The Comet goes around the sun in highly elliptical orbit and rarely comes close to earth. Most of the time Jupiter’s gravity deflects comets from Oort cloud and Kuiper belt away from the inner planetary system but sometimes it also deflects them towards inner solar system. Such comets can undergo change of orbit and spend more time in inner planetary system. As a result they are exposed to radiation and gravitational gradient making them fragile (Figure 1). Examples like those of Comet Shoemaker Levy 9 [1], comet 72 P and 332 P (Figure 2) show that it is not unusual for comets to break up into multiple pieces due to gravitational gradients and radiation. Impact of such nature would, therefore, creates a series of impressions on the ground. The known comet impact of Sahara desert show desert glass spread over 6000 sq.km. is possibly because of similar entry and impact pattern.

Figure 1 Comet disintegration due to radiation and gravitational gradient it’s an artistic presentation by author and not as per actual scale.

Effects of Radiation and Gravity on Comet

Comet Nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. This Initial Density of comet plays a crucial role in the resulting crater shape. Prof. Roddy and others conducted study “High explosive cratering analogs for bowl-shaped, central uplift, and multi ring impact craters” in which they have elaborated snowball craters along with Flynn creek crater (Figure 3). Key findings Of Snowball Impact Crater by J. Roddy [2] [3]

· Crater Was filled with water.

· A wide, shallow bowl-shape flat floor crater interrupted by prominent central uplift.

· Central uplift consisted of several connected mounds of irregularly uplifted clay beds.

· Concentric ring fractures developed in the rim due to differential motion.

· Entire rim near central wall was irregularly depressed and contain many nearly horizontal thrust faults.

Due to disintegration on the path and low density porous nature of impacting material comet impact lead to a unique pattern which is spread over a large area with multiple “wide, shallow bowl-shape flat floor craters”. These craters are filled with water resembling to large lakes/dry lakes with interconnecting network of faults and fractures. This results in to network or rivers and canals. These craters due to their unique features are difficult to identify compare to craters formed by rocky/metal asteroids (Figure 4). Such impact sits are rich in complex alloys and ultra high pressure minerals.

Comet nuclei are composed of an amalgamation of rock, dust, water ice, frozen carbon dioxide, carbon monoxide, methane, and ammonia. In addition to these gases the nuclei also contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane and perhaps more complex molecules such as long-chain hydrocarbons and amino acids. As a result in the event of impact of such body there is a strong possibility of complex alloy formation.

1) Qinsongite and its origin (BN)

H 3 BO 3 + NH 3 → Δ BN + 3H 2 O .

a) H₃BO₃: Natural Resource at Tibet

b) NH₃: Part of Comet composition

c) High Temperature& Pressure: Result of Impact

In 2013 International Mineralogical Association Recognized it as only known boron mineral formed in the deep earth mantle found in Luobusha ophiolite of Tibet autonomous Region in China (Table 1). Boron is rare in the universe, it is formed in minor amounts in cosmic ray spallation and may be found in cosmic dust or meteoroid. Boron is a rare element in the earth crust (0.001‰) however it can be highly concentrated by the action of water thus it is found in compounds such as borax, boric acid. Tibet lake region is rich source of borax.

Ammonia is a part of Comet composition, hence in the event of comet impact When Boric acid reacts with ammonia at high temperature and UHP above 10 GPa it can form cubic boron nitride. Impact of such nature will lead to transformation of silica and other elements leading to formation of quartz and other complex alloys.

Qingsongite is found in crystal in association with osbornite, Coesite, micro diamond and Ti rich Kyanite. If we look at the associated minerals that are found with “Qingsongite” then most of these minerals are known for their presence at impact sites. For mantle origin all these elements will require different conditions in the deep earth mantle hence it will be rare possibility that they are found in single crystal. Thus they have undergone the transformation on the surface itself indicating towards UHP impact in its formation. All these minerals are found in placer deposits which again indicate towards the shallow origin.

Associated Minerals with c-BN (Qingsongite) and Impact Origin

a) Osbornite (TiN): Formed in the star dust and now almost exclusively found in meteorites.

b) Micro Diamonds in Os, Ir inclusion: Fang et al. (2007) [4] and Yang J., Larissa Dobrzhinetskaya et al. (2006) [5] indicate towards the possibility of impact origin of these diamonds.

c) Coesite: Again a common finding at impact sites.

d) Ti rich Kyanite: Ti-rich Kyanite is a unique finding in Tibetan region Mr. Fang’s [4] study reveals that Ti presence in kyanite varies from (1.98 wt.‰ - 11.64 wt.‰). Analysis of dust of comet 81/P wild 2 [7] confirms the presence of Ti in the comet. Hence Kyanite association with Ti must be reviewed from the impact perspective.

2) Boron Carbide

Boron carbide is a specially hard material in the group of technical ceramics. This is not naturally available on earth. However this has been reported from Tibet Ophiolite along with osbornite, coesite, microdiamond and cBN. Boron carbide can be produced by using following reaction at temperature in the range of 1300˚C - 1400˚C.

a) 4H 3 BO 3 → Δ 2B 2 O 3 + 6H 2 O

b) B 2 O 3 + 3CO = 2 Β + 3CO 2

c) 4 Β + C = B4C

H₃BO₃: Borax is naturally available in Tibet lake region which is main source for boric acid.

CO: Solid Carbon Monoxide has been reported from comets. Halley’s comet had 15% CO, Ref. Sekanin (1991) [8].

3) Osbornite (TiN), Ti rich Kyanite and TiO₂ II

Osbornite is very rare natural nitride, originally formed in star dust and now almost exclusively found in meteorites. TiN has been reported from Tibet Ophiolite as natural origin however it provides no explanation on this rare occurrence and coexistence in a crystal which has most of the finds like coesite after stishovite, microdiamonds with OsIr inclusion which are known for impact origin. The study of star dust from Comet 81P/wild 2 [7] confirm the presence of Ti and osbornite (TiN) in comets. This also simplifies exceptional association of Ti rich kyanite reported by Fang et al. (2007) [4] with Raman peak reading not matching any known natural mineral or melt. TiO₂ II again is an indicator of either ultra high-pressure or shock induced environment with the temperature in the range of 500˚C - 1200˚C and pressure 4 - 9 Gpa in the formation process. TiO₂ II was first reported from Ries crater Germany. All these finds are strong indicator of impact in the formation.

4) Micro-Diamonds and Other Minerals

Microdiamonds along with coesite after stishovite, reported from placer deposits of Yarlungzangbo region of Tibetan Ophiolite. These samples have shallow origin. These microdiamonds have OsIr inclusion which is a common feature in the impact event. In nature Stishovites are formed at very high shock pressure close to 10 GPa and temperature in excess of 1200˚C, present during the hypervelocity meteorite impact. Minerals like Cr₂O₃ and FeO in the chromitite again strengthen the possibility of impact.

Such impact on land will allow UHP phase to have overprinted on the lithosphere. Very high temperature of impact event followed by rapid cooling would lead to encapsulation of the minerals within chromitite resulting in low oxygen fugacity of the material. This also explains the perfect preservation of the coesite as a consequence of such rapid cooling after shock as predicated by Fang et al. (2007) [4].

Comet Impacts are high velocity impacts and can lead to tektite formation a small glassy aerodynamical dusty earth material, which is thrown outward from the earth as ejecta by an impact and re arrive on earth after travelling through the atmosphere on their ballistic trajectory. As on date, it is believed that Indochinites are of Australian Strewn field, however, no impact crater has been identified. Australian Tektites are concentrated in southern Australia hence neither plate tectonics, nor ocean current can explain their presence in places like Laos, Vietnam. Impact in Tibet can explain Indochinites. Hence these Tektites may have resulted from Independent strewn, possibly from Tibet (Figure 5).

We identify a region between 82˚30'E and 90˚30'E and 29˚N and 33˚N in southern Tibet (Figure 6). The top panel shows the region of Tibet studied here. The second panel shows the lake region marked in Figure 6. The third panel shows the marking of each lake in the region. As can be seen from the figure, the craters seem to be roughly aligned. Gravitational Anomalies are observed in the

same lake region (82˚30'E, 29˚N and 90˚30'E, 33˚N) gravity anomaly (Figure 7). In the event of Impact such anomalies are common. Hence it will be prudent to study this in detail to confirm the findings.

Lake Characteristics (Based on Google Map Images)

1) These lakes are formed in a straight line creating the resemblance of geometric time impact.

2) These Lakes have 2 - 90 meter of depth.

3) Steep Slope facing circular feature.

4) Small lakes have crater-like appearance (created by angular impact).

5) Large lakes appear to be a combination of two or three water bodies/craters.

6) Fractures and fault lines interconnecting these lakes hinting towards impact that cracked the whole surface.

Industrial units near the origin of rivers starting from these lakes indicate alluvial/Placer mining activity (Figure 8). More than 30 such units near lakes can be seen on the satellite map (Google Map) with connecting road network (S205, 301, 302). This is a remote and inhabitable region thus operating such heavy industry supported by infrastructure indicate towards the large commercial interest in the lake region, hence lake region is the possible source of commercially important minerals. It will be prudent to collect the sample from this region to verify UHP impact instead of Yarlung-Zangbo Suture Zone (Figure 9).

Blue Flag: Industry/Placer mine

Green Box: Sample collection zone of earlier Studies

Sample collection zone (Yarlung Zangbo Region) approximately 200 km away from the proposed craters possible reason of non-evidence of Impact till date.