a short story about the geological … lohr.pdfalthough ophiolites do not crop out continously along...

A SHORT STORY ABOUT THE GEOLOGICAL HISTORY OF THE PAMIR 1

A SHORT STORY

ABOUT THE GEOLOGICAL HISTORY OF

THE PAMIR

Tina Lohr

review: Lothar Ratschbacher

University of Mining and Technology FreibergInstitute of Geology, Department of Tectonophysics

February 2001


Contents

Abstract 1

1. Introduction 2

2. Geological setting 42.1. The stratigraphy and development of the Pamiran syntax 42.2. Sedimentology changes of the western Tarim and Tadjik basins

during the Pamir overthrusting 6

3. From the former to the present position of the Pamir 8

References 11


A SHORT STORY ABOUT THE GEOLOGICAL HISTORY OFTHE PAMIR

Abstract

The Pamir is a part of the Cenozoic orogenic belt of Asia. During the development of thePamir an enormous amount of Cenozoic crustal shortening was ascertained. Thick sequencesof sedimentary deposits have been shifted over 300 km in northern direction and anaccordingly amount of lithospere has been subducted into the asthenosphere beneath thePamir. This slab of lithosphere with a dip of about 45°, a downdip lengh of nearly 300 km anda thickness of 20-25 km seems to be of continental origin. During this process the Pamirclosed the Tadjik-Yarkand basin and penetrated into the South Tien Shan.

The east-west-trending facies zones of Cretaceous and Paleogene sedimentary deposits withinthe Tadjik-Yarkand basin are abruptly truncated at the western edge of the Pamir. Today, thesediments crop out at the northern margin of the Pamir at least 200 km farther north. This 200km displacement of sedimentary strata and an additional amount of internal shortening withinthe Pamir of 100 km imply that the Northern Pamir has been displaced northward 300 km ormore with respect to the rest of Eurasia. The present rate of convergence across the Pamir isabout 20 mm/a.

1. Introduction

The young collision orogen in Middle Asian shows a wide variety of structural features(Fig.1). From the Paleozoic to the Cenozoic continental blocks of Gondwana origin weldedwith the Asian continental crust. Today, the Indian block penetrates into the Eurasianlandmass. During this collision the Indian subcontinent decreased its velocity to about onethird to nearly 44 mm/a (DeMets et al., 1990). This enormously amount of energy is effectedby the whole young orogen, but it is suggest that roughly half of the convergence might beabsorbed at the Trans-Alai Range along the northern arc of the Pamir (Fig. 2). This involve


an overthrusting of the Pamir onto the Alai Valley in the South Tien Shan at a rate of about20 mm/a and crustal shortening over a N-S distance of more than 300 km was the result.

The collision of the Indian block with Eurasia implys the release of a hugh amount of kineticenergy that is accomodated mostly by lithospheric thickening and lateral extrusion along greatstrike-slip faults. The Pamiran syntax penetrated through the former Tadjik-Yarkland basininto the South Tien Shan, forming the thrust belts of the Northern, Central and SouthernPamir. In addition, material “flow” along great strike-slip faults into western and easternregions. The dextral Herat Fault and the sinistral Chaman Fault transfer material to thesouthwest to build up the Hindu Kush. A similar process takes place at the eastern site of thePamir. The sinistral Altyn-Tagh and Karakash faults and the dextral Karakorum fault displacethe material towards southeast into the Tibet. From here it is transported into a southeasterndirection around the eastern syntax of the Himalaya. This region is characterize by largestrike-slip faults: the sinistral Kunlun, Kang-Ting and Kansu faults and the dextral Red RiverFault. The Kunlun Shan is seperated in an eastern Kunlun and a western Kunlun by thesinistral Altyn-Tagh fault. This fault also separates the Tarim basin from the eastern Quaidambasin.

Figure 1. Simplified map of active tectonics in Asia (Twiss and Moores, 1992)WK – western Kunlun, EK – eastern Kunlun


With 7495 m the Pik Kommunizma in Tadschikistan is the highest point within the Pamir.Other adjacent states are Afghanistan and China. The Pamiran orogen has an extention of 500to 600 km N-S as well as E-W.

The Pamir is lateraly limited by two basins: the Tarim Basin and the Tadjik Depression. Thenorthern margin is marked by the South Tien Shan, the Hindu Kush is the southwesternborder and Kunlun Shan, Karakorum and Himalaya are situated in the southeast. The Tibetianhigh plateau lies between the Kunlun Shan and the Karakorum (Fig. 2).

2. Geological setting

2.1. The stratigraphy and development of the Pamiran syntax

The Pamir is characterized by a thick continental crust of about 70 km (Chen and Molnar,1981; Holt and Wallace, 1990). Geophysical observations show an oblique subduction zonesubmerges to the SSE (Billington et al., 1977) beneath the Pamir. This subduction zoneindicate a large Mesozoic thrust fault at the Trans-Alai range.

Figure 2. Simplified map of the Pamir and surrounding regions (Burtmanand Molnar, 1993).


The Pamir is subdivided into four main zones: Nothern, Central, Rushan-Pshart and SouthernPamir (Fig. 3).

The Northern Pamir represents the late Paleozoic suture zone between the Central Pamir andthe rest of Asia. This suture zone wraps around the Pamir, from the western Hindu Kush inAfghanistan, through the Northern Pamir to the Kunlun of northern Tibet. The area of theNorthern Pamir contains mainly Carboniferous igneous and sedimentary rocks of an oceanicenvironment. These are dominantly mafic rocks and tholeiitic basalts covered by limestone,siltstone and sandstone (Budanov and Pashkov, 1988; Leven, 1981). More westernly in theDarvaz Range serpentine melange crops out which is overlained by a mighty layer of pillowbasalt with tholeiitic character (Pospelov, 1987). In the upper Carboniferous the oceanicsuccession is covered by conglomerate and limestone (Pospelov, 1987). These marinesedimentary strata imply the existence of an activ continental margin at the northern part ofthe Northern Pamir with a southward dipping of the subduction zone. This ocean basin closedin late Carboniferous time. In the south of the Northern Pamir andesitic rocks are exposedcontaining sediments of Carboniferous age. They are assumed to be remnants of an island arcor of an intracontinental rift – but details are not clear. A similar geological situation as in theNorthern Pamir has been derived in the eastern continuation of the Pamir, in the Kunlun Shanas well as in the western continuation in the Hindu Kush.

The Central Pamir is an area which contains deformed and metamorphosed Precambrian andPaleozoic rocks – sedimentary deposits of sandstone, limestone and marl. Evidence ofvolcanic activities has not been found. The suggestion of a plattform is based upon thedeposition of detrital and carbonatic sediments in shallow water from late Paleozoic to earlyJurassic time. Therefore, this part of the Pamir is assumed to be another continental fragmentwhich collided with Asia probably in the middle Jurassic.

The Rushan-Pshart zone marks the late Mesozoic suture of the Southern Pamir to the CentralPamir. This region represents a Perm/Trias alternation of marine sediments, predominantly

Figure 3. Structural map of the Pamiran syntax, Takjik Depression andsurrounding regions. Sutures of ophiolite belts are shown by heavy black lines.NP – Northern Pamir, CP – Central Pamir, SP – Southern Pamir. (Burtman andMolnar, 1993)


limestone and radiolarite, and rocks of magmatic origin like pillow-basalt, andesite, tuffs andalso lenses of ultramafic rocks. Deep-water terrigenous deposits of Jurassic and Cretaceousage complete this succession. These deposits were covered by Cretaceous redbeds. TheRushan-Pshart zone is an important area of latest Paleozoic to early Mesozoic rifting and theformation of a small ocean basin (Shvol’man, 1978) which closed in the late Jurassic or earlyCretaceous time. Although ophiolites do not crop out continously along this Mesozoic sutur, arelatively continuosly belt seems to be around the western syntax of the Himalaya. Therefore,the Rushan-Pshart zone marks a localized convergence, but a major oceanic terrain may nothave been consumed. The Rushan-Pshart zone seems to correlate with the Farah Rud basin inwestern Afghanistan (Boulin, 1981; Burtman 1982).

The Southern Pamir is subdivided into the Southwestern Pamir and the Southeastern Pamirbecause of the distingtly different geology. Metamorphosed Precambrian rocks and Mesozoicand Paleogene granits are the dominat rocks exposed in the Southwestern Pamir (Pashkov andBudanov, 1990). The oldest rocks in the Southeastern Pamir are late Carboniferous to earlyPermian sandstone, siltstone, clay and limestone. This sequence is followed by Triassiclimestone, radiolarite and siltstone which contains rare basaltic lava and tuff. The Jurassicunconformity of reef limestone is overlained by Cretaceous sediments includingconglomerates as well as dacit, andesite, tuff and limestone. The folding took place in Jurassictime and the tectonic reactivation in Cenozoic time when deformation occurred throughoutthe Pamir.

The Indus-Tsang-po suture zone is a third belt of ophiolites follows the Tsang-po and Indusvalley in southern Tibet, wraps around the Southern Pamir, and seems to continue intosouthern Pakistan, Afghanistan and Iran. In the west, this belt diverges into separat ophioliticbelts (e.g., Shyok suture) that surround fragments of continental crust or ancient island arcs.Together, the Indus-Tsang-po and Shyok ophiolite belts represents the suture zone of anorthdipping subduction zone due to the Cenozoic penetration of the Indian prong into thesouthern margin of Eurasia. Commonly, the Shyok suture is associated with the Pangongsuture (Fig. 3) further east.

The remnants of three ocean basins described above bend around the syntax of the Pamir fromthe west in Afghanistan to the east across the Tibetan plateau. Two of them, the late Paleozoicsuture and the early Cenozoic Indus-Tsang-po suture, seem to mark zones were a wide area ofoceanic lithosphere was subducted to great depths and where fragments of continental crustmoved over long distances to collide with southern Eurasia (Fig. 4). The sutures are closertogether in the Pamiran syntax then father east or west, indicating stronger shortening in thePamir than in the Tibet and Hindu Kush.

Euf

Eurasia Northern Pamir CentralPamir

Rushan-Pshart zone

Southern Pamir India SN

Paleozoicsuture

Mesozoicsuture

Shyok-Indus-Tsang-posuture

Figure 4. North-South cross-section through the different continental blocks, collided with Eurasia.


2.2. Sedimentology changes of the western Tarim and Tadjik basinsduring the Pamir overthrusting

Before the beginning of the collision between India and Eurasia in Late Eozean time a widesedimentary basin, the Tadjik-Yarkand basin, occupied the region now covered by the Pamir.It extends over the whole Tadjik Depression to the Yarkand Depression at the western end ofthe Tarim basin. Late Cretaceous and Paleogene marine sediments were deposited within thisbasin. But these east-west-trending facies zones were trunced abruptly by the Vakhsh andTrans-Alai overthrusts (Fig. 3). During the penetration of the Pamir over this depression intothe South Tien Shan, the sedimentary cover was scraped of the basement and transported intonorthern direction.

The Tadjik sedimentary basin is divided into two domains by the Vakhsh and Trans-Alaioverthrusts. The “Tien Shan” domain comprises the South Tien Shan and the central andwestern parts of the Tadjik Depression. The “Outer Pamir” domain includes the Pamir Alairegion and the eastern part of the Tadjik Depression. Paleomagnetic measurements in bothareas show large declination anomalies in the outer Pamir domain, but not in the Tien Shandomain. The facies zones in the Tien Shan domain have not been much distorted. Thestratigraphy of the outer Pamir zone changed gradually. In the Early Cretaceous a largelynonmarine sequence of sandstone but also marine sediments like limestone, marl and claywere deposited in this area. The thickness of sedimentation increased from the north up to thesouth to about 1400 meter. The greatest extention of the Tadjik sedimentary basin is assumedto have been established in Late Cretaceous time. Sedimentary rocks of marine or lagoonalenvironment reached a thickness of about 1300 meter and contained sandstone, gypsum, clay,limestone and conglomerates. Paleogene marine conditions prevailed in the center of thebasin. The oldest nonmarine sandstone and clay were deposited in Early Oligocene time at themargin of the depression. In the more inner parts the sedimentation continued to the upperEarly Oligocene. The marine deposits of predominatly limestone, marl and sandstone wereaccumulated to 1300 meter. In late Eocene time, soon after the beginning of the collisionbetween India and Eurasia, the isolation of the Tadjik and Yarkand parts of the basin hadbegan. A 4 to 6 km thick sequence of nonmarine Neogene sediment was accumulated withinthe basin. This accumulation correlates with the raise of the Pamir and the South Tien Shan.

A comparison of the distorted facies zones of the outer Pamir domain with the undistortedfacies zones of the Tien Shan domain allow to calculate the amount of northwarddisplacement of the Pamir with respect to the South Tien Shan to about 200 kilometers. Thisdisplacemant is supported by a detachment of Tithonium gypsum and salt deposits,underlying the Cretaceous and Paleogene cover within the Tadjik-Yarkand basin.

The Tarim basin was created by the collision of the Changtang block with Eurasia during theLate Triassic – Early Jurassic and the Mega-Lhasa block during the Late Jurassic – EarlyCretaceous (Fig. 5). The northern margin of the Tarim basin is overthrust by the western TienShan and its western margin is overthrust by the Pamir (Tapponnier and Molnar, 1979). Anarrow and deep early to middle Jurassic transtensional basin within the Tarim basin is aresult of the tectonical regime at that time. This basin was formed by a dextral strike-slipsystem produced pull-apart basins.


The largest faults of this system are a northwest trending dextral strik-slip fault located in thenorthwestern edge of the Tarim basin within the western Tien Shan and another dextral strike-slip fault on the southwestern margin of the basin along the Kunlun Shan. The first one hasbeen reactivated as the Talas-Ferghana fault (Fig. 2) and the second one probaby is anancestor to the Late Cenozoic Main Pamir Thrust (This thrust appears to be a continuation ofthe Paleozoic suture Fig. 3). The southwestern Tarim basin contains a sequence of more thansix kilometers of fluvial and lacustrine deposits, the majority of this Mesozoic - Cenozoicsequence is presently buried by Neocene deposits. The basin sequence is subdivided into fourstratigraphic successions. The lower one represents a thick, but spatially small transtensionalbasin of Early to Middle Jurassic age. It contains sediments of humid environment: lacustrine,swamp and braided fluvial systems. Also alluvial fan systems characterize this sequence at itsbase. The second stratigraphic succession is built up by a broad but thin compressional basinwhich existed during the Upper Jurassic and Lower Cretaceous time. The more aridconditions allowed only low-energy meandering fluvial and alluvial plain systems. The thirdstratigraphic succession represented an epicontinental sea connected to the Tethys seawayprobaby through the Tadjik basin during the Middle Cretaceous up to the Eocene. Thereforeshallow marin deposits are typical. The last succession is the Neogene foreland basin and isfilled with arid fluvial and lacustrine sediments. The onset of the closure of the western Tarimbasin may be during the Early Oligocene.

The existance of a marine environment in the outer Pamir domain of the Tadjik sedimentarybasin was only few time earlier and longer then in the eastern part of the Tadjik-Yarkandbasin.

3. From the former to the present position of the Pamir

Paleomagnetic measurements from the outer zone of the Pamir corroborate the bending ofthe structural belts (Bazhenov and Burtman, 1990). The fold axes trend parallel to the arc ofthe Pamir. The declinations vary perfectly with the trends of these fold axes. Therefore, it isassumed that folding preceded the rotation of the structural belts of the Pamir (Bazhenov and

Figure 5. Schematic map of Central Asia showinglocations of major tectonic boundaries and faults in theHimalayan orogenic system (Sobel, 1999).


Burtman, 1981, 1982). The paleomagnetic reconstruction of the former position of the Pamirarc produced a location 300 to 700 km farther south of its present limit with respect toEurasia. This amount of at least 300 km is a compound of the more than 200 kmdisplacement of the fazies zones within the Tadjik Depression and an additional amount ofmore than 100 km internal crustal shortening within the Pamir, occurred in Cenozoic time.The calculated positions from Early Cretaceous to present time are shown in Fig.6.

A slab of lithosphere has been underthrust beneath the Pamir. Seismicity shows a zone ofintermediate-depth earthquakes dipping south-southeast beneath the Pamir (Fig. 7). Theearthquakes occur mostly in a narrow zone not more than 30 km thick (Isacks andBarazangi, 1977) but emerge from depths between 150 and 300 km. This seems to imply aslablike body of presumably cold material (Billington et al., 1977; Roecker et al., 1980) witha thickness of 20-25 km underthrust beneath the Pamir and the Hindu Kush. Preciselylocated earthquakes reveal a gap between the seismic zones beneath the Hindu Kush and thePamir (Chatelain et al., 1980). Seismicity below the Hindu Kush defines a zone that dipssteeply north-northwestward to a depth of more than 300 km (Fig. 8).

The continental crust of the Pamir has a thickness of about 70 km (Chen and Molnar, 1981;Holt and Wallace, 1990), from 75 km in the Northern Pamir to 65 km in the Central andSouthern Pamir (Beloussov et al., 1980). This is in contrast to the 40 km thin crust beneaththe Tadjik Depression. In the west of the depression the lithosphere thins to 32.5 km(Kulagina et al., 1974). This reveal an eastward dip of the Moho of 5° to 6°.

The composition of the slab subducted beneath the Pamir is uncertain. Because of theproportions of this slab, it is assumed that the Pamir may be an island arc and that a smallocean, as an extention of the Black Sea or the Caspian Sea occupied the present area of thePamir (Chatelain et al., 1980; Leith 1985). To control this theory a detailed investigation ofseismic wave velocities was introducted. Due to the existance of oceanic lithosphere beneathan island arc high wave velocities were expected. But the opposite was descend: lower P-and S-wave velocities near the seismic zone than outside it (Roecker, 1982)!

Figure 6. Map showing present and reconstructed positions of the outer Pamirarc from paleomagnetic data. (Burtman and Molnar, 1993).

(1) present position of the outer arc of the Pamir(2) reconstructed position for the beginning of Neogene time(3) reconstructed position for early Cretaceous time(4) summary of paleomagnetic declinations from early Cretaceous sites


An explanation for the lower wave velocities could be the subduction of relatively thincontinental crust beneath the Pamir (Roecker, 1982). But, is a subduction of continentalcrust into the asthenosphere possible? The continental crust seems to be too buoyant tosubmerge into the asthenosphere because of its much lower density. Calculations for severalsimple subduction conditions show that continental crust of a thickness of about 35 kmshould be too buoyant to submerge into the asthenosphere (McKenzie, 1969; Molnar andGray, 1979). In contrast, crust with thickness of about 10 km should sustain suchsubduction. In connection with other petrophysical parameters the possibility of deepsubduction of about 20 km thickcontinental crust cannot beeliminated (Molnar and Gray,1979). The discovery of the high-pressure minerals Coesit and

Ellenbergerit foundedin the Western Alps and inNorway indicate the subductionof continental crust ingreat depth of more than 100 km.Thus, there are no reasons forpresuming that continental crustnever is subducted!

Figure 7. Cross-section of seismicity and topographythrough the Pamir (Burtman and Molnar, 1993).


References

Bazhenov, M. L., and Burtman, V.S., 1981, Formation of the Pamir-Punjab syntaxis: Implications from paleomagneticinvestigations of Lower Cretaceous and Paleogene rocks of the Pamirs, in Contemporary scientific researches in Himalaya:Dehra Dun, India, Bishen Singh Mahendra Pal Sing, p. 71-81.

Figure 8. Block diagram illustrating lithosphericstructure of the Pamir-Hindu Kush region (Burtmanand Molnar, 1993).


Bazhenov, M. L., and Burtman, V.S., 1982, The kinematics of Pamir arc: Geotectonics, v. 16 (English translation), p. 288-301.Bazhenov, M. L., and Burtman, V.S., 1990, Stuctural arcs of the Alpine Belt: Carpathians-Caucasus-Pamir (in Russian):Moscov, Nauka, 168 p.Belousssov, V. V., and 11 others, 1980, Structure of the lithosphere along deep seismic sounding profile: Tien Shan-Pamirs-Karakorum-Himalayas: Tectonophysics, v. 70, p. 193-221.Billington, S., Isacks, B. L., and Barazangi, M., 1977, Spatial distribution and focal mechanisms of mantle earthquakes inthe Hindu-Kush-Pamir region: A contorted Benioff zone: Geology, v.5, p. p. 699-704.Boulin, J., 1981, Afghanistan sructure, greater India concept and eastern Tethys evotlution: Tectonophysics, v. 72, p. 261-287.Budanov. B. I., and Pachkov, B. R., 1988, On the scale of early Carboniferous and Permian vulcanism in the eastern part ofthe Northern Pamir (in Russian): Bulletin MOIP (of the Moscow Society for the Investigation of Nature), GeologicalSection, v, 63, p. 33-38.Burtman, V. S., 1982, Development of the Pamir-Punjab syntaxis: Geotectonics (English translation), v. 16, p. 383-388.Burtman, V. S., and Molnar, P., 1993, Geological and geophysical evidence for deep subduction of continental crustbeneath the Pamir: Geological Society of America Special Paper, 281, p. 76.Chatelain, J.-L., Roecker, S. W., Hatzfeld, D. and Molnar, P., 1980, Microearthquake seismicity and fault plane solutions inthe Hindu-Kush region and their tectonic implication: Journal of Geophysical Research, v. 85, p. 1365-1387.Chen, W.-P., and Molnar, P., 1981, Constraints on the seismic wave velocity structure beneath the Tibetian Plateau andtheir tectonic implications: Journal of Geophysical Research, v. 86, p. 5937-5962.DeMets, C., Gordon, R. G., Argus, D. F., and Stein, S., 1990, Current plate motions: Geophysical Journal International, v.101, p. 425-478.Holt, W. E., and Wallace, T. C., 1990, Crustal thickness and upper mantle velocities in the Tibetian Plateau region from theinversion of regional Pn1 waveforms: Evidence for a thick upper mantle lid beneath southern Tibet: Journal of GeophysicalResearch, v. 95, p.12499-12526.Isacks, B. L., and Barazangi, M., 1977, Geometry of Benioff zones: Lateral segmentation and downwards bending of thesubducted lithosphere, in Twalwani, M., and Pitman, W. C. III, ids., Island arcs, deep sea trenches, and bach-arc basins:Maurice Ewing Series 1, Washington, D.C., American Geophysical Union, p. 99-114.Kulagina, M. V., Lukk, A. A., and Kulagin, B. K., 1974, Bloch structure of the earth’s crust of Tadjikstan, in Searches forprecursors of earthquades in prediction polygons: Moscow, Nauka, p. 70-84.Leith, W., and Alvarez, W., 1985, Structure of the Vakhsh fold-and-thrust belt, Tadjik SSR: Geologic mapping on a Landsatimage base: Geological Society of America Bulletin, v. 96, p. 875-885.Leven, E. Ya., 1981, The age of Paleozoic volcanogenic formations of the Northern Pamir (in Russian): Izvestiya, AkademiNauk, USSR, Geology Series, 9, p. 137-140.Matte, Ph., and eight others, 1996, Tectonics of western Tibet, between the Tarim and the Indus: Earth and PlanetaryScience Letters, 142, p. 311-330.Pashkov, B.R., and Budanov, V. I., 1990, The tectonics of the zone of intersection between the Southeastern andsouthwestern Pamir (in Russian): Geotektonika, no. 3, p. 70-79.Pospeloc, I I., 1987, Formations and tectonic development of the late Variscides of the South Tien Shan and NorthernPamir (in Russian), in Pushcharov, Yu. M., and Khvorova, I. V., eds., Early geosynclinal formations and structures:Moscow. Nauke, p. 149-178.Roecker, S. W., and six others, 1980, Seismicity and fault plane solutions of intermediate depth earthquakes in the Pamir-Hindu Kush region: Journal of Geophysical Research, v. 85, p. 1358-1364.Roecker, S. W., Tucker, B., King, J., and Hatzfeld, D., 1982, Estimates of Q in Central Asia as a function of frequency anddepth using the coda of locally recorded earthquakes: Bulletin of the Seismological Society of America, v. 72, p. 129-149.Ruzhentsev, S. V., and Shvol’man, V. A., 1982, The Pamirs, in Mahel, M.,ed., Alpine structural elements: Carpathian-Balkan-Caucasus-Pamir orogenic zone: Bratislava, VEDA, p. 115-130.Shvol’man, V. A., 1978, Relicts of the Mesotethys in the Pamirs: Himalayan Geology, v. 8, Part 1, p.369-378.Sobel, E. R., 1999, Basin Analysis of the Jurassic-Lower Cretaceous southwest Tarim basin, NW China: GSA Bulletin, v.111, n. 5.Tapponnier, P. P., and Molnar, P., 1979, Active faulting and Cenozoic tectonics of the Tien Shan, Mongolia, and Baykalregions: Journal of Geophysical Research, v. 84, p. 3425-2459.Twiss, R. J., and Moores, E. M., 1992, Strutural Geology, figure p. 115

a short story about the geological … lohr.pdfalthough ophiolites do not crop out continously along...

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