, someresearchers proposed that theMudanjiang Ocean existed between the Songnen and Jiamusi blockswas part of the Paleo-Pacific Ocean. Here, through geochemical and geochrono- logical studies on the widespread granitoids in the Lesser Xing'an-Zhangguangcai Range in the eastern Songnen Block, we verify that these magmatic rocks show volcanic arc affinity with increased mantle contribution from east to thewest of the range, likely related to a flattening subduction of theMudanjiang Ocean. In addition, a uni- versal westward younging trend for over 70 Myr can be observed for the granitoids throughout the Lesser Xing'an-ZhangguangcaiRange, indicating a long-lastingsubductionof theMudanjiangOcean.More interestingly, the oldest ages of the granitoids in the east display a northward younging trend from275Ma to 218Ma, suggest- ing that the subduction of the Mudanjiang Ocean had been initiated at latest by 275 Ma in the south and then progressively expanded to the north. Based on these observations, we proposed a new tectonic evolution model for theMudanjiang Ocean, i.e., a Triassic-Jurassicwestward scissor-like subduction and closure, to contrib- ute to the understanding of the early subduction of the Paleo-PacificOcean

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Ore-Bearing Magmatic Systems with Complex Sn–Au–Ag Mineralization in the North-Eastern Verkhoyansk–Kolyma Orogenic Belt, Russia

Minerals ◽

10.3390/min11030266 ◽

2021 ◽

Vol 11 (3) ◽

pp. 266

Author(s):

Vera A. Trunilina ◽

Andrei V. Prokopiev

Keyword(s):

Active Continental Margin ◽

Orogenic Belt ◽

Crustal Extension ◽

Margin Setting ◽

The North ◽

Magmatic Rocks ◽

Isotopic Methods ◽

North Eastern ◽

Magmatic Stage ◽

Mineral Compositions

This paper reports the results of a study of magmatic rocks with Sn–W–Au–Ag mineralization from the Kuranakh, Elikchan, and Istekh ore fields in the Northern batholith belt of the north-eastern Verkhoyansk–Kolyma orogenic belt in Eastern Russia. Using petrographic, mineralogical, geochemical, and isotopic methods, we determined the mineral compositions, petrochemistry, and geochemistry of magmatic rocks, the P–T conditions of their generation and crystallization, and their geodynamic affinity. The studied magmatic rocks have common geochemical characteristics that likely reflect the influence of fluids supplied from a long-lived, deep-seated mantle source. The ore fields are characterized by Sn–W–Au–Ag–Pb polygenetic mineralization. The magmatic and metallogenic evolution comprised five stages for the formation of magmatic rocks and ores. During the first stage (Berriasian–Barremian), arc-related magmatic rocks formed in an active continental margin setting and were associated with Au–Ag mineralization. The second, third, and fourth stages (Aptian–Campanian) took place in a crustal extension and rift setting, and were accompanied by Au–Ag and Sn–W mineralization. During the fifth (post-magmatic) stage, Sn–Ag–Sb and Pb–Ag mineralization occurred.

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Permafrost as a climatic indicator in northern Victoria Land, Antarctica

Annals of Glaciology ◽

10.3189/172756499781821111 ◽

1999 ◽

Vol 29 ◽

pp. 131-135 ◽

Cited By ~ 18

Author(s):

M. Guglielmin ◽

F. Dramis

Keyword(s):

Ground Ice ◽

Patterned Ground ◽

Thermal Inversion ◽

Ground Temperatures ◽

The North ◽

Victoria Land ◽

Investigation Methods ◽

Isotopic Analyses ◽

History Of ◽

Rock Glaciers

AbstractKnowledge of permafrost characteristics and distribution in Antarctica and their relationships with present and past climates is still poor. This paper reports investigations on permafrost in an area located between Nansen Ice Sheet to the south and Mount Melbourne (2732 m a.s.l.) to the north. Investigation methods included geomorphological surveys and geoelectrical soundings as well as crystallography, chemical and isotopic analyses of the ground ice. Geomorphological surveys helped to explain the relationships between periglacial landforms (e.g. rock glaciers and patterned ground) and the glacial history of the area. Geoelectrical soundings allowed us to define different ground-ice units in the ice-free areas. Each unit was characterised by a different type of permafrost (dry or ice-poor permafrost, marine or continental massive buried ice and sub-sea permafrost). To identify the nature of ground ice, trenches were dug and some shallow boreholes were drilled to a maximum depth of-3.6 m in massive buried ice. Samples of both ice-poor permafrost and massive ice were collected and analyzed. Chemical, isotopic δ18O and crystal analyses were also carried out. The relationships between climate and thermal regimes of the active layer and the upper part of permafrost were determined using a monitoring station for ground temperatures at Boulder Clay Glacier, near the Italian Antarctic station. During winter, there were several significant thermal-inversion events in the ground, which cannot be explained only by air-temperature changes, suggesting a possible influence of winter snowfall, even if these events are usually considered very rare.

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Late Paleozoic tectonism of the Bogda region in Chinese North Tianshan: Insights from sedimentary provenance analysis

10.5194/egusphere-egu21-16422 ◽

2021 ◽

Author(s):

Qian Wang ◽

Guochun Zhao ◽

Yigui Han ◽

Jinlong Yao

Keyword(s):

Detrital Zircon ◽

Detrital Zircons ◽

Late Paleozoic ◽

Provenance Analysis ◽

The North ◽

Tectonic Transition ◽

Isotopic Analyses ◽

Zircon Morphology ◽

Detrital Zircon Ages ◽

T Values

The Chinese North Tianshan (CNTS) extends E-W along the southern part of the Central Asian Orogenic Belt and has undergone complicated accretion-collision processes in the Paleozoic. This study attempts to clarify the late Paleozoic tectonism in the region by investigating the provenance of the Late Paleozoic sedimentary successions from the Bogda Mountain in the eastern CNTS by U-Pb dating and Lu-Hf isotopic analyses of detrital zircons. Detrital zircon U-Pb ages (N=519) from seven samples range from 261 &#177; 4 Ma to 2827 &#177; 32 Ma, with the most prominent age peak at 313 Ma. There are Precambrian detrital zircon ages (~7%) ranged from 694 to 1024 Ma. The youngest age components in each sample yielded weighted mean ages ranging from 272 &#177; 9 Ma to 288 &#177; 5 Ma, representing the maximum depositional ages. These and literature data indicate that some previously-assumed &#8220;Carboniferous&#8221; strata in the Bogda area were deposited in the Early Permian, including the Qijiaojing, Julideneng, Shaleisaierke, Yangbulake, Shamaershayi, Liushugou, Qijiagou, and Aoertu formations. The low maturity of the sandstones, zircon morphology and provenance analyses indicate a proximal sedimentation probably sourced from the East &#173;Junggar Arc and the Harlik-Dananhu Arc in the CNTS. The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in the Harlik-Dananhu Arc. Zircon &#603;Hf(t) values have increased since ~408 Ma, probably reflecting a tectonic transition from regional compression to extension. This event might correspond to the opening of the Bogda intra-arc/back arc rift basin, possibly resulting from a slab rollback during the northward subduction of the North Tianshan Ocean. A decrease of zircon &#603;Hf(t) values at ~300 Ma was likely caused by the cessation of oceanic subduction and subsequent collision, which implies that the North Tianshan Ocean closed at the end of the Late Carboniferous. This research was financially supported by the Youth Program of Shaanxi Natural Science Foundation (2020JQ-589), the NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).

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The Issue Of The Central Asian Northern Pilgrimage Route In The Russian-Bukhara Diplomatic Relations In The XVIII Century (On The Example Of The Activities Of Ambassador Ernazar Maqsud Oglu)

The American Journal of Interdisciplinary Innovations and Research ◽

10.37547/tajiir/volume02issue11-19 ◽

2020 ◽

Vol 02 (11) ◽

pp. 99-104

Author(s):

Tanieva Guldona Mamanovna ◽

Keyword(s):

Middle Ages ◽

Russian Empire ◽

Extensive Study ◽

Economic Relations ◽

Xviii Century ◽

The North ◽

Central Direction ◽

Central Asian ◽

History Of ◽

The Russian Empire

In the Middle Ages, Central Asian pilgrims traveled to Mecca in three directions: the North direction ‒ through the Russian Empire, the central direction‒ through the territory of Persia, and the south direction ‒ along roads through India and the Arabian Sea. Therefore, the question of the directions of the Hajj was reflected in the diplomatic correspondence of the Central Asian khanates with Persia, India, the Russian and Ottoman empires тоо. Depending on the political, economic and ideological interests of these states, sometimes pilgrims were given permits to be sent to Mecca through their territories, and sometimes not. The degree of intensity of pilgrimage movements, in most cases, depended on the activities of interstate ambassadors. On the issue of eliminating various prohibitions and obstacles in the movements of pilgrimage roads, the Central Asian ambassadors were active and historical documents reveal these data to us. In this period the Central Asian ambassadors, who were sent to the reception of the governors those neighbor states on other issues, in most cases negotiated precisely on the direction of the Hajj of the Central Asian pilgrims also. One of such far-sighted ambassadors was a rich merchant from Bukhara, who lived in the XVIII c. Ernazar Maksud ogli officially sent several times by the Central Asian rulers to the Russian Empire. In this article analyzes the question of how the problems of the Hajj road were solved at the international diplomatic level by the example of the activities this ambassador. The history of negotiations between Ernazar and the Russian emperors on matters of the northern direction of the Hajj road and their results illuminated on base documents on this issue, which stored in the fund of the Archive of Foreign Policy of the Russian Empire (AFPRE). The scientific conclusions of this article serve for an extensive study of the issues of diplomatic and economic relations between the Central Asian khanates and the Russian Empire in the XVIII century, revealing the history of the embassy relations of the khanates and the history of the pilgrimage of the Hajj of the Central Asian people and the features of the directions of roads from Central Asia to Mecca.

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New paleomagnetic results of the earliest Permian dykes in South Mongolia and their implications for the paleogeography of the Eastern CAOB

10.5194/egusphere-egu21-15599 ◽

2021 ◽

Author(s):

Donghai Zhang ◽

Guochun Zhao ◽

Baochun Huang ◽

Qian Zhao ◽

Hai Zhou ◽

...

Keyword(s):

Secular Variation ◽

North China ◽

High Coercivity ◽

The North ◽

Magnetic Carriers ◽

Central Asian ◽

Paleomagnetic Study ◽

History Of ◽

Temperature Component ◽

Funded Project

Debates of the Permo-Carboniferous paleogeography of the eastern Central Asian Orogenic Belt (CAOB) mainly focus on the existence, extent, and thereby evolutionary history of the Paleo-Asian Ocean (PAO) in this period. South Mongolia locates at a key position that denotes the southernmost margin of the Mongolia block. Here, we present a paleomagnetic study on the earliest Permian dykes near the Khanbogd of South Gobi Province in Mongolia to better constrain the paleo-position of the Mongolia block. Zircon U-Pb dating results of the studied dykes indicate an emplacement age of 299 &#177; 3 Ma. Magnetites are the dominant magnetic carriers as revealed by the synthesized rock magnetic experiments. A likely primary high coercivity/temperature component was isolated from 66 of 125 samples and displays consistent reverse polarity, which coincides with the Kiaman Reverse Superchron that overlapping the emplacement age of our studied dykes. Accordingly, a ~299 Ma paleomagnetic pole is calculated at &#955;/&#966; = &#8722;4.1&#176;N/146.3&#176;E (dp = 3.8, dm = 5.8, n = 66). Potential influence from Paleo-Secular Variation (PSV) is excluded following the Deenen et al. (2011) procedure. Our new results present a ~30.9&#176;N paleolatitude for the Mongolia block, which differs from the lower paleolatitude of the North China and Xilinhot blocks as well as the much higher paleolititude of Siberia. Surrounded by these blocks of different paleolatitude, the PAO and Mongol-Okhotsk Ocean both remained wide open at least by the earliest Permian.Acknowledgments This research was funded by the Natural Science Foundation of China (NSFC) (41902229, 41730213, 42072264, 41902229, 41972237), China Postdoctoral Science Foundation funded project and Hong Kong RGC GRF (17307918).ReferencesDeenen, M. H. L. , Langereis, C. G. , Van, H. D. J. J. , & Biggin, A. J. . (2011). Geomagnetic secular variation and the statistics of palaeomagnetic directions. Geophysical Journal International(2), 509-520.

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Uplift history of the Western Ecuadorian Andes: new constraints from low-temperature thermochronology

10.5194/egusphere-egu2020-5228 ◽

2020 ◽

Author(s):

Audrey Margirier ◽

Peter Reiners ◽

Ismael Casado ◽

Stuart Thomson ◽

Alexandra Alvarado ◽

...

Keyword(s):

Strike Slip ◽

South American ◽

South American Plate ◽

Ridge Subduction ◽

The North ◽

Western Cordillera ◽

Deformational History ◽

History Of ◽

Long Term Impact

The Cenozoic growth of the Ecuadorian Andes has been strongly influenced by the compressional reactivation of inherited crustal anisotropies, strike-slip faulting and uplift, and the erosional effects of a wet tropical climate superposed on the deforming orogen. Some authors have linked uplift in the Western Cordillera to the interaction between the South American Plate and the subduction of the oceanic Carnegie Ridge. However, recent studies have alternatively suggested that the tectonic evolution of a northward-escaping crustal sliver in western Ecuador along the Pallatanga strike-slip zone may equally well explain mountain building and topographic growth in this region. While the importance of the Pallatanga Fault has been recognized in the context of seismic hazards, its long-term impact on the development of topography and relief has not been explored in detail. To evaluate the possible roles of oceanic ridge subduction and/or strike-slip motion in prompting the growth of the Western Cordillera, we present new thermochronological data to constrain the deformational history of the Western Cordillera at different latitudes. We focus on two sites in the vicinity of the Pallatanga strike-slip fault (3&#176;S and 1&#176;30&#8217;S) and a location farther to the north (0&#176;30&#8217;N). Our apatite and zircon (U-Th-Sm)/He dates range from 26.0 &#177; 0.4 Ma to 3.9 &#177; 0.1 Ma and from 23.7 &#177; 0.3 to 5.9 &#177; 0.1 Ma, respectively. The three sampled sites record a clear age-elevation relationship. The inverse modeling of apatite and zircon (U-Th-Sm)/He dates and upcoming apatite fission-track data is expected to provide new constraints on the recent uplift and exhumation history of the Western Ecuadorian Andes and thus furnish information on the paleo-geographical evolution of the northern Andes.

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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

Geological Society of America Bulletin ◽

10.1130/b35515.1 ◽

2020 ◽

Vol 132 (11-12) ◽

pp. 2367-2381 ◽

Cited By ~ 1

Author(s):

Guangyan Zhou ◽

Christopher M. Fisher ◽

Yan Luo ◽

D. Graham Pearson ◽

Long Li ◽

...

Keyword(s):

Northern China ◽

Hf Isotope ◽

Crustal Evolution ◽

The North ◽

Central Asian ◽

History Of ◽

Specific Affinity ◽

Isotope System ◽

Host Rocks ◽

Nd Model Age

Abstract 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.

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Are Wilson Cycles preserved in Archean cratons? A comparison of the North China and Slave cratons

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2013-0163 ◽

2014 ◽

Vol 51 (3) ◽

pp. 297-311 ◽

Cited By ~ 17

Author(s):

Timothy M. Kusky ◽

Xiaoyong Li ◽

Zhensheng Wang ◽

Jianmin Fu ◽

Luo Ze ◽

...

Keyword(s):

North China Craton ◽

Plate Tectonics ◽

North China ◽

Passive Margin ◽

The North ◽

Tectonic History ◽

History Of ◽

Pacific Slab ◽

Arc Setting ◽

Back Arc

A review and comparison of the tectonic history of the North China and Slave cratons reveal that the two cratons have many similarities and some significant differences. The similarities rest in the conclusion that both cratons have a history of a Wilson Cycle, having experienced rifting of an old continent in the late Archean, development of a rift to passive margin sequence, collision of this passive margin with arcs within 100–200 Ma of the formation of the passive margin, reversal of subduction polarity, then eventual climactic collision with another arc terrane, microcontinental fragment, or continent. This cycle demonstrates the operation of Paleozoic-style plate tectonics in the late Archean. The main differences lie in the later tectonic evolution. The Slave’s post-cratonization history is dominated by subduction dipping away from the interior of the craton, and later incorporation into the interior of a larger continent, whereas the North China Craton has had a long history of subduction beneath the craton, including presently being located above the flat-lying Pacific slab resting in the mantle transition zone, placing it in a broad back-arc setting, with multiple mantle hydration events and collisions along its borders. The hydration enhances melting in the overlying mantle, and leads to melts migrating upwards to thermochemically erode the lithospheric root. This major difference may explain why the relatively small Slave craton preserves its thick Archean lithospheric root, whereas the eastern North China Craton has lost it.

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