The Xigaze ophiolite: fossil ultraslow-spreading ocean lithosphere in the Tibetan Plateau

2020 ◽  
pp. jgs2020-208
Author(s):  
Tong Liu ◽  
Chuan-Zhou Liu ◽  
Fu-Yuan Wu ◽  
Henry J.B. Dick ◽  
Wen-Bin Ji ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Spreading Rate ◽  
Southwest Indian Ridge ◽  
The Tibetan Plateau ◽  
Crustal Accretion ◽  
Ocean Ridges ◽  
Magma Supply ◽  
Spreading Ridges ◽  
Ocean Lithosphere ◽  
Lower Crustal

The crust and mantle in both ophiolites (fossil ocean lithosphere) and in modern oceans are enormously diverse. Along-axis morphology and lower crustal accretion at ultraslow-spreading ocean ridges are fundamentally different from those at faster-spreading ridges, and are key to understanding how crustal accretion varies with spreading rate and magma supply. Ultraslow-spreading ridges provide analogs for ophiolites, to identify those that may have formed under similar conditions. Parallel studies of modern ocean lithosphere and ophiolites therefore can uniquely inform the origin and genesis of both. Here we report the results of structural and petrological studies on the Xigaze ophiolite in the Tibetan Plateau, and compare it to the morphology and deep drilling results at the ultraslow-spreading Southwest Indian Ridge. The Xigaze ophiolite has a complete but laterally discontinuous crust, with discrete diabase dikes/sills cutting both mantle and lower crust. The gabbro units are thin (∼350 m) and show upward cyclic chemical variations, supporting for an episodic and intermittent magma supply. These features are comparable to the highly focused magmatism and low magma budget at modern ultraslow-spreading ridges. Thus we suggest that the Xigaze ophiolite represents an on-land analog of ultraslow-spreading ocean lithosphere.

scholarly journals Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1069-1073 ◽  
Author(s):  
Ingo Grevemeyer ◽  
Nicholas W. Hayman ◽  
Dietrich Lange ◽  
Christine Peirce ◽  
Cord Papenberg ◽  
...  
Keyword(s):  
Spreading Rate ◽  
Maximum Depth ◽  
Southwest Indian Ridge ◽  
Spreading Center ◽  
Ocean Ridges ◽  
Spreading Ridges ◽  
Brittle Layer ◽  
Full Rate ◽  
Slow Spreading ◽  
The Caribbean

Abstract The depth of earthquakes along mid-ocean ridges is restricted by the relatively thin brittle lithosphere that overlies a hot, upwelling mantle. With decreasing spreading rate, earthquakes may occur deeper in the lithosphere, accommodating strain within a thicker brittle layer. New data from the ultraslow-spreading Mid-Cayman Spreading Center (MCSC) in the Caribbean Sea illustrate that earthquakes occur to 10 km depth below seafloor and, hence, occur deeper than along most other slow-spreading ridges. The MCSC spreads at 15 mm/yr full rate, while a similarly well-studied obliquely opening portion of the Southwest Indian Ridge (SWIR) spreads at an even slower rate of ∼8 mm/yr if the obliquity of spreading is considered. The SWIR has previously been proposed to have earthquakes occurring as deep as 32 km, but no shallower than 5 km. These characteristics have been attributed to the combined effect of stable deformation of serpentinized mantle and an extremely deep thermal boundary layer. In the context of our MCSC results, we reanalyze the SWIR data and find a maximum depth of seismicity of 17 km, consistent with compilations of spreading-rate dependence derived from slow- and ultraslow-spreading ridges. Together, the new MCSC data and SWIR reanalysis presented here support the hypothesis that depth-seismicity relationships at mid-ocean ridges are a function of their thermal-mechanical structure as reflected in their spreading rate.

scholarly journals IODP Expedition 335: Deep Sampling in ODP Hole 1256D

2012 ◽  
Vol 13 ◽  
pp. 28-34 ◽  
Author(s):  
D. A. H. Teagle ◽  
B. Ildefonse ◽  
P. Blum ◽  
Keyword(s):  
Theoretical Models ◽  
Spreading Rate ◽  
Ocean Crust ◽  
Ocean Drilling Program ◽  
Drill Cuttings ◽  
Ocean Drilling ◽  
Ocean Ridges ◽  
Integrated Ocean Drilling Program ◽  
Geological Conditions ◽  
Ocean Lithosphere

Observations of the gabbroic layers of untectonized ocean crust are essential to test theoretical models of the accretion of new crust at mid-ocean ridges. Integrated Ocean Drilling Program (IODP) Expedition 335 ("Superfast Spreading Rate Crust 4") returned to Ocean Drilling Program (ODP) Hole 1256D with the intention of deepening this reference penetration of intact ocean crust a significant distance (~350 m) into cumulate gabbros. Three earlier cruises to Hole 1256D (ODP 206, IODP 309/312) have drilled through the sediments, lavas, and dikes and 100 m into a complex dike-gabbro transition zone. <br><br> Operations on IODP Expedition 335 proved challenging throughout, with almost three weeks spent re-opening and securing unstable sections of the hole. When coring commenced, the comprehensive destruction of the coring bit required further remedial operations to remove junk and huge volumes of accumulated drill cuttings. Hole-cleaning operations using junk baskets were successful, and they recovered large irregular samples that document a hitherto unseen sequence of evolving geological conditions and the intimate coupling between temporally and spatially intercalated intrusive, hydrothermal, contact-metamorphic, partial melting, and retrogressive processes. <br><br> Hole 1256D is now clean of junk, and it has been thoroughly cleared of the drill cuttings that hampered operations during this and previous expeditions. At the end of Expedition 335, we briefly resumed coring before undertaking cementing operations to secure problematic intervals. To ensure the greatest scientific return from the huge efforts to stabilize this primary ocean lithosphere reference site, it would be prudent to resume the deepening of Hole 1256D in the nearest possible future while it is open to full depth. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.13.04.2011" target="_blank">10.2204/iodp.sd.13.04.2011</a>

scholarly journals Mantle rock exposures at oceanic core complexes along mid-ocean ridges

Geologos ◽  
2015 ◽  
Vol 21 (4) ◽  
pp. 207-231 ◽  
Author(s):  
Jakub Ciazela ◽  
Juergen Koepke ◽  
Henry J.B. Dick ◽  
Andrzej Muszynski
Keyword(s):  
Partial Melting ◽  
Geophysical Methods ◽  
Ex Situ ◽  
Crustal Rocks ◽  
New Class ◽  
Ocean Ridges ◽  
Common Structure ◽  
Spreading Ridges ◽  
Slow Spreading ◽  
Lower Crustal

Abstract The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.

Has the Tibetan plateau risen in the Early/Mid–Miocene? Constraints from plate–motion reconstructions and seismicity of the Indian Ocean lithosphere

2021 ◽  
Author(s):  
Giampiero Iaffaldano
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
Tectonic Setting ◽  
Plate Motion ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
Plate Motions ◽  
The Indian Ocean ◽  
Ocean Lithosphere

Summary Magnetisation records and seismic stratigraphy of the Indian Ocean lithosphere indicate that the Early/Mid–Miocene onset of diffuse contractional deformation coincided with slowdowns of the Indian and Capricorn plate motions. At present day such deformation is evidenced by the seismicity of the Indian ocean floor. Deformation onset and past plate–motion slowdowns have been interpreted as consequences of a sudden uplift of the Tibetan plateau by 1 to 2 km, as this – following previous estimates – would generate a tectonically–significant force between 4 · 1012 and 8 · 1012 N/m. However, this view remains at odds with paleo–altimetry estimates from geological and geochemical data, which indicate no increase in plateau altitude throughout the Miocene. Here I use well–established models of viscous/brittle dynamics in inverse mode in order to constrain the amount of force that should be delivered by the Tibetan region to the Indian tectonic setting in order to explain the observations above. Results constrain such a force within the range from 4.3 · 1011 to 3.5 · 1012 N/m. By comparison with previous estimates of the force associated with topography increase, these analyses suggest that the Early/Mid–Miocene onset of contractional deformation and plate–motion slowdowns within the Indian Ocean require minimal uplift of the Tibet plateau of a few hundred meters. The seemingly–contradicting inferences on Early/Mid–Miocene Tibetan uplift that come from geophysical and geological/geochemical observations can be reconciled by noting that the required uplift amount is less than what is resolvable by modern paleo–altimetry techniques.

Crustal thickening and uplift of the Qiangtang Terrane, Tibetan Plateau during the Late Cretaceous to Early Palaeocene: geochronology and geochemistry of the Saiduopugangri granite

2020 ◽  
Author(s):  
xue li ◽  
Guo-Sheng Sun ◽  
Gen-Yi Liu ◽  
Huan Zhou ◽  
Zi-Ling Shan ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Late Cretaceous ◽  
Crustal Thickening ◽  
Magma Source ◽  
Geodynamic Setting ◽  
The Tibetan Plateau ◽  
Weighted Mean ◽  
Lower Crustal ◽  
Qiangtang Terrane ◽  
Shoshonitic Series

There continues to be debate regarding the timing of the collision between the Indian and Eurasian plates and the uplift of the Tibetan Plateau. This study presents zircon U–Pb geochronology, whole-rock geochemistry, and Lu–Hf isotopic data for the Saiduopugangri granite of the Qiangtang Terrane, located within the core of the Tibetan Plateau. These data provide the basis for the geodynamic setting, petrogenesis, and characteristics of its magma source. Zircons from the Saiduopugangri granite yield a weighted-mean 206Pb/238U age of 62.72 ± 0.06 Ma, indicating that these rocks formed during the early Palaeocene. The rocks are members of the highly calc-alkaline to shoshonitic series, with weak peraluminous characteristics. Trace elements are characterised by high Sr (483–616ppm), and low Y (6–10ppm) and Yb (1ppm) content, typical of a high Sr and low Yb granite. The εHf(t) of zircon range from −2.14 to 2.35, with two-stage Hf model ages (TDM2) ranging from 1182 to 895Ma. These data suggest that the Saiduopugangri granite magma was derived from the melting of lower-crustal clastic meta-sedimentary rocks and mantle-derived basalts. The high Sr and low Yb granite characteristics and experimental results indicate that melting occurred at >1.2 GPa and >750 °C, consistent with a crustal thickness greater than 50km. Magmatism occurred from the Late Cretaceous to the early Palaeogene and is broadly synchronous with the collision timing between the Indian and Eurasian plates. The Saiduopugangri granite provides evidence of crustal thickening of the Tibetan Plateau and its age and petrogenesis constrain the timing of the initial uplift.

The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements

2020 ◽  
Author(s):  
Han-Ao Li ◽  
in-Gen Dai ◽  
Le-Tian Zhang ◽  
Ya-Lin Li ◽  
Guang-Hao Ha ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Lower Crust ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Gps Measurements ◽  
Southern Tibet ◽  
Magnetotelluric Data ◽  
Deep Process ◽  
Lower Crustal Flow ◽  
Lower Crustal

&lt;p&gt;The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology&lt;sup&gt;1&lt;/sup&gt;. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data&lt;sup&gt;2&lt;/sup&gt;. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau&lt;sup&gt;3&lt;/sup&gt;. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Key words:&lt;/strong&gt; N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&lt;/sup&gt;Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3&lt;/sup&gt;Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., B&amp;#252;rgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgements:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang&amp;#65292;Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.&lt;/p&gt;

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